FOSSIL PLANTS




                      CAMBRIDGE UNIVERSITY PRESS
                      ~London~: FETTER LANE, E.C.
                          C. F. CLAY, MANAGER

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[Illustration: Part of a transverse section of a Permian Osmundaceous
  Fern stem, _Thamnopteris Schlechtendalii_ (Eichwald). _a_, outer
  xylem; _b_, inner xylem. For description, see page 329. (After
  Kidston and Gwynne-Vaughan. Very slightly reduced.)]




                             FOSSIL PLANTS

                       A TEXT-BOOK FOR STUDENTS
                         OF BOTANY AND GEOLOGY

                                  BY

                       A. C. SEWARD, M.A., F.RS.
      PROFESSOR OF BOTANY IN THE UNIVERSITY; FELLOW OF ST JOHN’S
      COLLEGE AND HONORARY FELLOW OF EMMANUEL COLLEGE, CAMBRIDGE

                        WITH 265 ILLUSTRATIONS

                                VOL. II

                              CAMBRIDGE:
                        AT THE UNIVERSITY PRESS
                                 1910


                             ~Cambridge~:
                      PRINTED BY JOHN CLAY, M.A.
                       AT THE UNIVERSITY PRESS.




                                PREFACE


I regret that pressure of other work has prevented the completion of
this Volume within a reasonable time since the publication of Volume
I. Had Volume II been written ten years ago, the discoveries made in
the course of the last decade would have given an out-of-date character
to much of the subject-matter. It is more especially in regard to the
Ferns and the extinct members of the Gymnosperms that our outlook has
been materially altered by recent contributions to Palaeobotany. It is,
however, some satisfaction to be able to add that recent progress has
been relatively slight in that part of the subject dealt with in the
first volume.

The original intention was to complete the whole work in two volumes.
Soon after the second volume was begun, it became evident that the
remaining divisions of the plant-kingdom could not be included within
the compass of a single volume. I decided, therefore, to take the
consequences of having embarked on too ambitious a plan of treatment,
and to preserve uniformity of proportion by reserving the seed-bearing
plants for a third volume. The third volume will include the
Pteridosperms, other than those briefly described in the final chapter
of the present volume, and other classes of Gymnosperms. I propose also
to devote such space as is available within the limits of a text-book
to the neglected subject of the geographical distribution of plants at
different stages in the history of the earth. It is my intention to
complete Volume III with as little delay as possible. As I have written
elsewhere, the past history of the Flowering plants needs special
treatment, and anything more than a mere compilation can be adequately
attempted only after considerable research and with the assistance
of botanists possessing a special knowledge of different families of
Angiosperms. The need of a critical examination of available data in
regard to the geological history of this dominant group will not be
lost sight of.

I am well aware that while certain genera have received an undue share
of attention in the present volume, others have been ignored or treated
with scant consideration. For this inconsistency I have no excuse
to offer, beyond the statement that the subject is a large one, and
selection is necessary even though the work consists of three volumes.

The publication in 1909 of a collection of excellent photographs of
Palaeozoic Plants, with brief descriptive notes, by Mr Newell Arber, as
one of a series of popular “Nature Books,” bears striking testimony to
the remarkable spread of interest in the study of the vegetation of the
past, which is one of the outstanding features in the recent history of
botanical science.

In the list of illustrations I have mentioned the source of all figures
which have been previously published. I would, however, supplement the
statement of fact with an expression of thanks to corporate bodies and
to individuals who have allowed me to make use of blocks, drawings, or
photographs.

I wish to thank my colleague, Mr A. G. Tansley, for placing at my
disposal several blocks originally published in the pages of the _New
Phytologist_. To Professor Bertrand of Lille and to his son Dr Paul
Bertrand I am indebted for several prints and descriptive notes of
specimens in their possession. My friends Dr Nathorst of Stockholm
and Dr Zeiller of Paris have generously responded to my requests for
information on various points. I wish especially to thank Dr Kidston
for several excellent prints of specimens in his collection and for the
loan of sections. I have profited by more than one examination of his
splendid collection at Stirling. Professor Weiss has generously allowed
me to borrow sections from the Manchester University collections, more
especially several which have been reproduced in the chapter devoted
to the genus _Lepidodendron_. To Professor F. W. Oliver my thanks are
due for the loan of sections from the collection under his charge at
University College. I have pleasure also in thanking Dr Scott, not
only for lending me sections of a Lepidodendron and for allowing me
to use some drawings of _Miadesmia_ originally made by Mrs Scott for
reproduction in his invaluable book, _Studies in Fossil Botany_, but
for kindly undertaking the laborious task of reading the proofs of this
volume. It would be unfair to express my gratitude to Dr Scott for many
helpful suggestions and criticisms, without explicitly stating that
thanks to a friend for reading proofs must not be interpreted as an
attempt to claim his support for all statements or views expressed. The
General Editor of the Series, Mr A. E. Shipley, has also kindly read
the proofs. I am under obligations also for assistance of various kinds
to Prof. Thomas of Auckland, New Zealand, to Mr Boodle of Kew, to Mr
D. M. S. Watson of Manchester, to Mr T. G. Hill of University College,
and to Mr Gordon of Emmanuel College, Cambridge. I am indebted to the
kind offices of Miss M. C. Knowles for the photograph of the specimen
of _Archaeopteris hibernica_ in the Irish National Museum, Dublin,
reproduced on page 561.

Many of the illustrations are reproduced from drawings by my wife:
those made from the actual specimens are distinguished by the addition
of the initials M. S. I am grateful to her also for some improvements
in the letter-press. For the drawings made from sections and for some
of the outline sketches I am responsible. I have availed myself freely
of the facilities afforded by Professor McKenny Hughes in the Sedgwick
Museum of Geology for the examination of specimens under the charge of
Mr Newell Arber, the University Demonstrator in Palaeobotany. It is
a pleasure to add that, as on former occasions, I am indebted to the
vigilance of the Readers of the University Press for the detection of
several errors which escaped my notice in the revision of the proofs.

                                                        A. C. SEWARD.

  BOTANY SCHOOL, CAMBRIDGE.
      _March_ 12, 1910.




                           TABLE OF CONTENTS


                              CHAPTER XII
        =SPHENOPHYLLALES= (continued from Volume I.). Pp. 1–16.

                                                                    PAGE

  _Sphenophyllum_                                                    1–7
  _Cheirostrobus_                                                   7–12
  =Sphenophyllales and Psilotaceae=                                12–16

                             CHAPTER XIII
                       =PSILOTALES.= Pp. 17–29.

  _Psilotum_ and _Tmesipteris_                                     17–24
  Fossils described by authors as being closely allied to
      _Psilotum_                                                   24–26
  _Psilophyton_                                                    26–29

                              CHAPTER XIV
                      =LYCOPODIALES.= Pp. 30–91.

  =Recent Lycopodiales= (General)                                  30–33
  Lycopodiaceae (Recent)                                           33–49
  Selaginellaceae (Recent)                                         49–58
  Isoetaceae (Recent)                                              58–66
  =Fossil Lycopodiales=                                            66–91
  Isoetaceae (Fossil)                                              66–68
  _Pleuromeia_                                                     68–73
  Herbaceous fossil species of Lycopodiales                        73–91
  _Lycopodites_                                                    76–84
  _Selaginellites_                                                 85–88
  _Lycostrobus_                                                    88–91
  _Poecilitostachys_                                                  91

                              CHAPTER XV
                =ARBORESCENT LYCOPODIALES.= Pp. 92–195.

  =Lepidodendron=                                                 93–181

       i. General                                                  93–97

      ii. Leaves and Leaf-cushions                                97–105

     iii. _Lepidophloios_                                        105–109

      iv. The anatomy of _Lepidodendron vasculare_               109–123

       v. Lepidodendron stems as represented by casts and
          impressions of partially decorticated specimens        123–128
            _a._ _Knorria_ 124–126; _b._ _Bergeria_ 126, 127;
               _c._ _Aspidiaria_  127, 128.

      vi. Lepidodendroid axes known as _Ulodendron_ and
          _Halonia_                                              128–139
            _a._ _Ulodendron_ 128–135; _b._ _Halonia_ 135–139.

     vii. Anatomical characters of vegetative Lepidodendron
          shoots                                                 139–181
            1. _Lepidodendron esnostense_ 139, 140; 2. _L.
                rhodumnense_ 140; 3. _L. saalfeldense_ 141;
                4. _L. fuliginosum_ 141–160; 5. _L. Harcourtii_
                160–163; 6. _L. Wünschianum_ 163–171; 7. _L.
                macrophyllum_ 171; 8. _L. Veltheimianum_
                171–177; 9. _L. Pedroanum_ 177, 178; 10. _L.
                australe_ 178–181.

    viii. Fertile shoots of Lepidodendreae                       181–195
            A. _Lepidostrobus_ 181–191. i. _Lepidostrobus
                variabilis_ 187, 188; ii. _L. oldhamius_
                188–190;  iii. _L. Brownii_, etc. 190, 191.
            B. _Spencerites_ 192–195.


                              CHAPTER XVI
                      =SIGILLARIA.= Pp. 196–226.

       i. General 196–210; ii. Leaves 210–215; iii. Fertile
           shoots 215–218; iv. The structure of Sigillarian
           stems 218–224; v. _Sigillaria Brardi_ 224–226.


                             CHAPTER XVII
                       =STIGMARIA.= Pp. 227–247.


                             CHAPTER XVIII
                    =BOTHRODENDREAE.= Pp. 248–270.

    _Bothrodendron_ 248–264. _a._ _B. minutifolium_ 251–253;
        _b._ _B. punctatum_ 254, 255; _c._ _B. kiltorkense_
        255–259. Anatomy of vegetative shoots of
        _Bothrodendron_ 260–262; Cones of _Bothrodendron_
        262–264.
    _Pinakodendron_                                                  264
    _Omphalophloios_                                             264–266
    General considerations                                       266–270


                              CHAPTER XIX
                =SEED-BEARING PLANTS CLOSELY ALLIED TO
              MEMBERS OF THE LYCOPODIALES.= Pp. 271–279.

       i. _Lepidocarpon_ 271–275; ii. _Miadesmia_ 275–279.


                              CHAPTER XX
                       =FILICALES.= Pp. 280–323.

    I. =Leptosporangiate Filicales=                              283–316
        Eufilicineae 284–316. Osmundaceae 285, 286;
          Schizaeaceae 286–291; Matonineae 291–293; Loxsomaceae
          293; Hymenophyllaceae 294; Cyatheaceae 294–296;
          Dennstaedtiinae 296; Polypodiaceae 296; Parkeriaceae
          297; Dipteridinae 298.
            The habit, leaf-form, and distribution of ferns
          300–309; The anatomy of ferns 309–316.

   II. =Marattiales=                                             316–321

  III. =Ophioglossales=                                          321–323


                              CHAPTER XXI
                     =FOSSIL FERNS.= Pp. 324–394.

    =Osmundaceae= 324–346; =Schizaeaceae= 346–351; =Gleicheniaceae=
        351–355; =Matonineae= 355–363; =Hymenophyllaceae= 363–365;
        =Cyatheaceae= 365–375; =Polypodiaceae= 375–380; =Dipteridinae=
        380–394.


                             CHAPTER XXII
                 =MARATTIALES (FOSSIL).= Pp. 395–411.

    _Ptychocarpus_ 397; _Danaeites_ 398; _Parapecopteris_ 398;
        _Asterotheca_ 398–400; _Hawlea_ 400; _Scolecopteris_ 401, 402;
        _Discopteris_ 402–404; _Dactylotheca_ 404–406; _Renaultia_ 406;
        _Zeilleria_ 407; _Urnatopteris_ 407; _Marattiopsis_ 407–409;
        Danaeopsis 409; Nathorstia 410, 411.


                             CHAPTER XXIII
                      =PSARONIEAE.= Pp. 412–426.


                             CHAPTER XXIV
                =OPHIOGLOSSALES (FOSSIL).= Pp. 427–431.


                              CHAPTER XXV

                    =COENOPTERIDEAE.= Pp. 432–472.

    I. Botryoptereae                                             434–443

   II. Zygoptereae                                               443–470


                             CHAPTER XXVI
            =HYDROPTERIDEAE AND SAGENOPTERIS.= Pp. 473–483.

    Marsiliaceae 473–475; Salviniaceae 475–477; _Sagenopteris_ 477–483.


                             CHAPTER XXVII
                 =GENERA OF PTERIDOSPERMS, FERNS, AND=
                _PLANTAE INCERTAE SEDIS_. Pp. 484–580.

    _Taeniopteris_ 485–494; _Weichselia_ 494–496; _Glossopteris_
        496–512; _Gangamopteris_ 512–517; _Lesleya_ 517–519;
        _Neuropteridium_ 519–523; _Cardiopteris_ 523–525; _Aphlebia_
        525–529; _Sphenopteris_ 529–532; _Mariopteris_, _Diplotmema_,
        _Palmatopteris_ 532–537; _Cephalotheca_ 537; _Thinnfeldia_
        537–544; _Lomatopteris_ 544–546; _Cycadopteris_ 546;
        _Ptilozamites_ 546–548; _Ctenopteris_ 548–550; _Dichopteris_
        550–552; _Odontopteris_ 552–556; _Callipteris_ 557–559;
        _Callipteridium_ 560; _Archaeopteris_ 552–565; _Neuropteris_
        565–571; _Cyclopteris_ 571, 572; _Linopteris_ 572, 573;
        _Alethopteris_ 573–576; _Lonchopteris_ 576; _Pecopteris_
        576–580.


  INDEX                                                      Pp. 609–624




                         LIST OF ILLUSTRATIONS

Several of the illustrations are printed from blocks for which I am
    indebted to learned societies or to individuals. The sources from
    which clichés were obtained are mentioned within square brackets.

  FRONTISPIECE. _Thamnopteris Schlechtendalii_ (Eich.). From a
    photograph given to me by Dr Kidston and Mr Gwynne-Vaughan. (Page 329.)

  FIG.                                                              PAGE
  112. _Sphenophyllostachys_                                           2
  113. ╭  _Sphenophyllostachys Römeri_                                  3
       ┤ _Sphenophyllum trichomatosum_
       ╰ _S. majus_
  114, 115. _Sphenophyllostachys fertilis_                          4, 5
               [Council of the Royal Society of London.]
  116. _Sphenophyllostachys Dawsoni_                                   6
          [Mr A. G. Tansley, Editor of the New Phytologist.]
  117. ╭  _Cheirostrobus pettycurensis_                                 8
       ╰ _Pseudobornia ursina_
  118. _Psilotum triquetrum_                                          18
  119. _Psilotum triquetrum_ (anatomy)                                20
  120. _Tmesipteris tannensis_                                        22
  121. _Lycopodium_ (seven species)                                   35
  122. _Lycopodium squarrosum_                                        36
  123. _Lycopodium cernuum_                                           37
  124. _Lycopodium obscurum_                                          38
  125. _Lycopodium_ (anatomy of stem)                                 41
  126. _Lycopodium_ (anatomy of cones)                                45
  127–129. _Lycopodium cernuum_ (cone)                             47–49
             [Council of the Royal Society of Edinburgh.]
  130. _Selaginella grandis_                                          50
  131. _Selaginella_ (anatomy)                                        52
  132. ╭  _Isoetes echinospora_                                        59
       ╰ _I. lacustris_
  133. _Isoetes lacustris_ (anatomy)                                  62
  134. _Pleuromeia Sternbergi_                                        70
  135. _Selaginellites_ and _Lycopodites_                             80
  136. _Lycopodites lanceolatus_                                      81
            [Council of the Geological Society of London.]
  137. _Lycopodites falcatus_                                         83
  138. _Selaginellites primaevus_                                     86
  139. _Lycostrobus Scotti_                                           89
  140. _Picea excelsa_                                                94
  141. _Lepidodendron Sternbergii_                                    97
  142. _Sigillaria_ (leaves)                                          98
  143. _Lepidodendron_ (leaves)                                       99
  144. _Lepidodendron Veltheimianum_                                 101
  145. Lepidodendron leaf-cushion                                    102
  146. Lepidodendron and Lepidophloios leaf-cushions                 104
  147. Lepidophloios leaf-cushion                                    108
  148–155. _Lepidodendron vasculare_                             112–122
  156. _Knorria mirabilis_                                           125
  157. _Lepidodendron Veltheimianum_ (_Ulodendron_)                  129
  158. Diagrammatic section illustrating the branch-theory of the
         Ulodendroid scar                                            132
    [Council of the Manchester Literary and Philosophical Society.]
  159. _Pinus clausa_                                                134
  160. _Lepidophloios scoticus_                                      135
  161. _Halonia tortuosa_                                            136
  162–167. _Lepidodendron fuliginosum_                           143–147
           [Council of the Cambridge Philosophical Society.]
  168. _Lepidodendron vasculare_ and _L. fuliginosum_                148
  169. _Lepidodendron fuliginosum_                                   149
  170–172. _L. fuliginosum_                                      150–152
  173. _Lepidodendron obovatum_                                      154
  174–176. _Lepidodendron aculeatum_                            155, 156
             [Oxford University Press: Annals of Botany.]
  177. _Stigmaria radiculosa_                                        157
  178. Stigmarian rootlet                                            158
  179. _Lepidodendron Harcourtii_ and _L. fuliginosum_               162
  180. _Lepidodendron Wünschianum_                                   163
  181, 182. _L. Wünschianum_                                    165, 166
  183, 184. _L. Wünschianum_                                    168, 169
                   [Editor of the New Phytologist.]
  185. _Lepidodendron Veltheimianum_                                 173
  186. _L. Veltheimianum_ and _L. macrophyllum_                      176
  187. _Lepidodendron australe_                                      179
         [Dr H. Woodward, Editor of the Geological Magazine.]
  188, 189. _Lepidostrobus_                                     183, 184
  190. _Lepidodendron_ and _Lepidostrobi_                            186
  191. _Lepidostrobus_                                               188
  192. _Spencerites insignis_                                        193
             [Oxford University Press: Annals of Botany.]
  193. _Sigillaria elegans_, _S. rugosa_, _S. tessellata_,
         _Omphalophloios anglicus_                                   197
  194. _Sigillaria McMurtriei_                                       199
  195. _Sigillaria mammillaris_                                      199
  196. _Sigillaria Brardi_, _S. laevigata_, and _Lepidodendron
         Wortheni_                                                   200
  197. _Carica_ sp.                                                  202
  198, 199. _Sigillaria_                                        205, 206
  200. _Sigillaria Brardi_                                           212
  201. _Sigillariostrobus_                                           216
  202. _Sigillaria elegans_ and _S. elongata_                        220
  203. _Sigillaria Brardi_                                           225
  204, 205. _Stigmaria ficoides_                                227, 228
  206. _Cyperus papyrus_                                             230
  207, 208. Stages in the development of _Sigillaria_                236
  209. _Stigmariopsis_                                               237
  210. _Stigmaria_                                                   241
  211. _Bothrodendron punctatum_                                     250
  212. _Bothrodendron minutifolium_, _B. punctatum_, _B.
         kiltorkense_ and _Lepidostrobus Olryi_                      252
  213. _Bothrodendron minutifolium_                                  254
  214. _Bothrodendron Leslei_                                        258
                   [Trustees of the British Museum.]
  215. _Bothrodendron mundum_                                        259
  216. _Bothrostrobus_                                               263
    [Council of the Manchester Literary and Philosophical Society.]
  217. _Omphalophloios_                                              265
  218. _Lepidocarpon Lomaxi_                                         273
  219. _Miadesmia_ and _Bothrodendron_                               276
  220. _Angiopteris evecta_ and _Cycas revoluta_                     283
  221. _Osmunda cinnamomea_, _O. regalis_, and _Todea barbara_       286
  222. _Schizaea elegans_                                            287
  223. _Aneimia rotundifolia_                                        288
  224. _Aneimia flexuosa_, _A. phyllitidis_, _Hymenophyllum_,
         _Matonia pectinata_, _Thyrsopteris elegans_, _Gleichenia_   289
  225. _Gleichenia dicarpa_                                          290
  226. _Gleichenites Rostafinskii_, _Gleichenia dicarpa_, _G.
         dichotoma_                                                  290
  227. _Matonia pectinata_                                           292
                    [Council of the Royal Society.]
  228. _Matonia pectinata_                                           293
  229. _Thyrsopteris elegans_, _Cyathea spinulosa_, _Dicksonia
         coniifolia_, _D. culcita_, _Davallia concinna_, _Alsophila
         excelsa_                                                    294
  230. _Dicksonia Bertervana_                                        295
                   [Trustees of the British Museum.]
  231. _Dipteris quinquefurcata_, _D. conjugata_, _D. Wallichii_,
         and _Polypodium quercifolium_                               297
  232. _Davallia aculeata_                                           299
  233. _Polypodium Billardieri_                                      302
  234. _Polypodium quercifolium_                                     303
  235. _Hemitelia capensis_                                          304
  236 _a_, 236 _b_. _Pteris aquilina_                           305, 306
              [Council of the Linnean Society of London.]
  237. _Matonia pectinata_, _Matonidium_, _Gleichenia dicarpa_, and
         _Trichomanes reniforme_ (anatomy)                           310
  238. _Trichomanes scandens_                                        311
                   [Editor of the New Phytologist.]
  239. _Platyzoma microphylla_                                       312
                   [Editor of the New Phytologist.]
  240. _Cyathea Imrayana_                                            313
                   [Editor of the New Phytologist.].
  241. _Angiopteris evecta_ and _Marattia fraxinea_                  317
  242. _Angiopteris evecta_ and _Danaea_                             318
  243, 244. _Angiopteris evecta_                                     319
  245. _Marattia fraxinea_, _M. Kaulfussii_, _Kaulfussia_, and
         _Marattiopsis Münsteri_                                     320
  246. _Ophioglossum vulgatum_                                       322
  247. _Botrychium virginianum_                                      322
  248. _Zalesskya gracilis_                                          327
  249. _Zalesskya diploxylon_                                        328
  250. _Thamnopteris Schlechtendalii_                                330
  251. _Lonchopteris virginiensis_                                   331
  252. _Osmundites Dunlopi_                                          333
  253, 254. _Osmundites Kolbei_                                 334, 335
                 [Editor of the Geological Magazine.]
  255. _O. Kolbei_                                                   336
  256. _Cladophlebis denticulata_, _Todites Williamsoni_,
         _Discopteris Rallii_, _Kidstonia heracleensis_, and
         _Todeopsis primaeva_                                        340
  257, 258. _Cladophlebis denticulata_                          342, 345
  259. _Klukia exilis_                                               348
           [Council of the Cambridge Philosophical Society.]
  260. _Ruffordia Goepperti_                                         349
  261. _Chrysodium lanzaeanum_, _Lygodium Kaulfussi_, _Marattia
         Hookeri_                                                    350
  262. _Gleichenites longipennis_, _G. delicatula_, _G.
         Nordenskioldi_ and _G. Zippei_                              354
  263. _Gleichenites hantonensis_                                    356
             [Council of the Palaeontographical Society.]
  264. _Laccopteris elegans_                                         357
                    [Council of the Royal Society.]
  265. _Matonidium Wiesneri_, _Marattiopsis marantacea_,
         _Gleichenites_ _gracilis_, _Laccopteris Goepperti_, and
         _L. Muensteri_                                              358
  266.  _Laccopteris polypodioides_                                  359
                   [Trustees of the British Museum.]
  267. _Laccopteris_                                                 359
                   [Trustees of the British Museum.]
  268. ? _Laccopteris polypodioides_                                 360
                   [Trustees of the British Museum.]
  269. _Matonidium Goepperti_                                        362
               [Editor of the Encyclopaedia Britannica.]
  270. _Senftenbergia elegans_, _Oligocarpia Brongniartii_,
         _Trichomanes sp._, _Hymenophyllum tunbridgense_,
         _Sphenopteris (Hymenophyllites) quadridactylites_           364
  271. _Coniopteris hymenophylloides_                                368
    [Council of the Manchester Literary and Philosophical Society.]
  272. _C. hymenophylloides_                                         369
  273. _Coniopteris quinqueloba_                                     370
  274. _Coniopteris arguta_                                          371
  275. _Coniopteris arguta_ and _C. hymenophylloides_                372
  276. _Oncopteris Nettvalli_                                        373
  277. _Protopteris punctata_                                        373
  278. _Laccopteris polypodioides_, _L. Muensteri_, _Dicksonia_,
         _Onychiopsis Mantelli_, _Hausmannia Sewardi_, _H.
         Kohlmanni_, and _Protopteris Witteana_                      374
  279. _Adiantides antiquus_ and _A. lindsayoides_                   376
  280. _Onychiopsis Mantelli_                                        379
  281. _Dictyophyllum exile_                                         381
  282. _Dictyophyllum Nilssoni_, _Rhizomopteris Schenki_,
         _Camptopteris spiralis_, and _D. exile_                     382
  283. _Dictyophyllum rugosum_                                       384
                   [Trustees of the British Museum.]
  284. _Thaumatopteris Münsteri_                                     386
  285. _Clathropteris meniscoides_                                   387
  286. _Clathropteris egyptiaca_                                     388
                 [Editor of the Geological Magazine.]
  287. _Camptopteris spiralis_                                       389
  288. _Hausmannia dichotoma_                                        391
  289. _Hausmannia sp._                                              393
  290. _Alethopteris lonchitica_, _Lonchopteris rugosa_,
         _Sphenopteris Hoeninghausi_, _Parapecopteris
         neuropteroides_,and _Pecopteris (Dactylotheca) plumosa_     399
  291. _Ptychocarpus unita_, _Asterotheca Sternbergii_, _Danaeites
         sarepontanus_, _Hawlea Miltoni_, _H. pulcherrima_,
         _Scolecopteris elegans_                                     400
  292. _Dactylotheca plumosa_                                        405
  293. _D. plumosa_                                                  406
  294. _Nathorstia angustifolia_ and _N. latifolia_                  410
  295. _Psaronius_                                                   414
  296. _Psaronius infarctus_, _P. coalescens_, _P. musaeformis_,
         and _P. asterolithus_                                       416
  297. _Pecopteris Sterzeli_                                         419
  298. _Caulopteris peltigera_ and _Megaphyton insigne_              421
  299. _Ptychopteris_                                                423
  300. _Dicksonia antarctica_                                        424
  301. _Rhacopteris sp._                                             427
  302. _Noeggerathia foliosa_                                        429
  303. _Chiropteris Zeilleri_                                        430
                 [Annals of the South African Museum.]
  304. _Tubicaulis solenites_                                        435
                   [Editor of the New Phytologist.]
  305. _Botryopteris cylindrica_                                     439
  306. _Botryopteris ramosa_                                         441
  307. _Botryopteris antiqua_                                        442
  308. _Clepsydropsis antiqua_, _Etapteris Scotti_, _Diplolabis
         forensis_, _Zygopteris primaria_, _Stauropteris
         oldhamia_                                                   444
  309. _Diplolabis forensis_, _Botryopteris forensis_,
         _Corynepteris coralloides_, _Schizopteris pinnata_          445
  310. _Metaclepsydropsis duplex_, _Stauropteris oldhamia_,
         _Ankyropteris scandens_                                     450
  311. _Ankyropteris Grayi_                                          451
  312. _Thamnopteris Schlechtendalii_, _Ankyropteris corrugata_,
         _A. bibractensis_                                           453
  313. _Ankyropteris bibractensis_                                   454
  314. _Ankyropteris corrugata_                                      457
  315. _Ankyropteris corrugata_                                      458
                   [Editor of the New Phytologist.]
  316, 317. _Ankyropteris corrugata_                            459, 460
  318. _Etapteris Scotti_                                            462
                   [Editor of the New Phytologist.]
  319. _Etapteris_, _Botryopteris forensis_                          463
  320. _Stauropteris oldhamia_                                       464
                   [Editor of the New Phytologist.]
  321. _Stauropteris oldhamia_                                       467
  322. _Stauropteris oldhamia_                                       468
                   [Editor of the New Phytologist.]
  323. _Stauropteris_                                                469
                   [Editor of the New Phytologist.]
  324. _Asterochlaena laxa_                                          472
                   [Editor of the New Phytologist.]
  325. Sporocarp-like bodies (? _Sagenopteris_)                      478
  326. _Regnellidium diphyllum_, _Sagenopteris rhoifolia_            479
  327. _Sagenopteris Phillipsi_                                      480
                   [Trustees of the British Museum.]
  328. _Sagenopteris Phillipsi_                                      481
         [Council of the Manchester Literary and Philosophical
                               Society.]
  329. _Taeniopteris multinervis_, _Lesleya Delafondi_               487
  330. _Taeniopteris Carnoti_, _T. spatulata_, _T. coriacea_         490
  331. _Taeniopteris Carruthersi_                                    491
                 [Annals of the South African Museum.]
  332. _Taeniopteris vittata_                                        493
  333. _Weichselia Mantelli_, _W. erratica_                          495
  334. _Glossopteris Browniana_                                      499
            [Council of the Geological Society of London.]
  335, 336. _Glossopteris Browniana_                            500, 501
                   [Trustees of the British Museum.]
  337. _Vertebraria indica_                                          502
  338. _Vertebraria indica_, _Onoclea struthiopteris_                503
  339. Glossopteris fronds attached to rhizome                       504
  340, 341. _Glossopteris indica_, _G. angustifolia_            506, 507
                   [Trustees of the British Museum.]
  342. _Glossopteris angustifolia_ var. _taeniopteroides_            508
                 [Council of the Geological Society.]
  343. _Blechnoxylon talbragarense_                                  509
  344. _Glossopteris retifera_                                       511
                   [Trustees of the British Museum.]
  345. _Gangamopteris cyclopteroides_                                515
                   [Trustees of the British Museum.]
  346. _Arberia sp._                                                 517
  347. _Lesleya simplicinervis_                                      518
  348. _Neuropteridium validum_                                      520
                   [Trustees of the British Museum.]
  349. _Neuropteridium intermedium_                                  522
  350. _Cardiopteris frondosa_                                       524
  351. _Gunnera manicata_                                            527
  352. _Sphenopteris obtusiloba_, _Pecopteris arborescens_,
         _Sphenopteris furcata_                                      529
  353. _Sphenopteris affinis_                                        531
  354. _Palmatopteris_, _Mariopteris_, _Diplotmema Zeilleri_,
          _Neuropteris macrophylla_, _N. heterophylla_, _N.
          Scheuchzeri_, _Alloiopteris Essinghii_                     535
  355. _Cephalotheca mirabilis_                                      536
  356. _Thinnfeldia odontopteroides_, _Ptilozamites_                 539
                 [Council of the Geological Society.]
  357. _Thinnfeldia odontopteroides_                                 540
                 [Council of the Geological Society.]
  358. _Thinnfeldia odontopteroides_                                 541
                 [Annals of the South African Museum.]
  359. _Thinnfeldia rhomboidalis_                                    542
  360. _Lomatopteris jurensis_, _L. Schimperi_, _Thinnfeldia
          rhomboidalis_                                              544
  361. _Ptilozamites Heeri_                                          547
  362. _Ctenopteris cycadea_                                         549
  363. _Dichopteris visianica_                                       551
  364. _Alethopteris lonchitica_, _Mariopteris muricata_,
         _Odontopteris_ cf. _alpina_                                 553
  365. _Odontopteris minor_                                          554
  366. _Odontopteris genuina_, _Callipteridium gigas_, _Callipteris
         Pellati_, _C. lyratifolia_                                  557
  367. _Callipteris conferta_                                        559
  368. _Archaeopteris hibernica_                                     561
  369. _Archaeopteris hibernica_, _A. archetypus_, _A.fissilis_, _A.
         fimbriata_                                                  564
  370. _Neuropteris_ with Cyclopteris leaflets                       566
              [From a block received from Mr Carruthers.]
  371. _Neuropteris heterophylla_                                    568
  372. _Neuropteris macrophylla_                                     569
  373. _Neuropteris Scheuchzeri_                                     570
  374. _Linopteris neuropteroides_                                   573
  375. _Alethopteris Serlii_                                         575
  376. _Pecopteris arborescens_                                      578




                           ERRATA IN VOL. I

Page  16, line 4.  For “The North American Tulip tree” read The Tulip
            tree of North America and China.

  „   66, line 2 from the bottom.  For “Browera” read Berowra.

  „  127, line 3 and 4 from bottom.  For _Achyla_ and _Palaeachyla_ read
            _Achlya_ and _Palaeachlya_.

  „  145, lines 4 and 5.  For “Upper Greensand” read Lower Eocene.

  „  162, line 3 from bottom.  For “_Corallina barbata_” read
            _Cymopolia barbata_.

  „  170, line 20.  For “sporangiaphore” read sporangiophore.

  „  185, line 2.  The genera _Udotea_ and _Halimeda_, members of the
            Siphoneae, are incorrectly included under the Corallinaceae.

  „  191, line 11 from bottom.  Omit _Chondrus crispus_, which is one of
            the Florideae and not a Brown Alga.

  „  202, line 13.  For “_Halmeda_” read _Halimeda_.

  „  250, line 11.  For “three” read the.

  „  381, line 10.  For “_Calamopytus_” read _Calamopitys_.




                            CHAPTER XII[1].

                    SPHENOPHYLLALES (_concluded_).

                           _Sphenophyllum_.


The account of the Sphenophyllales given in the first volume[2] of this
work must be extended and somewhat modified in the light of recent work
on the fertile shoots of _Sphenophyllum_.

_Sphenophyllostachys Dawsoni_ (Will.) was described as consisting of
an axis bearing superposed whorls of bracts connate at the base in
the form of a shallow funnel-shaped collar giving off from the upper
surface and close to the axis of the cone two concentric series of
sporangiophores. Occasionally there are three series, as represented in
fig. 112. In another type of strobilus, _Sphenophyllostachys Römeri_[3]
each sporangiophore terminates in two pendulous sporangia (fig. 113,
A; see also fig. 107, C, vol. I.). It has already been pointed out
that the common occurrence of detached strobili necessitates their
description under distinct specific names; it is only by a rare
accident that we can assign fossil cones to their vegetative shoots.
There are, however, reasons for believing that _Sphenophyllostachys
Dawsoni_ is the strobilus of the plant originally described by
Sternberg[4] from impressions of foliage-shoots as _Rotularia
cuneifolia_. Another difficulty presented by petrified material is
that of determining, with certainty, whether two imperfect specimens,
differing from one another in features which do not appear to be of
sufficient importance to warrant specific separation, are forms of one
species or portions of specifically distinct cones. It has been pointed
out by Scott[5] that the strobilus known as _Sphenophyllostachys
Dawsoni_ probably includes two distinct species, one being the cone
of _Sphenophyllum cuneifolium_ Sternb., and the other the cone of
_S. myriophyllum_ Crép[6]. The stem of _S. myriophyllum_ agrees
anatomically with the type known as _Sphenophyllum plurifoliatum_ Will.
and Scott[7].

[Illustration: FIG. 112. Sketch of a radial longitudinal section of
  _Sphenophyllostachys_. There are usually two concentric series of
  sporangia on the sporophylls, not three as shown in the figure.
  The upper figure (after Zeiller) shows the linear bracts in
  surface-view.]

In addition to the two types of cone already mentioned,
_Sphenophyllostachys Dawsoni_ and _S. Römeri_, others have been
described by Kidston from carbonised impressions. One of these is the
fertile branch of _Sphenophyllum majus_[8]. The basal portions of the
bracts of each whorl form a narrow collar round the axis of the cone;
the free portion of each bract consists of a lamina divided into two
equal bifid lobes bearing on its upper surface one group, or possibly
two groups, of four sessile sporangia between the narrow coherent bases
of the laminae and the sinus between the terminal lobes (fig. 113, C).
Another characteristic feature is the greater length of the internodes;
this renders the cone less compact and less sharply differentiated from
the vegetative shoots than those of other species. A specimen in Dr
Kidston’s collection illustrates the peculiar character of the fertile
portion of this species; it consists of an axis bearing a succession of
lax sporophylls succeeded above and below by whorls of sterile leaves.
In this species, therefore, we cannot speak of a compact strobilus at
the end of a shoot of limited growth, but of axes in which sterile and
fertile leaves are borne alternately[9], a condition recalling the
alternation of foliage leaves and sporophylls in _Tmesipteris_ and in
_Lycopodium Selago_.

[Illustration: FIG. 113.

  A. _Sphenophyllostachys Römeri._ (Solms-Laubach.)
  B. _Sphenophyllum trichomatosum_ Stur.
  C. _Sphenophyllum majus._ Bronn. (A–C. After Kidston.)]

Another form of cone, also from the Middle Coal Measures, is referred
by Kidston to _Sphenophyllum trichomatosum_ Stur[10] (fig. 113, B):
this is characterised by the more horizontal position of the bracts,
which “do not appear to be so much or so suddenly bent upwards in their
distal portion as in some other species of _Sphenophyllum_,” and by
sessile sporangia borne singly on the upper face of each bract.

[Illustration: FIG. 114. _Sphenophyllostachys fertilis_ (Scott).
  (After Scott.) Diagram of a node in longitudinal section, showing
  one sporophyll and the base of the opposite one. _v.l._ ventral
  lobe of sporophyll; _v.s._ one of the segments into which it
  divides; _v.s′._ stump of another segment; _d.l._ dorsal lobe;
  _d.s._, _d.s′._ segments of dorsal lobe.]

A more recent addition to our knowledge of the fertile shoots of
_Sphenophyllum_ is due to Scott who has described a new type of cone
under the name _Sphenophyllum fertile_[11]. The petrified specimen
on which the species was founded was discovered by Mr James Lomax in
the Lower Coal Measures of Lancashire; it represents a portion of a
cone 6 cm. long and approximately 12 mm. broad. The axis contains a
single vascular cylinder agreeing in essentials with the type of stem
structure known as _Sphenophyllum plurifoliatum_. The nodal regions,
which exhibit the slight swelling characteristic of the genus, bear
several (probably twelve) appendages connate at the base and forming
a narrow flange encircling the axis. Each bract, the base of which
forms part of the narrow collar surrounding the axis, consists of two
lobes, ventral and dorsal, divided palmately into several (sometimes
four) segments or sporangiophores (fig. 115). Each sporangiophore
terminates distally in an oblong or oval lamina bearing two sporangia
on its adaxial face (fig. 114). The space between the axis and the
periphery of the cone is thus occupied by crowded peltate laminae,
each with its pair of sporangia. A single vascular bundle supplies
each sporangiophore and bifurcates in the distal lamina into two
branches which extend to the bases of the sporangia. The sporangia
agree in structure with those of other species of _Sphenophyllum_: the
spores are of one size and elliptical, characterised by the presence
of several sharp ridges or flanges encircling the spore-wall in the
direction of the major-axis. _Sphenophyllostachys fertilis_ differs
from all previously recorded types in the absence of sterile bracts.
The appendages of the cone-axis are all fertile, a striking contrast
to the differentiation into protective and sporangia-bearing bracts
which constitutes a constant feature in the cones of _Sphenophyllum_
and _Calamites_. It is possible, as Scott suggests, that the absence of
sterile segments is the result of modification of the more usual type
of strobilus; instead of the dorsal and ventral lobes of the bracts
sharing between them the duties of protection and spore-production,
the whole of each bract is constructed on the plan of the maximum
spore-output, the laminar terminations of the sporangiophores
serving the purpose of protection. The cone may be described as
more specialised than the normal type of strobilus for reproductive
purposes[12].

[Illustration: FIG. 115. _Sphenophyllostachys fertilis_ (Scott).
  (After Scott.) Diagram of a single sporophyll as it would appear
  in a transverse section of the cone; showing one lobe (dorsal or
  ventral). _ax_, part of axis to which the sporophylls are attached.]

[Illustration: FIG. 116. _Sphenophyllostachys Dawsoni._ (After
  Thoday.) A. Larger spores; B, abortive spores; C, mature spores
  showing the characteristic spines.]

It has been stated, on evidence which is unsatisfactory, that
_Sphenophyllum_ possesses two kinds of spores. While regarding the
genus as homosporous on the evidence before us, it is interesting
to find that cases occur in which the spores in the same sporangium
exhibit a marked difference in size. Attention has been called by
Williamson and Scott[13] to variation in the dimensions of spores: a
more pronounced difference in size has been recorded by Mr Thoday[14]
who gives 120μ as the maximum and 90μ as the minimum diameter of the
spores in a cone of _Sphenophyllostachys Dawsoni_. The presence of
several abortive spores in the sporangium (fig. 116) containing the
larger spores favours the view that this difference in size may be the
first step towards the development of heterospory.

It is clear that the types of strobilus designated
_Sphenophyllostachys_ (figs. 112–114) present a divergence of
characters too great to be comprised under one genus; but in the
absence of fuller information, we cannot do otherwise than follow the
only logical custom of grouping them together as examples of strobili
borne by plants which, in the present state of our knowledge, are most
conveniently referred to the genus _Sphenophyllum_.


                           _Cheirostrobus._

This generic name was applied by Dr Scott[15] to a calcified cone
obtained by Mr James Bennie in 1883 from the Lower Carboniferous
plant-beds of Pettycur near Burntisland on the Firth of Forth.
_Cheirostrobus_ is distinguished from _Sphenophyllostachys_ by its
greater breadth (3.5 cm.); externally it agrees more closely with the
fertile shoots of _Lepidodendron_ than with those of _Sphenophyllum_.
A single vascular cylinder having the form of a fluted Doric column
(fig. 117, B, _x_) occupies the axis of the cone: it consists for
the most part of reticulate tracheae which tend to assume a short
or isodiametric form in the central region; the smaller protoxylem
tracheids with the spiral form of pitting constitute the sharp and
prominent ridges at the periphery of the xylem-cylinder. In the
outer part of the cylinder the metaxylem[16] consists exclusively of
tracheae, but towards the centre of the axis these are associated with
numerous parenchymatous cells.

The xylem is therefore centripetal in origin as in _Sphenophyllum_
and in nearly all recent and fossil members of the Lycopodiales. In
the type-specimen of _Cheirostrobus_ the vascular cylinder of the
cone consists entirely of primary xylem, but secondary xylem has been
found in a more recently discovered specimen[17]. Secondary xylem
occurs also in the peduncle of the cone. No appreciable remains of
phloem have been found. The cortex consists of slightly elongated
rather thick-walled tissue containing secretory sacs. Crowded
superposed whorls of bracts (or sporophylls), usually twelve in each
whorl, are borne on the axis and each sporophyll receives a single
vascular bundle from one of the vertical ridges of the xylem column
(fig. 117, A, _lt_). The members of each whorl are connate at the
base: from this narrow collar each sporophyll branches into an upper
or dorsal and a lower or ventral limb (fig. 117, A, _f_ and _s_).
Each limb divides palmately at a short distance from its origin into
three slender segments, which extend in a horizontal direction and
terminate in large laminar expansions (fig. 117, B, _s_) to afford
a protective covering to the surface of the cone. The upper set of
three segments, constituting sporangiophores (fig. 117, A, B, _f_) or
fertile divisions of the sporophyll, expand distally into comparatively
bulky laminae; each of these bears on its adaxial face four diagonally
placed outgrowths which form the short pedicels of very long and narrow
sporangia. The three lower segments—the sterile divisions of the
sporophylls—(fig. 117, A, B, _s_) are similar to the upper set except
in their greater length and in the kite-shaped form of their distal
laminae which are provided with lateral lobes. The single vascular
strand which supplies each sporophyll is represented at _lt_ in fig.
117, B; at _lt′_ the strand has divided into four, the three upper
bundles in the figure supply the sterile segments and the single lower
bundle ultimately divides into three which supply the fertile segments.
A pair of blunt processes (fig. A, _s_) extend downwards over the ends
of the underlying fertile lamina and two slender prolongations extend
upwards through several internodes.

[Illustration:
  FIG. 117. A, B. _Cheirostrobus pettycurensis_ Scott. (After Scott.)
            C, D. _Pseudobornia ursina_ Nath. (After Nathorst.)

  A. Diagrammatic radial longitudinal section of part of the
     cone-axis and two sporophylls. _lt_, bundle passing out to
     sporophyll; _f_, fertile segment of sporophyll showing two
     sporangia; _s_, sterile (lower) segment.
  B. Part of transverse section. _x_, stele; _lt_, _lt′_, bundles on
     their way to sporophylls; _a_, tips of sterile segments of lower
     sporophylls.
  C. Palmately branched leaf (½ natural size).
  D. Node of stem showing leaf-bases.]

An economical arrangement of the long and narrow sporangia and of the
sporophyll-segments between the axis and the periphery of the cone
is rendered possible by the interlocking of the sterile and fertile
segments by means of a groove in the upper face of the latter for
the accommodation of the former. The sporangia are characterised by
their unusually long and narrow form: the length of a sporangium may
reach 1 centimetre. In the structure of the wall the sporangia of
_Cheirostrobus_ agree closely with those of _Calamostachys_[18] and
_Sphenophyllostachys_. The spores are of one size only. The vascular
cylinder of the peduncle, originally described by Williamson[19] as
the peduncle of a large _Lepidostrobus_ (the cone of _Lepidodendron_),
is characterised by the presence of a short radially disposed zone
of secondary tracheids, a feature, as Scott points out, which may
extend into the axis of the cone. It is noteworthy that the protoxylem
elements are not always external, but occasionally occur internal to
one or two of the outermost metaxylem tracheae: the usual exarch[20]
structure of the central cylinder is not therefore absolutely
constant, but may be replaced by a mesarch arrangement.

The presence of a few sterile leaves on the peduncle below the fertile
portion of the cone, which agree in their lobed laminae with the
sporophylls, is the only fact which we possess as to the form of the
vegetative characters of the genus.

The above description is sufficient to indicate the extraordinary
complexity and high degree of specialisation of _Cheirostrobus_. The
sporophylls, with their trilobed segments, and the crowded sporangia of
exceptional length attached only by a narrow base constitute striking
peculiarities of the genus.

It is unfortunate that we are still without any satisfactory evidence
as to the nature of the plant the cones of which have been made the
type of a new genus and a new family. _Cheirostrobus_ affords an
interesting example of a type of reproductive shoot constructed on
a plan _sui generis_, and may be classed with some other extinct
genera as instances of the production in the course of evolution
of architectural schemes which appear to have been ill adapted for
competition with equally efficient though much simpler types. But the
discovery of these isolated forms of restricted geological range among
the relics of the Palaeozoic vegetation frequently supplies a key to
phylogenetic problems. _Cheirostrobus_ by its complex combination of
features characteristic of the Equisetales, the Lycopodiales and the
genus _Sphenophyllum_ throws a welcome light on the inter-relationships
of groups which represent divergent series. The combination of
morphological features in this generalised type led the author of the
genus to describe it as a descendant of an old stock which existed
prior to the divergence of the Equisetales and Lycopodiales.

The discovery of this new type of strobilus naturally led to a search
among Lower Carboniferous plants for vegetative shoots exhibiting
characters conformable with the whorled and branched leaves of
_Cheirostrobus_. In _Sphenophyllum_ we have a genus obviously
comparable with _Cheirostrobus_ as regards the form and disposition
of the leaves, but the differences between the cones and the striking
similarity of the vascular cylinder of the latter to that of
_Lepidodendron_ demonstrate conclusively that we must look elsewhere
for the vegetative members of the plant which produced cones of the
_Cheirostrobus_ type.

[Sidenote: PSEUDOBORNIA]

In 1902 Professor Nathorst[21] instituted the generic name
_Pseudobornia_ for plants of which imperfect examples had previously
been referred by Heer[22] to _Calamites_ under the name _C. radiatus_.
Heer’s plants were obtained from Upper Devonian rocks of Bear Island
in the Arctic seas and additional specimens were brought from the
same locality by the Swedish Polar Expedition of 1898. _Pseudobornia_
possesses jointed stems (fig. 117, D) bearing whorled and shortly
stalked leaves, often four in number, at each node. The leaves are
palmately branched with fine serrated edges (fig. 117, C). Certain
specimens, which are no doubt correctly described by Nathorst as
cones, are characterised by a thick axis bearing whorled leaves
with sporangia on their lower surfaces, but the material is not
sufficiently well preserved to render possible a recognition of
structural details. It has been suggested by Scott that _Pseudobornia_
may possibly be referable to the Sphenophyllales and that the stem of
_Cheirostrobus_ “may have had something in common with” Nathorst’s
genus[23]. The beds in which the stems occur are of Upper Devonian age,
while _Cheirostrobus_ was found in Lower Carboniferous rocks: this
difference in age is not, however, a serious objection to the validity
of the comparison. We cannot do more than express the view that
_Pseudobornia_, so far as can be ascertained without an examination of
petrified material or of more perfect impressions of strobili, exhibits
vegetative features not inconsistent with the morphological characters
of the fertile shoots known as _Cheirostrobus_.

                   •       •       •       •       •

The institution of a special group-name for the reception of
_Sphenophyllum_ is justified by the sum of its morphological features,
which do not sufficiently conform to those of any existing group of
Pteridophytes to warrant its inclusion in a system of classification
based on recent genera. In the case of _Cheirostrobus_ we are limited
to the characters of the cone and its peduncle. The suggestion that
the Devonian fossils known as _Pseudobornia_ may represent the foliage
shoots of a plant closely related to _Cheirostrobus_ has still to
be proved correct. Although we may find justification in the highly
complex and peculiar structure of _Cheirostrobus_ for the recognition
of the genus as a type of still another group of Pteridophytes, it
would be unwise to take this step without additional knowledge.

The undoubted similarity between _Cheirostrobus_ and _Sphenophyllum_
coupled with striking points of difference favours the inclusion of the
two genera in distinct families placed, for the present at least, in
the group Sphenophyllales.


                       Group =SPHENOPHYLLALES=.

               =Sphenophylleae=: genus _Sphenophyllum_.
               =Cheirostrobeae=: genus _Cheirostrobus_.

It has recently been proposed to include the family Psilotaceae,
comprising the two recent genera _Psilotum_ and _Tmesipteris_, as
another subdivision of the Sphenophyllales. This proposal had been made
by Professor Thomas[24] primarily on the ground that the sporophylls
of _Tmesipteris_ and _Psilotum_ appear to afford the closest parallel
among existing plants to the peculiar form of sporophyll characteristic
of the Sphenophyllales. The morphological interpretation of the
sporophylls of both _Sphenophyllum_ and _Cheirostrobus_ has been the
source of considerable discussion[25]. If we regard each sporophyll
as a leaf with two lobes, one fertile and one sterile, except in the
case of _Sphenophyllostachys fertilis_ in which both are fertile, an
obvious comparison may be made with the fern _Ophioglossum_; but the
difference between a single fern frond, consisting of a comparatively
large sterile lamina bearing a fertile branch composed of a long axis
with two rows of sporangia embedded in its tissues, and the whorled
sporophylls of _Sphenophyllum_ is considerable.

[Sidenote: PSILOTACEAE]

A brief reference may be made to the principal reasons which have
led to the suggestion that the Psilotaceae should be included in
the Sphenophyllales. The shoots of _Tmesipteris_ bear simple foliage
leaves spirally disposed on a slender axis, and in association with
these occur sporophylls consisting of a short axis bearing a pair of
small lobes and a bilocular synangium[26] (fig. 120, B). The synangium
is seated on a very short stalk given off from its sporophyll at the
base of the pair of laminae: the synangium with its short stalk may be
spoken of as the sporangiophore. In most cases the synangium appears
to be sessile on the sporophyll, but occasionally the much reduced
stalk is prolonged and forms an obvious feature. Dr Scott[27] suggested
that the Tmesipteris synangium with its axis may correspond to the
ventral lobe (or sporangiophore) of _Sphenophyllum_. In the latter
genus the whorled sporophylls consist in most species of a dorsal
and a ventral lobe, the latter serving as a sporangiophore bearing
one or more sporangia; in _Tmesipteris_ the sporophylls are spirally
disposed and each consists of a bilobed sterile portion bearing a
septate sporangium or bilocular synangium on a very short ventral lobe.
Professor Bower[28], in his account of the development and structure of
the sporophylls of _Tmesipteris_, drew attention to the comparatively
frequent occurrence of abnormal sporophylls and spoke of the plant as
unstable. More recently Professor Thomas[29] of Auckland has carefully
examined living plants, with the result that variations of different
kinds are proved to be exceedingly common. He finds that sporophylls
occur which exhibit repeated dichotomy of the axis (fig. 120, D, F) and
thus each may bear four instead of two leaf-lobes and three synangia,
one at the first fork and one at each of the forks of the second
order[30].

Other abnormalities occur in which the synangium is raised on a
distinct stalk instead of being more or less sessile at the point from
which the leaf-lobes diverge. A third form of departure from the normal
is that in which there is no synangium on the bilobed sporophyll, its
place being taken by a leaf-lobe. The deduction from the occurrence of
these abnormalities is that the synangium of _Tmesipteris_ represents
a ventral leaf-lobe, as Scott suggested. Professor Thomas draws
attention to the resemblance between _Tmesipteris_ sporophylls and
the foliage-leaves of _Sphenophyllum_, which are either simple with
dichotomously branched veins or the lamina is deeply divided into two
or more segments. In some types of _Sphenophyllostachys_ the bracts
are simple (_S. Dawsoni_), but in others (_Sphenophyllum majus_, fig.
113, C) they are forked like the foliage-leaves and bear a close
resemblance to the abnormal sporophylls of _Tmesipteris_. Moreover,
in _Sphenophyllostachys Römeri_ (fig. 113, A) each ventral lobe of
a sporophyll bears two sporangia, a condition almost identical with
that represented by the occasional occurrence of a synangium on a
comparatively long stalk in _Tmesipteris_. Similarly the more elaborate
sporophylls of _Cheirostrobus_ may be compared with the branched
sporophylls of _Tmesipteris_ (fig. 120). This agreement between the
sporophylls of the Palaeozoic and recent genera acquires additional
importance from the very close resemblance between the exarch stele
of _Sphenophyllum_ and that of the genus _Psilotum_, which conforms
to the Palaeozoic type not only in the centripetal character of the
primary xylem and in its exarch structure, but also in the occasional
occurrence of secondary xylem[31], and in the stellate form of its
transverse section. The occasional mesarch structure of the stele of
_Cheirostrobus_ finds a parallel in the mesarch xylem groups in the
stem of _Tmesipteris_. It is thus on the strength of these resemblances
that Thomas and Bower would remove the Psilotaceae from the group
Lycopodiales and unite them with _Sphenophyllum_ and _Cheirostrobus_
in the Sphenophyllales. While admitting the validity of the comparison
briefly referred to above, I prefer to retain the Psilotaceae
as a division of the Pteridophyta including only _Psilotum_ and
_Tmesipteris_.

[Sidenote: SPHENOPHYLLUM]

In his recent book on _The Origin of Land Flora_, Prof. Bower raises
objection to the use of the term ventral lobe in speaking of the
sporangium-bearing stalk or sporangiophore borne on the sporophyll
of _Sphenophyllum_. He points out that the use of this term implies
the derivation of the sporangiophore by metamorphosis of part of a
vegetative leaf, an opinion untenable in the absence of proof. The
designation sporangiophore is no doubt preferable to that of ventral
lobe as it carries with it no admission of particular morphological
value; as a further concession to a non-committal attitude we may
provisionally at least regard a sporangiophore as an organ _sui
generis_ “and not the result of modification of any other part[32].”

The view put forward by Prof. Lignier[33] that the Sphenophyllales are
descendants of primitive ferns is not convincing, and his comparison
of _Sphenophyllum_ with _Archaeopteris_ lacks force in view of our
ignorance as to the nature of the reproductive organs of the latter
genus. That the Sphenophyllales are connected with the Equisetales and
with the Psilotales by important morphological features is clear; but
the comparison between the sporophylls of the extinct genera with those
of the existing genus _Tmesipteris_, though helpful and possibly based
on true homology, cannot be considered as settling the morphological
value of the sporangiophores of _Sphenophyllum_ and _Cheirostrobus_.

I do not propose to discuss at length the different views in regard
to the morphological nature of the sporangiophore of _Sphenophyllum_.
The comparison, which we owe in the first instance to Scott, with the
synangium of the Psilotales with its short stalk, though not accepted
by Lignier as a comparison based on true homology, is one which
appeals to many botanists and is probably the best so far suggested.
The further question, whether these sporangiophores are to be called
foliar or axial structures is one which has been answered by several
authors, but it is improbable that we shall soon arrive at a decision
likely to be accepted as final. Discussions of this kind tend to
assume an exaggerated importance and frequently carry with them the
implication that every appendage of the nature of a sporangiophore
can be labelled either shoot or leaf. We treat the question from an
academic standpoint and run a risk of ignoring the fact that the
conception of stem and leaf is based on morphological characteristics,
which have been evolved as the result of gradual differentiation of
parts of one originally homogeneous whole. There is much that is
attractive in the view recently propounded by Mr Tansley that a leaf is
not an appendicular organ differing _ab initio_ from the axis on which
it is borne, but that it is in phylogenetic origin a “branch-system of
a primitive undifferentiated sporangium-bearing thallus[34].” Admitting
the probability that this view is correct, our faith in the importance
of discussions on the morphological nature of sporangiophores is
shaken, and we realise the possibility that our zeal for formality and
classification may lead to results inconsistent with an evolutionary
standpoint[35].




                             CHAPTER XIII.

                              PSILOTALES.


The two recent genera _Psilotum_ and _Tmesipteris_ are usually spoken
of as members of the family Psilotaceae which is included as one of the
subdivisions of the Lycopodiales. It is probable, as Scott[36] first
suggested, that these two plants are more nearly allied than are any
other existing types to the Palaeozoic genus _Sphenophyllum_.

We may give expression to the undoubted resemblances between
_Tmesipteris_ and _Psilotum_ and the Sphenophyllales by including the
recent genera as members of that group, originally founded on the
extinct genus _Sphenophyllum_; this is the course adopted by Thomas[37]
and by Bower[38]: or we may emphasise the fact that these two recent
genera differ in certain important respects from _Lycopodium_ and
_Selaginella_ by removing them to a separate group, the Psilotales.
The latter course is preferred on the ground that the inclusion of
_Psilotum_ and _Tmesipteris_ in a group founded on an extinct and
necessarily imperfectly known type, is based on insufficient evidence
and carries with it an assumption of closer relationship than has been
satisfactorily established.

The genus _Tmesipteris_ (fig. 120, A) is represented by a single
species _T. tannensis_ Bertr.[39] which usually occurs as an epiphyte
on the stems of tree-ferns in Australia, New Zealand, and Polynesia.
_Psilotum_, with two species _P. triquetrum_ Sw. (fig. 118) and
_P. complanatum_ Sw., flourishes in moist tropical regions of both
hemispheres, growing either on soil rich in organic substances or as an
epiphyte. Both genera are considered to be more or less saprophytic.

[Illustration: FIG. 118. _Psilotum triquetrum_ (½ natural size).

  A. Synangium.
  B. Sporophyll after removal of the synangium. (M.S.)]

_Psilotum._ The common tropical species _P. triquetrum_ (fig. 118) is
characterised by an underground rhizome which forms a confused mass
of dark brown branches covered with filamentous hairs as substitutes
for roots and gives off erect repeatedly forked aerial shoots. In _P.
complanatum_[40] the habit is similar to that of the more abundant
and better-known species, but the pendulous shoots are characterised
by their broader and flatter form. In both species the function of
carbon-assimilation is performed by the outer cortex of the green
branches, as the small size of the widely-separated foliage leaves
renders them practically useless as assimilating organs.

The sporophylls consist of a short axis terminating in two small
divergent forks and bearing on its adaxial surface a trilocular or in
rare cases a bilocular synangium (fig. 118, A and B). The walls of the
loculi are composed of several layers of cells and dehiscence takes
place along three lines radiating from the centre of the synangium.
Professor Thomas[41] has recorded “fairly numerous instances in
_Psilotum_ of a second dichotomy of one branch of the first fork, or,
less frequently, of both branches”: instead of one synangium subtended
by the two slender leaflets of the forked sporophyll-axis, there
may be two synangia and three leaf-lobes or three synangia and four
leaf-lobes. The occurrence of both these abnormalities in _Psilotum_
and _Tmesipteris_ shows a decided tendency in the Psilotales to a
repeated dichotomy of the sporophylls[42].

A single stele[43] with a fluted surface occupies the axis of an
aerial shoot (fig. 119, A); the axial region is occupied by a core of
elongated mechanical elements (_s_), which may occasionally extend to
the periphery of the xylem and break the continuity of the band of
scalariform tracheae (fig. 119, A, _a_). The tracheae form the arms of
an irregularly stellate stele and each arm is terminated by protoxylem
elements (fig. 119, B, _px_). The rays of the xylem cylinder, which
may be as many as six or eight in the upper part of the aerial shoots,
become reduced in number as the rhizome is approached, assuming a
diarch structure near the junction. In the rhizome the xylem forms
an approximately triangular group of tracheae without any core of
mechanical elements. Three to four layers of parenchyma succeeded
externally by an ill-defined phloem (fig. 119, A, _p_) surround the
xylem and a fairly distinct endodermis (fig. 119, A and B, _e_)
encloses the whole. To Mr Boodle[44] is due the interesting discovery
that in some parts of the rhizome the parenchymatous zone surrounding
the scalariform tracheae may become the seat of meristematic
activity which results in the production of secondary tracheae
often characterised by a sinuous longitudinal course. There is no
definite cambium, but the radially disposed tracheae and the adjacent
parenchymatous elements clearly demonstrate the secondary nature of the
tissue immediately external to the group of primary xylem. Fig. 119, C,
drawn from a section kindly supplied by Mr Boodle, shows the secondary
xylem elements at _x_² associated with radially disposed thin-walled
cells abutting on the primary xylem, _x_¹. It is probable that this
added tissue may be a remnant of a more extensive secondary thickening
characteristic of the ancestors of the recent species. In their manner
of occurrence and sinuous course these secondary tracheids bear a
resemblance to the secondary xylem of _Lepidodendron fuliginosum_[45].
The stele of the aerial shoot bears a fairly close resemblance to the
vascular axis of _Cheirostrobus_, and its three-rayed form in the lower
portions of the green branches recalls that of the _Sphenophyllum_
stele, except that the axial xylem elements of the Palaeozoic genus
are usually represented in _Psilotum_ by mechanical tissue. The
cortex consists of three regions (fig. 119, A), an outer zone of
chlorophyllous tissue (_a_) rich in intercellular spaces succeeded by
a band of mechanical tissue (_b_) which gradually passes into an inner
region of larger and thinner-walled cells (_c_).

[Illustration: FIG. 119.

  A. Diagram of transverse section of aerial shoot of _Psilotum
     triquetrum_. _a_—_c_, cortex; _p_, phloem; _e_, endodermis; _s_,
     stereome; _x_, xylem; _a_, gap in xylem.
  B. Enlarged view of one of the angles of the xylem shown in A.
     _px_, protoxylem.
  C. Part of transverse section of an approximately triangular
     rhizome stele showing a portion of the metaxylem _x_¹; _px_,
     protoxylem elements; _x_², secondary xylem.]

[Sidenote: TMESIPTERIS]

The genus _Tmesipteris_[46] agrees with _Psilotum_ in general habit
and in its epiphytic and probably in some degree saprophytic mode
of life. Its brown rootless rhizome, which grows among the roots of
tree-ferns or rarely in the ground, gives off pendulous or erect
shoots reaching a length of two feet and bearing lanceolate mucronate
leaves 2–3 cm. long (fig. 120, A) attached by decurrent leaf-bases.
The sporophylls, replacing the upper leaves or occurring in more or
less well-defined zones alternating with the foliage leaves, consist
of a short axis terminating in a pair of lanceolate lobes and bearing
on its adaxial surface an elongated bilocular synangium attached to a
very short stalk (fig. 120, B). Reference has already been made to the
divergent opinions as to the morphological nature of the sporophylls
or sporangiophores, but recent investigations distinctly favour the
view that a sporophyll is best interpreted as a stalked leaf with
two sterile laminae and an almost sessile, or in some cases a more
obviously stalked, synangium; the whole sporophyll is characterised
by the possession of a ventral and a dorsal lobe[47]. The drawings
reproduced in fig. 120, D and F, illustrate some of the frequent
variations described by Thomas in plants which he observed in the
New Zealand forests. The sporophyll shown in fig. 120, D and F, has
branched twice and bears three synangia.

[Illustration: FIG. 120. _Tmesipteris._

  A. Foliage leaves.
  B. Sporophyll and bilocular synangium.
  C. Diagram of transverse section of stele. _px_, protoxylem.
  D, F. Abnormal sporophylls. (From drawings made by Prof. Thomas and
     generously placed at my disposal. A.C.S.)
  E. Portion of C enlarged.]

The aerial branches of _Tmesipteris_ possess a central cylinder of
separate xylem groups in which the protoxylem occupies an internal
position (fig. 120, C and E, _px_) enclosing an axial parenchymatous
region. The cells of a few layers of the inner cortex immediately
outside the endodermis are rendered conspicuous by a dark brown
deposit. The cortex as a whole is composed of uniform parenchymatous
tissue. In the lower part of the aerial shoots and in the rhizome the
xylem forms a solid strand without protoxylem elements and conforms
more clearly to that of _Psilotum_.

In this short account of the anatomy of _Tmesipteris_ no mention
is made of the effect produced on the stele by the departure of
leaf-traces and of vascular stands to supply branches. Miss Sykes[48]
in a recently published paper on the genus has shown that the exit of
a leaf-trace does not break the continuity of the xylem of the stele,
while the exit of a sporophyll-trace is marked by an obvious gap.
Evidence is adduced in support of the conclusion that this difference,
which at first sight appears to be one of morphological importance,
is in reality merely a question of degree and “is due to the earlier
preparation for the formation of ‘sporophyll’ than leaf-traces.”
Miss Sykes gives her adherence to the view that the “sporophylls” of
_Tmesipteris_ are branches and not leaves, but despite the arguments
advanced this interpretation seems to me less probable than that which
recognises the sporophyll as a foliar organ. Prof. Lignier[49] has
pointed out that if Miss Sykes’s conclusion as to the axial nature
of the sporophyll in _Tmesipteris_ is accepted, it diminishes the
force of the comparison between the sporophylls of that genus and
_Sphenophyllum_ as those of the latter can hardly be regarded as other
than foliar organs.

Both members of the Psilotales may, as Boodle has suggested, be
regarded as descendants of a common parent in which the aerial
stems possessed a fluted or stellate cylinder of mesarch xylem.
There can be no doubt as to the significance of the morphological
resemblances between the Psilotales and the genera _Sphenophyllum_
and _Cheirostrobus_, but the position of _Tmesipteris_ and _Psilotum_
in the plant-kingdom may probably be best expressed by adopting the
group-name Psilotales rather than by transferring the recent genera
to the Sphenophyllales. One of the most striking differences between
the Psilotales and the genus _Lycopodium_ is in the form of the
sporophylls and sporangia; in _Lycopodium_ a single sporophyll bears
a unilocular sporangium, but in the Psilotales the sporophyll may
be described as a bilobed structure homologous with a foliage-leaf,
bearing a sporangiophore which consists of a short stalk terminating
in a bilocular or trilocular synangium; the short stalk receives a
special branch from the vascular bundle of the sterile portion of the
sporophyll[50].


            _Fossils described by authors as being closely
                         allied to_ Psilotum.

A search through palaeobotanical literature reveals the existence
of a very small number of specimens which have been identified as
representatives of the Psilotales. An inspection of the material or
published drawings leads one to the conclusion that practically no
information of a satisfactory kind is available in regard to the past
history of the two southern genera _Psilotum_ and _Tmesipteris_, which
are regarded by some botanists as relics of an ancient branch[51] of
pteridophytes.

[Sidenote: PSILOTITES, ETC.]

In 1842 Münster[52] instituted the genus _Psilotites_ for a small
impression of a slender branched axis from Jurassic rocks near Mannheim
in Germany which he named _Psilotites filiformis_; Schimper[53]
spoke of the specimens as too doubtful for determination, an opinion
with which every botanist would cordially agree. Goldenberg’s species
_Psilotites lithanthracis_[54] from the Saarbrücken coal-field is
founded on impressions of axes: some of these are dichotomously
branched and bear small oval projections, which may be rudimentary
leaves or possibly leaf-scars. More recently Kidston[55] described
specimens of branched axes from the Lanarkshire coal-field bearing
a row of lateral thorn-like projections under the title _Psilotites
unilateralis_; but these fragments, as Dr Kidston himself admits, are
of no botanical value.

In a paper on fossil Salvinias, Hollick[56] mentions _Salvinia
reticulata_, originally described by Heer and by Ettingshausen and _S.
Alleni_ Lesq.[57] a Tertiary species, and calls attention to their very
close resemblance in form, nervation, and apex to the leaves of the
genus _Tmesipteris_: he refers both species to that genus. The drawings
reproduced by Hollick represent leaves with a midrib and numerous
anastomosing lateral veins, whereas in _Tmesipteris_ the lamina of the
leaf has a midrib without lateral branches. An enlarged drawing of the
outlines of the epidermal cells would correspond closely with the small
reticulations in the fossil leaves and it may be that there has been
some confusion between veins and cell-outlines. In any case there would
seem to be no reason for the use of the recent generic name[58].

Among other fossils assigned to the Psilotales we have Marion’s genus
_Gomphostrobus_ from the Permian of France and Germany[59]. Marion
placed this plant in the Coniferales on the strength of its resemblance
to _Walchia_ and _Araucaria_, but Potonié[60] is inclined to recognise
in the leaves and monospermic sporophylls characters suggestive of
Lycopodiaceous affinity.

The latter author in 1891[61], in ignorance of Marion’s proposal to
adopt the name _Gomphostrobus_, instituted a genus _Psilotiphyllum_
for the sporophylls of a species originally described by Geinitz[62]
as _Sigillariostrobus bifidus_, but he subsequently adopted Marion’s
designation and with some hesitation included the French and German
specimens in the Psilotales. As stated elsewhere[63], Potonié’s
arguments in favour of his view hardly carry conviction, and it is
probably more in accordance with truth to deal with _Gomphostrobus_ in
the chapter devoted to the Coniferales.


                            _Psilophyton._

The generic title _Psilophyton_, instituted by the late Sir
William Dawson[64], has become familiar to geologists as that of
a Pre-Carboniferous plant characteristic of Devonian and Silurian
rocks in Canada, the United States of America, and Europe. From the
botanist’s point of view the name stands for miscellaneous remains
of plants of different types and in many cases unworthy of record.
The genus was founded on impressions of branched axes from the
Devonian strata of New Brunswick resembling the rachis and portions of
lateral pinnae of ferns or the forked slender twigs of a Lycopod. The
type-species _Psilophyton princeps_ Daws. as represented on somewhat
slender evidence in Dawson’s restoration, which accompanies the
original description of the genus and has since been copied by several
authors, is characterised by the possession of a horizontal rhizome
bearing numerous rootlets and giving off dichotomously branched aerial
shoots with spinous appendages, compared with rudimentary leaves, and
terminating in slender branchlets bearing pendulous oval “spore-cases”
from their tips. Some of the branchlets exhibit a fern-like vernation.
The plant is spoken of by Dawson as apparently a generalised type[65],
resembling in habit and in its rudimentary leaves the recent genus
_Psilotum_ and presenting points of contact with ferns. Specimens were
found in an imperfectly petrified state showing a central cylinder of
scalariform tracheae surrounded by a broad cortical zone of parenchyma
and fibrous tissue.

Among other species described by the author of the genus we need only
mention _Psilophyton robustius_, characterised by vegetative shoots
and “spore-cases” similar to those of the type-species; but, as
Solms-Laubach[66] has pointed out, the petrified sections referred by
Dawson to _P. robustius_ are of an entirely different anatomical type
from that of _P. princeps_[67].

British fossils from the Old Red Sandstone from the north of Scotland,
Orkney and Caithness, originally figured by Hugh Miller and compared
by him with algae but more especially with recent Lycopods, were
subsequently placed by Carruthers[68] in the genus _Psilophyton_ as _P.
Dechianum_, the specific designation being chosen on the ground that
the Scotch specimens are specifically identical with fossils described
by Goeppert[69] as _Haliserites Dechianus_.

Various opinions have been expressed in regard to the nature of
the Devonian species _Haliserites Dechianus_ Goepp. with which
Carruthers[70] identified Miller’s Old Red Sandstone plant: reference
may be made to a paper by White[71] containing figures of dichotomously
branched impressions described as species of _Thamnocladus_ which he
includes among the algae.

In describing some Belgian impressions of Devonian age as
_Lepidodendron gaspianum_ Daws. Crépin[72] states that Carruthers has
come to regard the specimens named by him _Psilophyton Dechianum_
as branches of a Lepidodendron; he also quotes Carruthers as having
expressed the opinion that the name _Psilophyton_ had been employed by
Dawson for two kinds of fossils, some being twigs of _Lepidodendron_
while others, identified by Dawson as the reproductive branches of
species of _Psilophyton_, represent the spore-cases of ferns comparable
with Stur’s genus _Rhodea_[73]. One of the examples figured by
Carruthers[74] as _P. Dechianum_ from Thurso (preserved in the British
Museum, no. 52636), measuring 34 cm. in length and 8 mm. broad, bears
a close resemblance to a fern rhizome covered with ramental scales such
as that of a species of _Davallia_. Other Belgian specimens described
by Gilkinet[75] as _Lepidodendron burnotense_, like Crépin’s species,
are no doubt generically identical with some of the Scotch and Canadian
fossils placed in the genus _Psilophyton_, though Penhallow[76]
considers that the species _Lycopodites Milleri_ is more correctly
referred to _Lycopodites_ than to _Psilophyton_.

A more recent paper on the Geology of the Perry basin in South-eastern
Maine by Smith and White[77] contains a critical summary of the
literature on _Psilophyton_ and drawings of specimens. The latter
afford good examples of Pre-Carboniferous plant fragments, such as are
often met with in various parts of the world, which conform in habit to
the New Brunswick specimens made by Dawson the type of his genus.

An examination of material in the Montreal Museum and of Hugh Miller’s
specimens in the Edinburgh collection leads me to share the opinion
of Count Solms-Laubach that the name _Psilophyton_ has been applied
to plants which should not be included under one generic title. As
Kidston[78] pointed out, the Canadian species _Psilophyton robustius_
is not generically distinct from British and Belgian specimens
referred to _Lepidodendron_; it may possibly be identical with the
Bohemian plants on which Stur founded his genus _Hostinella_[79]. The
Devonian plants described by Stur have since been examined by Jahn[80]
who regards them as vascular plants, and not as algae to which Stur
referred them; he mentions two species of _Psilophyton_ but gives no
figures.

The “spore-cases” of Dawson may be found to be the microsporangia
or perhaps the small seeds of some pteridosperm; the forked axes
with a smooth surface and others figured by Miller and by Dawson,
with the surface covered with scales suggesting the ramenta of a
fern, may be the rachises or rhizomes of filicinean plants. Other
specimens may be Lepidodendron twigs, as for example the petrified
fragments figured by Dawson as _Psilophyton princeps_; while the stem
identified as _P. robustius_ is most probably that of a Gymnosperm.
It is doubtful whether a useful purpose is served by retaining the
genus _Psilophyton_. It was in the first instance instituted on the
assumption, which cannot be upheld, that the abundant material in the
New Brunswick beds bore a sufficiently close resemblance to the rhizome
and aerial branches of _Psilotum_. _Psilophyton_ has served as a name
for miscellaneous plant fragments, many of which are indeterminable. Dr
White concludes his account of the genus with the following words[81]:

“The examination of such so-called Psilophyton material as I have seen
shows the existence in America of two or more groups, represented
by several fairly well-marked species which possess stratigraphical
value, and which should be carefully diagnosed and illustrated. It is
probable also that additional material throwing light on the structure
and relationships of these very remarkable early types of land-plants
will be discovered at some locality. The inspection of the material in
hand emphasises the need, as was pointed out by Solms-Laubach, for the
revision of the material referred by various authors to _Psilophyton_,
together with a thorough re-examination and re-publication of the
types.”

Until a thorough re-examination has been made of the Canadian material,
with a view to determine whether there exist substantial reasons for
the retention of Dawson’s genus, it is undesirable to continue to make
use of this name for Pre-Carboniferous fossils which are too incomplete
to be assigned with certainty to a definite group of plants. Dr White
draws attention to the similarity of some of the Perry basin specimens
to Nathorst’s genus _Cephalotheca_[82] from Devonian rocks of Bear
Island in the Arctic regions, a comparison which might be extended to
other genera and which serves to illustrate the possibility that many
of the specimens labelled _Psilophyton_ may eventually be recognised as
examples of well defined generic types belonging to more than one group
of plants.




                             CHAPTER XIV.

                             LYCOPODIALES.


The recent members of the Lycopodiales are considered apart from
the extinct genera in order that our examination of the latter may
be facilitated by a knowledge of the salient characteristics of the
surviving types of this important section of the Pteridophyta. A
general acquaintance with the extinct as well as with the recent genera
will enable us to appreciate the contrasts between the living and the
fossil forms and to realise the prominent position occupied by this
group in the Palaeozoic period, a position in striking contrast to
the part played by the diminutive survivors in the vegetation of the
present day. In the account of the recent genera special attention is
drawn to such features as afford a clue to the interpretation of the
fossils, and the point of view adopted, which at times may appear to
lead to an excessive attention to details, is necessarily somewhat
different from that represented in botanical text-books[83].

                           A. =HOMOSPOREAE.=

        =Lycopodiaceae=: genera _Phylloglossum_, _Lycopodium_.

                          B. =HETEROSPOREAE.=

                =Selaginellaceae=: genus _Selaginella_.
                =Isoetaceae=: genus _Isoetes_.

The existing plants included in the Lycopodiales are in nearly all
cases perennial herbaceous pteridophytes, exhibiting in their
life-histories a well marked alternation of generations. The sporophyte
(asexual generation) is characterised by the relatively small size
of the leaves except in the genus _Isoetes_ (fig. 132) and in the
Australian and New Zealand genus _Phylloglossum_. The stems are usually
erect or trailing, pendulous in epiphytic species or small and tuberous
in _Isoetes_ and _Phylloglossum_. The repeated forking of the shoots
(monopodial and dichotomous branching) is a prominent feature of the
group. The vascular tissue of the stem usually assumes the form of a
single axial strand (stele) (fig. 125), but the shoots of some species
of _Selaginella_ often contain two or more distinct steles (fig. 131).
The group as a whole is characterised by the centripetal development of
the xylem composed almost entirely of scalariform tracheids: secondary
xylem and phloem of a peculiar type occur in _Isoetes_, and the
production of secondary xylem elements in a very slight degree has been
noticed in one species of _Selaginella_ (_S. spinosa_)[84]. The roots
are constructed on a simple plan, having in most cases only one strand
of spiral protoxylem elements (monarch structure). In _Lycopodium_,
in which stem and root anatomy are more nearly of the same type than
in the majority of plants, several protoxylem strands may be present.
The sporangia are axillary or, more frequently, borne on the upper
surface of sporophylls, which are either identical with or more or less
distinct from the foliage leaves; in the latter case the sporophylls
often occur in the form of a well defined strobilus (cone) at the tips
of branches.

The gametophyte (sexual generation) is represented by prothalli which,
in the homosporous genera, may live underground as saprophytes, or the
upper portion may develop chlorophyll and project above the surface of
the ground as an irregularly lobed green structure (_e.g._ _Lycopodium
cernuum_)[85]. In the heterosporous forms the prothalli are much
reduced and do not lead an independent existence outside the spore by
the membrane of which they are always more or less enclosed. The sexual
organs are represented by antheridia and archegonia; the male cells
are provided with two cilia except in _Isoetes_ which has multiciliate
antherozoids like those of the ferns.

The existing Lycopods, though widely distributed, never grow in
sufficiently dense masses to the exclusion of other plants to form a
conspicuous feature in the vegetation of a country. The inconspicuous
rôle which they play among the plant-associations of the present era
affords a striking contrast to the abundance of the arborescent species
in the Palaeozoic forests of the northern hemisphere.

                   •       •       •       •       •

=Lycopodiaceae.= _Lycopodium_, represented by nearly 100 species,
forms a constituent of most floras: epiphytic species predominate in
tropical regions, while others flourish on the mountains and moorlands
of Britain and in other extra-tropical countries. For the most part
_Lycopodium_ exhibits a preference for a moist climate and appears to
be well adapted to habitats where the amount of sunlight is relatively
small and the conditions of life unfavourable for dense vegetation.
Mountains and islands constantly recur as situations from which species
have been recorded. Some species are essentially swamp-plants, _e.g._
_Lycopodium inundatum_, a British species, and _L. cruentum_ from
the marshes of Sierra Nevada. A variety of the American species, _L.
alopecuroides_ (var. _aquaticum_) affords an instance of a submerged
form, which has been collected from an altitude of 12–14,000 ft. on the
Andes and Himalayas. It is noteworthy that a considerable variety of
habitats is represented within the limits of the genus and that many
species are sufficiently hardy to exist in circumstances which would be
intolerable to the majority of flowering plants[86].

The British species frequently spoken of as Club Mosses, include
_Lycopodium Selago_, _L. annotinum_, _L. clavatum_, _L. alpinum_, and
_L. inundatum_.

                   •       •       •       •       •

=Selaginellaceae.= The species of _Selaginella_, over 300 in number,
are widely spread in tropical and subtropical forests, growing on the
ground with trailing, suberect or erect stems climbing over taller and
stouter plants or as pendulous epiphytes on forest trees.

_Selaginella lepidophylla_, a tropical American type, popularly known
as the Resurrection plant, and often erroneously spoken of as the Rose
of Jericho[87], possesses the power of rolling up its shoots during
periods of drought and furnishes an example of a species adapted to
conditions in marked contrast to those which are most favourable to the
majority of species.

The only British species is _Selaginella spinosa_ named by Linnaeus
_Lycopodium selaginoides_ and occasionally referred to as _Selaginella
spinulosa_ A. Br. (not to be confounded with a Javan species _S.
spinulosa_ Spring[88]).

                   •       •       •       •       •

=Isoetaceae.= _Isoetes_ (fig. 132), of which Mr Baker in his _Handbook
of the Fern-Allies_ enumerates 49 species, is a type apart, differing
in habit as in certain other characters from the other members of the
Lycopodiales. Some botanists[89] prefer to include the genus among the
Filicales, but the balance of evidence, including resemblances between
_Isoetes_ and extinct Lycopodiaceous plants, would seem to favour its
retention as an aberrant genus of the group Lycopodiales. Some species
are permanently submerged, others occur in situations intermittently
covered with water, and a few grow in damp soil. _Isoetes lacustris_
is found in mountain tarns and lakes of Britain and elsewhere in
Central and Northern Europe and North America. _Isoetes hystrix_[90], a
land-form occurs in Guernsey, North-East France, Spain and Asia Minor.


                            Lycopodiaceae.

The monotypic genus _Phylloglossum_, represented by _P. Drummondii_ of
Australia and New Zealand, though interesting from the point of view of
its probable claim to be considered the most primitive type of existing
Lycopodiaceous plants, need not be dealt with in detail. A complete
individual, which does not exceed 4 or 5 cm. in length, consists of a
very small tubercle or protocorm bearing a rosette of slender subulate
leaves and prolonged distally as a simple naked axis which overtops the
foliage leaves and terminates in a compact cluster of small scale-like
sporophylls, each subtending a single sporangium[91].

_Lycopodium._ It would be out of place in a volume devoted mainly
to fossil plants to attempt a comprehensive account of the general
morphology of recent species, and indeed our knowledge of the
anatomical characters of the genus is still somewhat meagre. For
purposes of comparison with extinct types, it is essential that some of
the more important morphological features of existing species should
be briefly considered. The additions made to our knowledge of the
gameophyte[92] of European and tropical species during the last two
decades have revealed a striking diversity in habit.

In several species, grouped round the widely distributed type
_Lycopodium Selago_ Linn., the comparatively short, erect or suberect,
shoots form fairly compact tufts; the ordinary foliage-leaves function
as sporophylls, and the sporangia are not localised on special portions
of shoots. From this type, we pass to others in which the fertile
leaves tend to be confined to the tips of branches, but hardly differ
in form from the sterile. A further degree of specialisation is
exhibited by species with well-defined cones composed of leaves (or
bracts), the primary function of which is to bear sporangia and to
afford a protective covering to the strobilus[93].

_Lycopodium rufescens_ Hook. An Andian species with stout dichotomously
branched erect stems bears on the younger shoots crowded leaves with
their thick and broadly triangular laminae pointing upwards, but on the
older and thick shoots the laminae are strongly reflexed (fig. 121,
A). The lower part of the specimen represented in fig. 121, A, shows
tangentially elongated scars and persistent leaf-bases or cushions left
on the stem after the removal of the free portions of the leathery
leaves, a surface-feature which also characterises the Palaeozoic genus
_Lepidodendron_. The reflexed leaves and persistent leaf-cushions are
clearly seen in the piece of old stem of _Lycopodium dichotomum_ Jacq.,
a tropical American species reproduced in fig. 121, B. Such species
as _L. erythraeum_ Spring, and others with stiff lanceolate leaves
exhibit a striking resemblance to the more slender shoots of some
recent conifers, more especially _Araucaria excelsa_, _A. Balansae_,
_Cryptomeria_, _Dacrydium_ and other genera.

[Illustration: FIG. 121. _Lycopodium._

  A. _Lycopodium rufescens._
  B. _L. dichotomum._
  C. _L. tetragonum._
  D. _L. nummularifolium._
  E. _L. Dalhousianum._
  F. _L. casuarinoides._
  G. _L. volubile._

  (From specimens in the Cambridge Herbarium and Botanic Garden. M.S.)]

[Illustration: FIG. 122. _Lycopodium squarrosum._ The branches of the
  larger shoot terminate in cones. (From a plant in the Cambridge
  Botanic Garden. Reduced.)]

In _Lycopodium tetragonum_ Hook., (fig. 121, C), a species from the
Alpine region of the Andes, the long, pendulous and repeatedly forked
branches bear four rows of fleshy ovate leaves and simulate the
vegetative characters of certain conifers.

[Sidenote: LYCOPODIUM]

[Illustration: FIG. 123. _Lycopodium cernuum._
  (From a specimen in the Cambridge Herbarium. ½ nat. size.)]

_L. squarrosum_ Forst. (fig. 122) a tropical species from India,
Polynesia, and other regions, is characterised by its stout stems
reaching a diameter of 2·5 cm., bearing long pendulous branches with
large terminal cones composed of sporophylls differing but slightly
from the foliage leaves. The plant represented in the photograph serves
as a good illustration of the practical identity in habit between
Palaeozoic and recent genera.

[Illustration: FIG. 124. _Lycopodium obscurum._]

_L. Dalhousianum_ Spring, from the mountains of the Malay Peninsula
and Borneo, has larger leaves of finer texture with a distinct midrib
reaching a length of 2–3 cm. (fig. 121, E). Another type is illustrated
by _L. nummularifolium_ Blume, also a Malayan species, in which the
leaves are shorter, broadly oblong or suborbicular, and the branches
terminate in narrow and often very long strobili (sometimes reaching
a length of 30 cm.) with small bracts in striking contrast to the
foliage leaves (fig. 121, D). A similar form of long and slender
strobilus occurs in _L. Phlegmaria_ Linn., a common tropical Lycopod:
the frequent forking of the strobili noticed in this and other species
is a character not unknown among fossil cones (_Lepidostrobi_).

_L. cernuum_ Linn. (fig. 123), another widely spread tropical type,
offers an even closer resemblance than _L. squarrosum_ to the fossil
Lepidodendra. The stiff erect stem, reaching in some cases a length
of several feet, bears numerous repeatedly forked branches, with
crowded linear leaves, terminating in short cylindrical cones with
broadly ovate sporophylls. A similar habit characterises the North
American species _L. obscurum_ Linn. (fig. 124) bearing cones several
centimetres in length.

_L. casuarinoides_ Spring (fig. 121, F) an eastern tropical species,
is worthy of notice as exhibiting a peculiar form of leaf consisting
of a very small lamina, 3 mm. in length, borne on the top of a long
decurrent base, which forms a narrow type of leaf-cushion, bearing
some resemblance to the long and rib-like cushions of certain species
of _Sigillaria_, and recalling the habit of slender fossil twigs
referred to the Coniferae under such names as _Widdringtonites_,
_Cyparissidium_, _Sphenolepidium_.

_L. volubile_ Forst. (fig. 121, G) a New Zealand species, in habit
and leaf-form bears a close resemblance to the Jurassic _Lycopodites
falcatus_ Lind. and Hutt. (fig. 137): it is also a representative of a
few species of _Lycopodium_ which agree with the majority of species of
_Selaginella_ in having two kinds of sterile leaves, comparatively long
falcate leaves forming two lateral rows and smaller appressed leaves on
the upper surface of the branches.

These examples suffice to illustrate the general appearance presented
by the vegetative shoots of recent species of which the foliage
leaves vary considerably—from the small scale-leaves of _Lycopodium
tetragonum_, to the very slender linear subulate leaves of such a
species as _L. verticillatum_ Linn. or the long and broader lamina of
_L. Dalhousianum_ (fig. 121, E). It is obvious that fragments of the
various types preserved as fossils might well be mistaken either for
some of the larger mosses or for twigs of conifers. As Dr Bommer[94]
has pointed out in his interesting paper on “Les causes d’erreur dans
l’étude des empreintes végétales” some dicotyledonous plants may also
simulate the habit of Lycopods: he cites _Phyllachne clavigera_ Hook
(Candolleaceae), _Tafalla graveolens_ Wedd (Compositae) and _Lavoisiera
lycopodioides_ Gard. (Melastomataceae). Another point illustrated
by fig. 121 is the close agreement in habit and in the form of the
leaves and leaf-cushions between the recent plants and the Palaeozoic
Lepidodendreae.

In his masterly essay “On the vegetation of the Carboniferous Period,
as compared with that of the present day” Sir Joseph Hooker called
attention to the variation in the shape and arrangement of the
leaves in the same species of _Lycopodium_. The three woodcuts which
he publishes of _Lycopodium densum_, a New Zealand species, afford
striking examples of the diversity in habit and leaf-form and justify
his warning “that if the species of _Lepidodendron_ were as prone to
vary in the foliage as are those of _Lycopodium_, our available means
for distinguishing them are wholly insufficient[95].”

As we have already noticed, there is a considerable diversity among
recent species, both as regards habitat and habit; in the anatomy
of the stem also corresponding variations occur within the limits
of a well-defined generic type of stele. In species with creeping
stems, such as _L. clavatum_[96], the stele exhibits an arrangement
of vascular tissue characteristic of the plagiotropic forms. The
xylem consists of more or less horizontal plates of scalariform
tracheae, each surrounded by small-celled parenchyma, alternating with
bands or groups of somewhat ill-defined phloem. The protoxylem and
protophloem elements occupy an external position (exarch), pointing
to a centripetal development of the metaxylem. This centripetal or
root-like character of the primary xylem is an important feature in
recent as in fossil Lycopods. The close agreement between the roots and
stems of recent species in the disposition of the vascular elements
also denotes a simpler type of anatomy than occurs in the majority of
vascular plants in which stem and root have more pronounced structural
peculiarities. A pericycle, 2–6 cells in breadth, encloses the xylem
and phloem bands and this is succeeded by an endodermis, 2–3 cells
broad, with vaguely defined limits. In _L. clavatum_, as in _L.
alpinum_, another British species, the broad cortex is differentiated
into three fairly distinct regions; abutting on the endodermis is a
zone several layers broad of thick-walled cells constituting an inner
cortex modified for protection and support; the central region consists
of larger and thinner-walled cells adapted for water-storage and
aeration; beyond this is an outer cortical zone of firmer and thicker
elements. The prominent leaf-bases or leaf-cushions (fig. 125, A, _lc_)
give to the surface of a transverse section a characteristic appearance
which presents the closest agreement with that of the younger shoots of
_Lepidodendron_. From the peripheral protoxylem groups small strands of
xylem are given off, which follow a steeply ascending course through
the cortex to the single-veined leaves. The leaf-traces, in several
species at least, are characterised by a mesarch structure (fig. 125,
F, G), the spiral protoxylem elements occupying an approximately
central position. The mesophyll of the leaves varies in regard to the
extent of differentiation into a palisade and spongy parenchyma; in all
cases there is a single vascular bundle occasionally accompanied by a
secretory duct.

[Illustration: FIG. 125.

  A. _Lycopodium dichotomum._ Transverse section of stem: _lc_,
     leaf-cushion; _lt_, leaf-trace; R, roots.
  B. _L. cernuum_, portion of cortex of fig. H, enlarged.
  C. _L. saururus._ Cortex: _lt_, leaf-trace; _a_, thin-walled
     tissue; _b_, thick-walled tissue; _lc_, lacuna.
  D. _L. saururus._ Stele: _x_, xylem; _p_, phloem.
  E. Portion of fig. D, enlarged: _px_, protoxylem; _p_, phloem.
  F. Transverse section of leaf of _Lycopodium_.
  G. Vascular bundle of leaf: _px_, protoxylem.
  H. _L. cernuum_: _b_, branch of stele; _c_–_c″_, cortex; _s_, space
     in cortex; _lt_, leaf-trace.
  I. Stele of fig. H, enlarged (phloem omitted).]

In erect stems of _Lycopodium_, as represented by _L. cernuum_ (figs.
123, 125, H, I), _L. Dalhousianum_, _L. squarrosum_ (fig. 122) and
many others, the stele presents a characteristic appearance due to the
xylem plates being broken up into detached groups or short uniseriate
bands with the interspaces occupied by phloem islands. This type of
structure bears a superficial resemblance to that in the single stele
of certain species of the fern _Lygodium_[97], but it is distinguished
by the islands of phloem scattered through the stele. In other species
the xylem tends to assume the form of a Maltese cross (_e.g._ _L.
serratum_ Thbg.) or it may be disposed as =V=-shaped and sinuous bands
terminating in broad truncate ends composed of protoxylem elements.
This form of the xylem and the distribution of the phloem groups are
shown in fig. 125, D, E, drawn from a section of a plant of _Lycopodium
saururus_ Lam.[98] collected by Mr A. W. Hill at an altitude of 15,000
feet on the Andes of Peru. The position of the protoxylem is shown fig.
125, E, _px_.

While several species possess a cortex of three distinct zones (fig.
125, H, _c_, _c_′, _c_″), in others the extra-stelar tissue is much
more homogeneous, consisting of thin-walled parenchyma or in some
cases of thick-walled elements; as a general rule, however, there
is a tendency towards a more compact arrangement in the inner and
outer portions of the cortex as contrasted with the larger and more
loosely connected cells of the middle region. In certain types the
middle cortex contains fairly large spaces, as in the swamp-species
_L. inundatum_, which with _L. alopecuroides_ exhibits another feature
of some interest first described by Hegelmaier[99]. If a transverse
section of the stem of _L. inundatum_ be examined the leaf-traces are
seen to be accompanied by a circular canal containing mucilage which
extends into the lamina of the leaf. In a specimen of _L. cernuum_[100]
obtained at a height of 2500 ft. by Professor Stanley Gardiner in
the Fiji Islands, the leaf-traces (fig. 125, B _lt_) were found to
be accompanied for part of their course by a well-marked secretory
space (fig. 125, B, _s_). There is little doubt that the presence of
these mucilage canals is directly connected with a certain type of
habitat[101] and attention is called to them in view of a resemblance
which they offer to a characteristic strand of tissue, known as the
parichnos, which is associated with the leaf-traces of _Lepidodendreae_
and _Sigillarieae_. In the section shown in fig. 125, H, the xylem of
the stele forms more continuous bands than is often the case in _L.
cernuum_ which has already been described as having its xylem in small
detached groups. The presence of the smaller branch-stele (fig. 125, H,
_b_) affords an example of monopodial branching. The outer cortex of
_L. saururus_ (fig. 125, C) exhibits a somewhat unusual feature in the
distribution of the thicker-walled tissue (_b_) which encloses a patch
of more delicate parenchyma (_a_) with large lacunae (_lc_) in the
region of the leaf-bases, and presents the appearance of an irregular
reticulum. This arrangement of the mechanical tissue in the outer
cortex is comparable with that in stems of some species of _Sigillaria_.

In certain species of _Lycopodium_ the roots[102], which arise
endogenously from the axial vascular cylinder, instead of passing
through the cortex of the stem by the shortest route, bend downwards
and bore their way in a more or less vertical direction before emerging
at or near the base of the aerial shoot. The transverse section of _L.
dichotomum_ represented in fig. 125, A, shows several roots (R) in the
cortex; they consist of a xylem strand of circular or crescentric form
accompanied by phloem and enclosed by several layers of root-cortex.
The roots of _Lycopodium_ do not always present so simple a structure
as those of _L. dichotomum_; the xylem may have an irregularly stellate
form with as many as ten protoxylem groups.

_Reproductive Shoots[103]._ In _Lycopodium Selago_ the foliage
leaves serve also as sporophylls and, as Professor Bower[104] has
pointed out, the branches exhibit to some extent a zonal alternation
of sterile and fertile leaves; in other species, in which foliage
leaves and sporophylls are practically identical, the sporangia occur
sporadically on the ordinary leaves. In species with well-defined
terminal cones the lower sporophylls may bear arrested sporangia and
thus form transitional stages between sterile and fertile leaves, a
feature which occurs also in the male and female flowers of many recent
Araucarieae[105]. The sporangia[106] (fig. 126, D, F) are usually
reniform and compressed in a direction parallel to the surface of the
cone-scales; they are developed from the upper surface and close to
the base of the fertile leaf to which they are attached by a short and
thick stalk (_e.g._ _L. inundatum_) or by a longer and more slender
pedicel (_L. Phlegmaria_, fig. 126, E). On maturity the sporangia open
as two valves in the plane of compression and the line of dehiscence
is determined in some species at least by the occurrence of smaller
cells in the wall. In transverse sections of cones in which the
sporangia are strongly saddle-shaped, the sporophylls may appear to
bear two sporangia. This is well shown in the section of a cone of
_L. clavatum_ shown in fig. 126, F. The sporangia _a_ and _b_ are cut
through in an approximately median plane showing the irregular outline
of the sterile pad (_p_) of tissue in the sporogenous cavity. Those
at _c_ and _d_ have been traversed at a lower level and the two lobes
of the saddle-shaped sporangia are cut below the attachment to the
sporophyll. The distal laminae of the sporophylls, cut at different
levels, are seen at the periphery of the cone.

[Illustration: FIG. 126.

  A. _Lycopodium cernuum_, longitudinal section of strobilus; _a_,
     band of lignified cells.
  B. _L. cernuum._ Cell from sporangium wall.
  C. _L. cernuum._ Sporophyll and sporangium; _lt_, vascular bundle.
  D. _L. clavatum._ Part of radial longitudinal section of strobilus;
     _p_, sterile tissue.
  E. _L. Phlegmaria._ Sporophyll and stalked sporangium.
  F. _L. clavatum._ Transverse section of strobilus; _p_, sterile pad.]

In longitudinal radial section of some cones the sporangia appear to
occupy an axillary position, but in others (_e.g._ _L. clavatum_)
they are attached to the horizontal portion of the sporophyll almost
midway between the axis of the cone and the upturned distal end of the
sporophyll (fig. 126, D). The wall of a sporangium frequently consists
of 2–3 cell-layers and in some cases (_e.g._ _L. dichotomum_), it may
reach a thickness of seven layers, resembling in this respect the
more bulky sporangia of a certain type of Lepidodendroid cone. The
sporogenous tissue is separated from the stalk of the sporangium by
a mass of parenchymatous tissue which may project as a prominent pad
(fig. 126, D, F, _p_) into the interior of the sporogenous cavity. This
basal tissue (the subarchesporial pad of Bower[107]) has been observed
in _L. clavatum_ to send up irregular processes of sterile cells among
the developing spores, suggesting a comparison with the trabeculae
which form a characteristic feature of the sporangia of _Isoetes_ and
with similar sterile strands noticed by Bower[108] in _Lepidostrobus_
(cone of _Lepidodendron_).

Each sporophyll is supplied by a single vascular bundle which according
to published statements never sends a branch to the sporangium base.
The fertile tips of the foliage shoots of _L. cernuum_ (figs. 126, A–C)
afford good examples of specialised cones. The surface of the cone is
covered by the broadly triangular laminae of sporophylls (fig. 126, C)
which in their fimbriate margins resemble the Palaeozoic cone-scales
described by Dr Kidston[109] as _Lepidostrobus fimbriatus_. The distal
portions of the sporophylls are prolonged downwards (fig. 126, A)
to afford protection to the lower sporangia, their efficiency being
increased by the lignified and thicker walls (A, _a_) of the cells in
the lower portion of the laminar expansion. The cells of the sporangial
wall are provided with strengthening bands which in surface-view
(fig. 126, B) present the appearance of prominent pegs. Since the
appearance of Miss Sykes’s paper on the sporangium-bearing organs of
the Lycopodiaceae, Dr Lang[110] has published a more complete account
of the structure of the strobilus of _Lycopodium cernuum_ in which he
records certain features of special interest. The importance of these
morphological characters is increased by their agreement, as shown
by Lang, with those of the Palaeozoic cone _Spencerites_[111]. The
sporophylls of a cone (12 mm. long by 3 mm. in diameter) of _Lycopodium
cernuum_ show an abrupt transition from the foliage leaves, but like
these they occur in alternate whorls of five. A large sporangium is
attached to the upper face of each sporophyll close to the base of
the obliquely vertical distal lamina (fig. 127); each sporophyll,
which is supplied with a single vascular bundle, has a large
mucilage-cavity (_m_) in its lower region. “The mucilaginous change”
in the sub-sporangial portion of a sporophyll “extends to the surface
involving the epidermis, so that this portion of the sporophyll-base
may be described as consisting of a mass of mucilage bounded below by
a structureless membrane[112].” Dehiscence of the sporangia occurs at
the middle of the distal face (fig. 127, _x_). As seen in the radial
section (fig. 127, _ma_) the outer margin of the base of the sporophyll
bears a short outgrowth. The leaf-bases of each whorl hang down between
the sporangia of the alternating whorl below, and the base of each
sporophyll is coherent with the margins of the two sporophylls of
the next lower whorl between which it lies, the sporangia being thus
closely packed and lying in a pocket “open only on the outer surface
of the cone.” Fig. 128 represents a transverse section through a cone
in the plane AA of fig. 127; this traverses the sporangia and their
subtending bracts (_b_) of one whorl and the dependent bases of the
sporophylls of the next higher whorl in the region of the mucilage-sacs
(_m_), which are bounded at the periphery by the outer tissue of the
sporophylls (_a_). A transverse section in the plane BB of fig. 127
is shown in fig. 129: the pedicels and a part of each vascular strand
are seen at _b_ radiating from the axis of the cone; one sporophyll
(_sp, a_) is cut through in the region of the pad of tracheal tissue
that characterises the short sporangial stalks. The upper portions of
the sporangia of the next lower whorl, which project upwards against
the mucilaginous bases of the sporophylls above (cf. fig. 127, BB) are
shown at _c_ and external to them, at _a_, the section has cut through
the outer persistent portions of these sporophyll bases.

[Illustration: FIG. 127. Radial longitudinal section of the cone of
  _Lycopodium cernuum_. (After Lang.)]

[Illustration: FIG. 128. Transverse section of the cone of _Lycopodium
  cernuum_, in its plane AA of fig. 127. (After Lang.)]

[Illustration: FIG. 129. Transverse section of the cone of _Lycopodium
  cernuum_ in the plane BB of fig. 127. (After Lang.)]

As Lang points out, this highly complex structure is an expression of
the complete protection afforded to the sporangia of a plant met with
in exposed situations in the tropics; it is also of importance from a
morphological standpoint as exhibiting an agreement with the extinct
type of Lycopod cone represented by _Spencerites_.


                          =Selaginellaceae.=

_Selaginella_ differs from _Lycopodium_ in the production of two kinds
of spores, megaspores and microspores, and, in the great majority
of species, in the dimorphic character of the foliage leaves, which
are usually arranged in four rows, the laminae of the upper rows
being very much smaller than those of the lower (fig. 130, 1–3). The
smaller leaves are shown more clearly in fig. 130, 1_a_. It is obvious
from an examination of a Selaginella shoot, such as is shown in fig.
130, that in fossil specimens it would often be almost impossible to
recognise the existence of two kinds of leaves. Some species, _e.g._
_Selaginella spinosa_[113], the sole British representative of the
genus, are homophyllous and agree in this respect with most species
of _Lycopodium_. Another feature characteristic of _Selaginella_, as
contrasted with _Lycopodium_, is the presence of a ligule in both
foliage leaves and sporophylls. This is a colourless thin lamina
attached by a comparatively stout foot to the base of a pit on the
upper surface and close to the lower edge of the leaf (fig. 130, 4,
_l_; fig. 131, E, F, _l_).

[Illustration: FIG. 130. _Selaginella grandis._ (1–3, nat. size.)]

In an erect species, such as _S. grandis_ Moore[114] (fig. 130 and
fig. 131, G) from Borneo, the main shoots, which may attain a height
of 2–3 feet, bear small and inconspicuous leaves of one kind, but the
lateral and repeatedly forked shoots are heterophyllous. The passage
from the homophyllous to the heterophyllous arrangement is shown in
the transition from the erect to the dorsiventral habit of the lateral
shoots (fig. 130, 2). The monopodially or dichotomously branched shoots
produce long naked axes at the forks; these grow downwards to the
ground where they develop numerous dichotomously forked branches. For
certain reasons these naked aerial axes were named rhizophores and have
always been styled shoots, the term root being restricted to repeatedly
forked branches which the rhizophores produce in the soil. It has,
however, been shown by Professor Harvey-Gibson[115] that there is no
sufficient reason for drawing any morphological distinction between
rhizophores and roots, the term root being applicable to both.

Our knowledge of the anatomy of _Selaginella_, thanks chiefly to the
researches of Harvey-Gibson[116], is much more complete than in the
case of _Lycopodium_. The stems, which may be either trailing or erect,
are usually dorsiventral, and it is noteworthy that different shoots of
the same plant or even the same axis in different regions may exhibit
considerable variation in the structure and arrangement of the vascular
tissue. In the well-known species, _Selaginella Martensii_, the
stem, which is partly trailing, partly ascending, possesses a single
ribbon-shaped stele composed of scalariform tracheids with two marginal
protoxylems formed by the fusion of the leaf-traces of the dorsal
and ventral leaves respectively. As in _Lycopodium_ the metaxylem
tracheae are as a rule scalariform, but reticulate xylem elements are
by no means unknown. The tracheal band, surrounded by parenchymatous
elements, is enclosed by phloem with external protophloem elements.
The characteristic features of the stele are shown in the diagrammatic
drawing of a section of another species—_S. Willdenowii_—represented in
fig. 131, A.

[Illustration: FIG. 131.

  A. _Selaginella Willdenowii._ Transverse section of stem: _a_,
     outer cortex; _p_, phloem; _t_, trabeculae.
  B. _S. spinosa_, stem: _px_, protoxylem.
  C. _S. laevigata_ var. _Lyallii_, section of stele: _t_, ridge of
     xylem cylinder; _e_, endodermis.
  D. _S. rupestris_, seedlings with cotyledons (_c_) protruding
     beyond the sporophylls (_b_).
  E. Transverse section of _Selaginella_ leaf-base: _l_, ligule;
     _lt_, leaf-trace.
  F. Portion of G. enlarged.
  G. _S. grandis._ Longitudinal section of strobilus: _bb_,
     sporophyll-trace; _l_, ligule.

  (A, B, C, E, F, after Harvey-Gibson; D, after Miss Lyon.)]

A pericycle composed of one or two layers of chlorophyll-containing
cells encircles the whole stele which is suspended in a lacuna by
trabeculae (fig. 131, A, B, _t_) connecting the pericycle with the
inner edge of the broad cortex. The trabeculae consist in part of
endodermal cells characterised by cuticular bands. The cortex is
usually differentiated into three fairly distinct regions. Mechanical
tissue of thick-walled fibres constitutes the outer region (_a_); the
middle cortex consists of thinner-walled parenchyma, the elements of
which become smaller and rather more compactly arranged in the inner
zone. The middle cortex is frequently characterised by the presence
of spaces and by the hyphal or trabecular structure of the tissue, a
feature which, as Bower[117] pointed out, is common to many recent
and fossil members of the Lycopodiales. In some cases, _e.g._ _S.
erythropus_, from tropical America, the cortex of the creeping stem
consists entirely of thick-walled cells. _Selaginella grandis_ (fig.
130) has “a short decumbent stem rooted at close intervals[118],”
from which thick erect aerial shoots rise to a height of one foot or
more. In the apical region these erect axes give off repeatedly forked
foliage shoots on which the spiral phyllotaxis of the homophyllous axis
is gradually replaced by four rows of two kinds of leaves (fig. 130,
2). The anatomy of this species agrees with that of _S. Martensii_.
The trailing or semi-erect and homophyllous shoots of _Selaginella
spinosa_[119] present a distinct type of vascular anatomy. The upper
part of the ascending stem has an axial strand of xylem with seven
peripheral groups of spiral protoxylem tracheae (fig. 131, B); in
the trailing portion of the shoot the protoxylem elements occur as
one central group in the solid rod of metaxylem through which the
leaf-traces pass on their way to the axial protoxylem. This type is
important as affording an exception, in the endarch structure of the
xylem, to the usual exarch plan of the stelar tissues. This species is
the only one in which any indication of the production of secondary
xylem elements has so far been recorded. Bruchmann[120] has shown
that, in the small tuberous swelling which occurs at the base of the
young shoot (hypocotyl), a meristematic zone is formed round the axial
vascular strand and by its activity a few secondary tracheids are added
to the primary xylem. With this exception _Selaginella_ appears to
have lost the power of secondary thickening, the possession of which
constitutes so striking a feature of the Palaeozoic Lycopods. Another
type is represented by _S. inaequalifolia_, an Indian species, the
shoots of which may have either a single stele or as many as five,
each in its separate lacuna. The homophyllous _S. laevigata_ var.
_Lyallii_ Spr., a Madagascan species, affords a further illustration
of the variation in plan of the vascular tissues within the genus.
There is a considerable difference in structure between the erect
and creeping shoots; in the former there may be as many as 12–13
steles, which gradually coalesce before the vertical axis joins the
creeping rhizome to form one central and four peripheral steles. In the
rhizome there is usually a distinct axial stele without protoxylem,
surrounded by an ill-defined lacuna and enclosed by a cylindrical
stele (solenostele)[121] usually two tracheae in width with four
protoxylem strands on its outer edge. The continuity of the tubular
stele is broken and, in transverse section, it assumes the form of a
horse-shoe close to the base of an erect shoot to which a crescentic
vascular strand is given off. Harvey-Gibson[122] has figured a section
of the rhizome of this type in which the axial vascular strand is
represented by a slight ridge of tracheae (fig. 131, C, _t_) projecting
towards the centre of the axis of the tubular stele. The cylindrical
stele consists of xylem with external and internal phloem (_p_):
cuticularised endodermal cells occur at _e_ and _e_.

Reference has already been made to the descending naked branches
given off from the points of ramification of the foliage shoots of
_Selaginella_. It has been shown by Harvey-Gibson[123] that these
branches, originally designated rhizophores by Nägeli and Leitgeb,
as well as the dichotomously branched roots which they produce below
the level of the ground, possess a single vascular strand of monarch
type. It is interesting to find that in some species the aerial portion
of the rhizophore has a xylem strand with a central protoxylem, an
instance of endarch structure like that in certain portions of the
shoot-system of _S. spinosa_. The root-anatomy of _Selaginella_ and
the dichotomous habit of branching afford points of agreement with the
subterranean organs of _Lepidodendron_ and _Sigillaria_.

_Leaves._ The leaves of _Selaginella_[124] usually consist of a
reticulum of loosely arranged cells, but in some cases part of the
mesophyll assumes the palisade form. The single vascular bundle
consists of a few small annular or spiral tracheae and at the apex of
the lamina the protoxylem elements are accompanied by several short
reticulated pitted elements. Both foliage leaves and sporophylls are
characterised by the possession of a ligule, a structure which may
present the appearance of a somewhat rectangular plate (fig. 130,
4, _l_, and fig. 131, E–G, _l_) or assume a fan-shaped form with a
lobed or papillate margin. The base, composed of large cells, is sunk
in the tissue of the leaf close to its insertion on the stem (fig.
131, E, _l_) and enclosed by a well-marked parenchymatous sheath. The
sheath is separated from the vascular bundle of the leaf by one or
more layers of cells, and in some species these become transformed
into short tracheids. The ligule is regarded by Harvey-Gibson[125] as
a specialised ramentum which serves the temporary function of keeping
moist the growing-point and young leaves.

_Cones._ The terminal portions of the branches of _Selaginella_ usually
bear smaller leaves of uniform size which function as sporophylls, but
in this genus the fertile shoots do not generally form such distinct
cones as in many species of _Lycopodium_. In _S. grandis_ (figs. 130,
3; 131, G) the long and narrow strobili consist of a slender axis
bearing imbricate sporophylls in four rows: each sporophyll subtends
a sporangium situated between the ligule and the axis of the shoot.
The sporangium may be developed from the axis of the cone or, as in
_Lycopodium_, from the cells of the sporophyll[126]. In some species
the lower sporophylls bear only megasporangia, each normally containing
four megaspores, the microsporangia being confined to the upper part of
the cone. This distribution of the two kinds of sporangia is, however,
by no means constant[127]: in some cases, _e.g._ _S. rupestris_, cones
may bear megasporangia only, and in the cone of _S. grandis_, of which
a small piece is represented in fig. 131, G, all the sporangia were
found to contain microspores.

The occurrence of two kinds of spores in _Selaginella_ constitutes
a feature of special importance from the point of view of the
relationship between the Phanerogams, in which heterospory is a
constant character, and the heterosporous Pteridophytes. One of the
most striking distinctions between the Phanerogams and the rest of the
vegetable kingdom lies in the production of seeds. Recent work has,
however, shown that seed-production can no longer be regarded as a
distinguishing feature of the Gymnosperms and Angiosperms. Palaeozoic
plants which combined filicinean and cycadean features resembled the
existing Phanerogams in the possession of highly specialised seeds.
This discovery adds point to the comparison of the true seed with
structures concerned with reproduction in seedless plants, which in
the course of evolution gave rise to the more efficient arrangement
for the nursing, protection, and ultimate dispersal of the embryo. In
the megaspore of _Selaginella_ we have, as Hofmeister was the first
to recognise in 1851, a structure homologous with the embryo-sac of
the Phanerogam. The embryo-sac consists of a large cell produced in a
mass of parenchymatous tissue known as the nucellus which is almost
completely enclosed by one or more integuments. Fertilisation of the
egg-cell within the embryo-sac takes place as a rule while the female
reproductive organ is still attached to the parent-plant and separation
does not occur until the ovule has become the seed.

In a few cases, notably in certain plants characteristic of Mangrove
swamps, continuity between the seed and its parent is retained until
after germination. The megasporangium of _Selaginella_ dehisces[128]
along a line marked out by the occurrence of smaller cells over the
crest of the wall. It has been customary to describe the megaspores
as being fertilised after ejection from the sporangia. This earlier
separation from the parent and the absence of any protective covering
external to the spore-wall constitute two distinguishing features
between seeds and megaspores. In _Selaginella apus_, a Californian
species, Miss Lyon has shown that fertilisation of the egg-cell usually
takes place while the megaspore is still in the strobilus. On examining
withered decayed strobili of this species which had been partially
covered with the soil for some months after fertilisation of the
megaspores, several young plants were found with cotyledons and roots
projecting through the crevices of the megasporangia[129]. From this,
adds Miss Lyon, “it seems safe to assume that an embryo may have two
periods of growth separated by one of quiescence quite comparable to
those of seed plants with marked xerophilous features.”

In another Western American species _S. rupestris_ described by the
same writer the cotyledons of young plants were found protruding
from the imbricate sporophylls of a withered cone (fig. 131, D).
This species is interesting also from the occasional occurrence
of one instead of four megasporangia in a sporangium; a condition
which affords another connecting link between the heterosporous
Pteridophytes, on the one hand, and the seed-bearing Phanerogams in
which the occurrence of a single embryo-sac (megaspore) in each ovule
is the rule. The cones of _Selaginella rupestris_ retain connexion
with the plant through the winter and fertilisation occurs in the
following spring. After the embryo has been formed the megasporangium
“becomes sunken in a shallow pit formed by the cushion-like outgrowth
of the sporophyll around the pedicel.” It is suggested that this
outgrowth may be comparable with the integument which grows up from
the sporophyll in the fossil genus _Lepidocarpon_[130] and almost
completely encloses the sporangium. In the drawings given by Miss Lyon
no features are recognisable which afford a parallel to the integument
of _Lepidocarpon_. I have, however, endeavoured to show, by a brief
reference to this author’s interesting account of the two Californian
species, that the physiological and morphological resemblances between
the megasporangia of _Selaginella_ and the integumented ovules of the
seed-bearing plants are sufficiently close to enable us to recognise
possible lines of advance towards the development of the true seed.

Professor Campbell[131] records an additional example of a
_Selaginella_—probably _S. Bigelovii_—from the dry region of Southern
California in which the spores become completely dried up after the
embryo has attained some size, remaining in that state until the more
favourable conditions succeeding the dry season induce renewed activity.


                             =Isoetaceae.=

The genus _Isoetes_ is peculiar among Pteridophytes both in habit and
in anatomical features. In its short and relatively thick tuberous
stem, terminating in a crowded rosette of subulate leaves like those of
_Juncus_ and bearing numerous adventitious roots, _Isoetes_ presents an
appearance similar to that of many monocotyledonous plants. The habit
of the genus is well represented by such species as _Isoetes lacustris_
and _I. echinospora_[132] (fig. 132) both of which grow in freshwater
lakes in Britain and in other north European countries. The latter
species bears leaves reaching a length of 18 cm. The resemblance in
habit between this isolated member of the Pteridophytes and certain
Flowering plants, although in itself of no morphological significance,
is consistent with the view expressed by Campbell that _Isoetes_ may be
directly related to the Monocotyledons[133].

[Illustration: FIG. 132. _Isoetes echinospora_ (After Motelay and
  Vendryès).

  A. Stem of _I. lacustris._
  B. Base of sporophyll: _l_, ligule; _spg_, sporangium partially
     covered by velum.]

There is as a rule little or no difference between the foliage leaves
and sporophylls; in _I. lacustris_ the latter are rather larger and
in the terrestrial species _I. hystrix_[134] the sterile leaves are
represented by the expanded basal portions only, which persist like the
leaf-bases of _Lepidodendron_ as dark brown scales to form a protective
investment to the older part of the stem. The innermost leaves are
usually sterile; next to these are sporophylls bearing megasporangia,
and on the outside are the older sporophylls with microsporangia. The
long and slender portion of the leaf becomes suddenly expanded close
to its attachment to the stem into a broad base of crescentic section
which bears a fairly conspicuous ligule (figs. 132, B, _l_, 133, E,
_l_) inserted by a foot or glossopodium in a pit near the upper part
of the concave inner face. The ligule is usually larger than that
of _Selaginella_, though of the same type. The free awl-like lamina
contains four large canals bridged across at intervals by transverse
diaphragms, and in the axial region a single vascular bundle of
collateral structure. Other vascular elements, in the form of numerous
short tracheids occur below the base of the transversely elongated
ligule.

Stomata are found on the leaves of _I. hystrix_, _I. Boryana_[135],
and in other species which are not permanently submerged. Both
microsporangia and megasporangia are characterised by their large
size and by the presence of trabeculae or strands of sterile tissue
(fig. 133, E, H, _t_) completely bridging across the sporangial
cavity or extending as irregular ingrowths among the spore-producing
tissue. Similar sterile bands, though less abundant and smaller, are
occasionally met with in the still larger sporangia of _Lepidostrobus_;
these may be regarded as a further development of the prominent pad
of cells which projects into the sporangial cavity in recent species
of _Lycopodium_ (fig. 126, D, _p_). The sporangia are attached by a
very short stalk to the base of a large depression in the leaf-base
below the ligule, from the pit of which they are separated by a ridge
of tissue known as the saddle, and from this ridge a veil of tissue
(the velum) extends as a roof over the sporangial chamber (fig. 133,
E, _v_). In most species there is a large gap between the lower edge
of the velum and that of the sporangial pit, but in _I. hystrix_
this protective membrane is separated from the base of the leaf by a
narrow opening, the resemblance of which to the micropyle of an ovule
suggested to one of the older botanists the employment of the same
term[136]. Mr T. G. Hill[137] has called attention to the presence
of mucilage canals in the base of the sporophylls of _I. hystrix_,
which he compares with the strands of tissue known as the parichnos
accompanying the leaf-traces of _Lepidodendron_ and _Sigillaria_ in
the outer cortex of the stem. The transverse section shown in fig.
133, H and I, shows two of these mucilage canals in an early stage
of development; a strand of parenchymatous elements distinguished
by their partially disorganised condition and more deeply stained
membranes (fig. 133, I) runs through the spandrels of the sporophyll
tissue close to the upper surface. There is a close resemblance
between the structure of these partially formed mucilage-canals and
the tissue which has been called the secretory zone in Lepidodendron
stems. Fig. 133, H, also shows a large microsporangium with prominent
trabeculae (_t_) lying below the velum. A longitudinal section (fig.
133, E) through a sporophyll-base presents an appearance comparable
with that of an Araucarian cone-scale with its integumented ovule
and micropyle. The megaspores are characterised by ridges, spines,
and other surface-ornamentation[138]. Though usually unbranched, the
perennial stem of _Isoetes_ (fig. 132) has in rare cases been found to
exhibit dichotomous branching, a feature, as Solms-Laubach[139] points
out, consistent with a Lycopodiaceous affinity. The apex is situated
at the base of a funnel-shaped depression. The stem is always grooved;
in some species two and in others three deep furrows extend from the
base up the sides of the short and thick axis towards the leaves: from
the sides of these furrows numerous slender roots are given off in
acropetal succession. A stele of peculiar structure occupies the centre
of the stem; cylindrical in the upper part (fig. 133, A), it assumes a
narrow elliptical or, in species in which there are three furrows, a
triangular form in the lower portion of the tuberous stem.

[Sidenote: ISOETES]

The stem of _I. lacustris_ represented in fig. 132, A, from which the
laminae of the leaves have been removed from the summit affords an
example of a species with two furrows. The drawing shows the widely
gaping sides of the broad furrow with circular root-scars and a few
simple and dichotomously branched roots. A short thick column of
parenchymatous tissue projects from a slightly eccentric position on
the base of the stem.

[Illustration: FIG. 133. _Isoetes lacustris_.

  A. Transverse section of stem: _cr_, cortex; _x_, _x²_ xylem; _c_,
     cambium; _a_, thin-walled tissue; _lt_, leaf-traces; _b_, dead
     tissue.
  B, C, D. Portions of A enlarged.
  E. Longitudinal radial section of sporophyll-base: _v_, velum; _l_,
     ligule; _bb_; vascular bundle; _m_, megaspores; _t_, sterile
     tissue.
  F. Longitudinal section through the base of a root.
  G. Transverse section of root.
  H. Transverse section of sporophyll, showing sporangium with
     trabeculae, _t_; leaf-trace, (_lt_), and two groups of secretory
     cells.
  I. A group of secretory cells enlarged.]

The primary vascular cylinder[140] consists of numerous spiral,
annular or reticulate tracheids (fig. 133, A, _x_) which are either
isodiametric or longer in a horizontal than in a vertical direction,
associated with parenchyma. Lower in the stem crushed and disorganised
xylem elements are scattered through a still living trabecular network
of parenchymatous tissue. From the axial cylinder numerous leaf-traces
(fig. 133, A, _lt_) radiate outwards, at first in a horizontal
direction and then gradually ascending towards the leaves. The vascular
cylinder is of the type known as cauline; that is, some of the xylem is
distinct in origin from that which consists solely of the lower ends
of leaf-traces. As in _Lycopodium_ the development of the metaxylem is
centripetal.

Von Mohl[141], and a few years later Hofmeister[142], were the first
botanists to give a satisfactory account of the anatomy of _Isoetes_
but it is only recently[143] that fresh light has been thrown upon the
structural features of the genus the interest of which is enhanced
by the many points of resemblance between the recent type and the
Palaeozoic Lepidodendreae. A striking anatomical feature is the power
of the stem to produce secondary vascular and non-vascular tissue;
the genus is also characterised by the early appearance of secondary
meristematic activity which renders it practically impossible to draw
any distinct line between primary and secondary growth. A cylinder of
thin-walled tissue (fig. 133, A, _a_) surrounds the primary central
cylinder and in this a cambial zone, _c_, is recognised even close
to the stem-apex; this zone of dividing cells is separated from the
xylem by a few layers of rectangular cells to which the term prismatic
zone has been applied. The early appearance of the cambial activity
on the edge of the vascular cylinder is shown in fig. 133, C, which
represents part of a transverse section of a young stem. A leaf-trace,
_lt_, is in connexion with the primary xylem, _x′_, which consists of
short tracheids, often represented only by their spiral or reticulately
thickened bands of lignified wall, and scattered parenchyma. Some of
the radially elongated cells on the sides of the leaf-trace are seen
to be in continuity on the outer edge of the stele, at _st_, with
flattened elements, some of which are sieve-tubes. The position of a
second leaf-trace is shown at _lt′_. External to the sieve-tubes the
tissue consists of radially arranged series of rectangular cells, some
of which have already assumed the function of a cambium (_c_). The
tissue produced by the cambium on its inner edge consists of a varying
amount of secondary xylem composed of very short spiral tracheids; a
few of these may be lignified (fig. 133, A, _x²_) while others remain
thin.

Phloem elements, recognisable by the presence of a thickened reticulum
enclosing small sieve-areas (fig 133, B, _s_) are fairly abundant,
and for the rest this intracambial region is composed of thin-walled
parenchyma. In longitudinal section these tissues present an appearance
almost identical with that observed in a transverse section. Fig.
133, B represents a longitudinal section, through the intracambial
zone and the edge of the stele, of a younger stem than that shown
in fig. 133, A. Most of the radially disposed cells internal to
the meristematic region are parenchymatous without any distinctive
features; a few scattered sieve-tubes (_s_) are recognised by their
elliptical sieve-areas and an occasional tracheid can be detected. The
cambium cuts off externally a succession of segments which constitute
additional cortical tissue (fig. 133, A, _cr_) of homogeneous
structure, composed of parenchymatous cells containing starch and
rich in intercellular spaces. As the stem grows in thickness the
secondary cortex reaches a considerable breadth and the superficial
layers are from time to time exfoliated as strips of dead and crushed
tissue (fig. 133, A, _b_). The diagrammatic sketch reproduced in fig.
133, A, serves to illustrate the arrangement and relative size of the
tissue-regions in an _Isoetes_ stem. In the centre occur numerous
spirally or reticulate tracheae scattered in parenchymatous tissue
which has been considerably stretched and torn in the peripheral
region of the stele; the radiating lines mark the position of the
leaf-traces (_lt_) in the more horizontal part of their course. The
zone between the cambium (_c_) and the edge of the central cylinder
consists of radially disposed secondary tissue of short, and for the
most part unlignified, elements including sieve-tubes and parenchyma;
the secondary xylem elements consist largely of thin-walled rectangular
cells with delicate spiral bands, but discontinuous rows of lignified
tracheae (_x²_) occur in certain regions of the intracambial zone. The
rest of the stem consists of secondary cortex (_cr_) with patches of
dead tissue (_b_) still adhering to the irregularly furrowed surface.
The structure of the cambium and its products is shown in the detailed
drawing reproduced in fig. 133, D. Many of the elements cut off on the
inner side of the cambium exhibit the characters of tracheids: most
of these are unlignified, but others have thicker and lignified walls
(_tr_).

_I. hystrix_ appears to be exceptional in retaining its leaf-bases,
which form a complete protective investment and prevent the exfoliation
of dead cortex. Each leaf-trace consists of a few spiral tracheids
accompanied by narrow phloem elements directly continuous with the
secondary phloem of the intracambial zone. Dr Scott and Mr Hill have
pointed out that a normal cambium is occasionally present in the stem
of _I. hystrix_ during the early stages of growth; this gives rise
to xylem internally. The few phloem elements observed external to
the cambium may be regarded as primary phloem, a tissue not usually
represented in an Isoetes stem[144]. The occasional occurrence of this
normal cambium, may, as Scott and Hill suggest, be a survival from a
former condition in which the secondary thickening followed a less
peculiar course. The lower leaf-traces become more or less obliterated
as the result of the constant increase in thickness of the broad zone
of secondary tissues through which they pass.

The adventitious roots are developed acropetally and arranged in
parallel series on each side of the median line of the two or three
furrows. The three arms of the triangular stele of _I. hystrix_ and
the two narrow ends of the long axis of the stele of _I. lacustris_,
which in transverse section has the form of a flattened ellipse, are
built up of successive root-bases. A root of _Isoetes_ (fig. 133, G)
possesses one vascular bundle, _x_, with a single strand of protoxylem,
_px_, thus agreeing in its monarch structure with the root-bundle in
_Selaginella_ and many species of _Lycopodium_. The cortical region
of the root consists of a few layers of outer cortex succeeded by
a large space, formed by the breaking down of the inner cortical
tissue, into which the vascular bundle projects (fig. 133, F). The
peculiarity of the roots in having a hollow cortex and an eccentric
vascular bundle was noticed by Von Mohl[145]. In the monarch bundles,
as in the fistular cortex and dichotomous branching, the roots of
_Isoetes_ present a striking resemblance to the slender rootlets of the
Palaeozoic _Stigmaria_ (see Page 246). The longitudinal section through
the base of a root of _Isoetes lacustris_ shown in fig. 133, F, affords
a further illustration of certain features common to the fossil and
recent types.


                         FOSSIL LYCOPODIALES.

                              Isoetaceae

The geological history of this division of the Pteridophyta is
exceedingly meagre, a fact all the more regrettable as it is by no
means improbable that in the surviving genus _Isoetes_ we have an
isolated type possibly of considerable antiquity and closely akin to
such extinct genera as _Pleuromeia_ and _Sigillaria_. If Saporta’s
Lower Cretaceous species _Isoetes Choffati[146]_, or more appropriately
_Isoetites Choffati_, is correctly determined, it is the oldest fossil
member of the family and indeed the most satisfactory among the more
than doubtful species described as extinct forms of _Isoetes_.


                              Isoetites.

The generic name _Isoetites_ was first used by Münster[147] in the
description of a specimen, from the Jurassic lithographic slates of
Solenhofen in Bavaria, which he named _Isoetites crociformis_. The
specific name was chosen to express a resemblance of the tuberous
appearance of the lower part of the imperfectly preserved and
indeterminable fossil to a Crocus corm.

Impressions of Isoetes-like leaves from the Inferior Oolite of
Yorkshire figured by Phillips[148] and afterwards by Lindley[149] as
_Solenites Murrayana_ were compared by the latter author with _Isoetes_
and _Pilularia_, but these leaves are now generally assigned to Heer’s
gymnospermous genus _Czekanowskia_. An examination of the structure of
the epidermal cells of these Jurassic impressions convinced me that
they resemble recent coniferous needles more closely than the leaves
of any Pteridophyte. The genus _Czekanowskia[150]_ is recognised by
several authors as a probable member of the Ginkgoales.


                    _Isoetites Choffati._ Saporta.

The late Marquis of Saporta founded this species on two sets of
impressions from the Urgonian (Lower Cretaceous) of Portugal which,
though not found in actual organic connexion, may possibly be portions
of the same plant. Small relatively broad tuberous bodies reaching
a breadth of 1 cm. are compared with the short and broad stem of
_Isoetes_, which they resemble in bearing numerous appendages radiating
from the surface like the roots of the recent species; on the exposed
face of the stem occur scattered circular scars representing the
position of roots which were detached before fossilisation. Other
impressions are identified as the basal portions of sporophylls bearing
sporangia: these suggest the expanded base of the fertile leaves of
_Isoetes_ with vertically elongated sporangia, some of which have
a smooth surface while in others traces of internal structure are
exposed; the interior consists of an irregular network with depressions
containing carbonised remains of spores.

While recognising a general resemblance to the sporophylls of
_Isoetes_, certain differences are obvious: there is no ligule in
the fossil leaves nor are there any distinct traces of vascular
strands such as occur in the leaves of recent species. The form of
the sporangium, more elongated than in the majority of recent forms,
is compared by Saporta with that in a south European species _Isoetes
setacea_ Spr.

Such evidence as we have lends support to the inclusion of these
Portuguese fossils in the genus _Isoetites_, but apart from the fact
that we have no proof of any connexion between the stems and supposed
sporophylls, the resemblance of the latter to those of _Isoetes_ is,
perhaps, hardly sufficient to satisfy all reasonable scepticism.

The generic name _Isoetopsis_ was used by Saporta as more appropriate
than _Isoetes_ for some Eocene fossils from Aix-en-Provence which are
too doubtful to rank as trustworthy evidence of the existence of the
recent genus. The species, _Isoetopsis subaphylla_[151] is founded on
impressions of small scales, 4 mm. long, bearing circular bodies which
are compared with sporangia or spores.

Other records of fossils referred to _Isoetes_ need not be described
as they have no claim to be regarded as contributions towards the past
history of the genus. Heer’s Miocene species _Isoetites Scheuzeri_ and
_I. Braunii_ Unger[152] from Switzerland are based on unsatisfactory
material and are of no importance.


                              Pleuromeia.

The generic name _Pleuromeia_, was suggested by Corda[153] for a fossil
from the Bunter Sandstone, the original description of which was based
by Münster[154] on a specimen discovered in a split stone from the
tower of Magdeburg Cathedral.

The majority of the specimens have been obtained from the neighbourhood
of Bernburg, but a few examples are recorded from Commern and other
German localities: all are now included under the name _Pleuromeia
Sternbergi_. Germar, who published one of the earlier accounts of the
species, states that Corda dissented from Münster’s choice of the name
_Sigillaria_ and proposed the new generic title _Pleuromeia_. One of
the best descriptions of the genus we owe to Solms-Laubach[155] whose
paper contains references to earlier writers. Illustrations have been
published by Münster, Germar[156], Bischof[157], Solms-Laubach and
Potonié[158].

  _Pleuromeia Sternbergi._ (Münster.)
              Fig. 134.

  1842. _Sigillaria Sternbergii_, Münster.
  1854. _Sagenaria Bischofii_, Goeppert[159].
  1885. _Sigillaria oculina_, Blanckenhorn.
  1904. _Pleuromeia oculina_, Potonié.

_Pleuromeia Sternbergi_ is represented by casts of vegetative and
fertile axes, but the preservation of the latter is not sufficiently
good to enable us to draw any very definite conclusions as to the
nature of the reproductive organs. Casts of the stems reach a length
of about 1 metre and a diameter of 5–6 cm., or in some cases 10 cm.;
all of them are in a more or less decorticated state, the degree
of decortication being responsible for differences in the external
features which led Spieker[160] to adopt more than one specific name.

Fig. 134, A, represents a sketch, made some years ago, of a specimen
in the Breslau Museum which contains several examples of this species,
among others those described by Germar in 1852. The cylindrical cast
(38 cm. long by 12 cm. in circumference), which has been slightly
squeezed towards the upper end, bears spirally arranged imperfectly
preserved leaf-scars and the lower end shows the truncated base of one
of the short Stigmaria-like arms characteristic of the plant. As shown
clearly in a specimen originally figured by Bischof and more recently
by Potonié[161], the stem-base is divided by a double dichotomy into
four short and broad lobes with blunt apices and bent upwards like
the arms of a grappling iron (fig. 134, D). The surface of this
basal region is characterised by numerous circular scars (fig. 134,
D; 4 scars enlarged) in the form of slightly projecting areas with a
depression in the centre of each. These are undoubtedly the scars of
rootlets, remains of which are occasionally seen radiating through the
surrounding rock. As seen in fig. 134, D, _a_, the fractured surface
of a basal area may reveal the existence of an axial vascular cylinder
giving off slender branches to the rootlets.

[Illustration: FIG. 134. _Pleuromeia Sternbergi._

  A. Cast of stem in the Breslau Museum (⅓ nat. size). (A.C.S.)
  B. “_Sigillaria oculina_” Blanckenhorn. (After Weiss).
  C, D. Leaf-scars and base of stem: _a_, vascular tissue. (After
     Solms-Laubach.)]

The bulbous enlargement at the base of the Brown seaweed _Laminaria
bulbosa_ Lam.[162] simulates the swollen base of _Pleuromeia_; but a
confusion between these two plants is hardly likely to occur. Above
the Stigmaria-like base the gradually tapered axis, in the less
decorticated specimens, bears spirally disposed transversely elongated
areas consisting of two triangular scars between which is the point
of exit of a leaf-trace. The form of the leaf-scars is best seen on
the face of a mould figured by Solms-Laubach (fig. 134, C): in this
case the two triangular areas appear as slight projections separated
by a narrow groove marking the position of the vascular bundle of the
leaf. The curved lines above and below the leaf-scar probably mark the
boundary of the leaf-base. The two triangular scars are compared by
Solms-Laubach and by Potonié with the parichnos-scars of _Sigillaria_
and _Lepidodendron_ (cf. fig. 146, C), but the large size of the
Pleuromeia scars constitutes an obvious difference though possibly not
a distinction of importance.

The occurrence of a vertical canal filled with carbonaceous material
in some of the stems throws light on the internal structure: the
canal, which is described by Solms-Laubach as having a stellate
outline in transverse section recalls the narrow central cylinder
of a Lepidodendron stem, and this comparison is strengthened by the
presence of obliquely ascending grooves which represent leaf-traces
passing through the cortex. In specimens which have lost more of the
cortical tissues the surface is characterised by spirally disposed,
discontinuous vertical grooves representing portions of leaf-traces
precisely as they appear in similar casts of _Lepidodendron_. There
is no direct evidence of the existence of secondary wood in the stem,
but, as Potonié has pointed out, the greater transverse elongation of
the leaf-scars in the lower part of a cast (fig. 134, A) points to the
production of some secondary tissue either in the vascular cylinder or
cortex, or possibly in both regions.

In some specimens of _Pleuromeia_ the upper portion is clothed with
crowded and imbricate sporophylls which reach a length of 2·5 cm., a
maximum breadth of 2·7 cm., and a thickness of 1 mm. Each sporophyll
has a thin wing-like border, and on the lower face are several parallel
lines. Solms-Laubach describes the sporangium or ovule as attached to
the lower surface of the sporophyll and this opinion has been confirmed
by Fitting[163] who has also brought forward satisfactory evidence in
favour of the sporangial nature of the reproductive organs. Fitting
found numerous spores in the Bunter Sandstone near Halle; these are
flattened circular bodies 0·5–0·7 mm. in diameter with a granulated
surface and the three converging lines characteristic of spores
produced in tetrads. The comparison made by this author between the
sporophylls of _Pleuromeia_, which bore the sporangia on the lower
surface instead of on the upper as in other lycopodiaceous plants, and
the pollen-sacs of Conifers, is worthy of note in reference to the
possible relationship between Conifers and Lycopods.

A comparison of the _Isoetes_ stem represented in fig. 132, A, with the
base of a _Pleuromeia_ shows a striking similarity, but, as Fitting
points out, the Stigmaria-like arms of the fossil contained a vascular
cylinder whereas the blunt lobes of _Isoetes_ consist exclusively of
cortical tissue, the roots being given off from the grooves between the
lobes of the tuberous stem.

The position of _Pleuromeia_ must for the present be left an open
question; it is, however, clear that the plant bears a close
resemblance in the form of its base to the Stigmarian branches of
_Lepidodendron_ and _Sigillaria_. The vegetative shoot appears to be
constructed on a plan similar to that of these two Palaeozoic genera,
but the strobilus is of a different type. It would seem probable that
_Pleuromeia_ may be closely allied to _Isoetes_ and to the arborescent
Lycopods of Palaeozoic floras. It is not improbably a link in a chain
of types which includes _Sigillaria_ on the one hand and _Isoetes_ on
the other.

It is not improbable that a specimen from the Lower Bunter of Commern
which Blanckenhorn made the type of a new species, _Sigillaria
oculina_ (fig. 134, B) is specifically identical with _Pleuromeia
Sternbergi_. An examination of a cast of the type-specimen in the
Berlin Bergakademie led me to regard the fossil with some hesitation
as a true _Sigillaria_, but a more extended knowledge of _Pleuromeia_
lends support to the view adopted by Potonié[164] that Blanckenhorn’s
plant is not genetically distinct from _Pleuromeia Sternbergi_. The
resemblance between _Sigillaria oculina_ and some of the Palaeozoic
species of _Sigillaria_ emphasised by Weiss[165] has given rise to the
belief that the genus _Sigillaria_ persisted into the Triassic era; it
is, however, highly probable that the Bunter specimen has no claim to
the generic name under which it has hither to been known.

The Bunter Sandstone in which _Pleuromeia_ is the sole representative
of plant-life, at least in certain localities, is usually considered to
be a desert formation. We may not be far wrong in accepting Fitting’s
suggestion that in this isolated species we have a relic of the sparse
vegetation which was able to exist where the presence of lakes added a
touch of life to the deadness of the Triassic desert.

_Pleuromeia_ is recorded by Fliche as a rare fossil in the Middle Trias
of France in the neighbourhood of Lunéville[166].


              Herbaceous fossil species of Lycopodiales.

The history of our knowledge of fossil representatives of the
Lycopodiales, as also of the Equisetales, affords a striking
illustration of the danger of attempting to found a classification
on such differences as are expressed by the terms herbaceous and
arborescent in the sense in which they are usually employed. As we have
seen[167], the presence of secondary wood in stems of the Palaeozoic
plant now known as _Calamites_ led so competent a botanist as Adolphe
Brongniart to recognise a distinct generic type _Calamodendron_, which
he placed in the Gymnosperms, reserving the designation _Calamities_
for species in which no indication of secondary thickening had been
found.

Similarly, the genus _Sigillaria_ was regarded as a Gymnosperm because
it was believed to be distinguished from _Lepidodendron_ by the power
of forming secondary vascular tissues; the latter genus, originally
thought to be always herbaceous, was classed with the Pteridophytes.
At the time when this unnatural separation was made between stems with
secondary wood and those in which no secondary wood was known to exist,
botanists were not aware of the occurrence of any recent Pteridophyte
which shared with the higher plants the power of secondary growth in
thickness provided by means of a meristematic zone. It is true that the
presence or absence of a cambium does not in practice always coincide
with the division into herbaceous and arborescent plants: no one would
speak of a Date-Palm as a herbaceous plant despite the absence of
secondary wood.

The danger which should be borne in mind, in adopting as a matter of
convenience the term herbaceous as a sectional heading, is that it
should not be taken to imply a complete inability of the so-called
herbaceous types to make secondary additions to their conducting
tissues. The specimens on which the species of _Lycopodites_ and
_Selaginellites_, (genera which may be designated herbaceous,) are
founded are preserved as impressions and not as petrifications; we
can, therefore, base definitions only on habit and on such features
as are shown by fertile leaves and sporangia. We are fully justified
in concluding from evidence adduced by Goldenberg more than fifty
years ago and from similar evidence brought to light by more recent
researches, that there existed in the Palaeozoic era lycopodiaceous
species in close agreement in their herbaceous habit with the lycopods
of present-day floras. It has been suggested[168] that the direct
ancestors of the genera _Lycopodium_ and _Selaginella_ are represented
by the species of _Lycopodites_ and _Selaginellites_ rather than by
_Lepidodendron_ and _Sigillaria_, the arborescent habit of which has
been rendered familiar by the numerous attempts to furnish pictorial
reproductions of a Palaeozoic forest. Until we are able to subject the
species classed as herbaceous to microscopical examination we cannot
make any positive statement as to the correctness of this view, but
such facts as we possess lead us to regard the suggestion as resting on
a sound basis.

Palaeobotanical literature abounds in records of species of
_Lycopodites_, _Lycopodium_, _Selaginella_ and _Selaginites_, which
have been so named in the belief that their vegetative shoots bear
a greater resemblance to those of recent lycopodiaceous plants than
to the foliage shoots of _Lepidodendron_. Many of these records are
valueless: _Lepidodendra_, twigs of _Bothrodendron_[169] species
of conifers, fern rhizomes, and _Aphlebiae_[170] have masqueraded
as herbaceous lycopods. It is obvious that an attempt to identify
fossils presenting a general agreement in habit and leaf-form with
recent species of lycopods must be attended with considerable risk of
error. Recent Conifers include several species the smaller branches
of which simulate the leafy shoots of certain species of _Lycopodium_
and _Selaginella_, and it is not surprising to find that this
similarity has been responsible for many false determinations. Among
Mosses and the larger foliose Liverworts there are species which in
the condition of imperfectly preserved impressions, might easily be
mistaken for lycopodiaceous shoots: an equally close resemblance is
apparent in the case of some flowering plants, such as New Zealand
species of _Veronica_, _Tafalla graveolens_ (a Composite), _Lavoisiera
lycopodiodes_ Gard.[171] (a species of Melastomaceae), all of which
have the habit of Cupressineae among the conifers as well as of certain
lycopodiaceous plants. It may be impossible to decide whether fossil
impressions of branches, which are presumably lycopodiaceous, bear
two kinds of leaves[172] like the great majority of recent species of
_Selaginella_. _Selaginella grandis_, if seen from the under surface,
would appear to have two rows of leaves only and might be confused with
a small twig of such a conifer as _Dacrydium Kirkii_, a New Zealand
species.

The New Zealand conifers _Dacrydium cupressinum_ Soland. and
_Podocarpus dacrydioides_ Rich. closely simulate species of
_Selaginellites_ and _Lycopodites_: in the British Museum a specimen
of the latter species bears a label describing it as _Lycopodium
arboreum_ (Sir Joseph Hooker and Dr Solander; 1769). The twigs of the
Tasmanian conifer _Microcachyrs_ _tetragona_ Hook. f. are very similar
in habit to shoots of the recent _Lycopodium tetragonum_ (fig. 121, C).

In the description of examples of _Lycopodites_ and _Selaginellites_
I have confined myself to such as appear to be above suspicion either
because of the presence of spore-bearing organs or, in a few cases,
because the specimens of sterile shoots are sufficiently large to show
the form of branching in addition to the texture of the leaves. The
two generic names _Lycopodites_ and _Selaginellites_ are employed for
fossil species which there are substantial grounds for regarding as
representatives of _Lycopodium_ and _Selaginella_. The designation
_Selaginellites_ is adopted only for species which afford evidence of
heterospory; the name _Lycopodites_, on the other hand, is used in
a comprehensive sense to include all forms—whether homophyllous or
heterophyllous—which are not known to be heterosporous. This restricted
use of the generic name _Selaginellites_ is advocated by Zeiller[173],
who instituted the genus, and by Halle[174] in his recent paper on
herbaceous lycopods.


                             Lycopodites.

The generic term _Lycopodites_ was used by Brongniart in 1822[175]
in describing some Tertiary examples of slender axes clothed with
small scale-like leaves which he named _Lycopodites squamatus_. These
are fragments of coniferous shoots. In the _Prodrome d’une histoire
des végétaux fossiles_[176] Brongniart included several Palaeozoic
and Jurassic species in _Lycopodites_ and instituted a new genus
_Selaginites_, expressing a doubt as to the wisdom of attempting to
draw a generic distinction between the two sets of species. In a later
work[177] he recognised only one undoubted species, _Lycopodites
falcatus_. The first satisfactory account of fossils referred to
_Lycopodites_ is by Goldenberg[178] who gave the following definition
of the genus:—“Branches with leaves spirally disposed or in whorls.
Sporangia in the axil of foliage leaves or borne in terminal strobili.”

It was suggested by Lesquereux[179] that Goldenberg’s definition,
which was intended to apply to herbaceous species, should be extended
so as to include forms with woody stems but which do not in all
respects agree with _Lepidodendron_. Kidston[180] subsequently adopted
Lesquereux’s modification of Goldenberg’s definition. We cannot draw
any well-defined line between impressions of herbaceous forms and those
of small arborescent species. We use the name _Lycopodites_ for such
plants as appear to agree in habit with recent species of _Lycopodium_
and _Selaginella_ and which, so far as we know, were not heterosporous:
it is highly probable that some of the species so named had the
power of producing secondary wood, a power possessed by some recent
Pteridophytes which never attain the dimensions of arborescent plants.

It has been shown by Halle[181], who has re-examined several of
Goldenberg’s specimens which have been acquired by the Stockholm
Palaeobotanical Museum, that some of his species of _Lycopodites_
are heterosporous and therefore referable to Zeiller’s genus
_Selaginellites_.

In 1869 Renault described two species of supposed Palaeozoic Lycopods
as _Lycopodium punctatum_ and _L. Renaultii_[182], the latter name
having been suggested by Brongniart to whom specimens were submitted.
These species were afterwards recognised by their author as wrongly
named and were transferred to the genus _Heterangium_[183], a
determination which is probably correct; it is at least certain that
the use of the name _Lycopodium_ cannot be upheld.

We have unfortunately to rely on specimens without petrified tissues
for our information in regard to the history of _Lycopodites_ and
_Selaginellites_. Among the older fossils referred to _Lycopodites_
are specimens from Lower Carboniferous rocks at Shap in Westmoreland
which Kidston originally described as _Lycopodites Vanuxemi_[184],
identifying them with Goeppert’s _Sigillaria Vanuxemi_[185] founded
on German material. In a later paper Kidston transferred the British
specimens of vegetative shoots to a new genus _Archaeosigillaria_[186].


                  _Lycopodites Stockii_ Kidston[187].

The plant so named was discovered in Lower Carboniferous strata of
Eskdale, Dumfries, Scotland; it is represented by imperfectly preserved
shoots bearing a terminal strobilus and was originally described by
Kidston as apparently possessing two kinds of foliage leaves borne
in whorls. The larger leaves have an ovate cordate lamina with an
acuminate apex, while the smaller leaves, which are less distinct,
are transversely elongated, and simulate sporangia in appearance.
Dr Kidston’s figure of this species has recently been reproduced by
Professor Bower[188] who speaks of the supposed smaller leaves as
sporangia, a view with which the author of the species agrees. It would
appear that this identification is, however, based solely on external
resemblance and has not been confirmed by the discovery of any spores.
Assuming the sporangial nature of these structures, this Palaeozoic
type represents, as Bower points out, a condition similar to that in
some recent species of _Lycopodium_ in which sporangia are not confined
to a terminal strobilus but occur also in association with ordinary
foliage leaves. The strobilus consists of crowded sporophylls which are
too imperfect to afford any definite evidence as to their homosporous
or heterosporous nature. As Solms-Laubach[189] points out, this type
recalls _Lycopodium Phlegmaria_ among recent species.


                    _Lycopodites Reidii_ Penhallow.

Professor Penhallow[190] instituted this name for a specimen measuring
8 cm. long by 6 mm. in breadth, collected by Mr Reid from the Old Red
Sandstone of Caithness, consisting of an axis bearing narrow lanceolate
leaves some of which bear sporangia at the base.


                 _Lycopodites Gutbieri_ Goeppert[191].

1894, _Lycopodites elongatus_ Kidston[192] (not Goldenberg).

The species, figured by Geinitz as _Lycopodites Gutbieri_[193], from
the Coal-Measures of Saxony is probably a true representative of the
genus. The Saxon specimens are heterophyllous; the larger lanceolate
and slightly falcate leaves arranged in two rows, are 4–5 mm. long
while the smaller leaves are one half or one third this size; some of
the dichotomously branched shoots terminate in long and narrow strobili
not unlike those of Zeiller’s species _Selaginellites Suissei_[194].
Kidston[195] has included under this specific name some fragments
collected by Hemingway from the Upper Coal-Measures of Radstock,
Somersetshire, but as only one form of leaf is seen the reasons for
adopting Goeppert’s designation are perhaps hardly adequate.


                 _Lycopodites ciliatus_ Kidston[196].

Under this name Kidston describes a small specimen, obtained by
Hemingway from the Middle Coal-Measures of Barnsley in Yorkshire,
consisting of a slender forked axis bearing oval-acuminate leaves
approximately 5 mm. long with a finely ciliate margin. Associated with
the leaves were found spores which Kidston regards as megaspores.


              _Lycopodites macrophyllus_ Goldenberg[197].

This species, originally described by Goldenberg from the Coal-Measures
of Saarbrücken has been re-examined by Halle[198] who is unable to
confirm Goldenberg’s statement as to heterophylly. The shoots closely
resemble _Selaginellites primaevus_[199] (Gold).

[Illustration: FIG. 135. _Selaginellites and Lycopodites._ (After
  Halle.)

  A. _Selaginellites primaevus_ (Gold.). × 10.
  B. Megaspore of _Selaginellites elongatus_ (Gold.). × 50.
  C. _Lycopodites Zeilleri_ Halle. (Nat. size.)
  D. _Selaginellites elongatus_ (Gold.). × 2.]


            _Lycopodites Zeilleri_ Halle[200]. Fig. 135, C.

Halle has founded this species on specimens, from the Coal-Measures
of Zwickau in Saxony, characterised by dimorphic lanceolate leaves in
four rows, the larger being 4–6 mm. long: the smaller leaves have a
ciliate edge. A comparison is made with the recent species _Selaginella
arabica_ Baker, _S. revoluta_ Bak., and _S. armata_ Bak. in which the
leaves are described as ciliate. In the absence of sporangia and spores
the species is placed in the genus _Lycopodites_.

  _Lycopodites lanceolatus_ (Brodie). Fig. 136.

  1845 _Naiadita lanceolata_, Brodie[201].
       _Naiadea acuminata_, Buckman[202].
  1850 _Naiadea lanceolata_, Buckman[203].
       _Naiadea petiolata_, Buckman[204].
  1900 _Naiadites acuminatus_, Wickes[205].
  1901 _Naiadita lanceolata_, Sollas[206] (figures showing habit of the
        plant).
  1904 _Lycopodites lanceolatus_, Seward[207] (figure showing habit of the
        plant).

[Illustration: FIG. 136. _Lycopodites lanceolatus_ (Brodie). (After
  Miss Sollas. × 40.)

  _a_, Sporangium wall; _b_, leaf.
  _c_, remains of tubular elements in stem.]

Specimens referred to this species were originally recorded by Brodie
from Rhaetic rocks in the Severn valley, the name _Naiadita_ being
chosen as the result of Lindley’s comparison of the small and delicate
leaves with those of recent species of the Monocotyledonous family
Naiadaceae. The species may be described as follows:

Plant slender and moss-like in habit. The axis, which is delicate and
thread-like, bears numerous linear acuminate or narrow ovate leaves
reaching a length of approximately 5 mm. Under a low magnifying power
the thin lamina of the leaves is seen to have a superficial layer of
polygonal or rectangular cells arranged in parallel series (fig. 136
_b_). There is no trace of midrib or stomata. The sporangia are more or
less spherical and short-stalked, situated at the base of the foliage
leaves and containing numerous tetrads of spores. The spores have a
diameter of 0·08 mm.

Buckman founded additional species on differences in the shape of the
leaves but, as Miss Sollas has pointed out, such differences as he
noticed may be detected on the same axis. It was stated in an earlier
chapter[208] that Starkie Gardner, on insufficient evidence, proposed
to place Brodie’s plant among the Mosses. The discovery by Mr Wickes
of new material at Pylle hill near Bristol afforded an opportunity
for a re-examination of the species: this was successfully undertaken
by Miss Sollas who was able to dissolve out spores from the matrix by
dilute hydrochloric acid, and to recognise the remains of internal
structure in the slender axes by exposing successive surfaces with
the aid of a hone. It was found that sporangia occurred at the base
of some of the leaves containing numerous tetrads of spores, the
individual spores having a diameter of 0·08 mm., apparently twice
as large as those of any recent species of _Lycopodium_. Fig. 136
shows a sporangium, _a_, at the base of a leaf, _b_. Indications of
tubular elements were recognised in the stem and it is noteworthy
that although the outlines of epidermal cells on the leaves are well
preserved no stomata were found. The leaves of the recent American
species _Lycopodium alopecuroides_ Linn. var. _aquaticum_ Spring[209],
which lives under water, possess stomata. It is probable that in
_Lycopodites lanceolatus_ the leaves had a very thin lamina and
may have been similar in structure to those of recent Mosses; the
plant possibly lived in very humid situations or grew submerged.
Miss Sollas’s investigations afford a satisfactory demonstration of
the lycopodiaceous nature of this small Rhaetic species: as I have
elsewhere suggested[210], the generic name _Lycopodites_ should be
substituted for that of _Naiadita_. Examples of this species may be
seen in the British Museum.

The Rhaetic species from Scania, _Lycopodites scanicus_ Nath.[211] (_in
litt._), recently re-described by Halle and originally referred by
Nathorst to _Gleichenia_ affords another example of the occurrence of a
small herbaceous lycopod of Rhaetic age.

[Illustration: FIG. 137. _Lycopodites falcatus_ L. and H. From the
  Inferior Oolite of Yorkshire. (Nat. size. M.S.)]

  _Lycopodites falcatus_ Lind. and Hutt. Fig. 137.

  1831 _Lycopodites falcatus_, Lindley and Hutton[212].
  1838 _Muscites falcatus_, Sternberg[213].
  1870 _Lycopodium falcatum_, Schimper[214].

In 1822 Young and Bird[215] figured a specimen from the Inferior
Oolite rocks of the Yorkshire coast bearing “small round crowded
leaves,” which was afterwards described by Lindley from additional
material obtained from Cloughton near Scarborough as _Lycopodites
falcatus_. The example represented in fig. 137 shows the dichotomously
branched shoots bearing two rows of broadly falcate leaves. A careful
examination of the type-specimen[216] revealed traces of what
appeared to be smaller leaves, but there is no satisfactory proof of
heterophylly. No sporangia or spores have been found. This British
species has been recorded from Lower Jurassic or Rhaetic rocks of
Bornholm[217] and a similar though probably not identical type,
_Lycopodites Victoriae_[218], has been recognised in Jurassic strata
of Australia (South Gippsland, Victoria). An Indian plant described
by Oldham and Morris[219] from the Jurassic flora of the Rajmahal
hills as _Araucarites_ (?) _gracilis_ and subsequently transferred by
Feistmantel to Schimper’s genus _Cheirolepis_[220] may be identical
with the Yorkshire species. The Jurassic fragments described by Heer
from Siberia as _Lycopodites tenerrimus_[221] may be lycopodiaceous,
but they are of no botanical interest.

Other examples of Mesozoic Lycopods have been recorded, but in the
absence of well-preserved shoots and sporangia they are noteworthy only
as pointing to a wide distribution of _Lycopodites_ in Jurassic and
Cretaceous floras[222].

From Tertiary strata species of supposed herbaceous lycopods have been
figured by several authors, one of the best of which is _Selaginella
Berthoudi_ Lesq.[223] from Tertiary beds in Colorado. This species
agrees very closely in the two forms of leaf with _Selaginella
grandis_, but as the specimens are sterile we have not sufficient
justification for the employment of the generic name _Selaginellites_.


                            Selaginellites.

This generic name has been instituted by Zeiller[224] for specimens
from the coal basis of Blanzy (France). It is applied to heterosporous
species with the habit of _Selaginella_: Zeiller preferred the
designation _Selaginellites_ to _Selaginella_ on the ground that
the type species differs from recent forms in having more than four
megaspores in each megasporangium. It is, however, convenient to extend
the term to all heterosporous fossil species irrespective of the
spore-output.


                   _Selaginellites Suissei_ Zeiller.

This species was described in Zeiller’s preliminary note[225] as
_Lycopodites Suissei_, but he afterwards transferred it to the genus
_Selaginellites_. In habit the plant bears a close resemblance
to _Lycopodites macrophyllus_ of Goldenberg; the shoots, 1–3 mm.
thick, are branched in a more or less dichotomous fashion and bear
tetrastichous leaves. The larger leaves reach a length of 4–6 mm.
and a breadth of 2–3 mm.; the smaller leaves are described as almost
invisible, closely applied to the axis, oval-lanceolate and 1–2 mm.
long with a breadth of 0·5–0·75 mm. Long and narrow strobili (15
cm. by 8–10 mm.) terminate the fertile branches; these bear crowded
sporophylls with a triangular lamina and finely denticulate margin.
Oval sporangia were found on the lower sporophylls containing 16–24
spherical megaspores 0·6–0·65 mm. in diameter. The outer membrane
of the spore is characterised by fine anastomosing ridges and thin
plates radiating from the apex and forming an equatorial collarette.
The microspores have a diameter of 40–60μ and the same type of outer
membrane as in the megaspores. The megaspores of the recent species
_Selaginella caulescens_, as figured by Bennie and Kidston[226],
resemble those of the Palaeozoic type in the presence of an equatorial
flange. It is interesting to find that, in spite of the occurrence of
16–24 megaspores in a single sporangium the size of the fossil spores
exceeds that of the recent species.


  _Selaginellites primaevus_ (Gold.). Fig. 135, A, fig. 138.

  1855 _Lycopodites primaevus_, Goldenberg[227].
  1870 _Lycopodium primaevum_, Schimper[228].
  1907 _Selaginellites primaevus_, Halle[229].

[Illustration: FIG. 138. _Selaginellites primaevus_ (Gold.). (After
  Goldenberg.)]

In habit this species, first recorded by Goldenberg from the
Coal-Measures of Saarbrücken, is similar to _S. Suissei_ Zeill.

The drawing reproduced in fig. 138 is a copy of that of the
type-specimen: another specimen, named by Goldenberg, is figured
by Halle in his recently published paper. The leaves appear to be
distichous: no smaller leaves have been detected, though Halle is
inclined to regard the plant as heterophyllous. The sporophylls, borne
in slender terminal strobili, are smaller than the foliage leaves and
spirally disposed (fig. 138; smaller specimen). Halle succeeded in
demonstrating that some of the sporangia contained a single tetrad of
spores, each spore having a diameter of 0·4–0·5 mm. No microspores
were found, but it is clear that the species was heterosporous and
that it agrees with recent species in having only four spores in the
megasporangium.


  _Selaginellites elongatus_ (Gold.). Fig. 135, B, D.

  1855 _Lycopodites elongatus_, Goldenberg[230].
  1870 _Lycopodium elongatum_, Schimper[231].

The shoots of this species resemble the recent _Lycopodium
complanatum_; they differ from those of _Selaginellites primaevus_ in
their long and narrow branches which bear two forms of leaf. The longer
leaves, arranged in opposite pairs, are slightly falcate; the smaller
leaves are appressed to the axis and have a triangular cordate lamina.
Another peculiarity of this species is the occurrence of sporangia in
the axil of the foliage leaves, a feature characteristic of the recent
_Lycopodium Selago_. In recent species of _Selaginella_ the sporophylls
are always in strobili. No microspores have been found nor the walls
of megasporangia, but tetrads of megaspores were isolated by Halle:
the spores have three radiating ridges (fig. 135, B) connected by
an equatorial ridge. Halle estimates the number of spores (0·45 mm.
in diameter) in a sporangium at 20 to 30. In size as in number the
spores exceed those of recent species and agree more nearly with the
megaspores of _S. Suissei_.

It would seem to be a general rule that the spores (megaspores) of the
fossil herbaceous species exceeded considerably in dimensions those
of recent forms and on the other hand were smaller than those of the
Palaeozoic arborescent species.

There can be little doubt that some of the Mesozoic and Tertiary
species included under _Lycopodites_ agree more closely with the
recent genus _Selaginella_ than with _Lycopodium_, but this does
not constitute an argument of any importance against the restricted
use of the designation _Selaginellites_ which we have adopted. From
a botanical point of view the various records of _Lycopodites_ and
_Selaginellites_ have but a minor importance; they are not sufficiently
numerous to throw any light on questions of distribution in former
periods, nor is the preservation of the material such as to enable us
to compare the fossil with recent types either as regards their anatomy
or, except in a few cases, their sporangia and spores. The Palaeozoic
species are interesting as revealing less reduction in the number of
spores produced in the megasporangia. Among existing Pteridophytes the
genus _Isoetes_ agrees more closely than _Selaginella_, as regards
the number of megaspores in each sporangium, with such fossils as
_Selaginellites Suissei_ and _S. elongatus_.

It would seem that in most Palaeozoic species heterospory had
not reached the same stage of development as in the recent genus
_Selaginella_ in which the megaspores do not exceed four in each
sporangium. In _Selaginellites primaevus_, however, the heterospory
appears to be precisely of the same type as in existing species.


                             Lycostrobus.

The generic name _Lycostrobus_ has recently been instituted by
Nathorst[232] for certain specimens of a lycopodiaceous strobilus, from
the Rhaetic strata of Scania, which he formerly referred to the genus
_Androstrobus_[233].


               _Lycostrobus Scotti_ Nathorst. Fig. 139.

The fossil described under this name is of special interest as
affording an example of a Mesozoic lycopodiaceous cone comparable in
habit and in size with some of the largest examples of Palaeozoic
Lepidostrobi, the cones of _Lepidodendron_. The Swedish fossil from
Upper Rhaetic strata of Helsingborg (Scania) was originally designated
_Androstrobus Scotti_, the generic name being adopted in view of the
close resemblance of the form of the strobilus to the male flower of
a Cycad. A more complete examination has shown that the bodies, which
were thought to be pollen-sacs—though Nathorst recognised certain
differences between them and the pollen-sacs of lycopods—are the
megaspores of a lycopod. Microspores have also been identified. The
axis of the cone has a breadth of 2 cm. with a peduncle which may be
naked or provided with a few small scales; the sporophyll region of
the axis reached a length of at least 12 cm. The spirally disposed
sporophylls terminate in a rhombic distal end which may represent
the original termination or they may have been prolonged upwards as
free laminae. Each sporophyll bears on its upper face a single large
sporangium containing either megaspores or microspores: the megaspores,
0·55–0·60 mm. in diameter, are finely granulate and bear small warty
thorns or more slender pointed appendages. The microspores, after
treatment with eau de Javelle, were found to measure 36–44μ while
others which had been treated with ammonia reached 54μ in diameter.
Nathorst describes the microspores as occurring in spherical groups
or balls, which it is suggested may be compared with the groups of
spores separated by strands of sterile tissue (trabeculae) in the
large sporangia of _Isoetes_ (cf. fig. 133, H). If this comparison is
sound it would point to a more complete septation of the sporangium in
_Lycostrobus_ than in any recent species of _Isoetes_. The size of the
strobilus would seem to indicate the persistence into the Rhaetic era
of an arborescent lycopodiaceous type; but the appearance and manner
of preservation of the axis is interpreted by Nathorst as evidence of
a herbaceous rather than a woody structure. He is disposed to regard
_Isoetes_ as the most nearly allied existing genus.

[Illustration: FIG. 139. _Lycostrobus Scotti_, Nath. (After Nathorst;
  ⅘ nat. size.)]

The comparison made by Nathorst with _Isoetes_ is based on a
resemblance between the spores of the two genera and on the evidence,
which is not decisive, of the existence of sterile strands of tissue
in the sporangia of _Lycostrobus_. This similarity is however hardly
of sufficient importance to justify the inclusion of the Rhaetic
strobilus in the Isoetaceae. In size and in the arrangement and form
of the sporophylls the cone presents a much closer resemblance to
_Lepidodendron_ than to _Isoetes_. It is probably advisable to regard
this Rhaetic type simply as a lycopodiaceous genus which we are unable,
without additional information, to assign to a particular position.

The opinion expressed by Professor Fliche[234] that the plant described
by Schimper and Mougeot as _Caulopteris tessellata_, a supposed
tree-fern stem, from Triassic rocks of Lorraine, is more probably a
large lycopodiaceous stem, either a _Lepidodendron_ or a new genus, is
worthy of note in reference to Nathorst’s account of _Lycostrobus_.

In habit the fossil strobilus may be compared with the Triassic genus
_Pleuromeia_, but the position of the sporangia on the sporophylls
constitutes a well-marked difference. The most important result of
Nathorst’s skillful treatment of this interesting fossil by chemical
microscopic methods is the demonstration of the existence of a large
heterosporous type of lycopodiaceous cone in a Rhaetic flora.


                           Poecilitostachys.

Under this generic name M. Fliche[235] has briefly described a fertile
lycopodiaceous shoot from the Triassic rocks of Epinal in France:
the type species _Poecilitostachys Hangi_ consists of a cylindrical
axis, 10 cm. × 5 mm., deprived of leaves and terminating in a rounded
receptacle bearing a capitulum of bracts or fertile leaves. Detached
megasporangia containing small globular bodies found in association
with the capitulum are compared with the megasporangia of _Isoetes_.




                              CHAPTER XV.

                       Arborescent Lycopodiales.


Among the best known plants in the Palaeozoic floras are the genera
_Lepidodendron_ and _Sigillaria_, types which are often spoken of as
Giant Club-Mosses or as ancestors of existing species of _Lycopodium_
and _Selaginella_. Of these genera, but more particularly of
_Lepidodendron_, we possess abundant records in a condition which
have made it possible to obtain fairly complete information not only
in regard to habit and external features but as to the anatomical
characters of both vegetative and reproductive shoots. The structure
of _Lepidodendron_ differs too widely from that of recent Club-Mosses
(species of _Lycopodium_) to justify the statement that this
prominent member of the Palaeozoic vegetation may be regarded as a
direct ancestor of any living plant. There is at least no doubt that
_Lepidodendron_ and _Sigillaria_ must be included in the Pteridophyta.
The description by Dr Scott[236] of the genus _Lepidocarpon_, founded
on petrified specimens of strobili, demonstrated the existence of a
type of lycopodiaceous plant in the Carboniferous period distinguished
from all living representatives of the group by the possession
of integumented megaspores, which may fairly be styled seeds.
_Lepidocarpon_ and another seed-bearing plant _Miadesmia_ are described
under a separate heading as lycopodiaceous types characterised by an
important morphological feature, which among recent plants constitutes
a differentiating character between the Pteridophytes and the
Phanerogams.


                            Lepidodendron.

                             i. _General._

The genus _Lepidodendron_ included species comparable in size with
existing forest trees. A tapered trunk rose vertically to a height of
100 feet or upwards from a dichotomously branched subterranean axis
of which the spreading branches, clothed with numerous rootlets, grew
in a horizontal direction probably in a swampy soil or possibly under
water. A description by Mr Rodway[237] of Lycopods on the border of a
savannah in Guiana forming a miniature forest of Pine-like Lycopodiums
might, with the omission of the qualifying adjective, be applied with
equal force to a grove of Lepidodendra. The equal dichotomy of many of
the branches gave to the tree a habit in striking contrast to that of
our modern forest trees, but, on the other hand, in close agreement
with that of such recent species of _Lycopodium_ as _L. cernuum_ (fig.
123), _L. obscurum_ (fig. 124) and other types. Linear or oval cones
terminated some of the more slender branches (fig. 188) agreeing in
size and form with the cones of the Spruce Fir and other conifers or
with the male flowers of species of _Araucaria_, _e.g. A. imbricata_.
Needle-like leaves, varying considerably in length in different
species, covered the surface of young shoots in crowded spirals and
their decurrent bases or leaf-cushions formed an encasing cylinder
continuous with the outer cortex. The fact that leaves are usually
found attached only to branches of comparatively small diameter would
seem to show that _Lepidodendron_, though an evergreen, did not retain
its foliage even for so long a period as do some recent conifers.

By the activity of a zone of growing tissue encircling the cylinder of
wood the main trunk and branches grew in thickness year by year: the
general uniformity in size of the secondary conducting elements affords
no indication of changing seasons. As the branches grew stouter and
shed their leaves the surface of the bark resembled in some degree that
of a Spruce Fir and other species of _Picea_, in which the leaf-scars
form the upper limit of prominent peg-like projections, which, at
first contiguous and regular in contour, afterwards become less regular
and separated by grooves (fig. 140) and at a later stage lose their
outline as the bark is stretched to the tearing point (fig. 140, C).
The leafless branches of _Lepidodendron_ were covered with spirally
disposed oval cushions less peg-like and larger than the decurrent
leaf-bases of _Picea_, which show in the upper third of their length
a clean-cut triangular area and swell out below into two prominent
cheeks separated by a median groove and tapering with decreasing
thickness to a pointed base, which in some forms (_e.g. Lepidodendron
Veltheimianum_, fig. 185, C, D), is prolonged as a curved ridge to the
summit of a lower leaf-cushion.

[Illustration: FIG. 140. _Picea excelsa._ Shoots of different ages
  showing changes in the appearance of the leaf-cushions: a leaf
  attached to a cushion in fig. A. (Slightly enlarged.)]

A portion of the cushion below the triangular leaf-scar often shows
transverse gaping cracks or depressions (fig. 185, C) such as occur
on a smaller scale on the older cushions of a Fir twig (fig. 140).
Secondary thickening, as in recent trees, is not confined to the
vascular cylinder but at an early stage, frequently before there are
any signs of secondary wood, the outer region of the broad cortex
becomes the seat of active cell-formation which results in the addition
of a considerable thickness to the bark. At a later stage of increase
in girth, the leaf-cushions are stretched apart and the original
surface-features become obliterated by vertical cracks and by the
exfoliation of the superficial tissues[238].

Some species of _Lepidodendron_ produced branches characterised by
spiral or vertical series of scars; these in older shoots were replaced
by depressions having a diameter of several inches and comparable in
appearance, as also perhaps in manner of formation, with the scars
left on the stem of a Kauri Pine (_Agathis australis_)[239] on the
abscission of lateral branches by a natural process. These shoots,
known as _Ulodendron_, are described in a subsequent section. (Page
128.)

A fully-grown _Lepidodendron_ must have been an impressive tree,
probably of sombre colour, relieved by the encircling felt of green
needles on the young pendulous twigs. The leaves of some species were
similar to those of a fir while in others they resembled the filiform
needles of the Himalayan Pine (_Pinus longifolia_). The occasional
presence of delicate hyphae in the tissues of _Lepidodendron_
demonstrates susceptibility to fungal pests.

Architecturally, if one may use the term, _Lepidodendron_ owed its
power of resistance to the bending force of the wind to its stout
outer bark formed of thick-walled elements produced by the activity of
a cylinder of cortical meristem (figs. 148, 172, etc.). The vascular
axis, of insignificant diameter in proportion to the size of the stem
(figs. 152, 153, 172, 181, A), must have played a subordinate part,
from a mechanical point of view, as compared with the solid mass of
wood of a Pine or an Oak.

                   •       •       •       •       •

Within the compass of a text-book it is impossible, even if it were
desirable, to include an account of the majority of the species of the
widely distributed Palaeozoic genus _Lepidodendron_. In spite of the
great number of known species of this common member of Carboniferous
floras, our knowledge of the type as a whole is deficient in many
points, and such information as we possess needs systematising and
extending by comparative treatment based on a re-examination of
available data.

In order to appreciate the meaning of certain external features
characteristic of Lepidodendron stems it is essential to have some
knowledge of the internal structure.

A dual system of terminology has been unavoidably adopted for
species of _Lepidodendron_: the majority of specific names have been
assigned to fossils known only in the form of casts or impressions,
while petrified fragments, which unfortunately seldom show the
surface-features, have received another set of names. A glance at the
older palaeobotanical literature reveals the existence of several
generic designations, which fuller information has shown to have been
applied to lepidodendroid shoots deprived of some of their superficial
tissues before fossilisation and differing considerably in appearance
from the more complete branches of the same species[240]. It has in
some instances been possible to correlate the two sets of specimens,
casts or impressions, showing external features, and petrified
fragments. We may reasonably expect that future discoveries will enable
us to piece together as definite specific types specimens at present
labelled with different names.

A well-preserved leaf-cushion of a _Lepidodendron_—the most obvious
distinguishing feature of the genus—is rhomboidal or fusiform and
vertically elongated (fig. 146, C, E; fig. 185, C, D): in exceptional
cases it may reach a length of 8 cm. and a breadth of 2 cm. The
cushion as a whole represents a prominent portion of the stem or
branch comparable with the elevation on the twig of a Spruce Fir and
the leaf-base of a _Lycopodium_ (cf. fig. 121, A, lower portion) which
appears in a transverse section of a branch as a rounded prominence
(cf. _Lycopodium_, fig. 125, A and H). Disregarding differences in
detail, a typical Lepidodendron leaf-cushion is characterised by a
clearly defined smooth area often situated in the middle region (fig.
146, C, _s_). This is the leaf-scar or place of attachment of the base
of the leaf which was cut off by an absciss-layer while the branch was
comparatively young, as in recent forest trees and in some species of
Ferns. On the leaf-scar are three smaller scars or cicatricules, the
central one is circular or more or less triangular in outline, the two
lateral scars being usually oval or circular. The central pit marks
the position of the single vascular bundle which constituted the
conducting tissue connecting the leaf with the main vascular system of
the stem. The two lateral scars (figs. 145, A, _p_; 146, C, _s_; 147,
_p_) represent the exposed ends of two strands of tissue, the forked
branches of a strand which pass from the middle cortex of the stem into
the leaf; this is known as the parichnos, a name proposed by Professor
Bertrand in 1891[241].

The specimen shown in fig. 141 shows the linear leaves attached to
their respective cushions.

[Illustration: FIG. 141. _Lepidodendron Sternbergii._ From a specimen
  in the British Museum (No. v. 1235) from the Coal-Measures of
  Shropshire. (Nat. size.)]

The lamina has a well-defined median keel on the lower surface and
on either side a groove in which sections of petrified leaves have
demonstrated the occurrence of stomata (cf. fig. 142).


                    ii. _Leaves and Leaf-cushions._

All Lepidodendron leaves, so far as we know, possessed a single
median vein only. In some species, as for example in _Lepidodendron
longifolium_ Brongn., they have the form of long and slender
acicular needles very similar to those of _Pinus longifolium_; in
_L. Sternbergii_ (fig. 141) they are much broader and shorter. In
external form as in internal structure it is often impossible to
distinguish between the leaves of _Lepidodendron_ and _Sigillaria_.
The distinguishing features enumerated by the late M. Renault cannot
be employed, with any great degree of confidence, as diagnostic
characters. In transverse section the lamina of a Lepidodendron
leaf presents the same appearance as that of the Sigillarian leaves
represented in fig. 142. Near the base the free part of the leaf is
usually sub-rhomboidal in section with short lateral wings, a ventral
keel and two stomatal grooves (fig. 142, A, B, _g_). The form and
arrangement of stomata are shown in fig. 143, A, which was drawn from
a piece of a leaf shown in surface-view in a section lent to me by
Professor Weiss. It should, however, be pointed out that the leaf
cannot be certainly identified with _Lepidodendron_ rather than with
_Sigillaria_, but as the leaves of these two genera are constructed on
the same plan the identification is of secondary importance.

[Illustration: FIG. 142. Leaves of _Sigillaria_ in transverse
  section. A, A′. Section in the Manchester University Museum (Q.
  631). B, C. Sections in Dr Kidston’s Collection.]

The single xylem bundle consists of primary tracheae only, at least in
such laminae as have been identified as Lepidodendroid. Surrounding
the xylem strand occur delicate parenchymatous cells in some cases
accompanied by darker and thicker-walled elements. As in _Sigillaria_,
the leaves of which are more fully described on page 210, a fairly
broad sheath of wider and shorter scalariform or spiral transfusion
tracheids surrounds the conducting strand (figs. 142, _t_; 143, B, C,
_t_). As Renault shows in the case of _Lepidodendron esnostense_[242],
the small leaves of which are 1·5–2 mm. broad at the base and several
centimetres long, the stomatal grooves and keel die out towards the
apex when the lamina assumes a more nearly circular form (fig. 143, C).

[Illustration: FIG. 143.

  A. Stomata in surface-view (_Lepidodendron_?). _a_, parenchyma;
     _t_, transfusion tracheae; _x_, xylem. (Manchester University
     Collection R. 723).
  B, C. _Lepidodendron esnostense_ Ren. (After Renault.)]

The area of the cushion excluding the leaf-scar is spoken of by some
writers as the field. Below the leaf-scar the kite-shaped cushion
tapers to a gradually narrowing basal position: in _Lepidodendron
Veltheimianum_, a species characteristic of Lower Carboniferous
strata, it is seen to be continuous, as a ridge with sloping sides,
with a lower cushion (fig. 185).

Below a leaf-scar the cushion frequently shows a pair of oval areas on
which a fine pitting may be detected in well-preserved impressions,
these oval scars, as seen in fig. 185, D, are practically continuous
at the upper end with the parichnos scars on the leaf-scar area;
this is explained by the fact that these infra-foliar scars also owe
their existence to patches of lacunar, aerenchymatous tissue in close
connexion with the parichnos[243].

Shortly before entering the base of the leaf-lamina the parichnos
divides into two arms which diverge in the outer cortical region right
and left of the vascular bundle, and passing obliquely upwards they
come close to the surface of the leaf-cushion just below the leaf-scar.
The diagram—fig. 144, B—shows a leaf-trace, _lt_, in the leaf-cushion,
as seen in a diagrammatic drawing of a vertical radial section of a
stem, the dotted lines, _p_, _p′_, show the two parichnos arms which
are represented as impinging on the surface of the leaf-cushion at
_p′_, and then bending upwards to pass into the leaf-base right and
left of the vascular bundle or leaf-trace. For convenience the arms of
the parichnos are represented in one plane though actually in different
vertical planes.

Fig. 144, A, shows the difference between a view of the original
surface of a _Lepidodendron_, as at _a_, where a leaf-cushion with a
leaf-scar is seen, and a view of an impression representing the outer
cortex, _b_, a short distance below the surface. The surface _b_,
in fig. 144, A, corresponds to the face _d_-_e_ in the diagrammatic
longitudinal section fig. 144, B: the outline of each cushion is
clearly visible and in the centre is seen the leaf-trace, _lt_, with
its parichnos.

The surface-features, _a_ (fig. 144, A), have been impressed on the
rock, _c_, (fig. 144, B) in which the specimen was entombed and by the
removal of the cast of the stem, that is the thickness _b_ to _e_ in
fig. 144, B, the form of the leaf-cushion is revealed. The presence of
the two infra-foliar parichnos scars at _p′_ (fig. 144, A) is explained
by the diagram, fig. 144, B, _p′_.

The relation of the parichnos to the oval scars below a Lepidodendron
leaf-cushion has been worked out in detail by Weiss who shows that, at
least in some species, the two arms do not bend downwards as shown in
the diagram, fig. 144, B, but pursue a straight gradually ascending
course as seen in fig. 145, A. Just below the leaf-scar region of
the cushion each arm comes into association with a group of lacunar,
aerenchymatous tissue, such as occurs in the roots of certain Mangrove
plants, and it is this aerenchyma which is exposed on the two oval
depressions below the leaf-scar. The structure of this aerenchyma
is shown in fig. 145, B; it consists in this species (_L. Hickii_
Wats.) of stellate cells which would constitute an efficient aerating
system. Probably, as Weiss suggests, these patches of aerenchyma were
originally covered by an epidermis provided with stomata, and it is
owing to the destruction of this superficial layer that the two oval
scars often form a prominent feature on Lepidodendron leaf-bases[244].
The diagram reproduced in fig. 144, B, may be taken as practically
correct, as the patches of aerenchyma described by Weiss do not differ
essentially from the parichnos tissue.

[Illustration: FIG. 144. _Lepidodendron Veltheimianum_ Sternb.

  A. Leaf-cushion and leaf-scar seen in surface-view at _a_; on the
     rest of the specimen a slightly lower surface is exposed. (After
     Stur.)
  B. Diagrammatic longitudinal section to explain the differences
     between its two surfaces _a_ and _b_ shown in fig. A.

     The shaded portion _c_ represents the rock matrix, the surfaces
     _ab_, _ed_, mark the outer and inner edge of the outer portion of
     the bark of the Lepidodendron stem. _lt_, leaf-trace; _p_, _p′_,
     parichnos.]

[Illustration: FIG. 145.

  A. Diagrammatic surface-view and longitudinal section of a
     Lepidodendron leaf-cushion.
  B. Aerenchyma below the leaf-scar. (After F. E. Weiss.)]

The parichnos scars are shown on the leaf-scar and cushion in fig. 146,
C. In the lower leaf-cushion shown in fig. 146, E, the infra-foliar
parichnos scars, _p_, are clearly seen, but the preservation of
the leaf-scar is not sufficiently good to show them on that part
of the fossil. In the upper cushion (fig. 146, E) the position of
the parichnos arms is shown on the leaf-scar, but the infra-foliar
parichnos scars are hidden by two small spiral shells. The genus
_Spirorbis_, to which these shells are referred, appears to have
persisted from the Silurian epoch to the present day. The comparatively
frequent occurrence of _Spirorbis_ shells on the leaves and other
parts of Palaeozoic plants, has recently been dealt with in a paper
by Barrois[245] who discusses in detail the habitats of these small
animals from the point of view of the conditions under which the plants
were preserved. In a note by Malaquin appended to Barrois’ paper the
belief is expressed that _Spirorbis_ lived on pieces of Palaeozoic
plants which lay under water.

The fact that with one exception all the Spirorbis shells on the
specimen of _Lepidodendron_, of which two leaf-cushions are shown in
fig. 146, E, occur on the large parichnos scars on the cheeks of the
cushions, suggests the possibility that the escape of gases from the
parichnos tissue may have rendered the position attractive to the
_Spirorbis_. It can hardly be accidental that the shells occur on the
parichnos strands. This fact recalls the view held by Binney[246] and
accepted with favour by Darwin[247] that _Lepidodendron_ and other
coal-forest trees may have lived with the lower parts of the stems in
sea water.

Above the leaf-scar is a fairly deep triangular or crescentic pit
(fig. 146, C, _l_) known as the ligular pit from the occurrence on
younger shoots of a delicate organ like the ligule of _Isoetes_ (fig.
132) embedded in a depression in the upper part of the leaf-cushion.
The ligule was first figured in _Lepidodendron_ by Solms-Laubach[248]
and described in English material by Williamson under the name of the
adenoid organ[249].

In some Lepidodendron stems a second triangular depression may occur
above the ligular pit, the meaning of which is not clear: this has been
called the triangulum by Potonié[250]. Stur[251] suggested that it may
represent the position occupied by a sporangium in Lepidodendron cones.

It is important to remember that as a branch increases in girth the
leaf-cushions are capable of only a certain amount of growth: when
the limit is reached they are stretched farther apart and thus the
narrow groove which separates them is converted in older stems into
a comparatively broad and flat channel, thus altering the surface
characters.

[Illustration: FIG. 146. Lepidophloios and Lepidodendron leaf-cushions.

  A, B, D, F, G, H, I. _Lepidophloios_. (Fig. A should be reversed.)
  C, E. _Lepidodendron aculeatum_.
  A, B. From a specimen in the Sedgwick Museum, Cambridge
     (leaf-cushion 3 cm. broad).
  C. From a specimen in the Sedgwick Museum, Cambridge (leaf-cushion
     4 cm. long).
  D. From a section in the Cambridge Botany School Collection.
  E. From a specimen in the Bunbury Collection, Cambridge Botany
     School, showing _Spirorbis_ shells (leaf-cushion 2 cm. long).
  F. From a section in the Williamson Collection, British Museum No.
     1, 973.
  G, H, I. From sections in the Cambridge Botany School Collection.]

Another feature worthy of notice in reference to the leaf-cushions
of _Lepidodendron_ is the occurrence in rare instances of alternate
zones of larger and smaller cushions. This variation in the size of
the leaf-cushions is by no means uncommon in the closely allied genus
_Sigillaria_; in _Lepidodendron_ it has been described by Potonié[252]
in _L. volkmannianum_ and more recently by Mr Leslie and myself[253] in
a South African species _L. vereenigense_.

Owing to the natural exfoliation of the superficial layers of the
outer bark at a certain stage in the growth of the plant, or in
some instances no doubt as the result of _post-mortem_ decay, which
destroys the delicate cells of the meristematic zone in the outer
cortex, isolated leaf-cushions and strips of the external surface are
occasionally met with as carbonised impressions.

The appearance presented by a Lepidodendron stem which has been
deprived of its superficial tissues may be dealt with more intelligibly
after we have become familiar with the anatomical characters.


                         iii. _Lepidophloios_.

Before proceeding further with the genus _Lepidodendron_ a
short account may be intercalated of the external features of a
lepidodendroid type of stem which it is customary to describe under a
distinct generic title _Lepidophloios_. This name is convenient for
diagnostic purposes though it seems clear that apart from the form of
the leaf-cushion (fig. 146, A) we are at present unable to recognise
any well-defined differences between the two forms _Lepidodendron_ and
_Lepidophloios_. For general purposes the name _Lepidodendron_ will be
used as including plants possessing leaf-cushions of the type already
described as well as those with the Lepidophloios form of cushion.

The generic name _Lepidophloios_ was first used by Sternberg[254]
for a Carboniferous species which he had previously described as
_Lepidodendron laricinum_. In 1845 Corda[255] instituted the name
_Lomatophloios_ for specimens possessing the same external characters
as those for which Sternberg had chosen the name _Lepidophloios_.
The leaf-cushions of _Lepidophloios_ differ from those of the true
_Lepidodendron_ in their relatively greater lateral extension (cf.
fig. 146, A and C), in their imbricate arrangement and in bearing
the leaf, or leaf-scar, at the summit. In some species referred to
_Lepidophloios_ the cushions are however vertically elongated and
in this respect similar to those of _Lepidodendron_: an example of
this type is afforded by _Lepidophloios Dessorti_ a French species
described by Zeiller[256]. In younger branches the cushions may be
directed upwards having the leaf-scar at the top; but in the majority
of specimens the cushions are deflexed as in figs. 146, D; 160, A. The
shoot of _Lycopodium dichotomum_ shown in fig. 121, B, with the leaves
in the reversed position bears a close resemblance to a branch of
_Lepidophloios_.

The photograph of _Lepidophloios scoticus_ Kidst.[257] reproduced in
fig. 160, A, illustrates the dichotomous branching of the stem and the
form of the cushions with the leaf-scars pointing downwards. In the
fertile branch of the same species shown in fig. 160, B, the leaf-scars
face upwards.

In most species the cushions are simply convex without a median keel,
but in some cases a median ridge divides the cushion into two cheeks as
in the genus _Lepidodendron_. The leaf-scar bears three small scars,
the larger median scar marking the position of the leaf-trace, while
the lateral scars are formed by the two arms of the parichnos: in some
examples of deflexed cushions, though not in all, a ligular pit occurs
on the cushion a short distance above the leaf-scar.

The drawing reproduced in fig. 146, A, showing the leaf-scar on the
upper edge of the cushion should have been reversed with the leaf-scars
pointing downwards. This figure represents part of the surface of a
specimen consisting of the outer cortex of a stem with leaf-cushions 3
cm. broad. The thickness of this specimen is 4 cm.: a section through
the line _ab_ is represented in fig. 146, D (reproduced in the correct
position, with the leaf-scars, _sc_, pointing downwards): internal
to the cushions is a band of secondary cortex (the shaded strip on
the outer edge of the section) which was formed on the outside of
the phellogen. The phellogen is a cylinder of actively dividing cells
in the outer part of the cortex of the stem, often spoken of as the
cork-cambium or cortical meristem, which produces a considerable amount
of secondary cortical tissue on its inner face and a much smaller
amount towards the stem surface. This delicate cylinder frequently
forms a natural line of separation between the outer shell of bark and
the rest of the stem. In the specimen before us, the thin-walled cells
of the phellogen were ruptured before petrification and the outer shell
of bark was thus separated as a hollow cylinder from the rest of the
stem: this cylinder was then flattened, the two inner surfaces coming
into contact. Fig. 146, D, represents a section of one half of the
thickness of the flattened shell.

This separation of the outer cortex, and its preservation apart
from the rest of the stem, is of frequent occurrence in fossil
lycopodiaceous stems. The flattened outer cortical shell of a
_Lepidophloios_, specifically identical with that shown in fig. 146, A
and D, was erroneously described by Dr C. E. Weiss in 1881 as a large
lepidodendroid cone[258].

Fig. 146, B, affords a view of the inner face of the specimen of which
the outer surface is seen in fig. 146, A: the surface shown in the
lower part of the drawing, on which the boundaries of the cushions are
represented by a reticulum, corresponds to the inner edge of the strip
of secondary cortical tissue represented by the vertically shaded band
in fig. 146, D.

The shaded surface in fig. 146, B, represents a slightly deeper level
in the stem which corresponds to the outer edge of the vertically
shaded band of fig. 146, D: the narrow tapered ridges (fig. 146, B)
represent the leaf-traces passing through the secondary cortex, and the
fine vertical shading indicates the elongated elements of which this
strip of secondary cortex is composed.

In the longitudinal section diagrammatically reproduced in fig. 146,
D, cut along the line _ab_ of fig. 146, A, the parenchymatous tissue
of the stout cushions has been partially destroyed, as at _a_; at
_s_ is seen the section of a Stigmarian rootlet which has found its
way into the interior of a cushion. Each leaf-trace is accompanied
by a parichnos strand as in the true _Lepidodendron_; at the base of
the leaf-cushion the parichnos branches into two arms which diverge
slightly right and left of the leaf-trace, finally entering the base of
the leaf lamina as two lateral strands (fig. 147, _p_). At one point
in fig. 146, D the section has shaved a leaf-trace represented by a
black patch resting on the parichnos just above the line _ef_, but it
passes through one of the parichnos arms _p′_ which debouches on to the
leaf-scar _sc_ at _p_. Had the section been cut along the line _cd_ of
fig. 146, A the leaf-trace would have been seen in a position similar
to that occupied by the parichnos _p′_ in fig. 146, D.

[Illustration: FIG. 147. _Lepidophloios_ leaf-cushion in tangential
  section. (From a section in the Williamson Collection, British
  Museum, No. 1973.)]

Fig. 147, A, affords a good example of a tangential section through
a _Lepidophloios_ leaf-cushion, 1 cm. broad, like that represented
in fig. 146, A, showing the vascular bundle _lt_, the two parichnos
strands, _p_, composed of large thin-walled cells (cf. _Isoetes_, fig.
133, H, I), and the ligular pit near the upper edge of the section
enclosing the shrunken remains of the ligule (fig. 147, B, _l_).

[Sidenote: LEPIDODENDRON]

Fig. 147, B, shows the form of the tangentially elongated leaf-cushions
of _Lepidophloios_ and their spiral disposition.

Fig. 146, F, represents a section similar to that shown in figs. 147,
A and B, but in this case the leaf-trace, _lt_, and the parichnos
strands, _p_, lie in a cavity formed by the destruction of some of the
leaf-cushion tissue. It is worthy of notice that the parichnos cells
have resisted decay more successfully than the adjacent tissue of the
cushion.

The diagrammatic sketches reproduced in fig. 146, H and I, were
made from a transverse section similar to one originally figured by
Williamson[259]: fig. 146, H, corresponding in position to the line
_gh_ in fig. 146, A, passes through the ligular pit, _l_, and cuts
across the parichnos in the act of branching; the leaf-trace passes
outwards beyond the =Y=-shaped parichnos strand. In the other section,
fig. 146, I, the parichnos is shown in a horizontal plane and the
leaf-trace, _lt_, appears in oblique transverse section. In both
sections and in fig. 146, G the shaded band at the base represents the
secondary cortical tissue external to the phellogen.

The transverse section represented in fig. 146, G, shows in the
left-hand cushion, _a_, the exit of the two parichnos arms and the
leaf-trace between them: it illustrates also the various forms assumed
by lepidodendroid leaf-cushions when cut across at different levels.


      iv. _The Anatomy_ of Lepidodendron vasculare _Binney_[260].
                        Figs. 148–155, 168, A.

In the earlier literature dealing with the anatomy of _Lepidodendron_
and _Sigillaria_ the presence or absence of secondary vascular tissue
was made the criterion of generic distinction and the distinguishing
feature between the classes Pteridophytes and Gymnosperms,
_Lepidodendron_ being relegated to the former class because it
was supposed to have no power of forming secondary wood, while
_Sigillaria_, characterised by a considerable development of such
tissue, was classed by Brongniart and afterwards by Renault as a
Gymnosperm. Binney[261] in 1865 recognised that the two types of stem
pass into one another, but it was Williamson[262] who provided complete
demonstration of the fallacy of the Brongniartian view.

These two undoubted Pteridophytes agree very closely in anatomical
structure and both are now recognised as arborescent genera of
Lycopodiaceous plants. In a paper published by Lomax and Weiss
in 1905[263] a specimen is described from the Coal-Measures of
Huddersfield, in which a decorticated stem with the anatomical
characters of Binney’s _Sigillaria vascularis_ gives off a branch
having the anatomical structure which it has been customary to
associate with the species _Lepidodendron selaginoides_, so-called by
Sternberg and founded by him on impressions showing well-preserved
external characters.

In 1862 Binney[264] described petrified specimens of vegetative shoots
from the Lower Coal-Measures of Lancashire under the names _Sigillaria
vascularis_ and _Lepidodendron vasculare_. These were afterwards
recognised as different states of the same species. A few years after
the publication of Binney’s paper Carruthers[265] identified Binney’s
species _Lepidodendron vasculare_ with Sternberg’s _L. selaginoides_.
The evidence on which this identification rests has not been stated,
but many writers have retained this specific designation for the
well-defined type of anatomical structure first described by Binney
as _L. vasculare_. The use of the specific name _selaginoides_ is,
however, open to objection. The species _Lepidodendron selaginoides_,
as pointed out by Kidston[266], is probably identical with the plant
which Brongniart had named _L. Sternbergii_ before the institution
of Sternberg’s species, and we are not in possession of convincing
evidence as to the connection of _L. Sternbergii_ (= _L. selaginoides_)
with specimens possessing the anatomy of Binney’s type. Binney’s
designation is therefore retained for the anatomical type described in
the following pages[267].

The most detailed account hitherto published of the anatomy of
_Lepidodendron vasculare_ is that by the late M. Hovelacque[268], based
on material from the Lower Coal-Measures of England.

[Illustration: FIG. 148. _Lepidodendron vasculare_ Binney.

  A. Transverse section. (Based on a section 2·5 cm. in diameter, in
     the Cambridge Botany School Collection.)
  B. Longitudinal section. (Drawn from a section in Dr Kidston’s
     Collection.)]

The small shoot, represented somewhat diagrammatically in fig. 148,
A, illustrates the anatomical features of a typical example of the
species: the shoot has a diameter of 2·5 cm. and its central cylinder
(_x_-_sc_) is 2·5 mm. in width.

Noticeable features are (i) the small size of the central cylinder
(or stele) in proportion to the diameter of the branch, (ii) the
production at a comparatively early stage of growth of a zone of
secondary wood, _x_², which gradually assumes the form of a complete
cylinder of unequal breadth, surrounding the primary xylem, _x_,
(iii) the formation of a secondary cortical tissue by a meristematic
cylinder (phellogen, _pl_) situated close to the leaf-cushion region
of the outer cortex. On the outer edge the stele consists of narrow
tracheae some of which show in longitudinal section the spiral form
of thickening characteristic of most protoxylem elements: towards
the centre of the stele the diameter of the tracheae gradually
increases and parenchymatous cells become associated with the
elongated scalariform elements. In the central region the stele is
composed of parenchymatous tissue arranged in vertical series of short
cells, interspersed with short tracheae distinguished by the greater
thickness of their walls and by their scalariform and reticulate
thickening bands. Some of these short tracheae are shown in vertical
section in fig. 149, B: the fine and broken lines connecting adjacent
thickening bands probably represent the remains of the original wall.
These delicate bands, which have been figured in various species of
lepidodendroid plants[269], are worthy of notice in connexion with the
recent work of Mr Gwynne-Vaughan[270] who has shown that in many recent
ferns the scalariform bands in the xylem elements are not connected
by a thin pit-closing membrane, but are separated from one another by
open spaces. In the Lepidodendron tracheae we seem to have a stage in
which the intervening membrane is in process of absorption. It is,
however, possible that the threads may be the result of contraction and
splitting of the membrane during drying or decay.

[Illustration: FIG. 149. _Lepidodendron vasculare_. _a_, immature
  tracheae; _m_, meristem; _mr_, medullary ray; _x_, xylem.

  A. Longitudinal section through the edge of the secondary wood.
  B. Short tracheae in the centre of the stele. (From a specimen from
     the Halifax Hard bed in Dr Kidston’s Collection.)]

The stele of _Lepidodendron vasculare_, before the addition of any
secondary xylem, may be described as a protostele, a term originally
proposed by Professor Jeffrey[271], in which the central part of the
conducting strand of xylem elements has been converted into rows of
parenchyma and short tracheids, the latter being better adapted to
storage than to conduction. It is probable that this type of stelar
anatomy, which distinguishes _L. vasculare_ from other species,
represents a comparatively primitive arrangement forming a transition
between the stele of _L. esnostense_, which consists of a solid rod
of tracheids, and the stele of _L. Harcourtii_ (fig. 179, A) and
other species in which the xylem forms a cylinder enclosing a large
parenchymatous pith.

Parenchymatous cells occur in contact with the outer edge of the
xylem-cylinder some of which are distinguished by an irregular
reticulate pitting. The tangential section represented in fig. 148, B,
illustrates the appearance of a shoot of _L. vasculare_ in which no
secondary xylem is present: the central strand of tissue consists of
the parenchyma abutting on the xylem with several leaf-traces (_lt_)
passing upwards in an almost vertical course from the outer edge of the
stele.

The secondary xylem (fig. 148, A, _x_²) consists of radially arranged
scalariform tracheae with associated rows of parenchymatous cells which
form medullary rays (fig. 149, _mr_). Leaf-traces pass through the
medullary rays in the secondary xylem cylinder in a direction at right
angles to the primary xylem stele from which they are given off, but at
the outer edge of the secondary xylem they bend suddenly upwards and
for a time follow a steep and almost vertical course.

In well-preserved longitudinal sections the outermost secondary xylem
tracheae are seen to be succeeded by a few narrow and vertically
elongated elements (fig. 149, A, _a_), which represent young
unlignified tracheae: these are followed by shorter parenchymatous
cells (_m_) forming part of a meristematic zone from which the
secondary xylem receives additions.

Returning to fig. 148, A; the zone of secondary wood, _x_², composed
of scalariform tracheids and medullary rays, is succeeded by a few
layers of parenchymatous cells and beyond this is a broader zone, _sc_,
to which the term secretory zone has been applied[272]; this is made
up of small parenchymatous cells varying in size and of larger spaces
which appear to have been formed by the disorganisation of thin-walled
elements. The whole zone presents a characteristic appearance due to
the association of small cells, large clear spaces, and a certain
amount of dark-coloured material suggestive of tissue disorganisation
and secreted products. The anatomical characters of the secretory zone
are shown in the photograph, fig. 168, A, _sc_. Several leaf-traces
are seen in transverse section in the secretory zone (black dots in
fig. 148, A, _sc_; fig. 154, C, _lt_): each trace consists of a strand
of narrow tracheae accompanied by a few encircling layers of small
parenchymatous cells. As a trace continues its steeply ascending course
through the secretory zone, it becomes associated with a strand of
that tissue and assumes the form of a collateral vascular bundle, the
outer part of which does not consist of typical phloem but of shorter
elements derived from the secretory zone. Beyond the secretory zone
we find a more homogeneous tissue composed of parenchymatous elements
slightly extended tangentially (figs. 148, A, _c_¹; fig. 168, A, _c_);
this is spoken of as the inner cortical region. In the great majority
of sections of _L. vasculare_ as of other species of the genus, the
broader middle cortex (fig. 148, _c_²) is occupied by mineral matter,
introduced subsequent to decay of the tissue; or it is represented by
patches of delicate tissue composed of loosely arranged parenchymatous
cells varying considerably in size and shape, some being small, oval
or polygonal elements while others have the form of sinuous hypha-like
tubes.

In this middle cortical region may be seen leaf-traces passing outwards
in an almost horizontal course (fig. 148, A, _lt_): after leaving the
inner cortex the leaf-traces bend somewhat abruptly outwards to follow
a more direct path through the middle and outer cortex. The ring of
tissue, _s_, seen in the middle cortex of fig. 148, A, belongs to a
Stigmarian rootlet.

The outer cortex (fig. 148, A and B, _c_³) consists of homogeneous
parenchyma which is stronger and more resistant to decay than the
looser middle cortex. The leaf-traces, as shown in fig. 148, B, pass
through this region in a rather steeply ascending direction: each is
seen to be enclosed by a space originally occupied by a strand of
middle cortical tissue which accompanies lepidodendroid leaf-traces on
their under side and has already been described as the parichnos, (pp.
97, 100–103; figs. 146, 147).

The surface of the stem shown in section in fig. 148, A, is composed of
broad leaf-cushions. A single leaf-trace with its parichnos passes into
each cushion, but in the neighbourhood of the base of a cushion the
parichnos bifurcates (cf. fig. 146, H, I) and the arms diverge slightly
to the right and left finally passing beyond the cushion into the
lamina of the leaf, their position being shown, as already explained,
by the two small lateral scars on the leaf-scar area.

The diagrammatic sketch of a radial longitudinal section through a
leaf-cushion represented in fig. 150 illustrates the relation of the
leaf-trace to the leaf-cushion. The trace consists of xylem, _x_, above
and a strand of the secretory zone, _st_, below; the parichnos tissue
was originally present on the under side of the leaf-trace at _a_. The
external surface, _bc_, marks the limit of the leaf-scar through the
middle of which passes the vascular strand _lt_.

The lower gap _a_ has been formed by the tearing of thin-walled cells
of the phellogen, the meristematic tissue from which a considerable
amount of secondary cortical tissue or phelloderm has been produced
at _pd_. On the outside of the cushion, _c_, the cells are somewhat
crushed and distinguished by their darker colour from the bulk of the
parenchymatous tissue _d_.

This section also illustrates another characteristic feature of
_Lepidodendron_, namely the presence of a ligule and a ligular pit:
the former is represented by a carbonised patch of tissue and the
latter extends from the surface of the cushion at _b_, just above the
leaf-scar, almost to the level of the leaf-trace, _lt_. A comparison of
this section with figs. 146 and 147 will make clear the relation of the
several parts of the cushion and leaf-scar.

The gaps _gg_, seen in fig. 148, A and B, mark the position of the
delicate meristematic zone or phellogen which arises close to the bases
of the leaf-cushions; the phellogen has already produced a few rows of
radially disposed elements, represented by short radial lines in the
drawing, which constitute secondary cortical tissue.

[Illustration: FIG. 150. _Lepidodendron vasculare_. Leaf-cushions in
  longitudinal section. (From a specimen in Dr Kidston’s Collection.)]

In older shoots the amount of the secondary cortical tissue developed
on the inner side of the phellogen is considerable (cf. figs. 152, 153).

The structure of the cortex of a shoot in which secondary growth, both
in the stele and in the outer cortex, has progressed further than in
the specimen shown in fig. 148 is represented in fig. 151.

[Illustration: FIG. 151. _Lepidodendron vasculare_. An older stem than
  that shown in fig. 148. (From a section in the Manchester Museum.
  No. 351.)]

The section (fig. 151, A) measures 7 × 3·8 cm. in diameter; the
primary xylem is surrounded by a fairly broad cylinder of secondary
wood (fig. 151, E, _x_ and _x²_). The almost smooth surface of the
primary wood (fig. 151, E, _x_) is succeeded by the secondary xylem,
_x²_, characterised at its inner edge by the tapered ends of the
radial rows of scalariform tracheids between which occur several
delicate parenchymatous cells (fig. 151, E, _a_). The occurrence
of such isodiametric elements, often exhibiting a delicate spiral
thickening band, is a characteristic feature of the boundary between
primary and secondary wood in lepidodendroid stems. The secondary wood
is penetrated by numerous medullary rays and in some of them are seen
strands of narrow spirally thickened tracheae—the leaf-traces—which
are in organic continuity with the exarch protoxylem of the primary
wood. The leaf-traces are oval and mesarch. The space, _c²_, (fig.
151, A) originally occupied by the delicate middle cortex, is succeeded
by a shell of outer cortex composed chiefly of secondary tissue
(phelloderm, _pd_) passing towards the inner boundary of this region
into the primary outer cortex _g_ (fig. 151, A and C). The radially
disposed elements which make up the bulk of the phelloderm are
associated with concentric rows of secretory strands, represented by
tangentially arranged dots in fig. 151, A: on the outer edge of the
phelloderm a few patches of primary cortex are still preserved, as at
_c_, fig. A. One of these is shown on a larger scale in fig. B; at _m_
the phelloderm is interrupted by a gap beyond which the cells have
thinner walls and show signs of recent division; this is probably the
position of the phellogen. The tissue _b_, fig. 151, B, consists of
secondary cortex succeeded beyond _d_ by the parenchymatous tissue of
the leaf-cushion, in which the remains of a ligule, _l_, are seen in
the ligular pit. This section corresponds in position to a line drawn
across fig. 150 at the level of _b_. In this specimen we have two kinds
of secondary cortical tissue: that formed external to the phellogen,
from _m_ to _d_ in fig. 151, B, is less in amount than that produced
internal to the phellogen. We cannot make any satisfactory statement
as to the nature of this secondary tissue, whether or not any of it
agreed in composition with the cork which is usually formed external to
the phellogen in recent plants. As the stem of a _Lepidodendron_ grew
in girth the leaf-cushions became separated by intervening depressions
composed of the secondary cortex formed external to the phellogen, but
at a later stage the cushions were thrown off, leaving the outer edge
of the phelloderm as the superficial tissue. This exposed tissue became
fissured as growth and consequent stretching continued, producing the
appearance seen on the surface of the still older stem represented in
fig. 153.

The inner edge of the phelloderm seen at _e_ in fig. 151, C, passes
suddenly into the inner primary region of the outer cortex (fig. 151, A
and C, _g_) which comprises two types of parenchymatous tissue, patches
of isodiametric cells, _g_, _g_, alternating with radially arranged
areas consisting of tangentially elongated elements (fig. C, _f_, _f_;
fig. D) which extend as wedges into the phelloderm.

The longitudinal section represented in fig. 152, B, shows an equal
bifurcation of a stem in which no secondary xylem is present; in the
lower part of the section the xylem and the outgoing leaf-traces are
seen in radial section and at the upper end of each arm the leaf-traces
alone, _lt_, are exposed, as in fig. 148, B. It is interesting to
notice the large amount of phelloderm which has been produced in the
fork of the branch, at _pd_, where greater strength is required.

[Illustration: FIG. 152.  _Lepidodendron vasculare._ Sections of
  dichotomously branched shoot.

  A. From a section (10·5 × 9 cm.) in the Cambridge Botany School
     Collection.
  B. From a section (8 cm. long) in the Cambridge Collection.]

The section represented diagrammatically in fig. 152, A, has lost the
outermost part of the cortex together with the leaf-cushions; it
consists largely of secondary cortex composed of radially disposed
phelloderm cells and tangentially placed secretory strands (represented
by the discontinuous black lines in the drawing): the dotted region
in the central part of the axis is composed of primary cortical
parenchyma, and the two spaces surrounding the steles contain portions
of the lacunar middle cortex. Each stele possesses a narrow crescentic
zone of secondary xylem; the amount is greater in the case of the
right-hand stele, of which a small piece is shown on a larger scale;
the striking contrast in size between the outer and more internal
secondary tracheae is no doubt the expression of some unfavourable
condition of growth. The position of the secretory zone beyond the
secondary xylem is shown at _sc_, fig. 152, A.

[Illustration: FIG. 153. _Lepidodendron vasculare._
  (From a specimen (16 × 7·5 cm.) in the Manchester Museum.)]

An example of a large and partially decorticated stem is afforded by
the specimen (16 × 7·5 cm.) shown in fig. 153. The irregularly ribbed
surface is formed of rather thick-walled phelloderm, in which occur
tangentially arranged rows of secretory strands. The tapered form of
the secondary cortex as it abuts internally on the primary cortex is
shown very clearly in the drawing (cf. fig. 151, C). The stele in this
much older stem consists mainly of secondary wood.

[Illustration: FIG. 154. _Lepidodendron vasculare._ Shoot (2·8 cm.
  diam.) with two steles.

  (From a specimen from Halifax in the Williamson Collection, British
  Museum, No. 340.)]

An interesting example of a small shoot, the largest diameter of which
is 2·8 cm., is shown in fig. 154, A: the section was cut a short
distance above the bifurcation of the stele into two approximately
equal branches. The outer part of the cortex consists of phelloderm,
_pd_, with the usual rows of secretory tracts, and primary outer
cortex _g_; the middle cortex is represented by patches of parenchyma
with a few leaf-traces. To one of the steles, _s′_ (fig. 154, A), a
crescent-shaped band of secondary xylem has been added; the other
stele, _S_, possesses no fully developed secondary elements.

Fig. 154, B and C, illustrates the anatomical features immediately
external to the primary xylem of the smaller stele, _s_. The
comparatively broad band of radially disposed parenchyma, _m_, is
connected with the outermost elements of the xylem by a few rather
dark and small crushed parenchymatous cells. The band _m_, which we
may speak of as the meristematic zone, clearly consists of cells in a
state of division; it is in this region that the secondary xylem is
produced. Beyond the leaf-trace, (fig. 154, C, _lt_), occurs a portion
of the secretory zone, some of the smaller cells of which show signs
of disorganisation; but most of this tissue has been destroyed (fig.
154, B, _sc_). The outer edge of the secretory zone is shown in fig.
154, D abutting on the cells of the inner cortex, _c′_. The leaf-trace
shown in the inner cortex in fig. 154, B illustrates the more oval or
tangentially extended form of the xylem in this region, in contrast to
the more circular outline which it exhibits on the inner side of the
secretory zone.

[Illustration: FIG. 155. _Lepidodendron vasculare_. Outer edge of
  secondary xylem: _m_, meristematic zone; _mr_, medullary ray.
  (Drawn from the section shown in fig. 168, A).]

The transverse section, part of which is reproduced in fig. 168, A,
illustrates a characteristic feature, namely the juxtaposition of the
outermost tracheae of the secondary xylem and much smaller cells of
the meristematic zone. This is seen in fig. 155, which shows a small
piece of fig. 168, A, on a larger scale. In plants with a normal
cambium the segments cut off from the initial layer fit on to the
elements of the xylem or phloem to which they are to form additions,
but in _Lepidodendron_ it seems to be a general rule to find each
of the most external lignified elements abutting on a group of two
or three much smaller cells. It is difficult to believe that the
meristem shown in fig. 155, _m_, could produce secondary xylem elements
equal in size to those already formed: in all probability had growth
continued there would have been a marked difference between the size
of the secondary tracheids, as in fig. 152, A, _x²_, where there was
no doubt some cause which interfered with normal cambial activity.
This disparity in size between the secondary xylem elements and the
adjacent parenchymatous tissue of the meristematic zone is by no means
exceptional and may be described as the general rule. It is at least
certain that in _Lepidodendron vasculare_, as in other species, the
secondary xylem was succeeded by a broad band of parenchymatous tissue,
from which new tracheae and medullary-ray elements were produced, and
not by a narrow cambium such as occurs in recent plants.


          v. Lepidodendron _stems as represented by casts and
           impressions of partially decorticated specimens._

The differentiation of the outer cortex of a _Lepidodendron_ into
comparatively thin-walled and more resistant tissue has been the cause
of unequal decay and the consequent formation of shrinkage cavities. In
addition to the unequal resisting power of contiguous tissues, another
important factor in determining the nature of casts and impressions is
the existence of the cylinder of delicate cells in the outer cortex of
stems and branches. As already pointed out, this meristematic cylinder
or phellogen constitutes a natural line of separation, as in the case
of the cambium layer between the wood and the external tissues in a
fresh Sycamore twig. The result of the separation of an outer shell of
bark from the rest of the stem and the results of unequal decay in the
more superficial tissues, have necessarily led to the preservation of
the same specific type under a variety of forms.

Our knowledge of the anatomy of Lepidodendron stems enables us to
recognise in fossils of very different appearance specimens in various
conditions of preservation of one and the same type. Such names as
_Knorria_, _Bergeria_ and _Aspidiaria_ are examples of generic titles
instituted before any adequate knowledge of Lepidodendron anatomy was
available.

Differences in age as well as different degrees of decortication have
contributed in no small measure to the institution of generic and
specific names which more recently acquired knowledge has shown to be
superfluous.


_a._ _Knorria._

The designation Knorria, after a certain G. W. Knorr of Nürnberg, was
proposed by Sternberg in 1826[273] for casts of Palaeozoic stems of a
type figured more than a century earlier by Volkmann[274]. Goeppert, in
his earlier works, published drawings of fossil stems which he referred
to Sternberg’s genus: one species he at first called _Didymophyllum
Schollini_. He afterwards[275] described some specimens which showed
that the features characteristic of _Knorria_ may occur on partially
decorticated stems with leaf-cushions of the true Lepidodendron type.
His specimens, preserved in the Breslau Museum, demonstrate the
accuracy of his drawings and conclusions. Goeppert, and after him
Balfour[276], drew attention to the different appearances presented
by branches of _Araucaria imbricata_ when preserved with the surface
intact and after partial decortication, as illustrating possible
sources of error in the determination of fossil stems.

Although it is now a well-established fact that fossils bearing the
name _Knorria_ are imperfect lepidodendroid stems, the use of the term
may be conveniently retained for descriptive purposes. The specimen
from the Commentry coal-field of France, shown in fig. 156, affords
some excuse for the institution of several generic names for different
states of preservation or decortication of one species. The cortical
level exposed at _e_ is characterised by spirally disposed peg-like
ridges with truncated apices: it is this form of cast which is usually
designated _Knorria_. The ridges vary in size and shape in different
types of stem; they may be narrow as shown at _e_, fig. 156, or short
and broad with rounded distal ends. In some cases they are forked at
the apex, as in the partially decorticated specimen of _Lepidodendron
Veltheimianum_ represented in fig. 185, A.

[Illustration: FIG. 156. A dichotomously branched Lepidodendroid stem
  (_Knorria mirabilis_ Ren. and Zeill.). (After Renault and Zeiller.)
  (¼ nat. size.) The original specimen is in the Natural History
  Museum, Paris.

  _a–g_, surface features exposed as the result of different degrees
  of decortication. (See vol. I. p. 102, fig. 23).]

The _Knorria_ state represents the impression or cast of the outer
cortical region too deep below the leaf-cushion region to retain
any indications of the cushion-form; the ridges are the casts of the
spaces produced in the cortex by the decay of the sheath of delicate
cells surrounding each leaf-trace and by the decay of the thin-walled
cells of the parichnos. The occasional forked apex of a ridge is the
expression of the fact that the cast was made at the region where the
parichnos divides into two arms (cf. p. 100). In certain specimens it
is possible to connect the Knorria casts with associated lepidodendroid
stems which may be determined specifically; but when we have no
evidence as to surface-features the fossils may be designated casts
of lepidodendroid stems in the Knorria condition. Such casts are
illustrated by numerous drawings in palaeobotanical literature[277].


_b._ _Bergeria._

This is another name first used by Sternberg in his classic work,
_Die Flora der Vorwelt_, for casts of lepidodendroid plants such as
Steinhauer[278] had previously figured as _Phytolithus cancellatus_.
Brongniart[279] recognised that the application of the generic title
_Lepidodendron_ should be extended to include specimens referred by
Sternberg to _Bergeria_, and a few years later Goldenberg[280] realised
that this name does not stand for well-defined generic characters.
The correctness of these views was, however, first satisfactorily
demonstrated by Carruthers[281] and by Feistmantel[282].

If a Lepidodendron stem loses its superficial layers of outer
cortex and in this condition is embedded in sand or mud, the cast
is distinguished from that of a perfect stem by the absence of
the leaf-scars and by other features. It may, however, still show
spirally disposed areas, corresponding approximately to the original
leaf-cushions, which are characterised by a small depression or pit
either at the apex or near the centre of each oval area: the pit marks
the position of the leaf-trace and its parichnos strand. In some
cases the exposed surface may be smooth without any indication of
leaf-cushions, while narrow spirally arranged grooves represent the
obliquely ascending vascular bundles passing through the cortex to the
leaves.

Fig. 185, B, shows the Bergeria state of _Lepidodendron Veltheimianum_,
which differs from the Knorria condition in the fact that decortication
had not extended below the level at which the form of the leaf-cushions
could be recognised. It is clear that no sharp line can be drawn in all
cases between the different degrees of decortication as expressed by
the terms _Knorria_ and _Bergeria_.

A list of synonyms of _Knorria_, _Bergeria_, and _Aspidiaria_ forms of
stem and a detailed treatment of their characteristic features may be
found in a recent work by Potonié[283].


_c._ _Aspidiaria._

In one of the earliest English books on fossil plants, the
_Antediluvian Phytology_ by Artis[284], a specimen from the
Carboniferous sandstone of Yorkshire is figured as _Aphyllum
cristatum_, and a similar fossil is described as _A. asperum_. These
are impressions of Lepidodendron stems in which the characteristic
leaf-cushions are replaced by smooth and slightly convex areas with
a narrow central ridge. To this type of specimen Presl gave the
name _Aspidiaria_[285], under the impression, shared by subsequent
writers, that the supposed external features were entitled to generic
recognition.

It is to Stur[286] that we owe the first satisfactory interpretation
of fossils included under the name _Aspidiaria_: he showed that on the
removal of the projecting convex areas from some of his specimens a
typical Lepidodendron leaf-cushion was exposed (fig. 144, A, _a_). The
Aspidiaria condition (fig. 144, A, _b_) represents the inner face of
the detached shell of outer bark of a Lepidodendron stem, while in the
Bergeria casts we have a view of the external face of a stem deprived
of its superficial tissues.

In a Lepidodendron stem embedded in sediment the more delicate portions
of the leaf-cushions would tend to shrink away from the internal and
more resistant tissues of the outer cortex, thus producing spaces
between each cushion; further decay would cause rupture of the
leaf-traces and the superficial tissues would thus be separated from
the rest of the stem. The tendency of Lepidodendron stems to split
along the line of phellogen in the outer cortex is seen in fig. 148,
A, _g_. The deposition of sediment on the exposed inner face of this
cortical shell would result in the production of a specimen of the
Aspidiaria type: the reticulum enclosing the spirally disposed convex
areas is formed by the impression of the firmer tissue between the
leaf-cushions.


     vi. _Lepidodendroid axes known as_ Ulodendron _and_ Halonia.

_a_. _Ulodendron._

This generic name was suggested by Lindley and Hutton[287] for two
specimens from the English Coal-measures characterised by leaf-cushions
like those of a _Lepidodendron_, but distinguished by the presence of
two vertical rows of large and more or less circular cup-shaped scars.
These authors, while recognising the possibility that the fossils
might be identical with _Lepidodendron_, regarded them as generically
distinct. The generic title _Ulodendron_, though no longer denoting
generic rank, is still applied to certain shoots of lycopodiaceous
plants which may belong to the genera _Lepidodendron_, _Bothrodendron_,
and according to some authors[288], also to _Sigillaria_.

The large specimen from the Belgian coal-measures, represented in fig.
211, affords a good example of the Ulodendron form of shoot of the
genus _Bothrodendron_, which is described on page 249. The specimen
shown in fig. 157 shows the _Ulodendron_ shoot of _Lepidodendron
Veltheimianum_.

Casts of large Ulodendron scars are occasionally met with as separate
fossils bearing a resemblance to an oval shell.

In Steinhauer’s paper on _Fossil Reliquiae_[289] a drawing is given of
a Ulodendron stem under the name _Phytolithus parmatus_ and a similar
stem specifically identical with that shown in fig. 157 was figured by
Rhode[290], one of the earliest writers on fossil plants, under the
comprehensive designation “Schuppenpflanze.”

[Illustration: FIG. 157. _Lepidodendron Veltheimianum._ Ulodendron
  condition. (From a photograph by Dr Kidston of a specimen from the
  Calciferous Sandstone series, Midlothian; ⅖ nat. size.) [Kidston
  (02) Pl. LVII.]

There has been no lack of ingenuity on the part of authors in offering
suggestions as to the meaning of these large cup-like depressions,
and there is still difference of opinion as to their significance.
Lindley and Hutton[291] described them as the scars of branches or
masses of inflorescence. Sir Joseph Hooker[292] speaks of a specimen
of _Ulodendron_, shown to him by Mr Dawes, on which a large organ,
supposed to be a cone, was inserted in one of the depressions, but
he was unable to arrive at any conclusion as to the real nature of
the fossil. While most authors have seen in the scars pressure-areas
formed by the pressure of sessile cones against the surface of a
growing branch, others, as for example Geinitz[293], have described
the depressions as branch-scars. Carruthers[294] regarded the scars
as those of adventitious roots and Williamson referred to them as the
scars of reproductive shoots. The depressions vary considerably in
size. The Belgian example shown in fig. 211 possesses scars 9 cm. in
diameter. A specimen of _Bothrodendron_ in the Manchester Museum from
the Lancashire Coal-Measures, to which Williamson[295] has referred,
bears two rows of scars 11–12 cm. in diameter on a stem 112 cm. in
girth and 233 cm. long. The scars occur in two alternate series, on
opposite faces of the axis, the distance between the successive scars
in the same row being 29 cm. The surface-features of this large stem
are not preserved.

Before considering the nature and origin of the scars it is important
to remember the considerable size to which they may attain; other
points of importance are the occurrence, either in the centre of each
depression or in an excentric position, of an umbilicus or slightly
projecting boss, in the centre of which is a pit formed by the decay of
an outgoing vascular strand. The sloping sides of the scars sometimes
bear elevations resembling leaf-cushions like those on the rest of
the stem surface. In the specimen shown in fig. 157 the lower margin
of each cup shows indistinctly the outlines of what appear to be
leaf-cushions, while the rest of the sloping face is characterised by
radial ridges, which may be due to bracts or leaves.

It is obvious that in these cups we have the scars of some lateral
organ, but the evidence afforded by specimens of which the depressions
contain the remains of such organs is by no means conclusive. A
Ulodendron has been figured by D’Arcy Thompson[296], in which the lower
part of a lateral organ is attached by a narrow base to one of the
scars, but the preservation is not sufficiently good to enable us to
decide whether the organ is a cone or a vegetative shoot. Kidston[297]
has described other examples showing portions of organs in connexion
with the scars, but an examination of the specimens in his collection
failed to convince me that his interpretation of them as strobili is
correct.

The phenomenon known as cladoptosis, as shown on a stem of the Conifer
_Agathis_[298] and certain Dicotyledonous trees such as _Castilloa_,
suggests a possible explanation of the Ulodendron scars. This
comparison was made by Shattock[299] in 1888, but he did not accept the
resemblance as a real one. An objection may be urged to the cladoptosis
hypothesis that in _Ulodendron_ the branch, whether vegetative or
reproductive, was not attached to the whole of the depressed area.
On the other hand, a lateral branch originally attached by a narrow
base may have continued to increase in diameter until its base became
slightly sunk in the bark of the stem, thus producing a cup-like
depression which, on the fall of the branch, would retain traces of the
original surface-features of the stem.

Mr Watson[300] of Manchester recently published a paper on Ulodendron
scars, in which he adduces fresh and, as it seems to me, satisfactory
arguments in favour of the branch-scar hypothesis. Fig. 158, from
one of Mr Watson’s blocks, illustrates the nature of his evidence.
He points out that in the obverse half of a large specimen of
_Bothrodendron_ in the Manchester Museum, the umbilicus consists of a
cylindrical hole, 18 mm. deep and 8 mm. in diameter, surrounded by a
projecting ring of mineral material which doubtless represents some
portion of the original plant: on the reverse half of the specimen
the continuation of the ring is seen as a prominent cone fitting into
the cup-like depression in the obverse half: the conical cast shows
that numerous small vascular strands were given off from this ring of
tissue, and these strands have the same arrangement and size as the
dots which are found on typical Ulodendron scars. He interprets the
ring surrounding the umbilicus as the remains of the primary wood and
the small strands as leaf-traces supplying the branch.

[Illustration: FIG. 158. Diagrammatic section through the base of a
  branch to illustrate the Branch theory of the Ulodendroid scar.
  (After Watson.)]

In the diagrammatic section shown in fig. 158 the outer cortex of the
main stem is represented by _oc_ 1; this consists of secondary tissue.
The corresponding tissue in the branch is seen at _oc_ 2. The stele of
the stem is shown at Tr. St. and that of the branch at Br. St.; _lt_,
_lt_, mark the position of the leaf-traces. If we assume the branch
to be detached along the line LS, the depression would show numerous
spirally arranged dots representing the points of exit of leaf-traces
and the vascular axis would be exposed in the umbilicus. This
explanation appears to me to be in harmony with the surface-features
of Ulodendron scars on both Bothrodendron and Lepidodendron stems. The
occasional occurrence of leaf-cushions on a portion of a Ulodendron
scar is a difficulty on the cladoptosis hypothesis. Assuming that true
leaf-cushions occur, their presence may, as Watson suggests, be due to
the folding back of a piece of the outer cortex of the branch which has
been “crushed down on to the area of the scar[301].”

Since this account was written a note has been published by M.
Renier[302] in which he describes a specimen of _Bothrodendron_ from
Liège, one face of which shows a projecting Ulodendroid scar with an
excentric umbilicus. On the other face is a dichotomously branched
shoot with surface-features corresponding to those on the scar; the
evidence that the scar represents the base of the branch is described
as indisputable.

Stur[303] held the view that the depressions on Ulodendron stems
represent the places of attachment of special shoots comparable with
the bulbils of _Lycopodium Selago_, or, it may be added, with the short
branches occasionally produced on _Cycas_ stems. If the depressions
were formed by the pressure of the bases of cones, it is clear that
the size of the cavity must be an index of the diameter of the cone.
The larger Ulodendron scars exceed in diameter the base of any known
lepidodendroid strobilus. Another obvious difficulty, which has not
been overlooked by Kidston who holds that the scars were produced
by sessile cones, is that in _Lepidodendron Veltheimianum_ strobili
were borne at the tips of slender branches; the same difficulty is
presented by _Bothrodendron_ (Fig. 213). It is unlikely that two types
of strobili were produced on the same plant, particularly as the cone
of _L. Veltheimianum_ was heterosporous.

The cones of certain species of _Pinus_ remain attached to the tree
for many years and their bases become embedded in the stem; this is
particularly well shown in the drawing of a cone of _Pinus clausa_
(fig. 159), for which I am indebted to Mr Sudworth, Dendrologist in
the United States Forest Service. Mr Sudworth has drawn my attention
to _P. attenuata_ and _P. muricata_ in illustration of the same
phenomenon[304]. The example shown in fig. 159 cannot, however, be
matched by any known specimen of _Ulodendron_; in the case of the
depressions on the stem of a Pine the cone-base fits the circular scar,
but in the fossil stems it is practically certain that this was not the
case.

[Illustration: FIG. 159. _Pinus clausa._ ½ nat. size.]

There can be little doubt that certain Palaeozoic Lycopods shed their
branches by a method similar to that employed by the Kauri Pine of New
Zealand and by some species of Dicotyledons. The evidence adduced in
the case of _Bothrodendron punctatum_ is a strong argument in favour of
extending the same explanation to other Ulodendron shoots.

[Illustration: FIG. 160.

  A. _Lepidophloios scoticus_ Kidst. From a specimen from the
     Calciferous Sandstone, Midlothian, in Dr Kidston’s Collection;
     rather less than ⅓ nat. size.
  B. _L. scoticus_ cone. From a specimen from the Calciferous
     Sandstone of Midlothian in Dr Kidston’s Collection; slightly
     reduced.]


_b._ _Halonia._

The branched axis with _Lepidophloios_ leaf-cushions, represented
in fig. 160, A, illustrates a special form of shoot described by
Lindley and Hutton[305] under the generic name _Halonia_. The original
specimens referred to this genus are decorticated axes showing remains
of Lepidodendroid leaf-cushions. The spirally disposed circular scars
in the specimen of _Halonia_ (_Lepidophloios scoticus_[306]) shown in
fig. 160 constitute the characteristic feature of the genus; they may
have the form, as in fig. 160, A, of circular discs with a central
umbilicus marking the position of a vascular strand, or, as in the
sandstone cast of _Halonia tortuosa_ shown in fig. 161[307], they may
appear as prominent tubercles. The latter example illustrates the
condition characteristic of partially decorticated stems.

[Illustration: FIG. 161. _Halonia tortuosa_ L. and H. From a specimen
  in Dr Kidston’s Collection, from the Lower Coal-measures of
  Ayrshire (No. 1561); ⅔ nat. size.]

In 1883 Williamson[308] described a specimen, now in the Leeds
Museum, which convinced him that _Halonia_ is merely a special form
of _Lepidodendron_ concerned with the production of fertile shoots or
strobili. Feistmantel[309] also recognised that _Halonia_ _regularis_
is identical in the form of the cushions with the type known as
_Lepidophloios laricinus_. It is worthy of note that under the name
_Halonia_, Feistmantel[310] figured a piece of decorticated axis
characterised by two rows instead of the usual spiral series of large
cup-shaped scars. Recent researches have, however, tended to break down
the distinction between _Ulodendron_ and _Halonia_ founded respectively
on the biseriate and spiral arrangement of the scars or tubercles.

The interpretation of Halonial branches as cone-bearing members of
Lepidodendroid plants has passed into a generally accepted statement
of fact, but, so far as I know, only one specimen has been figured in
which strobili are seen attached to an Halonia axis. This specimen,
described by Grand’Eury[311] from the coal-field of Gard, is hardly
sufficiently well-preserved to constitute a demonstration of the
correctness of the generally received view, which, as is not unusual,
has been repeated by one writer after another without due regard being
paid to the nature of the evidence on which the statement is based. It
may, indeed, be correct to describe Halonial branches as cone-bearing,
but there are certain considerations which make one pause before
unhesitatingly accepting this explanation. The vascular strand which
passes from the central cylinder of the shoot to the tubercle or scar
is composed of a solid rod of xylem distinguished from the main stele
by the absence of a pith. In such petrified peduncles as have been
discovered the stele is of the medullated type. The common occurrence
of strobili terminating slender branches of lepidodendroid plants,
though not a fatal objection to their attachment to Halonial shoots,
shows that in many cases the cones were borne at the tip of leafy
shoots. It may be that some of the Halonial scars are in origin like
those of the Ulodendron axes of _Bothrodendron_ and mark the position
of deciduous vegetative branches.

The first account of the anatomy of _Halonia_ we owe to Dawes[312];
this was followed by a fuller description by Binney[313]. The
history of our knowledge of this type of branch has been given
by Carruthers[314], who expressed the opinion that Halonia is
merely a fertile condition of _Lepidophloios_ and possibly of other
lepidodendroid plants. He was also inclined to regard the Halonial
tubercles as younger stages of the larger scars characteristic of the
genus _Ulodendron_. Williamson’s contributions to our knowledge of
_Halonia_ are of primary importance; he supplied further proof of the
Lepidodendroid nature of these branches and advanced our knowledge of
their anatomy. In an early paper[315] he expressed the view that the
differences on which _Halonia_ and _Ulodendron_ are separated are such
as result from a difference in age and are not of generic importance.
In the last memoir, of which he was sole author, published by the Royal
Society[316], Williamson brought forward further evidence in support of
this well-founded opinion.

That the fossils known as _Halonia_ are branches of a lepidodendroid
plant is at least certain, and it is probable that the lateral
branches which they bore were fertile, though satisfactory proof of
this is lacking. We know also that Halonia branches are characterised
by the Lepidophloios form of leaf-cushion; there is, however, no
sufficient reason to assume that such branches were never attached
to stems with the cushions of the Lepidodendron form. The further
question, namely whether Williamson was correct in his contention as
to the absence of any essential distinction between _Ulodendron_ and
_Halonia_, does not admit of an unchallenged answer. In 1903 Weiss[317]
described the anatomy of a specimen of a biseriate _Halonia_ branch of
_Lepidophloios_. The form of the leaf-cushions is unfortunately not
very well preserved, but Weiss figures other specimens with two rows
of tubercles on which the leaf-cushions are sufficiently distinct to
justify a comparison with those of _Lepidophloios_. He believes with
Williamson that it is the presence of tubercles in place of scars which
distinguishes _Halonia_ from _Ulodendron_, and that the arrangement of
the tubercles or scars is a matter of little importance. He expresses
the opinion justified by the evidence available that the absence or
presence of tubercles is merely due to accidents of preservation or,
one may add, to difference in age. Kidston[318] dissents from Weiss’s
description of his specimen as a biseriate _Halonia_; he regards it as
a Ulodendron branch of _Sigillaria discophora_ (König). Until specimens
with more clearly preserved external features are forthcoming it is
impossible to settle the point in dispute, but on the facts before
us there would seem to be a _prima facie_ case in favour of Weiss’s
contention.

The designation _Halonia_ may be retained as a descriptive term for
Lepidodendroid shoots characterised by spirally disposed scars or
tubercles and bearing leaf-cushions of the Lepidophloios type. In the
case of specimens showing prominent tubercles, the superficial tissues
are usually absent and, as in the fossil represented in fig. 161, the
name _Halonia_ does not necessarily imply the presence of leaf-cushions
of a particular type.


    vii. _Anatomical characters of Vegetative Lepidodendron shoots_
                 (_Lepidodendron and Lepidophloios_).

The type already described under the name _Lepidodendron vasculare_
differs from those dealt with in the following pages chiefly in the
anatomy of the stele. The simplest and probably most primitive type of
Lepidodendron stem is that in which the xylem forms a solid rod; the
type of stele most frequently represented is that of _L. Harcourtii_,
_L. fuliginosum_, and other species in which the diameter of the stele
is greater and a cylinder of primary xylem encloses a comparatively
large parenchymatous pith.


1. _Lepidodendron esnostense_, Renault[319].

This species was founded by Renault on petrified specimens from the
Culm beds of Esnost in France. The surface of a young twig bears
prominent leaf-cushions of elongated rhomboidal form similar to those
of _Lepidodendron obovatum_ (fig. 173) and other species. In older
branches the primary cortex is replaced by a considerable thickness
of radially disposed secondary cortical tissue which, as shown in
tangential section, consists of a reticulum of elongated pointed
elements with comparatively thick walls enclosing meshes filled with
large-celled parenchyma. It is worthy of note that if such a branch
were exposed to decay, the earlier destruction of the more delicate
tissue in the meshes of the secondary cortex would produce a series of
oval depressions, corresponding to the parenchymatous areas, separated
by a projecting reticulum of the more resistant elements: a cast of
this partially decayed surface would be indistinguishable from that
of some types of _Sigillaria_ or of a _Lyginodendron_. The inner
regions of the cortex of the type-specimens have not been preserved.
The xylem, which is the only part of the stele represented, has the
form of a protostele or solid cylinder of scalariform tracheids with
peripheral groups of narrower protoxylem elements which mark the
points of exit of the leaf-traces: in a branch 1–2 cm. wide the xylem
column has a diameter of 3 mm. The small leaves (fig. 143, B, C),
similar to those of a _Sigillaria_, are sub-rhomboidal in section
near the base and approximately circular near the apex[320]. The
mesophyll consists of palisade cells having the appearance of typical
chlorophyll-tissue. The heterosporous strobili attributed to this
species bore microsporangia on the upper and megasporangia on the lower
sporophylls; the megaspores, of which a considerable number occur in
each megasporangium, are identical in size with those of another Culm
form, _Lepidodendron rhodumnense_. Some of these have retained traces
of prothallus tissue, and in one spore Renault figures what he regards
as an archegonium: the drawing is by no means convincing.


2. _Lepidodendron rhodumnense_, Renault[321].

The species from the Culm of Combres (Loire) agrees in its solid xylem
cylinder and in the differentiation of the secondary cortex, as also in
the association of two kinds of spore, with _Lepidodendron esnostense_.
A comparison of the leaves of the two types reveals certain differences
which may be of specific rank, but, apart from minor differences, these
Culm species may be classed under one anatomical type.


3. _Lepidodendron saalfeldense_, Solms-Laubach[322].

This Devonian species was founded on a specimen 3 × 2·5 cm. broad
at the base, which shows the stumps of four branches recalling the
dichotomously branched arms of _Stigmaria_ and _Pleuromeia_. If these
are in reality the remains of Stigmaria-like horizontal branches the
species affords an interesting example of a Lepidodendron axis with
a subterranean rhizome of the type which has been found in several
Sigillarian stems. In the upper end of the axis the stele consists of a
solid strand of xylem which is not sufficiently well preserved to show
the position of the protoxylem groups. A transverse section taken near
the base reveals a type of stele differing from that at the upper end
in being composed of radially disposed tracheids and in its resemblance
to the stele of _Stigmaria_.


4. _Lepidodendron fuliginosum_, Williamson. Figs. 162–172, 179, E.

  1871. _Lepidodendron Harcourtii_, Binney, Palæont. Soc., p. 48, Pl.
        VII. fig. 6.
  1872. _Halonia regularis_, Binney, Palæont. Soc., p. 89, Pl. XV.
  1881. _Lepidodendron Harcourtii_, Williamson, Phil. Trans. Roy.
        Soc., Vol. 172, p. 288, Pls. XLIX–LII.
  1887. _Lepidodendron fuliginosum_, Williamson, Proc. Roy. Soc.,
        Vol. XLII. p. 6.
  1891. _Lepidodendron Williamsoni_, Solms-Laubach, Fossil Botany, p.
        226.
  1893. _Lepidophloios fuliginosus_, Kidston, Trans. Roy. Soc.
        Edinburgh, Vol. XXXVIII. p. 548.

The name _Lepidodendron fuliginosum_ was proposed by Williamson in
1887 for petrified stems previously included by him in Witham’s
species _L. Harcourtii_, but subsequently recognised as a distinct
type characterised by “the greater uniformity in the composition
of the entire cortex” and by other features some of which do not
constitute distinctive characters. The species agrees with _L.
Harcourtii_ and with _L. Veltheimianum_ in having a medullated stele;
it is distinguished not only by the more frequent preservation of
the middle cortex, a fact due to a difference in minute structure,
but chiefly by the peculiar structure of the secondary tissue
added to the stele; this is in part composed of radial series of
parenchymatous cells and of a varying amount of tracheal tissue
the elements of which are narrower than in other species and are
characterised also by their sinuous vertical course. As is pointed
out in the sequel, the anatomical features of _L. fuliginosum_, as at
present understood, are not confined to one type of _Lepidodendron_
stem. Specimens have been described with leaf-cushions of the form
characteristic of _L. aculeatum_, _L. obovatum_ and _Lepidophloios_
combined with the anatomical features of Williamson’s species: it is
possible that the two species _L. obovatum_ and _L. aculeatum_ are
not really distinct[323], but it is certain that shoots with both the
_Lepidodendron_ and _Lepidophloios_ cushions may have the same type of
anatomical structure.

A more detailed knowledge of the structural features of Lepidodendron
shoots may enable us to define anatomical species with more exactness
than is possible at present. There can, however, be little doubt that
well-marked anatomical features may be associated with more than one
specific form of shoot as defined by the form of the leaf-cushions.

Solms-Laubach proposed the name _Lepidodendron Williamsoni_ for the
anatomical type _L. fuliginosum_ of Williamson, but the latter name has
been generally adopted.

In the following account special attention is directed to the nature
and origin of the secondary stelar tissue and to the secretory
zone, as difference of opinion exists as to the interpretation of
these features. Among the best examples of shoots of _Lepidodendron
fuliginosum_ without secondary tissue or in which it is feebly
developed are those originally described by Binney. The stele includes
a large parenchymatous pith, the cells of which frequently show signs
of recent division, a feature observed also in the pith of the large
stem of _L. Wünschianum_, represented in figs. 181, 182. The primary
xylem cylinder has an irregularly crenulate outer edge like that of _L.
Wünschianum_ and _L. Harcourtii_ and the protoxylem elements occupy an
exarch position. Isodiametric reticulately-pitted elements are met with
both on the inner and outer edge of the xylem.

[Illustration: FIG. 162. _Lepidodendron fuliginosum._ Part of the
  stele in transverse section. (Binney Collection, Sedgwick Museum,
  Cambridge.)]

[Illustration: FIG. 163. _Lepidodendron fuliginosum._ Longitudinal
  section. (Binney Collection, Cambridge.)]

Figs. 162 and 163 illustrate the structure of the outer portion of the
xylem and adjacent tissues in a section of a shoot 3·8 cm. × 2·5 cm. in
diameter, which is in the act of branching, as shown by the occurrence
of two steles of equal size. A figure of the complete section will
be found in Binney’s memoir[324], and additional illustrations were
published in 1899[325].

[Illustration: FIG. 164. _Lepidodendron fuliginosum_. Leaf-trace.
  (Binney Collection, Cambridge.)]

The primary xylem (figs. 162, 163, _x_) is succeeded by 2–3 rows of
polygonal cells with dark contents and associated with isodiametric
tracheae: these pass into clearer parenchymatous tissue, _a_,
characterised by the arrangement of the cells in vertical series,
to which the term meristematic zone has been applied. The secretory
zone, _s_, abutting on the meristematic zone, consists of more or less
disorganised parenchymatous cells and broader and more elongated
spaces; it is interrupted here and there by an outgoing leaf-trace,
as at _lt_ 1 and _lt_ 2 in fig. 162. The secretory zone is succeeded
by a homogeneous inner cortex like that described in _L. vasculare_;
part of this region is seen at the upper edge of fig. 162. The broad
middle cortex, which is separated from the inner cortex by a sharply
defined boundary, is composed of rather small lacunar parenchymatous
tissue consisting of sinuous tubular elements interspersed among
isodiametric cells of various sizes (fig. 166, _p_). In the middle
cortical region the leaf-traces pursue an almost horizontal course; one
is shown in fig. 164, in oblique longitudinal section, in a reversed
position; the xylem, _x_, should be on the inner side of the secretory
tissue, _s_. The clear space between the two parts of the vascular
bundle was originally occupied by a few layers of parenchymatous
cells, as seen in the transverse sections, figs. 165 and 166. In some
specimens the leaf-traces pass through the middle cortex in a much
more vertical course, as shown by the section represented in fig. 165.
This section illustrates the structure of a typical leaf-trace with
unusual clearness; it shows the tangentially elongated group of xylem,
the strand of tissue which occupies the position of phloem, _s_ (to
which the term secretory zone is applied), the compact parenchyma
between the two parts of the bundle, and surrounding the whole a
narrow sheath sharply contrasted by the smaller and more uniform size
of the cells from the middle cortex, a few cells of which are seen in
the photograph. The middle cortex shows a well-defined junction with
the more compact outer cortical region, which consists of primary
parenchyma passing externally into a zone of phelloderm composed of
thick-walled and more elongated cells. A noticeable feature in many
Lepidodendron shoots is the occurrence of a circle of strands of
secretory cells often surrounding fairly large ducts just internal to
the edge of phelloderm: similar strands form irregularly concentric
circles, as was pointed out in the case of _L. vasculare_, in the
phelloderm itself.

[Illustration: FIG. 165. _Lepidodendron fuliginosum._ Leaf-trace: _x_,
  xylem; _s_, secretory zone. (Binney Collection, Cambridge.)]

[Illustration: FIG. 166. _Lepidodendron fuliginosum._ Leaf-trace: _p_,
  parichnos. (Binney Collection, Cambridge.)]

Fig. 166 shows a leaf-trace in the outer cortex accompanied by its
crescent-shaped parichnos, _p_, derived from the middle cortex and
by means of which the outer cortex and the lamina of the leaves are
connected with the inner region of the shoot. This lacunar middle
cortex and parichnos doubtless constitute an aerating tissue-system
which after leaf-fall is exposed directly to the air at the ends of the
parichnos arms on the leaf-scars.

Some of the sections in the Binney Collection (Sedgwick Museum,
Cambridge) show early stages in the production of secondary xylem: in
the section represented in fig. 167 the secretory zone is succeeded
on its inner face by a zone of radially elongated cells, _m_, which
are clearly in a meristematic condition. The same section shows also
the more radially extended form of the xylem of a leaf-trace with its
internal protoxylem, _px_, in contrast to the tangentially elongated
form which is assumed during its passage through the cortex (cf. figs.
165, 166).

[Illustration: FIG. 167. _Lepidodendron fuliginosum._ (Binney
  Collection, Cambridge.)]

Some sections of _Lepidodendron fuliginosum_ in the Manchester
University Collection are of special interest from the point of view of
the method of secondary thickening. In the section reproduced in fig.
168, B, the meristematic zone is seen to consist in part of radially
elongated elements, _m_, with parallel cross-walls evidently of recent
origin. The same tissue is shown also in fig. 168, C, _a_, D, _a_,
and in fig. 169, A, _a_ This band of meristem, which we may speak of
as the cambium, occurs in the outer region of the meristematic zone
immediately internal to the secretory zone, _sc_.

[Illustration: FIG. 168.

  A. _Lepidodendron vasculare._ (Botany School, Cambridge.)
  B. _Lepidodendron fuliginosum._ (From a specimen from Shore,
     Lancashire, in the Cambridge Botany School Collection).
  C. _L. fuliginosum._ (“Biseriate Halonia” of Weiss No. 257,
     Manchester University Museum.)
  D. _L. fuliginosum._ (Manchester Univ. Museum.)]

The result of the activity of this cambium band is the production of
secondary parenchyma and tracheal tissue. In fig. 179, E, drawn from
a portion of the section represented in fig. 168, B, a projecting arm
of primary xylem is seen at _x_; this is followed by 2–3 layers of
parenchymatous cells, some of which have dark contents, and beyond
this is seen a group of secondary elements, _tr_, cut across somewhat
obliquely, which are evidently products of the cambial cells on the
inner margin of the secretory zone, _sc_. The longitudinal section
(fig. 169, D) shows the cambial cells, a, next the secretory zone,
_sc_, passing internally into crushed and imperfectly preserved
elongated elements which are presumably miniature tracheae, and these
are succeeded by older and more completely lignified xylem elements,
_x_. In larger shoots the amount of secondary tissue is considerably
greater; it may consist almost entirely of short-celled parenchyma
(fig. 168, C, from _x_ to _sc_), or it may include a large proportion
of radially disposed and vertically elongated tracheae (fig. 168,
D, _x_², and fig. 170, A, _x_²), or it may consist of parenchyma
containing scattered groups of tracheae (fig. 169, A, _x_²)[326].

[Illustration: FIG. 169. _Lepidodendron fuliginosum._

  A, B. (Manchester University Collection. No. Q. 645 A.)
  B, C. (Manchester. No. 257.)
  D. (Manchester. No. 6.)]

Fig. 169, A, is a diagrammatic sketch of the tissues—1 mm. wide—between
the primary xylem, _x_, and the inner cortex. The primary xylem is
succeeded by short parenchymatous cells followed by a zone of radially
elongated elements passing occasionally into rows of narrow scalariform
tracheae, some of which, owing to their sinuous longitudinal course
(fig. 171, C), are seen in oblique section, as at C, fig. 169, A. At
its outer edge this secondary tissue, _x_², consisting of parenchyma
and tracheae, passes into the cambial band (fig. 169, B, _a_).

[Illustration: FIG. 170. _Lepidodendron fuliginosum._ (From sections in
  the Manchester Museum.)]

The radial longitudinal section represented in fig. 168, C, is
taken from the fossil described by Weiss as a biseriate _Halonia_;
it agrees sufficiently closely in structure with others referred
to _Lepidodendron fuliginosum_ to be classed as an example of this
anatomical type. A complete transverse section of the stem measures 9
× 6·3 cm.; the breadth of the tissues between the edge of the primary
xylem and the outer edge of the secretory zone is 2·5 mm. The middle
cortical region, characterised by the sooty appearance, which led
Williamson to choose the specific name _fuliginosum_, is traversed
by the leaf-traces and is sharply differentiated from both the inner
and outer cortex. The longitudinal section (fig. 168, C) shows the
outer edge of the primary xylem, _x_, abutting on a band of dark and
small-celled parenchyma which passes into the broad zone of secondary
tissue, _m_, the inner region of which consists of fairly thick-walled
elements in radial series passing externally into the thin-walled cells
of the cambial region, _a_, on the inner edge of the secretory zone,
_sc_. This section shows also the interruption of the secretory zone
by an outgoing leaf-trace, _lt_, the lower part of which, _sc_, is
continued downwards into the secretory zone. The exit of a leaf-trace
produces a gap in the secretory zone of the stem, but not in the xylem.
If we applied the term phloem to the secretory zone—a course adopted by
Prof. F. E. Weiss and some other authors, but which I do not propose
to follow—we should speak of a phloem foliar-gap as a characteristic
feature of a Lepidodendron shoot. This applies to other species of the
genus as well as to _L. fuliginosum_.

[Illustration: FIG. 171. _Lepidodendron fuliginosum._ (From sections in
  the Manchester Museum.)]

Fig. 171, A, shows more clearly the broad zone of secondary parenchyma
with the thinner-walled cambial region, _a_; the latter is represented
on a larger scale in fig. 171, B. The section shown in fig. 168,
D, and in fig. 170, A, affords an example of a stem in which the
secondary tissue consists largely of narrow scalariform tracheae,
_x_²; the primary stele has a diameter of 1 cm.; the secondary xylem,
_x_², forms a fairly broad zone of parenchyma and tracheal elements
through which leaf-traces pass vertically, a fact of some interest in
comparison with the horizontal course which they pursue through the
medullary rays in the normal secondary wood of _L. vasculare_ and _L.
Wünschianum_. The secondary tracheae pass gradually into thin-walled
cambial cells (_a_, fig. 168, D; 170, A) with parallel tangential
walls. Fig. 171, C, shows the sinuous course of the secondary
tracheae as seen in longitudinal section, and a few small groups of
parenchymatous cells, _mr_, which may be of the nature of medullary
rays, enclosed between the winding scalariform tracheae.

[Illustration: FIG. 172. _Lepidodendron fuliginosum._ From a section
  (4 × 3·4 cm.) in the Williamson Collection, British Museum (No.
  379), figured by Williamson, _Phil. Trans. R. Soc._ =1881=, Pl. 52.]

The secretory zone of _Lepidodendron fuliginosum_ agrees essentially
with that of other species; it usually presents the appearance shown
in fig. 168, B, _sc_; fig. 169, B and C; fig. 170, B (longitudinal
section); fig. 171, D, _sc_. The comparatively large clear spaces which
characterise this tissue, as seen in fig. 168, B, appear to owe their
origin to groups of small cells which gradually break down and give
rise to spaces containing remnants of the disorganised elements, as in
fig. 171, D, and fig. 169, B, _b_. The secretory tissue seen in fig.
170, B, consists of large and small parenchymatous cells without any of
the broad sacs or spaces such as are shown in fig. 169, C.

Fig. 172 represents a diagrammatic sketch of a transverse section (4
× 3·4 cm. in diameter) of a young shoot from the Lower Coal-Measures
of Lancashire figured by Williamson[327] in 1881 as _Lepidodendron
Harcourtii_. It shows the features characteristic of _L. fuliginosum_
and is of importance as affording an example of a shoot giving
off a branch from the stele to supply a lateral axis of the type
characteristic of _Halonia_. The exit of the branch-stele forms a
gap in the main stele; a ramular gap as distinguished from a foliar
gap. The outgoing vascular strand is at first crescentic, but becomes
gradually converted into a solid stele. The primary xylem of the main
stele (black in the figure) consists of a ring six tracheae in breadth;
this is succeeded by a few layers of dark parenchymatous cells and a
band of radially elongated elements, _a_, which abuts on the secretory
zone. The middle lacunar cortex, _c_², with _Stigmaria_ rootlets,
_s_, is fairly well preserved. In the outer cortex occur several
leaf-traces, _lt_, accompanied by spaces originally occupied by the
parichnos strand, _p_. A band of secondary cortex, consisting chiefly
of phelloderm, is seen at _pd_. The prominent leaf-cushions, some of
which show the parichnos, _p_, appear to be of the Lepidophloios type.

                   •       •       •       •       •

It remains to consider the external characters of Lepidodendroid shoots
possessing the anatomical features represented by the comprehensive
species _Lepidodendron fuliginosum_.

Certain sections exhibiting this type of structure were described by
Binney in 1872 as _Halonia regularis_[328] on evidence supplied by Mr
Dawes, who stated that they were cut from a specimen bearing Halonia
tubercles. The section represented in fig. 172 is no doubt from an
Halonia axis. In 1890 Cash and Lomax[329] stated that they had in
their possession a stem of the _L. fuliginosum_ type with the external
features of _Lepidophloios_; this identification has been confirmed by
Kidston[330] and Weiss[331]. It is, however, equally clear that certain
species with the elongated leaf-cushions of _Lepidodendron_ must be
included among examples of shoots with the anatomical characters of _L.
fuliginosum_.

[Illustration: FIG. 173. _Lepidodendron obovatum._ (From a specimen
  lent by Dr D. H. Scott.)]

Dr Scott[332] published in 1906 a short account of the structure
of a specimen from the Lower Coal-Measures of Lancashire, the
external features of which were identified by Kidston with those of
_Lepidodendron obovatum_ Sternb. Dr Scott generously allowed me to have
drawings made from his specimen; these are reproduced in fig. 173. The
form of the leaf-cushion is by no means perfect; there is a well-marked
median ridge, and the small circular scar near the upper end of some
of the cushions may represent the ligular cavity. At the base of the
leaf-cushions a cortical meristem has produced a zone of secondary
cortex; at _c_ a second meristem is seen in the outer cortex: the dark
dots in the cortex mark the positions of leaf-trace bundles. The inner
cortex, _d_, is a more compact tissue surrounding the imperfectly
preserved secretory zone. From the medullated stele a lateral branch,
_b_, is being given off; its crescentic form becoming changed to
circular as it passes nearer to the surface.

[Illustration: FIG. 174. _Lepidodendron aculeatum._
  (Cambridge Botany School.)]

[Illustration: FIG. 175. _Lepidodendron aculeatum._
  (Cambridge Botany School.)]

A type of _Lepidodendron_, _L. Hickii_, founded on anatomical
characters by Mr Watson[333], is believed by him to possess
leaf-cushions like those of _L. obovatum_; if this is so, it is
interesting, as he points out, to find two distinct anatomical types
associated with one species. Watson thinks it probable that the
“species” _L. obovatum_ includes at least two widely different species.
This merely emphasizes the importance of correlating structure and
external characters as far as available data permit.

[Illustration: FIG. 176. _Lepidodendron aculeatum._
  (Cambridge Botany School.)]

The specimen, of which part of the surface is shown in fig. 174, is
in all probability _L. aculeatum_ Sternb. This was described by me
in detail in _The Annals of Botany_ (1906) as another example of the
co-existence of the _Lepidodendron fuliginosum_ type of anatomy with
a true _Lepidodendron_. The locality of the specimen is not known.
The leaf-cushions are 1·5 cm. long with tapered upper and lower ends;
a ligular cavity may be recognised on some parts of the fossil,
also faint indications of leaf-trace scars. The tubercles (fig.
174, A–C, _t_) probably represent leaf-traces which the shrinkage
of the superficial tissues has rendered visible in the lower part
of their course. The circular scar, _s_ (fig. B), on the partially
decorticated surface is apparently a wound. The stele is sufficiently
well preserved to justify its reference to _L. fuliginosum_. The
irregularly crenulated edge of the primary xylem, _x_ (fig. 175),
is succeeded by a broad band of parenchyma (the meristematic zone),
_m_, and beyond this are remnants of the secretory zone, _s_. The
structure of the leaf-traces corresponds with that of other specimens
of the type, but the much steeper course of these vascular strands,
_lt_, _lt′_ (fig. 176), is a feature in which this example differs
from most of those referred to _L. fuliginosum_. Such evidence as is
available would seem to point to the absence of trustworthy criteria
enabling us to separate, on anatomical grounds, _Lepidophloios_ and
_Lepidodendron_[334].

[Illustration: FIG. 177. _Stigmaria radiculosa_ (Hick). (From sections
  in the Manchester University Collection.)]


_Stigmaria radiculosa_ (Hick).

We have no proof of the nature of the subterranean organs of
_Lepidodendron fuliginosum_, though it is not improbable that the
specimens described below may be correctly assigned by Weiss to that
species. Prof. Weiss[335] has made an interesting contribution to
our knowledge of a type first described by Hick[336] under the name
_Tylophora radiculosa_, a designation which he afterwards altered
to _Xenophyton radiculosum_[337] and for which we may now substitute
_Stigmaria radiculosa_ (Hick). Prof. Williamson expressed the opinion
that _Xenophyton_ exhibited considerable affinity with _Stigmaria
ficoides_ and Weiss’s further study of the species leads him to regard
Hick’s plant as probably the Stigmarian organ of _Lepidodendron
fuliginosum_. The diagrammatic transverse section represented in fig.
177, A (4·5 cm. in diameter), shows an outer cortex of parenchyma,
_c_³, consisting in part of radial rows of secondary tissue and of a
band of compact parenchyma bounded by the wavy line _a_; at _sc_ is
a series of secretory strands exactly like those in a corresponding
position in _Lepidodendron fuliginosum_ and other species of the genus.
The greater part of the organ is occupied by a lacunar and hyphal
middle cortex identical in structure with that shown in fig. 178, B,
drawn from a rootlet. At _d_, fig. 177, A, the middle cortex has been
invaded by a narrow tongue of outer cortical tissue. The stele is
characterised by a large pith filled with parenchyma; in _Stigmaria
ficoides_[338] the general absence of pith-tissue has led to the
inference that the stele was hollow. The xylem is represented by a ring
of bundles separated by broad medullary rays; each bundle contains a
few small, apparently primary, elements on its inner edge but is mainly
composed of radial rows of secondary tracheae _x_², fig. 177, B. On
the outer face of the secondary xylem occur a few smaller and thinner
walled cells, _c_, having the appearance of meristematic tissue; from
these additional tracheae were added to the xylem. This meristematic
zone occurs, as in the stems of _Lepidodendron_, immediately internal
to the secretory tissue, sc; at _c_¹, fig. 177, B, is seen the inner
cortical tissue.

[Illustration: FIG. 178. _Rootlet of Stigmaria._ (From a section in the
  Manchester Collection.)]

In surface-view a specimen figured by Hick[339] shows a number of
circular scars agreeing in shape and arrangement with the rootlet scars
of _Stigmaria ficoides_. At _b_ in fig. 177, A, the basal portion of
a rootlet is shown in organic connexion with the outer cortex. The
rootlet-bundles are given off from the stele as in other examples of
_Stigmaria_; each bundle consists of a triangular strand of xylem with
an endarch protoxylem at the narrow end accompanied by a portion of
the secretory tissue as in the leaf-traces. As in _Stigmaria ficoides_
the rootlets are attached to the outer cortex above a cushion of small
cells. It is interesting to find that rootlet-bundles, as seen in
tangential section of the main axis, are associated with a parichnos
strand, but this is on the xylem side of the vascular strand, whereas
in the case of leaf-traces the parichnos is on the other side of the
bundle.

Fig. 178, A, represents a transverse section of a rootlet (6 mm.
in diameter) associated with _Stigmaria radiculosa_ and probably
belonging to this species. The xylem strand _x_ is composed of a group
of tracheae with a single protoxylem strand, _px_, at the pointed end
and with small metaxylem elements at the broad end next the space
originally occupied by the so-called phloem. A parenchymatous sheath,
_c′_, surrounds the bundle, and beyond this is the broad middle cortex,
a small portion of which is shown on a larger scale in fig. 178, B; as
Weiss points out, some of the outermost cells of the lacunar cortex
(_m_) are clearly in a state of meristematic activity.

The preservation of the middle cortex and the small quantity of
secondary xylem are characters which this _Stigmaria_ shares with
_Lepidodendron fuliginosum_, and although decisive evidence is still to
seek, we may express the opinion that Weiss’s surmise of a connexion
between _Stigmaria radiculosa_ and _Lepidodendron fuliginosum_ is
probably correct.


5. _Lepidodendron Harcourtii._ Fig. 179, A–D.

In 1831 Mr Witham[340] published an anatomical description of a
fragment of a _Lepidodendron_ which he named _Lepidodendron Harcourtii_
after Mr C. G. V. Vernon Harcourt from whom the specimen was originally
obtained. The fossil was found in rocks belonging to the Calciferous
series in Northumberland. Witham reproduced the account of this
species in his classic work on _Fossil Vegetables_[341], and Lindley
and Hutton[342], who examined Mr Harcourt’s material, published a
description of it in their _Fossil Flora_ in which they expressed
the view that _Lepidodendron_ is intermediate between Conifers and
Lycopods. Adolphe Brongniart[343] included in his memoir on _Sigillaria
elegans_ an account of Witham’s species based on material presented to
the Paris Museum by Mr Hutton and Robert Brown. Dr Kidston[344] has
shown that the actual transverse section figured by Witham is now in
the York Museum; a piece of stem in the same Museum, which is not the
specimen from which Witham’s section was cut, supplied the transverse
section figured by Brongniart. The figures given by Lindley and Hutton
do not appear to have been made from the York specimens. In 1887
Williamson[345] published a note in which he pointed out that some of
the specimens described by him as _L. Harcourtii_ should be transferred
to a distinct species, which he named _L. fuliginosum_. Subsequently
in 1893 he gave a fuller account of Witham’s species; it has, however,
been shown by Dr Kidston and by Mr Watson[346] that certain specimens
identified by Williamson as _L. Harcourtii_ differ sufficiently from
that type to be placed in another species, for which Watson proposes
the name _L. Hickii_.

A paper on _L. Harcourtii_ published by Bertrand[347] in 1891 extends
our knowledge of this type in regard to several anatomical details.
It was recognised by Williamson that the absence of secondary wood
in shoots possessing the anatomical characters of _L. Harcourtii_
is a feature to which no great importance should be attached. It is
possible that the large stems from the Isle of Arran described by
Williamson[348] as _Lepidodendron Wünschianum_, in which the secondary
wood is well developed, may be specifically identical with the smaller
specimens from Northumberland and elsewhere which are recognised as
examples of Witham’s type.

The diagrammatic sketch shown in fig. 179, A, was made from a section
figured by Williamson in 1893[349]; it has a diameter of 9 × 8·5 cm.
The stele is of the medullated type like that of _L. Wünschianum_,
and the outer edge of the primary xylem is characterised by sharp and
prominent projecting ridges similar to those of _L. fuliginosum_ but
rather more prominent. Parenchymatous cells succeed the xylem, as in
other species, but in this case there is no indication of meristematic
activity; beyond this region occur occasional patches of a partially
destroyed secretory zone. Remains of a lacunar tissue are seen in the
middle cortical region; also numerous leaf-traces, _lt_, consisting
of a tangentially elongated xylem strand accompanied by a strand of
secretory zone tissue enclosed in a sheath of delicate parenchyma. In
the inner part of the outer cortex, _c_³, the leaf-traces lie in a
space originally occupied by the parichnos; in the outer portion of
the same region a band of secondary cortex, _pd_, has been formed;
immediately internal to this occur numerous patches of secretory
tissue, represented by small dots in the drawing close to _pd_; one is
shown on a larger scale in fig. B.

The position of the phellogen is seen at _a_; external to this are
radial rows of rather large cells with dark contents.

[Illustration: FIG. 179.

  A–D. _Lepidodendron Harcourtii_, Witham.
  E. _Lepidodendron fuliginosum_, Shore, Lancashire.
  A, B. From a specimen in the Williamson Collection, British Museum
     (No. 380), from Airdrie, Scotland.
  C, D. From sections in the Collection of Dr Kidston, from Shore,
     Lancashire.]

Fig. 179, C, _x_, shows the characteristic form of the primary xylem
edge, beyond which are seen oval or circular leaf-traces with a mesarch
protoxylem, _lt_, _px_. It is possible that this specimen may not
be specifically identical with Witham’s species, but it represents
a very similar if not identical type; it may on the other hand be
referable to _L. fuliginosum_. The importance of the specimen, apart
from its precise specific position, is that it serves to illustrate the
general appearance of the xylem surface met with in both species, _L.
Harcourtii_ and _L. fuliginosum_. A tangential longitudinal section,
taken through the line _ab_ in fig. C, is represented in fig. 179, D.
The xylem of the leaf-traces _lt_, consisting chiefly of scalariform
tracheae, alternates with patches of crushed and delicate parenchyma
which immediately abut on the primary xylem; at _p_, _p_, the section
passes through some of the projecting arms of the xylem cylinder; at
_m_ is seen a patch of meristematic zone tissue. This section together
with the similar section of _Lepidodendron vasculare_ described on a
previous page demonstrates that the projecting ridges of the primary
xylem form apparently vertical bands: they are not characterised by a
lattice-work arrangement as described by Bertrand and by other authors
who have accepted his conclusions. If a reticulum of intersecting
ridges were present on the face of the xylem cylinder its existence
would be revealed by such a section as that represented in fig. 179, D.

[Illustration: FIG. 180. _Lepidodendron Wünschianum._ From Arran. (⅕
  nat. size.) (Sedgwick Museum, Cambridge.)]


6. _Lepidodendron Wünschianum_ (Williamson). Figs. 180–184.

Reference was made in Volume I. to the occurrence of large stems of
a Lepidodendron in volcanic beds of Calciferous sandstone age in the
island of Arran[350]. These were discovered and briefly described by Mr
Wünsch in 1867[351] and afterwards named by Carruthers _Lomatophloyos
Wünschianus_[352]. Mr Carruthers visited the locality and published
an account of the peculiar method of preservation of the plant
remains[353]. It is, however, to Williamson[354] that we owe the more
complete description of these Arran stems. Portions of large stems
from the Arran beds are preserved in the British Museum, the Sedgwick
Museum, Cambridge, and in the Manchester Museum. The section of one of
these is shown in fig. 180; an outer shell of bark encloses a mass of
volcanic ash in which are embedded several woody cylinders originally
described as “internal piths[355],” and by Carruthers as young stems
produced from spores which had germinated in the hollow trunk of a
large tree. The true interpretation was supplied by Williamson who
showed that a stem of the dimensions of that represented by the outer
cortex, _e_, fig. 180, must have possessed a single stele of the size
of those seen in the interior of the hollow trunk. The additional woody
cylinders, or steles, were derived from other stems, and carried,
probably by water, into the partially decayed trunk. In addition to
large Lepidodendron stems Williamson described smaller shoots as well
as an Halonial branch and made brief reference to some cones described
by Binney[356] in 1871 from the same locality.

The following account of _Lepidodendron Wünschianum_ is based on an
exceptionally fine specimen discovered by Mr T. Kerr of Edinburgh in
Calciferous sandstone volcanic ashes at Dalmeny in Linlithgowshire. The
material from this locality described by Mr Hill and myself[357] was
generously placed in my hands by Dr Kidston of Stirling. Fig. 181, A,
shows a transverse section, 33 cm. in diameter, consisting of a shell
of outer cortical tissue enclosing a core of light-coloured volcanic
ash; on the decay of the more delicate middle cortex the cylindrical
stele dropped to one side of the hollow trunk. The stele, fig. 182, has
a diameter of 6·5 cm.; the centre is occupied by concentric layers of
silica, _s_, surrounded externally by the remains of a parenchymatous
pith, _p_, made up of isodiametric and sinuous hypha-like elements
like those in the middle cortex of Lepidodendron shoots. On the inner
edge of the primary xylem, _x′_, occur several isodiametric tracheae
with fine scalariform and reticulate thickening bands like those in
the central region of the stele of _Lepidodendron vasculare_: it is
probable that these elements are vestiges of conducting tissue which in
ancestral forms formed a solid and not a medullated stele.

[Illustration: FIG. 181. _Lepidodendron Wünschianum._ Calciferous
  Sandstone, Dalmeny. (A, Sedgwick Museum, Cambridge. B–F, Botany
  School, Cambridge.)]

[Illustration: FIG. 182. _Lepidodendron Wünschianum._ The stele of
  the stem shown in fig. 181, A. (Cambridge Botany School.)]

The primary xylem is limited externally by an unequally fluted surface
with exarch protoxylem elements; it is, however, noteworthy that there
is not always a very clearly defined difference between the small
protoxylem and the large centripetally developed tracheae. Immediately
beyond the primary xylem occur numerous thin-walled parenchymatous
cells with spiral and reticulate pitting; beyond these is the broad
zone of secondary xylem, _x_², composed of scalariform tracheae and
numerous medullary rays consisting of one, two, or several rows of
radially elongated elements with spiral and reticulate pitting. In
tangential sections the rays are seen to vary considerably in size,
some being made up of a single row of cells while others are longer and
broader; through the latter leaf-traces pass horizontally. Portions of
medullary rays are seen at _mr_ in fig. 181, C and E.

The leaf-traces given off from projecting ridges on the outer edge
of the primary xylem pass upwards for a short distance and then bend
outwards through a broad medullary ray; on reaching the limit of
the secondary xylem they again bend sharply upwards, appearing in
transverse section at _lt_ fig. 181, B. Each leaf-trace consists at
first of long tracheae accompanied by numerous thin-walled spiral
and reticulate parenchymatous cells derived from the tissue in
contact with the outer edge of the primary wood. Fig. 181, B, shows
a leaf-trace near the edge of the secondary xylem; it consists of a
group of primary tracheae, with narrower protoxylem elements, _px_,
near the outer margin, almost completely enclosed by radially disposed
series of smaller and more delicate tracheae. These secondary elements
of the leaf-trace are apparently added during its passage through
the medullary ray, but additions are also made to this tissue by
the meristematic zone, _m_, fig. 181, B and E. In contact with the
outermost tracheae of normal size at the edge of the secondary xylem
there are some smaller lignified elements, as at _a_, fig. 181, E, and
at T, fig. 183; this juxtaposition of large and small tracheae has been
referred to in the description of _L. vasculare_.

Prof. Williamson[358], in his account of the Arran specimens of this
species, expressed the opinion that the trees probably perished “in
consequence of the mephitic vapours which filled the atmosphere”; it
maybe that in the striking difference in the diameter of the conducting
elements on the margin of the wood we have evidence of approaching
death.

Beyond the most recently formed tracheae we have a band of delicate
parenchymatous cells (_m_, figs. B and E, 181; C, figs. 183, 184)
forming the meristematic zone[359]. The longitudinal section
represented in fig. 184 shows some recently formed narrow tracheae, T,
and beyond these the meristematic zone composed of thin-walled short
cells, C, arranged in horizontal rows. It is this small-celled tissue
to which the name phloem has been applied by some authors[360], a
term which seems to me to be misleading and inappropriate. In passing
through this zone of dividing cells the leaf-traces become surrounded
by an arc of meristem from which elements are added to the radially
placed rows of secondary tracheae. Beyond the meristematic region
portions of the secretory zone are preserved, consisting of large
sacs or spaces and small dark cells as seen in figs. 181, B, E, _sc_,
F; 183, 184. This tissue has the same structure as in _L. vasculare_
and in _L. fuliginosum_: it is a striking fact that there are no
indications of any additions to the secretory zone even in stems with
such a large amount of secondary xylem as in the Dalmeny specimen (fig.
182, _x_²). If the secretory zone were of the nature of phloem we
should expect to see signs of additions made to it in the course of
growth. In this connexion it is worth mentioning that in the recent
fern _Botrychium_ (Ophioglossaceae) secondary xylem is formed in the
stem, but apparently no additions are made to the phloem. The structure
of the secretory zone tissue as seen in the longitudinal section
fig. 184, S, is also a serious difficulty in the way of accepting
the designation phloem as employed by Scott and Weiss. Between the
secretory zone and the outer cortical region, no tissues have been
preserved. The shell of bark consists chiefly of radial rows of
elongated cells with rather thick walls characterised by the occurrence
of small intercellular spaces and by tangentially placed bands of
secretory cells and sacs (fig. 181, D, _s_). Immediately internal to
the secondary cortex or phelloderm occur groups of secretory tissue as
shown in the section of _L. Harcourtii_ (fig. 179, B).

[Illustration: FIG. 183. _Lepidodendron Wünschianum._ From the
  specimen shown in fig. 181, S, secretory zone; C, meristem; T,
  immature tracheae.]

[Illustration: FIG. 184. _Lepidodendron Wünschianum._ Longitudinal
  section of the specimen represented in transverse section in fig.
  183.]

The large tree shown in transverse section in fig. 181, A, has
lost its leaf-cushions; the bark, as seen in the lower part of the
photograph, presents a fissured appearance like that with which we
are familiar on an old Oak or Elm stem. A radial longitudinal section
through the phelloderm revealed the existence of a crushed leaf-trace
passing outwards in an approximately horizontal course accompanied
by a strand of parenchymatous tissue[361] having the characteristic
structure of a parichnos. It is probable that the surface of this
partially decorticated stem differed in appearance from that of an old
_Sigillaria_ (cf. fig. 198) in the much smaller and less conspicuous
parichnos strands.

In addition to the large stems of _L. Wünschianum_ from Arran and
Dalmeny numerous examples of smaller axes from the former locality are
represented in the Williamson collection (British Museum). Some of
the twigs are characterised by a solid stele (protostele) giving off
numerous leaf-traces accompanied by short spirally thickened tracheids
like those which occur at the outer edge of the primary xylem in
the larger stem: these extend into the leaf where they are arranged
round the vascular bundle like the transfusion tracheids[362] in many
recent conifers. The surface of these smaller shoots bears large
leaf-cushions which are seen in longitudinal section to have the form
characteristic of _Lepidophloios_. It is worthy of note that a section
of a bifurcating axis of this species from the Calciferous Sandstone of
Craigleith (British Museum Collection[363]), although its diameter is
19 × 14 cm., shows no signs of secondary wood. This late appearance of
secondary xylem and other anatomical features suggest the possibility
of the specific identity of _L. Wünschianum_ and _L. Harcourtii_[364].

In 1871 Binney[365] described a specimen of a heterosporous cone,
_Lepidostrobus Wünschianus_, from Arran exhibiting the ordinary
features of lepidodendroid strobili; this was probably borne by
_Lepidodendron Wünschianum_.


7. _Lepidodendron macrophyllum_ (Williamson). Fig. 186, C.

The diagrammatic sketch reproduced in fig. 186, C, was made from the
transverse section of a small twig, slightly less than 2 cm. in its
longest diameter, originally figured by Williamson[366] in 1872.
Earlier in the same year Carruthers[367] published a short account
of the same form based on specimens collected by Mr Butterworth
from the Coal-Measures of Lancashire near Oldham, but both authors
refrained from instituting a new specific name. In a later publication
Williamson spoke of the type as _Lepidodendron macrophyllum_[368].
Williamson’s species has nothing to do with _Lycopodites macrophyllus_
of Goldenberg[369]. The most striking feature of this rare form is
the large size of the leaf-cushions, which are of the _Lepidophloios_
type, in proportion to the diameter of the shoot. The stele consists
of a ring of xylem, all of which is primary in the sections so far
described, enclosing a parenchymatous pith: a Stigmarian rootlet is
shown at _s_.


8. _Lepidodendron Veltheimianum_ Sternb. (General account). Figs. 157,
185, 186, A, B.

  1820. “Schuppenpflanze,” Rhode, Beit. zur Pflanzenkunde der
        Vorwelt, Pl. III. fig. 1.
  1825. _Lepidodendron Veltheimianum_, Sternberg, Flora der Vorwelt,
        Pl. LII. fig. 5.
  1836. _Pachyphloeus tetragonus_, Goeppert, Die fossilen
        Farnkräuter, Pl. XLIII. fig. 5.
  1852. _Sagenaria Veltheimiana_, Goeppert, Foss. Flora des
        Übergangsgebirges, Pls. XVII–XXIV.
  1875. _Lepidodendron Veltheimianum_, Stur, Culm Flora, p. 269, Pls.
        XVIII–XXII.
  1886. _Lepidodendron Veltheimianum_, Kidston, Catalogue of
        Palaeozoic plants, British Museum, p. 160.
  1901. _Lepidodendron Veltheimianum_, Potonié, Silur und Culm Flora,
        p. 116, figs. 72–76.
  1904. _Lepidodendron Veltheimianum_, Zalessky, Mém. Com. Géol.
        Russie, Pl. IV. figs. 4, 5.
  1906. _Lepidodendron Veltheimi_, Potonié, Königl. Preuss. geol.
        Landesanstalt, Lief. III.

The above list may serve to call attention to a few synonyms[370]
of this plant, and to a selection of sources from which full
information may be obtained as to the history of our knowledge of this
characteristic and widely spread Lower Carboniferous type.

_Lepidodendron Veltheimianum_ is represented by casts of stems,
the largest of which hitherto described reaches a length of 5·22
metres with a maximum diameter of 63 cm.; this specimen, figured
by Stur[371], consists of a tapered main axis giving off smaller
lateral shoots, some of which exhibit dichotomous branching. Fig.
185, C and D, represent the external features of a well-preserved
cast and impression respectively. Oblique rows of prominent cushions
wind round the surface of the stem and branches: each cushion is
prolonged upwards and downwards in the form of a narrow ridge with
sloping sides which connects adjacent cushions by an ogee curve. At
the upper limit of the broader kite-shaped portion of the cushion
the ligular pit forms a conspicuous feature; immediately below this
is the leaf-scar with its three small scars,—the lateral parichnos
strands and the central leaf-trace. The two oval areas shown in fig.
185, D, just below the lower edge of the leaf-scars, represent the
parichnos arms which impinge on the surface of the cushions on their
way to the leaves, as explained on a previous page. It is possible
that these areas were visible on the living stem as strands of loose
parenchyma comparable with the lenticel-like pits on the stipules of
_Angiopteris_[372] and the leaf-bases of Cyatheaceous ferns, or it may
be that their prominence in the specimen before us is the result of
the decay of a thin layer of superficial cortex which hid them on the
living tree. Fig. 185, B, illustrates the appearance of a stem in a
partially decorticated condition (_Bergeria_ state). A further degree
of decortication is seen in fig. 185, A, which represents the _Knorria_
condition.

[Illustration: FIG. 185. _Lepidodendron Veltheimianum._ From specimens
  in Dr Kidston’s Collection. (Approximately nat. size.)]

Fig. 157 shows a Ulodendron axis of this species; in the lower part the
specimen illustrates the partial obliteration of the surface features
as the result of the splitting of the outer bark consequent on growth
in thickness of the tree. By an extension of the cracks, shown in an
early stage in fig. 157, the leaf-cushions would be entirely destroyed
and the surface of the bark would be characterised by longitudinal
fissures simulating the vertical grooves and ridges of a Sigillarian
stem. The large stumps of trees shown in the frontispiece to Volume I.
are probably, as Kidston[373] suggests, trunks of _L. Veltheimianum_ in
which the leaf-cushions have been replaced by irregular longitudinal
fissures. In old stems of _Sigillaria_ the enlarged parichnos areas
constitute a characteristic feature (p. 205), but it does not follow
that the absence of large parichnos scars is a distinguishing feature
of all _Lepidodendra_.

In this species, as in others, the form of the leaf-cushion exhibits
a considerable range of variation dependent on the thickness of the
shoot; the contiguous cushions of young branches become stretched apart
as the result of increasing girth of the whole organ, and casts of
still older branches may exhibit very different surface-features[374].
The leaves as seen on impressions of slender branches are comparatively
short, reaching a length of 1–2 cm. It is important to notice that
leafy twigs of this species may bear terminal cones[375] resembling
in form those of _Picea excelsa_ and other recent conifers, though
differing essentially in their morphological features.

The fossil stumps of trees represented in the frontispiece to Volume
I. bear horizontally spreading and dichotomously branched root-like
organs having the characters of _Stigmaria ficoides_[376]. Geinitz has
suggested that _Stigmaria inaequalis_ Göpp. may be the underground
portion of _Lepidodendron Veltheimianum_.

It is unfortunately seldom possible to connect petrified
_Lepidodendron_ cones with particular species of the genus based on
purely vegetative characters, but it is practically certain that we are
justified in recognising certain strobili described by Williamson[377]
from the Calciferous Sandstone series of Burntisland on the Firth of
Forth as those of _Lepidodendron Veltheimianum_. Williamson believed
that the cone which he described belonged to the plant with shoots
characterised by the anatomical features of his species _Lepidodendron
brevifolium_ (= _L. Veltheimianum_), a conclusion which is confirmed by
Kidston[378]. The cone of _L. Veltheimianum_, which reached a diameter
of at least 1 cm. and a length of 4 cm., agrees in essentials with
other species of _Lepidostrobus_; the axis has a single medullated
stele of the same general type as that of the vegetative shoots of
_Lepidodendron fuliginosum_ and _L. Harcourtii_. The sporophylls are
described by Williamson as spirally disposed, and Scott notices that
in some specimens they are arranged in alternate whorls; as in recent
Lycopods both forms of phyllotaxis may occur in the same species. The
heterosporous nature of this strobilus, to which Scott first applied
the name _Lepidostrobus Veltheimianus_, is clearly demonstrated by the
two longitudinal sections contributed by Mr Carruthers and figured by
Williamson in 1893[379].

Each sporophyll, attached almost at right angles to the cone-axis,
bears a radially elongated sporangium seated on the median line of
its upper face; its margins are laterally expanded as a thin lamina;
from the middle of the lower face a narrow keel extends downwards
between two sporangia belonging to a lower series. From the base of a
sporangium a mass of sterile tissue penetrates into the spore-producing
region as in the large sporangia of _Isoetes_ (cf. fig. 191, H, _a_,
and fig. 133, H). The distal and free portion of the sporophylls is
bent upwards as a protecting bract. Some of the sporangia in the upper
part of the cone produced numerous microspores, while 8–16 megaspores
occur in the lower sporangia. The megaspores, having a mean diameter
of 0·8 mm. “quite 40 times the size of the microspores[380],” are
characterised by tubular capitate appendages, and by a conspicuous
three-lobed projection (fig. 191, E)[381] which, as Scott suggests,
may represent the outer spore-wall which has split as the result of
germination. It is not improbable, as shown in fig. 191, I, that this
cap was present before germination. The megaspores represented in fig.
191, I, illustrate their characteristic form as seen in a section of a
megasporangium, _Sm_; the open beak-like portion of the larger spore is
probably the apical region which has split along the three-rayed lines.
These lines form a characteristic feature of both recent and extinct
spores and denote their origin in tetrads. The spore shown in fig. 191,
E[382], illustrates the external features. The apical region of the
prothallus of a megaspore of _Lepidodendron Veltheimianum_ described
by Mr Gordon[383] consists of smaller cells than those occupying the
greater part of the spore-cavity, a differentiation which he compares
with that of the prothallus of _Selaginella_.

[Illustration: FIG. 186.

  A, B. _Lepidodendron Veltheimianum._ (Botany School, Cambridge.)
  C. _Lepidodendron macrophyllum._ (British Museum. No. 377.)
  _x_, Primary xylem; _x_², secondary xylem; _s_, Stigmarian rootlet.]

There can be little doubt that the petrified shoots described by
Williamson[384] from the Calciferous Sandstone beds of Burntisland as
_Lepidodendron brevifolium_ are identical with specimens possessing
the external features of _L. Veltheimianum_. In 1872 Dawson expressed
the opinion that Williamson’s species should be referred to _L.
Veltheimianum_, and evidence subsequently obtained confirms this
view. The stele of this species is of the medullated type, differing
from that of _L. fuliginosum_ and _L. Harcourtii_ in the absence of
prominent ridges on the external surface of the primary xylem, and from
_L. vasculare_ in the possession of a parenchymatous pith. In younger
twigs the cortex consists of fairly homogeneous tissue, but in older
branches there is a greater distinction between a delicate middle
cortex and a stronger outer cortex. Fig. 186, A, represents a stem
in which the vascular cylinder is composed of a primary xylem ring,
_x_, 1·5 mm. broad, succeeded by a zone of secondary wood 1·2 cm. in
breadth. The junction between the primary and secondary xylem is shown
on a larger scale in fig. 186, B. The tissues abutting on the secondary
xylem have not been preserved; the outer cortex, which consists
chiefly of secondary elements, is divided superficially into unequal
ridges corresponding to the leaf-cushions which have been more or less
obliterated as the result of growth in thickness of the stem.


9. _Lepidodendron Pedroanum_ (Carruthers).

In 1869 Mr Carruthers described some specimens of vegetative stems and
isolated sporangia, collected by Mr Plant in Brazil, as _Flemingites
Pedroanus_[385]. From a more recent account published by Zeiller[386]
it is clear that Carruthers’ species is a true _Lepidodendron_; an
examination of the type-specimens in the British Museum confirms this
determination. The contiguous leaf-cushions have rounded angles similar
in form to those of _Lepidodendron Veltheimianum_ and _L. dichotomum_,
but it is not unlikely that the Brazilian plant is specifically
distinct from European species. A figure of one of the specimens on
which Carruthers founded the species is given by Arber[387] in his
_Glossopteris Flora_. The Brazilian plant is chiefly interesting as
affording proof of the existence of _Lepidodendron_ in the southern
hemisphere; the species has also been recognised in South Africa from
material collected by Mr Leslie at Vereeniging[388].

As Zeiller[389] has suggested, it is not improbable that the fossils
described by Renault[390] from Brazil as _Lycopodiopsis Derbyi_ may be
the petrified stems of _Lepidodendron Pedroanum_. The structure of the
central cylinder of Renault’s species is of the type represented by _L.
Harcourtii_; the xylem forms a continuous ring and does not consist of
separate strands of tracheae as Renault believed.


10. _Lepidodendron australe_ (M’Coy). Figs. 187, A–C.

Specimens described under this name are interesting rather on account
of their extended geographical range and geological antiquity than
on botanical grounds. The drawings reproduced in fig. 187 illustrate
the characteristic appearance of this Lower Carboniferous and Upper
Devonian type, as represented by a specimen recently described[391]
from the Lower Karroo (Dwyka) series, which is probably of
Carboniferous age, near Orange River Station, South Africa. The surface
is divided into polygonal or rhomboidal areas (figs. A and B) 8–9 mm.
long and 7–8 mm. broad, arranged in regular series and representing
leaf-scars, comparable with those of _Sigillaria Brardi_ and other
species, or possibly partially decorticated leaf-cushions. A short
distance below the apex of each area there is a more or less circular
prominence or depression (fig. 187, B) and on a few of the areas there
are indications of a groove (fig. A, _g_) extending from the raised
scar to the pointed base, as at _g_, _g_.

[Illustration: FIG. 187. _Lepidodendron australe._ Fig. A, nat. size.]

In examining the graphitic layer on the surface of the South African
specimen shown in fig. 187, A, use was made of a method recently
described by Professor Nathorst[392]. A few drops of collodion were
placed on the surface, and after a short interval the film was removed
and mounted on a slide. The addition of a stain facilitated the
microscopic examination and the drawing of the collodion film. The
cell-outlines (fig. 187, C) on the surface of the polygonal areas
may be those of the epidermis, but they were more probably formed by
a subepidermal tissue; the scar, which interrupts the continuity of
the flat surface, may mark the position of a leaf-base, or, assuming
a partial decortication to have occurred prior to fossilisation, it
may represent a gap in the cortical tissue caused by the decay of
delicate tissue which surrounded the vascular bundle of each leaf in
its course through the cortex of the stem. If the impression were
that of the actual surface of a _Lepidodendron_ or a _Sigillaria_,
we should expect to find traces of the parichnos appearing on the
leaf-scar as two small scars, one on each side of the leaf-bundle.
In specimens from Vereeniging described in 1897[393] as _Sigillaria
Brardi_, which bear a superficial resemblance to that shown in fig. A,
the parichnos is clearly shown. On the other hand, an impression of a
partially decorticated Lepidodendroid stem need not necessarily show
the parichnos as a distinct feature: owing to its close association
with the leaf-trace in the outer cortex, before its separation in the
form of two diverging arms, it would not appear as a distinct gap apart
from that representing the leaf-bundle. The absence of the parichnos
may be regarded as a point in favour of the view that the impression
is that of a partially decorticated stem. Similarly, the absence of
any demarcation between a leaf-cushion and a true leaf-scar such as
characterises the stems of Lepidodendra and many Sigillariae is also
favourable to the same interpretation.

In 1872 Mr Carruthers[394] described some fossils from Queensland,
some of which appear to be identical with that shown in fig. 187
under the name _Lepidodendron nothum_, Unger[395], a species founded
on Upper Devonian specimens from Thuringia. The Queensland plant is
probably identical with Dawson’s Canadian species, _Leptophloeum
rhombicum_[396]. In 1874 M’Coy[397] instituted the name _Lepidodendron
australe_ for some Lower Carboniferous specimens from Victoria,
Australia: these are in all probability identical with the Queensland
fossils referred by Carruthers to Unger’s species, but as the identity
of the German and Australian plants is very doubtful[398] it is better
to adopt M’Coy’s specific designation.

Krasser[399] has described a similar, but probably not specifically
identical, type from China; from Devonian rocks of Spitzbergen
Nathorst[400] has figured, under the name _Bergeria_, an example of
this form of stem, and Szajnocha[401] has described other specimens
from Lower Carboniferous strata in the Argentine.

_Lepidodendron australe_ has been recorded from several Australian
localities[402] from strata below those containing the genus
_Glossopteris_ and other members of the Glossopteris, or, as it has
recently been re-christened, the Gangamopteris[403] Flora.


               viii. _Fertile shoots of_ Lepidodendron.

A. _Lepidostrobus._

The generic name _Lepidostrobus_ was first used by Brongniart[404]
for the cones of _Lepidodendron_, the type-species of the genus being
_Lepidostrobus ornatus_, the designation given by the author of the
genus to a Lepidostrobus previously figured by Parkinson[405] in his
_Organic Remains of a Former World_. The generic name _Flemingites_
proposed by Carruthers[406] in 1865, under a misapprehension as to
the nature of spores which he identified as sporangia, was applied
to specimens of true _Lepidostrobi_. Brongniart also instituted the
generic name _Lepidophyllum_ for detached leaves of _Lepidodendron_,
both vegetative and fertile; the specimen figured by him in 1822 as
_Filicites_ (_Glossopteris_) _dubius_[407], and which was afterwards
made the type-species of the genus, was recognised as being a portion
of the lanceolate limb of a large single-veined sporophyll belonging to
a species of _Lepidostrobus_.

In an unusually large _Lepidophyllum_, or detached sporophyll of
_Lepidostrobus_, in the Manchester University Museum, the free laminar
portion reaches a length of 8 cm.

It is not uncommon to find _Lepidodendron_ preserved in the form of a
shell of outer cortex, which has become separated along the phellogen
from the rest of the stem; as the result of compression the cylinder
of bark may assume the appearance of a flattened stem covered with
leaf-cushions. A specimen preserved in this way was described by
E. Weiss as a cone of _Lomatophloios macrolepidotus_ Gold., and is
quoted by Solms-Laubach and other authors[408] as an example of an
unusually large _Lepidostrobus_. An examination of the type-specimen
in the Bergakademie of Berlin convinced me that Weiss had mistaken
the partially destroyed leaf-cushions for sporophylls, and Stigmarian
rootlets, which had invaded the empty space, for sporangia[409].

In external appearance some species of _Lepidostrobus_ bear a
superficial resemblance to the cone of a Spruce Fir (_Picea excelsa_),
but the surface of a lycopodiaceous strobilus is usually covered by
the overlapping and upturned laminae which terminate the more or less
horizontal sporangium-bearing portion of the sporophyll.

Fig. 188 affords a good example of a long and narrow _Lepidostrobus_.
This specimen from the Middle Coal-Measures of Lancashire has a length
of 23 cm.; like other _Lepidostrobi_ it is borne at the tip of a
slender shoot. The fossil is sufficiently well preserved to show the
characteristic radially elongated form of the large sporangia and the
long and upturned distal portions of the sporophylls.

We may briefly describe _Lepidostrobus_ as follows:—Cylindrical
strobili consisting of an axis containing a single cylindrical stele
which agrees generally with that of the vegetative shoots of _L.
Harcourtii_ and other species. The amount of parenchymatous pith
varies in different forms; in some the primary xylem is almost solid.
The middle cortical region, which has usually been destroyed before
fossilisation, possesses the loose lacunar structure characteristic
of this region in the vegetative branches. The thicker walled outer
cortex is continued at the periphery into crowded, usually spirally
disposed sporophylls, each of which consists of a more or less
horizontal pedicel, which may be characterised by a keel-like median
ridge on its lower surface, while to the central region of the upper
face is attached a large radially elongated sporangium. One of the
chief differences between a _Lepidodendron_ cone and those of the
recent genus _Lycopodium_ is the greater radial elongation of the
sporangia in the former. Some species of _Lepidostrobus_ may have been
homosporous; some are known to be heterosporous. In the latter the
megasporangia borne on the lower sporophylls usually contain several
megaspores as in _Isoetes_ (cf. fig. 133, E). Beyond the distal end of
the sporangium the sporophyll becomes broader in a horizontal plane and
is bent upwards as a lanceolate limb; it may also be prolonged a short
distance downwards as a bluntly triangular expansion.

[Illustration: FIG. 188. _Lepidostrobus._ Middle Coal-Measures,
  Bardsley, Lancashire. From a specimen in the Manchester Museum.
  (½ nat. size.)]

There can be little doubt that the Palaeozoic _Lepidodendra_, like
_Lycopodium cernuum_ (fig. 123) and other recent Lycopods, usually
bore their cones at the tips of slender shoots. The fertile shoot of
_Lepidophloios scoticus_ shown in fig. 160, B, affords one of several
instances supporting this statement; similar examples are figured
by Brongniart[410], Morris[411], and by more recent writers. The
apparently sessile cone figured by Williamson[412] from a specimen in
the Manchester Museum is certainly not _in situ_, but is accidentally
associated with the stem.

The general absence of secondary wood in the steles of _Lepidostrobi_
is, as Dr Kidston[413] points out, consistent with the view that the
cones were shed on maturity and that fertilisation probably took place
on the ground, or perhaps on the surface of the water where the slender
hairs of the megaspores (fig. 191, F, I) may have served to catch the
microspores.

[Illustration: FIG. 189. _Lepidostrobus._ Section through the apical
  region of a cone above the axis. (Manchester University
  Collection.)]

Fig. 189 is an accurate representation of a transverse section,
6 mm. in diameter, of what is no doubt the apical portion of a
_Lepidostrobus_ from the Coal-Measures of Shore, Lancashire. The
section cuts across the upturned free laminae above the level of the
apex of the cone-axis. Each lamina contains a small vascular bundle
composed of a few tracheae and some thin-walled cells surrounded by
delicate mesophyll tissue. Immediately in front of the distal end
of a sporangium a small ligule is borne on the upper face of the
sporophyll (fig. 191, A, B, _l_) occupying the same position as in
_Selaginella_ (cf. fig. 131, F). Strands of vascular tissue pass in a
steeply ascending course from the xylem to the pedicels of sporophylls,
finally curving upwards and ending in the upper limb. Each vascular
bundle consists of a strand of xylem, apparently of mesarch structure,
accompanied by a few layers of parenchyma on its outer face and by
a group of cambiform elements, the whole being enclosed in a sheath
of parenchyma continuous with the inner cortex of the cone axis. The
vascular bundle is accompanied by a parichnos in the outer cortex and
in the sporophyll.

Reference has already been made to the belief on the part of some
palaeobotanists that the large scars of _Ulodendron_ represent
attachment-surfaces of sessile cones, and reasons have been given
against the acceptance of this view.

There is considerable range in the size of _Lepidostrobi_. An
incomplete specimen, 33 cm. long and 6 cm. broad, which may have been
50 cm. in length, is described by Renault and Zeiller[414] from the
Commentry Coal-field. The larger cones afford a striking demonstration
of the enormous spore-output of some species of _Lepidodendron_.

Among the earliest accounts of the anatomy of _Lepidostrobus_ are those
by Hooker[415] and Binney[416]. One of the specimens described by the
former author (fig. 190) affords an interesting example of an unusual
manner of fossilisation; a hollow stem or _Lepidodendron_ is filled
with sedimentary material containing several pieces of _Lepidostrobi_
in an approximately vertical position.

[Illustration: FIG. 190. _Lepidodendron_ stem with _Lepidostrobi_.
  (After Hooker.)

  A. Side-view showing leaf-cushions on the left-hand side and the
     _Knorria_ condition on the right.
  B. View of transverse section; _s_, sections of _Lepidostrobi_.]

The fact that _Lepidostrobi_ usually occur as isolated specimens
renders it impossible in most cases to refer them to particular species
of _Lepidodendron_. Neither external features nor anatomical characters
afford satisfactory criteria by which to correlate vegetative and
fertile shoots; in some measure this is due to the imperfection of
our knowledge as regards the range of structure within the limits of
species; it is also due to lack of information as to the extent to
which the transition from sterile to fertile portions of a shoot is
accompanied by anatomical differences. Prof. Williamson wrote: “I have
for many years endeavoured to discover some specific characters by
which different _Lepidostrobi_ can be distinguished and identified, but
thus far my efforts have been unsuccessful[417].” In a few cases, such
as those mentioned in the description of _Lepidodendron Veltheimianum_
and _L. Wünschianum_, it has been possible to correlate cones and
vegetative shoots.

The most complete account we possess of the anatomy of _Lepidodendron_
cones is that by Mr Maslen[418], who first demonstrated the occurrence
of a ligule on the sporophylls, and thus supplied a missing piece of
evidence in support of the generally accepted view as to the homology
of the sporangium-bearing members and foliage leaves.


i. _Lepidostrobus variabilis_ (Lindley and Hutton).

  1811. “Strobilus,” Parkinson, Organic Remains, Vol. I. p. 428, Pl.
        IX. fig. 1.
  1828. _Lepidostrobus ornatus_, Brongniart, Prodrome, p. 87.
  1831. _L. variabilis_, Lindley and Hutton, Foss. Flora, Pls. X. XI.
  1831. _L. ornatus_, Lindley and Hutton, Foss. Flora, Pl. XXVI.
  1837. _L. ornatus_ var. _didymus_, _Ibid._ Pl. CLXIII.
  1850. _Arancarites Cordai_, Unger, Genera et Spec. Plant. foss. p.
        382.
  1875. _Lepidostrobus variabilis_, Feistmantel, Palaeontographica,
        Vol. LXIII. Pl. XLIV.
  1886. _L. variabilis_, Kidston, Cat. Palaeozoic Plants, p. 197.
  1890. _L. ornatus_, Zeiller, Flor. Valenciennes, p. 497, Pl. LXXVI.
        figs. 5, 6.
  ——    _L. variabilis_, Zeiller, Flor. Valenciennes, p. 499, Pl.
        LXXVI. figs. 3, 4.

Under this specific name are included strobili from Upper Carboniferous
rocks which, in spite of minor differences, may be considered as one
type. The cylindrical cones vary considerably in size, some reaching a
length of 50 cm. or more. The sporophylls are attached by a pedicel,
4–8 mm. long, at right angles to the axis, while the distal portion
forms an oval lanceolate limb 10–20 mm. in length. The sporangia are
4–8 mm. long.

The branched example figured by Lindley and Hutton[419] as a variety
(L. _ornatus_ var. _didymus_) illustrates a phenomenon not uncommon in
both Palaeozoic and recent lycopodiaceous strobili.

[Illustration: FIG. 191. _Lepidostrobus._

  A–D. _L. oldhamius._
  B, C, D. From sections in the Binney Collection, Cambridge.
  E. Megaspore. (After Kidston.)
  F. Megaspore (Coal-Measures, Halifax). (After Williamson.)
  G. Megaspore of _Lepidostrobus foliaceus_. (After Mrs Scott.)
  H. Tangential section of sporangium. (After Bower.)
  I. Part of sporangium wall, _Sm_, of the cone of _Lepidodendron
     Veltheimianum_, enclosing two megaspores. (Cambridge Botany
     School.)]


ii. _Lepidostrobus oldhamius_ Williamson[420]. Fig. 191, A–D.

Williamson[421] instituted this term for strobili previously
described by Binney[422], without adequate evidence, as the cones of
_Lepidodendron Harcourtii_. In shape and in the main morphological
features this type resembles _L. variabilis_, which is however known
only in the form of casts and impressions. A cone of _L. oldhamius_,
2–3 cm. in diameter, possesses a medullated stele consisting of a
ring of primary xylem (fig. 191, D, _x_) with exarch protoxylem and
no secondary elements. Maslen found several short tracheae at the
periphery of the xylem and states that these led him to compare the
cone with the vegetative shoots of _Lepidodendron vasculare_, but
the common occurrence of such elements in different types of shoot
renders them of little or no specific value. The inner cortex is like
that of vegetative shoots of _Lepidodendron_ and the middle cortex,
which was no doubt of the type described in _Lepidostrobus Brownii_,
is represented by a gap in the sections, beyond which is the stronger
outer cortex (fig. 191, D) passing into the horizontal pedicels of the
sporophylls. The section of the axis reproduced in fig. 191, D, was
figured by Binney[423] as _Lepidodendron vasculare_. The leaf-traces,
several of which are seen in the middle cortical region in fig. D,
_lt_, consist of a strand of scalariform tracheae, with a mesarch
protoxylem, succeeded by a few parenchymatous cells; beyond these there
is usually a small gap which was originally occupied by a strand of
thin-walled cells. It is important to note that in one sporophyll-trace
figured by Maslen[424] there is a strand of thin-walled elongated
elements abutting on the xylem, which he describes as phloem. This
tissue is certainly more like true phloem than any which has hitherto
been described in the leaf-traces of vegetative shoots. The state
of preservation is not, however, sufficiently good to enable us to
recognise undoubted phloem features.

In such cones as I have examined no tissue has been seen which shows
the histological features characteristic of the secretory zone of
vegetative shoots: the “phloem” (Maslen) occupies the position in
the sporophyll bundle which in the vascular bundles of foliage
leaves is occupied by a dark-celled and partially disorganised
tissue in continuity with the secretory zone of the main stele. It
may be that in the strobili this tissue occurred in a modified
form, but even assuming that the section figured by Maslen shows
true phloem, an assumption based on slender evidence, this is not
sufficient justification for the application of the term phloem to a
tissue occupying a corresponding position in vegetative shoots and
distinguished by well-marked histological features.

The sporophyll-traces, as seen in the outer cortex in fig. 191, D,
are partially surrounded by a large crescentic space, _p_, which was
originally occupied by the parichnos. The sporangia are attached along
the middle line of the sporophyll and, as in _Lepidostrobus Brownii_,
a cushion of parenchyma projects into the lower part of the sporangial
cavity (fig. 191, A, _a_; C, _a_).

The diagrammatic sketch of part of a section in the Binney Collection
reproduced in fig. 191, B, shows the position of the ligule, _l_. No
megaspores have been discovered in any specimens of this type; the
microspores, which occur both singly and in tetrads, have a length of
0·02–0·03 mm.

The drawing shown in fig. 191, A, based on a section in the Binney
Collection, illustrates the general arrangement of the parts of a
typical _Lepidostrobus_. I have made use of this sketch instead of that
given by Maslen, as his figure conveys the idea that the sporophylls
are superposed, whereas, whether they are verticillate or spiral, a
radial longitudinal section would not cut successive sporangia in the
same plane.


iii. _Lepidostrobus Brownii_ (Brongn.).

In 1843 a specimen of a portion of a petrified cone was purchased by
the British Museum, assisted by the Marquis of Northampton and Robert
Brown, for £30 from a French dealer. This fossil, from an unknown
locality, was briefly described by Brown in 1851[425] and named by him
_Triplosporites_, but in a note added to his paper he expressed the
opinion that the generic designation _Lepidostrobus_ would be more
appropriate. Brongniart afterwards named the cone _Triplosporites_
_Brownii_[426], and Schimper[427] described it in his _Traité_ as
_Lepidostrobus Brownii_. The type-specimen is preserved in the British
Museum and the Paris Museum possesses a piece of the same fossil.

The central axis of the cone has a stele of the type characteristic
of _Lepidodendron fuliginosum_ and _L. Harcourtii_, and the xylem
is surrounded by a thin-walled tissue described by Bower[428] as
possibly phloem; but in the absence of longitudinal sections it is
impossible to say how far the tissue external to the xylem agrees with
that in Lepidodendron stems. The sporophylls consist of a horizontal
portion, to the upper face of which the radially elongated sporangia
are attached, one to each sporophyll; beyond the distal end of the
sporangium the sporophyll bends sharply upwards as a fairly stout
lamina. The wall of the sporangium is composed of several layers of
cells, as shown in a drawing published by Bower[429]; in the interior
occur groups of microspores, and from a ridge of tissue which extends
along the whole length of the sporangium irregular trabeculae of
sterile tissue project into the sporangial cavity, as in _Isoetes_
(fig. 191, H: cf. fig. 133, H).

Further information in regard to _Lepidostrobus Brownii_ has recently
been supplied by Prof. Zeiller[430], who recognises the existence of a
ligule, and draws attention to some interesting histological features
in the tissue of the sporophylls[431].


_Spores of Palaeozoic Lycopodiales._

The calcareous nodules from the Coal seams of Yorkshire and Lancashire
are rich in isolated spores, many of which are undoubtedly those of
_Lepidostrobi_. Examples of spores were figured by Morris[432] in 1840,
and their occurrence in coal has been described by several authors,
one of the earliest accounts being by Balfour[433]. The drawings of
Palaeozoic and recent spores published by Kidston and Bennie[434]
demonstrate a striking similarity between the megaspores of existing
and extinct Lycopods, the chief difference being the larger size of the
fossils.

The general generic name _Triletes_, originally used by Reinsch[435],
is a convenient term by which to designate Pteridophytic spores which
cannot be referred to definite types.

It is usual to find more than four megaspores in each megasporangium
in Palaeozoic and not infrequently, as we have seen, in Mesozoic
lycopodiaceous strobili, but in some Palaeozoic cones, e.g.
_Bothrostrobus_ (fig. 216) and _Lepidostrobus foliaceus_[436], a single
tetrad only appears to have reached maturity.

The occurrence of long simple or branched and sometimes capitate hairs
is a common feature of Carboniferous megaspores (fig. 191, E, F, I).
It is possible that these appendages served to catch the microspores,
thus facilitating fertilisation. A peculiar form of megaspore has
been described by Mrs Scott[437], and assigned by her to _Lepidostrobus
foliaceus_, the megasporangium of which apparently contained only
four spores. As shown in fig. 191, G, a large bladder-like appendage
characterised by radiating veins is attached to the thick spore-coat;
it is suggested that this excrescence may be compared with the
“swimming” apparatus of the recent water-fern _Azolla_. The epithet
swimming which it is customary to apply to the appendages of _Azolla_
megaspores would seem to be inappropriate if Campbell[438] is correct in
stating that spores of _Azolla_ are incapable of floating.


B. _Spencerites._

_Spencerites insignis_ (Williamson). Fig. 192.

  1878. _Lepidostrobus sp_., Williamson, Phil. Trans. R. Soc., p.
        340, Pl. XXII.
  1880. _Lepidostrobus insignis_, Williamson, Phil. Trans. R. Soc.,
        p. 502, Pl. _XV_. figs. 8–12.
  1889. _Lepidodendron Spenceri_, Williamson, Phil. Trans. R. Soc.,
        p. 199, Pl. VII. figs. 20–22; Pl. VIII. fig. 19.
  1897. _Spencerites insignis_, Scott, Phil. Trans. p. 83, Pls.
        XII–XV.

Another type of lycopodiaceous strobilus, differing sufficiently from
_Lepidostrobus_ to deserve a special generic designation, is that
originally described by Williamson[439], from the Lower Coal-Measures
of Yorkshire, as a type of _Lepidostrobus_, _L. insignis_, but
afterwards[440] more fully investigated and assigned to a new genus
by Scott[441]. It should be pointed out that in a later publication
Williamson spoke of the lycopodiaceous axis, which he suspected might
belong to his _L. insignis_, as possibly worthy of recognition as a
distinct generic type.

[Illustration: FIG. 192. _Spencerites insignis_ (Williamson). (After
  Miss Berridge.)]

Of the two species included by Scott in his genus _Spencerites_ only
one, _S. insignis_, need be considered. Since the publication of
Scott’s paper our knowledge of this type has been extended by Miss
Berridge[442] and by Prof. Lang[443].

The axis of the strobilus has a stele characterised by a pith
of elongated elements, most of which have thin walls; the xylem
cylinder possesses about twenty protoxylem strands forming more or
less prominent exarch ridges. The cortex exhibits a differentiation
comparable with that in the shoots of _Lepidodendron_. The sporophylls
are arranged in alternating verticils, each whorl consisting of ten
members: the narrow horizontal pedicel of a sporophyll, containing a
single vascular bundle, as shown in fig. 192, is expanded distally
into a prominent upper lobe bearing a cushion of small and delicate
cells, to which the sporangium is attached, and prolonged obliquely
upwards as a free leaf-like lamina. The lower blunt prolongation of
the sporophylls appears to form a thick dorsal lobe, but, as Lang has
pointed out, it is highly probable that the present form of the dorsal
lobe is of secondary origin, and is “due to the disappearance of a
mucilage cavity from a large sporophyll base[444].” As Miss Berridge
remarks, the vascular bundle of the sporophyll does not give off a
branch to the ventral lobe and sporangium. In attachment, in shape, and
in the structure of the wall the sporangia differ markedly from those
of _Lepidostrobi_. The spores, which also constitute a characteristic
feature of the genus, have a maximum diameter of 0·14 mm.; they are
described as oblate spheroids with a broad hollow wing running round
the equator (fig. 192) comparable with the air-sacs of the pollen
of _Pinus_. Scott points out that the spores of _Spencerites_ are
intermediate in size between the microspores of _Lepidodendron_ and
the megaspores of _Lycopodium_; it is difficult therefore to decide
to which category they should be referred. _Spencerites_ is clearly
distinct from _Lepidostrobus_; the absence of a ligule, the manner of
attachment of the sporangia, and the form and size of the spores, are
characteristic features.

A comparison of _Spencerites_ with the strobili of _Lycopodium cernuum_
(figs. 123, 126–129) has recently been made by Lang, who draws
attention to the striking agreement as regards general plan and even
detailed structural features between the Palaeozoic and the recent
type of strobilus. It is interesting to find, as Lang points out, that
in the original account of the fossil cone by Williamson, the view
is expressed that the sporangiophores were confluent. An examination
of the section figured by Williamson[445] led Lang to confirm this
opinion. It would be out of place to enter here into a detailed
comparison of _Spencerites insignis_ and the cone of _Lycopodium_,
but the resemblances are considered by Lang to be sufficiently
close to suggest that the striking similarity may be indicative of
relationship[446].

It is worthy of notice that the radial section of _Spencerites_ (fig.
192) presents a fairly close resemblance to a corresponding section
through a cone-scale of _Agathis_ (Kauri Pine)[447]. In each case the
megasporangium is attached by a narrow pedicel to the sporophyll and
the latter has a similar form in the two plants, though the extent of
the resemblance is somewhat lessened by Lang’s more complete account
of the Palaeozoic type. If the _Spencerites_ sporangia possessed an
integument the similarity with the _Agathis_ ovule would of course be
much closer: recent palaeobotanical investigations have shown that
ovules and sporangia are not separated by impassable barriers.

[Since this Chapter was set up in type a paper has appeared by Dr Bruno
Kubart on a new species of _Spencerites_ spore, _S. membranaceus_,
from the Ostrau-Karwiner Coal-basin (Austria). The spores are larger
than those of _S. insignis_ and in some the cells of a prothallus are
preserved. Kubart figures a section of a spore containing a group
of seven cells, a central cell, which he regards as an antheridial
mother-cell, surrounded by six wall-cells. Kubart (90).]




                             CHAPTER XVI.

                             =Sigillaria.=


                             i. _General._

In view of the close resemblance between _Lepidodendron_ and
_Sigillaria_, another lycopodiaceous plant characteristic of
Carboniferous and Permian floras, a comparatively brief description of
the latter genus must suffice, more particularly as _Lepidodendron_
has received rather an undue share of attention. _Sigillaria_,
though abundantly represented among the relics of Palaeozoic floras,
especially those preserved in the Coal-Measures, is rare in a petrified
state, and our knowledge of its anatomy is far from complete. In
external form as in internal structure the difference between the two
genera are not such as enable us to draw in all cases a clearly defined
line of separation.

In the _Antediluvian Phytology_, Artis[448] figured a fossil from the
Carboniferous sandstones of Yorkshire which he called _Euphorbites
vulgaris_ on account of a superficial resemblance to the stems of
existing succulent Euphorbias. Rhode[449] also compared Sigillarian
stems with those of recent _Cacti_. The specimen described by Artis
is characterised by regular vertical and slightly convex ribs bearing
rows of leaf-scars in spiral series, like those on the cushions of
_Lepidodendron_. A few years earlier Brongniart[450] had instituted the
genus _Sigillaria_[451] for plants with ribbed but not jointed stems
bearing “disc-like impressions” (leaf-scars) disposed in quincunx; the
type-species named by the author of the genus _Sigillaria scutellata_
is identical, as Kidston[452] points out, with _Euphorbites vulgaris_
of Artis and with the plant afterwards figured by Brongniart as _S.
pachyderma_[453]. Brongniart in 1822 figured another type of stem
characterised by the absence of ribs and by prominent spirally arranged
cushions bearing relatively large leaf-scars like the upper part of
the specimen shown in fig. 203; this he named _Clathraria Brardii_, a
well-known and widely distributed Carboniferous and Permian species
now spoken of as _Sigillaria Brardi_ (figs. 196, A–C; 203). A third
type of stem figured by Brongniart as _Syringodendron striatum_[454]
agrees with _Sigillaria scutellata_ in having ribs, but differs in the
substitution of narrow oval ridges or depressions for leaf-scars; this
is now recognised as a partially decorticated _Sigillaria_, in which
the vascular bundle of each leaf is represented by a narrow ridge or
depression. The name _Syringodendron_, originally used by Sternberg, is
conveniently applied to certain forms of Sigillarian stems which have
lost their superficial tissues. A fourth generic name, _Favularia_, was
instituted by Sternberg[455] for Sigillarian stems with ribs covered
with contiguous leaf-scars of hexagonal form and prominent lateral
angles (fig. 193, A; fig. 200, G).

[Illustration: FIG. 193.

  A. _Sigillaria elegans_ Brongn.
  B. _Sigillaria rugosa_ Brongn. Middle Coal-Measures.
  C. _Omphalophloios anglicus_ Kidst. Barnsley.
  D. _Sigillaria elegans_ Brongn.
  E. _Sigillaria tessellata_ Brongn.

  (A, B, C, E, about ¾ nat. size. Dr Kidston’s Collection.)]

The generic or sub-generic title _Rhytidolepis_, also instituted
by Sternberg, is applied to ribbed Sigillarian stems such as _S.
scutellata_, _S. rugosa_ (fig. 193, B), _S. mammillaris_ (fig. 195),
or _S. laevigata_ (fig. 196, D). Goldenberg[456] proposed the name
_Leiodermaria_ for smooth Sigillarian stems with leaf-scars not in
contact with one another (fig. 196, C).

The shoot system of _Sigillaria_ consisted of a stout stem tapering
upwards to a height of 100 feet[457] or more as an unbranched column,
with its dome-shaped apex[458] covered with linear grass-like
leaves or, in some species, such as _Sigillaria Brardi_[459], _S.
Eugenii_[460], etc., the main trunk was occasionally divided by
apparently equal dichotomy. The younger portions of the stem or
branches were in some species clothed with leaves separated by a narrow
zigzag groove surrounding their hexagonal bases, while in other
forms each leaf was seated on a more or less prominent cushion having
the form illustrated by _Sigillaria McMurtriei_ (fig. 194) or by the
example represented in fig. 200, H; or as in the ribbed species shown
in figs. 193, B, and 195, the leaves in vertical series were separated
from one another by longer portions of the ribs. As in _Lepidodendron_
the cushions are frequently characterised by irregular transverse
wrinklings and other[461] surface-ornamentation which in some instances
at least may have been produced as the result of _post-mortem_
shrinkage of superficial tissue. From the rarity of shoots with the
foliage attached, it would seem that the leaves persisted for a
comparatively short time and were cut off by an absciss-layer leaving
behind a well-marked leaf-scar area. The linear leaves, reaching in
rare cases a length of one metre (e.g. _S. lepidodendrifolia_) but
usually much shorter, possessed a single median bundle, and the lower
face was characterised by two stomatal grooves and a median keel. It is
not uncommon to find leaf-bases of _Sigillaria_ detached from the stem
and preserved as separate impressions. The term _Sigillariophyllum_
used by Grand’Eury[462] may be applied to detached leaves, though it
is by no means easy to distinguish between the foliage of _Sigillaria_
and _Lepidodendron_. A comparison of a typical species of _Sigillaria_,
such as _S. rugosa_ (fig. 193, B) or _S. Brardi_ (fig. 196, A–C) with
a typical _Lepidodendron_ reveals obvious differences in the form of
the leaf-cushion, but in some cases the distinction becomes purely
arbitrary.

[Illustration: FIG. 194. _Sigillaria McMurtriei_ Kidst. From a
  specimen from the Upper Coal-Measures of Radstock, in the British
  Museum (V. 952). Nat. size.]

[Illustration: FIG. 195. _Sigillaria mammillaris._ (Rhytidolepis
  form.) From a specimen in the Manchester Museum. _p_, parichnos;
  _l_, ligule-pit; _t_, leaf-trace; _c_, cushion; _s_, leaf-scar.]

[Illustration: FIG. 196.

  A–C. _Sigillaria Brardi._ (A after Germar; B, C after Zeiller.)
  D. _Sigillaria laevigata._
  E. _Lepidodendron Wortheni_ (D and E after Zeiller).]

Immediately above the centre of the upper boundary of a Sigillarian
leaf-scar a ligule pit may often be detected, as shown in fig. 195,
_l_, and in some cases, e.g. a specimen figured by Germar[463] (fig.
196, A) as _Sigillaria spinulosa_ (identical with _S. Brardi_), some
circular scars with a central pit surrounded by a raised rim occur
on the surface of the stem, either singly or in pairs, near the
leaf-scars; these, it is suggested, may represent the position of
adventitious roots or, as Germar thought, of some deciduous spinous
processes. The leaf-scars are frequently hexagonal in shape, with the
lateral angles either rounded (fig. 200, F) or sharply pointed (fig.
200, G, H); each scar bears three smaller scars as in _Lepidodendron_,
a central circular, oval or crescentic leaf-trace scar and larger oval
or slightly curved scars formed by the two parichnos arms (fig. 195,
_p_). The larger size of the parichnos arms, the individual cells of
which may often be detected as a fine punctation, is a distinguishing
feature of the genus, but otherwise the structure is very similar to
that in _Lepidodendron_. As shown in figs. 195, 200, F, G, the three
scars may occur nearer the upper than the lower margin of the leaf-base
area.

_Lepidodendron Wortheni_[464] (fig. 196, E), described from North
America by Lesquereux[465], by Zeiller[466] from France, and by
Kidston[467] from the Upper and Middle Coal-Measures of England,
may be quoted as a _Lepidodendron_ bearing a close resemblance to
_Sigillaria_. The shoots bear cushions two or three times as long
as broad and without the usual median division, but with numerous
irregular and discontinuous transverse wrinklings. _Lepidodendron
Peachii_ Kidston[468] affords another example of a form agreeing both
with _Sigillaria_ and with _Lepidodendron_. An Upper Devonian type
described by White[469] as _Archaeosigillaria primaeva_ affords a
striking instance of the combination on one stem of Sigillarian and
Lepidodendroid leaf-cushions.

The difference between the original surface of a Sigillaria stem and
that of partially decorticated specimens is seen in figs. 196, C and
D; in fig. C the bark of _Sigillaria Brardi_ shows the characteristic
wrinklings of the superficial tissue, while at a slightly lower level
the leaf-scars are replaced by the parichnos casts, a, and fine
longitudinal striations represent the elongated phelloderm cells laid
bare by the exfoliation of the surface-layers. Similarly, in the rib
of _Sigillaria laevigata_ (fig. 196, D) the parichnos arms, _p_, and
the longitudinal striations are exposed at the lower level, while the
surface is smooth and bears rows of widely separated leaf-scars.

[Illustration: FIG. 197. _Carica sp._ From the Royal Gardens, Kew.
  (Much reduced.) M.S.]

The older part of a Sigillarian stem may present an appearance very
different from that of the younger shoots. The leaf-cushions may be
stretched apart as the result of elongation and increase in girth,
while in some cases the arrangement of the leaf-scars may vary on the
same axis as the result of inequalities in growth or changing climatic
conditions. The contiguous arrangement of the leaf-scars and narrow
cushions characteristic of the Clathrarian form of stem, as was first
demonstrated by Weiss[470], and afterwards illustrated by Zeiller[471]
and Kidston, may be gradually replaced (on the same specimen) by a more
distant disposition of the leaf-scars separated by a smooth intervening
surface of bark. The specimen of _S. Brardi_ reproduced in part in
fig. 203, and first figured by Kidston, affords an example of three
“species” on one piece of stem, _S. Brardi_ Brongn., _S. denudata_
Goepp. and _S. rhomboidea_ Brongn.[472]

The piece of _Carica_ stem, represented in fig. 197, illustrates the
danger of trusting to the disposition of leaves as a specific criterion.

Similarly, in the ribbed forms the degree of separation of the
leaf-scars is by no means uniform in a single species[473]. Some
authors have adopted a two-fold classification of Sigillarian stems
proposed by the late Prof. Weiss[474] of Berlin, who divided the
Sigillariae into (A) Sub-Sigillariae, comprising Leiodermariae and
Cancellatae, and (B) Eu-Sigillariae, including _Favulariae_ and
_Rhytidolepis_. Grand’Eury[475] adopts the terms _Rhytidolepis_ and
_Leiodermaria_ for ribbed and smooth stems respectively, the type to
which the name _Clathraria_ was applied by Brongniart being in some
cases at least the young form of Leiodermarian stems. While recognising
the artificial distinction implied by such terms as _Rhytidolepis_,
_Leiodermaria_, and other sub-generic titles, we may conveniently speak
of the two main types of _Sigillaria_ stems as ribbed and smooth.

Still older stems of _Sigillaria_ are not uncommon from which the
leaf-scars and other superficial tissues have been exfoliated,
leaving exposed a longitudinally fissured surface of secondary cortex
characterised by pairs of considerably enlarged parichnos strands
(fig. 198) which are sometimes partially or wholly fused into one
(_Syringodendron_ state of _Sigillaria_). The single or double nature
of the elliptical or circular parichnos areas is doubtless due to the
degree of exfoliation, which may extend sufficiently deep into the
cortex to reach the level of the parichnos before the single strand has
bifurcated (cf. _Lepidodendron_, p. 100). In the Museums of Manchester,
Newcastle, and other places casts of large Sigillaria stems may be
seen, which illustrate the differences in breadth and regularity of
the vertical ribs, and in the size and shape of the parichnos areas
in different regions of a partially decorticated stem. A cast of a
ribbed species in the Manchester Museum, having a length of 185 cm.
and a breadth of 56 cm., shows in the upper portion straight vertical
grooves and broad ribs bearing pairs of parichnos scars 11 mm. long;
in the lower portion the ribs tend to become obliterated and the
parichnos scars, 2 cm. in length, may be partially fused and arranged
in much less regular vertical series. A feature of these older ribbed
Sigillarian stems is the increase in the number of the ribs from below
upwards. Kidston[476] has described a specimen in the Sunderland
Museum, 6 feet 6 inches long, with a circumference at the slightly
bottle-shaped base of 5 feet. On the lower portion of the stem there
are 29 broad ribs; about one-third the height many of these bifurcate,
producing as many as 40 ribs in the upper part where the cast has a
circumference of 3 feet. The increase in number of the ribs is due in
part to bifurcation, but also to the intercalation of new ones. As
Kidston points out, this example shows that as a stem grew in length
additional leaves were developed at the apex. A similar stem, which
illustrates very clearly the increase in the number of ribs from below
upwards, may be seen in the Newcastle Museum.

Grand’Eury[477] has described an example of an old stem of a ribless
species of _Sigillaria_, _Syringodendron bioculatum_, bearing single
and double parichnos areas of nearly circular form and with a
diameter of 1–2 cm. In a specimen figured by Renault and Roche[478]
(_Syringodendron esnostense_) from the Culm strata in France, the
parichnos scars reach a length of 3 cm. As seen in the fragment of a
ribbed _Sigillaria_ represented in fig. 198, the large parichnos areas
exhibit a distinct surface pitting in contrast to the fine longitudinal
striation of the rib; the difference in surface-appearance is due to
the nature of the tissue, which in the parichnos consists of fairly
large parenchymatous elements with groups of secretory cells[479], and
in the exposed cortex of elongated elements. The vertical line in the
middle of fig. 198, which occurs in the middle of the rib, has probably
been formed by splitting of the bark.

[Illustration: FIG. 198. _Sigillaria_ with large parichnos areas. (⅓
  nat. size.) M.S.]

Grand’Eury’s description of fossil forests of Sigillariae in the
rocks of the St Étienne[480] district affords a striking picture of
these arborescent Pteridophytes; he speaks of the stems of some of
the trees as swollen like a bottle at the base, characterised by the
Syringodendron features and terminating below in short repeatedly
forked roots of the type known as _Stigmariopsis_. Other specimens
of _Sigillaria_ stumps show a marked decrease in girth towards the
base; this tapered form is regarded by Grand’Eury as the result of the
development of aerial columnar stems from underground rhizomes.

The nature of the root-like organs of _Sigillaria_ is dealt with in the
sequel: a brief reference may, however, be made to the occurrence of
stumps of vertical trunks which pass downwards into regularly forked
and spreading arms. These arms lie almost horizontally in the sand or
mud like the underground rhizomes of _Phragmites_ and other recent
plants growing in swampy situations where water is abundant and where
deeper penetration of the soil would expose them to an insufficient
supply of oxygen[481]. It is certain that _Sigillaria_ had no tap-root,
but was supported on spreading subterranean organs bearing spirally
disposed long and slender rootlets which absorbed water from a swampy
soil.

[Illustration: FIG. 199. Partially decorticated stem of _Sigillaria_
  showing two zones of cone-scars. From a cast in the Sedgwick
  Museum, Cambridge. M.S. (⅕ nat. size.)]

The regularity of the leaf-scar series on a Sigillarian stem may be
interrupted by the occurrence of oval scars with a central scar and
surrounding groove (fig. 193, E); these occur in zones at more or less
regular intervals on the stem, as seen in the partially decorticated
cast represented in fig. 199. Zeiller has pointed out that the rows of
oval or circular scars, which mark the position of caducous stalked
strobili, may occur between the leaf-scars in vertical series, each of
which may include as many as 20 scars, while in other cases a single
series of such cone-scars may encircle the stem[482]. The zones are
usually of uneven breadth, as in _S. Brardi_, and their occurrence
produces some deformation of the adjacent leaf-scars.

By the earlier writers _Sigillaria_ was compared with succulent
Euphorbias, Cacti, and Palms; Brongniart[483] at first included
undoubted Sigillarian stems among Ferns, but after investigating
an agatized stem from Autun, he referred _Sigillaria_ to the
Gymnosperms[484] on the ground that it had the power of producing
secondary wood. It was then supposed that _Lepidodendron_ possessed
only primary xylem, and that the presence of a vascular meristem in
_Sigillaria_ necessitated its separation from the lycopodiaceous genus
_Lepidodendron_ and its inclusion in the higher plants. By slow degrees
it was recognised, as in the parallel case of the genus _Calamites_,
that the presence or absence of secondary vascular tissue is a
character of small importance. Williamson, whose anatomical researches
played the most important part in ridding the minds of palaeobotanists
of the superstition that secondary growth in thickness is a monopoly
of the Phanerogams, spoke in 1883 of the conflict as to the affinities
of _Lepidodendron_ and _Sigillaria_ as virtually over but leaving
here and there “the ground-swell of a stormy past[485].” In 1872
the same author had written: “If then I am correct in thus bringing
the Lepidodendra and Sigillariae into such close affinity, there is
an end of M. Brongniart’s theory, that the latter were gymnospermous
exogens, because the cryptogamic character of the former is disputed by
no one; we must rather conclude as I have done that the entire series
represents, along with the Calamites, an exogenous group of Cryptogams
in which the woody zone separated a medullary from a cortical
portion[486].”

In 1879 Renault[487] expressed the opinion that Brongniart by his
investigation of the anatomy of _Sigillaria elegans_ had established in
a manner “presque irréfutable” that _Sigillaria_ must be classed as a
Gymnosperm showing affinity with the Cycads.

In 1855 Goldenberg[488] described some strobili which he regarded as
those of _Sigillaria_ and recognised their close resemblance to a
fertile plant of _Isoetes_. He was led to the conclusion, which had
little influence on contemporary opinion, that _Sigillaria_ is related
to _Isoetes_ and must be classed among Pteridophytes. To these long
and narrow strobili Schimper gave the name _Sigillariostrobus_[489].
In 1884 Zeiller[490] supplied confirmation of Goldenberg’s view by
the discovery of cones borne on pedicels with Sigillarian leaf-scars,
thus demonstrating the generic identity of cones and vegetative
shoots, which Goldenberg had connected on the evidence of association.
Zeiller’s more recent work[491] and the still later researches of
Kidston[492] have added considerably to our knowledge of the morphology
of Sigillarian cones. Grand’Eury’s remark made so recently as 1890[493]
that opinion in regard to the Gymnospermous nature of _Sigillaria_ is
losing ground every day, bears striking testimony to the pertinacity
with which old beliefs linger even in the face of overwhelming proof of
their falsity.

It is remarkable, in view of the abundance of vegetative shoots,
how rarely undoubted Sigillarian strobili have been found; this
may, however, be in part due to a confusion with Lepidostrobi
which so far as we know do not differ in important respects from
Sigillariostrobi[494].

There can be no doubt that _Sigillaria_ usually produced its cones
on slender pedicels which bore a few leaves or bracts in irregular
verticils, or in short vertical series on comparatively stout stems, an
arrangement reminding us of the occurrence of flowers on old stems of
_Theobroma_ and other recent Dicotyledons. As Renault[495] pointed out
the fertile shoots are axillary in origin.

Dr Kidston[496] is of opinion that certain species of _Sigillaria_
bore cones sessile on large vegetative shoots characterised by two
opposite rows of cup-like depressions like those in the Ulodendron
form of _Lepidodendron Veltheimianum_ (fig. 157). He has described
the Ulodendron condition of two species, _Sigillaria discophora_
(König) and _S. Taylori_ (Carr.); the cup-like depressions may have a
diameter of several centimetres and are distinguished from those of
_Bothrodendron_ by the almost central position of the umbilicus. The
specimens which he figures as _S. discophora_ are identified by him
with the stem figured by König as _Lepidodendron discophorum_ and by
Lindley and Hutton[497] as _Ulodendron minus_. We have already dealt
with the nature of Ulodendron shoots, expressing the opinion that in
spite of the often quoted specimen described by D’Arcy Thompson[498],
in which a supposed cone occurs in one of the cups, there is no
satisfactory case of any undoubted cone having been found attached to
the large Ulodendron scars. It is more probable that the Ulodendron
depressions represent the scars of branches, either elongated axes,
or possibly in some cases deciduous tuberous shoots which served as
organs of vegetative reproduction. A specimen figured by Kidston as
_Sigillaria Taylori_ from the Calciferous sandstone of Scotland[499]
bears a row of slightly projecting “appendicular organs” attached to a
Ulodendron axis; but these furnish no proof of their strobiloid nature.
The main question is, are these Ulodendron shoots correctly identified
by Kidston as Sigillarian? The surface of the specimens shows crowded
rhomboidal scars surrounded in some cases by a very narrow border
or cushion; the general appearance is, as Kidston maintains, like
that of _Sigillaria Brardi_ in which the leaf-scars are contiguous
(e.g. fig. 203, upper part). None of the leaf-scars exhibit the three
characteristic features, the leaf-trace and parichnos scars, but only
one small scar appears on each leaf-base area. In a more recent paper
Kidston figures a small piece of a stem from Kilmarnock, which he
identifies as _Sigillaria discophora_, showing the three characteristic
scars on the leaf-base area. There is no doubt as to the Sigillarian
nature of this specimen, but it is not clear if the piece figured is
part of a Ulodendron shoot[500].

Prof. Zeiller[501] retains the older name _Ulodendron minus_ Lind.
and Hutt. in place of König’s specific designation and dissents
from Kidston’s identification of _Ulodendron minus_ and _U. majus_
of Lindley and Hutton as one species; he is also inclined to refer
these Ulodendron axes to _Lepidodendron_. In spite of the superficial
resemblance to _Sigillaria_ of the specimens described by Kidston,
and which I have had an opportunity of examining, I venture to regard
their reference to that genus as by no means definitely established.
We must recognise the difficulty in certain cases of drawing any
satisfactory distinction between _Sigillaria_ and _Lepidodendron_ based
on external features, and while giving due weight to the conclusions
of so experienced a palaeobotanist as my friend Dr Kidston, I venture
to think we are not in a position to state with confidence that
_Sigillaria_ possessed Ulodendron shoots.


                             ii. _Leaves._

The leaves of _Sigillaria_ agree closely with those of _Lepidodendron_;
they are either acicular (fig. 200, D) like Pine needles or broader
and flatter like the leaves of _Podocarpus_. Their attachment to
comparatively thick branches[502] shows that they persisted, in some
cases at least, for several years as in _Araucaria imbricata_. The
lower surface of the lamina was characterised by a prominent keel (fig.
142, A and C) which dies out towards the apex; on either side of it
are well-defined stomatal grooves (figs. 142, _g_, _g_; 143, A; 200,
D, _g_). The upper face may be characterised by another groove (fig.
142, B) but without stomata. The occurrence of the stomatal grooves,
the abundance of transfusion tracheae (fig. 142, _t_) surrounding
the vascular bundle, and the presence of strengthening hypodermal
tissue suggest that the leaves of _Sigillaria_ were of a more or less
pronounced xerophilous type and had a fairly strong and leathery
lamina. The mesophyll tissue consists either of short parenchymatous
cells or of radially elongated palisade-like elements and has the
loose or lacunar arrangement characteristic of the aerating system in
recent leaves; the slight development or absence of palisade-tissue may
indicate exposure to diffuse light of no great intensity.

In most species there is a single vein, but in others the xylem forms
a double strand (fig. 142, B). Sections of the lamina near the apical
region present a more circular form, owing to the gradual obliteration
of the upper groove and lower keel and to the dying out of the stomatal
grooves.

The transverse section of the leaf diagrammatically represented in
fig. 142, A, A′, shows the two stomatal grooves, _g_, and a prominent
keel; the single vein consists of a small group of primary tracheae,
_x_, some delicate parenchyma, and a brown patch of imperfectly
preserved tissues, _a_, resembling the secretory zone tissue of a
_Lepidodendron_. The whole is surrounded by a sheath of rather wide
and short thinner-walled spiral or reticulate tracheids, which may
be spoken of as transfusion tracheae, _t_, and compared with similar
elements in the leaves of many recent Conifers. To this tissue Renault
applies the epithet “water-bearing” and it is very likely that this
may have been its function. The shaded portions of the lamina, in fig.
142, A, represent the distribution of thicker-walled hypodermal tissue.
The section of a leaf 3 mm. wide shown in fig. 142, C, shows an almost
identical structure; the transfusion tracheae are richly developed
especially on the sides and lower surface of the vascular strand.
This leaf occurs in association with a petrified stem of _Sigillaria
scutellata_[503].

[Illustration: FIG. 200.

  A. _Sigillaria Brardi_ [= _S. elegans_ Brongn. (39)]. Transverse
     section of stem.
  B. _Sigillaria Brardi_ [= _S. spinulosa_, Renault and Grand’Eury
     (75)]: _c_³, outer cortex; _x_, _x_², xylem. (After Renault
     and Grand’Eury.)
  C. _S. Brardi_, primary xylem element. (A and C after Brongniart.)
  D. Leaf of _Sigillaria Brardi_: _g_, _g_, stomatal grooves; _ep_,
     piece of epidermis of stem. (After Renault.)
  E. _Sigillaria Brardi._ Tangential section of leaf-bases: _p_,
     parichnos. (After Renault.)
  F, G, H. Sigillaria leaf-scars and cushions. (After Weiss.)]

Renault[504] has shown that the leaf-traces of _Sigillaria spinulosa_
(= _S. Brardi_) are accompanied in the outer cortical region of the
stem by a fairly large amount of secondary xylem; in sections of the
free lamina which he figures the secondary elements are much less
obvious and represented by a few tracheae only. Similarly, in the
leaf-base of _S. Brardi_ (fig. 200, E) the xylem consists of both
primary and secondary elements (_x_, _x_²), but in the lamina the
latter is poorly if at all represented. In the lamina of the leaves
of _S. Brardi_ the primary xylem forms a narrow slightly curved band
with two lateral groups of narrower, presumably protoxylem elements;
this is surrounded by delicate parenchyma styled by Renault, on very
slender evidence, phloem (“liber”). Some dark cells below the xylem are
described as sclerous tissue, and surrounding the bundle is a sheath of
transfusion tracheae (dotted area in fig. 200, E). It is possible that
the elements spoken of with hesitation by Renault as secondary xylem
are transfusion tracheae.

There has probably been some confusion in the minds of authors between
sclerous tissue and dark secretory tissue in Sigillarian leaves; the
crescentic band, _a_, shown in fig. 142, B, which corresponds in
position with the sclerous tissue of Renault in _S. Brardi_ leaves,
appears to be of the nature of secretory tissue.

The diagram shown in fig. 142, B, illustrates a type of leaf very like
those already described, except that there are two xylem strands, _x_.
The difference between the double strand and the single bundle seen in
figs. 142, A, C and 200 E, is comparatively small, but it is a real
distinction. This type of leaf (fig. 142, B) was originally described
by Renault[505] under the generic title _Sigillariopsis_. The genus was
founded on a French petrified specimen consisting of part of a ribbed
stem possessing a stele of the Sigillarian type and characterised by
separate primary xylem strands, like those of _S. Brardi_ described
by Brongniart in 1839. Renault considered the presence of two xylem
strands in the leaf a sufficient reason for the institution of a new
genus and named the specimen _Sigillariopsis Decaisnei_. Prof. Bertrand
of Lille kindly photographed for me Renault’s type-specimen and sent
several prints with explanatory notes. The transverse section of the
leaves shows very clearly the two xylem strands; each strand consists
of a triangular group of primary tracheae with the protoxylem apex
pointing towards the lower surface of the lamina. Below each primary
strand of centripetal xylem is an arc composed of a few small tracheae
which Renault and Bertrand describe as secondary xylem; it is, however,
not clear from the photomicrographs that these are of secondary origin,
their position and appearance reminding one of the primary centrifugal
xylem of a cycadean foliar bundle. Below this centrifugal xylem is
another arc of imperfectly preserved elements described by Renault as a
protective sheath and by Bertrand as glandular tissue; the latter term
is probably the more correct as the tissue may well correspond to the
secretory-zone tissue of Lepidodendron stems. Fairly large groups of
transfusion tracheids occur on the flanks of the xylem. Prof. Bertrand
points out that one of his sections, cut nearer the apex of a leaf than
that figured by Renault with a single xylem strand, contains a double
strand and thus shows the latter’s description to be an incorrect
interpretation of the imperfectly preserved tissues.

The _Sigillariopsis_ type of leaf was recognised by Scott[506] in
English material on which he founded the species _Sigillariopsis
sulcata_. In a section which he has recently figured[507] a lacuna
below the two xylem strands is described as “representing secretory
tissue”; a band of transfusion tracheae almost encircles the pair of
bundles.

In a note published in 1907, Kidston[508] demonstrated the association
of _Sigillariopsis_ leaves with an undoubted Sigillarian stem of the
Rhytidolepis type and expressed his conviction that Renault’s genus is
identical with _Sigillaria_. The correctness of Kidston’s conclusion
has been proved by Arber and Thomas[509] who found that the leaf-traces
of _Sigillaria scutellata_ bifurcate during their course through the
outer region of the cortex and enter the leaf as two distinct strands
of primary xylem. In the section from Dr Kidston’s collection shown in
fig. 142, B, the lamina, 4 mm. wide, consists mainly of thin-walled
assimilating tissue composed of radially elongated cells abutting at
the periphery on hypodermal mechanical tissue, except at the edges of
the stomatal grooves which are bounded by the small-celled epidermis.
A broad sheath of thicker-walled elements, _s_, surrounds numerous
scattered transfusion tracheae, _t_, and below the two xylem strands,
_x_, which are embedded in delicate parenchyma there is a crescentic
band of dark tissue, _a_, resembling the smaller strand, _a_, in fig.
142, A′, and the secretory zone tissue of a Lepidodendron stem.


                 iii. _Fertile shoots of_ Sigillaria.

Reference has already been made to the manner of occurrence of strobili
on Sigillarian stems; it remains to describe the structure of these
reproductive shoots. _Sigillariostrobus_, the name given to Sigillarian
strobili, may be defined in general terms as follows:

Cylindrical cones, rarely dichotomously branched[510] as in species
of _Lycopodium_ and _Selaginella_, which may reach a length of 30 cm.
(_e.g._ _Sigillariostrobus nobilis_ Zeill.[511]) and a diameter 2–5
cm.; peduncle long and slender, sometimes bearing acicular bracts or,
after leaf-fall, characterised by leaf-cushions and leaf-scars like
those on vegetative shoots (fig. 201, E). The stalked cones are borne
in irregular verticils and in some species in vertical series, the
fertile zones being separated by comparatively long sterile portions
of the stem (fig. 199). The cones were deciduous and, in certain cases
if not in all, the individual sporophylls became detached from the
cone-axis on maturity. The slender axis bore spiral or verticillate
imbricate sporophylls attached at right angles or more or less
obliquely. The basal rhomboidal portion bore spores on its upper
surface (fig. 201, F), presumably enclosed in a somewhat radially
elongated sporangium (fig. B) and was prolonged distally into a narrow
lanceolate free portion, in some species with a ciliate border (fig.
D). The sporangia probably produced megaspores and microspores, but
such spores as have been recognised appear to belong to the former
category. The designation _Triletes_ is applied to isolated spores of
_Sigillaria_ or to those of _Lepidodendron_.

_Sigillariostrobus Tieghemi_ Zeiller[512] (figs. 201, E, F). In
this species, from the Coal-field of Valenciennes, the pedicel
bore acicular leaves or bracts attached to the upper portion of
leaf-cushions arranged in vertical series (fig. E). The cones reached a
length of 16 cm. and a breadth of 2·5–5 cm.; the sporophylls are borne
in alternating verticils with 8–10 in each whorl. Several megaspores
(2 mm. in diameter) appear to have been produced in tetrads in each
sporangium.

[Illustration: FIG. 201. _Sigillariostrobus._

  A, C. _Sigillariostrobus rhombibracteatus_ Kidst. (After Kidston.)
  A. Portion of strobilus.
  C. Megaspore.
  B, D. _Sigillariostrobus ciliatus_ Kidst. (After Kidston.)
  E, F. _Sigillariostrobus Tieghemi_ Zeill. (After Zeiller.)]


_Sigillariostrobus rhombibracteatus_ Kidston[513]. Fig. 201, A, C.

Kidston described this species from the Middle Coal-Measures of
England: it is similar in habit and in the form of the sporophylls
to _S. Tieghemi_, but rather smaller, and the more definitely
rhomboidal sporophylls have a ciliate margin. The cone was probably
heterosporous, but megaspores alone have so far been discovered. The
sporophylls bear a close resemblance to those of _Lycopodium cernuum_
(fig. 126, C). In some of the illustrations of this type given by
Kidston the naked cone-axis with its numerous sporophyll-scars is
clearly shown, reminding one of the naked axes of the cones of the
Silver Fir (_Abies pectinata_) or Cedar after the fall of the scales.

Our knowledge of Sigillarian cones is too incomplete to admit of a
detailed comparison with the strobili of _Lepidodendron_ or with those
of recent Pteridophytes. There can, however, be little doubt that
Goldenberg[514] was correct in his selection of _Isoetes_ as the most
nearly allied recent plant so far as the fertile leaves are concerned.
It would seem that the sporangia were comparatively delicate structures
which have left no clearly defined remains of their walls in the
carbonised specimens; Kidston, indeed, speaks of the hollow bases of
the sporophylls as holding the spores, but this is hardly likely to
have been the case. Our knowledge of the anatomy of _Sigillariostrobus_
is practically nil, but in one specimen of a _Sigillaria elegans_
stem Kidston[515] describes the structure of the tissues as seen
in a transverse section of a scar of a fertile shoot; from this we
learn that the stele was composed exclusively of primary tracheids
forming a solid strand without a pith. It is probable that the cones
of _Sigillaria_ were heterosporous, but in no instance have undoubted
microspores been discovered; the megaspores in each megasporangium
were fairly numerous as in _Isoetes_ (fig. 133, E). In one species,
_Sigillariostrobus major_ (Germar), from Permian rocks of France and
Germany, Zeiller[516] states that the whole of a single cone bore
megaspores (0·8–1 mm. in diameter) only; this is, however, not opposed
to the idea of heterospory, as we find instances in _Selaginella_ of
strobili bearing one kind of spore only (cf. p. 56).

In a few instances, it has been possible to correlate cones with
certain species of _Sigillaria_, but in most cases the strobili occur
as isolated fossils.


               iv. _The structure of Sigillarian stems._

The first account of the anatomy of _Sigillaria_ we owe to
Brongniart[517] who published a description of the internal structure
of an agatised stem, about 4 cm. in diameter, from Autun, which he
referred to _Sigillaria elegans_. It has, however, been shown by
Zeiller[518] and by Renault that this petrified fragment belongs to
Brongniart’s species _S. Menardi_, which is probably a young form of
_S. Brardi_. Brongniart’s specimen, now preserved in the Paris Natural
History Museum, is a very beautiful example of a silicified plant: on
part of the surface are preserved the hexagonal contiguous leaf-scars,
like those shown in fig. 193, A, and on the polished transverse section
is seen a relatively large stele consisting of a ring of secondary
xylem surrounding a series of crescentic groups of primary xylem (fig.
200, A) enclosing a wide pith occupied by concentric layers of silica.
A portion of the outer cortex is preserved, and this is separated
from the stele by a broad space filled with siliceous rock. The main
features of this type may be described in a few words. The primary
xylem differs from that of such Lepidodendron stems as have been
described in being made up of groups of scalariform and occasionally
reticulate (fig. 200, C) tracheae, having a plano-convex or more or
less crescentic form as seen in transverse section. These primary
strands, in contact with one another laterally, have their narrowest
elements on the outer edge. The leaf-traces are given off from the
middle of the abaxial face of each xylem strand (fig. 202, C, _lt_);
these pass obliquely outwards through medullary rays and then, as in
_Lepidodendron_, turn sharply upwards before bending outwards again
on their way to the leaves. Each leaf-trace consists of a group of
primary tracheae to which a few secondary tracheae are added during
the passage through the secondary wood. The secondary xylem forms a
continuous cylinder of tracheae with scalariform bands on both radial
and tangential walls; the medullary rays are numerous and consist of
long and narrow series, usually one cell broad, of parenchymatous
cells with occasional short rays one or more cells in depth.

The slightly greater breadth of the rays between each primary xylem
strand tends to divide the secondary wood into bundles corresponding
in breadth to the primary groups. The outer cortex closely resembles
that of _Lepidodendron_; it consists internally of radial series
of secondary, elongated and rather stout, elements abutting on the
parenchymatous tissue of the leaf-cushions.

The next contribution to our knowledge of the anatomy of _Sigillaria_
was made by Renault and Grand’Eury[519] who described the structure of
_Sigillaria spinulosa_ Germar[520], a species now recognised as the
Leiodermarian condition of _S. Brardi_, and probably, therefore, not
specially distinct from the specimen described by Brongniart in 1839 as
_S. elegans_. In Brongniart’s fossil the leaf-cushions are in contact
(Clathrarian form of _S. Brardi_: fig. 203, upper part) whereas in
the specimen now under consideration the leaf-scars are further apart
(Leiodermarian form of _S. Brardi_, fig. 203, lower part, and fig. 196,
C). It may be, as Scott suggests, that these two specimens are not
specifically identical but closely allied, an opinion based on certain
anatomical differences[521]; we may, however, include both under the
comprehensive name _S. Brardi_.

The primary xylem (fig. 200, B, _x_), is in some regions separated
into distinct strands, in others it forms a continuous band equal in
length to several of the separate groups. This type of stele, in which
the primary xylem consists in part of separate strands and in part of
a continuous cylinder, forms a transition between that represented
in fig. 200, A, and the steles of _Sigillaria elegans_ (fig. 202,
A) and most species of _Lepidodendron_. The tendency of the primary
xylem strands to become united laterally, forming broader bands,
was first described by Solms-Laubach[522] in a French specimen of
_Sigillaria spinulosa_ in the Williamson collection. The leaf-traces
arise from the middle of the concave outer face of the primary xylem
groups. The inner cortex is composed of small parenchymatous cells as
in _Lepidodendron_, and it is noteworthy that traces of partially
disorganised tissue, described as large canals, in the region external
to the secondary wood, bear a resemblance[523] to the secretory tissue
of _Lepidodendron_.

Other interesting features are presented by the structure of the outer
cortex and the parichnos. The outer cortex in the leaf-scar region is
composed of parenchyma, but for the most part it consists of radially
elongated groups of thin-walled parenchyma enclosed in a framework
of thicker-walled and elongated elements (fig. 200, B, _c_³). This
type of cortex, to which Brongniart applied the name _Dictyoxylon_,
would produce a cast in the case of a partially decorticated stem
characterised by a surface formed of irregularly oval and raised areas
bounded by narrow grooves; the greater prominence of the former being
due to the more rapid decay of the softer tissue, which would produce
depressions on the exposed face of the dead stem. Casts of this type
are not uncommon in Carboniferous rocks, and while some may belong to
the Pteridosperm _Lyginodendron_, others may be those of Sigillarian
stems.

[Illustration: FIG. 202.

  A. _Sigillaria elegans_ Brongn. (Section in Dr Kidston’s Collection
     cut from the specimen shown in fig. 193, D.)
  B, C. _Sigillaria elongata_ Brongn. _lt_, leaf-trace. (From
     specimens in the collection of Prof. Bertrand.)]

The large parichnos-strands, produced as in _Lepidodendron_, by the
forking of a single strand arising in the middle cortical region,
consist in part of tissue containing secretory canals, a structure like
that recently described by Miss Coward[524] in the large parichnos
strands of _Syringodendron_ stems.

An example of a decorticated specimen is described by Renault[525] as
_Sigillaria xylina_. This stem is presumably referred to _Sigillaria_
because the primary xylem consists of separate strands. It is
characterised by the unusually large development of secondary wood and
by the relatively small size of the pith. The xylem cylinder has a
diameter of 4–5 cm. and the pith is only 4–5 mm. in breadth.

Another example of a petrified Sigillaria stem has been described by
Kidston[526] as _S. elegans_ Brongn.[527] (fig. 193, D), a species
characterised by vertical rows of sub-hexagonal and contiguous
leaf-scars and by the presence of verticils of cone-scars. Fig. 193, D,
represents Kidston’s specimen in surface-view; one row of leaf-scars
is shown, but most of the superficial tissues have been destroyed.
The crushed stele, 13 mm. in its longest diameter, has a continuous
cylinder of primary xylem, (fig. 202, A, _x_) characterised by a
regularly crenulate outer margin with the smallest elements at the
edge; the prominent ridges separating the sinuses are rounded. The
leaf-traces arise from the bottom of each sinus; the leaf-bundles are
mesarch, and consist exclusively of primary elements. The secondary
xylem, _x²_, like that of the primary xylem, has a crenulate outer
edge. The most interesting feature of the outer cortex is afforded by a
tangential section which, in addition to the leaf-scars, cuts through a
cone-scar showing a solid primary stele surrounded by the cortex of the
cone-peduncle.

Another type of _Sigillaria_, probably _S. elongata_ Brongn. (fig.
202, B, C), which is very similar to _S. scutellata_ has been briefly
described by Prof. Bertrand[528], to whom my thanks are due for the
two photographs reproduced in fig. 202, B., C. His specimen, from the
Pas de Calais Coal-field, shows a ribbed Rhytidolepis form of surface
(fig. 202, B). The stele (fig. 202, C) agrees closely with that of _S.
elegans_ as described by Kidston, but the ridges on the fluted surface
of the primary xylem are more pointed. “In the immediate neighbourhood
of the origin of a leaf-trace, the spiral elements form a median band
in the middle of a sinus” and from this the leaf-traces are given off.
No secondary xylem was found in the leaf-traces at any part of their
course.

Bertrand compares the stele of _S. elongata_ with that of the type
of _Lepidodendron_ represented by the Burntisland species named by
Williamson _L. brevifolium_ (fig. 186) and now usually referred to
_L. Veltheimianum_; the chief distinguishing features are the greater
prominence in the French species of the surface-ridges or teeth of the
primary xylem, a feature which occurs in _L. Wünschianum_, and the
detachment of the leaf-traces from the bottom of each sinus (fig. 202,
C, _lt_) instead of from the sides of the sinus. It is, however, not
clear how far this latter distinction is a real one; in _Lepidodendron
Wünschianum_ the leaf-traces appear to arise, as in _Sigillaria_, from
the middle of each sinus.

Other types of ribbed Sigillaria stems have been briefly described by
Scott[529], Kidston[530], and more recently, by Arber and Thomas[531].

The specimen described by Scott agrees in the main with _S. elegans_ of
Kidston and with _S. elongata_ of Bertrand.

Kidston’s sections of _S. scutellata_ show a continuous primary xylem
cylinder with a slightly and irregularly crenulate outer margin. It
would seem that one important diagnostic character in Sigillarian stems
is afforded by the degree and form of the crenulations on the outer
surface of the primary xylem. _S. scutellata_ has been described also
by Arber and Thomas; these authors were the first to demonstrate the
presence of a ligule and ligular pit on the leaf-base in a petrified
stem, and they also contribute the important fact that the leaf-traces
in passing through the phelloderm bifurcate and enter the leaf as two
distinct vascular strands. This double bundle has been referred to in
the description of Sigillaria leaves. (Page 214.)

Although our knowledge of the anatomy of _Sigillaria_ has been
considerably extended since Williamson[532] drew attention to our
comparative ignorance of the subject, there are several points on which
information is either lacking or very meagre. As regards the stele,
it is in all types so far investigated, of the medullated type and
constructed on the same plan as that of _Lepidodendron Wünschianum_,
_L. Veltheimianum_, and other species. Secondary xylem was developed
at an early stage of growth, and its relation to the primary xylem,
from which as Kidston points out in his description of _S. elegans_,
it may be separated by a few parenchymatous elements, is like that
in _Lepidodendron_. The tendency of the outer face of the secondary
xylem to present a crenulate appearance in transverse sections may,
as Scott thinks[533], be a feature of some diagnostic importance,
but this is not a constant character in the genus. In origin and
in their mesarch structure, the leaf-traces closely resemble those
of _Lepidodendron_. The earlier account of the structure of the
leaf-traces of _Sigillaria_, which were described as possessing both
centrifugal and centripetal wood, led Mettenius[534] to draw attention
to an important anatomical resemblance between this genus and modern
Cycads. This comparison was, however, based on a misconception; the
Cycadean leaf-trace, consisting solely of primary wood, is not strictly
comparable with those of some species of _Sigillaria_, in which one
part of the xylem is primary and another secondary. The occasional
presence of secondary xylem in Sigillarian leaf-traces is matched in
some _Lepidodendra_[535], and cannot be accepted as a distinguishing
feature.

The origin of the leaf-traces from the middle of the sinuses on
the edge of the primary xylem is regarded as a difference; in
_Lepidodendron_ the leaf-traces are said to arise in some species
from the sides of the crenulations; but, as already pointed out,
this is a distinction of doubtful value. The division of the primary
xylem into separate strands in some stems of _Sigillaria_ of the
Clathrarian and Leiodermarian forms is a characteristic peculiarity;
but _S. spinulosa_ forms a connecting link between this type and the
continuous arrangement of the xylem in _S. elongata_ and _S. elegans_.
Kidston[536] has shown that the discontinuous primary xylem occurs in
Lower Permian species, a fact consistent with the view that the greater
abundance of the centripetally developed wood, characteristic of the
older species, represents a more primitive feature. This is not merely
a conclusion drawn from a consideration of geological age, but it is in
harmony with the view expressed by Scott[537] that as plants achieved
greater success in producing secondary centrifugal wood, the retention
of any considerable quantity of primary xylem became superfluous. As
yet we know very little of the structure of the perixylic tissues of
_Sigillaria_, but there is no sufficient reason for supposing that
these differ in essentials from those in _Lepidodendron_. The middle
and outer cortical tissues are practically identical in the two genera.
The parichnos is of the same type, except that in _Sigillaria_ it
reached greater dimensions in the outer part of its course.


                V. _Sigillaria Brardi_[538] Brongniart.
                       Figs. 196, A–C; 200; 203.

  1822. _Clathraria Brardi_, Brongniart, Classif. Vég. foss., Pl. XII.
        fig. 5.

  1828. _Sigillaria Brardi_, Brongniart, Hist. Vég. foss. p. 430, Pl.
        CLVIII. fig. 4.

        _S. Menardi_, _ibid._ Pl. CLVIII.

  1836. _Lepidodendron Ottonis_, Goeppert, Fossil Farnkr. Pl. XLII.

  1839. _S. elegans_, Brongniart, Arch. Mus. Nat. Hist. Paris, Vol. I.
        p. 406, Pl. XXV.

  1849. _S. spinulosa_, Germar, Verstein. Wettin und Löbejün, p. 59,
        Pl. XXV.

  1893. _S. mutans_, Weiss, Abhand. Preuss. Geol. Anst. [N.F.] Heft 2,
        Pl. VIII.

[Illustration: FIG. 203. _Sigillaria Brardi_ Brongn. (¾ nat. size).
  From a photograph of a specimen in Dr Kidston’s collection, from
  the Upper Transition Series of Staffordshire. Published by Kidston
  (02) Pl. LIX. fig. 1.]

The aerial shoots of this species are occasionally branched
dichotomously[539], the apical portions bearing short crowded
leaves[540]; the surface of the bark is either completely covered with
contiguous leaf-scars without definite leaf-cushions or with projecting
cushions forming a narrow sloping surface surrounding each leaf-scar.
Other parts of the plant may possess cushions similar in their
kite-shaped form to those of _Lepidodendron_, but without a median
vertical groove, or the leaf-scars may be spirally disposed at varying
distances apart on a comparatively smooth and longitudinally wrinkled
bark. The species exhibits striking instances of a transition between
the Favularian, Clathrarian, and Leiodermarian forms of stems. The
leaf-scars, which are hexagonal in outline,—the lateral angles pointed
and transversely elongated, the upper and lower angles rounded,—bear
three scars, the central leaf-trace and two straight or curved lateral
parichnos scars; a ligular pit occurs immediately above the centre of
the upper edge of the leaf-scar and occasionally circular elevations
with a central pit occur singly or in pairs below a leaf-scar (fig.
196, A). The linear leaves, which may persist on shoots having a fairly
large diameter[541], have a single median vein and two stomatal grooves
on the lower surface[542] (fig. 200, D).

Partially decorticated and younger shoots are characterised by the
occurrence of pairs of elliptical parichnos areas and a smaller median
leaf-trace scar. The surface of older stems, which may show signs
of longitudinal splitting (_Syringodendron_ state), bears pairs of
parichnos scars reaching a length of 2–2·5 cm. and a breadth of 10–13
mm. The regularity of the leaf-scar arrangement is interrupted at
intervals by the occurrence of more or less regular verticils of scars
marking the position of deciduous shoots. Grand’Eury[543] has figured
cones which he believes to be those of this species, and Zeiller
refers the large strobili, _Sigillariostrobus major_, to _Sigillaria
Brardi_[544].

The subterranean axes were characterised by spirally disposed
rootlet-scars like those of _Stigmaria ficoides_ (figs. 204, 205) and
by a cortical surface with the features of _Stigmaria rimosa_ Gold.[545]

The anatomy of the stele and leaves has already been described (p.
219). The stele of the Stigmarian portion of the plant consists of
a band of centripetal primary xylem and a cylinder of centrifugally
formed secondary wood with medullary rays containing vascular bundles
passing out to the rootlets[546].

_Sigillaria Brardi_ occurs not uncommonly in Permian rocks; it is
recorded from France[547], Germany[548], Pennsylvania[549], and
elsewhere. It is found in the Upper, Middle, and Lower Coal-Measures
of England[550] and in Permo-Carboniferous strata in Africa[551] and
Brazil[552].




                             CHAPTER XVII.

             UNDERGROUND RHIZOMES AND ROOTS OF PALAEOZOIC
                        LYCOPODIACEOUS PLANTS.


                             =Stigmaria.=

_Stigmaria ficoides_ is the name given to cylindrical casts met with
in Palaeozoic rocks, from the Devonian[553] to the Permian[554],
characterised by a smooth or irregularly wrinkled surface bearing
spirally disposed circular scars bounded by a raised rim and containing
a small central pit. It is not uncommon to find evidence of a partial
collapse of the substance of the plant as seen in fig. 204; this
is doubtless the expression of a shrinkage of the middle cortical
region, which was composed of a delicate and lacunar system of cells.
There can be no reasonable doubt that Stigmaria grew in water or
in swampy ground. Specimens are occasionally met with in which the
cast terminates in a bluntly rounded apex; such are, perhaps, young
branches which have not grown far from the base of the aerial stem
from which they arose (cf. fig. 207, B, C). Other examples occur,
such as Goeppert[555] figured and Gresley[556] has more recently
described, which are twisted and distorted as though obstacles had been
encountered in the ground in which they grew.

[Illustration: FIG. 204. _Stigmaria ficoides_ Brongn. M.S. (See Vol. I.
  p. 73.)]

[Illustration: FIG. 205. _Stigmaria ficoides._ From a specimen in the
  York Museum, from Bishop Auckland. _a_, base of rootlet showing
  vascular bundle scar. M.S.]

The circular scars mark the bases of long single and occasionally
forked appendages (rootlets) which spread on all sides into the
surrounding medium (figs. 205, 208). The occurrence of rootlets
radiating through the shale or sandstone affords proof that the
Stigmarias are often preserved in their position of growth. This
was recognised by Steinhauer[557] and Logan[558], and has been more
recently emphasised by Potonié[559] as an argument in favour of the
view that the beds containing such specimens are old surface-soils.

_Stigmaria_ usually shows regular dichotomous branching, the arms
spreading horizontally or slightly downwards and always arising
from four main branches in the form of a cross (fig. 207). The most
remarkable specimens found in England are described by Williamson[560]
in his monograph of _Stigmaria_. One of two large casts found near
Bradford in Yorkshire, and now in the Manchester Museum, shows four
large primary arms radiating from the base of an erect stump 4 feet in
diameter. Each arm divides a short distance from its base into two, and
the smaller branches extend almost horizontally for several feet[561].

An illustration published by Martin in 1809[562] shows a characteristic
feature of Stigmarian casts, namely the presence of a smaller axis,
usually occupying an eccentric position inside the larger. This
represents the cast of the fairly broad parenchymatous pith which,
on decay, left a space subsequently filled by sand or mud: at a
later stage the surrounding wood and cortex were removed and the
cavity so formed was similarly filled. A thin layer of coal formed
by the carbonisation of some of the tissues frequently surrounds the
medullary cast, and Steinhauer, whose account of the genus is much
fuller and more scientific than those of other earlier and many later
writers, recognised the true nature of this internal cast. Artis[563]
regarded it as the remains of a young plant, which he described as
“perforating its parent,” at length bursting it and assuming its place,
a gratuitously drastic interpretation.

In 1838[564] Lindley and Hutton figured a partially petrified specimen
of _Stigmaria_ obtained by Prestwich from Carboniferous rock of
Shropshire. This example showed a fairly broad cylinder of secondary
wood penetrated by medullary rays. The medullated stele consisted of a
pith surrounded by a small amount of primary xylem and by a cylinder
of secondary scalariform tracheae. The preservation of the tissues
abutting on the edge of the wood is usually very imperfect, and the
middle cortex of lacunar parenchyma has practically in every case
eluded the action of mineralising agents; the outer cortex, on the
other hand, consists of more resistant elements and is frequently well
preserved. As in _Lepidodendron_ and _Sigillaria_ stems, meristematic
activity produced a broad band of secondary cortex; and beyond this
were attached to cushion-like pads the numerous appendages, each
supplied with a single vascular bundle which arose from the primary
xylem and passed outwards through a medullary ray. There is abundant
evidence that the appendages were hollow, a fact in striking accord
with the aquatic and semi-aquatic habitat (cf. _Isoetes_ root, fig.
133, G).

[Illustration: FIG. 206. _Cyperus papyrus._ Piece of rhizome showing
  rootlet-scars. Nat. size. M.S.]

The piece of dried rhizome of _Cyperus papyrus_ shown in fig. 206 is
an almost exact counterpart of _Stigmaria ficoides_; the wrinkled and
shrivelled surface and the circular root-scars containing the remains
of a vascular bundle are striking features in common and, it may be
added, the two plants, though very different in structure and in
systematic position, illustrate anatomical adaptations to a similar
environment.


_Stigmaria ficoides_ Brongniart[565]. Figs. 204, 205, 207, 208.

  1809. _Phytolithus verrucosus_, Martin, Petrifact. Derb. Pls. XI–XIV.

  1818. _Phytolithus verrucosus_, Steinhauer, Trans. Phil. Soc.
        America, [N.S.] Vol. I. p. 268, Pl. IV.

  1820. _Variolaria ficoides_, Sternberg, Flora der Vorwelt, p. 22, Pl.
        XII.

  1822. _Stigmaria ficoides_, Brongniart, Mem. Mus. d’hist. nat. Paris,
        Pl. XII. fig. 7, p. 228.

  1825. _Ficoidites verrucosus_, Artis, Antediluvian Phytology, Pl. X.

  1840. _Stigmaria anabathra_, Corda, Flor. der Vorwelt, Pl. XIV.

The first figure of _Stigmaria_ is said to be by Petver in 1704;
Volkmann published illustrations of this common fossil in 1720 and
Parkinson in 1804[566]. Binney, whose researches may be said to have
inaugurated a new era in the investigation of fossil plants, wrote
in 1844: “Probably no fossil plant has excited more discussion among
botanists than the _Stigmaria_. It is the most common of the whole
number of plants found in the Coal-Measures, but there has hitherto
been the greatest uncertainty as to its real nature[567].” This
uncertainty still exists, at least in the minds of some who know enough
of the available data to realise that our knowledge is imperfect.

To pass to the questions of the affinity and nature of _Stigmaria_:
Brongniart[568] at first compared his genus with recent Aroideae, but
he afterwards[569] spoke of it as probably the root of _Sigillaria_.
Other writers regarded _Stigmaria_ as a dicotyledonous plant comparable
with Cacti and succulent Euphorbias. For many years opinion was divided
as to whether _Stigmaria_ represents an independent and complete plant
or the underground system of _Sigillaria_.

Artis[570], Lindley and Hutton[571], as well as Goldenberg[572],
believed it to be a prostrate plant unconnected with any erect aerial
stem. Goldenberg figured one of the slender rootlets terminating in an
oval body described as a reproductive organ. This seed-like impression
is either some extraneous body or an abnormal development at the end
of a rootlet. In 1842 Logan drew attention to the almost complete
monopolisation by _Stigmaria_ of the underclays, the rock which as
a general rule occurs below a seam of coal. He wrote: “The grand
distinguishing feature of the underclays is the peculiar character of
the vegetable organic remains; they are always of one kind (_Stigmaria
ficoides_) and are so diffused throughout every part of the bed, that
by their uniform effect alone the clay is readily recognised by the eye
of the miner[573].” This fact, which has played a very conspicuous part
in the perennial discussions on the origin of coal, led to the almost
general recognition of the underclays as surface-soils of the Coal
period forests.

The next step was the discovery of _Stigmaria_ in the Coal-Measures of
Lancashire and in the Carboniferous rocks of Cape Breton, Nova Scotia,
forming the basal branches of erect stems identified by Binney[574],
Bowman[575] and Richard Brown[576] as undoubted Sigillariae. In one
case Brown found what he considered to be convincing evidence of the
continuity between _Stigmaria_ and _Lepidodendron_.

In 1842 Hawkshaw[577] described certain fossil trees, the largest of
which had a circumference at the base of 15 ft., discovered, in the
course of excavations for a railway in Lancashire, in soft shale at
right angles to the bedding. The surface features were not sufficiently
clear to enable him to decide with certainty between _Sigillaria_ and
_Lepidodendron_, but while inclining to the former, it is interesting
to note that the occurrence of numerous Lepidostrobi near the root led
him to recognise the possibility of a connexion between the Stigmarian
roots and Lepidodendron stems. In 1846 Binney gave an account of
similar trees found at Dukinfield near Manchester: he spoke of one
stem as unquestionably a _Sigillaria_ with vertical ribs, furrows, and
scars, about 15 inches high and 4 ft. 10 inches in circumference. He
expressed his conviction that “_Sigillaria_ was a plant of an aquatic
nature[578].” Similar descriptions of rooted stems in the Coal-Measures
of Nova Scotia were published by Brown in 1845, 1846 and 1849; in the
last paper he figured a specimen, which has become famous, showing a
Syringodendron stem terminating in branching Stigmarian (or possibly
Stigmariopsis) roots bearing on the lower surface a series of what he
called conical tap roots[579]. A similar specimen discovered in Central
France nearly fifty years later demonstrated the accuracy of Brown’s
description.

Despite these discoveries the root-like nature of _Stigmaria_ was
not universally accepted. It was, however, generally agreed that
_Stigmaria_ formed the roots of _Sigillaria_; it was, moreover, held by
some that _Lepidodendron_ stems also possessed this type of root, an
opinion based on Brown’s record and on the occurrence of _Stigmaria_ in
beds containing _Lepidodendron_ but no _Sigillaria_ stems, as in the
volcanic beds of Arran and elsewhere, and on observations of Geinitz
and others[580]. There is now general agreement that _Lepidodendron_
and _Sigillaria_ had the same type of “root,” though the connexion of
_Stigmaria_ with the former was not so readily admitted, and indeed
the evidence in support of it is still very meagre. Goeppert and
other authors were unable to believe that the numerous species of
_Sigillaria_ possessed roots of so uniform a type, but Goeppert, by his
recognition of several varieties of _Stigmaria_, supplied a partial
answer to this objection.

Messrs Mellor and Leslie[581] have described and figured some large
casts of roots exposed in Permo-Carboniferous rocks in the bed of the
Vaal river at Vereeniging (Transvaal) which exhibit certain features
suggesting comparison with _Stigmaria_. Some of these reach a length
of 40–50 feet and, when complete, were probably not less than 100
feet long: in some of them the centre of the cast from which forked
arms spread almost horizontally shows a depression in the form of
a cross indicating a regular dichotomous branching like that of
_Stigmaria_. The authors incline to the belief that the roots belong
to _Noeggerathiopsis_ and not to a lycopodiaceous plant, though
Lepidodendroid stems are abundant in the sandstone a few feet higher
in the series. Despite the absence of any Stigmarian scars on the
surface of the fossil it is probable that these fine specimens are the
rhizomes of some lycopodiaceous plant, possibly _Bothrodendron_, which
is not uncommon in the Vereeniging beds.

Admitting that _Stigmaria_ is part of _Sigillaria_, the next question
is, is _Stigmaria_ a root in the ordinary sense, the underground
system formed on germination of the spore and of equal age with the
shoot, or did it bear a different relation to the Sigillarian stems?
To this question different answers would still be given. Goeppert[582]
discussed evidence in favour of the view that aerial Sigillarian shoots
were produced as vegetative buds on pre-existing Stigmarian axes,
like young moss plants on a protonema. At a later date Renault[583]
developed a similar view as regards _Sigillaria_; but we may pass on to
consider the more recent and complete observations of Grand’Eury[584]
and Solms-Laubach[585].

The recognition of two distinct types of Stigmariae in the
Coal-Measures of Central France led Grand’Eury[586] to institute a
new genus, _Stigmariopsis_. This type, which is characterised by a
difference in habit as well as by other distinguishing features,
is represented by such specimens as those figured by Goldenberg as
_Stigmaria abbreviata_, bearing lenticular scars spirally disposed on
a cortical surface characterised by irregular longitudinal wrinklings.
_Stigmariopsis_ has frequently been found in direct continuity with
Sigillarian stems of the Leiodermarian-Clathrarian type, spreading
obliquely downwards in the form of rapidly narrowing arms clothed with
slender and usually simple appendages; and from the under surface of
these arms short conical outgrowths are given off. It is probable,
as Solms-Laubach believes, that _Stigmariopsis_ was represented also
by long horizontally creeping rhizomes[587] of uniform breadth from
which ribless Sigillarian aerial shoots arose as bud-like outgrowths.
Grand’Eury, the author of the genus, confined the term to the shorter
and more rapidly tapered organs spreading from the base of erect
stems; the horizontal rhizomes of all Sigillarian stems he refers to
_Stigmaria_. The pith-casts of _Sigillariopsis_ may be recognised by
their long vertical ridges and grooves, a feature readily understood by
reference to the stem structure. The _Stigmariopsis_ rhizomes though
rare in England have been recognised by Dr Kidston[588] in the Middle
Coal-Measures of Yorkshire; he has figured a pith-cast very like that
illustrated in Solms-Laubach’s Memoir as _Stigmariopsis anglica_.

The surface-features of a _Stigmariopsis_ pith-cast are clearly shown
on a specimen from St Étienne in the Williamson collection[589].

[Sidenote: STIGMARIOPSIS]

The most complete account of Grand’Eury’s views in regard to the
anchoring and absorbing organs of _Sigillaria_ is given in his
monograph on the Coal-field of Gard[590], St Étienne, and these are
clearly stated also by Solms-Laubach[591] who confirms the conclusions
of the French author as to the manner of development of the aerial
shoots. Grand’Eury believes that both _Stigmaria_ and _Stigmariopsis_
are rhizomes and not true roots. The surface-features of _Stigmaria_
have already been described. This type Grand’Eury speaks of as
characterised by the uniform diameter and considerable horizontal
elongation of the bifurcated axes; he thinks they grew both as
floating rhizomes and on the ground: they may frequently be traced for
a considerable distance without showing any signs of connexion with
aerial shoots, but occasionally they have been seen in organic union
with Sigillarian stems. He believes that these rhizomes were produced
as the result of germination under water of the spores of _Sigillaria_
or _Lepidodendron_ and developed as long and branched aquatic
rhizomes capable of independent existence. Under certain conditions,
as he thinks in shallower water, the rhizomes produced bulb-like
outgrowths which grew into erect stems having the surface-features
of _Sigillaria_. This method of origin is practically the same as
that described by Goeppert in 1865. The vascular medullated cylinder
of these erect branches was in direct continuity with that of the
Stigmarian rhizomes.

[Illustration: FIG. 207. An early stage in the development of
  _Sigillaria_.

  A. Surface-features enlarged. (After Grand’Eury.)]

[Illustration: FIG. 208. Later stage in the development of
  _Sigillaria_; _Syringodendron_ with _Stigmariopsis_. (After
  Grand’Eury.)]

The next stage is that in which the undifferentiated bulb becomes
swollen at the base and develops four primary roots (fig. 207 B, C)
which grow obliquely downwards and produce numerous rootlets. Meanwhile
the parent rhizome gradually decays, finally setting free the aerial
stems which are now provided with spreading and forked roots (fig.
208) such as we are familiar with in English specimens as _Stigmaria
ficoides_, but which in the French specimens show the features of
_Stigmariopsis_. At this later stage conical outgrowths are formed
from the under surface of the Stigmariopsis arranged in a more or less
regular series surrounding the centre of the forked and spreading roots
(fig. 209). These conical and positively geotropic organs were long
ago described by Richard Brown as tap-roots. Grand’Eury’s conclusions
are briefly as follows: _Sigillaria_, and we may add _Lepidodendron_,
had no true roots and in this respect are comparable with _Psilotum_
(fig. 118): the organs which are described by Grand’Eury as roots
are correctly so named in a physiological sense, but morphologically
they do not strictly conform, either in origin or in the arrangement
of their appendages, to true roots. The question as to whether they
are entitled to the designation root is one which it is needless and
indeed futile to discuss in detail; it would be conceding too much to
a formal academic standpoint to refrain from applying to them the term
root, as that best describes their share in the life of the Sigillarian
stems. The horizontal Stigmarian axes are rhizomes in the ordinary
sense of the term and from these were developed Sigillarian shoots,
characterised in the lower portions by large parichnos strands. From
the base of the young bulbous shoots roots were formed: these roots
being, in the French specimens, of the _Stigmariopsis_ type.

[Illustration: FIG. 209. _Stigmariopsis_ and “tap-roots.” (After
  Grand’Eury.)]

These conclusions require some modification when applied to British
representatives of the arborescent Lycopodiales. The long spreading
and dichotomously branched root-like organs attached to the base of
Sigillarian and Lepidodendron stems are true examples of _Stigmaria
ficoides_ or other species. _Stigmariopsis_ occurs but rarely. This
marked difference between French and English specimens may be explained
if we adopt the opinion of Solms-Laubach, who believes that the true
_Stigmaria_ represents both the parent rhizome and the later-formed
roots of the Rhytidolepis Sigillarian species and of _Lepidodendron_,
the _Stigmariopsis_ form having the corresponding relation to the
Leiodermarian-Clathrarian species.

The opinion expressed by Williamson[592] in 1892 that Grand’Eury’s
hypothesis “appears to be identical with the vague and speculative
guesses that were prevalent among us in the early years of the present
[nineteenth] century” illustrates the strength of conviction based on
English specimens as to the root-nature of _Stigmaria_.

There is undoubtedly considerable confusion, which can be cleared
up only by further research, as to the precise relation between
_Stigmaria_ and _Stigmariopsis_ on the one hand and the different
types of _Sigillariae_ on the other. The main contention, and this is
the most important point, of Renault, Grand’Eury and Solms-Laubach as
to the manner of formation of the aerial shoots from rhizomes and the
subsequent production of forked roots and their ultimate separation
from the parent rhizome is, as I believe, correct. Williamson held
that _Stigmaria_ must be regarded as a true root; he found no evidence
to support the view that the large rooted stem discovered by Hawshaw,
Binney, and others had been originally produced from aquatic rhizomes.
It must, however, be remembered that Grand’Eury’s opinion is based
on evidence afforded by the exceptionally well displayed Sigillarian
forests of St Étienne, on a scale such as English strata have not
as yet afforded. Moreover, the absence of any parent-rhizome in
association with the rooted stumps described by Williamson and by
others is not a serious argument against their rhizome origin.

The specimen represented in fig. 209, which was examined _in situ_
by Solms-Laubach and Grand’Eury, shows a Sigillarian stem in the
Syringodendron condition bearing rows of paired parichnos scars;
from the base forked and rapidly tapering arms radiate through the
surrounding rock and, as shown by other specimens, these bear numerous
appendages like those of the English Stigmarias. The surface-features
of the arms are those of _Stigmariopsis_ and the centre of each, as
seen on the broken face, is occupied by a pith-cast characterised by
parallel longitudinal ridges resembling those on the medullary casts of
_Calamites_. It is noteworthy that the petrified rhizome originally
described by Renault as _Stigmaria flexuosa_, and afterwards identified
by him as the subterranean system of _Sigillaria Brardi_, possesses
a vascular cylinder composed of primary xylem strands of crescentic
transverse section lining the pith; a cast of the pith, after the
removal by decay of its delicate parenchymatous tissue, would exhibit
the surface-features of _Stigmariopsis_. _Stigmaria flexuosa_ no
doubt represents a true _Stigmariopsis_ rhizome. On the other hand,
as Williamson has shown, the inner surface of the wood of _Stigmaria
ficoides_ consists of a reticulum of xylem with meshes of medullary-ray
tissue; a cast of such a surface presents a very different appearance
from that of _Stigmariopsis_.

Returning to fig. 209: from the lower surface of the _Stigmariopsis_
arms numerous conical outgrowths, reaching a length of several
centimetres, project vertically downwards; these also possess
Stigmariopsis pith-casts and are identical with the “tap-roots” of
Richard Brown. The stump seen in fig. 209 shows the characteristic
hollow base of the erect stem: this is the region which, it is
believed, represents the position of the Stigmarian rhizome from which
the aerial shoot was developed. Although no remains of the parent
rhizome were found, traces of the rootlets which probably belonged to
it were found in the neighbourhood. The absence of the actual rhizome
is, however, not surprising as it would not persist after its aerial
Sigillarian branches had attained independence by the development of
their own dichotomously branched absorbing and holdfast organs.

The Stigmarian axes of Palaeozoic Lycopods are compared by Miss
Thomas[593] with the prop-roots of certain recent flowering plants
which grow in tropical tidal swamps; their roots grow downwards from
the stem at an angle of 50°-60° before spreading out horizontally.
This author also makes some interesting suggestions in regard to
the evidence afforded by anatomical structure as to the habitat of
_Sigillaria_ and _Lepidodendron_.


_Anatomy._

The more important anatomical features of _Stigmaria_ must be dealt
with briefly. Williamson’s monograph, published in 1887[594], is
considerably in advance of the work of that of any of the numerous
writers who had previously dealt with the subject. The diagrammatic
transverse section reproduced in fig. 210, H, illustrates the general
arrangement of the tissues. The medullated stele was described by
Williamson as consisting entirely of centrifugally developed secondary
xylem and distinguished, therefore, from the stele of a _Lepidodendron_
or _Sigillaria_ by the absence of a centripetally produced primary
xylem zone. The secondary xylem tracheae are characterised by
scalariform pits on both radial and tangential walls and, as shown in a
figure given by Solms-Laubach[595], the spaces between the transverse
bars are bridged across by fine threads, as in the tracheae of
_Lepidodendron_.

One of the largest specimens of a petrified _Stigmaria_ which I have
seen is one lent to me by Mr Lomax from the Coal-Measures of Halifax in
which the flattened transverse section measures 18 cm. × 3·5 cm., the
cylinder of wood being 1·1 cm. × 7 mm. in diameter.

In French examples of _Stigmaria_ or _Stigmariopsis_ it has been
demonstrated by Renault[596] that primary xylem strands occur very like
those in the stem of some species of _Sigillariae_ (see p. 219). If a
well-preserved section of an English _Stigmaria_ is examined it will
be seen that the edge of the secondary wood consists of a few narrower
elements which do not exhibit the radial seriation characteristic of
secondary elements.

A type of _Stigmaria_ characterised by centripetal primary wood has
been described by Weiss[597] and referred by him to _Bothrodendron
mundum_; the main results of his observations are stated in the
account of _Bothrodendron_ on a subsequent page. This discovery is
of considerable interest not only as rendering our knowledge of
_Bothrodendron_ remarkably complete but as confirmatory of Renault’s
account of French Stigmarian axes in which centripetal primary wood
is well developed between the secondary xylem and the centre of the
stele. The Stigmarian axis of Bothrodendron was originally figured
by Williamson as _Lepidodendron mundum_[598]. The chief difference
between Weiss’s specimen and those described by Renault[599] as the
Stigmarian axes of _Sigillaria Brardi_, is that in the English plant
the centripetal wood forms a cylinder of uniform breadth instead of a
band with a crenulated inner margin as figured by Renault.

[Sidenote: STIGMARIA]

[Illustration: FIG. 210. _Stigmaria._

  A. Transverse section of vascular bundle of rootlet and part of
     outer cortex. _t_, tracheae. (After F. E. Weiss.)
  B, C. Vascular bundle of rootlet; in C a series of small tracheae
     are shown extending from the protoxylem.
  D. Rootlets from the outer cortex of E.
  E. Part of a large _Stigmaria_: _St_, stele; _s_, intruded rootlet.
  F. Vascular bundle and tracheae passing obliquely towards the outer
     cortex, _c_³.
  G. Outer cortex of _Stigmaria_.
  H. Diagrammatic section of _Stigmaria_: _p_, phelloderm; _r_,
     rootlets.]

An interesting agreement between the French and English specimens
is the occurrence in the cortex of groups of reticulate elements:
in Weiss’s section these are short and wide and occur in the middle
cortex; in Renault’s plant they are more fusiform and occur in the
secondary cortical tissue. These elements appear to have been arranged
as an interlacing network in the middle cortex and were in close
connexion with the rootlet-bundles, comparable, as Weiss points out,
with the transfusion tracheids accompanying Lepidodendron leaf-traces.

It is probable that these short and wide tracheal elements served for
water-storage and thus afford another indication of the xerophilous
character of the Carboniferous Lycopods, a feature possibly connected
with a salt-marsh habitat.

The presence of conspicuous medullary rays gives the secondary xylem
of _Stigmaria_ the appearance of being divided into several more or
less distinct groups (fig. 210, E, _St_). In tangential longitudinal
section the xylem assumes the form of a broad reticulum with lenticular
meshes filled with medullary-ray tissue through which strands of xylem
are cut across in a transverse direction as they pass outwards from
the inner edge of the wood to supply the rootlets. In addition to
these broader or primary medullary rays, there were numerous secondary
rays composed of narrow plates of parenchymatous cells one or several
elements in depth. As Williamson pointed out, the medullary-ray tissue
consists in part of radially elongated tracheal elements with spiral or
scalariform thickening bands like those described in the same position
in Lepidodendron stems.

Our knowledge of the minute structure of the tissues abutting on the
secondary xylem is far from complete.

The xylem is succeeded by a zone of delicate cells which was the
seat of meristematic activity. It is noteworthy that in a section
figured by Williamson[600] there is the same disparity in size between
the outermost elements of the xylem and the adjacent cells of the
meristematic zone as in Lepidodendron stems. Beyond this region an
imperfectly preserved lacunar tissue occurs like that which I have
called the secretory zone in Lepidodendron stems; but information as
to the structure of this part of _Stigmaria_ is much more incomplete
than in the case of the aerial shoots. The middle cortex was of the
same lacunar type as in the stems, and the fact that it is never well
preserved in large Stigmarian axes suggests that it may have been
even more richly supplied than in the aerial stems with an aerating
system of spaces. The outer cortex, consisting in young examples of
large-celled parenchyma, became at an early stage of growth the seat of
cambial activity which resulted in the production of radially placed
series of secondary elements (fig. 210, H, _p_). The outer and older
elements of this secondary cortex are more tangentially stretched than
the inner cells, a necessary result of the position of the phellogen on
the internal edge of the tissue and of the increasing girth of the axis.

In comparatively young Stigmarian axes the outer cortex already
possesses a band of secondary radially disposed cells characterised
by the greater tangential extension of the more external elements;
usually this tissue terminates abruptly on the inner edge and the
line of separation no doubt marks the position of the phellogen.
Occasionally some delicate secondary elements are preserved internal
to the phellogen, and these in young specimens form a narrow cylinder
composed in part of radially elongated cells showing signs of recent
tangential divisions. In its earlier stage of activity the phellogen
seems to form a greater amount of secondary tissue on the outside, but
this is clearly not of the nature of cork, the tissue which occupies a
corresponding position in recent plants. The primary cortex shows no
signs of shrinkage or collapse as would be the case were it cut off
from the vascular system by a zone of impermeable cork.

Fig. 210, G, represents a piece of the external tissue of a specimen in
which the slightly flattened xylem cylinder measures 1·4 × 1 cm.; the
inner cortex has disappeared and fragments only of the middle cortex
are preserved. The outer cortex, with an average breadth of 2 mm.,
consists superficially of primary parenchyma with a somewhat uneven
surface and with a rootlet attached here and there; a short distance
below the surface is a band of conspicuous cells, _b_, characterised
by dark contents suggesting very imperfectly preserved fungal hyphae,
but the nature of the substance filling the cells cannot be made out
with certainty. It is, however, interesting to find that this dark
band constitutes an obvious feature (fig. 210 H, _b_); its position is
comparable with that of the dark-walled cells in the outer cortex of
rootlets. A short distance internal to this dark band tangentially
elongated cells form the outermost elements of the secondary cortex;
these become gradually narrower towards the interior and pass into
radial series of smaller cells of uniform size, as seen on the inner
edge of fig. 210, G. At the inner boundary of this tissue, just below
the region shown at the bottom of the drawing, was situated the
phellogen. Such traces of tissue as occur on the inner side of the line
where splitting has usually occurred, consist of thinner elements with
recently formed tangential walls and probably represent an early stage
in the development of phelloderm.

A much older section is shown in part in fig. 210, E. The secondary
xylem cylinder, _St_, is shown in the lower part of the section; beyond
this is a band of secondary tissue which reaches in some places a
breadth of 6 cm. The greater part of this tissue consists of phelloderm
of very uniform structure made up of radial series of cells: this
is interrupted in most parts of the section by a gap crowded with
intruded rootlets (a portion of this is enlarged in fig. 210, D).
Beyond this gap the secondary tissue consists of radial series of cells
characterised by the considerable tangential elongation of many of
the elements, precisely like the tissue figured by Williamson. In all
probability the gap represents a line of weakness due to the phellogen,
and if this is the case it is clear that in an old _Stigmaria_ the
phelloderm exceeded in amount the tissue formed external to the
phellogen. The secondary tissue on the inner side of the phellogen is
characterised by numerous irregular concentric lines superficially
resembling rings of growth in the wood of a Conifer: these are,
however, not the result of any periodic change in external conditions,
but are apparently due to crushing of the tissue and are possibly,
to some extent, the result of the presence of secretory strands like
those in the phelloderm of _Lepidodendron_. The surface of this
older rhizome retains patches of primary tissue, and an occasional
rootlet, as at _r_, fig. 210, E, is seen in connexion with the cortex;
the cortex has been vertically fissured as the result of secondary
growth and presents an appearance like that shown in _Lepidodendron
Wünschianum_ and _L. Veltheimianum_ (figs. 181, A, and 186, A).

The form in which a Stigmarian rootlet is usually preserved is shown
in fig. 210, D; the single vascular bundle strand with its endarch
protoxylem (fig. 210, B, _px_) is enclosed by a ring of inner cortical
parenchyma (fig. 210, F, _c_¹); the cells in immediate contact with
the xylem having usually disappeared. Beyond the middle cortical
space a second cylinder of parenchyma represents the outer cortex (F,
_c_³) in which a layer of dark-walled cells (_b_, fig. 210, F) may be
compared with the hypodermal band in the main Stigmarian axis (G, _b_).
These Stigmarian rootlets, usually less than 1 cm. in diameter, are the
commonest objects in sections of the calcareous nodules from English
coal-seams. A good example of their abundance is shown in fig. 210, D
and E; here they have invaded the space formed by the splitting of the
secondary cortical tissues along the line of the phellogen and a few
are seen here and there in the deeper layers of the phelloderm (_s_,
fig. 210, E). Not infrequently the close contact of these ubiquitous
rootlets with the tissues of the plant which they have invaded leads to
confusion between invader and invaded. Partially decayed tissues lying,
probably, under water were penetrated by Stigmarian rootlets in exactly
the same way as the roots of recent plants bore through vegetable
substances which happen to be in their path. The rootlet bundles are
in the first instance composed of the primary tracheae which line
the inner edge of the secondary xylem; these receive additions from
the meristematic zone, and thus, when seen in the cortex outside the
stelar region, are found to consist in part of primary and in part of a
fan-shaped group of secondary tracheae. On the other hand, the monarch
bundle as it appears in a free rootlet is usually composed entirely of
primary elements (fig. 210, A–C, F). It has been shown by Weiss[601]
that in the Stigmarian rhizome of what is probably _Lepidodendron
fuliginosum_, the rootlet bundle is accompanied by a parichnos strand,
but this has not been detected in the ordinary _Stigmaria ficoides_.
When free from the parent axis a rootlet usually consists of an
outer cylinder of cortex enclosing a broad space in which remnants
of lacunar tissue are sometimes seen. The relation of the external
features of a well-preserved Stigmarian rootlet-scar to the internal
structure of a petrified rootlet is very clearly seen on comparing
such sections as those represented in fig. 210, D, with the form of
the scar on a Stigmarian cast. A specimen figured by Hooker[602] in
1848 affords a good illustration of the structure of a rootlet-base as
seen in an unusually complete cast; this correlation of anatomical and
surface features is clearly described also by Williamson[603] and by
Solms-Laubach[604]. It is probable that even during life the rootlets
were hollow for a part at least of their length as are the roots of
_Isoetes_ (fig. 133, G).

An interesting discovery was made a few years ago which confirmed a
statement by Renault which Williamson was unable to accept, namely
that the xylem bundle of a rootlet occasionally gives off a delicate
tracheal strand at right angles to the long axis of a rootlet. In some
rootlets Weiss[605] found obliquely running delicate strands of xylem,
surrounded by a layer of parenchymatous tissue, in the space between
the vascular bundle and the outer cortical cylinder. It is clear that a
few spiral tracheids are occasionally given off from the protoxylem of
a rootlet bundle: these follow an oblique course to the outer cortex,
where in some cases they have been traced into connexion with short
and spirally marked cells resembling transfusion tracheae (fig. 210,
A). This arrangement may serve as a means of facilitating the passage
of water absorbed by the superficial cells into the xylem strand. It
should be noticed that, like roots of recent water-plants, the rootlets
of _Stigmaria_ had no root-hairs. Fig. 210, F, shows a transverse
section of part of a rootlet in which the outer cortical cylinder,
_c_³, is connected, as in the roots of _Isoetes_, with the sheath
surrounding the vascular bundle. A few obliquely cut tracheae are seen
in this section traversing the connecting band of parenchyma _t_, fig.
210, A.

A point of biological interest in connexion with Stigmaria rootlets is
the occasional presence of hypertrophied cells, the large size of which
is due to the attacks of a fungus named by Weiss[606] _Urophlyctites
stigmariae_.

In addition to _Stigmaria ficoides_, which is by far the commonest
form, a few other species have been founded on external characters.
One of these is represented by _Stigmaria stellata_, Goepp.[607],
characterised by the presence of radially disposed ridges and small
tubercles surrounding each rootlet-scar. Kidston refers to Goeppert’s
species as a Lower Carboniferous type. We have no evidence as to the
meaning of the stellate ridges and tubercles, nor have we any reason
to suppose that this form differed essentially in structure from
_Stigmaria ficoides_.




                            CHAPTER XVIII.

                           =Bothrodendreae.=


                    _Bothrodendron._ Figs. 211–216.

Although in many respects the genus _Bothrodendron_ agrees very closely
in habit and in its anatomical features with _Lepidodendron_, there are
reasons for referring it to a distinct family of Palaeozoic Lycopods.
As the following description shows, the external features do not differ
in any essential points from those of certain types of the genus
_Sigillaria_, particularly such a species as _S. rimosa_, Gold.[608],
which has recently been refigured and described by Nathorst[609] from
Goldenberg’s type-specimen in the Stockholm Museum. The small size of
the leaf-scars is, however, a characteristic feature of _Bothrodendron_
(fig. 212, F); but a more important point is the fact that in a
recently described[610] English example of a cone of _Bothrodendron_
(fig. 216), the sporangia are very like those of recent Lycopods, and
differ from the radially elongated sporangia of _Lepidostrobus_. On the
other hand, a French cone described by Zeiller[611] as _Lepidostrobus
Olryi_, which is probably a strobilus of _Bothrodendron_, has the
radially elongated type of sporangium (fig. 212, E). The comparative
abundance of _Bothrodendron_ in Lower Carboniferous and Devonian rocks
points to the greater antiquity of this member of the Lycopodiales as
compared with _Lepidodendron_.

The name _Bothrodendron_ was instituted by Lindley and Hutton[612]
for impressions of stems from the English Coal-Measures, characterised
by two opposite rows of large depressions like those shown in fig.
211 and, in one of the specimens, by “a considerable number of
minute dots, arranged in a quincuncial manner.” The minute dots were
recognised as leaf-scars and the cup-like cavities were described
as probably connected with the occurrence of large cones. On very
slender evidence this Palaeozoic plant, which was named _Bothrodendron
punctatum_, was considered by these authors as probably a member
of the Coniferales. The large stem from the Coal-Measures in the
neighbourhood of Mons, Belgium, shown in fig. 211, affords a good
illustration of _Bothrodendron_ in a partially decorticated condition,
exhibiting a row of depressions similar to those on the Ulodendron
form of _Lepidodendron Veltheimianum_ (fig. 157), but distinguished by
the eccentric position of the scar at the bottom of each cup-shaped
cavity: in the Belgian specimen, which is partially decorticated and
shows the leaf-traces as small dots, the depressions have a diameter of
9 cm. It is believed by some authors that these Ulodendron shoots of
_Bothrodendron_ and _Lepidodendron_ owe their characteristic appearance
to the pressure of large cones, but, as I have already stated, there
are reasons for preferring the view that these crater-like hollows are
the scars of deciduous branches. Our knowledge of the strobili borne by
Bothrodendron stems is still meagre, but we have no reason to assume
the existence of any cones large enough to produce by the pressure
of their bases such depressions as those shown in fig. 211. In one
species at least the strobili were borne terminally on slender shoots
(fig. 213). The Ulodendron condition has so far been recognised in one
species only, _B. punctatum_.

In his catalogue of Palaeozoic plants, Kidston[613] included
_Bothrodendron punctatum_ as a synonym of _Sigillaria discophora_
König, a mistake which he afterwards rectified[614]: the generic name
_Bothrodendron_ was generally ignored by authors in the belief that
the specimens described by Lindley and Hutton were not generically
distinct from the fossils originally figured by Rhode as _Ulodendron_.
It was Prof. Zeiller who first demonstrated that the English authors
were justified in their choice of a new designation for stems with
large depressions in association with minute leaf-scars. In 1859
Haughton[615] proposed a new family name Cyclostigmaceae for some Upper
Devonian plants from County Kilkenny, Ireland: he described three
species of his new genus _Cyclostigma_, _Cyclostigma kiltorkense, C.
minutum_, and _C. Griffithsi_; these are now generally recognised as a
single species of _Bothrodendron_, though, as Nathorst suggests, the
Irish plant should perhaps be separated as a sub-genus _Bothrodendron_
(_Cyclostigma_) by reason of certain minor differences which
distinguish it from other species of the genus.

[Illustration: FIG. 211. _Bothrodendron punctatum._ Part of a specimen
  from near Mons (Hainaut), in the Brussels Museum. (Reduced.)]

Another generic name, _Rhytidodendron_, was instituted by Boulay in
1876 for stems characterised by a finely wrinkled bark and small
spirally disposed leaf-scars. A short description of this type, which
occurs in the Middle and Lower Coal-Measures, may serve to illustrate
the external features of the commonest British example of the genus.


_a. Bothrodendron minutifolium_ (Boulay.) Figs. 212, A, C, D; 213.

  1875. _Lycopodium carbonaceum_ (_Lycopodites carbonaceus_),
        Feistmantel, Palaeontographica XXXIII., Pl. XXX. figs. 1, 2; p.
        183.

  1876. _Rhytidodendron minutifolium_, Boulay, Terr. Houill. Nord
        France, p. 39, Pl. III. fig. 1.

  1886. _Bothrodendron minutifolium_, Zeiller, Bull. Soc. Géol. France
        [iii] XIV. p. 176, Pl. IX. figs. 1, 2.

  1888. _Lepidostrobus Olryi_, Zeiller, Flor. Valenciennes, p. 502, Pl.
        LXXVII. fig. 1.

  1889. _Bothrodendron minutifolium_, Kidston, Trans. R. Soc.
        Edinburgh, Vol. XXXV. Pt. ii.

  1893. _Sigillaria_ (_Bothrodendron_) _minutifolia_, Weiss and
        Sterzel, K. Preuss. Geol. Landesanstalt, Heft 2, p. 49, Pl. I.
        figs. 3 and 4; Pl. II. figs. 8 and 9.

  1904. _Bothrodendron minutifolium_, Zalessky, Mém. Com. Géol. Russie,
        Pl. VI. fig. 6.

[Illustration: FIG. 212. _Bothrodendron._

  A. _Bothrodendron minutifolium_, var. _rotundata_ Weiss. After
     Weiss and Sterzel.
  B. _B. punctatum._ After Zeiller.
  C. _B. minutifolium._ After Weiss and Sterzel.
  D. _B. minutifolium._ After Zeiller.
  E. _Lepidostrobus Olryi._ After Zeiller.
  F. _Bothrodendron punctatum._ After Zeiller.
  G, H. _B. kiltorkense._ G, after Nathorst; H, after Weiss and
     Sterzel.]

In habit a plant of _Bothrodendron_ recalls _Lepidodendron_ and recent
species of _Lycopodium_; the slender dichotomously branched twigs
bearing numerous leaves (fig. 212, D), have been mistaken for shoots
of _Lycopodium_, and fragments of branches might well be identified
as impressions of Mosses. The leaf-scars on the smaller shoots occur
on elongated cushions (fig. 212, C, D) with a transversely wrinkled
surface; on the older branches the leaf-scars are separated by fairly
large areas of bark characterised by sinuous transverse grooves and
narrow ridges bearing numerous small pits, as shown on an enlarged
scale in fig. 212, A. The original surface-features are shown on the
left of the drawing, and a slightly deeper level in the cortex is
represented on the right-hand side. The absence of leaf-cushions on the
older shoots is probably the result of secondary thickening, which also
alters the size and shape of the leaf-scars. Each scar has three pits
on its surface, as in _Lepidodendron_; a central leaf-trace scar and
lateral parichnos scars. The circular pit above the leaf-scars, which
occurs in most species, marks the position of the ligule. The relation
of the short leaves, 5 mm. long, to the leaf-cushions is shown in fig.
212, D. The absence of leaves, except in impressions of slender twigs,
may be interpreted as an indication that they were shed at an early
stage and did not persist many years. The leaf-cushions of the smaller
shoots of _Bothrodendron minutifolium_ closely resemble those figured
by Weiss on a Devonian plant, _Lepidodendron Losseni_[616].

One of the few examples so far discovered of a Bothrodendron cone is
shown in fig. 213; this specimen, at least 10 cm. long, was found by
Mr Hemingway in the Middle Coal-Measures of Yorkshire and described
by Dr Kidston. Numerous sporophylls are attached at right angles to
the axis, the surface of which is protected by their upturned distal
portions; the arrangement of the parts appears to be the same as in
_Lepidostrobus_. A specimen figured by Zeiller as _Lepidostrobus
Olryi_, which Kidston is probably correct in identifying with
_Bothrodendron minutifolium_, shows that each sporophyll carries a
horizontally elongated sporangium (fig. 212, E).


_b. Bothrodendron punctatum_ Lindley and Hutton[617]. Figs. 211, 212 B,
F.

This species, which is less abundant than _B. minutifolium_, in British
Coal-Measures, has been described by several authors as _Ulodendron_
on account of the occurrence of large depressions, like those shown
in fig. 211, on certain branches of the plant. At the suggestion of
Dr Kidston, Prof. Zeiller[618] figured an English specimen of this
species, presented to the Paris Museum by Mr Hutton, in which the
leaf-scars are preserved on the bark of a stem with Ulodendron scars.
The surface of the bark is characterised by numerous small pits and
discontinuous vertical lines in contrast to the transverse lines of _B.
minutifolium_ (cf. fig. 212, A and F). The leaf-scars on the smaller
shoots may have a diameter of only 0·3–0·5 mm., while on the larger
branches they reach a breadth of 1 mm. The ligule-pit may be in contact
with the upper edge (fig. 212, F) of the leaf-scar or separated from it
by a short distance.

[Illustration: FIG. 213. _Bothrodendron minutifolium_ Cone. From a
  specimen in Dr Kidston’s Collection. (Slightly reduced. Kidston
  (02) Pl. LIX.)]


_c_. _Bothrodendron kiltorkense_ (Haughton). Fig. 212, G, H.

  1859. _Cyclostigma kiltorkense_, Haughton, Journ. R. Soc. Dublin,
        Vol. II. p. 418, Pls. XIV.–XVII.

  _C. minutum_, Haughton, Journ. R. Soc. Dublin, Vol. II. p. 418,
        Pls. XIV.–XVII.

  _C. Griffithsi_, Haughton, Journ. R. Soc. Dublin, Vol. II. p. 418,
        Pls. XIV.–XVII.

  1870. _Lepidodendron Veltheimianum_, Heer (_ex parte_), K. Svensk.
        Vet. Akad. Handl. Vol. IX. Pl. IX. figs. 2–4.

  _Cyclostigma kiltorkense_, _ibid_. Pl. XI. figs. 1–5.

  _Calamites radiatus_ (_ex parte_), _ibid_. Pl. III. fig. 2_a_: Pl.
        IX. fig. 2_b_.

  _Stigmaria ficoides minuta_, _ibid_. Pl. IX. fig. 2_c_.

  _Knorria imbricata_, _ibid_. Pl. X. fig. 4.

  1889. _Bothrodendron kiltorkense_, Kidston, Ann. Mag. Nat. Hist.
        [VI.], Vol. IV. p. 66.

  1894. _Bothrodendron kiltorkense_, Nathorst, K. Svensk. Vet. Akad.
        Handl. Vol. XXVI. No. 4, p. 65, Pls. XIV. XV.

  1902. _Bothrodendron (Cyclostigma) kiltorkense_, _ibid_. Vol. XXXVI.
        No. 3, p. 31, Pls. X.–XIV.

The specimens from the Upper Devonian rocks of Co. Kilkenny on which
Haughton founded this and two other species may be regarded as
representing one specific type. He described the circular leaf-scars
as arranged in alternating whorls. In habit the Irish species agrees
with _Bothrodendron minutifolium_, but the leaf-scars are more
elliptical (fig. 212, H) and the ligule-pit is usually absent. The
leaf-scar shown in fig. H is 1·2 mm. broad and 1·4 mm. in height. The
large collection obtained during the visit of a Swedish expedition
to Bear Island in 1898 under the leadership of Dr Nathorst has
materially increased our knowledge of this ancient type. The form
of the leaf-scars varies according to the age of the branch and
their disposition is far from constant even on the same specimen; in
some cases the scars are in fairly regular whorls (fig. 212, G; an
Irish specimen) while in others they are in regular spirals. This
irregularity of arrangement, which is well illustrated by Nathorst’s
figures of Bear Island and Irish specimens, finds its counterpart,
though in a less marked form, in recent species of _Lycopodium_, _e.g.
L. Selago_. Partially decorticated stems may present a superficial
resemblance to _Calamites_, the fissured bark simulating the ribs
of a Calamitean cast. Such stems, as Nathorst has pointed out, were
mistaken by Heer for _Calamites radiatus_. The smaller branches
are characterised by a smooth surface, and older shoots resemble
_Bothrodendron minutifolium_ in the presence of fine vertical lines.
The preservation of only one pit on the leaf-scars of many examples
led authors to conclude that the species is peculiar in this respect,
but Nathorst has shown that in more perfectly preserved specimens
each leaf-scar bears three small dots. A specimen from Ireland in the
British Museum[619] illustrates the dichotomous branching and the
longitudinal wrinkling of the bark; the leaf-scars are 2 mm. broad and
2·5 mm. deep.

Nathorst[620] has described some examples in which the leaf-scars
occur on the lower instead of on the upper end of the leaf-cushions;
these and other specimens with obscure surface-features he suggests
may be underground axes, comparable in habit with _Stigmaria_ though
not identical as regards details. It is pointed out that the absence
or scarcity of _Stigmaria_ in the Bear Island beds renders it unlikely
that _Bothrodendron_ bore typical Stigmaria branches. F. E. Weiss[621]
has recently described root-bearing organs possessing primary xylem
identical with that of _Bothrodendron mundum_; while closely resembling
_Stigmaria ficoides_ in certain anatomical characters, they clearly
represent a distinct type. This discovery of a Stigmaria-like axis
almost certainly belonging to _Bothrodendron_ is consistent with
Nathorst’s views on some of the Bothrodendron impressions from Bear
Island.

Information as to the cones of this species is restricted to a
description by Schimper[622] of a specimen in the Dublin Museum as
_Lepidostrobus Bailyanus_; this has sporophylls with a subtriangular
base bearing several megaspores and terminating distally in a slender
lamina 12 cm. in length.

An example of a _Bothrodendron_ with more prominent leaf-cushions than
those already mentioned is afforded by a species from Bear Island
described by Heer[623] as _Lepidodendron Wükianum_ and afterwards
referred by Nathorst[624] to _Bothrodendron_. The same type is recorded
also by Schmalhausen[625] from Lower Carboniferous or Devonian strata
of Siberia. Certain Scotch specimens from the Calciferous Sandstone,
which Kidston[626] referred to Heer’s species, are regarded by Nathorst
and, in part at least, by Weiss[627] and Sterzel as representing
a distinct species which these authors designate _Bothrodendron
Kidstoni_[628].

Without attempting the hopeless task of discriminating between
the various Carboniferous and Devonian specimens described under
the names _Cyclostigma_ or _Bothrodendron_, reference may be made
to the following records as illustrating the wide distribution of
the genus. Schmalhausen[629] records _Cyclostigma kiltorkense_
from Siberian rocks assigned to the Ursa stage (Devonian or Lower
Carboniferous). The fossil described by Dawson[630] from the Devonian
of Gaspé as _Cyclostigma densifolium_ probably represents a badly
preserved example of _Bothrodendron_: Weiss’s species _Cyclostigma
hercynium_[631] from Lower Devonian rocks of the Hartz district
may be identical with _Bothrodendron kiltorkense_. The supposed
identity of the latter species with _Dechenia Roemeriana_ Goepp., as
described by Potonié[632], appears to require confirmation[633], but
if this author is correct the connexion demonstrates the continuity
of Bothrodendron shoots and Stigmaria-like subterranean organs. The
specimens described from South Africa, from strata which may be
correlated with the Upper or possibly with the Lower Carboniferous
series of Europe, as _Bothrodendron Leslei_[634] in all probability
represents a species closely allied to the Irish and Bear Island
type. _Bothrodendron Leslei_ named after Mr Leslie whose discoveries
in the Carboniferous Sandstone of Vereeniging (Transvaal) have added
considerably to our knowledge of the South African Palaeozoic types,
is represented by imperfectly preserved casts characterised by more or
less circular scars displaying the same irregularity of arrangement
as in _Bothrodendron kiltorkense_. The leaf-scars appear to have
only one small pit, but this may not be an original feature. The
identification of this plant as _Bothrodendron_ receives support from
the discovery of rather more satisfactory specimens at Witteberg sent
to me for examination by Dr Schwarz[635]. These fossils bear a striking
resemblance to _B. kiltorkense_. _Cydostigma australe_[636] Feist.
described from the Lower Carboniferous rocks of New South Wales, though
too imperfectly preserved to refer with confidence to _B. kiltorkense_,
is no doubt a closely allied type.

[Illustration: FIG. 214. _Bothrodendron Leslei_ Seward.

  _b._ Natural size.
  _a, c._ Slightly enlarged.]

[Illustration: FIG. 215. _Bothrodendron mundum_ (Will.).

  A, B. From a specimen (No. 26) in the Cambridge Botany School.
  C. British Museum, Williamson Collection. (No. 416 b.)
  D, E. From a section in Dr Kidston’s Collection.]

Reference was made in Volume I. (p. 133) to the so-called paper coal
of Carboniferous age from Central Russia, which consists of masses of
thin strips of cuticle of Bothrodendron stems. The figures published
by Zeiller[637] show that the plant possessed an epidermis consisting
of polygonal cells interrupted by spirally disposed gaps marking the
position of leaves; the gaps measure 0·5–1·5 mm. in breadth and agree,
therefore, with the size of the leaf-scars of the smaller forms of
_Bothrodendron_. The specimens from the Russian mines were first
figured by Trautschold and Auerbach[638] as _Lepidodendron tenerrimum_
and afterwards referred by Zeiller to _Bothrodendron punctatum_[639].
Nathorst[640], however, states that an examination of the Russian
material leads him to retain the name originally proposed; he records
the same type from Upper Devonian rocks of Spitzbergen. The chief
interest of these Russian specimens is their manner of preservation,
which Renault has described as the result of bacterial action; he
claims to have recognised the actual bacteria associated with the
cuticular membranes[641].


           _Anatomy of vegetative shoots_ of Bothrodendron.

In 1889 Williamson[642] described several specimens of petrified
shoots from the Coal-Measures of Halifax which he named _Lepidodendron
mundum_: these are now known to be branches of a _Bothrodendron_. The
discovery was made by Mr Lomax[643] who found specimens showing the
external characters of _Bothrodendron_ and the anatomical characters
of _Lepidodendron mundum_. In some of the smaller twigs, the stele
consists of a solid core of xylem with external protoxylem; but in
the majority of specimens the centre of the xylem is replaced by
parenchymatous tissue, either as a small axial strand or, as in the
specimen shown in fig. 215, D, a wide pith, the elements of which
are arranged in regular vertical series. A diagrammatic section of
a small axis is represented in fig. 215, A: this branch, 2 mm. in
diameter, is composed of a broad outer cortex consisting exclusively of
primary tissue the outer cells of which are smaller and have thicker
walls than the more internal elements. The leaf-traces, _lt_, are
accompanied by a strand of delicate tissue, the parichnos. The stele
is almost solid; the tissues in contact with the xylem have not been
preserved but the inner cortex is represented by a few layers of small
parenchymatous cells, _c_¹. The larger section shown in fig. 215,
D, was cut from a specimen from Dulesgate of which the smooth surface
exhibits the characteristic leaf-scars of _Bothrodendron_. The section
measures 3 cm. in its longest diameter and the stele has a breadth of
3 mm. The outer cortex has a smooth surface and is composed of rather
thick-walled cells succeeded by a zone of secondary elements. The
middle cortex has disappeared and the space is partially occupied by
Stigmarian rootlets, _s_, and crushed patches of cortical tissue. The
position of a leaf-scar is seen at _a_; this is more clearly shown in
the enlarged drawing fig. E.

In his account of _Lepidodendron mundum_, Williamson[644] described
a section in which the primary wood is surrounded by a considerable
thickness of secondary xylem; a diagram of this is shown in fig. 215,
C. An examination of the section led me to compare the structure of
the outer cortical cells, characterised by radial rows of tangentially
elongated elements, with the outer cortex of _Stigmaria_. It has
recently been shown by Weiss[645] that this and other similar sections
present several points of agreement with _Stigmaria_, particularly
with _Stigmaria Brardi_ as described by Renault. At _s_ in fig. 215,
C, a vascular strand is seen passing through the outer cortex; this is
almost certainly the bundle of a rootlet: in the sections described by
Weiss rootlets are shown in a similar position. The chief anatomical
features of the Stigmaria-like organs of _Bothrodendron_ are:—the
considerable development of secondary xylem, the structure of the
outer cortex, which is practically identical with that of _Stigmaria
ficoides_, and the association of groups of short transfusion tracheids
with the bundles of the rootlets. It is very probable that the absence
of secondary xylem in the vegetative shoots of _Bothrodendron_ is
merely an accident and not a real distinction between the aerial and
subterranean branches of the plant; a supposition rendered probable by
the occurrence of secondary xylem in the axis of the cone described
by Watson. As Weiss points out, there are certain differences between
the true _Stigmaria_ and the corresponding organ of _Bothrodendron_;
the secondary xylem in _Bothrodendron_ is not broken up by broad
medullary rays as in the common _Stigmaria_, and in _Bothrodendron_ the
occurrence of a ring of primary xylem is another peculiarity.

In the vegetative shoots of _Bothrodendron mundum_ the stele differs
from those of _Lepidodendron_ in the narrower primary xylem ring and
in the large size of the metaxylem tracheae; from _Lepidodendron
Harcourtii_ and _L. fuliginosum_ the xylem is distinguished by its
smoother outer face which consists of numerous narrow xylem elements.

[Illustration: FIG. 216. _Bothrostrobus._ _l_, ligule. (After Watson.)]


_Cones_ of Bothrodendron (_Bothrostrobus_[646]).

The long and narrow cones referred to _Bothrodendron minutifolium_ from
English and French Coal-Measures are known only as impressions and it
is not possible to say whether they were heterosporous or homosporous;
the drawing given by Zeiller (Fig. 212, E) shows that the sporangia
were of the same form as those in _Lepidostrobus_, but we have no
more exact information as to their morphology. A recently published
description of a petrified strobilus by Mr Watson affords a welcome
addition to our knowledge. There is little doubt that this cone was
borne by a species of _Bothrodendron_; the evidence for this conclusion
is supplied by the agreement of the anatomical characters of the stele
with that of the vegetative shoots originally described by Williamson
as _Lepidodendron mundum_ and by the constant association of the cones
and vegetative shoots. In 1880 Williamson described a crushed cone
containing both megaspores and microspores which he spoke of as “a
diminutive organism, reminding us more of the dwarfed fruits of many
living Selaginellas than of the large _Lepidostrobi_[647].” Watson’s
specimens enable us to give a more complete account of this type. The
axis of the strobilus bears short sporophylls bent upwards into a
distal limb with a conspicuous ligule in a deep pit beyond the shortly
stalked sporangium. The length of the strobilus is estimated at 10 mm.;
the stele is of the same type as that of _Bothrodendron mundum_, but
it differs from the specimens of the vegetative shoots so far found
in having some secondary xylem. As shown in the sketch reproduced in
fig. 216 each sporophyll is characterised by two tangentially placed
grooves, _g_, on the lower face, and by numerous transfusion tracheids,
_tr_, above the vascular bundle, _vb_, immediately below the ligule,
_l_. Megasporangia and microsporangia occur on the same cone, the
megasporangia being on the lower sporophylls and containing a single
tetrad of megaspores. Fig. 219, E, shows a radial longitudinal section
of a microsporophyll bearing a sporangium on the adaxial side of the
ligule, _l_, below which is the single vascular bundle and a group of
short tracheids at _t_. The sporangia closely resemble those of species
of _Selaginella_ and _Lycopodium_ and, as pointed out by Watson[648],
they also recall the sporangia of the Palaeozoic genus _Spencerites_.
_Bothrostrobus_ is distinguished from _Spencerites_ by the presence
of a ligule, by the structure of the axis, and by the different
form of the sporophylls. The occurrence of four spores only in the
megasporangia is another character in which the extinct type resembles
recent Lycopods. It is impossible to decide whether Watson’s cone
represents a more or a less primitive type than _Lepidostrobus_: if we
accept Professor Bower’s views in regard to the evolution of vegetative
organs by the sterilisation of sporogenous tissue, we should probably
place _Lepidostrobus_ lower in the series than _Bothrostrobus_; but
the greater resemblance between the fertile and vegetative shoots of
_Bothrodendron_, as compared with the more pronounced difference in the
case of _Lepidodendron_, may be regarded as an argument in favour of
recognising _Bothrodendron_ as the more primitive type.

Another possible example of a _Bothrodendron_ cone has been described
by Nathorst from Spitzbergen as _Lepidostrobus_ _Zeilleri_[649]; this
appears to consist of an axis bearing spirally disposed sporangia
without any indication of sporophylls. This strobilus may belong to
_Bothrodendron tenerrimum_.


_Pinakodendron_.

The name _Pinakodendron_[650] was instituted by the late Prof. Weiss
for a type of stem closely resembling _Bothrodendron_ but differing in
the presence of a fine reticulation on the outer bark and in the form
of the leaf-scars. Weiss’s genus has been recognised by Kidston in
Dumfriesshire but our knowledge of the plant is as yet based solely on
a few small specimens.


_Omphalophloios_ (_a genus of uncertain systematic position_).

Figs. 193, C, 217.

This generic name was instituted by White[651] for certain specimens of
large stems originally described by Lesquereux from the Coal-Measures
of North America as _Lepidodendron mammillatum_ and _L. cyclostigma_.
The photograph reproduced in fig. 193, C, for which I am indebted to
Dr Kidston[652], represents a specimen described by him from the Upper
Coal-Measures of Somerset as _Omphalophloios anglicus_, and identified
with _Lepidodendron anglicum_ of Sternberg.

The surface of the impression shown in fig. 193, C, is characterised
by clearly defined rhomboidal areas or cushions (fig. 217, E) like
those of _Lepidodendron_, except in the absence of a median keel,
and similar to those on some forms of _Sigillaria Brardi_. A short
distance above the centre of each cushion is an oval or subcordate
region bounded by a rim-like margin and containing a small oval scar,
presumably that of a vascular strand. A triangular elevation which also
shows a small pit (Fig. 217, E, _a_) occurs below the oval area. The
appearance of the surface-features varies considerably on different
parts of a single specimen. Fig. 217, D, represents one of the numerous
figures published by White in his detailed account of the American
material. Each cushion bears a widely open =V=-shaped ridge, which is
described as a leaf-scar; above this is an oval area (2·5 mm. × 1·75
mm.), the surface of which is bounded by a narrow rim. Within the rim
is a smaller concave oval region with a small pit near its upper end.

[Illustration: FIG. 217. _Omphalophloios._

  D. After White. E. After Kidston.]

We cannot, in the absence of petrified material, arrive at any
satisfactory conclusion as to the meaning of these surface-features.
White considers that _Omphalophloios_ is probably a rhizome of one of
the arborescent Lycopods, but whether or not this is its true nature
must be left for future discoveries. The fact that the rootlet bundles
of some Stigmarian axes are accompanied by a parichnos strand, as Weiss
has shown, may prepare us for the discovery of surface-features on
_Stigmariae_ not unlike those of _Omphalophloios_. (Fig. 193, C.)

A possible comparison may be suggested also with _Sigillaria Brardi_
as figured by Germar (fig. 196, A) in which circular scars, which may
be the scars of rootlets, occur below the leaf-base areas. It is not
impossible that in the surface-features of _Omphalophloios_ we have
both leaf and rootlet scars represented.


_General considerations._

The solid xylem core characteristic of the stele of some species of
Palaeozoic Lycopodiales (e.g. _Lepidodendron esnostense_ and _L.
rhodumnense_) may probably, as Tansley and Chick[653] point out, be
regarded as the lineal descendant of a primitive axial strand of
water-conducting elements. In the course of evolution the centre of the
tracheal column became partially converted into parenchymatous tissue,
as in _Lepidodendron vasculare_. The arrangement of the short cells
in regular vertical series is reminiscent of an early stage in the
development of tracheae: instead of forming tubular conducting elements
the central part of the stelar meristem acquired the short-celled form;
some of the cells became lignified as isodiametric storage tracheae
while others persisted as thin-walled parenchyma.

The production of secondary xylem and an increase in the girth of the
whole stem led to reduction in the amount of centripetally developed
conducting channels. Some of these assumed a new rôle and a shape in
harmony with their functions. A later stage is represented by a further
encroachment of the central parenchyma on the cylinder of centripetal
xylem, as seen in _Lepidodendron Harcourtii_ and other species. The
next stage is afforded by ribless species of _Sigillaria_ in which
the primary xylem is broken up into separate conducting strands. As
Kidston[654] reminds us, it is in the geologically more recent species
of _Sigillaria_, such as _S. Brardi_, which persist into the Permian
era, that this more extreme case of reduction occurs. The older genus
_Lepidodendron_ seems to have retained to the last the complete
cylinder of primary xylem. In the stele of _Stigmaria_, the rhizome of
_Sigillaria_ and of _Lepidodendron_, reduction of the centripetal xylem
has passed beyond the stage represented by the broken cylinder of the
ribless Sigillarias. With the exception of the examples described by
Renault[655] and by Weiss[656], _Stigmaria_ is characterised by little
or no centripetal primary xylem. It is, however, noteworthy that
Renault’s _Stigmaria_, in which centripetal xylem forms a prominent
feature, is attributed to _Sigillaria Brardi_, a species in which the
vascular cylinder of the aerial stem illustrates a later and not an
earlier phase in the replacement of centripetal by centrifugal wood.

It would seem, as Lady Isabel Browne[657] says, that most Stigmarian
axes had reached a more advanced stage in specialisation than is shown
in the stelar structure of the aerial shoots. The relatively greater
and probably the more precocious development of secondary xylem in
_Stigmaria_ than in _Lepidodendron_ or _Sigillaria_ may have some
significance in relation to the smaller amount of “old wood[658]” (in a
phylogenetic sense) in their steles.

As is pointed out in a later chapter, recent researches into the
anatomy of extinct members of the Osmundaceae by Kidston and
Gwynne-Vaughan have brought to light a striking parallelism in
evolutionary sequence between the Lepidodendreae and the ancestors of
_Osmunda_ and _Todea_, the two surviving genera of one of the most
ancient families of ferns.

There can be little doubt as to a very close relationship between
_Sigillaria_, _Lepidodendron_, and _Bothrodendron_. _Sigillaria_ seems
to have outlived _Lepidodendron_ and _Bothrodendron_. The two latter
genera are recorded from Upper Devonian rocks in several localities,
_Bothrodendron_ being particularly abundant in the pre-Carboniferous
floras of Bear Island and other parts of the world. A remarkable
stem described by Dr White[659] as _Archaeosigillaria primaeva_ from
Upper Devonian shales of New York is spoken of by him as “one of the
most highly developed representatives of a fairly distinct archaic
group foreshadowing the later genera _Bothrodendron_, _Sigillaria_,
_Lepidodendron_ and _Lepidophloios_.” The type-specimen, when first
discovered, consisted of an apparently unbranched stem reaching a
length of 5 metres. From the swollen basal part Stigmaria-like
rootlets spread into the surrounding shale. At a higher level the
fissured bark shows indistinctly defined leaf-cushions which pass
gradually upwards into cushions and scars arranged in closer order
on regular vertical ribs. The surface-features in this region are
practically those of a ribbed _Sigillaria_. Traced farther upwards the
vertical ribs die out and cushions of the Lepidodendroid form cover
the surface of the bark. The leaf-scars, with a supraposed ligular
pit and two vertically elongated parichnos-scars, are said to bear
a closer resemblance to those of _Sigillaria_ and _Bothrodendron_
than to the leaf-areas of _Lepidodendron_. Nothing is known as to the
anatomy of this stem, nor have fertile shoots been discovered. In the
absence of more trustworthy evidence than is available conclusions of a
phylogenetic nature must be accepted at their true value. It is however
legitimate to describe _Archaeosigillaria primaeva_ as one of the
oldest examples of a lycopodiaceous plant which shows well-preserved
external features, and these are of exceptional interest as indicating
a combination of generic characters. This Devonian type lends support
to the view that _Lepidodendron_ and _Sigillaria_ are offshoots,
differing from one another in comparatively unimportant points, from a
common ancestral type.

The generally accepted statement that arborescent Palaeozoic
Lycopodiales bore their sporangia on specially modified leaves
(sporophylls) grouped in cones which were usually produced at the tip
of slender branches, has recently shared the fate of most rules. Prof.
Bower in his _Origin of a Land Flora_ mentions a Belgian specimen of
_Pinakodendron musivum_ Weiss from the Westphalian series (Middle
Coal-Measures), to be described by Dr Kidston, which bore its sporangia
“associated with the leaves of certain portions of the stem, without
any cone-formation. The fertile and sterile portions are distinguished
only by the presence or absence of sporangia[660].”

_Lepidodendron_ and _Sigillaria_ can hardly be claimed as the direct
ancestors of any existing type of Lycopodiales, but while exhibiting
points of contact with _Lycopodium_, _Selaginella_, and _Psilotum_ they
are perhaps more closely allied to _Isoetes_.

Lady Isabel Browne[661], who has recently published an excellent
summary of the evidence on the relation of the Lepidodendreae to
_Isoetes_, concludes her examination of the arguments by expressing the
opinion that there is a strong probability of the correctness of the
view that _Isoetes_ may be derived “from the Lepidodendraceae in the
widest sense of the word.” This decision seems to me to accord best
with the facts.

The further question as to the relation of these Palaeozoic genera to
plants higher in the scale must be reserved for fuller consideration
in another volume. An attempt will also be made to consider how far
anatomical structure may be used as a guide to the conditions under
which _Lepidodendron_ and _Sigillaria_ as well as other members of
the Permo-Carboniferous floras passed their lives. The secondary
xylem of _Lepidodendron_ and _Sigillaria_ affords a striking example
of water-conducting tissue of homogeneous structure comparable
with the wood of Conifers rather than with that of Angiosperms. It
was presumably formed, for the most part, under uniform climatic
conditions: the absence of rings of growth points to uninterrupted
supply to evergreen shoots exposed to no alternation of activity and
arrested growth. Attention has already been called to the absence of
any tissue corresponding to secondary phloem. Even in young shoots of
_Lepidodendron_, no tissue has been found external to the meristematic
zone agreeing in the form of its elements with the channels through
which the elaborated food is conveyed from the leaves of recent plants
to the regions of cell-building. That the ‘secretory zone’ may have
served this purpose, at least in young stems, is not improbable. On
the other hand, it is difficult to understand why older Lepidodendron
stems show no indication of additions to the secretory zone. If this
tissue served for the transport of proteids we should expect to find
provision made for its constant renewal _pari passu_ with the secondary
growth of the xylem. The conclusion seems to me inevitable that the
supply of building-material was otherwise provided for than in recent
vascular plants. The physiological division of labour may have been
less complete in the tissue-systems of the Palaeozoic Lycopods than
in the more highly specialised organs of such an extinct genus
as _Lyginodendron_ or than in recent plants. Our knowledge of the
anatomical structure of many extinct types has already reached a stage
when we should take greater heed of the _modus operandi_ of the complex
machinery revealed by a study of petrified stems. From the known we
proceed to interpret the unknown; but there is a danger of neglecting
the possibilities of evolution during the countless ages which separate
the forests of the Coal period from those of the present era. We may
easily allow preconceived ideas to warp our judgment in attempting
to distribute the manifold activities which made up the life of a
_Lepidodendron_ among the structural units of the plant-body.




                             CHAPTER XIX.

            =Seed-bearing plants closely allied to members
                         of the Lycopodiales.=


                          i. _Lepidocarpon._

In 1877 Williamson[662] published an account of some fossil seeds which
he referred to Brongniart’s genus _Cardiocarpon_[663], a generic title
for certain Gymnospermous seeds. Some of these he identified, on the
authority of the author of the species, with _Cardiocarpon anomalum_
Carruthers[664]. Several years later Wild and Lomax described a new
type of strobilus from the Lower Coal-Measures of Lancashire[665].
The result of this discovery and of the subsequent examination by
Scott of additional material, was to establish the fact that the seeds
described by Williamson and generally accepted as Gymnospermous, are
in reality sporangia belonging to a Lycopodiaceous cone. The seeds to
which Carruthers gave the name _Cardiocarpon anomalum_ are, however,
distinct from those described under the same name by Williamson and
are those of a true Gymnosperm. For this seed-bearing strobilus
Scott[666] instituted the generic name _Lepidocarpon_, which he thus
defined: “Strobili, with the characters of _Lepidostrobus_, but each
megasporangium was inclosed, when mature, in an integument, growing
up from the superior face of the sporophyll-pedicel. Integument,
together with the lamina of the sporophyll, completely enveloping
the megasporangium, or nucellus, leaving only an elongated, slit-like
micropyle above. A single functional megaspore or embryo-sac developed
in each megasporangium, occupying almost the whole of its cavity.
Megaspore ultimately filled by the prothallus or endosperm. Sporophyll,
together with the integumented megasporangium and its contents,
detached entire from the axis of the strobilus, the whole forming a
closed, seed-like, reproductive body. Seed-like organ horizontally
elongated, in the direction of the sporophyll-pedicel, to which the
micropylar crevice is parallel.”


_Lepidocarpon Lomaxi_, Scott. Fig. 218.

An immature cone of _L. Lomaxi_ is practically identical with a
_Lepidostrobus_; its sporangia are naked and only acquire their
integuments at a later stage. A mature strobilus has a diameter of at
least 3 cm. and is about 4 cm. in length. As in typical _Lepidostrobi_,
the axis bears spirally disposed sporophylls, and each sporophyll has a
long narrow pedicel approximately at right angles to the cone axis with
its distal end expanded into a broad and thick lamina (fig. 218, B).

At the distal end the pedicel has a thin marginal wing (fig. 218, C,
right-hand half) continuous with the upturned protective lamina. To the
upper face of each sporophyll is attached along the whole length as far
as the ligule, a single large sporangium; on each side of the base of
the sporangium the sporophyll forms a supporting cushion. The relation
of the sporangium to the ligule, _l_, is shown in fig. 218, B, and in
the tangential section, C, which illustrates the triangular form of the
sporangium near its distal end.

In mature cones, the sporangia assumed the form of seeds, the change
being due to the growth of an investing integument from the upper
face of the sporophylls on each side of the sporangia. Fig. 218, A,
illustrates the form of a sporangium as shown in tangential sections;
the vascular bundle is seen below the base of the sporangium and the
gaps right and left of it probably mark the position of parichnos
strands. On each side of the sporangium, _b_, a fairly thick wall of
tissue has grown up from the sporophyll, forming an integument which
overtops the apical ridge of the sporangium, leaving a narrow micropyle
in the form of a long crevice (_m_, fig. 218, B). At the proximal
end of the sporangium the integument forms an enclosing wall; at the
distal end it abuts on and is continuous with the upturned end of the
sporophyll. It is clearly established by Scott that the tissue which
invests the sporangia is not the upturned margins of the sporophyll,
but a new formation fully entitled to the designation integument. It
is noteworthy that the integument is not developed until a late stage
in the ontogeny of the strobilus; it is not formed until after the
production of the prothallus[667]. The diagrammatic sketch, fig.
218, B, shows the relation of the integument to the sporophyll and
sporangium, the outline of the latter being indicated by a broken
line. The columnar wall of the sporangium (fig. 218, A, _b_) forms a
closed beak within the micropylar crevice, and in the interior of the
sporangial cavity the slightly shrivelled membrane, _a_, represents the
single megaspore; traces of the aborted sister-cells of the megaspore
are occasionally met with. Scott describes a specimen in which the
megaspore is filled with tissue agreeing in appearance with the
prothallus in a megaspore of _Isoetes_ or _Selaginella_; no undoubted
archegonia or female organs have been discovered, nor has any spore
been found containing an embryo.

[Illustration: FIG. 218. _Lepidocarpon Lomaxi_, Scott.

  A and C. After Scott.
  B. Diagram of a single sporophyll: _m_, micropyle; _St_, stele.]

The axis of _L. Lomaxi_ has a medullated stele constructed on the same
plan as that of some species of _Lepidodendron_ and _Lepidostrobus_;
the vascular bundles supplying the sporophylls pass obliquely upwards
and outwards from the stele, _St_, fig. 218, B, and bend slightly
downward just before entering the pedicel of a sporophyll.

Dr Scott has also described a strobilus containing microsporangia
partially enclosed by a rudimentary integument. It is, however, of
considerable interest to find a partial development in the case of a
male flower of an integumentary outgrowth, which it would seem could
only be of real functional importance in the female shoot.

It is important to notice that specimens of a second species of
_Lepidocarpon_, _L. Wildianum_, are recorded from Lower Carboniferous
beds of Scotland, a fact which points to a considerable antiquity for
this seed-bearing Lycopodiaceous type[668].

The most important question to consider in regard to _Lepidocarpon_
is—are we justified in applying to the integumented sporangia the term
seed? The megaspore was not set free as it is in recent Pteridophytes,
such as _Azolla_ and other genera with which _Lepidocarpon_ may be
compared; it was on the other hand retained in the sporangium, as
may sometimes happen even in recent species of _Selaginella_ (cf.
fig. 131, D). Moreover, the megaspore is characterised by a thin
enclosing membrane in contrast to the thick coat of a spore which
is destined to be shed. The peculiar slit-like form of the micropyle
is a distinguishing feature, but this may be readily explained as
a convenient form in the case of a radially elongated sporangium.
The absence of an embryo, though a distinguishing feature of
_Lepidocarpon_, cannot be held to be a serious obstacle to the use of
the term seed; in recent Cycads the embryo, as Scott points out, may
not begin to develope until the seed has been shed. It is possible that
the seeds of _Lepidocarpon_ were not pollinated on the parent plant.

The lesson which this extinct type teaches, is that certain
Lycopodiaceous plants of the Palaeozoic era had reached an important
stage in the evolution of a seed. The morphological essentials of true
seeds had been acquired; but we do not know the biological conditions
under which pollination and fertilisation were effected. Another point
of considerable interest is the value of this discovery as an argument
in favour of the view that some Gymnosperms are derived from Lycopod
ancestors. Leaving the general question until later, it may at any rate
be stated that in _Lepidocarpon_ we have a demonstration of the fact
that the Lycopodiales were not always distinguished from Gymnosperms
by the absence of seeds. There are certain features in _Lepidocarpon_
shared by the seeds of Araucarieae[669] which may well mean something
more than mere parallel development in two distinct phyla of the
plant-kingdom[670].


                           ii. _Miadesmia._

In 1894 Prof. Bertrand[671] published an account of certain fragments
of petrified leaves and twigs of a small herbaceous Lycopodiaceous
plant, under the name _Miadesmia membranacea_, which he discovered
in English material in association with _Lepidodendron Harcourtii_.
Subsequently Scott recognised the megasporophylls of the same plant,
and microsporophylls have also been discovered. The most complete
account of _Miadesmia_ so far published we owe to Dr Benson[672],
whose description is based on specimens from several sources.


_Miadesmia membranacea_, Bertrand. Fig. 219, A–D.

[Illustration: FIG. 219. A–D _Miadesmia_; E _Bothrodendron_.

  A. Radial section of megasporophyll: _s_, sporangium; _m_,
     megaspore; _l_, ligule. (From a drawing kindly lent by Mrs D. H.
     Scott.)
  B, C. Leaf with ligule. (From a section in Dr Kidston’s Collection.)
  D. Transverse section of sporophyll. (After Scott.)
  E. Radial section of microsporophyll of _Bothrodendron_. (From a
     section in the Manchester Museum; Hick Collection R. 406.)]

The slender stem, characterised by unequal dichotomy, has a single
protostele composed of scalariform tracheids with 3–6 peripheral
protoxylem groups. A zone of delicate tissue surrounds the xylem; this
is described as phloem, but it is not clear whether the designation
is based on histological characters or primarily on its position.
The cortex consists of an inner lacunar tissue and an outer region
limited by a small-celled superficial layer sharply contrasted with
the underlying layers of larger cells. The stem of _Miadesmia_ is not
uncommon in sections of the Lancashire calcareous nodules, and may be
recognised by the delicate crushed tissue of which it mainly consists
and by large hypodermal parenchyma. The spirally disposed leaves bear
a conspicuous and relatively large ligule, 3 mm. long, in a deep pit
(fig. 219, B and C) roofed over by a few layers of tissue corresponding
to the velum in _Isoetes_ (cf. fig. 133, E, _v_). The fairly thick
central region of the lamina is expanded laterally into thin wings,
which in the living state probably bore delicate hairs. These delicate
leaves, apparently without stomata, were attached to the stem at an
acute angle, and Miss Benson suggests that their form and arrangement
may have enabled them to hold water by surface-tension. As seen in
fig. 219, B, C, which represents part of a transverse section near the
leaf-base, the ligule is a very characteristic feature, and the size
of the single vein is in keeping with the almost filmy nature of the
lamina.

In addition to the sections in British collections, I have been
enabled by the kindness of Prof. Bertrand to see photomicrographs of
the sections on which he founded the genus. One of these sections,
transverse to the stem and leaves, illustrates in a striking manner the
relatively large size of the leaves and ligules in proportion to the
delicate axis of the shoot.

The megasporangiate cone has an axis which agrees in its structure
with that of the vegetative stem and bears several megasporophylls
approximately at right-angles. As in the foliage leaves, the ligule
is prominent and large, and lies in a groove which contains also
the megasporangium; both ligule, _l_, and sporangium, _s_, as seen
in the transverse section represented in fig. 219, D, are covered
by an integument or velum which arises in the proximal part of the
leaf and leaves a circular micropylar opening at the beak-like apex
of the sporangium. The circular micropyle is surrounded by numerous
hairs borne on the integument and which presumably played the part
of a feathery stigma. A single megaspore with a thin membrane, _m_,
abuts on the fairly strong sporangial wall, _s_; in some cases the
sporangium and megaspore walls may be indistinguishable, a feature
suggesting comparison with seed-structure. Some megaspores have
been found filled with a prothallus. The longitudinal section shown
in fig. 219, A, illustrates the characteristic horizontal position
of the megasporophyll, as also the relation of the ligule, _l_, to
the sporophyll with its single vascular bundle, and to the hairy
integument, which overarches both sporangium and ligule; the line
_m_ shows the position of the megaspore-membrane, detached from the
sporangial wall on the upper side but in contact with it below.
The microsporophyll shown in 219, E, was originally referred to
_Miadesmia_ but has since been recognised by Watson[673] as that of a
_Bothrostrobus_.

_Miadesmia_ affords an example of a Palaeozoic plant comparable with
_Isoetes_ and _Selaginella_; it agrees also with _Lepidocarpon_ in
possessing true seeds, and with Watson’s _Bothrodendron_ cone in the
shape of the sporangia, which are more like those of _Selaginella_
than the radially elongated sporangia of _Lepidostrobus_. _Miadesmia_
agrees with _Selaginella_, e.g. _S. spinosa_, in its stelar structure,
in the form of the sporangia, and in the presence of a ligule. It
is distinguished by having only one instead of four megaspores in a
sporangium, in the possession of an integument which formed a close
investment to the spore and served as a stigma (comparable with the
stigma-like integument of the male flower of _Welwitschia_), and in the
shedding of the megasporophylls, which have been aptly compared with
winged seeds.

[Sidenote: LEPIDOCARPON]

On the ground of their general anatomical features _Lepidocarpon_
and _Miadesmia_ are clearly entitled to be included among extinct
representatives of the Pteridophyta. These plants had, however,
crossed what it has been customary to regard as the boundary between
Pteridophytes and Phanerogams: they possessed megasporangia with the
attributes of seeds. It has been suggested by Lester Ward[674] that
Pteridophytic seed-bearing plants shall be recognised as a distinct
phylum for which he proposes the name Pteridospermaphyta, a designation
implying exclusion from the Spermatophyta as usually understood. For
seed-bearing Lycopodiaceous genera he suggests the name Lepidospermae.
As knowledge of the Palaeozoic seed-plants increases revision of
existing classifications and group names will become necessary, but as
yet we are hardly in a position to draw up a satisfactory scheme of
grouping; we know little of _Lepidocarpon_ as a whole and it would be
premature to commit ourselves, even provisionally, to a classification
which is based on such meagre evidence as we possess. Moreover the
value to be attached to the seed-habit as a basis of classification can
hardly be estimated until fuller information is obtained.




                              CHAPTER XX.

                              FILICALES.


This division of the Pteridophyta includes both the true ferns
(Filicineae) and the less familiar water-ferns or Hydropterideae.
The almost complete absence of satisfactory evidence in regard to
the geological history of the latter renders this group of secondary
importance from a palaeobotanical standpoint, but, on the other hand,
we possess a wealth of material bearing on the past history and
relative antiquity of the true ferns.

The study of extinct types has so far rendered no substantial help
towards bridging the wide gap between the Filicales and the lower
plants. As Mr Tansley[675] says in his admirable lectures on _The
Evolution of the Filicinean Vascular System_, “The biggest gap in
the plant kingdom at the present time is undoubtedly that which
separates the Pteridophytes from the plants definitely below them in
organisation, and directly we try to step behind the ferns we tumble
into this abyss.” Resemblances long ago recognised between certain
ferns and the cycads, a section of the Gymnosperms, were regarded by
a few botanists as indications of blood-relationship, and the results
of recent researches into the morphological characters of extinct
Palaeozoic types are generally held to confirm these surmises. Prof.
Chodat[676] of Geneva has recently challenged the validity of the
arguments on which the affinity of cycads and ferns has been accepted
by the great majority of botanists. Whether or not his criticisms stand
the test of unbiassed examination, they must at least lead us to
substitute a critical consideration of the facts for a mere repetition
of conclusions which appeal to our imagination. Despite Prof. Chodat’s
warning, we may still quote with confidence a phrase used in another
connexion—ferns “are links in a chain and branches on the tree of life,
with their roots in a past inconceivably remote[677].”

[Sidenote: PTERIDOSPERMS]

Transitional forms which are regarded as pointing to a common origin
for ferns and cycads are known in abundance; other types have also been
discovered which lead some authors to go so far as to derive the whole
of the seed-bearing plants from an ancestry the descendants of which
are represented by existing ferns. While hesitating to allow the ferns
or fern-like plants the peculiar position of universal ancestors, we
must admit that there is no group of plants with a history of greater
importance from an evolutionary standpoint than that with which we are
now concerned.

There are, however, some difficulties to face in attempting to decipher
the history of the Filicineae as recorded in the earth’s crust. Few
fossil plants are so familiar as the well-preserved carbonaceous
impressions of compound leaves on the shales of our Coal-Measures,
which were referred by older authors to recent genera and species of
ferns and accepted by later writers as undoubted examples of Palaeozoic
ferns. The common belief in the dominance of ferns in Palaeozoic
floras is reflected in the novelist’s description of the Carboniferous
period, “when the forms of plants were few and often of the fern
kind[678].” We now know that very many of these Carboniferous leaves
belonged to plants differing widely in morphological characters from
the modern genera to which they exhibit so deceptive a resemblance.
These pseudo-ferns, recently christened Pteridosperms or seed-bearing
fern-like plants, are dealt with in a later chapter. The discovery
of this extinct group has added enormously to our knowledge of
plant-evolution and at the same time has rendered much more difficult
the task of unravelling the past history of the true ferns. As soon
as it was demonstrated that many familiar Palaeozoic “ferns” are not
ferns, some authors went far towards concluding that however close
might be the agreement between fossil and recent leaves suspicion of
close relationship must be set aside. Like the earlier writers who
described fossils as _lusus naturae_ fashioned by devilish agency
to deceive too credulous man, the discovery of seed-bearing plants
with the foliage of ferns threatened to disturb the mental balance of
palaeobotanists. The fact is, we cannot in some cases determine from
leaf-form alone whether or not a fossil is a true fern; we may, as
Professor Bower[679] suggests, regard all fern-like fossils as ferns
until they are proved to be Pteridosperms, or in a spirit of scientific
scepticism, we may at once admit that many Palaeozoic fern-like
leaves must await further evidence before their true position can be
determined. It is impossible, as Zeiller[680] says, in the present
state of our knowledge to range fern-like Palaeozoic plants in two
groups, one referred to Filicineae and the other to the Pteridosperms.

The following classification of the Filicales is based on that adopted
by Prof. Engler in the latest edition of his _Syllabus_[681] and on the
results of Bower’s[682] excellent work on the spore-bearing members of
recent ferns.

The members of the Filicales are characterised by the same well-marked
physiological division of labour in their vegetative parts as are the
Lycopods; the plant is the asexual generation (sporophyte), while the
sexual generation (gametophyte) is small and inconspicuous, either
an independent green prothallus or a tissue more or less completely
enclosed in the spore. The large size of the leaves, which in the young
state are usually coiled like a crozier (fig. 220, A), is a striking
characteristic of the ferns; they are megaphyllous in contrast to the
microphylly of the Lycopods.


                   I. =Leptosporangiate Filicales.=

In these homosporous and heterosporous plants the sporangia are
developed from single epidermal cells.

[Illustration: FIG. 220. Young fronds of (A) _Angiopteris evecta_ and
  (B) _Cycas revoluta_. (Reduced.)]

(_a_) _Eufilicineae._ The sporangia bear spores of one kind only; the
wall of a sporangium consists of one layer of cells. In the great
majority of cases the sporangia are characterised by the possession
of a conspicuous row of thick-walled brown cells, the annulus[683],
which serves as a mechanism for dehiscence and spore-dispersal. The
fertile leaves, identical in form with the sterile, or more or less
sharply contrasted, usually bear the sporangia on the under surface of
the lamina in definite groups or sori, and not on the upper surface or
grouped in strobili as in the Lycopodiales. The stem is dorsiventral or
radial in structure, creeping or erect, frequently clothed with chaffy
scales (ramenta) and less often with multicellular hairs. The sexual
generation is represented by a small green prothallus which lives for
a short period only and dies after nursing the fern-plant through its
earliest stages.


(_b_) _Hydropterideae._ Heterosporous water-ferns differing
considerably in habit from the true ferns. Each megasporangium
contains a single megaspore and several microspores are produced in
each microsporangium. The gametophyte is represented by tissue more or
less enclosed in the spore. [Genera _Salvinia_, _Azolla_, _Marsilia_,
_Regnellidium_, _Pilularia_. See Chapter XXVI.]


(_a_) _Eufilicineae._ The classification of the true ferns in common
use is based almost exclusively on the structure of the sporangium, the
form and position of the sori, and on the presence or absence of an
indusium (the tissue which in some ferns partially or completely covers
each sorus). In recent years there has been considerable activity
in the investigation of fern anatomy with a view to elucidating the
natural relationship between recent families or genera. The results
of these researches are on the whole consistent with the scheme and
grouping adopted in the _Synopsis Filicum_ of Hooker and Baker and in
general harmony with the main conclusions arrived at by Bower from an
intensive study of the development of fern sporangia. The following
classification is based on that of Bower who takes as a basis (i) the
relative time of appearance of the sporangia in a single sorus, (ii)
the structure of the sporangia and their orientation relative to the
whole sorus, (iii) the productiveness of sporangia (spore-output).

  Osmundaceae      ╭ _Simplices_ (Bower). The sporangia are relatively
  Schizaeaceae     ┤  large and all the sporangia in a sorus have a
  Gleicheniaceae   │  simultaneous origin: the annulus is oblique.
  Matonineae       ╰

                   ╭ _Gradatae_ (Bower). Sporangia arise in basipetal
  Loxsomaceae      │  succession on a more or less elongated receptacle
  Hymenophyllaceae │  (portion of the leaf lamina which projects as a
  Cyatheaceae      ┤  cushion or column on which the sporangia are
  Dennstaedtiinae  │  borne); annulus oblique; indusium, if present,
                   │  in the form of a cup or flap of tissue arising
                   ╰  from the base of the sorus.


                   ╭ _Mixtae_ (Bower). This division includes the
                   │  Polypodiaceae, by far the largest family of ferns.
  Polypodiaceae    │  The sporangia are characterised by their
  Parkeriaceae     ┤  relatively small size, the presence of a slender
                   │  stalk, the absence of regular orientation or
                   │  sequence in development, and by the presence of a
                   ╰  vertical annulus.


                   ╭ The Dipteridinae include species with the characters
  Dipteridinae     ┤  of the _Mixtae_, and one species in which the
                   ╰  sporangia develope simultaneously (_Simplices_).


               =Osmundaceae=[684]. (_Osmunda_, _Todea_.)

Sporangia large and rather stouter than those of other Leptosporangiate
ferns, borne in small groups (filmy species of _Todea_) in linear and
frequently confluent sori (_Todea barbara_; fig. 221, D) or clustered
round the axis of modified fertile pinnae with much reduced lamina
(_Osmunda_). The annulus is represented by a group of thicker-walled
cells a short distance below the apex (fig. 221, C). This family
stands apart among the ferns; in some respects, e.g. in the more
robust sporangia occasionally forming synangia, and in the presence
of stipular wings, it forms a transitional series between the
Leptosporangiate and Eusporangiate ferns. The only European species of
_Osmunda_, _O. regalis_, is almost cosmopolitan in range; other species
occur in North and South America, in the Far East, the Malay Peninsula,
and in other regions, more especially in the temperate zones. _Todea_
is represented by (i) the South African and Australian species, _T.
barbara_, a fern with a stem, which may reach a height of several feet,
thickly covered with adventitious roots and bearing large and somewhat
leathery fronds; (ii) filmy species in New Zealand, New South Wales,
New Caledonia, and elsewhere. A plant of the small tree-fern _Todea
Wilkesiana_ (Fiji, Samoa, and other islands) in the filmy-fern house at
Kew, to which my attention was drawn by my friend Mr A. W. Hill, has a
slender stem with the characteristic leaf-scars exposed; it presents
a striking similarity to some of the fossil species of Osmundaceae
described in a later chapter.

[Illustration: FIG. 221.

  A. _Osmunda cinnamomea_ (after Faull).
  B. _Todea barbara_, p, phloem; s, sclerenchyma.
  C. _Osmunda regalis_ (after Luerssen).
  D. _Todea barbara_ (½ nat. size).]


    =Schizaeaceae.= (_Schizaea_, _Aneimia_, _Lygodium_, _Mohria_.)

Sporangia borne singly and not in groups (sori), readily recognised by
the complete transverse apical annulus usually one layer of cells deep,
but occasionally two layers in depth on the side opposite the line of
dehiscence[685] (fig. 224, B). _Schizaea_ (fig. 222) with the exception
of one species in North America (_S. pusilla_) is characteristic of
Northern India, the Malay region, Australia, New Caledonia, S. Africa,
and elsewhere south of the Equator. _Aneimia_ (figs. 223, 224, A, B),
characterised by the fertile segments with reduced lamina, is chiefly
American: the monotypic genus _Mohria_, resembling in habit the
Polypodiaceous genus _Cheilanthes_, occurs in S. Africa and Madagascar,
while species of _Lygodium_ are widely spread tropical ferns, with one
species in temperate North America. This family has disappeared from
Europe.

[Illustration: FIG. 222. _Schizaea elegans._ (Slightly reduced.) A few
  of the segments terminate in narrow fertile lobes.]

[Illustration: FIG. 223. _Aneimia rotundifolia._ (From the Royal
  Gardens, Kew. ⅓ nat. size.)]


  =Gleicheniaceae= [_Gleichenia_, _Platyzoma_ (= _G. microphylla_)].

Sporangia form circular naked sori composed of a variable number
of sporangia, usually not more than ten and frequently fewer,
characterised by an obliquely horizontal and almost complete annulus
(fig. 224, I). In some species of _Gleichenia_ (sect. _Eugleichenia_)
the ultimate segments are very small and semicircular in form (fig.
226, C), in others (sect. _Mertensia_[686]) the segments are linear
(fig. 226, D), and in many species the fronds are distinguished by
the regular dichotomous branching (fig. 225), frequently showing an
arrested rachis bud in the forks[687] protected by modified pinnules
(fig. 226, D, E). In _Platyzoma_ the leaves are simple, reaching a
length of 20–30 cm., and bear small revolute oval segments.

[Illustration: Fig. 224.

  A. _Aneimia flexuosa._
  B. _A. phyllitidis._
  C. _Hymenophyllum dilatatum._
  D, E, F, G. _Matonia pectinata_; _i_, indusium.
  H. _Thyrsopteris elegans._
  I. _Gleichenia circinata._

  (A, B, after Prantl; C, G, H, I, after Bower.)]

[Illustration: FIG. 225. _Gleichenia dicarpa._ (⅓ nat. size.)]

[Illustration: FIG. 226.

  A, B. _Gleichenites Rostafinskii_, Raciborski.
  C. _Gleichenia dicarpa._ (Nat. size.)
  D, E. _Gleichenia dichotoma._ (Reduced.)

  (A, B, after Raciborski; C, after Hooker; D, E, after Goebel.)]

_Gleichenia_ is represented by several species in the tropics and
extends to south temperate and Antarctic latitudes. The species _G.
dichotoma_ (= _G. linearis_) is one of the more successful tropical
ferns, while _G. moniliformis_ (by some authors recognised as a
distinct genus, _Stromatopteris_) is peculiar to New Caledonia. The
monotypic genus _Platyzoma_ is a xerophilous Australian fern. The
Gleicheniaceae are unrepresented in existing north temperate floras.


                      =Matonineae.= (_Matonia._)

The genus _Matonia_, placed in the Cyatheaceae by Sir William Hooker
and compared by other authors also with the Gleicheniaceae, is now
included in a special family. The sori are circular and consist of
5–11 large sporangia (fig. 224, E, G) sessile on a central columnar
receptacle which spreads out into an umbrella-like indusium (D, _i_)
with its incurved margin tucked in below the ring of sporangia. The
indusium is detached when the sporangia are ripe. The annulus is
oblique and incomplete and often slightly sinuous; it agrees in the
main with that of _Gleichenia_. The species _Matonia pectinata_ is
characterised by dichotomously branched fronds (figs. 227, 228) with
long and slender petioles; the pinnae bear linear pinnules with forked
lateral veins and occasional lateral anastomoses (fig. 224, F). The
only other living representative is _M. sarmentosa_, discovered by Mr
Charles Hose at Niah, Sarawak[688]: this species has long pendulous
leaves apparently very different from those of _M. pectinata_, but
the branching of the frond may be regarded as a modification of a
primitive form of dichotomy[689]. A small bud occurs in the angle
between the forked linear segments and the rachis, as in some species
of _Gleichenia_[690]. _Matonia_ is confined to the Malay region: _M.
pectinata_ grows in Western Borneo and in various localities in the
Malay peninsula, while _M. sarmentosa_, has been found in one locality
only; the latter species has recently been transferred to a new genus
_Phanerosorus_, but in view of the practical identity in anatomical
structure and the close agreement as regards the sori of the two
species there would seem to be no justification for this change of
name[691].

[Illustration: FIG. 227. _Matonia pectinata._ (⅕ nat. size.) M.S.]


                            =Loxsomaceae.=

The New Zealand genus _Loxsoma_ has marginal sori with a cup-like
indusium surrounding an elongated receptacle bearing pear-shaped
sporangia provided with a complete oblique annulus. The genus is
chiefly interesting because of its isolated position; it agrees with
_Trichomanes_ (Hymenophyllaceae) in the structure of the sorus and
with species of _Dicksonia_ and _Davallia_ in habit; it shows some
resemblance also to Gleicheniaceae and Schizaeaceae[692]. A new type
of fern described by Christ[693] from Costa Rica as _Loxsomopsis
costaricensis_ affords a striking instance of discontinuous
distribution and emphasises the antiquity and generalised features of
the family.

[Illustration: FIG. 228. _Matonia pectinata._ From a photograph by Mr
  Tansley of a group of plants in a wood on Gunong Tundok, Mount
  Ophir.]


         =Hymenophyllaceae.= (_Hymenophyllum_, _Trichomanes_.)

The sporangia, which are attached to a columnar receptacle or
prolongation of a vein beyond the margin of the lamina, are
characterised by an obliquely transverse annulus (fig. 224, C). A
cup-like indusium surrounds the lower portion of the receptacle which
is two-lipped in _Trichomanes_ and entire in _Hymenophyllum_ (fig. 270,
C, D). These two filmy ferns have a wide distribution both in tropical
and extra-tropical regions; they are represented in the British
Isles by _Hymenophyllum tunbrigense_, _H. Wilsoni_, and _Trichomanes
radicans_.

[Illustration: FIG. 229.

  A. _Thyrsopteris elegans._    B. _Cyathea spinulosa._
  C. _Davallia concinna._       D. _Dicksonia coniifolia._
  E. _Alsophila excelsa._       F, G. _Dicksonia culcita._

  (A, after Diels and Kunze; B, D, F, G, after Hooker; E, after
     Bower.)]


   =Cyatheaceae.= (_Cyathea_, _Hemitelia_, _Alsophila_, _Dicksonia_,
                           _Thyrsopteris_.)

The sporangia occur in indusiate or naked sori and have an obliquely
vertical and incomplete annulus (fig. 229, E). In the great majority of
cases the fronds are large and highly compound, but _Cyathea sinuata_
Hook, a rare Ceylon species, bears simple narrow linear leaves. This
family includes, with few exceptions, all the tree ferns[694]. The
sori of _Dicksonia_ are enclosed in a two-valved indusium (fig. 229,
F. G); in the species represented in fig. 230 the fertile segments,
which terminate in cup-like indusia, are characterised by the absence
of a lamina and closely resemble those of _Thyrsopteris_ (fig. 229,
A). In _Cyathea_ the indusium has the form of a cup which is at first
closed and afterwards opens at the apex (fig. 229, B); in _Hemitelia_
the indusium is much reduced and in _Alsophila_ the sori are naked.
_Thyrsopteris_ is characterised by the reduced fertile pinnules bearing
stalked sori in deep cups (fig. 229, A). The appearance of this fern
“is very remarkable, for the cup-shaped sori hang down from the
fronds in masses, looking just like masses of millet seed[695].” The
sporangia are described by Bower[696] as large and of rather peculiar
form. As seen in fig. 224, H, the annulus is continuous; it forms a
twisted loop of cells which vary in shape and in the thickness of the
walls. The Cyatheaceae are for the most part tropical ferns with a wide
geographical range, usually in moist regions; they are, however, able
to flourish under widely different temperature conditions. In Tasmania,
as Diels[697] points out, tree ferns may occasionally be seen laden
with snow, and on the west coast of New Zealand they overhang the edge
of a glacier[698]. The monotypic genus _Thyrsopteris_ is confined to
Juan Fernandez. The Cyatheaceae no longer exist in Europe.

[Illustration: FIG. 230. _Dicksonia Bertercana_ Hook. Fertile and
  sterile pinnae. (Nat. size. British Museum Herbarium.)]


          =Dennstaedtiinae.= (_Microlepia_, _Dennstaedtia_.)

This sub-tribe, instituted by Prantl, has been revived by Bower on the
ground that the sori present features intermediate between those of
Cyatheaceae and the Polypodiaceous genus _Davallia_. The sporangia have
a slightly oblique annulus.


                           =Polypodiaceae.=

This section of the Leptosporangiate ferns, including several
sub-tribes, comprises the great majority of recent genera. The
sporangia form naked or indusiate sori and have a vertical incomplete
annulus. In _Plagiogyria_[699] the oblique annulus and soral features
suggest comparison with the Cyatheaceae. A more intimate acquaintance
with Polypodiaceous ferns will undoubtedly demonstrate the existence of
other generalised types[700].

From the point of view of the identification of fossil ferns it is
important to bear in mind the very close resemblance presented by some
Polypodiaceous species, e.g. species of _Davallia_ (fig. 229, C), to
Cyatheaceous ferns (cf. fig. 229, D).


                   =Parkeriaceae.= (_Ceratopteris._)

The almost spherical and scattered sporangia are characterised by the
peculiar form of the vertical annulus, which is composed of numerous
cells differing in their greater breadth and smaller depth from those
of a typical annulus. Exannulate sporangia have been described,
while others occur showing different stages between a rudimentary
and a complete ring. The single species of _Ceratopteris_, _C.
thalictroides_, is an annual aquatic fern widely spread in tropical
countries[701].

[Illustration: FIG. 231.

  A, A′. _Dipteris quinquefurcata_ (type-specimen in the Kew
     Herbarium).
  B, C, E, G. _D. conjugata._ (C, ⅛ nat. size.)
  D. _Polypodium quercifolium._
  F. _Dipteris Wallichii._

  (D, after Luerssen.)]


                     =Dipteridinae.= (_Dipteris._)

The genus _Dipteris_, formerly included in the Polypodiaceae, has been
assigned to a separate family partly on account of the slight obliquity
of the vertical annulus (fig. 231, G) and on other grounds[702]. The
four species _Dipteris conjugata_, _D. Wallichii_, _D. Lobbiana_ (=
_D. bifurcata_), and D. _quinquefurcata_ (fig. 231) are characterised
by a creeping rhizome bearing fronds reaching a length of 50 cm.; in
_D. conjugata_ and _D. Wallichii_ the lamina is divided by a median
sinus into two symmetrical halves, while in other species the leaf
is dissected into narrow linear segments. The main dichotomously
branched ribs are connected by lateral branches and these by tertiary
veins, the delicate branches of which end freely within the square or
polygonal areolae (fig. 231, A′, E). The naked sori are composed of
numerous sporangia and filamentous hairs: while in some species the
soral development conforms to that characteristic of the Mixtae, it has
been shown that in one species, _D. Lobbiana_ (= _D. bifurcata_[703]),
the sporangia develope simultaneously as in the Simplices. _Dipteris_
occurs in company with _Matonia_ on Mt Ophir and elsewhere in the Malay
peninsula; it extends to the Philippines, Samoa, New Caledonia, China,
New Guinea, and the subtropical regions of Northern India.

                   •       •       •       •       •

The impossibility of drawing a hard and fast line between the divisions
adopted in any system of classification is well illustrated by the
ferns. In the main, the three-fold grouping suggested by Bower is
probably consistent with the order of evolution of the true ferns.
The Polypodiaceae, which are now the dominant group, are in all
probability of comparatively recent origin, while the Gradatae and
Simplices represent smaller subdivisions with representatives in remote
geological epochs. The genera _Loxsoma_, _Matonia_ and _Dipteris_
afford examples of ferns exhibiting points of contact with more
than one of Bower’s subdivisions: they are generalised types which,
like many relics of the past, are now characterised by a restricted
geographical range.

[Sidenote: RECENT FERNS]

[Illustration: FIG. 232. _Davallia aculeata._ (⅖ nat. size.)]

It is noteworthy that while certain vegetative features may in some
cases be cited as family-characters, such features are not usually
of much value from a taxonomic point of view. While the typical tree
ferns are practically all members of the Cyatheaceae, a few members of
other families, e.g. _Todea barbara_ (Osmundaceae) and the monotypic
Indian genus _Brainea_ (Polypodiaceae), form erect stems several feet
in height; but these differ in appearance from the Palm-like type
of the Cyatheaceous tree ferns. On the other hand, the thin, almost
transparent, leaf of _Hymenophyllum tunbridgense_ and other filmy
ferns is a character shared by several species of _Todea_, _Asplenium
resectum_, and _Danaea trichomanoides_ (Marattiaceae); the filmy habit
is essentially a biological adaptation.

The form of frond represented by certain species of _Gleichenia_,
characterised by a regular dichotomy of the axis and by the occurrence
of arrested buds, is on the whole a trustworthy character, though
_Davallia aculeata_ (bearing spines on its rachis) (fig. 232) and
_Matonia sarmentosa_ have fronds with a similar mode of branching and
also bear arrested radius-buds. A limited acquaintance with ferns as a
whole often leads us to regard a certain form of leaf as characteristic
of a particular species, but more extended enquiry usually exposes
the fallacy of relying upon so capricious a feature. The form of leaf
illustrated by _Trichomanes reniforme_ is met with also in _Gymnogramme
reniformis_ and is fairly closely matched by the leaf of _Scolopendrium
nigripes_. The fronds of _Matonia pectinata_ (figs. 227, 228) bear
a close resemblance to those of _Gleichenia Cunninghami_, _Adiantum
pedatum_, and _Cheiropteris palmatopedata_[704].


          =The habit, leaf-form, and distribution of Ferns.=

The full accounts of the structure and life-history of the common
Male Fern, given by Scott in his _Structural Botany_ and by Bower in
the _Origin of a Land Flora_, render superfluous more than a brief
reference to certain general considerations in so far as they may
facilitate a study of fossil types.

In size Ferns have a wide range: at the one extreme we have the
filmy fern _Trichomanes Goebelianum_[705], growing on tree stems in
Venezuela, with leaves 2·5 to 3 mm. in diameter, and at the other the
tree ferns with tall columnar stems reaching a height of 40 to 50 feet
and terminating in a crown of fronds with a spread of several feet.
A common form of stem is represented by the subterranean or creeping
rhizome covered with ramental scales or hairs: the remains of old
leaves may persist as ragged stumps, or, as in _Oleandra_, _Polypodium
vulgare_ and several other species, the leaf may be cut off by the
formation of an absciss-layer[706] leaving a clean-cut peg projecting
from the stem. As a rule the branches bear no relation to the leaves
and are often given off from the lower part of a petiole, but in a
few cases, e.g. in the _Hymenophyllaceae_, it is noteworthy that true
axillary branching is the rule[707]. In the typical tree-fern the
surface resembles that of a Cycadean trunk covered with persistent
leaf-bases and a thick mass of roots. Among epiphytic ferns highly
modified stems are occasionally met with, as in the Malayan species
_Polypodium_ (_Lecanopteris_) _carnosum_ and _P. sinuosum_[708].

The leaves of ferns are among the most protean of all plant organs;
as Darwin wrote, “the variability of ferns passes all bounds[709].”
The highly compound tri- or quadripinnate leaves of such species as
_Pteris aquilina_, _Davallia_ and other genera stand for the central
type of fern frond; others exhibit a well-marked dichotomy, e.g.
_Lygodium_, _Gleichenia_, _Matonia_, etc., a habit in all probability
associated with the older rather than with the more modern products
of fern evolution. Before attempting to determine specifically fossil
fern fronds, it is important to familiarise ourselves with the range of
variability among existing species and more especially in leaves of the
same plant. A striking example of heteromorphy is illustrated in fig.
233. Reinecke[710] has figured a plant of _Asplenium multilineatum_
in which the segments of the compound fronds assume various forms.
In _Teratophyllum aculeatum var. inermis_ Mett., a tropical climbing
fern believed by Karsten[711] to be identical with _Acrostichum_
(_Lomariopsis_) _sorbifolium_,—an identification which Goebel[712]
questions,—the fronds which stand free of the stem supporting the
climber differ considerably from the translucent and much more delicate
filmy leaves pressed against the supporting tree. From this fern
alone Fée is said to have created 17 distinct species. In this, as in
many other cases, differences in leaf-form are the expression of a
physiological division of labour connected with an epiphytic existence.
Some tropical species of _Polypodium_ (sect. _Drynaria_), e.g. _P.
quercifolium_ (fig. 234 and fig. 231, D), produce two distinct types of
leaf, the large green fronds, concerned with the assimilation of carbon
and spore-production, being in sharp contrast to the small slightly
lobed brown leaves which act as stiff brackets (fig. 234, M) for
collecting humus from which the roots absorb raw material. Similarly in
_Platycerium_ the orbicular mantle-leaves differ widely from the long
pendulous or erect fronds fashioned like the spreading antlers of an
elk. In _Hemitelia capensis_, a South African Cyatheaceous species, the
basal pinnae assume the form of finely divided leaves identified by
earlier collectors as those of a parasitic _Trichomanes_ (fig. 235).
In a letter written by W. H. Harvey in 1837 accompanying the specimen
shown in fig. 235, he says, “Apropos of _Hemitelia_, be it known abroad
that supposed parasitical _Trichomanes_ ... is not a parasite, but a
part of the frond of _Hemitelia_.” The delicate reduced pinnae remain
on the stem and form a cluster at the base of the fronds[713].

[Illustration: FIG. 233. _Polypodium Billardieri_ Br. (¼ nat. size.)
  Middle Island, New Zealand. From specimens in the Cambridge
  Herbarium.]

[Illustration: FIG. 234. _Polypodium quercifolium._ (Much reduced: M,
  Mantle-leaves.)]

In many species the sporophylls are distinguished from the sterile
fronds by segments with little or no chlorophyllous tissue, as in
_Onoclea struthiopteris_[714] in which, each year, the plant produces
a funnel-shaped group of sterile leaves followed later in the season
by a cluster of sporophylls; or, as in many other genera, the fertile
leaves are distinguished also by longer petioles and thus serve as
more efficient agents of spore-dissemination. In _Ceratopteris_
the narrow segments of the taller fertile leaves are in striking
contrast to the broader pinnules of the submerged foliage leaves.
Leaf-form is in many cases obviously the expression of environment;
the xerophilous fern _Jamesonia_[715] from the treeless paramos of
the Andes[716] is characterised by its minute leaflets with strong
revolute margins and a thick felt of hairs on the lower surface; in
others, xerophilous features take the form of a covering of overlapping
scales (_Ceterach_), or a development of water-tissue as in the fleshy
leaves of the Himalayan fern _Drymoglossum carnosum_. In the Bracken
fern Boodle[717] has shown how the fronds may be classed as shade and
sun leaves; the former are spreading and softer, while the latter are
relatively smaller and of harder texture (fig. 236, _a_ and _b_). Even
in one leaf six feet high, growing through a dense bush of gorse and
bramble, the lower part was found to have the features of a shade leaf,
while the uppermost exposed pinnae were xerophilous.

[Illustration: FIG. 235. _Hemitelia capensis_ R. Brown. Nat. size.
  _a_, Pinna of normal frond. [From a specimen in the British Museum.
  M.S.]]

[Illustration: FIG. 236_a_. _Pteris aquilina._

   Part of leaf from greenhouse. (¼ nat. size.) After Boodle.]

[Sidenote: PTERIS]

The resemblance between some of the filmy Hymenophyllaceae and
thalloid Liverworts[718] is worthy of mention as one of the many
possible pitfalls to be avoided by the palaeobotanical student. The
long linear fronds of such genera as _Vittaria_ and _Monogramme_
might well be identified in a fossil state as the leaves of a
grass-like Monocotyledon, or compared with the foliage of _Isoetes_
or _Pilularia_. The resemblance of some fern leaves with reticulate
venation to those of Dicotyledons has led astray experienced
palaeobotanists; it is not only the anastomosing venation in the leaves
of several ferns that simulates dicotyledonous foliage, but the
compound leaves of many dicotyledons, e.g. _Paullinia thalictrifolia_
(Sapindaceae) and species of Umbelliferae, may easily be mistaken for
fronds of ferns.

[Illustration: FIG. 236 _b_. _Pteris aquilina._

  Leaf from the same plant grown out of doors. (¼ nat. size.)
  After Boodle.]

[Sidenote: RECENT FERNS]

The dichotomously lobed lamina of some Schizaeas, e.g. _S. dichotoma_
and _S. elegans_ (fig. 222), bears a close resemblance to the leaves of
_Baiera_ or _Ginkgo_[719]. The original description by Kunze[720] of
the South African Cycad _Stangeria paradoxa_ as a Polypodiaceous fern
illustrates the difficulty, or indeed impossibility, of distinguishing
between a sterile simply pinnate fern frond and the foliage of some
Cycads. The deeply divided segments of _Cycas Micholitzii_[721]
simulate the dichotomously branched pinnae of _Lygodium dichotomum_,
and the leaves of _Aneimia rotundifolia_ (fig. 223) and other species
are almost identical in form with the Jurassic species _Otozamites
Beani_, a member of the Cycadophyta.

There are certain facts in regard to the geographical distribution of
ferns to which attention should be directed. Mr Baker in his paper on
fern distribution writes: “With the precision of an hygrometer, an
increase in the fern-vegetation marks the wooded humid regions[722].”
If in a collection of fossil plants we find a preponderance of ferns
we are tempted to assume the existence of such conditions as are
favourable to the luxuriant development of ferns at the present day.
On the other hand, we must bear in mind the wonderful plasticity of
many recent species and the fact that xerophilous ferns are by no means
unknown in present-day floras.

Ferns are admirably adapted to rapid dispersal over comparatively wide
areas. Bower[723] estimates that in one season a Male Fern may produce
about 5,000,000 spores: with this enormous spore-output are coupled a
thoroughly efficient mechanism for scattering the germs and an unusual
facility for wind-dispersal. When Treub[724] visited the devastated
and sterilised wreck of the Island of Krakatau in 1886, three years
after the volcanic outburst, he found that twelve ferns had already
established themselves; the spores had probably been carried by the
wind at least 25 to 30 miles. It is not surprising, therefore, to find
that many ferns have an almost world-wide distribution; and, it may
be added, in view of their efficient means of dispersal, wide range
by no means implies great antiquity. Prof. Campbell[725] has recently
called attention to the significance of the wide distribution of
Hepaticae in its bearing on their antiquity; the spores are incapable
of retaining vitality for more than a short period, and it is argued
that a world-wide distribution can have been acquired only after an
enormous lapse of time. If we apply this reasoning to the Osmundaceae
among ferns, it may be legitimate to assume that their short-lived
green spores render them much less efficient colonisers than the
great majority of ferns; if this is granted, the wide distribution of
Osmundaceous ferns in the Mesozoic era carries their history back to a
still more remote past, a conclusion which receives support from the
records of the rocks.

The Bracken fern which we regard as characteristically British is a
cosmopolitan type; it was found by Treub among the pioneers of the New
Flora of Krakatau; in British Central Africa, it greets one at every
turn “like a messenger from the homeland[726]”; it grows on the Swiss
Alps, on the mountains of Abyssinia, in Tasmania, and on the slopes
of the Himalayas. The two genera _Matonia_ (fig. 228) and _Dipteris_,
which grow side by side on Mount Ophir in the Malay Peninsula, are
examples of restricted geographical range and carry us back to the
Jurassic period when closely allied types flourished abundantly in
northern latitudes. Similarly _Thyrsopteris elegans_, confined to Juan
Fernandez, exhibits a remarkable likeness to Jurassic species from
England and the Arctic regions.

The proportion of ferns to flowering plants in recent floras is a
question of some interest from a palaeobotanical point of view; but we
must bear in mind the fact that the evolution of angiosperms, effected
at a late stage in the history of the earth, seriously disturbed the
balance of power among competitors for earth and air. The abundance
of ferns in a particular region is, however, an unsafe guide to
geographical or climatic conditions. Many ferns are essentially social
plants; the wide stretches of moorland carpeted with _Pteris aquilina_
afford an example of the monopolisation of the soil by a single
species. In Sikkim Sir Joseph Hooker speaks of extensive groves of tree
ferns, and in the wet regions of the Amazon, Bates[727] describes the
whole forest glade as forming a “vast fernery.” In a valley in Tahiti
_Alsophila tahitiensis_ is said to form “a sort of forest almost to
the exclusion of other ferns[728].” In the abundance of _Glossopteris_
(figs. 334, etc.) fronds spread over wide areas of Permo-Carboniferous
rocks in S. Africa, Australia, and India, we have a striking instance
of a similar social habit in an extinct fern or at least fern-like
plant.

_Acrostichum aureum_, with pinnate fronds several feet long, is an
example of a recent fern covering immense tracts, but this species[729]
is more especially interesting as a member of the Filicineae
characteristic of brackish marshes and the banks of tropical rivers
in company with Mangrove plants and the “Stemless Palm” _Nipa_. This
species exhibits the anatomical characters of a water-plant and
affords an interesting parallel with some Palaeozoic ferns (species of
_Psaronius_) which probably grew under similar conditions.


                        =The Anatomy of Ferns.=

The text-book accounts of fern-anatomy convey a very inadequate idea
of the architectural characters displayed by the vascular systems
of recent genera. When we are concerned with the study of extinct
plants it is essential to be familiar not only with the commoner
recent types, but particularly with exceptional or aberrant types. The
vascular system of many ferns consists of strands of xylem composed
of scalariform tracheae associated with a larger or smaller amount of
parenchyma, surrounded either wholly or in part (that is concentric
or bicollateral) by phloem: beyond this is a pericycle, one layer
or frequently several layers in breadth, limited externally by an
endodermis, which can usually be readily recognised. The vascular
strands are embedded in the ground-tissue of the stem consisting of
thin-walled parenchyma and, in most ferns, a considerable quantity of
hard and lignified mechanical tissue. The narrow protoxylem elements
are usually characterised by a spiral form of thickening, but in
slow-growing stems the first-formed elements are frequently of the
scalariform type.

A study of the anatomy of recent ferns both in the adult state and
in successive stages of development from the embryo has on the whole
revealed “a striking parallelism[730]” between vascular and sporangial
characters in leptosporangiate ferns. For a masterly treatment of our
knowledge of fern anatomy from a phylogenetic point of view reference
should be made to Mr Tansley’s recently published lectures: within the
limits of this volume all that is possible is a brief outline of the
main types of vascular structure illustrated by recent genera.

[Illustration: FIG. 237.

  A. _Matonia pectinata_ (petiole).
  B. _M. pectinata_ (stem).
  C. _Gleichenia dicarpa_ (stem): _p_, petiole; _pp_, protophloem;
     position of protoxylem indicated by black dots.
  D. _Matonidium._
  E. _Trichomanes reniforme_: _pp_, protophloem. (C, E, after Boodle;
     D, after Bommer.)]

To Prof. Jeffrey[731] we owe the term protostele which he applied to
a type of stele consisting of a central core of xylem surrounded by
phloem, pericycle, and endodermis. While admitting that steles of this
type may sometimes be the result of the modification of less simple
forms, we may confidently regard the protostele as representing the
most primitive form of vascular system. The genus _Lygodium_ affords
an example of a protostelic fern; a solid column of xylem tracheae
and parenchyma is completely encircled by a cylinder of phloem
succeeded by a multi-layered pericycle and an endodermis of a single
layer of cells. In this genus the stele is characterised by marginal
groups of protoxylem; it is exarch. An almost identical type is
represented by species of _Gleichenia_, but here the stele is mesarch,
the protoxylem being slightly internal (fig. 237, C). _Trichomanes
scandens_ (fig. 238) has an exarch protostele like that of _Lygodium_;
but, as Boodle[732] has suggested, the protostelic form in this case
is probably the result of modification of a collateral form of stele
such as occurs in _Trichomanes reniforme_ (fig. 237, E). A second type
of stele has been described in species of _Lindsaya_[733] in which
the xylem includes a small group of phloem near the dorsal surface.
This _Lindsaya_ type is often passed through in the development of
“seedling” ferns and may be regarded as a stage in a series leading
to another well-marked type, the solenostele. The solenostele[734],
a hollow cylinder of xylem lined within and without by phloem,
pericycle, and endodermis, occurs in several genera belonging to
different families, e.g. _Dipteris_, species of _Pteris_, species of
_Lindsaya_, _Polypodium_, _Jamesonia_, _Loxsoma_, _Gleichenia_ and
other genera. In a smaller number of ferns the stele consists of what
may be called a medullated protostele similar to the common form of
stele in _Lepidodendron_: this type is found in species of _Schizaea_
and in _Platyzoma_ (fig. 239). It is important to notice that in
the solenostele and as a rule in the medullated protostele when a
leaf-trace passes out from the rhizome stele the vascular cylinder is
interrupted by the formation of a foliar gap (_Platyzoma_[735], fig.
239, is an exception). This fact has been emphasized by Jeffrey[736]
who draws a distinction between the Lycopodiaceous type of stele, which
is not broken by the exit of leaf-traces, and the fern stele in which
foliar gaps are produced: the former he speaks of as the cladosiphonic
type (_Lycopsida_) and the latter as the phyllosiphonic (_Pteropsida_).

[Illustration: FIG. 238. Stele of _Trichomanes scandens_: _px_,
  protoxylem; _s_, endodermis. From Tansley, after Boodle.]

[Illustration: FIG. 239. _Platyzoma microphylla_. _l.t._, leaf-trace;
  _i.e._, internal endodermis. (After Tansley; modified from
  Boodle.)]

The transition to a hollow cylinder of xylem from a protostele
may be described as the result of the replacement of some of the
axial conducting tracheae by parenchyma or other non-vascular
tissue consequent on an increase in diameter of the whole stele
and the concentration of the true conducting elements towards the
periphery[737].

The occurrence of the internal cylinder of phloem, pericycle, and
endodermis in a solenostele is rendered intelligible by a study of
fern seedlings and by a comparative examination of transitional types
connecting protosteles and solenosteles through medullated protosteles
and steles of the _Lindsaya_ type. A further stage in stelar evolution
is illustrated by what is termed the dictyostele, the arrangement of
vascular tissue characteristic of _Nephrodium Filix-mas_, _Cyathea_
(fig. 240), _Polypodium vulgare_ and many other common ferns.

[Illustration: FIG. 240. _Cyathea Imrayana._ (From Tansley after de
  Bary.) (Sclerenchyma represented by black bands.)]

If a solenostele is interrupted by leaf-gaps at intervals sufficiently
close to cause overlapping, a transverse section at any part of the
stele will show apparently separate curved bands of concentrically
arranged xylem and phloem, which on dissection are seen to represent
parts of a continuous lattice-work or a cylinder with the wall pierced
by large meshes. The manner of evolution of the dictyostele has been
ably dealt with by Gwynne-Vaughan[738] and other authors. In a few
ferns, e.g. _Matonia pectinata_[739], a transverse section of the
stem (fig. 237, B) reveals the presence of two or in some cases three
concentric solenosteles with a solid protostele in the centre: this
_polycylic_ type may be regarded as the expression of the fact that in
response to the need for an adequate water-supply to the large fronds,
ferns have increased the conducting channels by a method other than by
the mere increase of the diameter of a single stele. Fig. 237, A, shows
the vascular tissue of a petiole of _Matonia_ in transverse section.

The two genera of Osmundaceae, _Todea_ and _Osmunda_, are peculiar
among recent ferns in having a vascular cylinder composed of separate
strands of xylem varying considerably in shape and size, from
=U=-shaped strands with the concavity facing the centre of the stem
and with the protoxylem in the hollow of the =U=, to oval or more
or less circular strands with a mesarch protoxylem or without any
protoxylem elements (fig. 221, A, B). These different forms are the
expression of the change in contour or in structure which the parts
of the lattice-work undergo at different levels in the stem[740].
Beyond this ring of xylem bundles is a continuous sheath of phloem of
characteristic structure. A transverse section of a stem of _Osmunda
regalis_ may show 15 or more xylem strands; in _O. Claytoniana_ there
may be as many as 40. In _Todea barbara_ (fig. 221, B) the leaf-gaps
are shorter, and in consequence of the less amount of overlapping the
xylem cylinder becomes an almost continuous tube. The recent researches
of Kidston and Gwynne-Vaughan[741] have resulted in the discovery of
fossil Osmundaceous stems with a complete xylem ring, the stele being
of the medullated protostele type; in another extinct member of the
family the stele consists of a solid xylem core. The Osmundaceous
type of stele is complicated in _O. cinnamomea_ (fig. 221, A) by the
occurrence of local internal phloem and by an internal endodermis,
a feature which leads Jeffrey to what I believe to be an incorrect
conclusion that the vascular arrangement found in _Osmunda regalis_ has
been evolved by reduction from a stele in which the xylem was enclosed
within and without by phloem. New facts recently brought to light
enable us to derive the ordinary Osmundaceous type from the protostele
and solenostele. It is worthy of remark that the Osmundaceae occupy a
somewhat isolated position among recent ferns; their anatomy represents
a special type, their sporangia differ in several respects from those
of other leptosporangiate ferns and in some features _Osmunda_ and
_Todea_ agree with the Eusporangiate ferns. The possession of such
distinguishing characters as these suggests antiquity; and the facts
of palaeobotany, as also the present geographical range of the family,
confirm the correctness of this deduction.

Before leaving the stelar structure of leptosporangiate fern stems,
a word must be added in regard to a type of structure met with in
the Hymenophyllaceae. In this family _Trichomanes reniforme_ (fig.
237, E) may be regarded, as Boodle suggests, as the central type: the
stele consists of a ring of metaxylem tracheae, the dorsal portion
having the form of a flat arch and the ventral half that of a straight
band. This flattened ring of xylem encloses parenchymatous tissue
containing scattered tracheae some of which are protoxylem elements. In
_Trichomanes radicans_ the rhizome is stouter than in _T. reniforme_
and the stele consists of a greater number of tracheae. The stele is
cylindrical like that shown in fig. 238, but the centre is occupied by
two groups of protoxylem and associated parenchyma. In _Hymenophyllum
tunbrigense_ the stele is of the subcollateral type; the ventral plate
of the xylem ring has disappeared leaving a single strand of xylem with
endarch protoxylem and completely surrounded by phloem. _Trichomanes
muscoides_ possesses a still simpler stele consisting of a slender
xylem strand with phloem on one side only. Reference has already been
made to the occurrence in this family of the protostelic type. The
Hymenophyllaceae afford a striking illustration of the modification in
different directions of stelar structure connected with differences in
habit, and of the correlation of demand and supply as shown in the
varying amount of conducting tissue in the steles of different species.

The leaf-trace in a great number of ferns is characterised by its
=C=-shaped form[742] as seen in transverse section: this in some
genera, e.g. _Matonia_ (fig. 237, A), is complicated by the spiral
infolding of the free edges of the =C=; in other ferns (e.g. some
Cyatheaceae) (fig. 278, C) the sides of the =C= are incurved, while in
some species the xylem is broken up into a large number of separate
strands.

An elaborate treatment of the leaf-traces of ferns was published a few
years ago by MM. Bertrand and Cornaille[743] in which the authors show
how the various systems of vascular tissue in the fronds of ferns maybe
derived from a common type. As Prof. Chodat[744] justly remarks this
important work has not received the attention it deserves, the neglect
being attributed to the strange notation which is adopted[745].

The roots of ferns are characterised by a uniformity of plan in marked
contrast to the wide range of structure met with in the stem and to
a less extent in the leaves. The xylem may consist of a plate of
scalariform tracheae with a protoxylem group at each end, or the stele
may include six or more alternating strands of xylem and phloem.


        II. =Marattiales= (Eusporangiate isosporous Filicales).

The Marattiaceae, the single family of ferns included in the
Marattiales, comprise the genera _Angiopteris_, _Archangiopteris_,
_Marattia_, _Danaea_, and _Kaulfussia_, which are for the most
part tropical in distribution. These genera are characterised by
eusporangiate sori or synangia, the presence of stipules at the base of
the petioles, and by the complex arrangement of the vascular tissue. In
view of the fact that many fossil ferns show a close resemblance to the
recent Marattiaceae, the surviving genera are briefly described. The
prothallus is green and relatively large.

_Angiopteris._ This genus occurs in Polynesia, tropical Asia, and
Madagascar; it is characterised by a short and thick fleshy stem
bearing large bipinnate leaves which occasionally show a forking of
the rachis[746], a feature reminiscent of some Palaeozoic fern-like
fronds. One of the large plants of _Angiopteris evecta_ in the Royal
Gardens, Kew, bears leaves 12 feet in length with a stalk 6 inches
in diameter at the base. The sessile or shortly stalked and rather
leathery linear or broadly lanceolate pinnules have a prominent
midrib and dichotomously branched lateral veins. The surface of an
old stem is covered with the thick stumps of petioles enclosed by
pairs of fleshy stipules (fig. 241, A) and bears numerous fleshy
roots, which hang free in the air or penetrate the soil. The young
fronds (fig. 220, A) exhibit very clearly the characteristic circinate
vernation. The proximal part of each primary pinna is characterised by
a pulvinus-like swelling. The sporangia, in short linear elliptical
sori near the edge of the pinnules, consist of free sporangia (fig.
242, A–D) provided with a peculiar type of “annulus”[747], in the form
of a narrow band of thicker-walled cells, which extends as a broad
strip on either side of the apex. An examination of sections through
the sporangia of _Angiopteris_ in different planes[748] illustrates
the difficulty of determining the precise nature of the annulus in a
petrified sporangium which is seen only in one or two planes. Many of
the sporangia from the English Coal-Measures, compared by authors with
those of Leptosporangiate ferns, are in all probability referable to
the Marattiaceous type.

[Illustration: FIG. 241.

  A. _Angiopteris evecta._ (Considerably reduced.)
  B. _Marattia fraxinea._ Stipule. M.S.]

The vascular system[749] of the stem constitutes a highly complex
dictyostelic or polycylic type which may consist of as many as nine
concentric series of strands of xylem surrounded by phloem, with
large sieve-tubes and a pericycle which abuts on the parenchymatous
ground-tissue without any definite endodermal layer. A peculiarity in
the vascular strands is that the first-formed elements of the phloem
lie close to the edge of the xylem, the metaphloem being therefore
centrifugal in its development. The ground-tissue is devoid of
mechanical tissue and is penetrated by roots, a few of which arise
from the outer vascular strands while others force their way to the
surface from the more internal dictyosteles. Leaf-traces, consisting
of several strands, are given off from the outermost cylinder and a
segment of the second dictyostele moves out to fill the gap formed in
the outermost network, while the gap in the second cylinder receives
compensating strands from the third. A few layers below the surface of
the petiole there is a ring of thick-walled elements (_s_, fig. 243),
and in both petiole and stem numerous mucilage ducts and tannin-sacs
occur in the ground-tissue. It has been shown by Farmer and Hill[750]
that in some of the vascular strands in an _Angiopteris_ stem a few
secondary tracheae are added to the primary xylem by the activity of
the adjacent parenchyma. The vascular bundles in the petiole form more
or less regular concentric series; they have no endodermis and are
characterised also by the large size of the sieve-tubes (_st_, fig.
243).

[Illustration: FIG. 242. A–D. _Angiopteris evecta_.

  A. Apex of sporangium showing “annulus.”
  B. Sori.
  C. Sporangium.
  D. Section of sporangium, showing the two lateral bands of
     thick-walled cells.
  E. _Danaea_: _a_, roof of synangium, with pores; _b_, sporangial
     cavities; _v_, vascular bundle; _i_, indusium.

  (D, after Zeiller.)]

The roots of Marattiaceous ferns (fig. 244) are characterised by the
larger number of xylem and phloem groups; the stele is polyarch and not
diarch, tetrarch or hexarch as in most Leptosporangiate ferns.

[Illustration: FIG. 243. _Angiopteris evecta_. Section of petiole
  (considerably reduced) and of a single vascular bundle
  (magnified): _px_, protoxylem; _st_, sieve-tubes.]

[Illustration: FIG. 244. _Angiopteris evecta_. Transverse section of
  root, with part of the stele magnified: _s_, sieve-tubes; _p_,
  phloem; _px_, protoxylem.]

_Archangiopteris_. This monotypic genus, discovered by Mr Henry in
South Eastern Yunnan, was described by Christ and Giesenhagen in
1899[751]. The comparatively slender rhizome has a fairly simple
vascular system[752]. The simply-pinnate leaves bear pinnules like
those of _Danaea_, but the sori agree with those of _Angiopteris_
except in their greater length and in the larger number of sporangia.

_Marattia_. This genus, which extends “all round the world within
the tropics[753],” includes some species which closely resemble
_Angiopteris_, while others are characterised by more finely divided
leaves with smaller ultimate segments. The fleshy stipules occasionally
have an irregularly pinnatifid form (fig. 241, B). The sporangia are
represented by oval synangia[754] (fig. 245, A; the black patches
at the ends of the lateral veins) composed of two valves, which on
ripening come apart and expose two rows of pores formed by the apical
dehiscence of the sporangial compartments (fig. 245, A′, B). In
_Marattia Kaulfussii_ the sori are attached to the lamina by a short
stalk (fig. 245, B, B′) and the leaf bears a close resemblance to
those of the Umbelliferous genera _Anthriscus_ and _Chaerophyllum_.
The vascular system is constructed on the same plan as that of
_Angiopteris_ but is of simpler form.

[Illustration: FIG. 245.

  A. _Marattia fraxinea_. A′. A single synangium showing the two
     valves and pores of the sporangial compartments.
  B, B′. _M. Kaulfussii_.
  C. _Kaulfussia_ (synangium showing pores of sporangial
     compartments).
  D, E. _Marattiopsis Münsteri_.

  (C, after Hooker; D, E, after Schimper.)]

_Danaea._ Danaea, represented by about 14 species confined to tropical
America, is characterised by simple or simply pinnate leaves with
linear segments bearing elongated sori extending from the midrib
almost to the margin of the lamina. Each sorus consists of numerous
sporangia in two parallel rows united into an oblong mass partially
overarched by an indusium (fig. 242, E, _i_) which grows up from the
leaf between the sori. In the portion of a fertile segment shown in
fig. 242, E, the apical pores are seen at _a_; and at _b_, where the
roof of the synangium has been removed, the spore-bearing compartments
are exposed. The vascular system[755] agrees in general plan with that
characteristic of the family.

_Kaulfussia._ The form of the leaf (Vol. I. p. 97, fig. 22) closely
resembles that of the Horse Chestnut; the stem is a creeping
dorsiventral rhizome with a vascular system in the form of a “much
perforated solenostele[756].” The synangia are circular, with a median
depression; each sporangial compartment opens by an apical pore on the
sloping sides of the synangial cup (fig. 245, C)[757].

Copeland has recently described a Marattiaceous leaf which he makes
the type of a new genus, _Macroglossum alidae_. The sori are nearer
the margin than in _Angiopteris_ and are said to consist of a greater
number of sporangia. The photograph[758] of a single pinna which
accompanies the brief description hardly affords satisfactory evidence
in support of the creation of a new genus. The structure of a petiole
which I have had an opportunity of examining, through the kindness of
Mr Hewitt of Sarawak, shows no distinctive features.


        III. =Ophioglossales.= (Isosporous and Eusporangiate.)

The three genera, _Ophioglossum_, _Botrychium_, and _Helminthostachys_,
are characterised by the division of the leaves into a sterile
and a fertile lobe. The fertile lobe in _Ophioglossum_ bears two
rows of spherical sporangia sunk in its tissue; in _Botrychium_
and _Helminthostachys_ the spores are contained in large sporangia
with a stout wall[759]. The prothallus is subterranean and without
chlorophyll. In the British species of _Ophioglossum_, _O. vulgatum_
(the adder’s tongue fern), an almost cosmopolitan species, the sterile
part of the frond is of oval form and has reticulate venation. In _O.
pendulum_ and _O._ _palmatum_ the lamina is deeply lobed. In the genus
_Botrychium_, represented in Britain by _B. Lunaria_, both sterile
and fertile branches of the frond are pinnately divided, while in
_Helminthostachys_ the sporangia are borne on sporangiophores given off
from the margin of the fertile branch of a frond similar in habit to a
leaf of _Helleborus_.

[Illustration: FIG. 246. _Ophioglossum vulgatum._ Transverse section of
  petiole and single bundle: _p_, phloem; _px_, endarch protoxylem.]

[Illustration: FIG. 247. _Botrychium virginianum_: _e_, endodermis;
  _c_, cambium; _x_, xylem. A, diagrammatic section of stem; B,
  portion of the stele and endodermis enlarged.

  (A, after Campbell; B, after Jeffrey.)]

The stem of _Ophioglossum_ is characterised by a dictyostele of
collateral bundles with endarch protoxylem: the vascular system of the
leaf-stalk is also composed of several separate strands (fig. 246).
In _Botrychium_ the stele is a cylinder of xylem surrounded externally
by phloem. This genus affords the only instance among ferns of a
plant in which the addition of secondary tracheae occurs on a scale
large enough to produce a well-defined cylinder of secondary xylem
traversed by radial rows of medullary-ray cells[760] (fig. 247). The
unsatisfactory nature of the evidence in regard to the past history of
the Ophioglossales renders superfluous a fuller treatment of the recent
species.




                             CHAPTER XXI.

                             FOSSIL FERNS.


                            =Osmundaceae.=

From the Culm of Silesia, Stur[761] described impressions of sterile
fronds which he named _Todea Lipoldi_ on the ground of the similarity
of the finely divided pinnules to those of _Todea superba_ and
other filmy species of the genus. The type-specimen of Stur (in
the Geological Survey Museum, Vienna) affords no information as to
sporangial characters and cannot be accepted as an authentic record
of a Lower Carboniferous representative of the family. Another more
satisfactory but hardly convincing piece of evidence bearing on the
presence of Osmundaceae in pre-Permian floras has been adduced by
Renault[762], who described petrified sporangia from the Culm beds of
Esnost in France as _Todeopsis primaeva_ (fig. 256, F). These pyriform
sporangia are characterised by the presence of a plate of large cells
comparable with the subapical group of “annulus” cells in the sporangia
of the recent species (fig. 221).

Zeiller[763] has published a figure of some sporangia described by
Renault from Autun resembling the Osmundaceous type in having a plate
of thick-walled cells instead of a true annulus, but the plate is
larger than the group of cells in the recent sporangia, and both
sporangia and spores are smaller in the fossil. The sporangia from
Carboniferous rocks described by Weiss as _Sturiella_[764] bear some
resemblance to those of recent Osmundaceae, but there is no adequate
reason for referring them to this family.

The generic name _Pteridotheca_ is employed by Scott as a convenient
designation for unassigned petrified sporangia of Palaeozoic age with
an annulus and other characters indicating fern-affinity. In the
species _P. Butterworthi_[765] the sporangia are characterised by a
group of large cells suggesting comparison with the annulus, or what
represents the annulus, in Osmundaceae and Marattiaceae. Scott has also
described a sporangium from the Coal-Measures containing germinating
spores[766]; the structure is similar to that of recent Osmundaceous
sporangia, and it is interesting to note that germinating spores have
been observed in the recent species _Todea hymenophylloides_[767].

Additional evidence of the same kind is afforded by fertile specimens
of a quadripinnate fern with deeply dissected oval-lanceolate pinnules
described by Zeiller from the Coal-Measures of Heraclea in Asia Minor
as _Kidstonia heracleensis_[768] (fig. 256, E). Carbonised sporangia
were found at the base of narrow lobes of the ultimate segments and,
as seen in fig. 256, E, the sporangial wall is distinguished by a
plate of larger cells occupying a position like that of the “annulus”
of recent Osmundaceae. Zeiller regards the sporangia as intermediate
between those of Osmundaceae and Schizaeaceae. From the same locality
Zeiller describes another frond bearing somewhat similar sporangia as
_Sphenopteris_ (_Discopteris_) _Rallii_ (fig. 256, D)[769]: the term
_Discopteris_ was instituted by Stur for fertile fronds referred by him
to the Marattiaceae[770].

It is by no means safe to assume that these and such Upper
Carboniferous sporangia as Bower[771] compared with those of
_Todea_ were borne on plants possessing the anatomical characters
of Osmundaceae rather than those of the extinct Palaeozoic family
Botryopterideae. This brings us to the important fact, first pointed
out by Renault, that the Botryopterideae are essentially generalised
ferns exhibiting many points of contact with the Osmundaceae[772].
It is clear that whether or not we are justified in tracing the
Osmundaceae as far back as the Lower Carboniferous period, some of the
characteristics of the family were already foreshadowed in rocks of
this age.

Through a fortunate accident of preservation, unequivocal evidence of
the existence of Osmundaceae in the Palaeozoic era is supplied by the
Russian Upper Permian genera _Zalesskya_ and _Thamnopteris_.


                             _Zalesskya._

This generic title has been instituted by Kidston and
Gwynne-Vaughan[773] for two Russian stems of Upper Permian age, one
of which was named by Eichwald[774] _Chelepteris gracilis_, but the
probability that the type of the genus _Chelepteris_ is generically
distinct from Eichwald’s species necessitated a new designation for the
Permian fern.

In habit the stem of _Zalesskya_ resembles that of an _Osmunda_ or a
_Todea_, but it differs in the possession of a stele composed of a
continuous cylinder or solid column of xylem surrounded by phloem,
and by the differentiation of the xylem into two concentric zones.
The leaves are represented by petiole-bases only; the sporangia are
unknown. The stem and leaf-base anatomy fully justifies the inclusion
of _Zalesskya_ in the Osmundaceae.


_Zalesskya gracilis_ (Eichwald). Fig. 248.

The type-specimen is a partially decorticated stem, from Upper Permian
beds in Russia, provided with a single stele, 13 mm. in diameter,
surrounded by a broad thin-walled inner cortex containing numerous
leaf-traces and occasional roots: this was doubtless succeeded by a
sclerotic outer cortex. In its main features _Zalesskya gracilis_
agrees closely with _Z. diploxylon_ represented in fig. 249. The stele
consists of a continuous cylinder of xylem exhibiting a fairly distinct
differentiation into two zones, (i) a broader outer zone of narrower
scalariform tracheae (_x ii_, fig. 248) in which 20 to 25 protoxylem
strands (_px_) occur just within the edge, (ii) an inner zone of
broader and shorter tracheae (fig. 248, _x i_). The protoxylem elements
(_px_, fig. 248) are characterised by a single series of scalariform
pits, while the metaxylem elements have multiseriate pits like those
on the water-conducting elements of recent Osmundaceae. The tracheae
show an interesting histological character in the absence of the middle
substance of their walls, a feature recognised by Gwynne-Vaughan[775]
in many recent ferns. External to the xylem and separated from it
by a parenchymatous sheath is a ring of phloem, _ph_, composed of
large sieve-tubes and parenchyma separated from the inner cortex by a
pericycle 4 to 5 layers in breadth. The occurrence of a few sclerotic
cells beyond the broad inner cortex points to the former existence of
a thick-walled outer cortex. The leaf-traces are given off as mesarch
strands from the edge of the xylem; they begin as prominences opposite
the protoxylem and become gradually detached as xylem bundles, at first
oblong in transverse section, then assuming a slightly crescentic and
reniform shape, while the mesarch protoxylem strand takes up an endarch
position. As a trace passes further out the curvature increases and
the protoxylem strands undergo repeated bifurcation; it assumes in fact
the form and general type of structure met with in the leaf-traces of
_Todea_ and _Osmunda_. Numerous diarch roots, given off from the stele
at points just below the outgoing leaf-traces, pass outwards in a
sinuous horizontal course through the cortex of the stem.

[Illustration: FIG. 248. _Zalesskya gracilis_ (Eich.). Transverse
  section of part of the stele: _ph_, phloem; _x i_, _x ii_, xylem;
  _px_, protoxylem. (After Kidston and Gwynne-Vaughan. × 20.)]

[Illustration: FIG. 249. _Zalesskya diploxylon_. Kidston and
  Gwynne-Vaughan. Transverse section of stem. _ph_, phloem. (After
  Kidston and Gwynne-Vaughan. × 2½.)]

In _Zalesskya gracilis_ the xylem cylinder was probably wider
in the living plant than in the petrified stem. In _Zalesskya
diploxylon_[776], in all probability from the same Russian locality,
there can be little doubt that the xylem was originally solid to the
centre (fig. 249). In this species also the phloem forms a continuous
band (_ph_, fig. 249) consisting of four to six layers of sieve-tubes.


                            _Thamnopteris_.

_Thamnopteris Schlechtendalii_ (Eich.). Figs. 250, 312, A, Frontispiece.

In 1849 Brongniart[777] proposed the name _Thamnopteris_ for a species
of fern from the Upper Permian of Russia originally described by
Eichwald as _Anomopteris Schlechtendalii_. A new name was employed by
Brongniart on the ground that the fossil was not generically identical
with the species previously named by him _Anomopteris Mougeotii_[778].
Eichwald’s specimen has been thoroughly investigated by Kidston and
Gwynne-Vaughan[779]. The stem (Frontispiece) agrees in habit with
those of _Zalesskya_ and recent Osmundaceae; on the exposed leaf-bases
the action of the weather has etched out the horse-shoe form of the
vascular strands and laid bare numerous branched roots boring their way
through the petiole stumps. The centre of the stem is occupied by a
protostele 13 mm. in diameter consisting of solid xylem separated by a
parenchymatous sheath from a cylinder of phloem. The xylem is composed
mainly of an axial column of short and broad reticulately pitted
tracheae (fig. 250, _b_ and Frontispiece), distinguished from the
sharply contrasted peripheral zone of normal scalariform elements, _a_,
by their thinner walls and more irregular shape. The protoxylem, _px_,
is represented by groups of narrower elements rather deeply immersed in
the peripheral part of the metaxylem. A many-layered pericycle, _per_,
and traces of an endodermis, _en_, succeed the phloem, _ph_, which is
characterised by several rows of large contiguous sieve-tubes; beyond
the endodermis is a broad thin-walled inner cortex. The leaf-traces
arise as in _Zalesskya_, but the protoxylem in _Thamnopteris_ is at
first central; as the trace passes outwards a group of parenchyma
appears immediately internal to the protoxylem elements and gradually
assumes the form of a bay of thin-walled tissue on the inner concave
face of the curved xylem. The next stage is the repeated division of
the protoxylem strand until, in the sclerotic outer cortex, the traces
acquire the Osmundaceous structure (fig. 312, A, p. 453). The petiole
bases have stipular wings as in _Todea_ and _Osmunda_.

[Illustration: FIG. 250. _Thamnopteris Schlechtendalii_ (Eich.). Part
  of stele: _a_, outer xylem; _b_, inner xylem. (After Kidston and
  Gwynne-Vaughan. × 13.)]

[Sidenote: OSMUNDACEAE]

The striking feature exhibited by these Permian plants is the structure
of the protostele, which in _Thamnopteris_ and probably in _Zalesskya
diploxylon_ consists of solid xylem surrounded by phloem: this may be
regarded as the primitive form of the Osmundaceous stele. In _Osmunda
regalis_ and in other recent species of the genus the xylem cylinder
has the form of a lattice-work; in other words, the departure of
each leaf-trace makes a gap in the xylem and the overlapping of the
foliar-gaps results in the separation of the xylem into a number
of distinct bundles. In _Zalesskya gracilis_ the continuity of the
xylem is not broken by overlapping gaps; in this it agrees with
_Lepidodendron_. In _Thamnopteris_ the centre of the stele was occupied
by a peculiar form of xylem obviously ill-adapted for conduction, but
probably serving for water-storage and comparable with the short and
broad tracheae in _Megaloxylon_[780]. There is clearly a well-marked
difference in stelar anatomy between these two Permian genera and
_Todea_ and _Osmunda_: this difference appears less when viewed in
the light of the facts revealed by a study of the Jurassic species
_Osmundites Dunlopi_.

[Illustration: FIG. 251. _Lonchopteris virginiensis._ (After Fontaine.
  ½ nat. size.)]

As possible examples of Triassic Osmundaceae reference may be made
to some species included in Stur’s genus _Speirocarpus_[781]. _S.
virginiensis_ was originally described by Fontaine[782] from the Upper
Triassic rocks of Virginia as _Lonchopteris virginiensis_ (fig. 251)
and has recently been figured by Leuthardt[783] from the Keuper of
Basel. The sporangia, which are scattered over the lower surface of
the pinnules, are described as globose-elliptical and as having a
rudimentary apical annulus; no figures have been published. In habit
the frond agrees with _Todites Williamsoni_, but the lateral veins form
an anastomosing system like that in the Palaeozoic genus _Lonchopteris_
(fig. 290, B). There would seem to be an _a priori_ probability of
this species being a representative of the Osmundaceae and not, as
Stur believed, of the Marattiaceae. Seeing that _Lonchopteris_ is
a designation of a purely provisional kind, it would be convenient
to institute a new generic name for Triassic species having the
Lonchopteris venation, which there are good reasons for regarding as
Osmundaceous ferns.

Similarly _Speirocarpus tenuifolius_ (Emmons) (= _Acrostichites
tenuifolius_ Font.), which resembles _Todites Williamsoni_ (see p. 339)
not only in habit and in the distribution of the sporangia but also in
the venation, is probably an Osmundaceous species.


                             _Osmundites._

_Osmundites Dunlopi_, Kidston and Gwynne-Vaughan[784], fig. 252.

This species was found in Jurassic rocks in the Otago district of New
Zealand in association with _Cladophlebis denticulata_[785] (fig. 257).
The type-specimen forms part of a stem 17 mm. in diameter surrounded
by a broad mass of crowded leaf-bases. The stele consists of an almost
continuous xylem ring (fig. 252) enclosing a wide pith: the phloem and
inner cortex are not preserved but the peripheral region of the stem is
occupied by a sclerotic outer cortex. The mass of encasing leaf-bases
resolves itself on closer inspection into zones of foliage-leaf
petioles and the petioles of scale-leaves with an aborted lamina.
A similar association of two forms of leaf is seen in the existing
American species _Osmunda Claytoniana_ and _O. cinnamomea_. The cortex
and armour of leaf-bases are penetrated by numerous diarch roots.
The xylem cylinder, six to seven tracheae broad, is characterised
by the narrower diameter of its innermost elements and—an important
point—by the fact that the detachment of a leaf-trace does not break
the continuity of the xylem cylinder (fig. 252). Each leaf-trace is
at first elliptical in section; it then becomes curved inwards and
gradually assumes the horse-shoe form as in _Zalesskya_ and in the
recent species. The single endarch protoxylem becomes subdivided until
in the petiole it is represented by 20 or more strands.

[Illustration: FIG. 252. _Osmundites Dunlopi_ Kidst. and G.-V. Portion
  of xylem showing the departure of a leaf-trace. (After Kidston and
  Gwynne-Vaughan; × 36.)]

In the continuity of the xylem cylinder this species of _Osmundites_
shows a closer approach to _Todea barbara_ or _T. superba_ (fig. 221,
B) than to species of _Osmunda_; it differs from _Zalesskya_ in having
reached a further stage in the reduction of a solid protostele to one
composed of a xylem cylinder enclosing a pith. This difference is of
the same kind as that which distinguishes the stele of _Lepidodendron
rhodumnense_ from _L. Harcourtii_. In _Lepidodendron_ short tracheae
occasionally occur on the inner edge of the xylem cylinder, and in
recent species of _Todea_ the same kind of reduced tracheae are met
with on the inner edge of the xylem[786]. In both cases the short
tracheae are probably vestiges of an axial strand of conducting
elements which in the course of evolution have been converted into
parenchymatous cells. In _Lepidodendron vasculare_ the mixed parenchyma
and short tracheae in the centre of the stele represent an intermediate
stage in xylem reduction, and the arrangement in vertical rows of the
medullary parenchyma in _Lepidodendron_ is precisely similar to that
described by Kidston and Gwynne-Vaughan in _Thamnopteris_. In both
cases the rows of superposed short cells have probably been produced
by the transverse septation of cells which began by elongating as if to
form conducting tubes and ended by assuming the form of vertical series
of parenchymatous elements.

[Illustration: FIG. 253. _Osmundites Kolbei_ Sew. (⅓ nat. size.)]

In another Jurassic species, _Osmundites Gibbiana_[787], the xylem is
of the _Osmunda_ type and consists of about 20 strands instead of a
continuous or almost continuous cylinder.

[Illustration: FIG. 254. _Osmundites Kolbei._ (Leaf-scars.)]


_Osmundites Kolbei_ Seward, figs. 253–255.

This species was founded on a specimen obtained by Mr Kolbe from
the Uitenhage series of Cape Colony[788]. The fossil flora and fauna
of this series point to its correlation with the Wealden or Neocomian
strata of Europe[789]. The type-specimen consists of several pieces
of a stem (fig. 253) which reached a length of about 90 cm. On the
weathered surface the remains of petiole-bases are clearly seen and
on the reverse side of the smaller piece shown in the figure numerous
sinuous roots are present in association with the leaf-stalks. The
depression _c_ in the larger specimen may mark the position of a
branch: at _a_ fig. 253 (enlarged in fig. 254, _a_) the vascular strand
of a petiole is exposed as a broad =U=-shaped band and at _b_ (fig.
254, _b_) the form of the petiole-bases is clearly shown[790]. With the
stem were found imperfectly preserved impressions of fronds referred to
_Cladophlebis denticulata_, a common type of leaf which was found also
in association with the slightly older New Zealand stem, _Osmundites
Dunlopi_.

[Illustration: FIG. 255. _Osmundites Kolbei_ Sew. Transverse section,
  from a photograph supplied by Dr Kidston and Mr Gwynne-Vaughan.
  (2½ nat. size.)]

An examination of the internal structure of the South African stem
by Dr Kidston and Mr Gwynne-Vaughan has revealed many interesting
features, which will be fully described in Part IV. of their Monograph
on fossil Osmundaceous stems. I am greatly indebted to these authors
for allowing me to publish the following note contributed by Dr
Kidston:—

“The section of _Osmundites Kolbei_ Seward, shown in fig. 255, presents
the usual appearance of an Osmundaceous stock. The parts contained in
this section are the stele, inner and outer cortex and a portion of
the surrounding mantle of concrescent leaf-bases. The whole specimen
has suffered much from pressure, but if restored to its original form
the xylem ring must have been about 19 mm. in diameter. The number of
xylem strands is about fifty-six and several of them are more or less
joined as in the modern genus _Todea_. The tracheae are of the typical
Osmundaceous type, that is to say, the pits are actual perforations and
several series of them occur on each wall of the larger tracheae.

“The most interesting structural characteristic of _Osmundites Kolbei_
is not well seen in the figure owing to the compression of the xylem
ring. This consists in the occurrence of tracheae in the pith. In fact,
we have here a mixed pith, composed of parenchyma and true tracheae,
a condition which connects the _Osmundaceae_ with a parenchymatous
medulla with those possessing a solid xylem stele like _Zalesskya_ and
_Thamnopteris_ and so completes the series of transitions extending
from the older and solid-steled forms to the modern medullated members
of the _Osmundaceae_.”


_Osmundites skidegatensis_, Penhallow.

This lower Cretaceous Canadian species, first described by
Penhallow[791] and more recently by Kidston and Gwynne-Vaughan[792],
is remarkable for the large size of the stem, the stele alone having
a diameter of 2·4 cm. Penhallow figures a fragment of a leaf bearing
a superficial resemblance to that of _Osmunda Claytoniana_, which
may be the foliage borne by _Osmundites skidegatensis_. The xylem
cylinder is broken by the exit of leaf-traces into 50 or more strands
varying in size and shape, and it is noteworthy that the phloem is also
interrupted as each leaf-trace is given off. In recent species the
xylem cylinder is almost always interrupted, but the phloem retains its
continuity. In the Canadian fossil an internal band of phloem occurs
between the xylem and the pith, and this joins the external phloem at
each leaf-gap. This internal phloem finds an interesting parallel in
certain recent species[793], but in these the internal and external
phloem do not meet at the foliar gaps as they do in the extinct type.
In _Osmunda cinnamomea_ the internal phloem occurs only at the regions
of branching of the stem stele; in the fossil it is always present.

It is clear that _Osmundites skidegatensis_ represents the most complex
type of stem so far recognised in the Osmundaceae; it illustrates a
stage in elaboration of the primitive protostele in advance of that
reached by any existing species.

                   •       •       •       •       •

The primitive Osmundaceous stele was composed of solid xylem surrounded
by phloem (_Thamnopteris_ and _Zalesskya_); at a later stage the xylem
cylinder lost its inner zone of wide and short tracheae and assumed
the form seen in _Osmundites Kolbei_, in which the centre of the stele
consists of parenchyma with some tracheae. Another type is represented
by _O. Dowkeri_ in which the pith is composed wholly of parenchyma
and the xylem ring is continuous. From this type, by expansion of the
xylem ring and by the formation of overlapping leaf-gaps, the form
represented by _Osmunda regalis_ was reached. _Osmunda cinnamomea_,
with internal phloem in the regions of stelar branching, probably
represents a further stage, as Kidston and Gwynne-Vaughan believe, in
increasing complexity due to the introduction of phloem from without
through gaps produced by the branching of the stele. In _Osmundites
skidegatensis_ the leaf-gaps became wider and the external phloem
projected deeper into the stele until a continuous internal phloem
zone was produced. This most elaborate type proved less successful than
the simpler forms which still survive.


_Osmundites Sturii._

Impressions of fertile pinnae with narrow linear segments bearing
exannulate sporangia described by Raciborski from Lower Jurassic rocks
in Poland as _Osmunda Sturii_[794] may with some hesitation be included
in the list of Mesozoic Osmundaceae.


_Osmundites Dowkeri._

Under this name Carruthers[795] described a petrified stem from
Lower Eocene beds at Herne Bay, which in the structure of the stele
agrees closely with the Jurassic species _O. Gibbiana_ and conforms
to the normal Osmundaceous type. It is possible, as Gardner and
Ettingshausen[796] suggested, that the foliage of this species may be
represented by some sterile _Osmunda_-like fragments recorded from
the Middle Bagshot beds of Bovey Tracey and Bournemouth as _Osmunda
lignitum_.


_Todites._

This generic name[797] has been applied to fossil ferns exhibiting in
the structure of the sporangia and in the general habit of the fertile
fronds a close resemblance to the recent species _Todea barbara_ (fig.
221, D, p. 286).


_Todites Williamsoni_ (Brongniart) figs. 256, B, C, G.

  1828. _Pecopteris Williamsonis_, Brongniart, Prodrome, p. 57; Hist.
        vég. foss., p. 324, Pl. CX. figs. 1 and 2.

   ——   _P. whitbiensis_, Brongniart, Hist. vég. foss. p. 321, Pl. CIX.
        figs. 2–4.

   ——   _P. tenuis_, _ibid._ p. 322, Pl. CX. figs. 3, 4.

  1829. _Pecopteris recentior_, Phillips, Geol. Yorks. p. 148, Pl.
        VIII. fig. 15.

   ——   _P. curtata_, _ibid_. Pl. VIII. fig. 12.

  1833. _Neuropteris recentior_, Lindley and Hutton, Foss. Flora, Vol.
        I. Pl. LXVIII.

   ——   _Pecopteris dentata_, _ibid._ Vol. III., Pl. CLXIX.

  1836. _Acrostichites Williamsonis_, Goeppert, foss. Farn. p. 285.

  1841. _Neuropteris Goeppertiana_, Muenster, in Goeppert, Gattungen
        foss. Pflanz. Lief. 5 and 6, p. 104, Pls. VIII.–X.

  1856. _Pecopteris Huttoniana_, Zigno, Flor. foss. Oolit. Vol. I. p.
        133.

  1867. _Acrostichites Goeppertianus_, Schenk, Foss. Flor. Grenzsch. p.
        44, Pl. V. fig. 5, Pl. VII. fig. 2.

  1883. _A. linnaeaefolius_, Fontaine, Older Mesoz. Flora Virginia, p.
        25, Pls. VI.–IX.

   —    _A. rhombifolius_, _ibid_. Pls. VIII. XI.–XIV.

  1885. _Todea Williamsonis_, Schenk, Palaeont. Vol. XXXI. p. 168, Pl.
        III. fig. 3.

  1889. _Cladophlebis virginiensis_, Fontaine, Potomac Flora, p. 70,
        Pl. III. figs. 3–8; Pl. IV. figs. 1, 4.

[Illustration: FIG. 256.

  A. _Cladophlebis denticulata._
  B, B′. _Todites Williamsoni_ (fertile).
  C. _T. Williamsoni_ (sterile pinna).
  D. _Discopteris Rallii._
  E, E′. _Kidstonia heracleensis._
  F. _Todeopsis primaeva._
  G. _Todites Williamsoni_ (sporangium).

  [B, C, from specimens (13491; 39234) in the British Museum (B,
  very slightly reduced; C, ½ nat. size); D, E, after Zeiller; F,
  after Renault; G, after Raciborski.]]

It is hopeless to attempt to arrive at satisfactory conclusions in
regard to the applicability of the name _Todites Williamsoni_ to the
numerous fronds from Jurassic and Rhaetic rocks, agreeing more or less
closely with Brongniart’s type-specimen. Specimens from the Rhaetic may
not be specifically identical with those from the Jurassic; the main
point is that, whether actually identical or not, both sets of fossils
clearly represent the same general type of Osmundaceous fern[798] and
may for present purposes be included under the same designation. The
above synonymy, though by no means complete[799], serves to illustrate
the confusion which has existed in regard to this widely spread type of
Mesozoic fern.

_Todites Williamsoni_ may be briefly described as follows:—

  Frond bipinnate; long linear pinnae (20–30 cm.) of uniform breadth
  arise at an acute angle, or in the lower part of a frond, almost at
  right angles, from a stout rachis. Closely set pinnules attached
  by a broad base; slightly falcate, the side towards the rachis
  strongly convex and the outer margin straight or concave and
  bulged outwards towards the base of each segment, margin usually
  entire, or it may be slightly lobed. Fertile pinnules similar to
  the sterile; sporangia of the Osmundaceous type and often scattered
  over the whole lower surface of the lamina (fig. 256, B, B′, G).
  Venation of the _Cladophlebis_ type (cf. fig. 256, A).

It is not always easy to distinguish _Todites Williamsoni_ from
_Cladophlebis denticulata_, another common Jurassic fern, but in the
latter the pinnules are usually longer and relatively narrower and
the rachis is more slender (cf. fig. 256, B and 257). Schenk[800] and
Raciborski[801] have shown that the sporangia of _Todites_ conform
in the absence of a true annulus to those of _Todea_ (fig. 256, G)
and _Osmunda_. Nathorst[802] has recently figured a group of spores
of _Todites Williamsoni_ in illustration of the use of the treatment
of carbonised impressions with nitric acid and potassium chlorate.
This species, though widely distributed in Jurassic rocks, is hardly
distinguishable from the German Rhaetic fronds figured by Schenk from
Bayreuth as _Acrostichites Goeppertianus_[803], or from other fossils
referred to an unnecessarily large number of species by Fontaine[804]
from Upper Triassic rocks of Virginia[805].

It would seem from the paucity of later records of Osmundaceae that
the family reached its zenith in the Jurassic era. When we pass to
the later Tertiary and more recent deposits evidence is afforded in
regard to the geographical range of _Osmunda regalis_. It has been
shown to occur in the Pliocene forest-bed of Norfolk[806] as well as in
Palaeolithic and Neolithic deposits[807].

[Illustration: FIG. 257. _Cladophlebis denticulata._ (From a specimen
  in the British Museum from the Inferior Oolite rocks of Yorkshire.
  Slightly reduced.)]

A fertile frond from the Molteno (Rhaetic) beds of South Africa
referred to _Cladophlebis_ (_Todites_) _Roesserti_ (Presl)[808]
represents in all probability an Osmundaceous fern closely allied to
_Todites Williamsoni_. The same species is described by Zeiller[809]
from Rhaetic rocks of Tonkin and very similar types are figured by
Leuthardt[810] from Upper Triassic rocks of Basel as _Pecopteris
Rutimeyeri_ Heer, and by Fontaine[811] from rocks of the same age in
Virginia.


                            _Cladophlebis._

The generic name _Cladophlebis_ was instituted by Brongniart for
Mesozoic fern fronds characterised by ultimate segments of linear or
more or less falcate form attached to the pinnae by the whole of the
base, as in the Palaeozoic genus _Pecopteris_, possessing a midrib
strongly marked at the base and dividing towards the distal end of the
lamina into finer branches and giving off secondary forked and arched
veins at an acute angle. The term is generally restricted to Mesozoic
fern fronds which, on account of the absence or imperfection of fertile
pinnae, cannot be safely assigned to a particular family. In the case
of the species described below, the evidence in regard to systematic
position, though not conclusive, is sufficiently strong to justify its
inclusion in the Osmundaceae.


_Cladophlebis denticulata_ Brongniart. Figs. 256, A; 257, 258.

  1828. _Pecopteris denticulata_[812], Brongniart, Prodrome, p. 57;
        Hist. vég. foss. p. 301, Pl. XCVIII. figs. 1, 2.

   —    _P. Phillipsii_, Brongniart, Hist. p. 304, Pl. CIX. fig. 1.

This species is often confused[813] with _Todites Williamsoni_. The
name _Pecopteris whitbiensis_ has been used by different writers for
Jurassic fronds which are undoubtedly specifically distinct: specimens
so named by Brongniart should be referred to _Todites Williamsoni_,
while _P. whitbiensis_ of Lindley and Hutton[814] is Brongniart’s
_Cladophlebis denticulata_. It is impossible to determine with accuracy
the numerous examples described as _Pecopteris whitbiensis_, _Asplenium
whitbiense_, _Cladophlebis Albertsii_ (a Wealden species[815]),
_Asplenium_, or _Cladophlebis_, _nebbense_[816], etc., from Jurassic
and Rhaetic strata. The _Cladophlebis denticulata_ form of frond is one
of the commonest in recent ferns; it is represented by such species as
_Onoclea Struthopteris_, _Pteris arguta_, _Sadleria sp._, _Gleichenia
dubia_, _Alsophila lunulata_, _Cyathea dealbata_, and species of
_Polypodium_. It is, therefore, not surprising to find records of this
Mesozoic species from many localities and horizons. All that we can do
is to point out what appear to be the most probable cases of identity
among the numerous examples of fronds of this type from Mesozoic rocks,
particularly Rhaetic and Jurassic, in different parts of the world.
The name _Cladophlebis denticulata_ may be employed in a comprehensive
sense for fronds showing the following characters:—

  Leaf large, bipinnate, with long spreading pinnae borne on a
  comparatively slender rachis. Pinnules, in nearly all cases,
  sterile, reaching a length of 3–4cm., acutely pointed, finely
  denticulate or entire, attached by the whole of the base (fig.
  257). In the apical region the pinnules become shorter and broader.
  Venation of the _Cladophlebis_ type (fig. 256, A). Fertile pinnules
  rather straighter than the sterile, characterised by linear sori
  parallel to the lateral veins (fig. 258).

In endeavouring to distinguish specifically between fronds showing a
general agreement in habit with _C. denticulata_, special attention
should be paid to venation characters, the shape of the pinnules,
the relation of the two edges of the lamina to one another, and to
the amount of curvature of the whole pinnule. Unless the material is
abundant, it is often impossible to distinguish between characters of
specific value and others which are the expression of differences in
age or of position on a large frond, to say nothing of the well-known
variability which is amply illustrated by recent ferns. It is
remarkable that very few specimens are known which throw any light on
the nature of the fertile pinnae. Fig. 258 represents an impression
from the Inferior Oolite rocks of the Yorkshire coast in which the
exposed upper surface of the pinnules shows a series of parallel ridges
following the course of the lateral veins and no doubt formed by
oblong sori on the lower surface. There can be little doubt that the
specimen figured by Lindley and Hutton and by others as _Pecopteris
undans_[817] is, as Nathorst suggests, a portion of a fertile frond of
_C. denticulata_. A fertile specimen of a frond resembling in habit
_C. denticulata_, which Fontaine has described from the Jurassic
rocks of Oregon as _Danaeopsis Storrsii_[818], exhibits, as that
author points out, a superficial resemblance to the specimen named by
Lindley and Hutton _Pecopteris undans_. There is, however, no adequate
reason for referring the American fragment to the Marattiaceae. In the
absence of sporangia we cannot speak confidently as to the systematic
position of this common type; but there are fairly good grounds for
the assertion that some at least of the fronds described under this
name are those of Osmundaceae. The English specimen shown in fig.
258 is very similar to some Indian fossils figured by Feistmantel
as _Asplenites macrocarpus_[819], which are probably identical with
_Pecopteris australis_ Morris[820], a fern that is indistinguishable
from _Cladophlebis denticulata_. Renault[821] figured a fertile
specimen of the Australian fossil as _Todea australis_, which agrees
very closely with that shown in fig. 258, and the sporangia figured
by the French author are of the Osmundaceous type. Another example
of a fertile specimen is afforded by a Rhaetic fern from Franconia,
_Asplenites ottonis_, which is probably identical with _Alethopteris
Roesserti_ Presl [= _Cladophlebis_ (_Todites_) _Roesserti_], a plant
closely resembling _Cladophlebis denticulata_. Another argument in
favour of including _C. denticulata_ in the Osmundaceae is supplied
by the association of pinnae of this type with the petrified stem of
_Osmundites Dunlopi_ recorded by Kidston and Gwynne-Vaughan.

[Illustration: FIG. 258. Fertile pinnae of _Cladophlebis denticulata_.
  (From a Yorkshire specimen in the Sedgwick Museum, Cambridge.)]


                            =Schizaeaceae.=

Evidence bearing on the existence of this family in Carboniferous
floras is by no means decisive. The generic name _Aneimites_ proposed
by Dawson[822] for some Devonian Canadian plants resembling species of
the recent genus _Aneimia_, and adopted by White[823] for a species
from the Pottsville beds of Virginia, is misleading. The Canadian
plants give no indication of the nature of the reproductive organs, and
the fronds described by White are, as he shows, those of a Pteridosperm
and bore seeds.

An examination of the suspiciously diagrammatic drawings published by
Corda[824] of the small fertile pinnules of a Carboniferous fern from
Bohemia, which he named _Senftenbergia elegans_, leads us to conclude
that the sporangia are almost certainly those of a Schizaeaceous
species. The small linear pinnules bear two rows of sessile sporangia,
singly as in recent Schizaeaceae and not in sori, characterised by
4–5 rows of regular annular cells (fig. 270, A) surrounding the apex.
It has already been pointed out that the apical annulus of recent
Schizaeaceae, though normally one row deep, may consist in part at
least of two rows. Zeiller[825] examined specimens of Corda’s species
and decided in favour of a Schizaeaceous affinity; he describes the
sporangia as 0·85–0·95 mm. in length, with 3 to 5 and occasionally only
two rows of cells in the apical annulus. Zeiller’s figures (fig. 270,
A) confirm the impression that Corda’s drawings are more beautiful than
accurate. Stur[826], on the other hand, who first pointed out that the
type-specimens of _Senftenbergia_ came from the Radnitz beds of Bohemia
and not from the Coal-Measures, convinced himself that the sporangia
have no true annulus (fig. 270, E). He describes them as characterised
by a comparatively strong wall and by the presence of a band of narrow
vertical cells marking the line of dehiscence, features which lead
him to assign the plant to the Marattiales, a group which seems to
have exercised a dominating influence over his judgment. In a later
publication Zeiller[827] replies to Stur’s criticism but adheres to
his original opinion. Solms-Laubach[828], while expressing himself in
favour of Marattiaceous affinity, recognises that Zeiller’s arguments
cannot be set aside.

The question must remain open until further evidence is forthcoming;
but it would seem that this Carboniferous type, not as yet recognised
in Britain, possessed sporangia having a distinct resemblance to those
of the Schizaeaceae, though this similarity does not amount to proof of
the existence of the family in the Palaeozoic era.

Palaeozoic floras may be described as rich in generalised types,
types foreshadowing lines of evolution, which in the course of ages
led to a sorting and a redistribution of characters. It may be that
_Senftenbergia_ is one of these generalised types.

                   •       •       •       •       •

It is not until we ascend the geological series as far as the older
Jurassic rocks that we meet with a type which can with confidence be
classed with the Schizaeaceae, as least so far as sporangial characters
are concerned. The species _Klukia exilis_ is selected as the best
known and most widely-spread representative of Jurassic Schizaeaceae.


_Klukia exilis_ (Phillips)[829]. Fig. 259.

The generic name _Klukia_ was proposed by Raciborski[830] for a species
originally described by Phillips[831] from the Inferior Oolite of
the Yorkshire coast as _Pecopteris exilis_. Bunbury’s[832] discovery
(supplemented by additional evidence obtained by Raciborski) of
well-preserved sporangia justified the substitution of a distinctive
designation for the provisional term _Pecopteris_.

[Illustration: FIG. 259. _Klukia exilis_ (Phillips). (Figs. 1–3, × 40;
  fig. 4, × 3; fig. 5, nat. size.)]

The species may be defined as follows:—

  Frond tripinnate, of the _Cladophlebis_ type; pinnae linear,
  lanceolate, attached to the rachis at a wide angle. Ultimate
  segments short and linear, entire or, in the lower part of a frond,
  crenulate, 5 mm. long or occasionally longer. Sporangia 0·5 mm. in
  length, borne singly on the lower surface of the lamina in a row on
  each side of the midrib.

A re-examination[833] of the specimen described by Bunbury confirmed
his account of the structure of the sporangia. The pinna shown in
fig. 259 is characterised by unusually small fertile pinnules some
of which bear 10 sporangia in two rows; the annulus includes about
14 cells. Fertile specimens of this and similar forms are figured by
Raciborski[834] from Jurassic rocks of Poland, and good examples of the
English species may be seen in the Leckenby collection, Cambridge, in
the British Museum, the museums of Manchester, Scarborough, and other
places.

It is possible that specimens referred to _K. exilis_ by Yokoyama[835]
from Wealden strata in Japan may afford evidence of the persistence
of the species beyond the Jurassic era, but in view of the close
resemblance of the sterile fronds described from Wealden strata as
_Cladophlebis Brownii_[836] and _C. Dunkeri_[836] to those of _Klukia
exilis_, identity can be established only by an examination of fertile
specimens. A Jurassic fern recently described by Yabe[837] from Korea
as _Cladophlebis koraiensis_ may be identical with _K. exilis_ and
there is little doubt as to the existence of the species in Jurassic
Caucasian strata[838].

[Illustration: FIG. 260. _Ruffordia Goepperti_. (A, C, sterile; B,
  fertile; slightly reduced. Specimens from the Wealden of Sussex;
  British Museum; V. 2333, V. 2160, V. 2166.)]


_Ruffordia Goepperti_ (Dunk.). Fig. 260.

This Wealden fern[839] has been doubtfully assigned to the Schizaeaceae
on the ground of the resemblance of the sterile fronds to those of some
species of _Aneimia_, and because of the difference between the sterile
and fertile pinnae (Fig. 260). _Ruffordia_ cannot be regarded as a well
authenticated member of the Schizaeaceae.

[Illustration: FIG. 261.

  A, A′. _Chrysodium lanzaeanum._
  B, B′. _Lygodium Kaulfussi._
  C. _Marattia Hookeri._

  (After Gardner and Ettingshausen; A, B, ¾ nat. size.)]


_Lygodium Kaulfussi_, Heer. Fig. 261, B, B′.

Fragments of forked pinnules, agreeing very closely in venation and
general appearance with recent species of _Lygodium_, have been
identified by Gardner and Ettingshausen[840] from English Eocene beds
and by Knowlton from the Miocene beds of the Yellowstone Park[841]
as _Lygodium Kaulfussi_ Heer (fig. 261, B). Despite the absence of
sporangia it is probable that these fragments are correctly referred
to the Schizaeaceae. The sterile and fertile specimens figured by
Heer[842] from Tertiary beds of Switzerland agree very closely with
recent examples of _Lygodium_. Similar though perhaps less convincing
evidence of the existence of this family in Europe is furnished by
Saporta[843], who described two Eocene species from France.


                           =Gleicheniaceae.=

The application by Goeppert[844] and other earlier writers of the
generic name _Gleichenites_ to examples of Palaeozoic ferns was not
justified by any satisfactory evidence. One of Goeppert’s species,
_Gleichenites neuropteroides_, is identical with _Neuropteris
heterophylla_[845], a plant now included in the Pteridosperms.

The resemblance of sporangia and sori, whether preserved as carbonised
impressions or as petrified material, from Carboniferous rocks, to
those of recent species of Gleicheniaceae is in many cases at least the
result of misinterpretation of deceptive appearances. Williamson[846]
drew attention to the Gleichenia-like structure of some sections of
sporangia from the English Coal-Measures, but he did not realise the
ease with which sections of Marattiaceous sporangia in different planes
may be mistaken for those of annulate (leptosporangiate) sporangia.
In the regular dichotomous habit of Carboniferous fronds described as
species of _Diplothmema_ (Stur) and _Mariopteris_ (Zeiller)[847] we
have a close correspondence with the leaves of _Gleichenia_, but the
common occurrence of dichotomous branching among ferns is sufficient
reason for regarding this feature as an untrustworthy criterion of
relationship. It is, however, interesting to find that in addition
to the existence of some Upper Carboniferous ferns with sori like
those of recent Gleichenias, the type of stelar anatomy illustrated
by _Gleichenia dicarpa_ (fig. 237, C, p. 310) and other species is
characteristic of the primary structure of the stem of the Pteridosperm
_Heterangium_. We find in Carboniferous types undoubted indications of
anatomical and other features which in succeeding ages became the marks
of Gleicheniaceae.

Some Carboniferous fronds with short and small pinnules of the
_Pecopteris_ type, bearing sori composed of a small number of
sporangia, have been assigned by Grand’Eury and other authors to the
Gleicheniaceae; the same form of sorus is met with also on fronds with
Sphenopteroid segments. The former is illustrated by _Oligocarpia
Gutbieri_[848] and the latter by _O. Brongniarti_ described by Stur
and by Zeiller[849]. Zeiller has described the circular sori of
_Oligocarpia_ (fig. 270, B) as consisting of three to ten pyriform
sporangia borne at the ends of lateral veins and possessing a complete
transverse annulus, but Stur[850] believes that the annulus-like
appearance is due to the manner of preservation of exannulate
sporangia. In this opinion Stur is supported by Solms-Laubach[851]
and by Schenk[852]. Despite an agreement between _Oligocarpia_
and _Gleichenia_, as regards the form of the sori and the number
of sporangia, it is not certain that the existence of a typical
Gleicheniaceous annulus has been proved to occur in any Palaeozoic
sporangia[853].

From Upper Triassic beds of Virginia, Fontaine has figured several
fronds for which he instituted the genus _Mertensides_[854]. The habit,
as he points out, is not dichotomous, but the sori are circular and
are said to be composed in some species of four to six sporangia. No
satisfactory evidence is brought forward in support of the use of a
designation implying a close relationship with recent Gleichenias
(sect. _Mertensia_). One of the species described by Fontaine was
originally named by Bunbury _Pecopteris bullatus_[855], the imperfect
type-specimen of which is now in the Museum of the Cambridge Botany
School. In the form of the frond, the thick rachis, and in the pinnules
this Triassic species resembles _Todites Williamsoni_, but the
resemblance does not extend to the sori. Two of Fontaine’s species are
recorded by Stur from Austria[856], but he places them in the genus
_Oligocarpia_ and includes them in the Marattiaceae.

Leuthardt[857] figures what appears to be a Gleicheniaceous fern from
the Upper Triassic beds of Basel as _Gleichenites gracilis_ (Heer)
showing sori composed of five sporangia (fig. 265, C) with a horizontal
annulus. A Rhaetic species _Gleichenites microphyllus_ Schenk[858]
from Franconia agrees in the form of its small rounded pinnules with
_Gleichenia_, but no sporangia have so far been found.

An impression of a frond from Jurassic rocks of northern Italy figured
by Zigno as _Gleichenites elegans_[859] closely resembles in habit
recent species of _Gleichenia_; though no sporangia have been found,
the habit of the frond gives probability to Zigno’s determination.

A Jurassic species from Poland, _Gleichenites Rostafinskii_, referred
by Raciborski[860] to _Gleichenia_, exhibits a close agreement in habit
and in the form of the soral impressions to some recent species of
_Gleichenia_.

As we pass upwards to Wealden and more recent rocks it becomes clear
that the Gleicheniaceae were prominent members of late Mesozoic floras
in north Europe and reached as far north as Disco Island. In English
Wealden beds portions of sterile fronds have been found which were
assigned to a new genus _Leckenbya_[861], but it is probable that these
specimens would be more correctly referred to _Gleichenites_. Similarly
fragments of Gleichenia-like pinnae with very small rounded pinnules
occur in the Wealden rocks of Bernissart, Belgium[862], in north
Germany[863], and elsewhere. Conclusive evidence has been obtained by
Prof. Bommer of the existence of _Gleichenites_ in Wealden beds near
Brussels, where many plant remains have been found in a wonderful
state of preservation. The specimens, which I had an opportunity of
seeing some years ago, might easily be mistaken for rather old and
brown pieces of recent plants. Some of the Belgian fragments, of
which Prof. Bommer has kindly sent me drawings and photographs, are
characterised by an arrangement of vascular tissue identical with that
in the petioles and rhizomes of some protostelic Gleichenias. The stele
of one of the Belgian rhizomes appears to be identical with that of
_Gleichenia dicarpa_ (fig. 237, C. p. 310).

[Illustration: FIG. 262.

  A. _Gleichenites longipennis_ Heer.
  B. _G. delicatula_ Heer.
  C. _G. Nordenskioldi_ Heer.
  D. _G. Zippei_. (Corda.)

  (After Heer; A, B, D, very slightly reduced.)]


_Gleichenites Zippei_ (Corda). Fig. 262, D.

This species, originally described by Corda as _Pecopteris Zippei_[864]
and afterwards figured by Heer[865] as _Gleichenia Zippei_ (fig. 262,
D) from Urgonian rocks of Greenland, affords a striking example of a
Mesozoic member of the _Gleicheniaceae_. It is characterised by the
dichotomous branching of the frond and by the occurrence of arrested
buds in the forks. The long and slender pinnae, reaching a length of 9
cm. and a breadth of 6–8 mm., bear small crowded pinnules occasionally
with circular sori which are described by Heer as consisting of a small
number of sporangia (cf. fig. 262, C). Several other Lower Cretaceous
species are recorded by Heer from Greenland, some of which are probably
unnecessarily separated from _Gleichenites Zippei_. Examples of these
are represented in fig. 262, A, B, C.

A Gleicheniaceous species described by Debey and Ettingshausen
from Lower Cretaceous rocks of Aix-la-Chapelle as _Didymosorus
comptonifolius_[866] is very similar in habit to some of Heer’s
Greenland species: this should probably be referred to the genus
_Gleichenites_.


_Gleichenites hantonensis_, Wank. Fig. 263.

From the Eocene beds of Bournemouth, Gardner and Ettingshausen[867]
have described under the name _Gleichenia hantonensis_ what is in all
probability a true _Gleichenia_ (fig. 263). This species, originally
recorded by Wanklyn[868], is characterised by a slender forked rachis
showing what may be traces of arrested buds between the arms of the
branches, by circular sori of six or eight sporangia and by the
presence of peculiar tendril-like appendages on the pinnae. If the
description of the tendrils is correct, this British species affords
one of the few instances of ferns adapted for climbing and may be
compared with the recent species _Davallia aculeata_ (fig. 232, p. 299).


                             =Matonineae.=

The genera _Laccopteris_ and _Matonidium_ may be described as examples
of Mesozoic ferns exhibiting a very close agreement with _Matonia_.

_Laccopteris_. This genus, founded by Presl[869], may be described as
follows:—

  Frond pedate, in habit resembling _Matonia pectinata_, with
  pinnate or pinnatifid pinnae; ultimate segments linear, provided
  with a well-marked midrib giving off numerous dichotomously
  branched secondary veins which are in places connected by lateral
  anastomoses. Sori circular, forming a single row on each side of
  the midrib (fig. 278, B); sporangia 5–15 in each sorus, with an
  oblique annulus and tetrahedral spores. The presence of an indusium
  is not certainly established.

[Illustration: FIG. 263. _Gleichenites hantonensis_ Wank. (Restoration,
  after Gardner and Ettingshausen.)]

Schenk[870], who described several specimens of _Laccopteris_ from
Rhaetic rocks of Germany, compared the genus with _Gleichenia_ but
he also recognised the close resemblance to _Matonia pectinata_.
Zeiller[871] first established the practical identity of the sori and
sporangia of _Laccopteris_ and _Matonia_. The Rhaetic species, such as
_L. Muensteri_, _L. elegans_, and _L. Goepperti_, agree very closely
with _L. polypodioides_ and need not be described in detail.

[Illustration: FIG. 264. _Laccopteris elegans_ (Presl). (From a
  specimen in the British Museum; from the Lower Keuper of Bayreuth,
  Germany. Nat. size; part of pinnule × 3.)]

The Rhaetic species _Laccopteris elegans_, represented in fig. 264,
illustrates the characteristic habit of the genus and shows a feature
usually overlooked[872], namely the occurrence of anastomoses between
the lateral veins. The form of the sorus of another Rhaetic species is
shown in fig. 265, E. Schenk figures an interesting series of fronds of
_L. Goepperti_ in different stages of growth[873]; one of the younger
leaves is seen in fig. 265, D. An examination of Rhaetic specimens
of _Laccopteris_ in the Bergakademie of Berlin convinced me of the
correctness of the published descriptions of the sori.

[Illustration: FIG. 265.

  A. _Matonidium Wiesneri._ (Slightly enlarged.)
  B. _Marattiopsis marantacea._ (Slightly enlarged.)
  C. _Gleichenites gracilis._ (Slightly enlarged.)
  D. _Laccopteris Goepperti._ (Slightly reduced.)
  E. _L. Muensteri._ (Enlarged.)

  (A, after Krasser; B, C, after Leuthardt; D, E, after Schenk.)]


_Laccopteris polypodioides_ (Brongniart). Figs. 266–268; 278, A.

  1828. _Phlebopteris polypodioides_[874], Brongniart, Hist. vég. foss.
        p. 372, Pl. LXXXIII. fig. 1.

   —    _P. propinqua_, _ibid._ Pls. CXXXII. fig. 1, CXXXIII. fig. 2.

  1829. _Pecopteris caespitosa_, Phillips, Geol. Yorks. p. 148,
        Pl. VIII. fig. 10.

   —    _P. crenifolia_, _ibid._ Pl. VIII. fig. 10.

   —    _P. ligata_, _ibid._ Pl. VIII. fig. 14.

[Illustration: FIG. 266. _Laccopteris polypodioides_ (Brongn.). (× 14.)
  (Brit. Mus.)]

In habit this species closely resembles _Matonia_ and _Matonidium_, the
long petiole divides distally into several spreading pinnatifid pinnae
with linear ultimate segments (fig. 278, A). Circular sori (indusiate?)
occur in a single row on each side of the midrib containing 12–14 large
sporangia (fig. 266) characterised by an obliquely vertical annulus.
The midrib of the pinnules gives off secondary veins at a wide angle
and these form a series of elongated meshes parallel to the median rib,
as in the recent genus _Woodwardia_; forked and anastomosing branches
are given off from these to the edge of the lamina (fig. 267).

[Illustration: FIG. 267. Pinnules of _Laccopteris_.  (Enlarged.)

  A, B. From the Inferior Oolite of Yorkshire.
  C. From the Inferior Oolite of Stamford. (British Museum.)]

The specimen shown in fig. 268 is probably a young frond of this
species.

A very similar, possibly a specifically identical plant, was
described by Leckenby from English Jurassic rocks as _Phlebopteris
Woodwardi_[875], the distinguishing features of which are the greater
number of lateral veins and the smaller sori (fig. 267, A).

The name _Microdictyon_ was proposed by Saporta[876] for pinnules
differing slightly from those of _Laccopteris_ in venation characters:
he included _Laccopteris Woodwardi_ in this genus, but such differences
as are recognisable in the venation hardly justify the use of a
distinct generic title. Similarly, specimens described by Debey and
Ettingshausen[877] from Lower Cretaceous rocks of Aix-la-Chapelle as
species of _Carolopteris_ may also be included in _Laccopteris_.

[Illustration: FIG. 268. ? _Laccopteris polypodioides._ Nat. size. From
  a specimen in the Whitby Museum (Brit. Mus.).]


_Laccopteris Dunkeri_ (Schenk)[878].

This species is represented in several Wealden localities by fragments
of fertile pinnae similar to those of _L. polypodioides_. It is almost
impossible to distinguish small specimens of the Wealden fern from
Heer’s genus _Nathorstia_ (Marattiaceae) unless the sori are well
preserved. This species occurs in Wealden beds in England, Germany,
Belgium, and elsewhere and has been discovered by Dr Marcus Gunn in
Upper Jurassic plant-beds of Sutherlandshire (N.E. Scotland).

                   •       •       •       •       •

_Laccopteris_ is widely spread in Rhaetic, Jurassic and Lower
Cretaceous floras. It affords evidence of the former abundance in
northern latitudes of a family now represented by the two species of
_Matonia_ confined to a restricted area in the southern hemisphere.


                             _Matonidium._

Schenk[879] instituted this convenient term for fossil fern fronds
agreeing in habit and in their sori with _Matonia pectinata_ (figs.
227, 228, p. 292). Zeiller[880] has drawn attention to the fact
that the Mesozoic species differ from the surviving types in the
greater number of sporangia in each sorus, and, it may be added,
in _Matonidium_ the fertile pinnules are more richly supplied with
sori than are those of _Matonia_. Unfortunately our knowledge of the
structure of the sporangia of _Matonidium_ is less complete than in the
case of _Laccopteris_, but such evidence as is available justifies the
conclusion that _Matonia_ is a direct descendant of ferns which formed
a prominent feature in European Jurassic and Wealden floras. It is
interesting to find that in a Cretaceous species, described by Krasser
(fig. 265, A) since the publication of Zeiller’s paper, the sori appear
to be identical in distribution and in appearance with those of the
recent species.

I am indebted to Prof. Bommer for permission to reproduce the
unpublished drawing represented in fig. 237 D (p. 310) of a section of
the rhizome of _Matonidium_ from the Belgian Wealden beds of Hainaut
(“Flore Bernissartienne”). The section shows an arrangement of vascular
tissue identical with that in the recent species: there may be two
solenosteles and in addition a solid axial strand. The form of the
leaf-trace in the fossil appears to be identical with that in _Matonia
pectinata_ (fig. 237, A, p. 310).


_Matonidium Goepperti_ (Ettingshausen)[881]. Fig. 269.

Under this name are included specimens from Inferior Oolite and Wealden
strata in Britain and elsewhere. It is, however, not impossible that if
more information were available, we should find adequate reasons for
recognising two specific types. Fontaine[882], adhering rigidly to the
rules of priority, speaks of this species as _Matonidium Althausii_
(Dunker), but Ettingshausen’s specific term is better known.

[Illustration: FIG. 269. _Matonidium Goepperti_ (Ettings.). (A, B, ½
  nat. size; C, approximately nat. size.)]

  Fronds pedate and apparently identical in habit with those of
  _Matonia pectinata_; ultimate segments linear, slightly falcate and
  bluntly pointed. Sori circular or oval, numerous, containing 15
  to 20 sporangia with an oblique annulus, in two rows on the lower
  surface of the pinnules; indusium as in _Matonia_.

The English examples have so far afforded no information in regard to
sporangial structure, but Schenk[883] has recognised a distinct annulus
in German material. In his description of fossil plants from Lower
Cretaceous rocks in California, Fontaine[884] doubtfully identifies
two very small fragments as _Matonidium Althausii_; the evidence is,
however, wholly inadequate.


_Matonidium Wiesneri_, Krasser[885]. Fig. 265, A.

This Cenomanian (Cretaceous) species from Moravia appears to be
identical in habit with the older type. The pinnules are larger and
bear fewer sori. Krasser’s figures of the sterile pinnules show no
lateral anastomosing between the secondary veins, but the small
vascular network below each sorus (fig. 265, A) is identical with that
in _Matonia pectinata_. The indusiate sori contain about six sporangia
with an oblique annulus.

The very wide geographical distribution of the Matonineae during the
Mesozoic era affords a striking contrast to the limited range of the
Malayan survivals.


                          =Hymenophyllaceae.=

The frequent use of the generic name _Hymenophyllites_ as a designation
of Palaeozoic ferns, more particularly in the older literature, is
another instance of the undue importance which palaeobotanists have
always been prone to attach to external resemblances of vegetative
organs. The fragment of lamina described by Stur for the Culm Measures
of Austria as _Hymenophyllum waldenburgense_[886] has no claim to
consideration as evidence of Palaeozoic Hymenophyllaceae. On the other
hand, there are a few records of fertile fronds which, though not to
be accepted without reserve, are worthy of more careful examination.
Some petrified sporangia described by Renault[887] from the Culm of
Esnost are referred to _Hymenophyllites_ on account of the position
of the annulus, which appears to encircle about two-thirds of the
circumference; it is, however, not certain that the annulus is
horizontal as in the recent genus.

The Culm species _Rhodea patentissima_ described by Ettingshausen[888]
as _Hymenophyllites patentissima_ and subsequently referred by
Stur[889] to _Rhodea_, is regarded by these authors as closely allied
to _Hymenophyllum_ simply on the ground of the finely divided and
delicate sterile fronds; another species, _Rhodea moravica_ (Ett.),
which Ettingshausen referred to _Trichomanes_, is compared with
recent species of that genus. In neither case do we know anything of
sporangial characters.

[Illustration: FIG. 270.

  A, E. _Senftenbergia elegans._
  B. _Oligocarpia Brongniartii._
  C. _Trichomanes_ sp.
  D. _Hymenophyllum tunbrigense._
  F, G. _Sphenopteris_ (_Hymenophyllites_) _quadridactylites._

  (A, B, F, G, after Zeiller; D, after Hooker; E, after Stur.)]

A fertile sphenopteroid frond figured by Schimper as _Hymenophyllum
Weissi_[890] from the Coal-Measures of Saarbrücken bears some
resemblance to recent Hymenophyllaceae, but the figures are by no means
convincing: an examination of the type-specimens in the Strassburg
Museum led Solms-Laubach[891] to express dissent from Schimper’s
determination. A more satisfactory example is that afforded by the
fertile pieces of a frond described by Zeiller[892] from French
Coal-Measures as _Hymenophyllites quadridactylites_ (Gutbier). Some
of the ultimate segments with a truncated tip are preserved in close
association with a group of oval sporangia with a complete transverse
annulus (fig. 270, F, G). The position of the sporangia is such as to
suggest their separation from a terminal columnar receptacle like that
in _Trichomanes_ and _Hymenophyllum_. In his account of this species
from the Coal-Measures of the Forest of Wyre, Kidston[893] states that
Zeiller informed him that he had noticed traces of what appeared to be
a columnar receptacle in the French specimens.

The records of Hymenophyllaceae from the Mesozoic and Tertiary
formations are not such as need detain us. The facts bearing on
the geological history of this family are singularly meagre. There
is no evidence which can be adduced in favour of regarding the
Hymenophyllaceae as ferns of great antiquity, which played a prominent
part in the floras of the past.

It is interesting to find that the genus _Ankyropteris_[894], one of
the Botryopterideae (a group of Palaeozoic Ferns for which I propose
the name Coenopterideae), has a morphological character in common
with _Trichomanes_, namely the production of axillary buds: there are
also features in the stelar anatomy shared by the Botryopterideae and
Hymenophyllaceae[895]. These resemblances, though by no means amounting
to proof of near relationship, point to a remote ancestry for certain
features retained by existing members of the Hymenophyllaceae.


                            =Cyatheaceae.=

The specimens from the Culm rocks of Moravia on which Stur founded the
species _Thyrsopteris schistorum_[896] are too imperfectly preserved
to warrant the use of this generic name. Goeppert[897] in 1836
instituted the genera _Cyatheites_, _Hemitelites_, and _Balantites_
for species of Carboniferous ferns believed to be closely allied to
recent Cyatheaceae, but a fuller knowledge of these types has clearly
demonstrated that in all cases the reference to this family had no
justification.

The Upper Carboniferous species _Dicksonites Pluckeneti_, of which
Sterzel[898] described fertile specimens in 1886 as possessing circular
sori, has since been shown by Grand’Eury[899] to be a Pteridosperm
bearing small seeds. In _Sphenopteris_ (_Discopteris_) _cristata_
(Brongn.) Zeiller[900] has described sori very like those of _Cyathea_
and _Alsophila_, but differing in the exannulate sporangia: this
species, like so many of the Palaeozoic ferns, is probably more akin to
the Marattiaceae than to the Cyatheaceae.

We have as yet no satisfactory evidence of the existence of the
Cyatheaceae in Palaeozoic floras. It is not until we reach the Jurassic
period that trustworthy data are obtained. Raciborski[901] has
identified as Cyatheaceous fertile Jurassic fronds from Poland, but
his figures are inconclusive. In _Alsophila polonica_ it is not clear
whether the annulus is vertical or oblique, and in another supposed
member of the family, _Gonatosorus Nathorsti_, in which the indusium is
described as bivalvate, there is no proof of affinity to Cyatheaceae.

In attempting to decipher the past history of the Cyatheaceae it
is important to remember the close resemblance between the fertile
segments of some species of _Davallia_ (Polypodiaceae) and those of
_Dicksonia_ (fig. 229, C, D, p. 294). Unless the sporangia are well
enough preserved to show the position of the annulus, it is frequently
impossible to feel much confidence in the value of the grosser
features, such as the reduced lamina of the fertile segments and the
form of the sori. It is, however, probable that the widely-spread
Jurassic species _Coniopteris hymenophylloides_ is correctly referred
to the Cyatheaceae, but even in the case of this species the evidence
of external form needs confirmation by an examination of individual
sporangia.


                            _Coniopteris._

This genus was instituted by Brongniart[902] for fossil fronds
characterised by pinnules more or less intermediate between the
_Pecopteris_ and _Sphenopteris_ type and agreeing in the form of the
sori with the leaves of recent species of _Dicksonia_. It should
be noted that Stur included in this genus a species, _Coniopteris
lunzensis_[903] from the Upper Trias of Lunz, which he regarded as a
Marattiaceous fern.


_Coniopteris hymenophylloides_, Brongn. Figs. 271, 272, 275, B.

  1828. _Sphenopteris hymenophylloides_, Brongniart, Hist. vég. foss.
        p. 189, Pl. LVI. fig. 4.

  1829. _S. stipata_, Phillips, Geol. York. p. 147, Pl. X. fig. 8.

  1835. _Tympanophora simplex_, Lindley and Hutton, Foss. Flor. Pl.
        CLXX. A.

   —    _T. racemosa_, _ibid._ Pl. CLXX. B.

   —    _Sphenopteris arguta_, _ibid._ Pl. CLXVIII.

  1836. _Hymenophyllites Phillipsi_, Goeppert, Foss. Farn. p. 256.

  1849. _Coniopteris hymenophylloides_, Brongniart, Tableau, p. 105.

   —    _Coniopteris Murrayana_, _ibid._

  1851. _Sphenopteris nephrocarpa_, Bunbury, Quart. Journ. Geol. Soc.
        Vol. VII. p. 129, Pl. XII. fig. 1.

  1876. _Thyrsopteris Murrayana_, Heer, Flor. Foss. Arct. Vol. IV. (2)
        p. 30, Pls. I. II. VIII.

The above list represents a small selection of the names applied to
Jurassic ferns from different localities which there are good grounds
for regarding as referable to a single type[904].

  Frond tripinnate; pinnae linear acuminate, attached to the rachis
  at a wide angle; the pinnules vary considerably in size and
  shape; in some the lamina is divided into a few broad and rounded
  lobes (fig. 275, B) while in others the leaflets are dissected
  into narrow linear segments. The sori are borne at the ends of
  veins; the fertile pinnules have a much reduced lamina and, in
  extreme cases, bear a close resemblance to those of _Thyrsopteris
  elegans_ (fig. 229, A, p. 294). The sori are partially enclosed in
  a cup-like indusium and the sporangia appear to have an oblique
  annulus.

  Venation and habit of frond of the _Sphenopteris_ type.

[Illustration: FIG. 271. _Coniopteris hymenophylloides_ (Brongn.).
  Nat. size. From a specimen in the Manchester Museum.]

The pinna shown in fig. 271 is the type-specimen of _Sphenopteris
arguta_ Lind. and Hutt. from the Yorkshire Inferior Oolite and is
indistinguishable from the English examples on which Brongniart founded
his species _S. hymenophylloides_. Fig. 272 shows a specimen from
the York Museum illustrating the difference between the sterile and
fertile pinnae. The resemblance of some fertile pinnae of _Coniopteris
hymenophylloides_ to those of _Thyrsopteris elegans_ has led to a
frequent use, without any solid justification, of the generic name of
the Juan Fernandez fern for Jurassic and Wealden plants. It is not
impossible that some of the fossils described by Heer from Jurassic
rocks of Siberia[905] as species of _Thyrsopteris_ are Cyatheaceous
ferns, but it is impossible to say with certainty that they are
generically identical with the recent species. In his monograph of the
Potomac flora of Virginia[906] and Maryland, Fontaine has described as
species of _Thyrsopteris_ several specimens of fronds which afford
no evidence as to the nature of the sori or sporangia. Some of the
fronds referred by this author to _Thyrsopteris rarinervis_[907],
which I examined in the Washington Museum, are in all probability
examples of _Onychiopsis_, a genus included in the Polypodiaceae. The
fragments described by Lester Ward[908] as species of _Thyrsopteris_
from the Lower Cretaceous of the Black Hills of North America afford
no satisfactory evidence of relationship to the recent type. Similarly
Velenovský has described a Lower Cretaceous _Onychiopsis_ from
Bohemia[909] as a species of _Thyrsopteris_, although the fertile
segments bear little or no resemblance to those of the Cyatheaceous
genus. Some fertile portions of fronds described by Heer[910] as
_Asplenium Johnstrupi_ and afterwards as _Dicksonia Johnstrupi_[911]
from the Cretaceous beds (Kome series) of Greenland are very similar to
_Coniopteris hymenophylloides_.

[Illustration: FIG. 272. _Coniopteris hymenophylloides._ Specimen from
  the Inferior Oolite, Scarborough; in the York Museum. [M.S.]]


_Coniopteris quinqueloba_ (Phillips). Fig. 273.

This species, originally described by Phillips[912] as _Sphenopteris
quinqueloba_, is very similar in habit to _C. hymenophylloides_,
differing chiefly in the smaller size of the leaf and in the narrower
ultimate segments. The specimen shown in fig. 273, B, illustrates the
form of the sorus and sporangia.

[Illustration: FIG. 273. _Coniopteris quinqueloba_ (Phillips). A, × 2;
  B, considerably enlarged. From drawings supplied by Dr Nathorst.]


_Coniopteris arguta_ (Lind. and Hutt.[913]). Figs. 274, 275, A.

The sterile pinnae of this species bear pinnules of a type met with
in various species of ferns from different horizons; the smaller ones
are entire and slightly falcate, while on the lower part of a frond
the ultimate segments are longer and have a crenulate margin. The
fertile pinnae bear pinnules reduced to a midrib with a narrow border,
and terminating in a cup-like indusium (fig. 275, A). In habit the
sterile leaf (fig. 274) of this species is similar to the Jurassic
Schizaeaceous fern _Klukia exilis_.


                            _Protopteris._

Presl[914] instituted this genus for a Lower Cretaceous tree-fern
from Bohemia originally figured as _Lepidodendron punctatum_[915]
and assigned to a Palaeozoic horizon; it was afterwards named by
Corda[916] _Protopteris Sternbergii_ and referred by Brongniart[917]
to _Sigillaria_. The genus _Protopteris_ stands for fossil fern-stems
with the habit and, in the main, the structural features of recent
tree-ferns. Persistent leaf-bases and sinuous adventitious roots
cover the surface of the stems: the vascular system is of the
dictyostelic type characteristic of _Cyathea_ (fig. 240, p. 313) and
_Alsophila_. It is by the pattern formed by the vascular tissue on the
exposed surface of the leaf-bases that _Protopteris_ is most readily
recognised: the leaf-trace has a horse-shoe form with the ends curled
inwards and the sides more or less indented (fig. 277). The generic
name _Caulopteris_ is used by some authors in preference to Presl’s
genus; but _Protopteris_ is more conveniently restricted to Mesozoic
Cyatheaceous stems and _Caulopteris_ to Palaeozoic stems, with the
internal structure of _Psaronius_ (see Chap. XXIII.). Stenzel applies
_Caulopteris_ to Mesozoic stems in which the leaf-trace consists of
several separate strands and not of a continuous band.

[Illustration: FIG. 274. _Coniopteris arguta._ (Nat. size. From a
  specimen in the Sedgwick Museum, Cambridge.)]

[Illustration: FIG. 275.

  A. _Coniopteris arguta._ (Fertile pinnae; nat. size.)
  B. _C. hymenophylloides._

  A, from the Inferior Oolite of Yorkshire (British Museum); B, from
  Jurassic rocks in Turkestan. ]

Lower Cretaceous casts of tree-fern stems in the Prague Museum have
been described under the names _Alsophilina_ and _Oncopteris_; the
figures of the latter (fig. 276) given by Feistmantel[918] and by
Velenovský[919] show the petiole-bases arranged in vertical rows and
characterised by leaf-traces consisting of two separate strands in the
form of two =V=s lying on their sides.

Tree-fern stems described under various generic names are not
infrequently found in European Lower Cretaceous rocks: their
comparative abundance affords an example of striking changes in
geographical distribution since the latter part of the Mesozoic epoch.
The Cyatheaceae no longer exist in Europe and the arborescent species
of the genus have retreated to more southern regions.

[Illustration: FIG. 276. _Oncopteris Nettvalli._ (After Velenovský; ¾
  nat. size.)]

[Illustration: FIG. 277. _Protopteris punctata._ (After Heer; very
  slightly reduced.)]


_Protopteris punctata_ (Sternb.). Fig. 277.

The earliest information in regard to the anatomy of this widely
spread Lower Cretaceous fern we owe to Corda, who showed that the
species agrees in essentials with existing tree-ferns. The English
example described by Carruthers[920] from Upper Greensand beds in
Dorsetshire (now in the British Museum) shows only the external
features. The sandstone cast (14 cm. in diameter), of which a
portion is seen in fig. 277, was described by Heer from Disco Island
(Greenland) as a Carboniferous species[921], but afterwards correctly
assigned to the Cenomanian series[922] This species is recorded
also from the Lower Cretaceous of Bohemia by Frič and Bayer[923]
Among examples of petrified stems exhibiting a general agreement
with _Protopteris punctata_ are those described by Stenzel[924] from
Turonian rocks in Germany. In one of these, _Rhizodendron oppoliense_
Göpp., attention is drawn to branches given off from the stem stele
which have a solenostelic structure in contrast to the dictyostele of
the stem; also to the minute structure of the tracheae which appear to
have their ends perforated, a feature shown by Gwynne-Vaughan[925] to
be characteristic of the xylem elements of many ferns.

[Illustration: FIG. 278.

  A. _Laccopteris polypodioides_, Brongn. [From a specimen (39275) in
     the British Museum; slightly reduced.]
  B. _L. Muensteri._
  C. _Dicksonia_ (petiole stele).
  D. _Onychiopsis Mantelli_ (fertile segments).
  E. _Hausmannia Sewardi_ Richt.
  F. _H. Kohlmanni_ Bicht.
  G, H. _Protopteris Witteana_, Schenk. (x, xylem; R, roots.)

  (B, after Schenk; E, F, after Richter.)]

_Protopteris Witteana_ Schenk[926] (fig. 278, G, H), a Wealden species
recorded from Germany and England, represents a closely allied or
possibly an identical type. The section of the stem (fig. H) shows the
narrow vascular bands, x, of a dictyostele similar to that of recent
Cyatheaceous tree-ferns and a form of meristele (fig. G, x) resembling
that of _P. punctata_. Adventitious roots are seen in section at R
(figs. G and H).


                           =Polypodiaceae.=

Sections of petrified sporangia from the English Coal-Measures
(_Pteridotheca_ sp.) occasionally exhibit a striking resemblance to
those of recent Polypodiaceae[927], but in the absence of material
in which it is possible to recognise the true orientation of the
sporangia, the exact position of the annulus is almost impossible to
determine. We have as yet no satisfactory evidence of the existence of
true Polypodiaceae in the Palaeozoic era. It is noteworthy that apart
from the absence of ferns which can reasonably be included in this
family, the anatomical features of the Botryopterideae (Coenopterideae)
and of the Cycadofilices or Pteridosperms do not foreshadow those
of Polypodiaceous ferns. On the other hand, as we have already
noticed, anatomical characters of such families as the Gleicheniaceae,
Hymenophyllaceae, and Schizaeaceae are met with in certain generalised
Palaeozoic types. These facts are perhaps of some importance as
supplying collateral evidence in favour of the relatively more recent
origin of the dominant family of ferns in modern floras.

[Illustration: Fig. 279.
  A. _Adiantides antiques_ (Ett.). (½ nat. size.)
  B. _A. Lindsayoides_ (Sew.). (B′ nat. size.)

  (A, after Kidston.)]

The use of the generic name _Adiantites_ for fern-like fronds of
Lower Carboniferous age characterised by cuneate pinnules like
those of species of _Adiantum_, suggests an affinity which is in
all probability non-existent. It has been pointed out that this
generic name was applied in the first instance to the leaves of
the Jurassic plant _Ginkgo digitata_[928] and should, therefore,
be discarded. Schimper[929] used the designation _Adiantides_, and
Ettingshausen[930], more rashly than wisely, preferred _Adiantum_. The
specimens described by Kidston[931] as _Adiantides antiquus_ (Ett.)
(fig. 279, A) from the Carboniferous limestone of Flintshire are
portions of tripinnate fronds bearing cuneate segments with numerous
forked veins radiating from the contracted base of the lamina. It is
not improbable, in view of Dr White’s[932] discovery of seeds on a very
similar plant from the Pottsville beds of North America, that this
characteristic Lower Carboniferous genus is a Pteridosperm.

From Jurassic rocks in various parts of the world numerous fossils
have been described under the generic names _Aspidium_, _Asplenium_,
_Davallia_, _Polypodium_, and _Pteris_. In the great majority of
cases such records leave much to be desired from the point of view of
students who appreciate the dangers of relying on external similarity
between vegetative organs, and on resemblances founded on obscure
impressions of sori. The generic term _Woodwardites_[933], which
suggests affinity with the recent genus _Woodwardia_, has been used for
Rhaetic plants belonging to the Dipteridinae.

A plant described as _Adiantides Lindsayoides_ from Jurassic rocks
of Victoria[934], characterised by marginal sori which appear to
be protected by the folded-over edge of the leaflets, and by the
resemblance of the pinnules to those of recent species of _Lindsaya_,
may be a true Polypodiaceous fern; but in this case, as in many similar
instances, nothing is known of the structure of the sporangia. Some
sterile pinnae described by Yabe from Jurassic rocks of Korea as
_Adiantites Sewardi_[935] may perhaps be identical with the Australian
species.

In such a species as _Polypodium oregonense_ Font., from Jurassic rocks
of Oregon, the generic name is chosen because the “fructification seems
near enough to that of _Polypodium_ to justify the placing of the plant
in that genus[936].” But the fact that no sporangia have been found is
a fatal objection to this identification.


                            _Onychiopsis._

This generic name was instituted by Yokoyama[937] for a Japanese
Wealden species, previously described by Geyler[938] as _Thyrsopteris
elongata_, on the ground that, in addition to a similarity in habit of
the sterile fronds, the fertile pinnae present a close agreement to
those of the recent genus _Onychium_.


_Onychiopsis Mantelli_[939] (Brongn.). Figs. 278, D; 280, A and B.

The Japanese species _Onychiopsis elongata_ may perhaps be identical
with this common Wealden fern which, as Fontaine points out, should
be called _O. psilotoides_ if the rule of priority is to be observed
irrespective of long usage.

  1824. _Hymenopteris psilotoides_, Stokes and Webb, Trans. Geol. Soc.
        [ii.], Vol. I. p. 423, Pl. XLVI. fig. 7.

  1828. _Sphenopteris Mantelli_, Brongniart, Hist. vég. foss. p. 170,
        Pl. XLV. figs. 3–7.

  1890. _Onychiopsis Mantelli_, Nathorst, Denksch. Wien Akad. Vol.
        LVII. p. 5.


_Onychiopsis Mantelli_ may be defined as follows:—

  Frond bipinnate, ovate lanceolate, rachis winged; pinnae
  approximate, given off at an acute angle; pinnules narrow,
  acuminate, with a single vein; the larger segments serrate and
  gradually passing into pinnae with narrow ultimate segments.
  Fertile segments sessile or shortly stalked, linear ovate,
  sometimes terminating in a short awn-like prolongation.

The fertile segments (fig. 278, D) bear so close a resemblance to those
of species of _Onychium_ that it would seem justifiable to regard the
plant as a member of the Polypodiaceae. This fern is one of the most
characteristic members of the Wealden floras; it occurs in abundance
in the English Wealden, in Portugal, Germany, Belgium, Japan, Bohemia,
South Africa, and elsewhere. A piece of rhizome figured from the
English Wealden[940] is very similar to the creeping rhizomes of recent
species of Polypodiaceae. The English Wealden specimens shown in fig.
280, A and B, illustrate the difference in form presented by leaves
of this species; the smaller pinnae reproduced in fig. A are more
characteristic of the species than are those of the slightly enlarged
example represented in fig. 280, B.

[Illustration: FIG. 280. _Onychiopsis Mantelli._ (From Wealden
  specimens in the British Museum; No. 13495 and No. V. 2615. A,
  natural size; B, very slightly enlarged.)]

Among British Tertiary species referred to Polypodiaceae, it is
interesting to find what may well be an authentic record of a
fern closely allied to the recent tropical species _Acrostichum_
(_Chrysodium_) _aureum_. This Eocene species from Bournemouth is
described as _Chrysodium lanzaeanum_[941]. The frond is simply pinnate
and apparently coriaceous in texture, with lanceolate or oblong
lanceolate pinnules (fig. 261, A, A′, p. 350), differing from those of
_Acrostichum aureum_ in being sessile. A prominent midrib gives off
numerous anastomosing veins. No fertile pinnules have been found.

Specimens described by Forbes from the Eocene beds of the Island of
Mull as _Onoclea hebraidica_[942] bear a strong likeness to the North
American and Japanese recent species _Onoclea sensibilis_. Fertile
specimens referred to the latter species are recorded by Knowlton[943]
from Tertiary beds of Montana.

A species described by Saporta[944] from the Eocene of Sézanne as
_Adiantum apalophyllum_ is recorded by Gardner and Ettingshausen from
Bournemouth; an identification which is based on somewhat meagre
evidence.

The following remarks by Gardner and Ettingshausen are worthy of
repetition as calling attention to circumstances often overlooked in
analyses of fossil floras. They speak of ferns as relatively rare
in British Eocene rocks and add,—“the floras consist principally of
deciduous dicotyledonous leaves, which ... fell into the water and
were tranquilly silted over. Ferns, on the other hand, would require
some violence to remove them from the place of their growth, and their
preservation would consequently be exceptional, and they would be
mutilated and fragmentary. This may account for their rarity. Few as
the British ferns are in the number of species, they nevertheless form
the largest and most important series of Eocene ferns, even of Tertiary
ferns, yet described from one group of beds[945].”


                            =Dipteridinae.=

                           _Dictyophyllum._

This genus was founded by Lindley and Hutton for a pinnatifid leaf
from the Jurassic rocks of Yorkshire which they regarded as probably
dicotyledonous and named _D. rugosum_[946]. Several ferns of this genus
have since been found with well-preserved sori which demonstrate a
close similarity to the recent fern _Dipteris._ _Dictyophyllum_ may be
defined as follows:—

Fronds large and palmate, characterised by the equal dichotomy of the
main rachis into two arms which curve outwards and then bend inwards
(fig. 281); from the surface of each arm are given off numerous
spreading pinnae with a lamina more or less deeply dissected into
lobes varying in breadth and in the form of the apex. Each lobe has a
median vein, from which branches are given off approximately at right
angles and then subdivide into a reticulum, in the meshes of which the
veinlets end blindly (fig. 282, A and E). Sori composed of annulate
sporangia are crowded on the lower surface of the lamina. In habit
and in sporangial characters the genus closely resembles _Dipteris_,
and in the branching of the frond suggests comparison with _Matonia_.
The rhizome (_Rhizomopteris_) is creeping and dichotomously branched,
bearing leaf-scars with a horse-shoe form of vascular strand.

[Illustration: FIG. 281. _Dictyophyllum exile._ (After Nathorst; much
  reduced.)]

_Dictyophyllum_ is represented by several types to which various
specific names have been assigned, the distinguishing features being
the form of the pinna lobes, the degree of concrescence between the
basal portions of the pinnae, and similar features which in some cases
can only be safely used as criteria when large specimens are available
for comparison.


_Dictyophyllum exile_ (Brauns). Figs. 281, 282, D, E.

  1862. _Camptopteris exilis_, Brauns, Palaeontograph. IX. p. 54.

  1867. _Dictyophyllum acutilobum_, Schenk, Foss. Flor. Grenz. p. 77,
        Pls. XIX. XX.

  1878. _D. exile_, Nathorst, Flora vid Bjuf, I. p. 39, Pl. V. fig. 7.

   ——   _D. acutilobum_, _ibid._ Pl. XI. fig. 1.

The restoration, after Nathorst[947], shown in fig. 281 illustrates the
habit of this striking fern, examples of which or of closely allied
species are recorded from Rhaetic rocks of Germany, Scania, Persia,
Bornholm, Tonkin, China, and elsewhere[948]. The petiole, reaching
a length of 60 cm., forks at the apex into two equal arms leaving
between them an oval space and occasionally crossing one another. The
axes of these branches are twisted so that the pinnae, which may be
as many as 24 on each arm, and arise from the inner side, by torsion
of the axes assume an external position. An interesting analogy as
regards the twisted rachis of _Dictyophyllum exile_ and _Camptopteris_
is afforded by the leaves of the Cycads, _Macrozamia Fawcettiae_ and
_M. corallipes_, which are also characterised by the torsion of the
rachis. The habit, justly compared by Nathorst with that of _Matonia
pectinata_, affords another illustration of the common occurrence
in older ferns of a dichotomous system of branching. The pinnae,
characterised by circinate vernation, reach a length of 60 cm. and are
divided into linear lobes inclined obliquely or at right angles to the
pinna axis. The whole of the under surface of the lamina may be covered
with sporangia, 4–7 sporangia in each sorus; the annulus is incomplete
and approximately vertical (fig. 282, D). The rhizome is probably
represented by the dichotomously branched axis described by Nathorst
from Scania as _Rhizomopteris major_; the leaf-scars show a horse-shoe
leaf-trace.

[Illustration: FIG. 282.

  A. _Dictyophyllum Nilssoni._
  B. _Rhizomopteris Schenki._
  C. _Camptopteris spiralis._
  D, E. _Dictyophyllum exile._

  (After Nathorst; A, B, C, E, ⅔ nat. size.)]


_Dictyophyllum Nathorsti_ Zeiller[949].

This type, represented by a splendid series of specimens from
the Rhaetic beds of Tonkin, agrees very closely with _D. exile_.
It differs, however, in the basal parts of the pinnae which are
concrescent for a length of 5 to 8 cm. instead of free as in _D.
exile_; and, to a slight degree, in the form of the ultimate segments.
In habit and in soral characters the two species are practically
identical. Each sorus contains 5 to 8 sporangia, which are rather
larger than those of _Dipteris_.


_Dictyophyllum rugosum_, Lind. and Hutt. Fig. 283.

  1828. _Phlebopteris Phillipsii_, Brongniart, Hist. vég. foss. p. 377,
        Pl. CXXXII. fig. 3; Pl. CXXXIII. fig. 1.

  1829. _Phyllites nervulosis_, Phillips, Geol. Yorks. p. 148, Pl.
        VIII. fig. 9.

  1834. _Dictyophyllum rugosum_, Lindley and Hutton, Foss. Flor. II.
        Pl. CIV.

  1836. _Polypodites heracleifolius_, Goeppert, Foss. Farn. p. 344.

  1849. _Camptopteris Phillipsii_, Brongniart, Tableau, p. 105.

  1880. _Clathropteris whitbyensis_, Nathorst, Berättelse, p. 83.

This species, which is characteristic of Jurassic rocks, is less
completely known than the two types described above, but in the form
and venation of the pinnae there is little difference between the
Rhaetic and Jurassic plants. The leaves of the Jurassic species appear
to have been smaller and more like those of _Dipteris conjugata_ (fig.
231); there are no indications of the existence of the two curved
arms at the summit of the petiole which form so striking a feature
in _D. exile_ and _D. Nathorsti_. No sporangia have been found on
English specimens, but it is safe to assume their agreement with those
of other species. A more complete list of records of _D. rugosum_ is
given in the first volume of the British Museum Catalogue of Jurassic
plants[950].

[Illustration: FIG. 283. _Dictyophyllum rugosum_ (Lind. and Hutt.).
  (Brit. Mus. Nat. size.)]

Nathorst[951] has recently drawn attention to certain differences
between _Dictyophyllum_ and _Dipteris_. The pinnate division of the
pinnae is not represented in the fronds of the recent species, but this
method of lobing, which is a marked characteristic of _Dictyophyllum_,
is less prominent in _Clathropteris_; and in _Camptopteris lunzensis_
Stur[952], an Austrian Upper Triassic species, the pinnae are entire.
In _Dictyophyllum_ the sori cover the whole lower surface of the leaf;
in _Dipteris_ they are more widely separated and the sporangia have a
diameter of 0·02 mm., but in _Dictyophyllum_ the diameter is 0·4–0·6
mm. Moreover in _Dictyophyllum_ the sori contain 5 to 8 sporangia,
whereas in _Dipteris_ they are much more numerous. Despite these
differences it is clear, as Nathorst says, that _Dictyophyllum_,
_Clathropteris_, and _Camptopteris_ are existing types very closely
allied to _Dipteris_. It is a matter of secondary importance whether
we include all in the Dipteridinae or follow Nathorst’s suggestion and
refer the fossil genera to the separate family Camptopteridinae.


                           _Thaumatopteris._

This genus, founded by Goeppert[953] for a Rhaetic plant from Bayreuth,
is by some authors[954] regarded as identical with _Dictyophyllum_,
but it has recently been resuscitated by Nathorst[955] for specimens
which he names _T. Schenki_, formerly included by Schenk in his species
_T. Brauniana_[956]. It bears a close resemblance, in the long linear
pinnules with an entire or crenulate margin, to _Dictyophyllum Fuchsi_
described by Zeiller[957] from Tonkin, and it would seem hardly
necessary to adopt a distinctive generic designation. The sporangia
have a vertical or slightly oblique annulus and the rhizome is similar
to that of _Dictyophyllum exile_. The habit of the genus is shown in
fig. 284, which represents one of the German Rhaetic species.

[Illustration: FIG. 284. _Thaumatopteris Münsteri._ (From a specimen in
  the Bergakademie, Berlin; ⅓ nat. size.)]


                           _Clathropteris._

_Clathropteris meniscoides_, Brongn. Fig. 285.

_Clathropteris_, founded by Brongniart[958] for Rhaetic specimens from
Scania, agrees very closely with some species of _Dictyophyllum_,
but in view of the more rectangular form of the venation-meshes it
is convenient to retain both names. The type-species was originally
named _Filicites meniscoides_[959] and afterwards transferred to
_Clathropteris_. An examination of Brongniart’s specimens has
convinced Nathorst of the specific identity of _C. meniscoides_ and _C.
platyphylla_. The Tonkin leaves described by Zeiller[960] under the
latter name should, therefore, be included in _C. meniscoides_, which
may be thus defined:

  The petiolate frond is characterised by an equal dichotomy of
  the rachis, as in _Dictyophyllum_; each branch bore 5–15 pinnae,
  disposed _en éventail_, reaching a length of 20–30 cm. and fused
  basally as in _D. Nathorsti_ Zeill. Pinnae linear lanceolate,
  slightly contracted at the lower end and gradually tapered
  distally. The lamina, 3–14 cm. broad, is characterised by obtusely
  pointed marginal lobes. From the midrib of each pinna lateral
  veins are given off at a wide angle, and adjacent veins are
  connected by a series of branches which divide the lamina into a
  regular reticulum of rectangular and polygonal meshes (fig. 285).
  The sori are abundant and contain 5–12 sporangia like those of
  _Dictyophyllum_.

[Illustration: FIG. 285. _Clathropteris meniscoides._ From Rhaetic
  rocks near Erlangen. [M.S.]]

[Illustration: FIG. 286. _Clathropteris egyptiaca._ (Nat. size.) _a_,
  _b_, pieces of main ribs in grooves.]

What is probably the rhizome of this species has been described
by Nathorst (_Rhizomopteris cruciata_); it is similar to that of
_Dictyophyllum_, but the leaf-scars are more widely separated. This
species occurs in Upper Triassic, Rhaetic or Lower Jurassic rocks of
Scania, France, Germany, Switzerland, Bornholm, North America, China,
Tonkin, and Persia and is represented by fragments in the Rhaetic beds
of Bristol[961].


_Clathropteris egyptiaca_ Sew.[962] Fig. 286.

The specimen on which this species was founded was discovered in the
Nubian Sandstone east of Edfu; the age of the beds is uncertain, but
the presence of _Clathropteris_ suggests a Lower Jurassic or Rhaetic
horizon[963]. Seven strong ribs radiate through the lamina from the
summit of the petiole; at _a_ and _b_ small pieces of the projecting
ribs are shown in the grooves. From the main veins slender branches are
given off at right angles and, as seen in the enlarged drawing, these
again subdivide into a delicate reticulum with free-ending veinlets.

[Illustration: FIG. 287. _Camptopteris spiralis._ (After Nathorst. Much
  reduced.)]


                            _Camptopteris._


_Camptopteris spiralis_, Nath. Figs. 282, C; 287.

Nathorst proposed this generic name for Rhaetic fronds[964] resembling
those of _Clathropteris_ and _Dictyophyllum_, but differing in the
form of the pinnae and in habit. The habit of the type-species, _C.
spiralis_, is shown in fig. 287. An examination of the specimens in
the Stockholm Museum convinced me of the correctness of Nathorst’s
restoration[965]. Each of the forked arms of the rachis bore as many
as 150–160 long and narrow pinnae characterised by an anastomosing
venation (fig. 282, C) and by a spiral disposition due to the
torsion of the axes. The sporangia agree in essentials with those of
_Dictyophyllum_.


                             _Hausmannia._

A critical and exhaustive account of this genus has been given by Prof.
Von Richter[966] based on an examination of specimens found in the
Lower Cretaceous rocks of Quedlinburg in Germany. The name was proposed
by Dunker[967] for leaves from the Wealden of Germany characterised by
a deeply dissected dichotomously branched lamina. Andrae subsequently
instituted the genus _Protorhipis_[968] for suborbicular leaves with
dichotomously branched ribs from the Lias of Steierdorf. A similar
but smaller type of leaf was afterwards described by Zigno[969]
from Jurassic beds of Italy as _P. asarifolius_, and Nathorst[970]
figured a closely allied form from Rhaetic rocks of Sweden. While
some authors regarded _Hausmannia_ and _Protorhipis_ as ferns, others
compared them with the leaves of _Baiera_ (Ginkgoales); Saporta
suggested a dicotyledonous affinity for leaves of the _Protorhipis_
type. The true nature of the fossils was recognised by Zeiller[971],
who called attention to the very close resemblance in habit and in
soral characters to the recent genus _Dipteris_. A comparison of the
different species of _Dipteris_, including young leaves (fig. 231,
p. 297), with those of the fossil species reveals a very striking
agreement[972]. There can be no doubt, as Richter points out, that the
names _Hausmannia_ and _Protorhipis_ stand for one generic type.

_Hausmannia_ may be defined as follows:

  Rhizome creeping, slender, dichotomously branched; leaf-stalks
  slender (2–25 cm. long), bearing a leathery lamina (1–12 cm. long
  and broad), wedge-shaped below, occasionally cordate or reniform,
  entire or more or less deeply lobed into broad linear segments.
  The leaf is characterised by dichotomously branched main ribs
  which arise from the summit of the rachis as two divergent arms
  and radiate in a palmate manner, with repeated forking, through
  the lamina. Lateral veins are given off at a wide angle, and, by
  subdivision, form a fairly regular network similar to that in
  _Dictyophyllum_, _Clathropteris_, and _Dipteris_.


[Illustration: FIG. 288. _Hausmannia dichotoma._ (Specimens from
  the late Dr Marcus Gunn’s Collection of Upper Jurassic plants,
  Sutherlandshire; very slightly reduced.)]

_Hausmannia dichotoma_, Dunker[973]. Fig. 288, A, B.

This Wealden species, represented in the North German flora and in
beds of approximately the same age at Quedlinburg, has been discovered
by Dr Marcus Gunn in Upper Jurassic rocks on the north-east coast of
Scotland. The lamina (12 cm. or more in length) is divided into five
to seven linear segments and bears a close superficial resemblance
to leaves of _Baiera_ and to recent species of _Schizaea_ (fig. 222,
p. 287). Each segment contains one or two main ribs (fig. 288, A). A
similar form is described by Bartholin[974] and by Moeller[975] as _H.
Forchammeri_ from Jurassic rocks of Bornholm.

_Hausmannia Kohlmanni_, Richt. Fig. 278, F.

In this species, instituted by Richter from material obtained from the
Lower Cretaceous beds of Strohberg[976], the comparatively slender
rhizome bears fronds with petioles reaching a length in extreme cases
of 25 cm. but usually of about 10 cm. The lamina (1–7 cm. long and
1–10 cm. broad) is described as leathery, obcordate, and divided into
two symmetrical halves by a median sinus which, though occasionally
extending more than half-way through the lamina, is usually shallow.
The venation consists of two main branches which diverge from the
summit of the petiole (fig. 278, F) and subdivide into dichotomously
branched ribs; finer veins (not shown in the drawing) are given off
from these at right angles and form more or less rectangular meshes
as in other members of the Dipteridinae and in such recent ferns as
_Polypodium quercifolium_ (fig. 231, D, p. 297).

The imperfect lamina represented in fig. 289 may belong to _Hausmannia
Richteri_ or may be a distinct species; it shows some of the finer
veins connecting the shorter forked ribs, which formed part of the
reticulate ramifying system in the mesophyll. This specimen was
obtained from the plant-beds of Culgower on the Sutherlandshire coast,
which have been placed by some geologists in the Kimmeridgian series.

The smaller type represented in fig. 278, E, is referred by Richter
to a distinct species, _Hausmannia Sewardi_[977], founded on a few
specimens from the Lower Cretaceous strata of Strohberg. This species
is characterised by a stouter rhizome bearing smaller leaves consisting
of a short petiole (3–4 cm. long) and an obovate lamina (1–2 cm. long
and broad). There are usually two opposite leaflets on each leaf-stalk,
and these may be equivalent to the two halves of a single deeply
dissected lamina.

[Illustration: FIG. 289. _Hausmannia sp._ Upper Jurassic, near
  Helmsdale, Scotland. From a specimen in the British Museum. (Nat.
  size.)]

It is interesting to compare these different forms of _Hausmannia_ with
the fronds of recent species of _Dipteris_ represented in fig. 231. The
more deeply dissected type, such as _H. dichotoma_, closely resembles
_D. Lobbiana_ or _D. quinquefurcata_, while the more or less entire
fossil leaves (fig. 278, E, F and fig. 289) are very like the somewhat
unusual form of _Dipteris conjugata_ shown in fig. 231, B, p. 297.

Other species of the genus are recorded from Liassic rocks of
Steierdorf[978] (Hungary) and of Bornholm[979]. Nathorst[980] has
described a small Rhaetic species from Scania: a French Permian plant
described by Zeiller[981] and compared by him with _H. dichotoma_, may
be a Palaeozoic example of this Dipteris-like genus.

Some segments of leaves from the Eocene beds (Middle Bagshot) of
Bournemouth, and now in the British Museum, described by Gardner
and Ettingshausen[982] as _Podoloma polypodioides_, bear a close
resemblance in the venation to the lamina of _Dipteris conjugata_.




                             CHAPTER XXII.

                         Marattiales (Fossil).


The discovery of Pteridosperms has necessarily led to a considerable
modification of the views formerly held that existing genera of
Marattiaceae represent survivors of a group which occupied a dominant
position in the forests of the Coal age. Mr Arber writes:—“The
evidence, formerly regarded as beyond suspicion, that the eusporangiate
ferns formed a dominant feature of the vegetation of the Palaeozoic
period, has been undermined, more especially by the remarkable
discovery of the male organs of _Lyginodendron_ by Mr Kidston. At best
we can only now regard them as a subsidiary group in that epoch in the
past history of the vegetable kingdom[983].” Dr Scott expresses himself
in terms slightly more favourable to the view that the Marattiaceae
represent the aristocracy among the Filicales. He says:—“We now have to
seek laboriously for evidence, which formerly seemed to lie open to us
on all hands. I believe, however, that such careful investigation will
result in the resuscitation of the Palaeozoic ferns as a considerable,
though not as a dominant group[984].” Zeiller’s faith[985] in the
prospect of Marattiaceous ferns retaining their position as prominent
members of Palaeozoic floras, though shaken, is not extinguished: he
recognises that they played a subordinate part.

Reference has already been made to the impossibility of determining
whether Palaeozoic fern-like fronds may be legitimately retained in
the Filicales, or whether they must be removed into the ever widening
territory of the Pteridosperms. The difficulty is that the evidence
of reproductive organs is very far from decisive. In the absence of
the female reproductive organs, the seeds, we cannot in most cases be
certain whether the small sporangium-like bodies on fertile pinnules
are true fern sporangia or the microsporangia of a heterosporous
pteridosperm. What is usually called an exannulate fern sporangium,
such as we have in _Angiopteris_ and in many Palaeozoic plants, has
no distinguishing features which can be used as a decisive test. The
microsporophylls of the Mesozoic Bennettitales produced their spores
in sporangial compartments grouped in synangia like those of recent
Marattiaceae; and in the case of _Crossotheca_, a type of frond always
regarded as Marattiaceous until Kidston[986] proved it to be the
microsporophyll of _Lyginodendron_, we have a striking instance of the
futility of making dogmatic assertions as to the filicinean nature of
what look like true fern sporangia. In all probability Dr Kidston’s
surmise that the supposed fern sporangia known as _Dactylotheca_,
_Renaultia_, _Urnatopteris_ are the microsporangia of Pteridosperms
will be proved correct[987]. The question is how many of the supposed
Marattiaceous sporangia must be assigned to Pteridosperms? There is,
however, no reasonable doubt that true Marattiaceae formed a part
of the Upper Carboniferous flora. All that can be attempted in the
following pages is to describe briefly some of the numerous types of
sporangia recognised on Palaeozoic fern-like foliage, leaving to the
future the task of deciding how many of them can be accepted as those
of ferns. It is impossible to avoid overlapping and some repetition
in the sections dealing with true Ferns and with Pteridosperms. The
filicinean nature of the stem known as _Psaronius_ (see page 415) has
not as yet been questioned.

The nomenclature of supposed Marattiaceous species from Carboniferous
and Permian rocks is in a state of some confusion owing to a lack of
satisfactory distinguishing features between certain types to which
different generic names have been assigned. As we have already seen in
the case of supposed leptosporangiate sporangia, the interpretation
of structural features in petrified or carbonised sporangia does not
afford an example of unanimity among palaeobotanical experts.


                            _Ptychocarpus._

This generic name, proposed by the late Professor Weiss[988],
is applied to a type of fructification illustrated by the plant
which Brongniart named _Pecopteris unita_, a species common in the
Upper Coal-Measures of England[989]. It is adopted by Kidston for
fertile specimens from Radstock which he describes as _Ptychocarpus
oblongus_[990], but the precise nature of the fertile pinnules of this
species cannot be determined.


_Ptychocarpus unita_ (Brongn.[991]). Fig. 291, A, B. (= _Goniopteris
unita_, Grand’Eury.)

This species has tripinnate fronds with linear pinnae bearing
contiguous pinnules of the _Pecopteris_ type (fig. 291, B), 4–5 mm.
long, confluent at the base or for the greater part of their length.
On the under surface of the fertile segments, which are identical
with the sterile, occur circular synangia (fig. 291, A) consisting
of seven sporangia embedded in a common parenchymatous tissue and
radially disposed round a receptacle supplied with vascular tissue.
The synangium is described as shortly stalked like those of _Marattia
Kaulfussii_ (fig. 245, B′, p. 320). In shape, in the complete union of
the sporangia, and presumably in the apical dehiscence, _Ptychocarpus_
agrees very closely with _Kaulfussia_ (fig. 245); but we cannot be
certain that we have not a collection of microsporangia simulating a
fern synangium.

A synangium closely resembling _Ptychocarpus_ has been described
by Mr Watson[992] from the Lower Coal-Measures of Lancashire as
_Cyathotrachus altus_, but there is no convincing evidence as to the
nature of the plant on which it was borne.


                             _Danaeites._

This generic name, instituted by Goeppert[993], has been used by
authors without due regard to the nature of the evidence of affinity to
_Danaea_. The type named by Stur _Danaeites sarepontanus_[994] (fig.
291, E) bears small pecopteroid pinnules with ovoid sporangia in groups
of 8–16 in two contiguous series on the lower face of the lamina. The
sporangia dehisce by an apical pore and are more or less embedded in
the mesophyll of the segments. No figures have been published showing
any detailed sporangial structure, and such evidence as we have is
insufficient to warrant the conclusion that the resemblance to _Danaea_
is more than an analogy.


                           _Parapecopteris._

_Parapecopteris neuropteroides_, Grand’Eury. Fig. 290, D.

The plant described by Grand’Eury[995] from the Coal-fields of Gard
and St Étienne, and made the type of a new genus, is characterised
by pinnules intermediate between those of _Pecopteris_ and
_Neuropteris_[996] and by the presence of two rows of united sporangia
along the lateral veins, as in _Danaea_ and _Danaeites_.


                            _Asterotheca._

Certain species of _Pecopteris_ fronds from Carboniferous strata
are characterised by circular sori or synangia consisting of a
small number (3–8) of exannulate sporangia attached to a central
receptacle and free only at their apices. Strasburger[997] suggested
a Marattiaceous affinity for _Asterotheca_ and Stur[998] describes
the species _Asterotheca Sternbergii_ Goepp. (fig. 291, C, D) as an
example of a Marattiaceous fern. The latter author retains Corda’s
genus _Hawlea_[999] for the fertile fronds of the common Coal-Measures
species _Pecopteris Miltoni_, while on the other hand Kidston[1000]
includes this type in _Asterotheca_.


_Pecopteris_ (_Asterotheca_) _Miltoni_ (Artis).

  1825. _Filicites Miltoni_, Artis, Antedil. Phyt. Pl. XIV.

  1828. _Pecopteris Miltoni_, Brongniart, Prodrome, p. 58.

  1828. _Pecopteris abbreviata_, Brongniart, Hist. vég. foss. p. 337,
        Pl. CXV. figs. 1–4; Lindley and Hutton, Foss. Flor. Vol. III.
        Pl. 184.

  1845. _Hawlea pulcherrima_, Corda, Flor. Vorwelt, p. 90, Pl. LVII.
        figs. 7, 8.

  1877–1888. _Hawlea Miltoni_, Stur, Culm Flora, p. 293; Farne Carbon.
        Flora, p. 108, Pls. LIX. LX.

  1888. _Pecopteris_ (_Asterotheca_) _abbreviata_, Zeiller, Flor.
        Valenc. p. 186, Pl. XXIV. figs. 1–4.

[Illustration: FIG. 290.

  A. _Alethopteris lonchitica._  × 2½.  ╮ For description
  B. _Lonchopteris rugosa._  × 2.       ├ see   Chap. XXVII.
  C. _Sphenopteris Hoeninghausi._  × 4. ╯
  D. _Parapecopteris neuropteroides._
  E. _Pecopteris_ (_Dactylotheca_) _plumosa_ [= _P._ (_Dactylotheca_)
     _dentata_ Zeiller (88)].  × 4.

  (A–C, E, after Zeiller; D, after Grand’Eury.)]

The fronds of this species reached a length of more than 3 metres
and a breadth of 2 metres. They are characterised by the presence of
aphlebiae[1001] appressed to the rachis and by circular sori composed
of a small number (3–6) of sporangia. In habit and in the form of the
pinnules this type is similar to _Dactylotheca plumosa_.

[Illustration: FIG. 291.

  A, B. _Ptychocarpus unita._
  C, D. _Asterotheca Sternbergii._
  E. _Danaeites sarepontanus._
  F. _Hawlea Miltoni._
  G.  _Hawlea pulcherrima._
  H–K. _Scolecopteris elegans._

  (A, B, after Renault; C–G, after Stur; H, I, after Strasburger; K,
  after Sterzel.)]


                               _Hawlea._

Stur[1002] retains this generic name for sori in which the sporangia
are free and united only by the proximal end to a central receptacle
(fig. 291, F, G). He describes the individual sporangia as possessing
a rudimentary annulus, a comparatively strong wall, and terminating
in a pointed distal end. He emphasises the greater degree of cohesion
between the sporangia of _Asterotheca_ as the distinguishing feature
of that genus; but this is a character difficult to recognise in some
cases, and from the analogy of recent ferns one is disposed to attach
little importance to the greater or less extent to which sporangia are
united, at least in such cases as _Asterotheca_ and _Hawlea_ when the
cohesion is never complete.


                           _Scolecopteris._

Zenker[1003] gave this name to detached fertile pinnules from the Lower
Permian of Saxony, which he described as _Scolecopteris elegans_. He
recognised the fern nature of the sori and suggested that the pinnules
might belong to the fronds of one of the “Staarsteinen” (_Psaronius_),
a view which subsequent investigations render far from improbable.
The sori, which occur in two rows on the lower surface of the small
pecopteroid segments with strongly revolute margins (fig. 291, H–K),
contain 4–5 sporangia attached to a stalked receptacle comparable
with that of _Marattia Kaulfussii_. These pedicellate synangia were
fully described by Strasburger[1004], who decided in favour of a
Marattiaceous alliance. The lower portions of the distally tapered
sporangia are concrescent, the distal ends being free (fig. 291,
H). Stur includes in _Scolecopteris_ the common species _Pecopteris
arborescens_ (fig. 376), but Kidston[1005] states that the British
example of _Scolecopteris_ is _S. polymorpha_, Brongn. from the Upper
Coal-Measures.

_Scolecopteris elegans_ Zenk. furnishes an example of a plant, or plant
fragment, which has been assigned to the animal kingdom. Geinitz[1006]
described silicified pinnules as _Palaeojulus dyadicus_, the generic
name being chosen because of the resemblance to Millipedes such as
the genus _Julus_. The mistake is not surprising to anyone who has
seen a block of siliceous rock from Chemnitz crowded with the small
pinnules with their concave surfaces formed by the infolding of the
edges. Sterzel[1007], who pointed out the confusion between Myriapods
and Filices, has published figures which illustrate the deceptive
resemblance of the pinnules, with their curved lamina divided by
lateral veins into segments, to the body of a Millipede (fig. 291, K).
He points out that Geinitz searched in vain for the head and legs of
_Palaeojulus_ and expressed the hope that further examination would
lead to fresh discoveries: the examination of sections revealed the
presence of sporangia and demonstrated the identity of _Palaeojulus_
and _Scolecopteris_.


                            _Discopteris._

Stur[1008] instituted this genus for fertile fronds from the Upper
Carboniferous Schatzlarer beds, including two species _Discopteris
karwinensis_ and _D. Schumanni_. He described the small Sphenopteroid
pinnules as characterised by disc-shaped sori made up of 70–100
sporangia attached to a hemispherical receptacle: the absence of a
true annulus led him to refer the genus to the Marattiaceae. In his
memoir on the coal-basin of Heraclea (Asia Minor), Zeiller[1009]
instituted the species _Sphenopteris_ (_Discopteris_) _Rallii_ and
figured sporangia resembling those described by Stur in the possession
of a rudimentary “apical annulus.” He compared the sporangia with
those of recent Osmundaceae and Marattiaceae. In the later memoir on
the Upper Carboniferous and Permian plants of Blanzy and Creusot,
Zeiller[1010] gives a very full and careful description of fertile
specimens of _Sphenopteris_ (_Discopteris_) _cristata_, a fern
originally described by Brongniart as _Pecopteris cristata_[1011]. Many
of the Sphenopteroid pinnules of this quadripinnate fern frond show
the form and structure of the sori with remarkable clearness in the
admirable photographs reproduced in Plates I.–III. of Zeiller’s Blanzy
memoir. The lobed pinnules of this species are of oval-triangular
form, 5–15 mm. long and 2·5–6 mm. broad[1012]. An examination of the
type-specimens of _Discopteris_ from Vienna enabled Zeiller to correct
Stur’s original description of the sori: he found that the Austrian
and French specimens, though specifically distinct, undoubtedly belong
to one genus. The sori in _Discopteris cristata_ are globular, as in
the recent genera _Cyathea_ and _Alsophila_, and frequently cover
the whole face of the lamina. The individual sporangia are 0·4–0·5
mm. long and 0·15–0·2 mm. in diameter; they are exannulate, but for
the annulus is substituted a group of thicker-walled and larger
cells in the apical and dorsal region. The description by Stur of a
hemispherical receptacle seemed to indicate an important difference
between the Austrian and French species; but Zeiller found that this
feature does not actually exist and that it was so described as the
result of misinterpretation. Zeiller succeeded in isolating spores,
40–50 μ in diameter, from some of the sporangia of _D. cristata_ and
found that they exhibited the three-rayed pattern characteristic of
fern-spores and which is indicative of their formation in tetrads. The
conclusion arrived at is that the genus _Discopteris_, as represented
by _D. karwinensis_, _D. cristata_ etc., may be regarded as a true
fern and included in the Marattiaceae. As Zeiller points out, the
sori of _Discopteris_ differ from those of recent Marattiaceae in
their pluriseriate construction and agree in this respect with those
of the Cyatheaceae. The comparison already made[1013] between the
sporangia of _D. Rallii_ and those of recent Osmundaceae holds good:
the genus affords another example of a generalised type, in this case
probably a fern, combining features which are now distributed among the
Marattiaceae, Osmundaceae and Cyatheaceae.

                   •       •       •       •       •

In addition to genera founded on true synangia or groups of free
or partially united sporangia, the literature of Palaeozoic ferns
contains several generic names applied to sporangia which occur
singly on Sphenopteroid or Pecopteroid pinnules. The following may
serve as examples; but it should be stated that these will probably
be transferred eventually to the Pteridosperms. It is, however,
immaterial whether they are dealt with here or in the chapter devoted
to the seed-bearing “ferns.”


                            _Dactylotheca._

Zeiller[1014] created this genus for fertile fronds of _Pecopteris
dentata_ Brongn. (= _P. plumosa_ Artis[1015]), a common British species
in the Upper and Middle Coal-Measures. Stur[1016] included _P. dentata_
in his list of species of _Senftenbergia_, the genus to which reference
was made under the Schizaeaceae.


_Pecopteris_ (_Dactylotheca_) _plumosa_ (Artis). Figs. 290, E, 292, 293.

  1825. _Filicites plumosus_, Artis, Antedil. Phyt. p. 17, Pl. XVII.

  1828. _Pecopteris plumosa_, Brongniart, Hist. vég. foss. p. 348, Pls.
        CXXI. CXXII.

   ——   _P. dentata_, Brongniart, _ibid._ Pls. CXXIII. CXXIV.

   ——   _P. delicatulus_, Brongniart, _ibid_. Pl. CXVI. fig. 6.

  1832. _Sphenopteris caudata_, Lindley and Hutton, Foss. Flor. Vol. I.
        Pl. XLVIII.; Vol. II. Pl. CXXXVIII.

  1834. _Pecopteris serra_, Lindley and Hutton, _ibid._ Vol. II. Pl.
        CVII.

  1834. _Schizopteris adnascens_, Lindley and Hutton, _ibid._ Vol. I.
        Pls. C. CI.

  1836. _Aspidites caudatus_, Goeppert, Syst. fil. foss. p. 363.

  1838. _Steffensia silesiaca_, Presl, in Sternberg, Flor. Vorwelt,
        Vers. II. p. 122.

  1869. _Pecopteris silesiacus_, Schimper, Trait. pal. vég. Vol. I. p.
        517.

   ——   _Cyathocarpus dentatus_, Weiss, Flora der jüngst. Stk. und
        Roth. p. 86.

  1877. _Senftenbergia plumosa_, Stur, Culm Flora, II. p. 187 (293).

   ——   _S. dentata_, _ibid._

  1886. _Dactylotheca plumosa_, Kidston, Cat. Palaeozoic Plants, p. 128.

  1888. _Dactylotheca dentata_, Zeiller, Flor. Valenc. Pls.
        XXVI.–XXVIII.

For a fuller synonymy reference should be made to Kidston’s account of
this species[1017], from which the above list is compiled. The large
fronds of this species are tri- or quadripinnate. The pinnules vary
much in shape and size and in degree of lobing, according to their
position on the frond (fig. 293). The primary pinnae are subtended by
two Aphlebiae (fig. 293, A) appressed to the rachis, like the delicate
leaves of the recent fern _Teratophyllum aculeatum_ (see page 301). The
sporangia (0·5–0·65) are oval and exannulate and are attached parallel
to the lateral veins; they may occupy the whole of the space between
the midrib and the edge of the pinnules. This species occurs in the
Upper, Middle, and Lower Coal-Measures of Britain, reaching its maximum
in the Upper Coal-Measures. The aphlebiae undoubtedly served to protect
the young fronds, as shown by a specimen figured by Kidston (fig. 293,
B); they may also have served other purposes, as suggested by the
above comparison with _Teratophyllum_, in the mature frond. Lindley
and Hutton regarded the aphlebiae as leaves of a fern climbing up the
rachis; which they named _Schizopteris adnascens_, a confusion similar
to that already mentioned in the description of _Hemitelia capensis_
(see p. 304).

[Illustration: FIG. 292. _Dactylotheca plumosa._ (After Kidston.
  Slightly reduced.)]

[Illustration: FIG. 293. _Dactylotheca plumosa_: A. Rachis with
  Aphlebiae. B, _a_, young pinnae circinately folded. (After Kidston.
  A, B, ⅘ nat. size.)]


                             _Renaultia._

This name was proposed by Zeiller[1018] for Upper Carboniferous fertile
pinnae of the Sphenopteroid type, bearing ovoid sporangia either
singly or in marginal groups of 2 to 5 at the ends of the veins. The
appearance of the apical cells occasionally suggests the presence of a
rudimentary annulus. Kidston has recorded this type of fructification
in Britain[1019]. Stur describes fertile pinnules of the same type
under the generic name _Hapalopteris_[1020].


                             _Zeilleria._

This genus was founded by Kidston[1021] for fertile pinnae of a very
delicate fern, _Zeilleria delicatula_ (Sternb.) characterised by
filiform ultimate segments bearing an indusium-like body, spherical
when immature and splitting at maturity into four small valves.
Kidston, in his earlier paper, compared the species with recent
Hymenophyllaceae. In the same genus he includes _Z. avoldensis_[1022]
(Stur) assigned by Stur to _Calymmatotheca_, a genus described by some
authors as characterised by groups of radially elongated sporangia at
the tips of the pinnules; these supposed sporangia are now known to be
the valves of an indusium-like organ or cupule, as Stur asserted. There
can be little doubt that the fertile fronds placed in _Calymmatotheca_
and in _Zeilleria_ were borne by Pteridosperms.


                            _Urnatopteris._

The Upper Carboniferous fronds of a delicate Sphenopteris habit, to
which this name was assigned by Kidston[1023], were described by
him as _Eusphenopteris tenella_ (Brongn.)[1024] and compared with
Hymenophyllaceae; subsequently Kidston expressed the opinion that
_Urnatopteris_ may be a Marattiaceous fern, as Williamson[1025]
believed; he has since suggested that the sporangia are the
microsporangia of a Pteridosperm[1026]. The sterile and fertile pinnae
differ in the absence of a lamina in the latter. The sporangia (or
microsporangia) are characterised by a poricidal dehiscence.

The records from strata higher in the geological series than the
Permian, disregarding many of doubtful value, afford ample testimony to
the existence of Marattiaceae in Upper Triassic and Rhaetic floras.


                            _Marattiopsis._

The generic name _Danaeopsis_ was applied by Heer[1027] to an Upper
Triassic fern, previously described by Presl as _Taeniopteris
marantacea_. A splendid specimen from the Keuper of Stuttgart is
figured in Schimper’s Atlas[1028] showing the pinnate habit of the
frond and the broadly linear segments, 25 cm. × 3·5 cm., bearing rows
of contiguous sporangia. The large pinnules have a strong midrib
giving off curved and forked lateral veins. Presl’s species may most
appropriately be included in the genus _Marattiopsis_. A specimen of
_M. marantacea_ described by Leuthardt[1029] as _Danaeopsis marantacea_
from the Upper Trias of Basel shows a peculiarity in the venation;
the lateral veins often fork near their origin, as noticed by other
authors, but each vein forks a second time near the edge of the lamina
and the two arms converge, forming a series of intramarginal loops
(fig. 265, B).


_Marattiopsis Muensteri_ (Goepp.). Fig. 245, D, E.

This widely spread Rhaetic plant affords the best example of a
post-Permian species which may be accepted as an authentic record of
fossil Marattiaceae. Various generic names have been used for this
species; Goeppert originally described the plant as _Taeniopteris
Muensteri_[1030]; Schimper[1031] proposed the name _Marattiopsis_, and
Schenk[1032] substituted _Angiopteris_ on the ground that the fertile
pinnules resemble that genus rather than _Marattia_. _Marattiopsis_, if
interpreted as indicating a _family_ resemblance rather than special
affinity to the genus _Marattia_, would seem to be the more appropriate
designation.

This species has been figured by several authors and in many instances
with fertile pinnules; the best illustrations are those published by
Zeiller[1033] in his monograph of Tonkin plants.

  The pinnate fronds are characterised by a broad rachis bearing
  sessile broadly linear pinnules rounded at the base, obtusely
  pointed at the apex, reaching a length of 15–20 cm. and a breadth
  of 12–35 mm. From a well-marked midrib are given off secondary
  veins dichotomously branched close to their origin. The linear
  synangia near the ends of the veins contain two rows of sporangial
  compartments and open as two valves as in _Marattia_. (Cf. fig.
  245, A, p. 320.)

[Sidenote: DANAEOPSIS]

This species occurs in the Rhaetic beds of Scania, Franconia, and
Tonkin. A similar type is figured by Fontaine from Jurassic beds in
California as _Angiopteridium californicum_[1034], and Bartholin[1035]
and Moeller[1036] record _M. Muensteri_ from the Lias of Bornholm.
Schenk’s species from China[1037], _Angiopteris Richthofeni_, is
a closely allied species, and a similar form is recorded from
Jurassic and Caucasian strata[1038]. The microscopical examination by
Nathorst[1039] of a group of spores from a synangium of _M. Muensteri_
shows that they resemble those of recent Marattiaceae.

                   •       •       •       •       •

From the Upper Triassic plant beds of Lunz, Stur has included several
species of ferns in the Marattiaceae, and of these Krasser[1040]
has recently published full diagnoses but unfortunately without
illustrations. In addition to _Marattiopsis marantacea_ (Presl) the
list includes species referred to _Coniopteris_, to _Speirocarpus_,
a genus founded by Stur, to _Oligocarpia_, _Asterotheca_, and
_Bernouillia_ (Heer).

As already pointed out, some at least of these Austrian ferns are more
probably Osmundaceous than Marattiaceous.


_Danaeopsis Hughesi_, Feistmantel.

The pinnate fronds described by Feistmantel[1041] from the Middle
Gondwana rocks of India and recorded from Rhaetic strata in South
Africa[1042], China[1043], and Tonkin[1044], may belong to a member of
the Marattiaceae, but no fertile specimens have been described. The
close agreement between the sterile leaves from India and South Africa
and the fertile fronds of _Marattiopsis marantacea_ suggests generic
identity.

The Upper Triassic ferns described by Heer, Krasser[1045],
and Leuthardt[1046] as _Bernouillia_ have been referred to the
Marattiaceae, but without trustworthy evidence in favour of this
affinity.

The large leaves, 70 cm. long and 7 cm. broad, described by Zigno[1047]
from the Jurassic of Italy as _Danaeites Heeri_, are probably Cycadean.
The Polish Jurassic species _Danaea microphylla_[1048] is a more
satisfactory record.

[Illustration: FIG. 294.

  A, B. _Nathorstia angustifolia_, Heer. (After Heer. A, nat. size.)
  C, D. Sorus of _N. latifolia_, Nath. (After Nathorst. C, × 12;
        D, × 45.)]


                             _Nathorstia._

This name was instituted by Heer[1049] for pieces of pinnate fronds
from Lower Cretaceous rocks of Greenland. The resemblance of the long
pinnules to the fertile segments of _Laccopteris_ is so close that
generic identity might well be assumed, but it has recently been
shown by Nathorst[1050] that the soral characters justify Heer’s
use of a distinctive name for the Arctic fern. The circular sori
arranged in two rows (fig. 294, A, B) are superficially identical with
those of _Laccopteris_, but consist of concrescent sporangia forming
a circular synangium (fig. 294, C, D) like those of _Kaulfussia_
and _Ptychocarpus_. The lighter areas in fig. 294, D, represent
the sporangia: fig. C shows the radial disposition of the numerous
sporangial compartments round a central receptacle. From a stout midrib
lateral veins arise at right angles, but their distal terminations are
not preserved. It is probable, as Nathorst suggests, that Bayer’s[1051]
species _Drynaria fascia_ from the Lower Cretaceous rocks of Bohemia
should be referred to Heer’s genus. In the absence of well-preserved
sori it would be exceedingly difficult, or even impossible, to
distinguish between pinnules of _Laccopteris_ and _Nathorstia_.

A Tertiary species, _Marattia Hookeri_ (fig. 261, C, p. 350), described
by Gardner and Ettingshausen[1052] from the Eocene beds of the Isle of
Wight is referred by them to the Marattiaceae because of a resemblance
of the sterile pinnae to those of _M. Kaulfussii_; but this is
insufficient evidence of relationship.




                            CHAPTER XXIII.

                              Psaronieae.


This family name, first suggested by Unger, may be conveniently adopted
for the numerous species of petrified tree-fern stems characteristic
of the Lower Permian and Upper Carboniferous strata. In his monograph
_Über die Staarsteine_ published in 1854, Stenzel[1053] referred to
the Psaronieae as a special subdivision of the Filices most nearly
allied to the Polypodiaceae. There is now a consensus of opinion in
favour of including _Psaronius_ in the Marattiales, or at least of
regarding the genus as more closely allied to the Marattiaceae than to
any other family. While admitting that the balance of evidence is in
favour of this view, it is probably wiser to retain the distinctive
term Psaronieae on the ground that species of _Psaronius_ differ in
several respects from any recent ferns, and because of our comparative
ignorance in regard to the nature of the fructification.


                             _Psaronius._

This generic name was proposed by Cotta in his classic work _Die
Dendrolithen_[1054]. The stems so named, formerly included by
Sprengel[1055] in the genus _Endogenites_, had long been familiar as
petrified fossils. Most of the specimens described by the earlier
writers were obtained from Lower Permian rocks in the neighbourhood of
Chemnitz, Saxony. The mottled appearance presented by their polished
surfaces is said to have given rise to the appellation _Staarsteine_
(starling stones), a term expressing a resemblance, more or less
remote, to a starling’s breast. It has been suggested that this word
is a corruption of _Stern Steine_ or star stones[1056], a descriptive
term suggested by the stellate arrangement of the vascular strands in
transverse sections of the roots. Parkinson[1057], in his _Organic
Remains of a former World_, speaks of these stems as starry stones.
The history of our knowledge prior to 1854 is summarised by Stenzel.
At first compared with corals or the stems of sea-lilies, _Psaronii_
were recognised by Sprengel, who first used a lens in the examination
of the fossils, as fern stems most nearly allied to those of recent
Cyatheaceae. By other authors, e.g. Schlotheim and Sternberg, they
were referred to Palms, and by Brongniart considered to be the lower
portions of Lycopodiaceous (_Lepidodendron_) stems. Corda and many
subsequent authors selected the Marattiaceae as the most closely allied
family among existing plants.

_Psaronius_ is represented by specimens obtained from the Lower Permian
of Saxony and Upper Carboniferous rocks in Central France, also from
Bohemia, Brazil and North America. As yet a few fragments only have
been found in the English Coal-Measures. The genus was recognised by
Williamson[1058] who described the roots and a small piece of the
vascular tissue of a stem which he called _P. Renaulti_, and this
type has since been more fully described by Scott[1059]. The roots
of another species have been described by Butterworth[1060] as _P.
Cromptonensis_.

It was pointed out in the account of _Lepidodendron_ that several
generic names have been used for the same type of stem in different
states of preservation; in _Psaronius_ accidents of fossilisation have
been responsible for a similar confusion in nomenclature. The name
_Psaronius_ is applied to petrified specimens which, as a rule, lack
external features. Casts or impressions of Palaeozoic tree-fern stems
provided with leaf-scars are described as species of _Caulopteris_,
_Megaphyton_, and less commonly as _Ptychopteris_ (figs. 297–299).
The first name is applied to stems exhibiting spirally disposed
leaf-scars like those of recent tree-ferns; in _Megaphyton_ the scars
are distichously arranged, in two rows, while _Ptychopteris_ is applied
to decorticated stems. These terms are used for stems belonging to one
generic type and possessing the structure of Psaronius stems.

[Illustration: FIG. 295. _Psaronius_ stem with roots. (Much reduced.
  After Grand’Eury.)]

The researches of Grand’Eury[1061] led to the discovery that certain
Psaronius stems bore fronds of the _Pecopteris_ type some of which
bore sori of the _Asterotheca_ or _Scolecopteris_ type. The same
author[1062] has also contributed many interesting facts, obtained by
an examination of the relation of Psaronius stems to the sediments
of French Coal-fields in which they occur, in regard to habitat
and manner of growth. The specimen represented in fig. 295 shows a
portion of a Psaronius stem, the upper part of which illustrates the
Caulopteris state of preservation, while the lower part is covered
by a mass of roots. It is probable, as Rudolph[1063] suggests, that
this rich development of roots, which gives to an old Psaronius stem
the appearance of an elongated cone, may have served an important
mechanical purpose analogous to the secondary thickening in a
Dicotyledon or a Conifer. A specimen of _Psaronius Cottai_ in the
Hofmuseum, Vienna, is cited in illustration of the enormous breadth
of the root-system: the radii of the stem proper and of the encasing
cylinder of roots bear the ratio 17 to 165. The comparatively frequent
occurrence of a lacunar cortex in the roots points to the growth of
the stems in swampy ground, a conclusion in harmony with the evidence
afforded by the anatomical features of many other Palaeozoic genera.

                   •       •       •       •       •

_Psaronius_ may be briefly defined as follows:—

   Tree-fern stems, occasionally reaching a height of 50 feet
  or more, closely resembling in habit recent tree ferns, but
  exhibiting in the structure and arrangement of the vascular system
  a close agreement with recent Marattiaceae. Leaves, in such cases
  where a connexion between fronds and stems is known, large and
  highly compound and of the _Pecopteris_ type, borne in more or
  less crowded spirals (_Psaronius polystichi_), in four rows (_P.
  tetrastichi_), or in two opposite rows (_P. distichi_). Leaves
  deciduous, leaving a clearly defined oval scar containing the
  impression of the leaf-trace in the form of an open =U=, or a
  closed oval with a small inverted =V=-shaped band a short distance
  below the upper end of the long axis of the oval (figs. 297, 298);
  in _Megaphyton_ the alternate scars of the two opposite series
  are larger and characterised by a different form of meristele.
  The surface of the cortex below the leaf-scars occasionally shows
  impressions of pits similar to the lenticel-like organs on recent
  Tree-fern stems. The central region of the stem is occupied by a
  complex system of concentrically disposed steles (dictyosteles),
  which in transverse section present the appearance of flat or
  curved bands varying in extent and in degree of curvature. The
  vascular bands consist of xylem surrounded by a narrow zone of
  phloem; the xylem is composed either exclusively of tracheae or
  of tracheae and parenchyma; the protoxylem in the one instance in
  which it has been clearly recognised is endarch[1064]. The steles
  are embedded in parenchymatous tissue and in some species are
  associated with mechanical tissue (e.g. _P. infarctus_, fig. 296,
  A, B). The central or vascular region of the stem may be surrounded
  externally by a cylinder of mechanical tissue interrupted by
  outgoing leaf-traces and adventitious roots. The leaf-traces
  arise as single bundles from an internal stelar band and pursue
  an obliquely radial course towards the outside, eventually
  anastomosing with peripheral cauline steles, which in some species
  form with the leaf-traces the outermost zone of the vascular
  region. The leaf-traces have the form of loops which pass into the
  petioles as =V=-shaped meristeles or closed oval cylinders. As a
  leaf-trace passes out compensating strands occupy the foliar gap.

  The vascular region is surrounded by a parenchymatous cortex, which
  in younger plants, or in the apical region of an older plant, forms
  the surface of the stem to which the leaf-stalks are attached.
  From the peripheral steles, or from the more external bands of
  the vascular network, roots are given off which pass in a sinuous
  vertical course through the cortex, appearing on the surface
  between the leaf-bases. In older stems, after leaf-fall, the tissue
  immediately external to the vascular region produces secondary
  parenchyma with which the roots become intimately associated by
  their outermost cells. As a result of the secondary cortical
  development and the gradual increase in the number of roots
  invading the cortical tissue from above, the stem is enclosed by a
  cylinder of roots and associated parenchymatous tissue of secondary
  origin. In still older portions of a stem the more external roots
  are free from the stem-cortex and form a thick felted mantle, which
  increases in thickness towards the base of the tree.

  The roots (fig. 296, E) are polyarch, 5–10 groups of xylem
  alternating with strands of phloem, and similar in structure to
  those of recent species of _Marattia_ and _Angiopteris_; the
  stele is enclosed by an inner cortex of compact or lacunar tissue
  containing secretory sacs, and this is surrounded by a cylinder of
  mechanical tissue. In one or two instances secondary xylem has been
  observed wholly or partially enclosing the root-stele[1065].

[Illustration: FIG. 296.

  A. _Psaronius infarctus_ (P, peripheral steles; L, leaf-traces).
  B. _P. infarctus_, longitudinal tangential section through the
     peripheral region of the stem.
  C. _P. coalescens._
  D. _P. musaeformis._
  E. _P. asterolithus_ (root).

  (A—C, E, after Zeiller; D, after Stenzel.)]

Our knowledge of the anatomy of _Psaronius_ is based largely on
the investigations of Stenzel considerably extended by Zeiller’s
more intensive studies and, more recently, by the later work of
Stenzel[1066] and that of Rudolph. A striking fact, which has led to
various suggestions, is that in a transverse section of a _Psaronius_
stem with its encasing cylinder of roots no signs of leaf-traces are
met with in the root-region. If the roots simply penetrated the cortex,
as in some recent species of _Lycopodium_ (fig. 125, A) or as in
_Angiopteris_, we should expect to find leaf-traces in the outer region
(root-cylinder) of Psaronius stems. An explanation of the absence of
leaf-traces which was suggested by Stenzel, is that the cortical zone
formed a comparatively narrow band in the young leaf-covered stem;
after leaf-fall it became the seat of active growth in its inner layers
and so produced a constantly widening zone of secondary parenchyma,
which pushed the superficial cortical tissue with the leaf-bases or
leaf-scars farther out until it was exfoliated. Farmer and Hill[1067]
find it difficult to accept this explanation; but, as Rudolph shows,
the radial arrangement of the cortical cells between the adventitious
roots and their elongation in a radial direction are arguments in
support of the secondary nature of the cortical zone.

In sections of the adventitious roots of _Psaronius Renaulti_ figured
by Williamson[1068], the spaces between the cylindrical roots
are partially occupied by cell-filaments which, at first sight,
suggest root-hairs; it may well be, as Rudolph suggests, that these
felted hairs represent the outermost and looser part of the growing
secondary cortex which gradually passes into the covering mass of free
extra-cortical roots.

As Stenzel[1069] has shown, slender stems of _Zygopteris_ (=
_Ankyropteris_) are occasionally met with growing through the web of
Psaronius roots.


_Psaronius infarctus_ Unger. Fig. 296, A, B.

This species, which Zeiller[1070] has investigated from sections of
Unger’s material, illustrates a type in which the vascular tissue is
very richly developed and forms crowded concentric series of curved
plates associated, in the more peripheral series, with bands of
mechanical tissue. The outermost part of the vascular region consists
of (i) a series of loops or variously curved bands of conducting
tissue representing leaf-traces at different stages in their outward
course, (ii) a series of similar vascular strands (peripheral steles
of Zeiller) confined to the stem (cauline) and from which roots are
given off, and (iii) bands of mechanical tissue associated with the
leaf-traces and peripheral steles. The peripheral steles (fig. 296, A,
B, p) form anastomoses with the leaf-traces and contribute to their
formation.

The form of some of the vascular bands in the section of _Psaronius
infarctus_ shown in fig. 296, A, illustrates the occasional
anastomosing of one dictyostele with another: the different degrees
of looping of other bands represent stages in the giving off of
leaf-traces which eventually pass out as =V=-shaped meristeles. Beyond
the leaf-traces and sclerenchymatous bands the section consists of
transverse sections of adventitious roots.

The surface-features of _Psaronius infarctus_ are probably represented,
as Zeiller points out, by the cast described by Lesquereux as
_Caulopteris peltigera_ (fig. 298, A).

[Illustration: FIG. 297. _Pecopteris Sterzeli_: a, pinnule. (After
  Renault and Zeiller. ¹⁄₁₁ nat. size.)]

The Psaronius shown in fig. 297 is one of the few examples illustrating
the connexion between fronds and stem. The leaf (_Pecopteris Sterzeli_
Zeill. and Ren.[1071] is quadripinnate and is described as reaching a
length of at least 3 metres; the ultimate segments are entire or lobed.
The stem is characterised by elliptical scars, 6–8 cm. x 3·5–4 cm.,
with leaf-traces like those in _Caulopteris peltigera_. The fronds of
_Pecopteris Pluckeneti_, a Pteridosperm, bear a very close resemblance
to those of _P. Sterzeli_, which are as yet known only in a sterile
state.

                   •       •       •       •       •

_Psaronius brasiliensis_ Unger, a species founded by Unger on a
piece of silicified stem acquired by Martius in Brazil and now
in the Rio Museum, is a good example of a tetrastichous species.
Solms-Laubach[1072] has recently told the history of this type, which
is represented by sections, cut from the Rio stem, in several European
collections. A well-preserved section in the British Museum is figured
by Arber[1073] in his catalogue of the Glossopteris flora and by other
authors. Scott gives a concise description of the species in his
_Studies in Fossil Botany_[1074]. The roots of _P. brasiliensis_ are
stated by Pelourde[1075] to have a lacunar cortex.


_Psaronius musaeformis_ Corda[1076]. Fig. 296, D.

This species from the Lower Permian of Chemnitz and the Coal-Measures
of Bohemia affords an example of the distichous type in which the
leaves are borne in two rows. The vascular bands, as seen in a
section of the dictyosteles, occur in regular parallel series. The
stelar region is separated from the cylinder of encasing roots by a
sclerenchymatous sheath, broken at intervals where roots pass out from
the vascular region.

_Psaronius coalescens_[1077] (fig. 296, C) illustrates a somewhat
different arrangement of vascular tissue which approaches more
closely to the polycyclic structure characteristic of such recent
ferns as _Matonia_ and _Saccoloma_. A still closer resemblance to
the solenostelic type is seen in _Psaronius Renaulti_ from the Lower
Coal-Measures of England which Scott[1078] describes as characterised
by a single annular stele, interrupted only by the exit of leaf-traces.
As he points out, it is noteworthy that this species is distinguished
by the simplest form of stele met with in the genus; it is the oldest
species and may be regarded as the most primitive representative of
the genus _Psaronius_ so far discovered.

[Illustration: FIG. 298.

  A. _Caulopteris peltigera_.
  B. _Megaphyton insigne_.

  (After Grand’Eury.) Much reduced.]


 _Psaronius stems preserved as casts showing surface-features, or in a
                         decorticated state._

                           i. _Caulopteris_.

This generic name was instituted by Lindley and Hutton[1079] for
tree-fern stems from the English Coal-Measures showing circular or oval
scars arranged quincuncially. The vascular tissue of the petiole is
represented by a =U=-shaped impression on the scar, the ends of the =U=
being incurved, or by a closed oval ring with a wide-open and inverted
=V= near its upper end. The surface between the leaf-scars bears
the impression of adventitious roots. _Caulopteris_ is represented,
in the Upper Coal-Measures of England, by _C. anglica_[1080] Kidst.
The species _C. peltigera_ (fig. 298, A), originally described by
Brongniart as _Sigillaria_, illustrates the closed form of leaf-trace
and, as Zeiller suggests, it is the cast of a _Psaronius_ stem which
possessed a vascular system on the same plan as that of _P. infarctus_.
_C. Saportae_[1081] illustrates the open =U=-shaped type of petiole
stele.

_Caulopteris peltigera_ has scars measuring 6–9 by 4–6 cm.; it occurs
in the Commentry Coal-field of France in association with the fronds
known as _Pecopteris cyathea_, a species which Kidston regards as
identical with _P. arborescens_[1082].


                           ii. _Megaphyton_.

The first use of this name was by Artis[1083], who gave it to a long
flattened cast, _Megaphyton frondosum_, found in Carboniferous strata
in Yorkshire, characterised by two vertical rows of large scars and by
impressions of sinuous roots. Kidston records the genus from the Middle
and Upper Coal-Measures of Britain. A good example of this type of cast
is afforded by _M. McLayi_ Lesq.[1084] from the Coal-Measures of North
America, which has been recognised in European Carboniferous rocks.
The leaf-scars are rounded or oval, broader than high; the vascular
impression has the form of a closed ring (5–8 × 3–6 cm.), more or less
circular and with a tendency to a rectangular outline, characterised by
a deep inverted =U=-shaped sinus in the middle of the lower surface and
by a =W=-shaped impression of an internal strand (fig. 298, B)[1085].


                         iii. _Ptychopteris_.

This generic name, instituted by Corda[1086], is applied to
decorticated stems of _Psaronius_, the surface of which is that of the
vascular region on which the form of the leaf-scars is more or less
clearly defined. The scar-areas are limited by an impression of the
sclerenchymatous sheath enclosing the leaf-meristele, and internal
to this is the impression of the leaf-trace. In some specimens a
layer of coaly material which represents the carbonised cortex and
adventitious roots covers the _Ptychopteris_ cast. The _Ptychopteris_
cast represented in fig. 299 shows the decorticated surface of part of
a long stem on which the leaf-scars are arranged as in _Megaphyton_. An
example of _Ptychopteris_ is figured by Fontaine and White[1087] from
Virginia as _Caulopteris gigantea_.

[Illustration: FIG. 299. _Ptychopteris._ ⅙ nat. size. From the Middle
  Coal-Measures of Lancashire. (The Manchester Museum.)]

[Illustration: FIG. 300. _Dicksonia antarctica_ (half of stem in
  transverse section): _st_, stele; _s_, sclerenchyma.]


                       _Position of_ Psaronius.

A comparison of _Psaronius_ with the Marattiaceae and other recent
ferns leads to the conclusion that, on the whole, the evidence is in
favour of the view usually held, namely that this genus is more closely
related to the Marattiaceae than to any other recent ferns. It is,
however, important not to overlook the differences between _Psaronius_
and recent genera of Marattiaceae, or the resemblances between the
extinct genus and the Cyatheaceae. In habit _Psaronius_ agrees closely
with recent tree-ferns; in the vascular system and in the sequence
of events connected with the production of leaf-traces, there are
striking resemblances between _Psaronius_ and the Cyatheaceous fern
_Saccoloma adiantoides_ (= _Dicksonia Plumieri_ Hook.) as described
by Mettenius[1088]. The piece of stem of _Dicksonia antarctica_
represented in fig. 300 exhibits a fairly close agreement with species
of _Psaronius_, e.g. _P. infarctus_ (fig. 296, A, B). Moreover, the
peripheral steles, which Zeiller has shown are confined to the stem
and play an important part in the production of the roots and in the
anastomoses with leaf-traces, are not represented in any Marattiaceous
fern; on the other hand, they are comparable with the accessory strands
met with in stems of recent Cyatheaceous tree-ferns[1089] (cf. fig.
240). The complex system of concentric dictyosteles is a feature
more closely matched in _Angiopteris_ (Marattiaceae) than in any
Cyatheaceous genus, the chief difference being in the more band-like
form of the steles in _Psaronius_, though in a stem of _Angiopteris_
figured by Mettenius we see a close approach to the extinct type. The
position of the protoxylem has unfortunately not been clearly defined
in _Psaronius_ stems, but in _P. Renaulti_ it is stated by Scott[1090]
to be endarch, a position which some of the protoxylem strands occupy
in _Angiopteris_[1091]. The occurrence of large sieve-tubes described
by Scott in _P. Renaultii_ is another feature shared by recent
Marattiaceae. In many of the continental species of _Psaronius_ the
phloem has not been preserved, and our knowledge of this tissue is
comparatively meagre. In the Marattiaceae the roots arise mainly from
the inner portions of the stele, while in _Psaronius_ they are usually
formed from the external vascular bands. The formation of secondary
cortical tissue is a peculiarity of _Psaronius_; on the other hand, if
Butterworth[1092] is correct in referring to that genus the roots with
secondary xylem, which he describes as _P. Cromptonensis_, a comparison
may be made with the occurrence of secondary tracheae in the stem
steles of _Angiopteris_[1093].

The absence of mechanical tissue in the stem of _Angiopteris_ is
in contrast with its occurrence in the fossil stems and in recent
tree-ferns; but this is a character of secondary importance and one
which can be readily explained by the difference in habit between
_Angiopteris_ and _Psaronius_.

The roots of _Psaronius_, more especially as regards the stelar
structure, are in close agreement with those of Marattiaceae.

The reference to Marattiaceae of the great majority of fertile
fern-like fronds from Permian and Carboniferous rocks constituted a
strong _a priori_ argument in favour of including _Psaronius_ stems
in the same family, especially when it was known that leaves with
Marattiaceous synangia were borne by species of this genus. It is,
however, well to remember the change in our views as to the dominance
of Marattiaceae in Palaeozoic floras consequent on the discovery of
the Pteridosperms. The association of fronds bearing _Asterotheca_ and
_Scolecopteris_ types of fructification with _Psaronius_ stems recorded
by Grand’Eury[1094] is a point in favour of the Marattiaceous affinity
of this extinct genus, but it is not impossible that _Psaronius_ stems
bore fronds which produced Pteridosperm organs of reproduction. In
this connexion the specimen represented in fig. 297 is of interest,
as the fronds (_Pecopteris Sterzeli_) borne on the _Psaronius_ stems
are hardly distinguishable from the seed-bearing leaves known as
_Pecopteris Pluckeneti_.

The position of _Psaronius_ may be best expressed by assigning it
to a separate family, the Psaronieae, as advocated by Stenzel, and
by regarding it as one of the many instances of a generalised type
which in the sum of its characters approaches most nearly to the
Marattiaceae.




                             CHAPTER XXIV.

                       Ophioglossales (Fossil).


The fossils hitherto classed with the Ophioglossales are not such as
afford any satisfactory evidence in regard to the past history or
phylogeny of the group. In the generalised class of Palaeozoic ferns,
the Botryopterideae, we find certain characters suggesting comparison
with recent members of the Ophioglossaceae, but no trustworthy records
of these eusporangiate ferns are furnished by the older plant-bearing
strata.

[Illustration: FIG. 301. _Rhacopteris_ sp., Ballycastle, Ireland. From
  a specimen in the Manchester Museum. [M.S.]]

The genus _Rhacopteris_ (fig. 301), characteristic of the Culm flora,
has been compared with _Botrychium_, but on grounds which are wholly
inadequate. The species _R. paniculifera_ Stur[1095] is characterised
by a stout rachis bearing two rows of laterally attached rhomboidal
or subtriangular segments with a more or less deeply lobed margin
and spreading veins. The rachis branches distally into two arms, and
these are again symmetrically subdivided into fertile axes bearing
clusters of small spherical bodies 1 mm. broad, which Stur speaks of as
exannulate sporangia similar to those of _Botrychium_. He includes the
species in the Ophioglossaceae. As Zeiller[1096] pertinently remarks,
_Rhacopteris_ differs essentially in habit from any recent member of
this family. _Rhacopteris_ also includes species characterised by
leaflets deeply dissected into linear segments; an example of this
form is represented by _Rhacopteris flabellata_ (Tate) recorded by
Kidston[1097] from rocks of Calciferous Sandstone age in Flintshire.

The specimen described by Renault[1098] from the Carboniferous rocks
of Autun as _Ophioglossites antiqua_ is equally unconvincing: it
consists of a carbonised fragment, 7 cm. × 1·5 cm., regarded as part
of a fertile lamina characterised by a vertical series of transversely
elongated slits, 7 mm. wide, some of which, on slight magnification,
are seen to contain a mass of small orange-yellow granulations.
The slits are compared with the surface-openings of the sunken
sporangia of _Ophioglossum_, and the yellow bodies are identified as
spores. The material is too imperfect to justify the use of the name
_Ophioglossites_.


                            _Noeggerathia._

This genus of uncertain position may be briefly described here,
though it has little claim to recognition as a representative of the
_Ophioglossales_. It is characteristic of Lower Carboniferous rocks and
is compared by Stur[1099] with recent Ophioglossaceae. _Noeggerathia
foliosa_ Sternb. (fig. 302) may be cited as a typical example of the
genus. It consists of an axis bearing ovate leaves with numerous
spreading veins. The upper part of the axis forms a spike composed of
fertile leaves in the form of transversely oval bracts 2 cm. broad with
a serrate edge bearing on the upper face several sporangia (3 × 4 mm.)
in some of which spores have been seen (fig. 302, B, C). In another
form described by Weiss[1100] the bracts bear a greater number of
sporangia characterised by the presence of an arillus-like basal ring.

[Illustration: FIG. 302. _Noeggerathia foliosa._ (After Stur; A,
  reduced.) B, Fertile leaf; C, Sporangium.]

Geinitz[1101], who first described fertile specimens of _Noeggerathia_,
placed the genus in the Gymnosperms, and O. Feistmantel[1102] was in
favour of this view. C. Feistmantel[1103], who described the small
bodies in the sporangia, suggested comparison with Schizaeaceae, and
Weiss[1104] discussed various possibilities, asking but not answering
the question, are the so-called sporangia rightly so named or are
they fruits? Potonié[1105] places the genus in the Cycadofilices. An
important feature is the occurrence of the sporangia on the upper face
of the bracts as in Lycopodiales and _Sphenophyllum_, but in other
respects _Noeggerathia_ bears no resemblance to these two groups.
Sterile examples of the genus are similar in habit to _Rhacopteris_,
but in the latter genus the leaves or leaflets are laterally
attached and not obliquely inserted. Further, we may assume that in
_Rhacopteris_ the segments are leaflets of a compound leaf, whereas
in _Noeggerathia_ they are probably single leaves. We must leave the
position of this Lower Carboniferous genus undecided, merely expressing
the opinion that it is perhaps more nearly allied to the Cycads than to
any other group.

[Illustration: FIG. 303. _Chiropteris Zeilleri_, Sew. [From a specimen
  in the British Museum (v. 3268). Nat. size.]]

The plant figured by Lindley and Hutton from the English Coal-Measures
as _Noeggerathia flabellata_, which some authors quote as a species of
_Noeggerathia_, is generally recognised as a _Psygmophyllum_ and placed
with some hesitation in the Ginkgoales.


                            _Chiropteris._

This genus was founded by Kurr on a leaf characterised by anastomosing
venation from Keuper beds near Stuttgart. A resemblance in form and
venation to the leaves of recent species of _Ophioglossum_ led authors
to suggest the inclusion of Kurr’s specimen in the Ophioglossaceae.
We have, however, no justification for considering _Chiropteris_ as a
member of this family; it may be a fern, and that is all that can be
said. The leaf represented in fig. 303 is the type-specimen of a South
African Rhaetic species _Chiropteris Zeilleri_[1106]. The genus is
recorded also from Rhaetic rocks in Queensland.[1107]

Newberry[1108] describes some leaves from the Lower Cretaceous of
Montana as species of _Chiropteris_: one of his types, _C. spatulata_,
is almost certainly a _Sagenopteris_, similar to _S. Phillipsi_ (figs.
327, 328) or _S. Mantelli_. A second species, _C. Williamsii_, is
probably not generically identical with the specimen represented in
fig. 303.




                             CHAPTER XXV.

                 Coenopterideae.  ╭   I. Botryoptereae.
                                  ╰ II. Zygoptereae.


The term Botryopterideae, first used by Renault, has been applied to a
group of Palaeozoic ferns ranging from the Lower Carboniferous to the
Permian and containing several genera, the distinguishing features of
which are supplied by the anatomical structure of the stems or, in many
cases, by that of the petiolar vascular strand. Scott[1109] subdivides
the Botryopterideae into the Botryopteris and the Zygopteris sections.
In an admirable monograph recently published by Paul Bertrand[1110]
considerable changes are proposed in current nomenclature; he
substitutes the name Inversicatenales for Botryopterideae, a
designation, which as Scott remarks, is “probably too technical to
command general acceptance.” A more serious criticism is that the name
Inversicatenales has reference to a character (the inverse curvature
of the leaf-trace in relation to the axis of the stem) which is by no
means universal in the group[1111].

In the following account, necessarily incomplete, the generic
terminology of Bertrand is adopted, but this decision does not carry
with it any obligation to accept the name Inversicatenales. We may
speak of the types of Palaeozoic ferns dealt with in the following
pages as members of a group differing in many respects from any
existing genera of the Filicales, and exhibiting the characteristics
associated with generalised plants. Williamson, as early as 1883,
spoke of Renault’s Botryopterideae as comprising “altogether extinct
and generalised” types[1112]. For these generalised Palaeozoic ferns
I propose to use the name Coenopterideae[1113]. This term may be
adopted in a wider sense than Renault’s name Botryopterideae. The
name Primofilices proposed by Arber[1114] might be employed, but the
implication which it carries is an argument against its adoption. We
have not yet reached a stage in the investigation of extinct types at
which we are able to recognise what are actually primary or primitive
ferns. The search for origins will continue; as new discoveries are
made our point of view shifts and the primitive type of to-day may
to-morrow have to take a higher place. The epithet primitive or primary
is in reality provisional: to adopt such a name as Primofilices
suggests a finality which has not been, or is likely to be, achieved.
The true ancestral type—the _Urform_—which we strive to discover eludes
the pursuer like a will-o’-the-wisp.

Seeing that the number of true ferns of Palaeozoic age has been
recently considerably reduced and is likely to suffer further
reduction, the consideration of such undoubted Carboniferous and
Permian examples of the Filicales as are left acquires a special
importance. In the first place it is natural to ask whether the
Palaeozoic ferns include any types which, if not themselves ancestral
forms, may serve to indicate the probable lines of evolution of
existing families. It is probable that in the near future our knowledge
of the Coenopterideae will be considerably extended; as yet we possess
meagre information in regard to those characters on which most stress
has generally been laid in the classification of recent ferns,
namely the structure of the spore-bearing organs. The sporangia of
_Diplolabis_ and _Stauropteris_ (figs. 309, A; 322) are exannulate;
in the former genus they occur in sori or synangia consisting of a
small number of sporangia, while in the latter they are borne singly
at the tips of ultimate ramifications of a highly compound leaf. The
resemblance of the synangium of _Diplolabis_ to that of _Kaulfussia_
(fig. 245, C) is not shared in an equal degree by the sporangia of
_Stauropteris_, which are in some respects comparable with those of
the Ophioglossaceae. In the Zygoptereae, or at least in the case of
such fertile fronds as are known, and in _Botryopteris_ (fig. 319),
the sporangia occur in groups, and the pedicel of each sporangium
is supplied with vascular tissue as in _Helminthostachys_. Another
characteristic of the sporangia of the extinct types is the possession
of an annulus several cells in breadth, a peculiarity which supplies a
point of contact with the Osmundaceae. In the sporangia of _Kidstonia_
we have a similar though not an identical type (fig. 256, E, p. 340).
So far, then, as the evidence afforded by sporangial characters is
concerned, it points to comparison with the Ophioglossaceae, the
Osmundaceae, and the Marattiaceae. When we compare the steles of the
stems we find a wide range of structure. All the genera agree in being
monostelic; in _Tubicaulis_ and _Grammatopteris_ the protoxylem is
exarch, in _Botryopteris_ it is internal, while the foliar strand of
_Stauropteris_ and the stele of _Ankyropteris corrugata_ are mesarch.
The axillary branching of species of _Ankyropteris_ suggests comparison
with the Hymenophyllaceae.

The investigation of the vascular system of the petioles has afforded
results which in the hands of P. Bertrand have led to conclusions in
regard to inter-relationships. We must, however, not overlook the
danger of attributing can excessive importance to this single criterion
and of neglecting the facts of stem anatomy.


                           I. Botryoptereae.

                           _Grammatopteris._

Renault instituted this genus for petrified stems from the
Permo-Carboniferous beds of Autun. _Grammatopteris Rigolloti_[1115],
the type-species, is represented by a fragment, 12–15 mm. in diameter,
surrounded by crowded petioles characterised by a vascular strand in
the form of a short and comparatively broad plate with the smallest
tracheae at each end. The solid xylem of the stem stele (protostele)
has peripheral groups of protoxylem. Nothing is known as to the
form of the leaves, but sporangia similar to those of _Etapteris_
(_Zygopteris_) were found in association with the stem. It is possible,
as P. Bertrand suggests, that Renault’s species may be the stem of a
_Tubicaulis_.


                             _Tubicaulis._

_Tubicaulis solenites_ (Sprengel)[1116]. Fig. 304.

This species from the Lower Permian of Saxony has been fully described
by Stenzel[1117]. It is characterised by a very slender erect stem
bearing numerous spirally disposed leaves associated with adventitious
roots; the single stele (protostele) consists exclusively of tracheae,
described as intermediate between the scalariform and reticulate type,
surrounded by phloem. Leaf-traces are given off from the periphery
of the stele where groups of smaller elements occur; these have the
form of a wide-open =U=-shaped strand with the base of the =U= facing
the axis of the stem. As the trace passes out towards the leaves, the
ends of the =U= become more or less incurved. The stem is said to
reach a metre in length and to bear compound fronds a metre long. The
orientation of the leaf-trace with its concavity turned outwards is in
striking contrast to the relation between leaf-trace and stem in recent
ferns.

[Illustration: FIG. 304. _Tubicaulis solenites._ (From Tansley, after
  Stenzel.) Stem and petioles: the latter numbered in the order of
  their age.]


_Tubicaulis Sutcliffii_, Stopes[1118].

In this species the vascular axis, 2 mm. in diameter, is almost
cylindrical and of the protostelic type with the protoxylem “near
to or at the edge”: the tracheae are scalariform or reticulate. The
leaf-traces, when first separated from the edge of the stele, are oval
and gradually assume the curved form seen in _T. solenites_ (fig. 304)
with the convex side towards the axis of the stem. The transition from
the scalariform to the reticulate type of pitting on the tracheal walls
referred to by Miss Stopes has also been noticed in some recent ferns
(e.g. _Helminthostachys_) and in _Sigillaria_ (fig. 200, C, p. 212).
The fact that the scalariform type of pitting is practically universal
in the xylem of recent ferns, would seem to show that this character
has been acquired in the course of evolution and retained in preference
to the reticulate form characteristic of several Palaeozoic species.
The distinction between the two methods of pitting is one of little
phylogenetic importance.


                            _Botryopteris._

This genus, founded by Renault on a specimen from Autun, is represented
in the Lower Coal-Measures of England by _Botryopteris hirsuta_ (=
_Rachiopteris hirsuta_ Will.), _B. ramosa_ (= _R. ramosa_ Will.[1119])
(fig. 306) and _B. cylindrica_ (fig. 305), also by _B. antiqua_ (fig.
307) from the Culm of Pettycur, Scotland.

An important characteristic of the genus is the solid stele of the stem
which agrees with that of _Tubicaulis_ and _Grammatopteris_, except in
the central or peripheral position of the smallest tracheae.


_Botryopteris forensis_ Renault[1120]. Figs. 309, B; 319, D–G.

The stem of this species from the Upper Carboniferous of St Étienne
is 1·7 cm. x 7·5 mm. in diameter. The solid stele consists of
reticulate tracheae with the smallest elements on the outer edge.
The comparatively broad cortex of the type-specimen is traversed by
a leaf-trace in an almost vertical course and by vascular strands
passing horizontally to roots. The petioles are circular in section
and their vascular strand has the form of an ω in transverse section
(fig. 319, G), the three projecting arms pointing to the axis of the
stem. Both stem and leaves bore large multicellular hairs, spoken of
by Renault as equisetiform because of the finely toothed sheaths of
which they are composed. The compound fronds had fleshy lobed pinnules
with dichotomously branched veins (fig. 309, B); stomata are said to be
confined to the upper surface, an observation which leads Renault to
describe the plant as aquatic on evidence which is hardly convincing.

The pyriform and pedicellate sporangia are borne in groups of two to
six on the ultimate divisions of the frond; the wall is composed of
two layers of cells and on one side of the sporangium is an annulus
several cells in breadth (fig. 319, D, F). An interesting type of
sporangium described by Oliver[1121] from Grand’Croix in France may,
as he suggests, belong to _Botryopteris forensis_; the differences
between Renault’s and Oliver’s specimens being the result of the more
perfect preservation of the tissues in the latter. The sporangium
described by the English author is circular in section and measures
0·65 × 0·53 mm.; the wall is in part composed of a single layer of
cells and in part of two to three layers, a character recalling the
“annulate” sporangia of _Botryopteris_. Between the spore-mass and the
wall is an interrupted ring of short tracheal elements similar to the
xylem-mantle which occurs at the periphery of the nucellus of certain
Palaeozoic gymnospermous seeds. In the absence of proof of a connexion
between this sporangium and _Botryopteris_ it is convenient to use the
generic name _Tracheotheca_ subsequently proposed by Oliver[1122].
In the recent ferns _Helminthostachys_ and _Botrychium_, and, as
Oliver notices, in the microsporangia of the Australian Cycad _Bowenia
spectabilis_, vascular strands extend almost to the sporogenous tissue,
but the fossil sporangium is unique in having a tracheal layer in
immediate contact with the spores. These xylem elements may, as Oliver
suggests, have served the purpose of conveying water to the ripening
spores.


_Botryopteris hirsuta_ (Will.)[1123].

This English species has a slender axis bearing numerous leaves with
petioles equal in diameter to the stem. The surface of the vegetative
organs bears large multicellular hairs. The leaf-traces resemble
those of _B. forensis_, but the projecting teeth which terminate in
protoxylem elements are less prominent than in the French species;
the petioles were named by Felix _Rachiopteris tridentata_[1124]. As
a leaf-trace passes into the stele of the stem the three protoxylem
strands unite and take up an internal position in the solid stele. The
stele may, therefore, be described as endarch. The small tracheae at
the edge of the stele supply the xylem strands of adventitious roots.

Sporangia similar to those of _B. forensis_ have been found in
association with the English species.


_Botryopteris cylindrica_ (Will.). Fig. 305.

A plant originally described by Williamson[1125] from the Lower
Coal-Measures of England as _Rachiopteris cylindrica_ (fig. 305)
and afterwards more fully dealt with by Hick[1126], has a slender
stem with a cylindrical stele characterised by well-defined central
protoxylem elements in one or two groups. The leaf-traces are
semi-lunar in section with the protoxylem on the flatter side. The
stele of _Botryopteris cylindrica_ (fig. 305, A) is more cylindrical
in section than that of _B. ramosa_ (fig. 306) and shows more clearly
the differentiation into smaller central and larger peripheral
tracheae. In the section reproduced in fig. 305, B the stele is giving
off a branch almost identical in structure with the main vascular
axis. Scott[1127], in referring to the inclusion of this type in the
genus _Botryopteris_, expresses the opinion that its habit must have
been very different from that of other species, and he suggests the
institution of a new genus.

[Illustration: FIG. 305. _Botryopteris cylindrica_ (× 30). From
  sections in the Cambridge Botany School.]


_Botryopteris ramosa_ (Williamson). Fig. 306.

This species, which bears a close resemblance to _Botryopteris
hirsuta_, was originally described by Williamson from the Lower
Coal-Measures of England as _Rachiopteris ramosa_[1128], the specific
name being chosen on account of the numerous and crowded branches
given off from the main axis. The section shown in fig. 306, A,
illustrates Williamson’s description of the stem as being “always
surrounded [when seen in transverse sections] by a swarm of similar
sections of the large and small branches, though of varying shapes and
sizes.” The stele is composed of a solid and more or less cylindrical
rod of xylem tracheae of the reticulate type surrounded by phloem
(figs. A and D): one or more internal groups of smaller protoxylem
elements occur in an approximately central position (fig. A, _px_).
The stele is in fact endarch like those of _Selaginella spinosa_ and
_Trichomanes reniforme_, a feature which, as Tansley[1129] believes,
probably entitles the vascular axis to be considered a primitive form
of protostele. In the specimens represented in fig. 306 the phloem
and inner cortical tissues were almost completely destroyed before
petrifaction. The thick-walled outer cortex bears at its periphery
numerous multicellular hairs. Some of the xylem strands given off from
the stele no doubt supplied adventitious roots, but in most cases the
outgoing branches are leaf-traces and the numerous sections of axes
of different sizes seen in fig. A point to a repeated subdivision of
the crowded fronds. The structure of a petiole is shown in figs. C and
D. As seen in fig. C, the oval vascular strand has three protoxylem
groups, _px_, on its flatter side; a well-defined epidermal layer is
shown at _e_ in fig. C.

Fig. B shows at _a_ a section of a leaf-axis in the act of branching
and the row of branchlets at _b_ represents a further stage in
subdivision. At _sp_ in fig. A the section has cut through a single
sporangium characterised by a group of larger (“annulus”) cells on one
side of the wall.

[Illustration: FIG. 306. A–D. _Botryopteris ramosa_; stem and frond
  axes. (A × 7; B × 15; C × 26; D × 13. From sections in the Cambridge
  Botany School Collection.) _px_, protoxylem; _sp_, sporangium; _e_,
  epidermis.]

This slender fern with its numerous repeatedly branched leaves may
perhaps have lived epiphytically on more robust plants.


_Botryopteris antiqua_, Kidst. Fig. 307.

This species, recently described by Kidston[1130] from the Culm of
Pettycur near Burntisland, is represented by sections of a small
stem with a cylindrical stele 0·40 mm. in diameter composed entirely
of scalariform tracheae without any recognisable protoxylem. The
petioles are larger than the stem; the meristele (fig. 307) is oval
with protoxylem elements on the slightly more rounded adaxial face.
As Kidston suggests, this stem may belong to a scrambling plant which
required support to bear its relatively large leaves. An interesting
feature is the absence of projecting teeth in the leaf-trace, a
character in marked contrast to the ω form assumed by the petioles of
_Botryopteris forensis_ (fig. 319, G) and _B. hirsuta_. This leads
Kidston to suggest that the vascular strand of the petiole tends “to
become more simple ... as traced back in geological time.” The greater
similarity in this species between the stele of the stem and that of
the petiole is probably another mark of a more primitive type.

[Illustration: FIG. 307. _Botryopteris antiqua_: Petiolar vascular
  strand. (After Kidston: × 65.)]

                   •       •       •       •       •

In these three types, _Grammatopteris_, _Tubicaulis_, and
_Botryopteris_, we have monostelic plants, for the most part of very
small size, with leaf-traces varying in shape from the oblong band-form
in _Grammatopteris_, and the oval form of _Botryopteris antiqua_, to
the ω type represented in its most pronounced form by _B. forensis_. In
several species the stem stele is endarch. Our knowledge of the leaves
is very meagre: in _B. forensis_ they were repeatedly branched and
apparently bore small fleshy pinnules; the sporangia, though differing
from those of recent ferns, may be compared with the spore-capsules
of Osmundaceae as regards the structure of the annulus. The abundance
of hairs on the stems and leaves of some species, the tracheal sheath
in the sporangium described by Oliver[1131] as _Tracheotheca_ (=
_Botryopteris?_), and the apparent absence of a large well-developed
lamina, may perhaps be regarded as evidence of xerophilous conditions.


                           II. Zygoptereae.

Corda[1132] proposed the generic name _Zygopteris_ for petrified
petioles from the Permian of Saxony, included by Cotta in his genus
_Tubicaulis_, which he named _T. primarius_. Corda’s genus has been
generally used for petioles of Palaeozoic ferns characterised by
a vascular strand having the form of an =H= in transverse section
(fig. 308, D). Since the generic name was instituted, information
has been obtained in regard to the nature of the stems which bore
some of the petioles of the _Zygopteris_ type; and for other species
of _Zygopteris_, the stems of which are still unknown, new generic
names have been proposed. P. Bertrand[1133] retains _Zygopteris_ for
one species only, _Z. primaria_. Fig. 308, D, shows the character of
the petiolar vascular strand; the chief points are the comparatively
long cross-pieces (antennae of P. Bertrand) inclined at an angle of
45° to the plane of symmetry of the petiole axis, and the groups of
protoxylem elements shown by the white patches in fig. D. In this as in
other members of the Zygoptereae the main rachis of the leaf gives off
four sets of branches in pairs alternately from the right and left side
of the primary vascular axis. This method of branching of the stele in
the primary rachis of several members of the Coenopterideae shows that
the fronds bore pinnae laterally disposed, in some cases in one row
and in others in two rows on each side of the rachis. In a typical fern
frond, as represented by recent and most fossil species, branching
of the rachis occurs in the plane of the frond, that is in the plane
represented by the horizontal arm of xylem in _Zygopteris primaria_
connecting the two antennae or cross-pieces. In the Zygoptereae the
branches from the petiole vascular axis lie in a plane at right angles
to that of the frond; they lie in the transverse and not in the
horizontal plane. The two strands shown in fig. 308, B, 4, have been
formed by the division of a single strand, 3, in the transverse plane
(i.e. in the plane of the paper). As Tansley[1134] points out, a type
of branching superficially similar to, though not identical with this,
is seen in some recent species of _Gleichenia_ and _Lygodium_. In
this connexion it is worthy of note that a fern figured by Unger from
Thuringia as _Sphenopteris petiolata_ Goepp[1135] bears pinnae in two
rows on the rachis which are characterised by repeated branching and by
a very narrow lamina or by slender naked axes; the occurrence of this
form of frond in rocks containing _Clepsydropsis antiqua_ (fig. 308,
A) suggests a possible connexion between the petrified rachis and the
impressions of the leaves.

[Illustration: FIG. 308.
  A. _Clepsydropsis antiqua._
  B. _Etapteris Scotti._
  C. _Diplolabis forensis._
  D. _Zygopteris primaria._
  E–G. _Stauropteris oldhamia._

  The white patches in the xylem in figs. B–G mark the position of
  protoxylem elements.

  (A, after Unger; B–G, after P. Bertrand.)]

[Illustration: FIG. 309.

  A. _Diplolabis forensis._
  B. _Botryopteris forensis._
  C, D. _Corynepteris coralloides._
  E. _Schizopteris_ (_Etapteris_) _pinnata_.

  (A, B, after Renault; C, D, after Zeiller; E, after Renault and
  Zeiller.)]

The vascular strand of the rachis of _Zygopteris primaria_ (fig. 308,
D) is simpler than that of most of the Zygoptereae and exhibits a close
resemblance to the type of strand described by Renault as _Diplolabis_
(fig. 308, C).


                             _Diplolabis._

Renault[1136] instituted this genus for two species from the Culm beds
and Coal-Measures of France based on the structure of the petioles.
The stems are unknown. The main rachis has a stele similar to that of
_Zygopteris primaria_, but distinguished by its greater similarity,
in transverse section, to an =X= rather than to the letter =H=: the
long transverse bar in _Zygopteris_ is here much reduced in size.
The petiole of _Diplolabis forensis_[1137] Ren. (fig. 308, C) has a
diameter of 1·5–2 cm. From the antennae a pair of small bundles is
given off alternately from the right and left side, as in _Zygopteris_;
the members of each pair coalesce after leaving the antennae and then
separate to pass into the lateral branches of the frond. The position
of the protoxylem and the formation of the lateral xylem strands
previous to their separation are shown in fig. 308, C. On the side of
the vascular strand shown in fig. C, 2, the two lateral extensions
of the antennae are converging towards one another previous to their
separation and subsequent union. The ovoid sporangia occur in groups
of three to six and are coalescent below with a central receptacle;
they have no annulus, but the cells on the side next the receptacle are
smaller than those on the external wall (fig. 309, A). The synangial
form of the sorus suggests comparison with Marattiaceae.

The species described by Renault from the Culm of Esnost is regarded by
P. Bertrand as identical with that described by Solms, from the Culm
of Falkenberg, as _Zygopteris Roemeri_[1138]. _Diplolabis_ is compared
by P. Bertrand with _Metaclepsydropsis_, the generic name given to the
Lower Carboniferous petiole described by Williamson as _Rachiopteris
duplex_[1139].

Mr Gordon has recently described in a preliminary note a new type
of stem stele under the name _Zygopteris pettycurensis_ from the
Lower Carboniferous plant bed of Pettycur[1140]: he regards the
petioles attached to the stem as identical with _Zygopteris Roemeri_
Solms-Laubach[1141]. This species, founded by Solms-Laubach on
petioles only, is placed by Bertrand[1142] in the genus _Diplolabis_
and regarded as identical with _D. esnostensis_ Ren. The stele found
by Mr Gordon may therefore be assigned to the genus _Diplolabis_:
it includes two regions composed exclusively of tracheae and is
cylindrical in transverse section. The inner xylem zone consists of
short, square-ended, reticulately pitted elements and the outer zone
is composed of long and pointed conducting tracheae. The scalariform
protoxylem elements are situated between the two metaxylem zones.
As Mr Gordon says: this type of stem occupies a position “in the
Zygopteroid alliance” corresponding to that which _Thamnopteris
Schlechtendalii_ (p. 329) occupies in the Osmundaceous series. The
discovery of this stem supplies another link between the two fern
groups, Osmundaceae and Coenopterideae. Pelourde[1143] has described
an imperfectly preserved vascular strand from a locality near Autun as
the type of a new genus _Flicheia esnostensis_. Mr Gordon has pointed
out to me that this is a partially rotted petiole of _Diplolabis
esnostensis_ (= _Zygopteris Roemeri_).

In their recent account of fossil Osmundaceous genera, Kidston and
Gwynne-Vaughan[1144] speak of the central parenchyma of the existing
medullated stele as being derived from tracheal tissue. They add that
if the Zygopteroid line of descent is at all close to the Osmundaceous,
we must be prepared for the existence of a _Zygopteris_ with a solid
xylem like that of _Thamnopteris_: “such a discovery, in fact, we
hopefully anticipate[1145].” The new Pettycur stem amply justifies this
prophecy. It is noteworthy that Mr Gordon’s stem affords an instance
of the occurrence of a type of stele, similar in its cylindrical form
and in the absence of parenchyma to that of _Botryopteris_, in a plant
bearing leaves characterised by the _Zygopteris_ type of vascular
strand.


_Metaclepsydropsis duplex_ (Will.) fig. 310, A[1146]. [= _Rachiopteris
duplex_, Williamson 1874. _Asterochlaena_ (_Clepsydropsis_) _duplex_,
Stenzel 1889. _Clepsydropsis_, Renault 1896.]

The vascular axis of the main axis of the frond is characterised by the
hour-glass shape of the xylem which consists entirely of tracheae, most
of which are reticulately pitted. In a transverse section (fig. 310,
A) the two ends of the stele are dissimilar; at one end of the long
axis is a small bay of thin-walled tissue (phloem) enclosed by a narrow
band of xylem, and at the other the bay is open and has two protoxylem
groups. The latter represents the earliest stage in the production of
secondary bundles: at a later stage the bay is closed by the elongation
of the edges, the enclosed group of phloem is vertically extended, and
the protoxylem strands are more widely separated. The curved band of
xylem becomes detached as a curved arc and divides into two (fig. 310,
A). In a single section of this species one often sees several strands
of xylem enclosed in a common cortex with the main vascular axis; these
are the xylem bundles of lateral pinnae. _Metaclepsydropsis duplex_
shows the method of branching of the petiole vascular axis which has
already been noticed in _Diplolabis_ and _Zygopteris_. In reference
to this feature, Williamson wrote in 1872—“I know of no recent fern
in which the secondary branches of the petiole are thus given off in
pairs, which pairs are distichously arranged on the primary axis,
and each of which secondary petioles sustains ternary ones arranged
distichously.” By slightly altering the primary stele of this type of
frond, by narrowing of the constricted portion of the hour-glass and
extending the lateral groups of xylem obliquely upwards, the form of
stele shown in fig. 310, A, would be converted into the _Diplolabis_
type (fig. 308, C).


                           _Clepsydropsis._

Unger[1147] instituted this genus as a subdivision of Corda’s family
Rhaciopterideae[1148], the name having reference to the hour-glass
form of the vascular axis[1149]. The type-species _C. antiqua_ (fig.
308, A) is spoken of as the commonest fossil plant in the Devonian
rocks of Thuringia. In some sections the xylem has the form seen in
fig. 308, A, in which an invagination of thin-walled tissue occurs at
each end; in other sections (fig. 308, A′) the bays become islands in
the xylem. Solms-Laubach speaks of Unger’s species as _Rachiopteris_
(_Clepsydropsis_) _antiqua_. P. Bertrand[1150], who has recently
described Unger’s plant, while recognising that _C. antiqua_ and
_Metaclepsydropsis duplex_ closely resemble one another, draws
attention to certain differences in the structure of the xylem which he
regards as sufficient to justify a generic separation. The leaf-traces
of _Clepsydropsis_ are described by Bertrand as almost circular closed
rings of xylem instead of an arc as in _Metaclepsydropsis_.

[Illustration: FIG. 310.

  A. _Metaclepsydropsis duplex._
  B, C. _Stauropteris oldhamia._
  D. _Ankyropteris scandens._

  [A, from a section in Dr Kidston’s Collection (Lower Carboniferous);
  B, C, from sections in the Cambridge Botany School; D, after
  Stenzel.]]


                            _Ankyropteris._

Stenzel adopted this name for a subdivision of Corda’s genus
_Zygopteris_, applying it to a species described by Renault as _Z.
Brongniarti_, to a Permian species described by himself as _Z._
(_Ankyropteris_) _scandens_, and to _Z. Lacattii_ Ren.; _Rachiopteris
Grayi_ Will. and _Rachiopteris corrugata_ Will. are also included in
this genus. The characters emphasised by Stenzel[1151] are (i) the
double anchor-like form of the =H=-shaped petiole strand in which the
lateral arms (antennae) are curved like the flukes of an anchor, and
(ii) the emission of four rows of branches instead of two. The latter
distinguishing feature no longer holds good, as _Z. primaria_ also
gives off four rows of bundles and not two as Stenzel supposed. P.
Bertrand has adopted Stenzel’s genus in a narrower sense[1152].

[Illustration: FIG. 311. _Ankyropteris Grayi._ Stele. (From a section
  in Dr Kidston’s Collection, × 18.)]


_Ankyropteris scandens_ Stenzel[1153]. Fig. 310, D.

This Lower Permian species is very similar to or perhaps identical with
_Ankyropteris Grayi_ (Williamson). The stem of

_A. scandens_ was found in association with the roots of a _Psaronius_
stem evidently petrified _in situ_ as it burrowed, like _Tmesipteris_,
tropical aroids, and other recent plants, among the living roots of
the tree-fern. The stem, 10–11 mm. in diameter, bore fronds with an
=H=-shaped vascular strand, small scale-leaves, and adventitious roots.
The stele consists of a five-angled cylinder of scalariform tracheae
surrounding an axial strand of parenchyma containing scattered tracheae
of smaller diameter. This axial tissue extends as a narrow strip
into each of the short and obtusely truncated arms (cf. fig. 311).
A striking feature is the production of a shoot in the axil of the
foliage-leaves (fig. 310, D), a manner of branching characteristic of
_Trichomanes_ (see page 365).


_Ankyropteris Grayi_ (Will.). Fig. 311.

In describing this species, Williamson wrote—“That no classification
of these fossil ferns based solely upon transverse sections of the
petiolar bundles is or can be of much value, is clearly shown when
tested amongst those living ferns the classification of which is
chiefly based upon the sporangial reproductive organs[1154].” This is
a view entirely opposed to that which inspires P. Bertrand’s recent
monograph. Whether the value attached to the vascular structure
of petioles as a basis of classification is upheld or not, it is
noteworthy that since Williamson expressed his opinion, our knowledge
of the anatomy of ferns and of the value of anatomical evidence
has enormously increased. The slender stem[1155] of this Lower
Coal-Measures species agrees closely with that of _A. scandens_; it
bore spirally disposed fronds, scale-leaves, and roots. The stele
has the form of an irregular five-rayed star (fig. 311) in which
the relative length of the arms varies in different sections owing
to the separation of the distal ends to form leaf-traces. The axial
region is composed of parenchyma and associated narrow tracheae, as
in _A. scandens_. The xylem, with protoxylem elements at the ends and
especially at the angles of the arms, is completely surrounded by
phloem. The cortex consists internally of parenchyma which becomes
thicker-walled towards the periphery and bears multicellular epidermal
hairs. A leaf-trace is detached in the form of a triangular strand
and is formed by the tangential extension of the distal end of an arm
of the stele. The trace, on its way through the cortex, divides into
two; the outer branch gradually changes from a slightly curved band to
an =H=-shaped meristele; the inner branch, which supplied an axillary
shoot, is similar to the stele of the stem, but smaller. Scott[1156]
has recently recorded the occurrence of scale-leaves (aphlebiae) in
this species like those described by Stenzel in _A. scandens_.

[Illustration: FIG. 312.

  A. _Thamnopteris Schlechtendalii._ Leaf-trace: _px_, protoxylem;
     _s_, island of parenchyma. (After Kidston and Gwynne-Vaughan.)
  B. _Ankyropteris corrugata._ Single trachea with tyloses.
  C. _A. bibractensis._ Part of foliar strand. (After P. Bertrand.)]

Bertrand includes in _Ankyropteris_ Renault’s species _Zygopteris
bibractensis_[1157] and Williamson’s species _Rachiopteris
corrugata_[1158]: the former he names _A. bibractensis_ var.
_westphaliensis_. The fossil described by Williamson as _R.
irregularis_ or _inaequalis_[1159] are the secondary branches of _A.
bibractensis_.


_Ankyropteris bibractensis_, var. _westphaliensis_. Figs. 312, C; 313.

The rachis stele of this species, which is represented by portions of
fronds only, has the form of a double anchor (fig. 313); the antennae
are continued at the outer edge of their distal ends into a narrow
band (“filament” of P. Bertrand) (fig. 312, C, and 313, _a_) composed
of smaller tracheae and separated from the xylem of the antennae by a
strip of thin-walled tissue (phloem?). A group of protoxylem occurs at
the junction of the filament and antennae. The whole of the xylem is
surrounded by phloem.

[Illustration: FIG. 313. _Ankyropteris bibractensis_: _s_, stigmarian
  rootlet; _a_, narrow loop of xylem. (Cambridge Botany School; × 6).]

The section reproduced in fig. 313 shows the characteristic form of the
petiolar vascular axis, consisting of a horizontal band of metaxylem
with groups of much smaller tracheae on both the upper and lower
margins. At the junction between the antennae, curved like the flukes
of an anchor, and the horizontal band of xylem, the latter is only one
trachea in breadth. The narrow loops of smaller xylem elements are
shown on the outer edge, _a_ (fig. 313), of the antennae separated
from the arcs of larger tracheae by a dark line which represents a
crushed band of delicate tissue. The spaces enclosed by the incurved
antennae are largely occupied by parenchymatous ground-tissue.
The cylinder of outer cortex consists internally of comparatively
thin-walled parenchyma succeeded externally by a zone of dark and
thicker-walled cells characterised by a fairly regular arrangement in
radial series, as if formed by a secondary meristem; there is, however,
no indication of a meristematic layer. Below the small-celled epidermis
are a few layers of thinner-walled cells which are not arranged in
radial series. The structure of the outer part of the cortex is similar
to that in the petiole of recent species of _Angiopteris_ (fig. 243, p.
319) and _Marattia_, in which a more delicate hypoderm is succeeded by
a band of mechanical tissue.

The rachis of this type of frond gives off two rows of lateral branches
from the vascular axis, the plane of symmetry being at right angles to
the primary rachis. Each pinna bore at its base two aphlebiae supplied
with vascular strands from the leaf-traces.

We have no certain information in regard to the sporangia of this
species, but Scott points out that “pear-shaped sporangia, with a
very broad and extensive annulus, are commonly found associated with
_Zygopteris bibractensis_ and _Z. corrugata_ in the petrifactions of
the English Lower Coal-Measures[1160].”


_Ankyropteris corrugata_ (Will.). Figs. 312, B; 314–317.

The stem of this type of Zygoptereae was described by Williamson from
the Lower Coal-Measures of Lancashire as _Rachiopteris corrugata_ and
included by him in the sub-group Anachoropteroides. The stele (fig.
314, B) is oval in transverse section; it consists of a cylinder of
xylem tracheae enclosing a central region occupied by parenchymatous
tissue and scattered narrow scalariform tracheae. The central tissue
extends radially in the form of narrow arms which reach almost to the
outer edge of the tracheal tissue and divide it up into 5–7 groups. A
cylinder of thin-walled tissue encloses the xylem and in this occur
groups of large sieve-tubes (fig. 314, D, _Sv_).

In a section of this species in the Williamson Collection[1161] the
long axis of the stele has a length of 5 mm. and the diameter of the
stem as a whole is 2·5 cm. The greater part of the extra-stelar tissue
consists of large parenchymatous cells passing near the periphery into
a band of darker and thicker-walled tissue.

Reniform vascular strands traverse the cortex in an obliquely
ascending course on their way to the leaves, also smaller bundles,
some of which are given off directly from the stele, while others are
branches of the petiole vascular strands. The petioles described by
Williamson as _Rachiopteris insignis_[1162] were afterwards recognised
by him as those of _Ankyropteris corrugata_, though this conclusion
was not published[1163]. Williamson’s species _R. insignis_ must
not be confused with Unger’s Culm species _Arctopodium insigne_,
which Solms-Laubach[1164] refers to as _Rachiopteris insignis_. The
leaf-bundle of _Ankyropteris corrugata_ is at first reniform in contour
(fig. 314, C, _P_), but as it becomes free from the stem it gradually
assumes the =H=-shaped form (figs. 315–317). This petiolar strand
differs from that of _Ankyropteris bibractensis_ (fig. 313) in the
shorter and less strongly curved antennae; and, as Williamson first
noticed, the tracheae are frequently filled with thin-walled parenchyma
(fig. 312, B). The existence of scale-leaves or aphlebiae like those of
_Ankyropteris scandens_ and _A. Grayi_ has been recorded by Scott in
_A. corrugata_[1165].

The section represented in fig. 314, C, shows the relatively small size
of the stele _S_ in the stem of _Ankyropteris corrugata_. The main mass
of the cortex consists of uniform parenchyma passing near the surface
into darker and stronger tissue: two vascular bundles are shown in the
cortex, one of which forms the conducting strand of a petiole, _P_,
which has nearly freed itself from the stem: the other bundle, as shown
by the examination of a series of sections, eventually passes into
another leaf-stalk. A root of another plant has invaded the cortex at
_R_, fig. 314, C.

[Illustration: FIG. 314. _Ankyropteris corrugata._ _R_, intruded root;
  _P_, petiole; _S_, stele, _Sv_ sieve-tubes.

  A, B. From a section in the University College Collection.
  C. After Williamson.
  D. From a section in the Williamson Collection (British Museum).]

The form and structure of the stele is diagrammatically represented
in fig. 314, B. The outer portion (black) consists of a cylinder
of scalariform tracheae in which the position of groups of smaller
elements (protoxylem) is shown by the white patches. The xylem is
thus seen to be mesarch. The prominent group of xylem on the lower
right-hand side of the section consists of tracheae, cut across
in an oblique direction, which are about to pass out as a separate
strand. The centre of the stele is occupied by parenchymatous tissue
in which are included scattered tracheae, either singly or in small
groups. These medullary tracheae are rather narrower than those of the
main xylem cylinder. A characteristic feature is the radial outward
extension into the xylem of the medullary parenchyma, which tends
partially to divide the tracheal cylinder into broad groups.

[Illustration: FIG. 315. _Ankyropteris corrugata_ (Will.). Petiolar
  vascular strand. [From a section in the University College (London)
  Collection; after Tansley × 35.]]

Fig. 314, A, enlarged from fig. B, _a_, shows the mesarch position of a
protoxylem group, and a few of the parenchymatous cells of one of the
narrow arms of the axial tissue. At _Sv_ in fig. D a group of large
sieve-tubes is seen separated from the xylem by a few parenchymatous
cells, and beyond the sieve-tubes are some tangentially elongated
cells. Both the sieve-tubes, _Sv_, and the flattened cells resemble
tissues in a corresponding position in the steles of modern Osmundaceae.

In a section of _Ankyropteris corrugata_ in the Williamson Collection
the radial arrangement of the more external metaxylem elements suggests
the addition of secondary tracheae[1166]. This suggestion of secondary
thickening, a point which requires much more thorough investigation,
is interesting in relation to a new type of stem named by Scott
_Botrychioxylon_[1167], but not yet fully described. This generic
name has been given to a stem stele which closely resembles that of
_Ankyropteris corrugata_ except in the regular radial arrangement of
the peripheral xylem elements. The name _Botrychioxylon_ was chosen by
Scott because of the secondary xylem characteristic of the recent genus
_Botrychium_ (fig. 247, p. 322).

[Illustration: FIG. 316. _Ankyropteris corrugata._ Petiole. _a_,
  narrow xylem loop; _b_, spaces in cortex. From a section in the
  Cambridge Botany School Collection. (× 10.)]

In the petiolar vascular strand represented in fig. 315 the narrow band
of tracheae which forms a loop external to the antennae is clearly
seen, also the small-celled parenchyma between the loops and the larger
metaxylem elements of the antennae. The crushed tissue lying on the
outer face of each of the loops probably represents the phloem and
pericycle; the thin-walled elements above and below the horizontal band
of metaxylem are probably sieve-tubes.

Fig. 316 shows a transverse section of a petiole of this species: the
loops, _a_, of small tracheae are seen bending round the outer edge of
the antennae. The inner and more delicate cortical tissue is partially
preserved and spaces, _b_, have been formed in it as the result of
contraction previous to petrifaction. In the petiole represented in
fig. 317 the tracheae of the horizontal band are considerably crushed;
the section is, however, of interest because of the presence of
_Lyginodendron_ roots, _l_, in the space originally occupied by the
inner cortex.

[Illustration: FIG. 317. _Ankyropteris corrugata._ From a section in
  the Cambridge Botany School Collection. (× 9.)]

In a paper on the tyloses of _Rachiopteris corrugata_, Weiss[1168]
draws attention to the fact that similar inclusions have not been
found in the tracheae of recent ferns. The occurrence of thin-walled
parenchymatous cells in the large tracheae of _Ankyropteris corrugata_
petioles and of other species is a striking feature. Williamson[1169]
compared these cells with the tyloses in the vessels of recent
flowering plants, and in a later paper[1170] he suggested that the
included cells may belong to saprophytic or parasitic fungi. It is, as
Weiss points out, difficult to explain the occurrence of tyloses in
tracheae not immediately in contact with living parenchyma. It may be
that the pits in the tracheae of _Ankyropteris_ were open spaces as in
the xylem of recent ferns described by Gwynne-Vaughan, and if so this
would facilitate the invasion of the conducting elements by growing
cells. A comparison is made by Weiss between certain cell-groups found
by him in the tracheae of _Ankyropteris_ and by Miss Jordan[1171] in
the vessels of the recent dicotyledon _Cucumis sativus_. In a more
recent paper on tyloses Miss McNicol[1172] expresses the opinion that
pseudoparenchyma in the tracheae of the fossil petioles owes its origin
to fungal hyphae.

Williamson compared the petiole bundles of _Ankyropteris corrugata_
with those of recent Osmundaceae, a comparison based on the structure
of the leaf-trace before its separation from the stem and its
assumption of the =H=-form. It is noteworthy, however, that this
comparison has acquired a greater significance as the result of recent
work. The stele of _Ankyropteris_ bears a fairly close resemblance to
that of _Zalesskya_ described by Kidston and Gwynne-Vaughan; in both
types the xylem is represented by two kinds of tracheal tissue. In the
Permian Osmundaceous genus the centre of the stele consists of short
storage tracheids, while in _Ankyropteris_ we may regard the central
parenchyma and scattered tracheae as derivatives of the solid xylem
core of some ancestral type. Moreover, the appearance and arrangement
of the phloem and the tangentially elongated elements external to it
(fig. 314) remind one of the extra-xylem zone in recent Osmundaceae.
That the Osmundaceae and Zygoptereae are closely related groups
there can be little doubt; of this affinity and common origin[1173]
_Ankyropteris corrugata_ affords striking evidence.

The difference between the steles of _Ankyropteris Grayi_ and _A.
scandens_ (figs. 310, D; 311) and that of _Ankyropteris corrugata_ is
comparatively small. In the two former species the cylindrical form has
become stellate owing to the radial extension of the xylem arms. It may
be that this more elaborate style of vascular construction is connected
with the climbing habit of _A. scandens_ and possibly _A. Grayi_. The
radial extension of the xylem and the consequent alternation of the
yielding parenchymatous cortex and the more rigid tracheal arms would
probably render the water-conducting elements less liable to injury in
a twisting axis[1174]. In _Anachoropteris Decaisnii_[1175], described
by Renault, and more especially in _Asterochlaena laxa_[1176] Stenzel,
a Lower Permian type from Saxony (fig. 324), the xylem of the stele is
much more deeply lobed than in _Ankyropteris Grayi_ or _A. scandens_.

[Illustration: FIG. 318. _Etapteris Scotti_, P. Bert. (From Tansley,
  after Renault.)]


_Etapteris Scotti_. Figs. 308, B; 309, E; 318.

P. Bertrand has proposed this name for a species of petiole from the
Lower Coal-Measures of England referred by Binney[1177] to _Zygopteris
Lacattii_ Ren., and included by Williamson[1178] in his comprehensive
genus _Rachiopteris_. Bertrand[1179] regards the English species,
which is recorded also from Germany[1180], as distinct from Renault’s
type[1181] and therefore proposes a new name. The petiole stele has the
=H=-form, but its structure is simpler than that of the _Ankyropteris_
petiole.

The horizontal band of xylem has at each end two oval groups of
tracheae connected with it by a single row of xylem elements (fig.
318). From the lower part of each oval group a small strand is
detached; the two strands from one side of the stele coalesce and then
separate to pass into two pinnae. Fig. 308, B, shows four stages in the
giving-off of the secondary branches. This species, therefore, produces
four rows of branches in alternate pairs from the right and left sides
of the petiole.

The first stage is shown at 0, 0, fig. 308, B; the two projecting
groups of protoxylem mark the points of departure of a pair of small
strands. At 1, the projections are more prominent, and at 2 a pair of
strands has become detached: at a later stage, 3, these two strands
unite to divide later (4) into two slightly curved bundles.

[Illustration: FIG. 319.

  A–C. Sporangia of _Etapteris_ (?).
  D–G. _Botryopteris forensis_. (After Renault.)]

Our knowledge of the fructification of _Etapteris_ is based on
Renault’s account of sporangia, which he regarded as belonging to
_Zygopteris_ (_Etapteris_) _Lacattii_. They have the form of elongated
slightly curved sacs (2·5 × 1·3 mm.) borne in clusters (fig. 319, A–C)
on slender ramifications of the fertile frond, which is characterised
by the absence of a lamina. Each sporangium has a pedicel, and three
to eight sporangia are attached to a common peduncle; the walls of the
sporangia are at least two cell-layers in thickness and the annulus
consists of a band of thick-walled cells passing from the crest down
each side (figs. B and C), thus differing from the sporangia of
_Botryopteris_ (fig. 319, D, F) in which the broad annulus is confined
to one side.

[Illustration: FIG. 320. _Stauropteris oldhamia_. (After Tansley. From
  a section in Dr Scott’s Collection. × 60.)]

It is practically certain that the fronds described by Grand’Eury[1182]
as _Schizopteris pinnata_ (fig. 309, E) and _Schizostachys frondosus_
represent respectively the sterile and fertile leaves of _Etapteris_.
Zeiller[1183] gives expression to this by substituting the generic name
_Zygopteris_ for _Schizopteris_, and we may now speak of the leaves as
_Etapteris_. Dr White[1184] has referred to a new genus, _Brittsia_,
some impressions of pinnate fronds from the Coal-Measures of Missouri
which, as he points out, bear a close resemblance to _Schizopteris
pinnata_ Grand’Eury (fig. 309, E). No sporangia have been found; it is,
however, probable that _Brittsia problematica_ represents fragments of
a leaf borne by a plant closely allied to _Etapteris_ (_Zygopteris_).
The broad rachis bears crowded pinnae given off at a wide angle; the
small pinnules are rather deeply lobed or pinnatifid (3–10 mm. long
by 1·5–3 mm. broad). The lamina is traversed by irregularly lobed and
occasionally anastomosing veins. In the fertile pinnae the segments
have no lamina but bear bundles of pedicellate sporangia.

It should be noticed that the sporangia described by Renault and by
other authors as those of _Zygopteris_ (fig. 319, A–C) have not been
found in organic continuity with a frond showing a well-preserved
vascular strand. It is, however, certain that this characteristic
annulate sporangium, borne on branched and slender pedicels, was
produced on fronds with a much reduced lamina belonging to some species
of the Zygoptereae, _Etapteris_ and probably also _Ankyropteris_.


                            _Stauropteris._

This genus was instituted by Binney for petioles from the Lower
Coal-Measures of Oldham (Lancashire).

_Stauropteris oldhamia_ Binney[1185] is characterised by a stele (figs.
308, E–G; 310, C; 320; 321) composed of four groups of xylem which
Bertrand regards as homologous with the antennae of _Diplolabis_,
_Ankyropteris_, and _Etapteris_, the horizontal cross-piece of
these genera being absent in _Stauropteris_. Williamson spoke of
this species as “one of the most beautiful and also one of the most
perplexing of the plants of the Coal-Measures”; he discussed its
possible affinity with both Lycopods and ferns, deciding in favour of
the latter group[1186]. In transverse section the petiolar vascular
axis is approximately square, the xylem groups forming the ends of the
diagonals; the tracheal groups are separated by phloem and the centre
of the stele in the primary rachis is also occupied by that tissue,
which is connected by four narrow strips with the external phloem. The
structure of the petiolar vascular axis is very clearly shown in the
drawing by Mrs Tansley reproduced in fig. 320. Protoxylem elements
occur close to the surface of each of the four arms of the xylem; the
bays between the two lateral and the two lower xylem groups contain
large sieve-tubes. Portions of the inner cortex are seen in places
abutting on the small-celled pericyclic tissue.

The right and left halves of the stele are not absolutely identical
(fig. 320; fig. 308, E); this is due to the fact that secondary
branches are given off in four rows, two alternately from the right and
left sides. The preparation for the departure of the lateral strands
alters the configuration of the stelar xylem groups. The protoxylem
groups are not external but separated from the surface by one or two
layers of metaxylem. In fig. 308, E, the occurrence of two protoxylem
strands in the right-hand groups of metaxylem marks an early stage in
the detachment of branches. These two protoxylems are the result of
division of single protoxylem strands like those in the left-hand half
of the stele. At a later stage the petiolar stele assumes the form
shown in fig. 308, F, and two small bundles are detached to supply
aphlebiae: this is followed by the stage shown in fig. G, where two
four-armed strands are passing out to a pair of branches of the leaf
axis. The separation of these two meristeles leaves the right-hand half
of the stele in the condition seen on the left-hand side of fig. E.
The diagrammatic sketch represented in fig. 310, C, shows one pair of
branches in organic connexion with the rachis, and each of these arms
contains an obliquely cut vascular strand like those in fig. 308, G.

The cortex consists for the most part of fairly thick-walled parenchyma
(fig. 321) which in the hypodermal region is replaced by a zone of
thin-walled lacunar tissue. A few stomata have been recognised in the
epidermis[1187]. The lower left-hand branch seen in fig. 310, C, has
been shaved by the cutting wheel so that the aerenchymatous tissue,
_l_, is shown in surface-view: a portion of this tissue is enlarged in
fig. C′. The same delicate chlorophyllous tissue forms a folded and
shrivelled layer with an uneven margin on the surface of the rachis
and lateral branches. This hypha-like tissue, which was discovered by
Scott[1188] and figured by Bertrand[1189], doubtless represents the
much reduced lamina of the highly compound leaves; it may be compared
with the green outer cortex of _Psilotum_ shoots and with the lacunar
tissue in the capsule of the common moss, _Funaria hygrometrica_.

[Illustration: FIG. 321. _Stauropteris oldhamia_: _a_, sections of
  pinnae. (× 10. From a section in the Cambridge Botany School Coll.)]

The rachis reproduced in fig. 321 is surrounded by an enormous
number of sections, some transverse, others more or less vertical,
of branchlets of various sizes. Fig. 310, B, shows the three-rayed
vascular axis of a branch of a lower order than those seen in fig. C,
and the single vascular strands of still finer ramifications of the
leaf. The extraordinary abundance of axes of different sizes, many of
which are cut in the plane of branching, in close association with the
rachises of _Stauropteris_ affords a striking demonstration of the
extent to which the subdivision of the frond was carried in a small
space. The leaves must have presented the appearance of a feathery
plexus of delicate green branchlets devoid of a lamina, some of which
bore terminal sporangia. It may be that the delicate fronds were borne
on a slender rhizome which lived epiphytically in a moist atmosphere on
the stouter stems of a supporting plant.

The sporangia[1190] of _Stauropteris oldhamia_ are exannulate and
nearly spherical, with a wall of more than a single row of cells;
they occur at the tips of slender and doubtless pendulous branchlets.
The discovery by Scott[1191] of germinating spores (fig. 323) in a
sporangium of this type supplies an interesting piece of evidence
in favour of the fern nature of these reproductive organs. Similar
germinating spores have been described by Boodle[1192] in sporangia of
_Todea_.

[Illustration: FIG. 322. Sporangia of _Stauropteris oldhamia_. _St_,
  stomium: _p_, palisade tissue. (From Tansley, after D. H. Scott,
  from a drawing by Mrs D. H. Scott.)]


_Stauropteris burntislandica._

This Lower Carboniferous plant identified by Williamson with the
Oldham plant from the Lower Coal-Measures is referred by Bertrand to
a distinct species. In the structure of the rachis stele it agrees
closely with _Stauropteris oldhamia_; the main vascular strand gives
off four rows of branches, two from each side, and aphlebiae were
present at the common base of each pair of pinnae. Mrs Scott[1193],
who has recently described the sporangia of this species, speaks of
one specimen in which germinating spores were found. The same author
gives an account of some curious spindle-shaped bodies which she found
in association with _S. burntislandica_. The nature of these organs
is uncertain; Mrs Scott inclines to regard them as glands borne in
pairs on lateral pedicels of the frond: she adopts for these the name
_Bensonites fusiformis_ proposed by Dr Scott. If there is a reasonable
probability, as there certainly seems to be, in favour of connecting
these organs with _Stauropteris_, it is legitimate to question the
desirability of adding to the long list of names included in the group
Coenopterideae.

[Illustration: FIG. 323. Germinating spores from a sporangium of
  _Stauropteris_. (From Tansley, after D. H. Scott.)]


                    _Corynepteris._ Fig. 309, C, D.

This genus was founded by Baily[1194] on fragments of a fern from
Carboniferous rocks in County Limerick, Ireland, characterised by a
peculiar type of fructification which he named _Corynepteris stellata_.
More complete examples of the same genus have been described by
Zeiller[1195] from the Coal-field of Valenciennes. The sporangia are
large, ovoid, and sessile; the annulus (fig. 309, D) has the form of a
complete vertical band several cells in breadth: five to ten sporangia
are grouped round a receptacle. Zeiller describes two species as
_Sphenopteris (Corynepteris) coralloides_ Gutb. and _S. (Corynepteris)
Essinghii_ And.; in both the fronds are quadripinnate and bear
aphlebiae at the base of the pinnae. The former species is recorded
by Kidston[1196] from the South Wales Coal-field. A single pinnule of
_C. coralloides_ is shown in fig. 309, C. Potonié[1197] refers this
frond to his genus _Alloiopteris_: the portion of a pinna represented
in fig. 354, G shows the characteristic modified pinnule next the
rachis. Zeiller draws attention to the occurrence of two parallel
lines on the rachis of a specimen of _Corynepteris coralloides_ which
he figures[1198], and suggests that these may indicate the existence
of an =H=-shaped form of vascular strand like that of _Etapteris_ and
_Ankyropteris_. The sorus of _Corynepteris_ is comparable with that of
the Marattiaceae, but the broad annulus is a difference which suggests
affinity to _Etapteris_. The sorus is similar to that in _Diplolabis_
(fig. 309, A), but in that genus the sporangia are exannulate.

                   •       •       •       •       •

The vascular axis in the stems of different members of the
Coenopterideae assumes a variety of types. In _Botryopteris antiqua_
the xylem forms a solid protostele in which no protoxylem strands have
been recognised; in other species, e.g. _B. ramosa_, the cylindrical
stele is similar to that of _Trichomanes radicans_ (Hymenophyllaceae)
in the more or less central position of the protoxylem. In
_Botryopteris forensis_ the protostele is said to be exarch. The
probability is that the central Botryopteris type is the endarch
protostele, a form of vascular axis which may be regarded as primitive.
The leaf-traces of the Lower Carboniferous _Botryopteris antiqua_ are
simple oval strands differing but slightly from the cylindrical stele
of the stem. In the Upper Carboniferous British species the petiolar
vascular strand has become more specialised and farther removed from
that of the stem; in _B. forensis_ the distinction between leaf
and stem steles is still more pronounced. It is perhaps legitimate
to regard these types as representing an ascending series, the more
primitive of which are distinguished by the greater similarity between
leaf and stem, organs differentiated from a primitive thallus[1199],
that is from a vegetative body. Portions of this ultimately became
specialised as lateral members or leaves, while a portion acquired the
character of a radially constructed supporting axis or stem.

[Sidenote: ANKYROPTERIS, ETC.]

The vascular strand characteristic of the Zygoptereae is represented
by the =H=-shaped form as seen in _Ankyropteris corrugata_ or in a
more complex form in _A. bibractensis_. This style of strand may be
regarded as a development from the simple strands of _Grammatopteris_
and _Tubicaulis_ or _Botryopteris antiqua_ along other lines than
those followed by _B. forensis_. The extension of the xylem in two
symmetrically placed arms at the ends of the cross-piece of the =H=
is correlated with the habit of branching of the leaf-system which
forms one of the striking peculiarities of many of the Zygoptereae.
The solid type of stele characteristic of the Botryoptereae is closely
matched by that in the Lower Carboniferous stem discovered by Mr
Gordon[1200]. By the partial transformation of the central xylem region
into parenchymatous tissue and the concentration of water-conducting
elements in the peripheral region the style of _Ankyropteris corrugata_
was developed. The vascular strand of the older plant, which is of
the _Diplolabis_ type, may be regarded as a more primitive style than
that of the =H=-form of petiole strand represented by _Ankyropteris
corrugata_. A further stage in evolution is seen in the stem stele
of _Ankyropteris Grayi_ and _A. scandens_, both of which have the
=H=-form of meristele. This step in increasing complexity of stem
stele, though probably connected with the increasing specialisation of
the leaf-traces, as held by Mr Tansley, may also be associated with the
development of a climbing habit. In _Asterochlaena laxa_ Stenzel (fig.
324) and _A. ramosa_ (Cotta)[1201] the tendency towards a stellate
expansion of the originally cylindrical form of stele reaches a higher
degree, with the result that a style is evolved which agrees closely
with that of the conducting tissue of some existing Dicotyledonous
Lianes.

Attention has already been drawn to the generalised features exhibited
by the Coenopterideae both in the anatomy of the steles and in the
structure of the sporangia. The conclusion arrived at is that while
the Coenopterideae foreshadow in some of their characters more than
one group of more recent ferns, some at least of their members afford
convincing evidence of the correctness of the view—which is also that
of Dr Kidston and Mr Gwynne-Vaughan—that the Osmundaceae and the
Coenopterideae are offshoots of a common stock.

[Illustration: FIG. 324. _Asterochlaena laxa_: part of stem with
  petiole and a few roots. From Tansley, after Stenzel.]




                             CHAPTER XXVI.

                     HYDROPTERIDEAE ╭  Marsiliaceae.
                                    ╰ Salviniaceae.


The unsatisfactory and meagre records in regard to the past history
of these heterosporous Filicales render superfluous more than a brief
reference to the recent species.


                             Marsiliaceae.

This family is usually spoken of as including the two genera _Marsilia_
and _Pilularia_. Lindman[1202] has however founded a third genus,
_Regnellidium_, on a Brazilian plant which is distinguished by some
well-defined characters from all species of _Marsilia_. The members
of the Marsiliaceae live for the most part in swampy situations.
_Marsilia_ is represented in Europe by _M. quadrifoliata_ L. which
occurs in Portugal, France, Germany and other parts of the Continent,
extending also to Kashmir, Northern China, and Japan. Of the other 53
species, 17 are recorded from different regions in Africa, while others
occur in South America, Asia[1203], Australia, and elsewhere.

_Pilularia globulifera_ L. is the only British representative of the
Hydropterideae. The remaining four species of the genus occur in South
America, California, New Zealand, Australia, and _P. minuta_ Dur. is
met with in the South of France, Algeria, and Asia Minor in subtropical
or warm temperate regions.

The Marsiliaceae are regarded as more nearly related to the
Schizaeaceae than to any other family of homosporous ferns[1204].
Their heterospory, the production of sporangia in closed fruit-like
sporocarps, and the anatomical features associated with existence in
marshy habitats, tend to obscure the resemblances to the true ferns.

                   •       •       •       •       •

The genus _Marsilidium_ proposed by Schenk[1205] for a piece of an
axis, bearing apparently a whorl of six leaflets, from the Wealden of
Osterwald, cannot be regarded as satisfactory evidence of the existence
of the Marsiliaceae in the Wealden flora of North Germany.

The six leaflets of _Marsilidium speciosum_, having a length of 5
cm., are similar in shape to the four leaflets of recent species of
_Marsilia_, but they differ in the repeated dichotomy of the veins from
the reticulate venation of the recent forms. It is worthy of note,
however, that in Lindman’s Brazilian type _Regnellidium diphyllum_
(fig. 326, A), the leaflets are characterised by dichotomous and not by
anastomosing veins.

Hollick[1206] has described some impressions of imperfect orbicular
leaves with a “finely flabellate obscurely reticulated(?) venation”
from Cretaceous rocks of Long Island as _Marsilia Andersoni_, but
these are too fragmentary to be accorded this generic designation. My
friend Dr Krasser informs me that he is describing some well-preserved
leaves from Cretaceous beds of Grünbach in Lower Austria as _Marsilia
Nathorsti_[1207]. He compares these with the recent form _Marsilia
elata_, a variety of _M. Drummondi_.

Another Lower Cretaceous species _Marsilia perucensis_ has been figured
by Frič and Bayer[1208] as a stalked fruit-like body from Bohemia. This
was originally described by Velenovský as _M. cretacea_, but under
this name Heer[1209] had previously recorded a supposed sporocarp from
Greenland. These fossils have little claim to recognition as examples
of Marsiliaceous plants.

The fragment figured by Heer[1210] from Tertiary rocks of Oeningen
as _Pilularia pedunculata_ is too small to determine with reasonable
accuracy. Other supposed representatives of the family mentioned in
palaeobotanical literature are not of sufficient importance to describe.


                             Salviniaceae.

The two genera of Salviniaceae, _Salvinia_ and _Azolla_, are water
plants, and are usually described as annuals which survive the less
favourable season in the form of detached sporocarps. Goebel[1211]
states that all the tropical species of _Salvinia_ known to him have an
unlimited existence.

_Salvinia natans_, Hoffm., the only European species, extends from the
South of France to Northern China and the plains of India: the other
twelve species are mostly tropical. _Azolla_, represented by four
species, occurs in Western and Southern North America, South America,
Madagascar, Australia, New Zealand, and is widely spread in tropical
Asia and Africa.

Species of _Azolla_ frequently form a considerable proportion of the
floating carpet of vegetation on inland waters[1212] growing under
conditions which might be supposed favourable for preservation in a
fossil state.

The Salviniaceae, though probably rather farther removed than the
Marsiliaceae from the homosporous Filicineae, are considered by
Bower[1213] to be related to the Gradatae, but modified in consequence
of their aquatic habit and the assumption of heterospory.

No undoubted examples of fossil species of _Azolla_ have been
described. _Salvinia_, on the other hand, is represented by several
Tertiary species, for the most part founded on leaves only, and
Hollick[1214], who published a list of fossil Salvinias, has described
detached leaves as _Salvinia elliptica_ Newb. from what may be Upper
Cretaceous rocks from Carbonado, Washington. Some of the leaves
figured as Tertiary Salvinias are of no value as evidence of the former
distribution of the genus[1215].

From the Coal-beds of Yen-Bäi (Tonkin), probably of Miocene age,
Zeiller[1216] has figured some well-preserved impressions of oval or
orbicular leaves, 15 mm. long and 10–20 mm. broad, characterised by
reticulate venation and by cordate bases, which he refers to Heer’s
Swiss species _Salvinia formosa_[1217].

Dr Zeiller[1218] in the most recently published part of his series of
valuable résumés of palaeobotanical literature refers to a description
by Brabenec of specimens of this species from Bohemian Tertiary beds
showing both microspores and megaspores.

One of the most complete specimens so far discovered has recently
been described by Fritel[1219] from Eocene beds of the Paris Basin
as _Salvinia Zeilleri_. This species, founded on portions of stems
bearing floating leaves, submerged root-like leaves, and sporocarps, is
compared with a recent tropical American species _S. auriculata_.

It is noteworthy that no authentic records of Hydropterideae have been
discovered in Palaeozoic rocks[1220]. Comparisons have been made in
the case of the genera _Traquairia_ Carr. and _Sporocarpon_ Will. with
the reproductive organs of _Azolla_[1221], but these rest on a wholly
insufficient basis.

Dawson[1222] proposed the generic name _Protosalvinia_ for some spores
of Devonian age, which he regarded on inadequate grounds as evidence of
Palaeozoic Hydropterideae.

Zeiller[1223], in discussing the possible relationships of the
problematical type _Chorionopteris gleichenioides_ Cord., suggests a
possible alliance with the Hydropterideae. Corda founded the genus
_Chorionopteris_[1224] on some small fragments of pinnules, 6–7 mm.
long, found in the Carboniferous rocks of Radnitz in Bohemia.

The lobes of the pinnules are incurved distally to form a capsule,
containing four sporangia, which apparently opened on dehiscence into
four valves; the spores are of one size. The material is however
insufficient for accurate determination.

There is no evidence contributed by fossil records which indicates
a high antiquity for the Hydropterideae. It is unsafe to base any
conclusion on the absence of undoubted Palaeozoic representatives of
this group; but the almost complete absence of records in pre-Tertiary
strata is a fact which may be allowed some weight in regard to the
possible evolution of the heterosporous filicales at a comparatively
late period in the earth’s history.

A description of the Mesozoic genus _Sagenopteris_ may be conveniently
included in this chapter, though as in many other instances the
inclusion of a genus under the heading of a recent family name does not
by any means imply that the position of the extinct type is regarded as
settled.


                             Sagenopteris.

This generic name was applied by Presl[1225] to small fronds composed
of four or rarely two palmately disposed leaflets with a more or less
distinct midrib and anastomosing secondary veins. Schimper[1226]
compared _Sagenopteris_ with _Marsilia_, but did not regard the
resemblance as evidence of relationship. Nathorst[1227] expressed
the opinion that certain fruit-like bodies obtained from the Rhaetic
beds of Scania are of the nature of sporocarps and were borne by
_Sagenopteris_, with the leaves of which they were associated. He
published a drawing of part of a fruit showing on its partially
flattened surface some raised oval bodies which are considered to
be spores. Dr Nathorst kindly placed at my disposal the drawings
reproduced in fig. 325 made from some of his specimens found at Bjuf in
Scania.

In contour and superficial features, e.g. the veining on the wall,
these bodies bear a fairly close resemblance to the sporocarps of
recent species of _Marsilia_. They were found in association with
the leaves of _Sagenopteris undulata_ Nath., an abundant Scania type
similar in form to the English Jurassic species _S. Phillipsi_ (figs.
327, 328). Heer was independently led by an examination of some
examples of the Swedish “fruits” to compare them with the sporocarps
of _Marsilia_. A small spherical body is figured by Zigno[1228] close
to a leaf of his species _S. angustifolia_, which may be a sporocarp.
In a recent paper, Salfeld[1229] says that he found fructification
on the lower face of the leaflets of _S. Nilssoniana_ Brongn. from
German Jurassic rocks, but he brings forward no evidence in support
of this statement. The systematic position of _Sagenopteris_ is by
no means settled. In a previous account of the genus I expressed the
view that it is probably a member of the true ferns[1230], but the
resemblance of Dr Nathorst’s drawings to the Marsilian sporocarps
influences me in favour of his opinion that _Sagenopteris_ may belong
to the Hydropterideae. The evidence, as Solms-Laubach[1231] states,
is not wholly satisfactory: Schenk points out that the frequent
occurrence of detached _Sagenopteris_ leaflets suggests that they
easily fell off the petiole, whereas in _Marsilia_ the leaflets do not
fall off independently. The discovery of a new type of Marsiliaceae in
Brazil, which Lindman has described as _Regnellidium diphyllum_[1232]
(fig. 326, A), affords an additional piece of evidence bearing on
the comparison of _Sagenopteris_ with members of this family. In
_Regnellidium_ the leaves differ from those of _Marsilia_ in bearing
two instead of four leaflets, and in the former the veins are
repeatedly forked, and do not anastomose as in _Marsilia_. In the
possession of only two leaflets _Regnellidium_ agrees with some forms
of _Sagenopteris_ (fig. 328).

[Illustration: FIG. 325. Sporocarp-like bodies found in association
  with the leaves of _Sagenopteris_. (Nat. size. From drawings
  supplied by Dr Nathorst.)]

[Illustration: FIG. 326.

  A. _Regnellidium diphyllum_ Lind. Single leaf and stalked sporocarp.
     (⅞ nat. size. After Lindman.)
  B. Cuticle of _Sagenopteris rhoifolia_. (After Schenk.)]


_Sagenopteris Phillipsi_ (Brongniart)[1233]. Figs. 327, 328.

  1828. _Glossopteris Phillipsi_, Brongniart, Hist. vég. foss. p. 225,
        Pls. LXI. _bis_, LXIII.

  1838. _Sagenopteris Phillipsi_, Presl, in Sternberg’s Flor. Vorwelt,
        vii. p. 69.

[Illustration: FIG. 327. _Sagenopteris Phillipsi._

  A. From the type-specimens of Lindley and Hutton (_Glossopteris
     Phillipsi_). Gristhorpe Bay, Yorkshire. British Museum, No.
     39221. Slightly reduced. M.S.
  B. From a specimen in the British Museum (39222). Nat. size.
     Figured by Lindley and Hutton as _Glossopteris Phillipsi_.]

The fronds of this common Jurassic species, which is recorded from
many European localities, from North America, Australia, the Antarctic
regions[1234], and elsewhere, are very variable as regards the form,
size, and number of the leaflets.

  Frond petiolate, in some forms the petiole bears four linear or
  oval-lanceolate leaflets having a distinct midrib and oblique
  anastomosing veins. In others a shorter winged petiole bears one
  or two shorter and broader, somewhat obcuneate, leaflets without a
  midrib.

It is probable that Bunbury[1235] was correct in his opinion that the
specimen figured by Lindley and Hutton[1236] as _Otopteris cuneata_,
characterised by two leaflets (fig. 328), is not specifically distinct
from the normal form with four leaflets (fig. 327).

Similarly, such specimens as that represented in Pl. XVIII., fig.
3 of the first part of my _Jurassic Flora_, in which a short stalk
bears only one leaflet may, provisionally at least, be included in
Brongniart’s species. Yabe[1237] describes a form with two leaflets
from Jurassic rocks of Korea as _Sagenopteris bilobata_ which resembles
_S. Phillipsi_; and Moeller[1238] records a specimen similar to that
represented in fig. 328 from Bornholm as _S. cuneata_ (Lind. and Hutt.).

[Illustration: FIG. 328. _Sagenopteris Phillipsi._ From a specimen in
  the Manchester University Museum. Nat. size.]

The leaf shown in fig. 327, A, in which the longest segments are 4·5
cm. in length, represents the most abundant form and illustrates the
very close agreement between _S. Phillipsi_ and the Rhaetic species
_S. rhoifolia_. Fig. 327, B, which is drawn from a specimen figured by
Lindley and Hutton[1239], shows a leaf with longer (6·5 cm.) and much
narrower segments. Broader leaflets are occasionally met with in which
the lamina reaches a length of 11 cm.[1240]

Leaves with leaflets narrower (3 mm. broad) than those represented in
fig. 327, B, are described by Zigno[1241] from Jurassic beds of Italy
as _S. angustifolia_ and by Moeller[1242] from the Jurassic of Bornholm
as _S. Phillipsi_ f. _pusilla_. A coarser type of venation than that of
_S. Phillipsi_ is occasionally found in Jurassic examples, as in _S.
grandifolia_ Font.[1243] from Oregon and _S. Nathorsti_ Barth. from
Bornholm[1244].

                   •       •       •       •       •

_Sagenopteris_ is recorded also from several Rhaetic floras. The best
known species, _S. rhoifolia_ Presl[1245], is hardly distinguishable
from some forms of _S. Phillipsi_ or from the Italian Jurassic species
described by Zigno as _S. Goeppertiana_[1246], though the leaflets are
usually rather larger. This species was first described by Brongniart
as _Filicites Nilssoniana_[1247], and a few authors[1248] have adopted
this specific name because of its priority over Presl’s designation.
As Nathorst remarks, to give up the well-known name _S. rhoifolia_ for
_S. Nilssoniana_ is “mere pedantry.” The epidermis of _S. rhoifolia_
as figured by Schenk[1249] consists of cells with straight and not
undulating walls: stomata occur on the lower surface (fig. 326, B).

Rhaetic leaves of the type represented by _S. rhoifolia_ have a wide
geographical distribution.

The specimens described by Feistmantel from the Damuda series of India
as _Sagenopteris longifolia_ are no doubt fronds of _Glossopteris
longifolia_[1250].

The Wealden species _Sagenopteris Mantelli_ (Dunk.)[1251] agrees
closely in habit and in the form of the leaflets with _S. Phillipsi_
and _S. rhoifolia_. It is probable that some of the leaves described by
Velenovský[1252] from Lower Cretaceous rocks in Bohemia as _Thinnfeldia
variabilis_ are portions of _Sagenopteris_ fronds. _S. Mantelli_ is
recorded from several European localities, from California[1253], and
elsewhere.

_Sagenopteris_ appears to have been widely distributed during
the Rhaetic, Jurassic and Lower Cretaceous floras. The very great
similarity between the specimens recorded from these three formations
renders the genus an uncertain guide in regard to geological age.
Decisive evidence as to its position in the plant kingdom is at present
lacking: the inclusion of the genus as a possible member of the
Hydropterideae has still to be justified.




                            CHAPTER XXVII.

             GENERA OF PTERIDOSPERMS, FERNS, AND _PLANTAE
                           INCERTAE SEDIS._


The genera and species described in this Chapter are founded on
sterile leaves or portions of leaves, and in the great majority of
cases the reproductive organs are either imperfectly known or have
still to be discovered. Some of the genera, the smaller number, are
no doubt true ferns, while most of them may safely be regarded as
plants which will ultimately be shown to belong to some other group,
in most cases that of the Pteridosperms. It is possible that a few
of the types may be members of the Cycadophyta rather than of the
Pteridospermeae, but evidence as to systematic position is for the
most part of a negative kind or too incomplete to lead to any definite
expression of opinion as to the cycadean or pteridosperm nature of the
imperfectly known Palaeozoic or Mesozoic species. Many of the genera
are of little botanical interest, though even the most problematical
are of importance as criteria of geological age. Genera which there
is good reason for including in the Pteridosperms are dealt with in
this section, in order that the Chapter in Volume III. devoted to this
important group may be limited to more completely known types.

In most text-books it is customary to employ family names for sterile
fern-like fronds which possess similar venation features or have
in common certain vegetative characters, the value of which it is
impossible to estimate. In the following account family or group
names are not adopted, on the ground that such slight utility as
they may have is more than counterbalanced by the risk attending a
grouping under one name of plants which may agree only in unessential
characters. The practice of classifying fossil plants has been carried
to excess. Grouping together genera as a matter of convenience
unavoidably creates a prejudice in favour of actual relationship, which
may or may not exist.


                             Taeniopteris.

This generic name was instituted by Brongniart[1254] for simple
linear or broadly linear leaves with a prominent midrib from which
secondary veins, simple or dichotomously branched, are given off at
right angles or obliquely. The frond of the type-species _Taeniopteris
vittata_ (fig. 332), characteristic of Jurassic floras, was compared
by Brongniart with the pinnules of _Danaea_ and _Angiopteris_. Among
recent ferns the Taeniopteris form of frond and venation is represented
by _Oleandra neriiformis_, _Asplenium nidus_, and many other species.
Though usually applied to fronds which there is good reason for
regarding as simple leaves, the generic designation _Taeniopteris_ has
been extended to include pinnate fronds, e.g. the Upper Palaeozoic
species _T. jejunata_ Grand’Eury, and _T. Carnoti_ Ren. and Zeill.
(fig. 330, A). The compound fronds from the Lower Coal-Measures
of Missouri described by Dr White[1255] as _T. missouriensis_ are
characterised by decurrent and confluent Taeniopteroid pinnules. In a
later reference[1256] to this plant White pertinently adds, “perhaps it
belongs more properly in _Alethopteris_.”

Leaves of the _Taeniopteris_ type are described by several authors as
species of _Oleandridium_, _Angiopteridium_, _Danaeites_, _Marattia_,
and other genera. In such species of Taeniopteroid leaves as have
been dealt with in a former Chapter, the occurrence of sori justifies
the substitution of a name denoting a close relationship to existing
members of the Marattiaceae, but in the absence of fertile specimens
the provisional designation _Taeniopteris_ should be retained. It
is often difficult to decide between _Taeniopteris_ and _Nilssonia_
as the more suitable name to apply to fragments of fossil leaves
of Mesozoic age. _Taeniopteris_ is, however, distinguished from the
Cycadean genus by the greater prominence of the rachis, also by the
dichotomous branching of the secondary veins, usually close to their
origin and at varying distances between the axis of the frond and the
edge of the lamina. The genus _Taeniopteris_, though most abundant in
Rhaetic and Jurassic strata, occurs also in Upper Carboniferous and
Lower Permian rocks. The generic name _Macrotaeniopteris_ instituted by
Schimper[1257] has been used for leaves differing only in size from the
usual type of _Taeniopteris_, but there is no adequate reason for its
retention.

The species included in _Taeniopteris_ afford no satisfactory evidence
as to their systematic position. It is obviously unwise to adopt such
generic titles as _Oleandridium_, _Marattiopsis_, etc., merely because
of resemblance in the venation of sterile fragments to _Oleandra_ or
Marattiaceous ferns.

Some specimens of _Taeniopteris_ fronds described by Mr Sellards[1258]
from Permian rocks of Kansas, which are referred to later, have
furnished unconvincing evidence of reproductive organs.


_Taeniopteris multinervis_, Weiss. Fig. 329, A, B.

The late Dr Weiss[1259] instituted this species (which he designated
_Taeniopteris multinervia_, though the specific name _multinervis_
is constantly used) for a fragment of a leaf from the Lower Permian
of Lebach characterised by numerous forked veins given off at right
angles from a prominent rachis (fig. 329, B). This type of frond is
recorded from the Permian of Trienbach (Alsace) by Zeiller[1260], by
Renault[1261] and Zeiller[1262] from the Upper Carboniferous of Autun,
and from other localities. The lamina of the simple leaf reaches a
breadth of 6 cm. and a length of 40 cm. (fig. 329, A); the numerous
secondary veins (25–36 per cm. of lamina) are either at right angles
to the rachis or given off at an acute angle. The mesophyll consists
of polygonal cells some of which are elongated at right angles to the
surface of the lamina. A very similar form is described by Fontaine and
White from the Permian of Virginia as _T. Lescuriana_[1263].

[Illustration: FIG. 329.

  A. _Taeniopteris multinervis_, Weiss. (⅚ nat. size. After Zeiller.)
  B. _T. multinervis._ (Enlarged. After Zeiller.)
  C. _Lesleya Delafondi._ (× 2. After Zeiller.)]

It is futile to expect to be able to separate the numerous
_Taeniopteris_ leaves into well-defined species: all we can do is
to group the specimens under different names, using as artificial
distinctions such characters as the shape of the leaf, the number
of veins per centimetre, and the prominence of the rachis.
Another Virginian species of Permian age described by Fontaine
and White[1264], _T. Newberriana_, is said to bear sori, but no
satisfactory information is given as to the nature of these organs.
Specimens referred with some hesitation to this species and to a
similar species, _T. coriacea_, have been described by Sellards[1265]
from material obtained from Permian beds in Kansas. The lamina of the
simple linear fronds is characterised by the occurrence of small oval
bodies half immersed in the substance of the leaf between the secondary
veins (figs. 330, D, E). One of these bodies is represented in an
apparently dehisced condition in fig. 330, D. Sellards suggests the
possibility that these bodies are sporangia, but, as he points out,
they afford no indication of cellular structure nor are they in direct
connexion with the veins.


_Taeniopteris jejunata_, Grand’Eury[1266].

This species differs from _T. multinervis_ in its bipinnate fronds;
the linear or oval-linear pinnae are attached by a short stalk to
the primary rachis and reach a length of 25 cm.; the veins are less
crowded, 12–15 per centimetre.

_T. jejunata_ is recorded from the Coal-fields of the Loire and
Commentry[1267] in France, from the Lower Permian of Thuringia[1268],
and elsewhere.


_Taeniopteris Carnoti_, Ren. and Zeiller[1269]. Fig. 330, A.

This species, founded on portions of pinnate fronds from the Coal-field
of Commentry, is characterised by rather broader (25–30 mm.) pinnules,
with short pedicels and a cordate base, reaching a length of 25–30 cm.
The secondary forked veins are more numerous than in _T. jejunata_. In
_T. multinervis_ the pinnules are still broader and have a stronger
midrib.

                   •       •       •       •       •

Several species of _Taeniopteris_ have been described from
Triasso-Rhaetic rocks in Europe, India, Tonkin and elsewhere. In
some cases it is practically impossible to recognise clear specific
distinctions between Rhaetic and Jurassic types.

From the Damuda and Panchet series of India (Triasso-Rhaetic)
Feistmantel has described large sterile fronds as _Macrotaeniopteris
Feddeni_[1270] which reach a breadth of 20 cm.: these may be compared
with the Indian species _Taeniopteris lata_ Oldham[1271], and to _T.
gigantea_ from the Rhaetic of Franconia[1272] and Scania. A specimen
of this species figured by Nathorst[1273] from Scania has a lamina 33
cm. broad. Other examples are afforded by _M. Wianamattae_ Feist.[1274]
from rocks of the same age in Australia and by _Taeniopteris superba_
Sap.[1275] from Lower Rhaetic rocks near Autun.

From the Rhaetic of Tonkin, Zeiller records several species, among
which may be mentioned _T. Jourdyi_ Zeill.[1276] and _T. spatulata_
MacClelland (fig. 330, B, C). Both have simple fronds. Those of _T.
Jourdyi_ reach a length of 10–40 cm. and a breadth of 10–70 mm.; the
rachis is characterised by crowded and discontinuous transverse folds,
and the secondary veins (35–50 per cm.) are usually at right angles
to the rachis. This Tonkin species is compared by Zeiller with the
European Rhaetic species _T. tenuinervis_ Brauns.

The polymorphism of the fronds is a striking feature: in one
case described by Zeiller the lamina appears to be divided into
segments like those characteristic of the leaf of the Cycadean
genus _Anomozamites_. It is obviously difficult in many instances
to distinguish between detached Taeniopteroid pinnae of a compound
frond and complete simple leaves. In some compound fern fronds, as
in the recent Polypodiaceous genus _Didymochlaena_, the pinnules are
deciduous, and the same feature undoubtedly characterised the fronds of
many extinct species. A specimen figured by Zeiller which shows several
petioles of _T. Jourdyi_ attached to a thick stem[1277] demonstrates
the simple nature of the leaves. In other cases, e.g. _T. vittata_,
specimens occur in which the slightly enlarged petiole-base has a
clean-cut surface indicating abscission from a rhizome (fig. 332).

The fronds described by Zeiller as _T. spatulata_[1278] (fig. 330,
B, C) closely resemble Jurassic leaves from Victoria referred to
_Taeniopteris Daintreei_ McCoy[1279].

[Illustration: FIG. 330.

  A. _Taeniopteris Carnoti_, Ren. and Zeill. (Nat. size. After
     Renault and Zeiller.)
  B. _T. spatulata_, McClell. (Nat. size. After Zeiller.)
  C. _T. spatulata._ (× 3. After Zeiller.)
  D. Supposed sporangium of _T. coriacea._ (× 15. After Sellards.)
  E. _T. coriacea._ (× 2. After Sellards.)]

Whether specifically identical or not, these leaves represent a
type distinguished from the other species of the genus by the small
breadth of the linear-lanceolate or linear-spathulate lamina, which
may be 6–15 cm. in length and 3–12 mm. broad. The lamina is often
characterised by transverse folds (fig. 330, C).


_Taeniopteris Carruthersi._ Fig. 331.

  1872. _Taeniopteris Daintreei_, Carruthers, Quart. Journ. Geol. Soc.
        Vol. XXVIII. Pl. XXVII. fig. 6.

  1883. _T. Carruthersi_, Tenison-Woods, Proc. Linn. Soc. N. S. Wales,
        Vol. VIII. p. 117.

[Illustration: FIG. 331. _Taeniopteris Carruthersi_, Ten.-Woods. Nat.
  size.]

The simple fronds included under this specific name are characterised
by a strong midrib from which numerous simple or forked secondary veins
are given off at a right angle or slightly inclined. The breadth of the
lamina decreases gradually towards the petiole. The Australian species
named by McCoy _Taeniopteris Daintreei_, to which Carruthers referred
the Queensland fossils, has a much narrower and more linear form of
frond, and for this reason Tenison-Woods instituted a new specific
name. _T. Carruthersi_ represents a form of leaf met with in Rhaetic,
or possibly Upper Triassic, rocks in S. Africa[1280] and Australia. A
very similar, perhaps an identical type, was described from Argentina
by Geinitz[1281] as _T. mareyiaca_: among many other examples of
this form of frond may be mentioned _T. immersa_[1282] Nath. from
the Rhaetic rocks of Scania and _T. virgulata_ from the Rhaetic of
Tonkin[1283].

A comparison of _Taeniopteris Carruthersi_ or various other “species”
of Rhaetic fronds with the Jurassic species _T. vittata_ illustrates
the slight and unimportant differences on which specific separation is
based. It is hopeless to attempt to draw a satisfactory distinction
between the numerous Taeniopteris fronds from Upper Triassic and
Jurassic rocks.


_Taeniopteris vittata_, Brongniart. Fig. 332.

The simple leaves to which Brongniart applied this name are
characteristic of the Inferior Oolite flora of England, and examples of
the same type are recorded from Jurassic rocks of India, Poland, the
Arctic regions, Japan, China, Australia and other countries[1284].

  Leaf linear-lanceolate, reaching a length of more than 20 cm. and
  a breadth of 3 cm. The lamina increases gradually in breadth from
  the base and tapers towards the apex. Numerous secondary veins are
  given off at right angles from a broad midrib: the lateral veins
  may be simple or forked close to their origin, near the margin, or
  in the intermediate portion, of the lamina.

It is exceedingly difficult to use _Taeniopteris_ leaves of this
form as evidence in regard to the Jurassic or Rhaetic age of
plant-bearing strata. The species _T. tenuinervis_ Brauns, as figured
by Schenk[1285] from the Rhaetic rocks of Germany and Persia, and
recorded from several other regions, presents a close agreement with
_T. vittata_. _Oleandridium lentriculiforme_ Etheridge[1286] from the
Hawkesbury series of Australia is another similar leaf. The species _T.
vittata_ from the Yorkshire coast, represented in fig. 332, shows a
well-preserved petiole with a clean-cut base like that of the petioles
of _Oleandra neriiformis_ and other recent ferns which are detached
from the rhizome by the action of an absciss-layer.

[Illustration: FIG. 332. _Taeniopteris vittata._ (British Museum No.
  39217. ⅔ nat. size.)]

A broader form of frond with similar venation was described by
Lindley and Hutton[1287] as _Taeniopteris major_. An examination of
the type-specimen from the Inferior Oolite of Yorkshire, now in the
Manchester Museum, led me to doubt the necessity of specific separation
from _T. vittata_[1288].

A smaller frond of the same general type as _T. vittata_ is recorded
from Wealden strata of North Germany and England under the name _T.
Beyrichii_[1289].


                              Weichselia.

This generic name was instituted by Stiehler[1290] for impressions
of bipinnate sterile fronds, presumably ferns, from Lower Cretaceous
rocks near Quedlinburg. The same type of leaf from English Wealden
beds had previously been referred by Mantell and other authors to
_Pecopteris_, and by Brongniart to his genus _Lonchopteris_[1291].
It is, however, advisable to follow Nathorst’s example[1292] and
restrict the latter name to Palaeozoic species. As already suggested,
it would obviate confusion to substitute a new generic designation
for _Lonchopteris_ in the case of Triassic species which are probably
members of the Osmundaceae. The type-species of Stiehler, _Weichselia
Ludowicae_[1293], does not differ in any important character from
_Weichselia Mantelli_, the species originally described by Stokes and
Webb from the Wealden of England as _Pecopteris reticulata_.


_Weichselia Mantelli_ (Brongn.)[1294]. Fig. 333.

  1824. _Pecopteris reticulata_, Stokes and Webb, Trans. Geol. Soc.
        [2]. Vol. I. p. 423, Pls. XLVI. XLVII.

  1828. _Lonchopteris Mantelli_, Brongniart, Prod. p. 6; Hist. vég.
        foss. p. 369, Pl. CXXXI.

  1894. _Weichselia Mantelli_, Seward, Wealden Flora, Vol. I. p. 114.
        Pl. X. fig. 3.

  1899. _Weichselia reticulata_, Fontaine, in Ward, Ann. Rep. U. S.
        Geol. Surv. p. 651.

  Frond bipinnate, rachis broad; pinnae very long, of uniform breadth
  and with prominent axes; pinnules crowded, entire, with obtuse
  apex, usually oblong but more or less triangular or rounded towards
  the distal ends of the pinnae. The pinnules, which may reach a
  length of 9 cm., are characterised by a fleshy lamina attached by
  the whole breadth of the base; the two rows of segments on each
  secondary rachis are usually inclined towards one another so that
  they form with the axis of the pinna a wide-open =V= instead of
  lying in one plane (fig. 333, C). From a median rib are given off
  numerous anastomosing branches (fig. 333, B).

[Illustration: FIG. 333. _Weichselia Mantelli._

  A. Part of a frond from the Wealden of Sussex, England. (British
     Museum; v. 2630. ¾ nat. size.)
  B. Pinnule from Bernissart, Belgium (× 3).
  C. _Weichselia erratica_, Nath. Section of pinna. (After Nathorst.)]

This characteristic Wealden species is recorded from England, Germany,
France, Belgium, Austria, Russia, Bornholm, North America, and Japan.
It is by no means certain that _Weichselia Mantelli_ is a true fern: no
satisfactory evidence of fructification has been adduced.

The broad and strong rachis is comparable with that of a Cycadean leaf
and the thick lamina suggests a plant of xerophilous habit. I have
retained the specific name _Mantelli_ on the ground of long established
usage instead of following Fontaine in his adherence to strict priority.


                             Glossopteris.

The name _Glossopteris_ was proposed by Brongniart in 1822[1295] for an
imperfect leaf-impression which he called _Filicites_ (_Glossopteris_)
_dubius_, but the specimen so named has since been identified as
part of a sporophyll of a _Lepidostrobus_. The author of the genus
afterwards published[1296] a diagnosis, based on well-preserved
leaves from Permo-Carboniferous rocks in Australia and India, of the
type-species _Glossopteris Browniana_, the Indian examples being
distinguished as _G. Browniana_ var. _indica_ while the Australian
form was named _G. Browniana_ var. _australasica_. Schimper[1297]
afterwards raised the Indian fossils to specific rank as _G. indica_
though some authors[1298] have continued to consider the two forms as
insufficiently distinct to be regarded as different species.

The genus _Glossopteris_ may be defined as follows:

  Leaves simple, varying considerably in size, shape, and venation
  characters, but almost without exception characterised by
  repeatedly anastomosing lateral veins. The leaves are of two
  kinds: (i) _foliage leaves_; apparently always sterile, usually
  spathulate, with an obtuse apex, a well-marked midrib which may
  persist to the apex or die out in the upper half of the lamina,
  characterised by its slight prominence and comparatively great
  breadth especially in the basal part of the frond. In most cases
  the lamina extends as a narrow margin to the leaf-base, but in
  a few forms there is a short petiole (fig. 334). Though usually
  spathulate, the frond may be linear-lanceolate, or ovate; the
  apex is sometimes acute. Leaves vary in length from 3 to 40 cm.
  and may in larger forms have a breadth of 10 cm. Numerous lateral
  veins curve upwards and outwards to the margin of the lamina or
  pursue a straight course almost at right-angles to the midrib. (ii)
  _Scale-leaves_[1299] which differ from the foliage-leaves in their
  much smaller size and in the absence of a midrib; they are deltoid,
  oval or cordate in shape and generally terminate in an acute apex;
  the edge of the lamina may be slightly incurved so that the leaf
  presents a convex upper surface supplied with anastomosing veins.
  The scale-leaves, which vary in length from about 1 to 6 cm.,
  probably acted as sporophylls. The only evidence as to the nature
  of the fructification so far obtained is represented by empty
  sporangium-like organs (1·2–1·5 mm. long by 0·6–0·8 mm. broad)
  frequently associated with the scale-leaves[1300].

  The leaves, in some cases at least, were borne near together on a
  cylindrical stem or rhizome which produced branched adventitious
  roots[1301]. The fossils long known as _Vertebraria_ were
  recognised by Zeiller[1302] and by Oldham[1303] as the stems of
  _Glossopteris_.

The systematic position of _Glossopteris_ must for the present be left
an open question. Though usually spoken of as a fern, it is noteworthy
that despite the enormous abundance of its foliage leaves in the
Permo-Carboniferous strata of India, Australia, South Africa, and South
America, no single example has been discovered which shows undoubted
remains of sori or sporangia. Many authors have described fertile
leaves of _Glossopteris_; but it was not until Arber’s discovery of
sporangia in close association with the scale-leaves that any light was
thrown on the nature of the reproductive organs.

The probability is that _Glossopteris_ was not a true fern but a
member of that large and ever-increasing class, the Pteridosperms.
This opinion is based largely on negative evidence. Such sporangia as
have been described may have contained microspores and the plant may
have been heterosporous. The occurrence of seeds in association with
Glossopteris fronds recorded by more than one writer[1304], though
by no means decisive and possibly the result of chance association,
is favourable to this view. Dr White[1305] has suggested that the
small leaves described by Zeiller[1306] as _Ottokaria bengalensis_
from Lower Gondwana (Permo-Carboniferous) rocks of India, and similar
fossils recorded by himself from Brazil as _O. ovalis_, may represent
“sporangiferous” organs of _Glossopteris_ or _Gangamopteris_, “both of
which are probably pteridospermic.” There is, however, no conclusive
evidence in support of this suggestion.

The genus, whatever its position may be, has a special interest for
the geologist and for the student of plant distribution; it is a
characteristic member of a Permo-Carboniferous flora which flourished
over an enormous area, including India, South Africa,—extending from
Cape Colony to Rhodesia and German East Africa[1307],—Australia,
and South America[1308]. This flora, known as the Glossopteris
flora, differed considerably in its component genera from that which
overspread Europe and North America and some more southern regions in
the Upper Carboniferous and Permian periods.

The discovery by Amalitzky[1309] of _Glossopteris_, and other genera
characteristic of the Glossopteris flora, in the Upper Permian rocks
in Vologda (Russia) demonstrates the existence of a northern outpost
of the southern botanical province, and Zeiller’s discovery of the
genus in the Rhaetic flora of Tonkin[1310] shows that _Glossopteris_
persisted beyond the limits of the Palaeozoic epoch. Dr David
White[1311] has recently proposed to re-christen the Glossopteris flora
the Gangamopteris flora on the ground that _Gangamopteris_ is strictly
Palaeozoic in its range, whereas _Glossopteris_ persisted into the
Mesozoic era; this is perhaps hardly a sufficient reason for giving up
so well established a title as the Glossopteris flora. A fuller account
of this southern flora must be reserved for another volume.


_Glossopteris Browniana_, Brongniart[1312]. Figs. 334–36.

The specific name _Browniana_ is now applied to obtusely pointed
leaves which sometimes reach a length of 15 cm., but are usually
rather shorter. In form and venation they closely resemble the leaves
of the recent genus _Antrophyum_ and species of _Acrostichum_. The
comparatively broad midrib may be replaced in its proximal portion by
several parallel veins: from it are given off numerous lateral veins
which form a reticulum characterised by meshes approximately equal in
size and elongated in a direction parallel to the general course of the
secondary veins (fig. 334).

[Illustration: FIG. 334. _Glossopteris Browniana_, Brongn. A. Nat.
  size: B × 3½.]

The drawings, originally published by Zeiller[1313], reproduced in fig.
335 illustrate the venation and its range of variation; the meshes
are usually hexagonal and arranged as shown in figs. A and B, but
occasionally (fig. 335, C) they follow a more steeply inclined course.

Small leaves with a more or less distinct midrib, 2–3 cm. in length,
supply transitional stages between foliage- and scale-leaves. In the
true scale-leaves spreading and occasionally anastomosing veins take
the place of the midrib and lateral veins of the ordinary frond.
McCoy[1314] in describing some Australian specimens of _Glossopteris_
in 1847 spoke of scale-like appendages of the rhizome which he
compared with the large ramenta of _Acrostichum_ and other ferns. It
was, however, Zeiller[1315] who first recognised the leaf-nature of
these scales and adequately described them; additional figures of
scale-leaves have been published by Mr Arber[1316] and by myself[1317].
The importance of these small leaves has been considerably increased
by Mr Arber’s discovery of associated sporangia which, as he suggests,
were probably borne on their lower concave surface.

[Illustration: FIG. 335. _Glossopteris Browniana_, Brongn. (After
  Zeiller. × 2.)]

The sporangia (fig. 336) are compared by Arber with the microsporangia
of recent Cycads and with the Palaeozoic sporangia described by Zeiller
as _Discopteris Rallii_ (fig. 256, D); the latter are distinguished by
the well-defined group of thicker walled cells representing the annulus
of true fern sporangia. We know nothing as to the contents of the
Glossopteris sporangia, whether they contained microspores or whether
they are the spore-capsules of a homosporous plant.

[Illustration: FIG. 336. _Glossopteris Browniana_, Brongn. Sporangia.
  (× 30). After Arber.]

The rhizome of _Glossopteris Browniana_ has been described in detail by
Zeiller, who first demonstrated that the fossils originally assigned by
Royle[1318] to the genus _Vertebraria_ represent the stem of this and,
as we now know, of some other species of _Glossopteris_. _Vertebraria_
occurs in abundance in Permo-Carboniferous strata in association with
_Glossopteris_; the differences between Australian, Indian, and South
forms, though expressed by specific names, are insignificant. The stems
are usually preserved in the form of flattened, single or branched,
axes sometimes bearing slender branched roots and characterised by
one or two, or less frequently three, longitudinal grooves or ridges
(fig. 337) from which lateral grooves or ridges are given off at right
angles, dividing the surface into more or less rectangular areas 1
cm. or more in length. The surface of these areas is often slightly
convex and in some specimens the outlines of cells may be detected. Mr
Oldham has described some interesting examples of _Vertebraria_ from
India in which the longitudinal and transverse grooves are occupied
by a dark brown ferruginous substance or by the carbonised remains of
plant-tissues (fig. 338, C, D). In transverse section, a _Vertebraria_
cast appears to be divided into a number of wedge-shaped segments
radiating from a common centre. Prof. Zeiller[1319] has figured
specimens of _Vertebraria_ with portions of Glossopteris fronds still
attached.

[Illustration: FIG. 337. _Vertebraria indica_, Royle. Nat. size. (After
  Feistmantel.)]

The rhizome of _Glossopteris_, as represented by the Vertebraria
casts, is aptly compared by Zeiller[1320] with that of the recent
Polypodiaceous fern _Onoclea struthiopteris_. Sections of the recent
stem (fig. 338, E, F) show that the form is irregularly stellate
owing to the presence of prominent wings which anastomose laterally
at intervals as shown by the examination of a series of sections. The
leaf-traces are derived from the steles of adjacent wings. Fig. 338
(B and A) represents somewhat diagrammatically a longitudinal and
transverse view of a _Vertebraria_; the radiating arms represented in
the transverse section (fig. A) are the stem ribs or wings and the
segments between them are intrusions of sedimentary material. The
rectangular areas characteristic of the surface of a _Vertebraria_ are
the intruded segments of rock: these are separated at intervals by
transverse grooves, which mark the course of vascular strands given off
at each anastomosis of the longitudinal wings to supply the leaves.

[Illustration: FIG. 338.

  A, B. _Vertebraria indica._ (After Zeiller.)
  C, D. _V. indica._ (Nat. size. After Oldham.)
  E, F. _Onoclea struthiopteris._ (× 2. After Zeiller.)]

Mr Oldham, who discovered the connexion between _Glossopteris_ and
_Vertebraria_ independently of Dr Zeiller, does not agree with the
interpretation of the structural features of the rhizome which Zeiller
bases on a comparison between Vertebraria and _Onoclea struthiopteris_.
Oldham[1321] describes _Vertebraria_ as consisting of a central axis
“joined to an outer rind by a series of radial septa,” the spaces
between the septa being divided into chambers by transverse partitions.
His view is that the rhizome of _Glossopteris_ was a cylindrical
organ and not an irregularly winged axis like the stem of _Onoclea_.
Zeiller[1322] has replied in detail to Oldham’s interpretation and
adheres to his original view, that the rhizome consisted of a solid
axis with radial wings or flanges which at intervals anastomosed
transversely in pairs at the nodes. It may, however, be possible
that the spaces between the longitudinal and transverse grooves on a
Vertebraria axis, which have been filled with the surrounding rock,
were originally occupied in part at least by secondary wood, and the
transverse strips of carbonaceous material[1323] lying in the grooves
may represent medullary-ray tissue and accompanying leaf-traces. The
longitudinal striations seen in some specimens of _Vertebraria_ on the
areas between the grooves may be the impressions of woody tissue. It
is impossible without the aid of more perfectly preserved material to
arrive at a satisfactory conception of the structural features of a
complete Glossopteris rhizome.

[Illustration: FIG. 339. _Glossopteris_ fronds attached to rhizome.
  (From a specimen lent by Dr Mohlengraaff. Considerably reduced.)]

In the specimen of _Glossopteris Browniana_ shown in fig. 339
several leaves are attached to an axis which shows none of the
surface-features of _Vertebraria_. I am indebted to the kindness of
Dr Mohlengraaff of Delft for the loan of this specimen which was
obtained from Permo-Carboniferous rocks in the Transvaal. An axis
figured by Etheridge[1324] from an Australian locality bears a tuft
of _Glossopteris_ leaves, possibly _G. Browniana_; in place of the
rectangular areas characteristic of _Vertebraria_ it shows transversely
elongated leaf-scars or, on the internal cast, imbricate rod-like
projections which Etheridge suggests represent vascular bundles.


_Glossopteris indica_, Schimper. Figs. 340, A, 341.

It is a question of secondary importance whether or not the fronds
which Brongniart spoke of as a variety of _Glossopteris Browniana_
should be recognised as specifically distinct. The careful examination
by Zeiller of the venation characters has, however, afforded
justification for separating _G. Browniana_ and _G. indica_. We must
admit that the slight and not very constant differences in the size
and form of the meshes produced by the anastomosing of the lateral
veins are characters which cannot be recognised as having more than
a secondary value, though, as a matter of convenience, we employ
them as aids to determination. The arbitrary separation of sterile
leaves, which differ by small degrees from one another in form and in
the details of venation, by the application of specific names is a
thankless task necessitated by custom and convenience; it is, however,
idle to ignore the artificial basis of such separation. Mr Arber has
recently published, in his valuable _Glossopteris Flora_, an analytical
key which serves to facilitate the description and determination of
different types of frond[1325].

[Illustration: FIG. 340.

  A. _Glossopteris indica_, Schimper. (½ nat. size.)
  B. _Glossopteris angustifolia_, Brongniart. (Nat. size.) From Arber,
     after Feistmantel.]

The large leaves of _Glossopteris indica_, reaching a length in
extreme cases of 40 cm. and a breadth of 10 cm., are characterised
by a rather greater regularity in the arrangement of the meshes and
by the greater parallelism of the upper and lower sides of each mesh
(fig. 341) and by less difference in size between the venation meshes
than in _G. Browniana_, the leaves of which are usually smaller. The
relatively thick epidermis consists of rectangular cells with stomata
in depressions[1326]. The scale-leaves[1327], rather larger than those
of _G. Browniana_, are more or less rhomboidal with rounded angles and
reach a length of 1·5–6 cm. and a breadth of 1·5–2·5 cm. The rhizome is
practically identical with that of _G. Browniana_[1328].

[Illustration: FIG. 341. _Glossopteris indica_, Schimp. (× 1½.) From
  Arber, after Zeiller.]

This species occurs in great abundance in the Permo-Carboniferous
rocks of India, Australia, and in various parts of South Africa,
and elsewhere. It has been recognised also by Amalitzky[1329] in
Upper Permian beds in Russia and by Zeiller in the Rhaetic series of
Tonkin[1330].

[Illustration: FIG. 342. _Glossopteris angustifolia_ var.
  _taeniopteroides_. (× 3½.)]


_Glossopteris angustifolia_, Brongniart. Figs. 340, B; 342.

It is convenient to retain this designation for linear fronds with an
acute or obtuse apex and a venation-reticulum composed of long and
narrow meshes (fig. 340, B). It is by no means unlikely, as Arber
suggests, that the same plant may have produced leaves of the _G.
indica_ type and narrower fronds which conform to _G. angustifolia_.
In his description of some Indian specimens of _G. indica_, Zeiller
draws attention to the variation exhibited in regard to the extent
of anastomosing between the secondary veins: some examples with very
few cross-connexions agree more closely with _Taeniopteris_ than
with _Glossopteris_ as usually defined[1331]. The venation shown in
fig. 342 illustrates an extreme case of what is almost certainly a
Glossopteris leaf of the _G. angustifolia_ type. This specimen, which
was discovered by Mr Leslie in the Permo-Carboniferous sandstone of
Vereeniging (Transvaal), has been referred to a variety of Brongniart’s
species as _G. angustifolia_ var. _taeniopteroides_[1332] on account
of the almost complete absence of any cross-connexions. The reference
to _Glossopteris_, which my friend Dr Zeiller suggested, is amply
justified by the form of the leaf as a whole, by the angle at which
the lateral veins leave the midrib, a feature in contrast to the
wider angle at which the lateral veins are usually given off in
_Taeniopteris_ (figs. 329, 332), and by the similarity to the Indian
specimens already mentioned. Several authors have described leaves or
leaflets under the generic name _Megalopteris_[1333] from Carboniferous
and Permian rocks which bear a close resemblance to the South African
variety, but in some cases at least _Megalopteris_ is known to be a
pinnate and not a simple leaf. The leaf figured by Jack and Etheridge
as _Taeniopteris_ sp.[1334] from Queensland may also be an example of
_Glossopteris_. Comparison may be made also with the Palaeozoic leaves
described in the first instance by Lesquereux and more recently by
Renault and Zeiller as species of _Lesleya_[1335] (fig. 347).

[Illustration: FIG. 343. _Blechnoxylon talbragarense_, Eth.: _s_,
  scale-leaves; _x_, secondary xylem. (After Etheridge. A × 2; B × 3;
  C much enlarged.)]


_Blechnoxylon talbragarense_, Etheridge. Fig. 343.

Under this name Etheridge[1336] described some specimens from the
Permo-Carboniferous Coal-Measures of New South Wales, which he regards
as a fern, comparable, in the possession of a cylinder of secondary
xylem, with the recent genus _Botrychium_ and with _Lyginodendron_
and other members of the Cycadofilices. The slender axis (1–3 mm. in
diameter) appears to consist of a zone of radially disposed tissue
(fig. 343, C, _x_), which is probably of the nature of secondary
xylem, enclosing a pith and surrounded externally by imperfectly
preserved remnants of cortex. Unfortunately no anatomical details
could be made out, but the general appearance, if not due to inorganic
structure, certainly supports Etheridge’s determination. The stem
bore at intervals clusters of linear-lanceolate leaves (reaching 12
mm. in length) in close spirals (fig. 343, A and B); the leaves are
characterised by a strong midrib and forked secondary veins. Small
“pyriform” bodies of the nature of scale-leaves occur in association
with the fronds (fig. 343, B, _s_).

In his description of this interesting plant, Etheridge quotes an
opinion which I expressed in regard to the comparison of the stem
with those of _Botrychium_, _Lyginodendron_, and other genera.
No satisfactory evidence has been found as to the nature of the
fructification. Although the leaves of _Blechnoxylon_ are much smaller
than those of _Glossopteris_, I am now disposed to regard the genus
as closely allied or even generically referable to _Glossopteris_.
The crowded disposition of the leaves is like that in _Glossopteris_,
shown in fig. 339 and in the figures published by Etheridge and by
Oldham; the association of scale-leaves and foliage-leaves is another
feature in common. The absence of a reticulum of anastomosing veins
can no longer be considered a fatal objection to the suggestion that
the Australian type may be a species of _Glossopteris_. If the view
that _Blechnoxylon_ is not a distinct genus is correct, the occurrence
of secondary xylem is favourable to the opinion already expressed
that _Glossopteris_ is more likely to be a Pteridosperm than a true
fern. The data at present available render it advisable to retain Mr
Etheridge’s name: the comparison with _Glossopteris_ lacks confirmation.

[Sidenote: BLECHNOXYLON]

[Illustration: FIG. 344. _Glossopteris retifera._ (Nat. size. From
  Arber, after Feistmantel.)]


_Glossopteris retifera_, Feist. Fig. 344.

In some _Glossopteris_ leaves the anastomosing secondary veins form
a coarser reticulum, as in the example represented in fig. 344. The
name _G. retifera_ was given by Feistmantel[1337] to Indian fronds of
this type; similar forms have been described as _G. conspicua_ and _G.
Tatei_. The type illustrated by _G. retifera_ is recorded also from
Permo-Carboniferous rocks in Zululand[1338], Natal, the Transvaal, Cape
Colony, and the Argentine.


                            Gangamopteris.

In 1847 McCoy[1339] described a leaf-fragment from Permo-Carboniferous
rocks in New South Wales as _Cyclopteris angustifolia_. The
type-specimen of this species, which is now in the Sedgwick Museum,
Cambridge, has been re-described by Mr Arber[1340]. Subsequently[1341]
McCoy instituted the generic name _Gangamopteris_ for leaves, like
that previously referred by him to _Cyclopteris_, from the Bacchus
Marsh Sandstone, of New South Wales, but he did not publish a diagnosis
of the genus until several years later[1342]. Feistmantel[1343], who
has described many species of _Gangamopteris_ from the Lower Gondwana
strata of India, slightly modified the original diagnosis. The genus
is represented by sterile fronds only. We know nothing of the stem,
and such evidence as is available in regard to the form of the fertile
leaves is of a circumstantial kind. It is, however, highly probable
that _Gangamopteris_ is not a true fern but a Pteridosperm.

  Leaves simple, sessile, varying in shape; obovate or spathulate,
  broadly lanceolate or rarely linear; the apex is usually blunt
  (fig. 345) but occasionally gradually tapered. In general
  appearance a Gangamopteris leaf is similar to that of _Glossopteris
  indica_, the chief distinction being the absence of a midrib.
  Gangamopteris leaves are on the whole larger than those of
  _Glossopteris_; many of them reach a length of 20 cm. and some of
  the large Indian fronds are nearly 40 cm. long. The venation of
  _Gangamopteris_ shows a greater uniformity in the size and shape
  of the meshes than that of _Glossopteris_. The middle of the
  lamina, especially in the lower part, is occupied by a few vertical
  veins from which branches curve upwards and outwards towards the
  edge of the lamina. The secondary veins are connected by frequent
  anastomoses and agree very closely with those of _Glossopteris_.
  The lamina becomes narrower towards the base, which is either
  cuneate or in some cases slightly auriculate (fig. 345).

As I have elsewhere pointed out[1344], the presence or absence of a
midrib is not in itself a character of real taxonomic importance. In
the recent fern _Scolopendrium vulgare_ the frond has a prominent
midrib, while in _S. nigripes_ there is no median rib. Mr Arber has
expressed the opinion that “it is extremely doubtful whether the genus
_Gangamopteris_ should not be merged in _Glossopteris_[1345].” The
retention of the two names is, however, convenient, and it would tend
to confusion were we to carry to its logical conclusion the view that
the recognised distinction between the two genera may not be a mark of
generic difference.

_Gangamopteris_ is confined to Palaeozoic strata, a fact which
leads White[1346] to speak of the Gangamopteris rather than of
the Glossopteris Flora. It occurs in South America, South Africa,
Australia, and India, extending as far north as Kashmir; it has been
discovered by Amalitzky in Permian rocks of Russia[1347]. The Russian
rocks in which _Glossopteris_ and _Gangamopteris_ were found are no
doubt of Permian age. In Australia, South Africa, Brazil and Argentina,
and in the Indian Coal-fields, _Gangamopteris_ is a characteristic
genus of Lower Gondwana rocks. These strata are usually spoken of as
Permo-Carboniferous in order to avoid the danger of attempting on
insufficient data a precise correlation with European formations.

Feistmantel speaks of _Gangamopteris_ as most abundant in the
Talchir-Karharbári beds, though it is represented also in the overlying
Damuda series. In Australia the genus occurs in rocks which correspond
in position and in their plant fossils with the Talchir-Karharbári
beds of India; similarly, in South Africa and South America the
Gangamopteris beds are homotaxial with those of India and Australia.
The leaf described by Carruthers[1348] from Brazil as _Noeggerathia
obovata_ (the type-specimen is in the British Museum) is no doubt
specifically identical with _Gangamopteris cyclopteroides_ Feist.[1349]
In a paper by Mr Hayden on Gangamopteris beds in the Vihi Valley,
Kashmir, evidence is adduced in support of the conclusion that the
rocks are “not younger than Upper Carboniferous and may belong to the
base of that subdivision or even to the Middle Carboniferous[1350].”
It would seem that _Gangamopteris_ was a very widely spread genus
during the latter part of the Carboniferous period in the vast
Southern Continent to which the name Gondwana Land is often applied,
and that it flourished in the Southern Flora during at least part of
the Permian period: with other members of the Glossopteris Flora it
migrated to the North where it has been preserved in Permian rocks of
Northern Russia. The Glossopteris Flora must have had its birth in the
Southern hemisphere. The conclusion seems inevitable that the leaves
of _Glossopteris_ and _Gangamopteris_ in the shales and sandstones of
India, South Africa, South America, and Australia are relics of the
vegetation of a continent of which these regions are the _disjuncta
membra_. Darwin wrote to his friend Hooker in 1881, “I have sometimes
speculated whether there did not exist somewhere during long ages an
extremely isolated continent, perhaps near the South Pole[1351].” It is
probable that _Gangamopteris_ is one of the genera which flourished on
this continent.


_Gangamopteris cyclopteroides_, Feistmantel[1352]. Fig. 345.

  1876. Feistmantel, Records Geol. Surv. India, Vol. IX. Pt iii. p. 73.

The specimen represented in fig. 345 illustrates the characters of this
commonest representative of the genus.

[Illustration: FIG. 345. _Gangamopteris cyclopteroides_, Feist. (Nat.
  size. From Arber, after Feistmantel.)]


_Gangamopteris kashmirensis_, Seward.

  1905. Seward, Mem. Geol. Surv. India, Vol. II. Mem. ii.

This type agrees closely with _G. cyclopteroides_ in size and in the
form of the leaf, but it is distinguished by the flatter form of the
arch formed by the lateral veins, by their greater inclination to the
margin of the lamina, and by the more acutely pointed apex of the
lamina. This species, though not very sharply distinguished from _G.
cyclopteroides_, is important as coming from beds which have been
assigned on other than palaeobotanical evidence to an Upper or possibly
a Middle Carboniferous horizon[1353].

We have no definite information in regard to the nature of the
reproductive organs of _Gangamopteris_, but such evidence as there is
supports the view expressed by Dr White[1354] and shared by some other
authors that _Gangamopteris_ and _Glossopteris_ should be assigned to
the Pteridosperms. Despite the abundance of _Gangamopteris_ leaves,
no fertile specimen has been discovered. This negative evidence
may prove to be as correct as that which led Stur[1355] to exclude
_Neuropteris_, _Alethopteris_ and _Odontopteris_ from the ferns. The
only evidence of a positive kind is that furnished by Dr David White in
his recent Report on the Palaeozoic Flora of South Brazil. This author
describes some small Aphlebia-like leaves under two new generic names
_Arberia_[1356] and _Derbyella_[1357]. The differences between the two
sets of specimens, so far as can be determined from the reproductions
of imperfect impressions, are slight, and it is by no means clear that
a distinction of generic rank exists. These scale-leaves are on the
average about 2 cm. in length; the lamina is oval or rounded and has
more or less prominent lobes. In _Derbyella_ there are indications
of anastomosing veins. The specimens referred to _Arberia minasica_
are, as White points out, very similar to the fossil described by
Feistmantel from Lower Gondwana rocks of India as probably a portion of
an inflorescence of _Noeggerathiopsis_[1358]. Feistmantel’s specimen is
represented in fig. 346: the curled lobes may have originally borne
seeds. In the Brazilian examples the abruptly truncated lobes “bear
evidence of separation from reproductive bodies.” An important point
is the association of these scale-leaves with _Gangamopteris_ fronds
and with gymnospermous seeds of the _Samaropsis_ type. On the leaves
assigned to _Derbyella aurita_ circular depressions occur at the base
of the lobes which are described as probably due to sporangia.

Dr White’s discovery gives us increased confidence in expressing the
view that _Gangamopteris_ bore its reproductive organs on specialised
leaves very different from the sterile fronds; it also strengthens
the suspicion that the genus is a member of the class of seed-bearing
fern-like plants.

[Illustration: FIG. 346. _Arberia_ sp. (= _Noeggerathiopsis_ of
  Feistmantel). (Nat. size. After Feistmantel.)]


                               Lesleya.

This generic designation was instituted by Lesquereux[1359] for
simple oval-linear leaves from the Coal-Measures of Pennsylvania. The
leaves so named are probably generically identical with the specimen
doubtfully assigned by Brongniart[1360] to the Coal-Measures, and
made by him the type of the genus _Cannophyllites_ on the ground of
a resemblance to the leaves of the recent flowering plant _Canna_.
Fig. 347 illustrates the form of a _Lesleya_ leaf from the Coal-basin
of Gard, named by Grand’Eury _L. simplicinervis_[1361], a type in
which the veins are frequently unbranched and not repeatedly forked
as in most examples of the genus (fig. 329, C). The features of the
genus are, the oval-linear or lanceolate shape of the presumably
simple frond, its entire or, in one species at least (_L. Delafondi_,
Zeill.), finely dentate margin, the stout rachis giving off at a very
acute angle numerous dichotomously branched secondary veins. In _L.
Delafondi_ (fig. 329, C), described by Zeiller[1362] from the Lower
Permian of Autun, the frond may reach a length of more than 20 cm. and
a breadth of 8 cm. Similar species are represented by _L. ensis_[1363]
from the coal-field of Commentry, and _L. grandis_[1364] from Upper
Carboniferous rocks of North America. The genus is characteristic of
Upper Carboniferous and Lower Permian strata: the form of the leaf
and the direction of the secondary veins suggest comparison with
_Glossopteris_, but in _Lesleya_ there are no cross-connexions between
the veins. Nothing is known as to the fructification, a fact which
naturally evokes the opinion that the genus is a Pteridosperm[1365]
and not a true fern. Some years before the discovery of Pteridosperms,
Grand’Eury[1366] suggested that _Lesleya_ might be a Gymnosperm; his
opinion being based on the woody nature of the rachis and on the simple
venation of _Lesleya simplicinervis_.

[Illustration: FIG. 347. _Leslya simplicinervis_, Grand’Eury.
  (Reduced: after Grand’Eury.)]


                            Neuropteridium.

In their monograph of fossil plants from the Bunter Series of the
Vosges, Schimper and Mougeot[1367] described some pinnate leaves of
ferns as species of the genus _Neuropteris_. In 1869 Schimper[1368]
placed these in a new sub-genus _Neuropteridium_, in order to draw
attention to the fact that their fronds appear to be simply pinnate
and not bipinnate or tripinnate as in _Neuropteris_. The type-species
of _Neuropteridium_ is _N. grandifolia_ Sch. and Moug. from the
Bunter Sandstones of the Vosges. The genus includes Triassic European
species and the widely distributed Permo-Carboniferous species from
Brazil[1369] originally described by Carruthers as _Odontopteris
Plantiana_. It is probable that some Carboniferous plants, particularly
species from the lower members of the formation, referred to the genus
_Cardiopteris_, are not genetically distinct from the Indian and
southern hemisphere type _Neuropteridium validum_ (= _Odontopteris
Plantiana_).

  Fronds pinnate, linear; a broad rachis bears pinnules which may
  be either semicircular or broadly linear with an entire or lobed
  margin. The longer pinnules may exceed 6 cm. in length. The
  pinnules agree with those of _Neuropteris_ in being attached by
  the median portion of the lamina and not by the whole base, which
  is more or less auriculate. In some cases the repeatedly forked
  veins diverge from the centre of the pinnule base; in others there
  is a midrib which persists for a short distance only, and in some
  species the more persistent median vein gives the segments a closer
  resemblance to those of _Neuropteris_. Fructification unknown,
  with the exception of obscure indications of sporangia (?) on the
  fertile leaves of a Triassic species.

[Illustration: FIG. 348. _Neuropteridium validum_, Feist. Nat. size.
  From the Karharbári Coal-field, India. From Arber, after
  Feistmantel.]


_Neuropteridium validum._ (Feistmantel[1370]). Fig. 348.

  1869. _Odontopteris Plantiana_, Carruthers, Geol. Mag. Vol. VI. p. 9,
        Pl. VI. figs. 2, 3.

  1878. _Neuropteris valida_, Feistmantel, Mem. Geol. Surv. India,
        Foss. Flor. Gondwana Syst., Vol. III. p. 10, pl. II.–VI.

  1880. _Neuropteridium validum_, Feistmantel, _Ibid._ 2, p. 84.

The specimen represented in fig. 348 illustrates the main features
of _Neuropteridium validum_. This species is referred to by Dr
White[1371] as _N. Plantianum_ on the ground of priority, and with a
view to perpetuate the name of the English engineer Nathaniel Plant who
discovered the species in a Brazilian Coal-field in the province of Rio
Grande do Sul. Feistmantel’s specific name is however retained as being
much better known. An examination of Mr Plant’s specimen in the British
Museum led me[1372] to speak of the Brazilian species as identical with
_N. validum_ described by Feistmantel from Lower Gondwana rocks of
India. Zeiller[1373] had previously drawn attention to the resemblance
between the two sets of specimens. The frond of _N. validum_ may exceed
50 cm. in length. The lower pinnules may be entire and semicircular in
form while the upper and larger segments, which may reach a length of 5
or 6 cm., are characterised by broad lobes (fig. 348).

This type is represented in the flora of the Talchir-Karharbári series
(Lower Gondwana) of India[1374], in Permo-Carboniferous rocks of Brazil
and Argentine[1375], and in the sandstones of Vereeniging on the
borders of the Transvaal and Cape Colony. It is a characteristic member
of the Glossopteris Flora and occurs in association with _Glossopteris_
and _Gangamopteris_.


_Neuropteridium intermedium_ (Schimper). Fig. 349.

This species has been figured by Schimper and Mougeot[1376] from the
Bunter of the Vosges and more fully described by Blanckenhorn[1377]
from the Bunter beds of Commern. The pinnate leaves reach a length of
65 cm.; the lower semicircular pinnules pass gradually into broadly
linear segments characterised by an auriculate base and a Neuropteris
type of venation (fig. 354, D′, E). In the example reproduced in fig.
349 from one of Blanckenhorn’s figures, the fronds are attached to a
short and thick rhizome bearing roots and portions of old petioles.

[Illustration: FIG. 349. _Neuropteridium intermedium_ (Schimp.). (After
  Blanckenhorn. ¼ nat. size.)]

An example of another Triassic species is afforded by _Neuropteridium
grandifolium_ Schimp. and Moug., which agrees very closely with _N.
validum_ in the size and shape of the pinnules. The occurrence in
Lower Mesozoic European rocks of fronds hardly distinguishable from
the older southern species may be regarded as favourable to the view
already expressed, that some at least of the Permo-Carboniferous plants
migrated north of the Equator. The resemblance between the Vosges
Triassic species of _Schizoneura_[1378] and the examples of this genus
recorded from the Lower Gondwana rocks of India affords additional
evidence of a northern migration.

Our knowledge of the reproductive organs of _Neuropteridium_
is practically _nil_. There is no doubt that Zeiller[1379] and
Blanckenhorn[1380] are correct in regarding the Bunter fronds assigned
by Schimper and Mougeot to the genus _Crematopteris_ as the fertile
leaves of _Neuropteridium intermedium_ or some other species from the
same horizon. These fronds bear crowded pinnules similar to those of
_Neuropteridium intermedium_, _N. Voltzii_[1381], and other species,
exhibiting on the exposed surface numerous carbonaceous spots which may
be the remains of sporangia.


                             Cardiopteris.

Schimper[1382] applied this generic name to Lower Carboniferous
fronds of a simple-pinnate habit which had previously been described
as species of _Cyclopteris_. _Cardiopteris frondosa_ may serve as a
typical example. This species, originally described by Goeppert as
_Cyclopteris frondosa_ (fig. 350), is recorded from Lower Carboniferous
rocks in the Vosges district[1383] in Silesia, Moravia[1384], and
Thuringia[1385]. The pinnules, which are attached in opposite pairs to
a broad rachis, vary in length from 2 to 10 cm. and have a breadth of
2 to 8 cm.; in manner of attachment and venation they agree with those
of _Neuropteridium validum_. The venation is very clearly shown in a
drawing of some large pinnules figured by Stur[1386].

The specimen of _Cardiopteris frondosa_, a portion of which is shown
in fig. 350 on a slightly reduced scale, was originally figured by
Schimper from an unusually good example in the Strassburg Museum.
Schimper’s drawing hardly does justice to the original specimen.

A frond bearing rather narrower pinnules, alternately placed on the
rachis, which Fritsch has described as _Cardiopteris Hochstetterii_
var. _franconica_ from the Culm of Thuringia, bears a close resemblance
to _Neuropteridium validum_ but differs in the entire margin of the
pinnules. An Upper Carboniferous species from Russia described by
Grigoriew[1387] as _Neuropteris_, cf. _cordata_ var. _densineura_,
represents another form of similar habit.

[Illustration: FIG. 350. _Cardiopteris frondosa_ (Goepp.). (¾ nat.
  size. After Schimper.)]

Schuster[1388] has recently proposed a new generic name _Ulvopteris_
for a fragment of a pinna from the Coal-Measures of Dudweiler in
Germany bearing large pinnules, which he compares with those of
_Cardiopteris_ and species of _Rhacopteris_. The specimen appears to be
indistinguishable from some of those already referred to as conforming
to _Neuropteridium_, and it is difficult to recognise any reason for
the creation of a new generic name.

We cannot hope to arrive at any satisfactory decision in regard to the
precise affinity between _Neuropteridium validum_ and species referred
to _Cardiopteris_ and other genera so long as portions of sterile
fronds are the only tests at our disposal. It is difficult to determine
whether a specimen consisting of an axis bearing pinnules represents a
large pinna of a bipinnate frond or if it is a complete pinnate leaf.
There is, however, no adequate reason for supposing that the presumably
pinnate fronds from the Gondwana Land rocks are generically distinct
from the Lower Carboniferous European species _Cardiopteris frondosa_.
Granting the probability that both genera are Pteridosperms and
closely allied to one another, the two generic names may be retained
on the ground of long usage and in default of satisfactory evidence
confirmatory of generic identity. _Cardiopteris_ would thus stand for
a type of frond characteristic of the Lower Carboniferous strata of
Europe, while _Neuropteridium_ is retained for the Southern species _N.
validum_, and for others from the Trias of the Vosges.


                               Aphlebia.

This name was proposed by Presl[1389] for large leaf-like impressions
having a pinnate or pinnatifid form and characterised by a confused
irregular type of venation, or by a fine superficial striation or
wrinkling which simulates veins. Gutbier had previously described
similar fossils as _Fucoides_, and other authors have described
Aphlebiae as species of _Rhacophyllum_, _Schizopteris_, and other
genera[1390]. The term _Aphlebia_ is retained, not as denoting a
distinct genus but (i) as a descriptive name for detached leafy
structures similar to those figured by Presl, which are now recognised
as laminar appendages of the petioles of ferns or fern-like fronds, and
(ii) as an epithet for highly modified pinnules which frequently occur
at the base of the primary pinnae of Pecopteroid and Sphenopteroid
fronds (e.g. _Dactylotheca plumosa_, fig. 293)[1391].

Modified pinnules, similar in their reduced and deeply dissected
lamina to those represented in fig. 293, are frequently found at the
base of the primary pinnae of Palaeozoic species of _Sphenopteris_
and other genera of Pteridosperms or ferns, including members of
the Coenopterideae. Potonié[1392] gives a list of various types of
Aphlebiae in his paper on these organs. A striking case has recently
been described by Zeiller in a French Upper Carboniferous species,
_Sphenopteris Matheti_[1393]. It would seem that the larger examples of
Aphlebiae are more frequently associated with the compound leaves of
Pteridosperms than with those of Ferns[1394].

As examples of the larger types of Aphlebiae reference may be made to
_Aphlebia crispa_ (Gutb.)[1395], which reaches a length of nearly 60
cm. and has the form of a more or less triangular pinnate leaf divided
into decurrent deeply lobed segments, to a similar species represented
by _A. Germari_ (= _Schizopteris lactuca_ Germ.)[1396] which simulates
the leaves of endive (_Cichorium endivia_ L.), and to some large forms
figured by Grand’Eury[1397] as species of _Schizopteris_.

Aphlebiae such as that figured by Kidston[1398] as _Rhacophyllum
crispum_, with narrow ultimate segments, might easily be mistaken for
the impressions of an alga.

The term _Aphlebia_ may be applied also to the Cyclopteroid pinnules
on the petioles of some species of _Neuropteris_, _Odontopteris_
and _Archaeopteris_. Goebel[1399] has referred to the application
by Potonié and other authors of the term Aphlebioid to the pinnules
which serve as bud-protecting organs in recent fronds of _Gleichenia_
(fig. 226, p. 290); he expresses the opinion that it is superfluous
and misleading to make use of a special designation for structures
which are undoubtedly modified pinnules. In the case of fossils it is,
however, convenient to employ the term _Aphlebia_ as a descriptive
name for modified pinnules or stipular structures which cannot
be connected with definite species of fronds. It is clear that
some Aphlebiod leaflets, such as those of _Dactylotheca_, served
as protective organs for the unexpanded pinnae[1400], and in all
probability the large Aphlebiae served the same purpose as the fleshy
stipules of _Angiopteris_ and _Marattia_ which cover the uncoiled
fronds. The pinnatifid scale-leaves of considerable size (fig. 351)
which occur in the leaf-axils or as ochrea-like stipules on the fronds
of _Gunnera_ (a tropical and subtropical Dicotyledonous genus) bear a
very close resemblance to some Palaeozoic Aphlebiae, e.g. _Aphlebia
crispa_ (Gutb.). The recent and fossil scale-leaves may be regarded as
similar in function as in form; moreover the delicate coiled fronds
of Palaeozoic Pteridosperms or ferns, like those of some recent
flowering plants, may have been kept moist by a secretion of mucilage.
The pinnatifid stipules of _Marattia fraxinea_ (fig. 241, B, p. 317)
resemble certain fossil Aphlebiae, and the wrinkled surface of the
recent stipules presents an appearance similar to that which in some
fossil forms has been erroneously described as veining. It is not
improbable that mantle-leaves of such recent ferns as _Polypodium
quercifolium_ (fig. 234, M, p. 303) are comparable with some fossil
Aphlebiae which may have served as humus-collectors for Palaeozoic
epiphytes.

[Illustration: FIG. 351. Scale-leaf of _Gunnera manicata_. (Slightly
  reduced. M.S.)]

The filiform appendages on the petioles of the recent fern _Hemitelia
capensis_ (fig. 235, p. 304) have often been compared with the
aphlebioid leaflets of fossil fronds.

Potonié who has discussed the nature of Aphlebiae regards them as
vestiges of a once continuous lamina, which formed a winged border to
the branched axes of more primitive forms of fronds. It is possible
that the pinnules between the pinnae on the rachis of _Archaeopteris_
and the Cyclopteroid leaflets of _Neuropteris_ and _Odontopteris_ may
have the morphological significance attributed to them by Potonié. In
some cases it is probable that the Aphlebiae, whether vestiges or not,
served the purpose of protecting either the whole frond or individual
pinnae. Aphlebiae, though especially characteristic of Palaeozoic
leaves, are occasionally met with in the form of modified pinnules at
the base of the primary pinnae on Mesozoic ferns, e.g. in _Coniopteris
hymenophylloides_[1401].

In some fern fronds the lowest pinnule of each pinna differs in shape
or size from the normal ultimate segments, but it would be almost
affectation to extend the use of the term _Aphlebia_ to such pinnules.
The Jurassic species _Cladophlebis lobifolia_ (Phill.) is a case
in point[1402]. In this fern, which some authors speak of, without
sufficient reason, as _Dicksonia lobifolia_[1403], the lowest pinnule
is large and different in shape from the others.

[Illustration: FIG. 352.

  A. _Sphenopteris obtusiloba_. Pinnule. (Enlarged. After Zeiller.)
  B, C. _S. obtusiloba_. (⅞ nat. size. After Zeiller.)
  D. _Pecopteris arborescens_. (Slightly enlarged. After Zeiller.)
  E. _Sphenopteris furcata_ (= _Diplotmema furcatum_). (Slightly
     enlarged. After Zeiller.)]


                             Sphenopteris.

_Sphenopteris_ is one of the many generic names which we owe to
Brongniart[1404]. It is the generic designation used for a great number
of Palaeozoic and later fronds, most of which are those of true ferns
while some Palaeozoic species are undoubted Pteridosperms. The genus,
which is purely provisional, includes members of widely different
families possessing pinnules of the same general type, such as is
represented in some recent species of _Davallia_, _Asplenium_, and
other ferns.

  The fronds of _Sphenopteris_ may be bipinnate, tripinnate, or
  quadripinnate; the rachis may be dichotomously branched or the
  branching may be of the pinnate type characteristic of most recent
  ferns. The pinnules are small; they vary considerably in shape even
  in a single frond, but the chief characteristics are: the lobed
  lamina, contracted and often wedge-shaped at the base (fig. 352),
  the dichotomously branched veins radiating from the base or given
  off from a median rib at an acute angle. The lamina may be divided
  into a few bluntly rounded lobes (fig. 352, C) or deeply dissected
  into linear or cuneate segments (fig. 352, A, B, E).

Examples of Sphenopteroid leaves have already been described under
the genera _Coniopteris_, _Onychiopsis_, _Ruffordia_, etc. Among the
numerous examples of _Sphenopteris_ species from the Carboniferous
rocks mention may be made of _Sphenopteris obtusiloba_ Brogn.[1405]
(fig. 352, A–C), which occurs in the Middle and Lower Coal-Measures
of Britain[1406]. This type is characterised by the almost orbicular,
oval or triangular pinnules which may reach a length of 15 mm.; they
are occasionally entire, but more usually divided into 3 to 5 rounded
lobes. The forked veins radiate from the base of the pinnule. The
rachis may be dichotomously branched. Fructification unknown.

The species _S. furcata_ Brongn.[1407], characteristic of the Middle
and Lower Coal-Measures of Britain (fig. 352, E), is referred to under
Stur’s genus _Diplotmema_[1408] in which it is included by some authors
solely because of the dichotomous habit of branching of the pinnae.

The pinna represented in fig. 353 illustrates a similar type of
pinnule. This species, which is very common in the Calciferous
Sandstone of Scotland, was described by Lindley and Hutton as
_Sphenopteris affinis_[1409].

The fronds of _Sphenopteris affinis_ were discovered by Mr
Peach[1410] in a fertile condition, but he regarded the reproductive
organs as those of a plant parasitic on the _Sphenopteris_ fronds.
Kidston[1411] substituted Stur’s genus _Calymmatotheca_ for
_Sphenopteris_ on the ground that the sporangia figured by Peach
under the name _Staphylopteris Peachii_ bear a close resemblance
to the organs which Stur described as valves of an indusium in his
species _Calymmatotheca Stangeri_[1412]. An examination of Stur’s
specimens by Miss Benson[1413] and by Prof. Oliver and Dr Scott has
confirmed Stur’s interpretation of the appendages at the tips of the
fertile pinnae as valves of an indusial or cupular structure. The
superficially similar bodies on the fertile pinnae of _S. affinis_
are however true sporangia, and cannot legitimately be included in
the genus _Calymmatotheca_ as described by Stur. For this reason
Miss Benson institutes a new genus _Telangium_, the type-species
of which, _T. Scotti_ from the Lower Coal-Measures of Lancashire,
is based on petrified material. The Scotch species _Sphenopteris
affinis_ (= _Calymmatotheca affinis_ of Kidston) is also transferred
to _Telangium_; the sporangia are considered by Miss Benson to be
microsporangia. This with other species is no doubt correctly included
in the Pteridosperms. A complete frond of _Sphenopteris affinis_,
showing a regular dichotomy of the main axes, is represented by an
admirable drawing in Hugh Miller’s _Testimony of the Rocks_[1414].

[Illustration: FIG. 353. _Sphenopteris affinis_, Lind. and Hutt. From
  the Calciferous Sandstone of Burdiehouse (Scotland). (Sedgwick
  Museum, Cambridge.) M.S.]

Some of the Palaeozoic species of _Sphenopteris_ probably represent
the fronds of true ferns, but others are known to have been borne
by Pteridosperms. _S. Hoeninghausi_ (fig. 290, C, p. 399) is the
foliage of _Lyginodendron_, and Scott[1415] speaks of three species,
_S. dissecta_, _S. elegans_, and _S. Linkii_ as the leaves of
_Heterangium_. Grand’Eury[1416] has recorded the occurrence in French
Coal-Measures of seeds in association with other Sphenopteroid fronds.


                Mariopteris, Diplotmema, Palmatopteris.

The discovery of sporangia on the fronds of several Palaeozoic species
of _Sphenopteris_ and _Pecopteris_ has led to the institution of new
generic names, which indicate an advance in knowledge beyond the stage
implied by the use of those provisional designations based solely on
the form and venation of the pinnules. Other names have been created by
authors in place of _Sphenopteris_ and _Pecopteris_ on the ground that
a striking feature in the mode of branching of fronds is sufficiently
important to justify generic recognition even in the absence of
fertile specimens. As examples of designations based primarily on
the branch-system of compound leaves, the genera _Mariopteris_,
_Diplotmema_, and _Palmatopteris_ may be briefly considered (fig. 354
A–C). Dr Kidston[1417] is of opinion that the creation of new genera
for purely vegetative characters of fronds is of no real advantage, and
he prefers to retain the older provisional names for species known only
in the sterile condition. On the other hand, if we are sufficiently
familiar with specimens large enough to enable us to recognise a
well-defined morphological character, it may serve a useful purpose to
employ a generic designation for features which may have a phylogenetic
value. A comparative examination of Palaeozoic, Mesozoic, and recent
compound fronds, including both Pteridosperms and true ferns, brings
to light certain distinguishing features characteristic of the older
types which, as Potonié maintains[1418], point to the derivation of
the pinnate habit from a primitive dichotomous system of branching.
For a more complete discussion of this question reference should be
made to Potonié’s suggestive papers. Among recent ferns _Matonia_ and
_Dipteris_, two survivals from the past, afford instances of fronds
with a branching system of the dichotomous type.

Similarly, in _Gleichenia_, _Lygodium_, and more rarely in species of
Polypodiaceae (_e.g._ _Davallia aculeata_, fig. 232) dichotomy is a
striking feature of the fronds. In the great majority of recent ferns
the fronds have assumed a pinnate habit. Among Palaeozoic fern-like
fronds dichotomous branching of the main rachis and of the pinnae is
much more common. Potonié draws attention to several other features
which distinguish Palaeozoic fronds from the majority of later species:
the frequent occurrence of pinnules borne directly on the main rachis
(fig. 354, D), and of modified pinnules or Aphlebiae on the rachis
and petiole, are characters to which he attributes an evolutionary
significance. The main point is that a comparative examination of
leaf-form affords evidence in favour of the view that the modern type
of frond, with its naked rachis bearing two rows of pinnae, has been
derived from a less specialised type in which the distinction between
the parts of the leaf is much less evident. The primitive leaf was
probably a dichotomously branched axis provided with a continuous
lamina which eventually became broken up into separate lobes or
pinnules.

As the dichotomy of the frond became less regular, a pinnate habit was
acquired, as is clearly seen in many Palaeozoic types which constitute
connecting links between forked and pinnate fronds (fig. 354, D). The
Aphlebiae may be remnants of the once-continuous lamina on the petiole,
and the normal pinnules borne on the rachis may be regarded as the
attributes of fronds in which the division of physiological labour had
not reached the stage which characterises the leaves of recent ferns.


                            _Mariopteris._

This name, which is due to Zeiller[1419], is applied by him to
Palaeozoic fronds characterised by a double bifurcation of the rachis
of the primary pinnae. _Mariopteris muricata_ (= _Pecopteris muricata_
Schloth.) may be taken as the type of the genus. This species is
common in the Lower and Middle Coal-Measures of Britain and rare
in the Upper Coal-Measures[1420]. It is described by Kidston[1421]
as one of the most polymorphic and widely distributed Coal-Measure
species. The pinnules as seen in fig. 364, B, are of the Sphenopteroid
type. No fertile specimens are known, but it is significant that
Grand’Eury[1422] has recorded the association of _Mariopteris muricata_
and seeds.

The main rachis gives off alternate naked branches, each of which
bifurcates at its apex into two short naked axes, and these are again
forked, the ultimate branches having the form of bipinnate pinnae
provided with large Sphenopteroid pinnules (fig. 354, B). Zeiller
includes in _Mariopteris_ some species which Stur[1423] referred to
his genus _Diplotmema_. Possibly some of the Palaeozoic fronds with a
zigzag rachis may have been climbers like _Lygodium_.

[Illustration: FIG. 354.

  A. _Palmatopteris._
  B. _Mariopteris._ (A, B, after Potonié.)
  C. _Diplotmema Zeilleri_, Stur. (After Zeiller.)
  C′. _D. Zeilleri._ Pinnule. (× 3. After Zeiller.)
  D.  _Neuropteris macrophylla._ (British Museum.)
  D′. _N. macrophylla._ Pinnule. (Slightly enlarged. After Kidston.)
  E. _N. heterophylla._ Pinnule. (Slightly enlarged. After Zeiller.)
  F. _N. Scheuchzeri._ (Slightly reduced. After Kidston.)
  G. _Alloiopteris Essinghii._ (Enlarged. After Potonié.)]


                             _Diplotmema._

This generic name is employed by Zeiller[1424] and other authors in
a more restricted sense than that in which it was originally used by
Stur. The Upper Carboniferous species _Sphenopteris furcata_ Brongn.
(fig. 352, E) may serve as the type. This species occurs in the Middle
and Lower Coal-Measures of Britain[1425]. The main rachis gives off
branches as in _Mariopteris_, but in _Diplotmema_ each naked lateral
branch is forked at its apex into two opposite pinnae bearing deeply
dissected Sphenopteroid pinnules. Zeiller[1426] and Stur have recorded
fertile specimens of _Diplotmema_, but in no case have actual sporangia
been discovered. In the species _Diplotmema Zeilleri_ Stur (fig. 354,
C, C′) two Aphlebiae occur at the base of each secondary axis[1427].
It has been pointed out by Potonié that in _Diplotmema furcatum_ the
equal dichotomy of the lateral branches is not characteristic of the
frond as a whole. In the case of branches higher on the rachis the
dichotomy becomes unequal and the forked axis is gradually replaced by
a simple pinna (fig. 354, A). For this type of frond, Potonié proposed
the generic name _Palmatopteris_ in place of _Diplotmema_, which
he discards. The long comparatively slender rachis of _P. furcata_
suggests comparison with the liane species of _Lygodium_[1428].

[Illustration: FIG. 355.

  A. _Cephalotheca mirabilis_, Nath. Fertile pinnae. (Partially
     restored. After Nathorst.)
  B. _C. mirabilis._ Sterile pinnule. Nat. size. (After Nathorst.)]


                             Cephalotheca.

This genus was proposed by Nathorst[1429] for some peculiar bipinnate
fertile fronds from the Upper Devonian rocks of Bear Island. The pinnae
bear slender forked ultimate segments represented by a few detached
fragments (fig. 355, B), associated with the rachises. The fertile
pinnae are given off in opposite pairs from the main axis over which
they are concrescent (fig. 355, A). A mop-like cluster of sporangia is
borne on the lower surface and close to the base of a fertile pinna:
the exannulate sporangia are compared with those of _Scolecopteris_.
Nathorst compares _Cephalotheca_ with a Belgian species of Upper
Devonian age described by Crépin[1430] as _Rhacophyton condrusorum_ and
by Gilkinet[1431] as _Sphenopteris condrusorum_. A similar fossil is
also described by Baily[1432] as _Filicites lineatus_ from the Kitorkan
Grits of Ireland.

The position of _Cephalotheca_ cannot be definitely determined from
the available data, but it is more probable that it was a seed-bearing
Pteridosperm and not a true fern. Zeiller[1433] has recently expressed
the same opinion.


                             Thinnfeldia.

The genus _Thinnfeldia_, founded by Ettingshausen in 1852[1434] on
some Hungarian Liassic specimens, though frequently included in the
Filicales, cannot be said to occupy that position by virtue of any
well-authenticated filicinean features. It is by no means improbable
that many of the species referred to this genus are closely allied to
Palaeozoic Pteridosperms.

_Thinnfeldia_ may be briefly defined as follows:

  Fronds simple and pinnatifid, pinnate or bipinnate: rachis broad
  and occasionally dichotomously branched. Pinnules often fleshy or
  coriaceous; broadly linear, entire or lobed, provided with a midrib
  from which simple or forked secondary veins are given off at an
  acute angle: or the laminae may be short and broad without a midrib
  and traversed by several slightly divergent and forked veins.

  No satisfactory evidence of reproductive organs has so far been
  adduced.

The genus is chiefly characteristic of Upper Triassic, Rhaetic, and
Jurassic floras, though it was in all probability represented in
Permian floras. Several species, many of which are valueless, are
recorded also from Cretaceous and Tertiary formations. Search should
be made for fertile specimens or for evidence as to the association of
seeds with _Thinnfeldia_ fronds.

Some Permian fossils from Kansas which Sellards[1435] has made the
type of a new genus, _Glenopteris_, appear to be indistinguishable
generically from leaves of Lower Mesozoic age universally recognised as
typical examples of _Thinnfeldia_.


_Thinnfeldia odontopteroides_ (Morris)[1436]. Figs. 356–358.

This is a very variable species as regards the shape and size of
the ultimate segments and their venation. It is a type of extended
geographical range characteristic of Rhaetic or Upper Triassic rocks
in Australia, South Africa, India, South America, and various European
localities.

  Frond bipinnate; the broad rachis may be dichotomously branched.
  Pinnules with a thick lamina which may be almost semicircular in
  form, deltoid, broadly oval or broadly linear, and often confluent
  at the base. Short and broad pinnules occur on some fronds directly
  attached to the main rachis between the pinnae. The longer and
  narrower pinnules (fig. 356, C), resembling those of the Palaeozoic
  genus _Alethopteris_, have a well-defined midrib, while the smaller
  segments are characterised by several slightly divergent veins
  which spring directly from the rachis (fig. 356, A). Epidermal
  cells polygonal or, above the veins, rectangular in shape; stomata,
  which are slightly sunk, occur on both the upper and lower
  epidermis. Fertile specimens unknown.

The portion of a lobed pinnule shown in fig. 356, B, illustrates a
form of segment intermediate between the linear type with a midrib
and a row of shorter pinnules without a median vein. Fig. 356, D,
represents another instance of variation in the arrangement of the
veins in segments of different sizes. Various specific and generic
names have been assigned to Thinnfeldia fronds of Rhaetic age on the
ground of the occurrence of pinnules longer and narrower than those
usually associated with _T. odontopteroides_; but in view of the range
of variation met with in a single leaf it is advisable to extend rather
than to restrict the boundary of what we are pleased to regard as a
specific type.

[Illustration: FIG. 356.

  A–D. _Thinnfeldia odontopteroides_ (Morris).
  E. _Ptilozamites._ (E, after Nathorst.)]

The name _Thinnfeldia lancifolia_ has been applied by Morris to fossils
from Australia which may be identified with _T. odontopteroides_,
and the same designation is employed by Szajnocha and by
Solms-Laubach[1437] for Rhaetic specimens from South America. Similar
fronds are described by Geinitz[1438] as _Thinnfeldia tenuinervis_
from Argentine Rhaetic strata. _Odontopteris macrophylla_ Curran, _T.
falcata_ Ten.-Woods, _Gleichenia lineata_ Ten.-Woods, and _Cardiopteris
Zuberi_ Szaj. afford other examples of what are probably closely allied
forms[1439].

[Illustration: FIG. 357. _Thinnfeldia odontopteroides_ (Morris).
  ⅘ nat. size.]

Some exceptionally large examples of _T. odontopteroides_ are figured
by Feistmantel[1440] from the Hawkesbury series of New South Wales in
which the bipinnate frond has a breadth of 25–30 cm. A specimen from
the Molteno beds of South Africa, probably of Rhaetic age, represented
in fig. 357, illustrates a smaller leaf with pinnules of the linear
type, some of which are partially divided into shorter pinnules with
forked veins. The example represented in fig. 358, from Cyphergat (S.
Africa), shows two equal branches of a rachis with small contiguous
segments.

[Illustration: FIG. 358. _Thinnfeldia odontopteroides_. From a specimen
  in the British Museum (v. 2490). 1½ nat. size.]

Some specimens figured by Zeiller[1441] from the Rhaetic strata
of Tonkin as _Pecopteris (Bernouillia?_) sp. may be portions of
_Thinnfeldia_ fronds, and the large leaves which he refers to
_Ctenopteris Sarreni_ differ but slightly from the Australian specimens
described by Feistmantel as _T. odontopteroides_.


_Thinnfeldia rhomboidalis_, Ettingshausen. Figs. 359, 360, C.

Under this name Ettingshausen described the type-specimen of the genus
from Lower Lias strata at Steierdorf in Hungary. He assigned the plant
to the Coniferae on the ground of a resemblance of the pinnules to
the phylloclades of _Phyllocladus. Thinnfeldia rhomboidalis_ bears a
close resemblance to _T. odontopteroides_, but the pinnules are usually
longer and narrower, as shown in the English specimen from the Lower
Lias of Dorsetshire represented in fig. 359. The darker margin of the
pinnules shown in fig. 360, C, gives the impression of a revolute
lamina, but a microscopical examination points to a thicker cuticle at
the edge of the segments.

[Illustration: FIG. 359. _Thinnfeldia rhomboidalis_, Ettings. Slightly
  reduced. From an English Liassic specimen in the British Museum.
  [M.S.]]

The species is recorded from Jurassic rocks of France, Germany, Italy,
India, Australia, and elsewhere[1442].

Palaeobotanical literature contains numerous records of Jurassic,
Cretaceous and some Tertiary species referred to _Thinnfeldia_,
but many of these are probably not generically identical with _T.
odontopteroides_ or _T. rhomboidalis_. Mr Berry[1443] in a paper on
_The American species referred to Thinnfeldia_ concludes that the genus
is “a rather indefinite one ... and badly in need of revision.” He
regards the Middle and Upper Cretaceous American species as Conifers
related to _Phyllocladus_ and probably forming a link between the
Podocarpeae and Taxeae: for these forms he proposes the generic name
_Protophyllocladus_. The opinion has been expressed elsewhere[1444]
that this “problematical[1445]” genus rests on an unsatisfactory basis;
the available data do not justify the use of a name which implies the
existence in North American Cretaceous floras of a type related to
the New Zealand and Tasmanian Conifer _Phyllocladus_. We are not in a
position to assign a single species of _Thinnfeldia_ to the Filicales
or the Gymnosperms.

A leaflet from Jurassic rocks of Poland figured by Raciborski[1446]
shows what this author regards as the impression of a circular sorus:
no sporangia have been found. A specimen in the British Museum[1447],
which is said to come from Rhaetic beds in Queensland, shows a row
of contiguous polygonal prominences on each side of the midrib which
resemble the sori of a fern; but until sporangia are discovered we
cannot determine the precise nature of this apparently fertile frond.

A species described by Fontaine[1448] from the Potomac beds
(Wealden-Jurassic) of North America as _Thinnfeldia variabilis_ affords
a good example of a plant which cannot be identified with any degree
of confidence either as a fern or a seed-bearing type. Mr Berry draws
attention to the former application of this name by Velenovský to a
distinct Lower Cretaceous Bohemian species and proposes for Fontaine’s
plant the name _T. Fontainei_; he maintains that no one has doubted
the fern-nature of the Potomac plant. _T. variabilis_ may indeed be a
fern, but the evidence is not such as to preclude legitimate doubts
as to the correctness of this suggestion. Solms-Laubach[1449], in
referring to Schenk’s view that _Thinnfeldia_ and its allies may
represent a group intermediate between Ferns and Gymnosperms, admits
that it is a possible supposition; he is, however, inclined to consider
_Lomatopteris_ and _Cycadopteris_, “genera especially comparable with
_Thinnfeldia_” as more probably ferns.

At this point we may conveniently consider a series of genera which
occupy an equally uncertain position and bear a very close resemblance
to _Thinnfeldia_.

[Illustration: FIG. 360.

  A. _Lomatopteris jurensis_. (⅞ nat. size. After Kurr.)
  B. _L. Schimperi_. (⅞ nat. size. After Salfeld.)
  C. _Thinnfeldia rhomboidalis_, Ett. (Slightly enlarged. British
     Museum. No. 52672.)]


                             Lomatopteris.

The generic name _Lomatopteris_ was proposed by Schimper[1450] for some
bipinnate fronds originally described by Kurr[1451] from Jurassic rocks
of Württemberg as _Odontopteris (?) jurensis_ (fig. 360, A). I have
elsewhere expressed the opinion[1452] that this German species may be
identical with _Thinnfeldia rhomboidalis_ Ett. Kurr’s type-specimen,
a portion of which is reproduced in fig. 360, A, consists of a frond
or large pinna characterised by a prominent and broad rachis giving
off alternate linear pinnae bearing bluntly rounded, contiguous and
basally concrescent pinnules having a thick or revolute border and a
central rib. The lateral veins are visible in the ultimate segments
of Kurr’s fossil. Saporta[1453] has described several species, which
he refers to Schimper’s genus, from French Jurassic strata: it is,
however, difficult to recognise some of the examples represented in his
illustrations as specifically distinct forms. This author notices the
resemblance of _Lomatopteris_ to _Thinnfeldia_, not only in habit but
in the structure of the epidermal cells[1454]. In _Lomatopteris_ and
in _Thinnfeldia_ the cells have straight and not sinuous walls and the
slightly sunken stomata are surrounded by a ring of epidermal cells.
Salfeld[1455] has recently described portions of fronds from Jurassic
rocks of South-West Germany, which he identifies as _Lomatopteris
jurensis_. He disagrees with my view that _Lomatopteris_ does not
differ sufficiently from _Thinnfeldia_ to be accorded generic autonomy,
chiefly on the ground that the folded-over edge of the pinnules is
a distinguishing feature of _Lomatopteris_. There is, however, no
difference, in appearance at least, between the leaflets of some
species of _Thinnfeldia_, e.g. _T. rhomboidalis_ from Liassic rocks of
England[1456], and those referred to _Lomatopteris_. In a later paper,
Salfeld[1457] describes some Portlandian fragments from North Germany
as _Lomatopteris Schimperi_, identifying them with a Wealden fossil
of somewhat doubtful affinity, which Schenk[1458] makes the type of
his species. The Portlandian specimens are described as tripinnate,
with thick decurrent obtusely terminated pinnules with a revolute
edge. The general form of the frond is very similar to that of _L.
jurensis_. Salfeld publishes a photograph of a large specimen which he
describes as fertile and a drawing of a piece of a pinna: the latter
is reproduced in fig. 360, B. He speaks of sori occurring in two rows,
probably attached to lateral veins, in the groove between the midrib
and the revolute edge of the lamina. The sporangia are described as
“nicht näher bekannt[1459].” An examination of the figures reveals
nothing as to the nature of the “sori.” The specimens are considered
by Salfeld to afford decisive evidence against the view that
_Lomatopteris_ and _Thinnfeldia_ are generically identical. Nothing has
so far been published which constitutes a valid argument in favour of
retaining Schimper’s generic name.


                             Cycadopteris.

Zigno[1460] founded the genus _Cycadopteris_ on Italian Jurassic
impressions regarded by Schimper as indistinguishable from
_Lomatopteris_. As Solms-Laubach[1461] points out, the supposed sori
of _Cycadopteris_ described by Zigno are not convincing. There appear
to be no satisfactory reasons for separating _Cycadopteris_ from
_Lomatopteris_, nor do the fronds described under these names exhibit
any important differences from _Thinnfeldia_.


                             Ptilozamites.

Nathorst[1462] founded this genus on a remarkable series of
specimens from the Rhaetic Coal-beds of Scania and assigned it to
the Cycadophyta. The species _Ptilozamites Heeri_ may be taken as a
representative type. The leaves are linear and simply pinnate. In the
example shown on a much reduced scale in fig. 361 the frond is 53 cm.
long and 2·1 cm. broad. The upper edge of each pinnule is straight or
slightly concave; the lower edge is rounded; the veins are slightly
divergent and dichotomously branched (fig. 356, E, p. 539). In some of
Nathorst’s specimens the broad rachis is forked as in many Thinnfeldias.

As a comparison of fig. 356, A and E, shows, the pinnules of some
specimens of _Thinnfeldia odontopteroides_ are identical with those of
_Ptilozamites_. In the latter genus the rachis is either unbranched
or occasionally forked, while in _Thinnfeldia_ the branching may be
of the dichotomous or pinnate type. In _Ptilozamites_ the segments
appear to be always without a midrib, while a median vein frequently
occurs in those of _Thinnfeldia_. There can be little doubt as to the
very close alliance between the Rhaetic species referred to these two
genera. The name _Ptilozamites_ should perhaps be retained for such
long and narrow fronds as that shown in fig. 361: no species included
in _Thinnfeldia_ is known in which the rachis reached so great a length
without branching. The habit of _Ptilozamites Heeri_ predisposes one in
favour of Nathorst’s opinion that the fronds are Cycadean: we have no
information in regard to the nature of the reproductive organs.

[Illustration: FIG. 361. _Ptilozamites Heeri_, Nath. (⅓ nat. size.
  After Nathorst.)]


                             Ctenopteris.

This name was instituted by Saporta[1463], at Brongniart’s
suggestion, for Liassic species characterised by pinnules like those
of _Thinnfeldia_, but distinguished by the bipinnate habit of the
frond. Saporta compares the genus with the Palaeozoic leaves known as
_Odontopteris_, and with Italian Jurassic plants referred by Zigno to
his genus _Dichopteris_.

The name _Ctenozamites_ is applied by Nathorst[1464] to the type of
frond which Saporta, Zeiller, and other authors refer to _Ctenopteris_.
Nathorst instituted _Ctenozamites_ for fossils agreeing in the form and
venation of the pinnules with his genus _Ptilizamites_ but differing in
being bipinnate and not pinnate.

Fronds of _Ctenopteris_ are characteristic of the Jurassic and Rhaetic
series; they are known only in the sterile condition. As Zeiller[1465]
says, _Ctenopteris_ may be a member of the Cycadofilices, an extinct
group founded on Palaeozoic plants combining Cycadean and Filicinean
characters, and some of which are now known to be Pteridosperms. It is
probable that the genus is not a true fern: it is more likely to be a
member of the Cycadophyta or of some generalised extinct group.


_Ctenopteris cycadea_ (Brongniart). Fig. 362.

  1828. _Filicites cycadea_, Brongniart, Hist. Vég. foss. p. 387, Pl.
        CXXIX.

  1832. _Odontopteris cycadea_, Berger, Verstein. Coburg Geg. p. 23,
        Pl. III.

  1873. _Ctenopteris cycadea_, Saporta, Pal. Franç. Vol. I. p. 355,
        Pls. XL. XLI.

  Frond bipinnate, broad rachis giving off branches at an acute
  angle; pinnules broadly linear, slightly falcate, with several
  slightly divergent forked veins.

A frond very similar to the Lower Lias specimen from Dorsetshire
represented in fig. 362 was described by Leckenby as _Ctenis Leckenbyi_
(Bean MS.) from the Inferior Oolite of Yorkshire[1466]. Leckenby
recognised the possibility of a Cycadean affinity, but regarded
the bipinnate habit as an objection. The branched fronds of the
Australian Cycad _Bowenia_ supply an answer to this objection. Several
good examples of _Ctenopteris cycadea_ are figured by Schenk[1467]
from Rhaetic rocks of Persia. Zeiller’s Tonkin Rhaetic species, _C.
Sarrani_[1468], affords a striking illustration of the difficulty of
drawing a clear line of separation between _Ctenopteris_ and some
species of _Thinnfeldia_.

[Illustration: FIG. 362. _Ctenopteris cycadea_, Brongn. (½ nat. size.)
  From a specimen in the British Museum. [M.S.]]

_Ctenopteris_ is in all probability very closely related to
_Thinnfeldia_ and _Ptilozamites_.


                             Dichopteris.

This genus was proposed by Zigno[1469] for some large specimens from
the Jurassic plant-beds of Northern Italy.

  The bipinnate leaves are characterised by the great breadth of the
  rachis which is dichotomously branched in the distal region (fig.
  363); the linear pinnae reach a considerable length. Pinnules
  relatively small, oblong and slightly contracted at the base; the
  decurrent and confluent lamina forms a narrow wing to the main
  axis. Veins slightly divergent and forked, as in _Ptilozamites_.


_Dichopteris visianica_, Zigno. Fig. 363.

A specimen of this species in the Padua Museum has a total length of
83 cm. It has been elsewhere suggested[1470] that a fragment figured
by Zigno as a fertile example of this type is probably part of a frond
of the Osmundaceous fern _Todites_. Since this opinion was expressed I
have had an opportunity of examining the actual specimen at Padua: the
circular patches described by Zigno as sori appear to be irregularities
in the matrix and not an original feature.

Brongniart[1471] instituted the genus _Pachypteris_ for some
imperfectly preserved English Jurassic fossils from Whitby, which he
described as _P. lanceolata_. Specimens have since been described[1472]
from the Inferior Oolite rocks of the Yorkshire coast. Brongniart
described the pinnules as being without veins or as possessing only a
midrib. It is almost certain that the apparent absence of veins in most
specimens[1473] is due to the fleshy nature of the segments and that
the species _P. lanceolata_ should be transferred to _Dichopteris_.

Krasser[1474] has described a species from Cretaceous rocks of the
island of Lesina, off the Dalmatian coast, as _Pachypteris dalmatica_
which is very similar in habit to the English specimens and to Zigno’s
_Dichopteris visianica_. One of Krasser’s specimens is practically
identical with _Dichopteris lanceolata_ (Brongn.), while in others
the small pinnules are replaced in some of the pinnae by a continuous
lamina with a few distal serrations. The latter form a link between the
_Dichopteris_ and _Thinnfeldia_ type of segment. Krasser gives a full
résumé of opinions expressed by other authors in regard to the position
of _Pachypteris_ (= _Dichopteris_) and decides in favour of a Cycadean
alliance.

[Illustration: FIG. 363. _Dichopteris visianica_, Zigno. (⅓ nat. size.
  After Zigno.)]

A French Jurassic plant which Saporta[1475] made the type of a new
genus _Scleropteris_, and described as _S. Pomelii_, appears to be
indistinguishable from _Dichopteris_.

_Dichopteris_, though conveniently retained as a distinct genus, agrees
so closely, in the broad and forked rachis and in the fleshy pinnules,
with _Thinnfeldia_ that it would seem reasonable to regard the two
genera as members of the same group.

Several authors have drawn attention to the striking resemblance
in form and venation between the fronds of the Palaeozoic genus
_Odontopteris_ and those of _Ctenopteris_ and _Thinnfeldia_. In
_Odontopteris_, as in _Neuropteris_, another Palaeozoic genus, the
rachis occasionally bifurcates as in _Thinnfeldia_ and _Dichopteris_,
and the ultimate segments of some species of _Odontopteris_ (fig.
366, A) are practically identical with those of _Thinnfeldia_ and
_Ptilozamites_.

_Odontopteris_ is probably a Pteridosperm. There is no adequate reason
for supposing that this group of plants which played a prominent part
in the Permo-Carboniferous floras was no longer in existence during the
Mesozoic era.


                             Odontopteris.

Brongniart[1476] instituted the genus _Odontopteris_ for compound
fronds from the Coal-Measures characterised by pinnules attached by
the whole breadth of the base and traversed by numerous forked veins.
_Odontopteris_ is very rare in British Carboniferous rocks and “appears
to be restricted to the Middle and Upper Coal-Measures[1477].”

[Illustration: FIG. 364.

  A. _Alethopteris lonchitica_ (Schloth.). ½ nat. size.
  B. _Mariopteris muricata_ (Schloth.). × 2.
  C. _Odontopteris_ cf. _alpina_ (Presl). ⅗ nat. size.
  D. _O_. cf. _alpina_. Portion of pinna enlarged.

  (A–D. From photographs by Dr Kidston.)]

  Fronds large, bipinnate or tripinnate, the main rachis, which
  may be dichotomously branched, bears long linear pinnae with
  broadly linear or deltoid pinnules, acute or blunt, attached
  by the whole of the base; the lower margin of the lamina,
  which is usually entire and rarely lobed (e.g. _Odontopteris
  osmundaeformis_)[1478], is often decurrent on the axis of the
  pinna. The basal pinnule of each pinna is frequently attached by
  a contracted base, and the lamina may differ in form from that of
  the normal segments. Pinnules often occur on the main rachis,
  and in some species the petiole bears modified pinnules which are
  larger than the ultimate segments of the pinnae and in some cases
  Cyclopteroid in shape. The pinnules are traversed by numerous
  dichotomously branched veins; if a midrib is present it dies out in
  the basal part of the lamina. In some species (genus _Mixoneura_)
  pinnules of the Neuropteroid type, characterised by a well-defined
  midrib, occur in association with typical Odontopteroid pinnules on
  the same pinna.

[Illustration: FIG. 365. _Odontopteris minor_, Brongn. (Rather less
  than ⅓ nat. size. After Zeiller.) [The pinnules are omitted in the
  right-hand branch.]]

The species represented in fig. 364, C, D, from the Middle
Coal-Measures of Barnsley, Yorkshire, illustrates the form and venation
of the _Odontopteris_ type of pinnule. Another species, _O. Reichiana_
Gutb.[1479], is also recorded by Kidston from the Lower Coal-Measures
of Lancashire. Some unusually good specimens of the type-species of the
genus _Odontopteris minor_, Brongn., have been figured by Zeiller[1480]
from the Coal-Measures of Blanzy (fig. 365) which show the dichotomy
of the main axis and the occurrence of Aphlebiae on the petiole.
The late Dr Weiss[1481] divided _Odontopteris_ into two sections,
_Xenopteris_ and _Mixoneura_, the pinnules of the former having the
form shown in fig. 364, D; while in species of the latter sub-genus
some of the pinnules are identical in form and venation with those of
_Neuropteris_ except that they are attached by the whole breadth of
the base. Zeiller[1482] employs _Mixoneura_ as a generic designation.
In an American species _O. Wortheni_ Lesq.[1483] the pinnules bear
numerous hairs like those on some species of _Neuropteris_ (fig. 373,
p. 570). The large size of the fronds of _Odontopteris_ suggested
to Weiss[1484] that they were borne on the stems of tree-ferns, but
Grand’Eury’s[1485] examination of specimens in the Coal-beds of central
France led him to picture the plant as bearing a tuft of leaves on
a short subterranean stem. Renault and Zeiller[1486], on the other
hand, obtained evidence in the Commentry Coal-field of fronds borne on
elongated stems which grew on the ground and were supported by stronger
plants. Stur[1487] was the first to suggest that _Odontopteris_ should
be excluded from the ferns. Grand’Eury’s[1488] supposed fertile
pinnules of _Odontopteris_ do not afford any satisfactory evidence
of the sporangial nature of the small swellings which he figures at
the ends of the veins. This author pointed out several years ago
that the petioles of some species of _Odontopteris_ possess the
anatomical features of _Myeloxylon_, a type of leaf-stalk which is now
known to belong to Pteridosperms. In a recent paper Grand’Eury[1489]
records the association of _Odontopteris_ fronds with small seeds
(_Odontopterocarpus_), a discovery which leaves little or no doubt as
to the Pteridospermic nature of the genus. The fronds of _Odontopteris_
are very similar in habit to those of _Neuropteris_, another
Pteridospermic genus.

The similarity between some _Odontopteris_ and _Thinnfeldia_ leaves,
to which attention has already been called, is well illustrated by
_O. genuina_ Grand’Eury[1490], a pinnule of which is represented in
fig. 366, A. _Odontopteris_ is a fairly widespread genus in Upper
Carboniferous and Lower Permian rocks, and is recorded also from
Triassic strata: it is represented in the Coal-fields of North America
and in several parts of Europe[1491].

In some fronds included in _Odontopteris_ the pinnae are characterised
by a broad irregularly lobed lamina which also forms a winged border to
the rachis. Examples of this form are afforded by _Odontopteris Browni_
Sew.[1492] from the Burghersdorp Series (Triassic?) of Cape Colony, and
_O. Fischeri_ described by Brongniart[1493] from the Permian of Russia.
The Russian species would perhaps be more appropriately placed in the
genus _Callipteris_, as Weiss[1494] suggests; the absence of venation
in _O. Browni_ renders generic identification unsatisfactory.


[Illustration: FIG. 366.

  A. _Odontopteris genuina_ (Grand’Eury). (× 2⅝. After Renault and
     Zeiller.)
  B. _Callipteridium gigas_ (Gutb.). (× 2⅝. After Zeiller.)
  C. _Callipteris Pellati_ (Zeill.). (× 1¾. After Zeiller.)
  D. _C. lyratifolia_ (Goepp.). (× 1¾. After Zeiller.)]


                             Callipteris.

Brongniart[1495] instituted this genus for certain species of supposed
ferns previously referred to the genera _Pecopteris_, _Alethopteris_,
and _Neuropteris_. _Callipteris_ is a characteristic Permian plant
which is almost certainly a Pteridosperm. Zeiller has pointed out
that such descriptions of fertile specimens as have been written are
unsatisfactory. A few years ago, however, Grand’Eury[1496] recorded the
occurrence of seeds in association with Callipteris fronds in the Autun
district, and in some cases they were found attached to the pinnae
and rachis. The seeds are ovoid or spherical (5–10 mm. broad) and
smaller than those of _Neuropteris_. The drawings of fertile segments
published by Weiss[1497] afford no indication of reproductive organs.
Potonié[1498] figures some pinnules of _Callipteris conferta_ in which
the thick lamina is covered with sinuous grooves probably made by some
insect larvae: as he suggests, similar markings may have been mistaken
for the remains of sori. The occurrence of _Callipteris_ fronds
recorded by Weber and Sterzel[1499] in association with _Medullosa_
stems in the Lower Permian of Saxony is in accordance with Grand’Eury’s
conclusion.

  Fronds reaching 1 metre in length, bipinnate or tripinnate, main
  rachis frequently exhibiting a combination of dichotomous and
  pinnate branching. Pinnae linear, usually crowded, decurrent on the
  rachis; the pinnules on the lower side of the pinnae are continued
  on to the rachis. Pinnules of the Pecopteroid type, entire or
  slightly lobed, or of the Sphenopteroid type and more or less
  deeply dissected (fig. 366 C, D), the lamina of adjacent pinnules
  concrescent; on the lower pinnae the lamina may be continuous as in
  an Alethopteris pinnule. A midrib may extend almost to the bluntly
  rounded apex of the ultimate segments, giving off oblique, simple,
  or forked veins, the lowest of which arise directly from the
  rachis; in the Sphenopteroid forms the lateral veins are given off
  at a more acute angle.

A striking feature of the genus is the occurrence of pinnules on the
main rachis, as in _Odontopteris_. Zeiller has wisely extended the
application of _Callipteris_ to fronds possessing this character
irrespective of the entire or lobed form of the ultimate segments.
He found among the numerous examples of the genus obtained from
Autun[1500] and Lodève[1501] transitional forms connecting such
species as _C. conferta_ (fig. 367) and _C. Pellati_ Zeill. (fig. 366,
C) in which the Pecopteroid pinnules are slightly lobed, with _C.
lyratifolia_ (Goepp.) (fig. 366, D), _C. flabellifera_[1502] (Weiss),
and _C. Bergeroni_ Zeill. characterised by deeply lobed Sphenopteroid
segments.


_Callipteris conferta_ (Sternberg)[1503]. Fig. 367.

  1723. Scheuchzer, Herb. Diluv. Pl. II., fig. 3.

  1826. _Neuropteris conferta_, Sternberg, Flor. Vorwelt, p. 17.

  1849. _Callipteris conferta_, Brongniart, Tableau, p. 24.

This polymorphic species (fig. 367) is one of the most characteristic
Permian plants. The oval-linear pinnules, attached by the whole base,
occur on both pinnae and rachis; this feature, the thick texture of the
lamina, and the linear, obliquely set, pinnae render the fronds easily
recognisable. The fronds bore seeds.

[Illustration: FIG. 367. _Callipteris conferta_. From the Permian of
  Aschbach, Rhenish Prussia (British Museum, No. 39052).]

In a recent account of some Permian plants from Germany, Schuster[1504]
refers a portion of a frond to _Callipteris conferta_ (Sternberg) var.
_polymorpha_ Sterzel, which is characterised by unusually large and
polymorphic pinnules. In size and shape the pinnules recall those of
_Neuropteridium validum_ Feist.


                            Callipteridium.

The name _Callipteridium_, created by Weiss[1505] as a sub-genus of
_Odontopteris_, is applied by Zeiller and other authors to a few Upper
Carboniferous and Permian species characterised by the occurrence
of simply pinnate pinnae on the main rachis between the bipinnate
primary pinnae. Single pinnules are borne directly on the rachis of the
primary pinnae between the pinnate branches. The form and venation of a
typical pinnule are shown in fig. 366, B. _Callipteridium pteridium_,
originally recorded by Schlotheim as _Filicites pteridius_[1506],
has been fully described by Renault and Zeiller from unusually large
specimens found in the Commentry Coal-field[1507]. This species
illustrates the peculiar morphological features of the genus. The
main rachis of the tripinnate fronds, several metres long, shows a
combination of dichotomous and pinnate branching; from the zigzag
and forked axis are given off bipinnate pinnae and, between these,
shorter pinnate branches. The pinnules closely resemble those of
_Callipteris conferta_ but reach a greater length; the pinnules borne
on the rachises of the lateral branches differ from the others in their
broader base and more triangular lamina.

No fertile specimens have been found. It is probable that
_Callipteridium_ was not a true fern, and that White[1508] is correct
in including it among the Pteridosperms.


                            Archaeopteris.

In 1852 Forbes[1509] published a brief description of some supposed
fern fronds, found by the Geological Surveyors of Ireland in Upper
Devonian rocks of Kilkenny, under the name _Cyclopteris hibernica_.
The Irish specimens were more fully described by Baily[1510] in
1858. Fronds of the same type were referred by other authors to
_Cyclopteris_, _Adiantites_ or _Noeggerathia_, until Schimper[1511]
proposed the generic name _Palaeopteris_ on the ground that the fronds
described by Forbes and Baily are distinguished by the nature of
their fertile pinnae from the sterile leaves included in Brongniart’s
provisional genus _Cyclopteris_. The earlier use of _Palaeopteris_ by
Geinitz for an entirely different plant led Dawson[1512] to institute
the genus _Archaeopteris_. The genus _Archaeopteris_ may be defined as
follows:

  Fronds bipinnate, reaching a considerable length (90 cm.); the
  stout rachis bears long linear pinnae; sterile pinnules obovate
  or cuneate with an entire, lobed, fimbriate, or laciniate lamina
  traversed by divergent dichotomously branched veins. The fertile
  pinnae usually occur on the lower part of the rachis; pinnules with
  a much reduced lamina bear numerous fusiform or oval exannulate
  sporangia (fig. 369, A, E, H), sessile or shortly stalked,
  singly, or in groups of two or three. The base of the petiole is
  characterised by a pair of partially adnate stipules (fig. 369,
  C, D), and single pinnules or scales occur in some species on the
  rachis between the pinnae and on the petiole.

[Illustration: FIG. 368. _Archaeopteris hibernica_. (From a specimen in
  the Science and Art Museum, Dublin. Rather less than ⅙ nat. size.)]


_Archaeopteris hibernica_ (Forbes). Figs. 368, 369, A–C.

The specimen from Kilkenny represented in fig. 368 has a length of
over 80 cm. The upper pinnae bear numerous imbricate obovate pinnules
(fig. 369, A, B) with an entire or very slightly fimbriate margin,
while on the shorter lower pinnae the ultimate segments are reduced to
a slender axis bearing numerous fusiform sporangia, 2–3 mm. in length.
Kidston[1513] has pointed out that sporangia occasionally occur on the
edge of ordinary pinnules, and he first recognised the stipular nature
of the scale-like appendages which Baily noticed on the swollen petiole
base (5 cm. broad) of the Irish species (fig. 369, C). Restorations
of _Archaeopteris hibernica_ have been figured by Baily[1514] and
by Carruthers[1515], but the description of the fertile pinnae by
the latter author requires modification in the light of Kidston’s
description of the Dublin specimens.

                   •       •       •       •       •

_Archaeopteris_ is recorded from Upper Devonian rocks of the South of
Ireland, Belgium, Germany, Southern Russia, Bear Island, and Ellesmere
Land in the Arctic regions, Canada, Pennsylvania, and elsewhere.
Many of the specimens described under different names bear a close
resemblance, which in some cases probably amounts to specific identity,
to _A. hibernica_. _A. Jacksoni_ originally described by Dawson[1516]
and more recently by Smith and White[1517] from Devonian rocks of
Maine, the Canadian type _A. gaspiensis_ Daws., and some species
figured by Lesquereux[1518] from Pennsylvania, are examples of forms
which present a striking similarity in habit to the Irish species. The
Belgian Devonian fossils named by Crépin[1519] _Palaeopteris hibernica_
var. _minor_ are regarded by him as probably identical with Goeppert’s
species _Cyclopteris Roemeriana_ from the neighbourhood of Aachen. Heer
recorded _Archaeopteris Roemeriana_ from Upper Devonian beds in Bear
Island, and Nathorst[1520], who has published a more complete account
of the Arctic forms, draws attention to the resemblance of some of
them to _A. hibernica_. A species described by Schmalhausen[1521] from
the Upper Devonian of Southern Russia as _A. archetypus_ (fig. 369,
D) appears to differ from _A. hibernica_ in the slightly less reduced
lamina of the fertile segments. This species has been more adequately
illustrated by Nathorst[1522] from material collected in Ellesmere
Land: he is unable to confirm Schmalhausen’s statement that the pinnae
are spirally disposed.

The species _A. fimbriata_ (fig. 369, G) described by Nathorst from
Bear Island is characterised by the more deeply dissected lamina of the
sterile pinnules. In _A. fissilis_ Schmal. from Russia and Ellesmere
Land the lamina (fig. 369, E, F) is cut up into filiform segments: a
fertile pinnule of this species is represented in fig. 369, E.

Some sterile impressions figured by Krasser[1523] from Palaeozoic
strata (Lower Carboniferous or Upper Devonian?) in the province of
Nanshan in China as _Noeggerathia acuminifissa_ are considered by
Zeiller[1524] to be portions of an _Archaeopteris_ or _Rhacopteris_
frond. The resemblance to the former genus is however by no means close
enough to warrant a reference to _Archaeopteris_. The sterile specimens
described by Stur[1525] from the Culm of Altendorf as species of
_Archaeopteris_ are probably not generically identical with the Irish
and Arctic species. The dichotomous branching of the rachis in _A.
Tschermaki_ and _A. Dawsoni_ is a feature unknown in _Archaeopteris_.
In the absence of fertile pinnae the separation of _Archaeopteris_ from
_Rhacopteris_ is by no means easy.

[Illustration: FIG. 369.

  A. _Archaeopteris hibernica._ Fertile pinna. Dublin Geological
     Survey Museum. (Reduced. After Kidston.)
  B. _A. hibernica._ Pinnule. (Slightly enlarged. After Carruthers.)
  C. _A. hibernica._ Base of petiole. (Dublin Museum. After Kidston.)
  D. _A. archetypus._ Base of petiole: Ellesmere Land. (After
     Nathorst. ⅚ nat. size.)
  E. _A. fissilis._ Sporangia. (Slightly enlarged. After
     Schmalhausen.)
  F. _A. fissilis._ Sterile pinnule. Ellesmere Land. (Slightly
     enlarged. After Nathorst.)
  G. _A. fimbriata._ Bear Island. (After Nathorst. ⅚ nat. size.)
  H. _Archaeopteris sp._ Ellesmere Land. (After Nathorst. ⅚ nat.
     size.)]

_Archaeopteris_ was regarded by Carruthers as a fern closely allied
to recent species of Hymenophyllaceae, but this conclusion was based
upon an interpretation of the fertile segments which Kidston[1526]
has shown to be incorrect. The latter author regarded the presence of
stipules and the structure of the exannulate sporangia as evidence of
a Marattiaceous alliance. In a later reference to _Archaeopteris_,
Kidston expresses the opinion that the genus is not a true fern but
a member of the Cycadofilices or Pteridosperms, a view shared by
Grand’Eury[1527] and doubtless by many other palaeobotanists. The
sporangia of _Archaeopteris_ appear to be of the same type as those
of _Dactylotheca_ (fig. 290, E, p. 399). Schmalhausen gave expression
to his disagreement with Nathorst and other authors who referred
_Archaeopteris_ to the Marattiaceae by proposing the distinctive
group-name Archaeopterideae.

There can be little doubt that the reproductive organs of
_Archaeopteris_ so far discovered are microsporangia, and that the
plant bore seeds. The sporangia are larger than those of any known fern
and, as Kidston points out, they are similar to those of _Crossotheca_
which he has shown to be microsporangia of the Pteridosperm
_Lyginodendron_. The presence of stipules in _Archaeopteris hibernica_,
_A. fimbriata_, _A. archetypus_ (fig. 369, D) and probably throughout
the genus does not materially affect the question of taxonomic
position. Stipules are a characteristic feature of Marattiaceae and,
in a reduced form, of Osmundaceae, but similar appendages are borne at
the base of the petiole of the Cycad _Ceratozamia_. The occurrence of
Aphlebiae on the rachis of _Archaeopteris_ is a feature shared by the
fronds of _Neuropteris_ and other Pteridosperms.


                             Neuropteris.

The fronds for which Brongniart[1528] created this genus, though
suspected by Stur in 1883 as wrongly classed among the ferns, have only
recently been shown to be the leaves of Pteridosperms. As yet only one
case is recorded in which

_Neuropteris_ pinnae occur in organic connexion with seeds[1529],
but it is almost certain that the genus as a whole must be placed in
this generalised group. Renault[1530] pointed out that the petioles
of Neuropteris fronds from Autun had the anatomical features of
_Myeloxylon_ (petiole of _Medullosa_). Since Kidston’s important
discovery of seed-bearing pinnae of _N. heterophylla_, Grand’Eury[1531]
has recorded the association of Neuropteris fronds with seeds in
French Coal-fields. By some of the older authors _Neuropteris_ was
compared with _Osmunda_ because of a similarity in venation. In the
frequent dichotomy of the frond and in the occurrence of pinnules on
the rachis, _Neuropteris_ closely resembles _Odontopteris_[1532]: there
can be little doubt as to the close relationship of the Pteridosperms
possessing these two types of foliage. _Neuropteris_ may be defined as
follows:

  Fronds reaching a considerable size, probably in soma cases a
  length of 10 metres[1533]; bi- or tri-pinnate; the rachis may be
  dichotomously branched (figs. 354, D; 370); both rachis and petiole
  bear single pinnules, those on the latter frequently differ from
  the normal leaflets in their larger Cyclopteroid laminae (fig.
  370). Pinnules entire, rarely slightly lobed, broadly linear,
  attached by a small portion of the base, which is usually more or
  less cordate. In _N. Grangeri_ Brongn. the pinnules are attached by
  a short pedicel[1534]. The midrib always dies out before reaching
  the blunt or pointed apex of the lamina and gives off at an acute
  angle numerous secondary veins characterised by their arched course
  and repeated forking.

[Illustration: FIG. 370. _Neuropteris_ frond with _Cyclopteris_
  leaflets. English Coal-Measures. (From a block given to me by Mr
  Carruthers. A.C.S.)]

Potonié describes the secondary veins of the pinnules of _Neuropteris
pseudogigantea_[1535] as occasionally anastomosing, a feature which may
be regarded as a step towards the reticulate venation of the closely
allied genus _Linopteris_.

Renault[1536] described some petrified pinnules of _Neuropteris_ in
which the mesophyll shows a differentiation into upper palisade tissue
and lacunar tissue below; the lower epidermis is infolded at intervals
where grooves (probably stomatal) occur like those on the leaves of an
Oleander (_Nerium oleander_).

The rachises of Neuropteris fronds are described by Grand’Eury under
the generic name _Aulacopteris_[1537].


_Neuropteris heterophylla_, Brongniart[1538]. Figs. 354, E; 371.

This species is characteristic of the Lower Coal-Measures of Britain;
it occurs also in the Middle Coal-Measures and is a common type in
Upper Carboniferous rocks in various parts of the world. The fronds are
large and tripinnate, the rachis is often dichotomously branched and
Cyclopteroid pinnules may occur on the petiole. The pinnules, 5–20 mm.
in length and 3–8 mm. broad, have a rounded apex (fig. 354, E, p. 535).

[Illustration: FIG. 371. _Neuropteris heterophylla._ From a specimen in
  the Manchester Museum. ½ nat. size. M.S.]

As shown in fig. 371 which represents a primary pinna, the small
pinnules on the lower branches are gradually replaced in the upper
portion of the specimen by falcate segments.


_Neuropteris macrophylla_, Brongniart[1539]. Figs. 354, D, D′; 372.

The rachis of the large fronds of this species illustrates the
dichotomous habit of many Neuropteris fronds, also the occurrence on
the petiole of large Cyclopteroid pinnules (cf. fig. 370). The small
piece of a pinna reproduced in fig. 372 shows the slender attachment
of the segments, the blunt apex, and the Neuropteroid venation. Single
pinnules of this species may be distinguished from those of _N.
Scheuchzeri_ by the blunter apex, the absence of the pair of small
Cyclopteroid pinnules on the same branch and by the absence of hairs.
_N. macrophylla_ is characteristic of the Upper Coal-Measures of
Britain.

[Illustration: FIG. 372. _Neuropteris macrophylla_, Brongn. From a
  photograph by Mr Hemingway.]


_Neuropteris Scheuchzeri_, Hoffmann. Figs. 354, F; 373.

Fragments of this well-known Coal-Measure species were figured by
Scheuchzer in his _Herbarium Diluvianum_[1540] as _Lithosmunda minor_,
and by Lhywd (Luidius[1541]) as _Phyllites mineralis_ as early as
1760. _Neuropteris Scheuchzeri_, so named by Hoffmann in 1826, is
a type which many authors have described under different names.
Lesquereux[1542] figured it as _N. hirsuta_ from the Coal-fields of
Pennsylvania, and under the same name it is recorded by Fontaine and
White[1543] from Permian rocks of Virginia. The oval patches on the
surface of a pinnule described by these authors as sori are certainly
not of that nature. The same species is described by Bunbury[1544] from
Nova Scotia as _N. cordata_ Brongn. var. _angustifolia_. For a full
synonymy of the species reference should be made to lists published by
Kidston[1545], White[1546], and Zeiller[1547].

[Illustration: FIG. 373. _Neuropteris Scheuchzeri._ From a specimen (v.
  2009) in the British Museum. ¾ nat. size.]

The large tripinnate fronds are characterised by the long linear-
or oval-lanceolate pinnules (fig. 373)[1548] with a pointed apex
and numerous bristle-like hairs on the lamina; two much smaller
Cyclopteroid segments occur at the base of the pinnae which are
terminated by the linear leaflets (fig. 354, F, p. 535).

_Neuropteris Scheuchzeri_ is characteristic of the Upper and Middle
Coal-Measures of Britain and is recorded from several localities in
North America and the Continent. Zalessky[1549] has recently recorded
the species from the Coal-Measures of Donetz. The frequent occurrence
of detached pinnules points to a caducous habit. Even single leaflets
can, however, be identified by their large size, the pointed apex, and
hairy lamina. The hairs are preserved as fine oblique lines simulating
veins; they were so described by Roemer[1550] who took them for
cross-connexions between the secondary veins and referred the pinnules
to Gutbier’s genus _Dictyopteris_.

Another example of _Neuropteris_ with hairy pinnules is described from
the Commentry Coal-field by Renault and Zeiller as _N. horrida_[1551].
The oval-linear, bluntly rounded, pinnules are characterised by a
median band of hairs on each surface and a narrower strip at the edge
of the lamina.


                             Cyclopteris.

This generic name was created by Brongniart in 1828[1552] for specimens
which he believed to be complete single leaves of orbicular or reniform
shape similar to those of _Trichomanes reniforme_. The lamina is
traversed by numerous dichotomously branched veins which spread from
the centre of the base.

It was suspected by Lindley and Hutton[1553] that certain Cyclopteris
leaves belonged to the frond of a species of _Neuropteris_, and some
years later Lesquereux[1554] concluded that Brongniart’s genus was
founded on orbicular leaflets of _Neuropteris_. In 1869 Roehl[1555]
figured a specimen of _Neuropteris_ bearing Cyclopteroid pinnules on
its rachis. It is now universally admitted that _Cyclopteris_ is not a
distinct genus and that the specimens so named were borne as modified
pinnules on the main rachis of _Neuropteris_ and _Odontopteris_. It
is, however, convenient to retain the name for detached leaflets which
cannot be referred to the fronds on which they were borne. A specimen
found by Mr Hemingway in the Upper Coal-Measures of Yorkshire and
described in 1888[1556] affords a striking example of the large size
attained by what was probably a frond of _Neuropteris_. The piece of
main rachis reached a length of over 120 cm. and bore five pairs of
Cyclopteris pinnules, some of which were 7 cm. long and 5 cm. broad.
The complete frond must have reached a length of at least 4 metres.
Fig. 370 shows some typical Cyclopteroid leaflets on the petiole of a
_Neuropteris_ frond.


                              Linopteris.

The Upper Palaeozoic fronds included in this genus are more familiar
as species of _Dictyopteris_. Potonié[1557] has, however, pointed out
that the creation of this name by Lamouroux in 1809 for a genus of
Brown Algae which is still retained, makes it advisable to fall back
upon the designation _Linopteris_. Gutbier[1558] proposed the genus
_Dictyopteris_ in 1835: _Linopteris_ was first used by Presl[1559] in
1838. The fronds so named are identical with species of _Neuropteris_
except in the anastomosis of the secondary veins; _Linopteris_
bears to _Neuropteris_ the same relation as _Lonchopteris_ bears to
_Alethopteris_. As in _Neuropteris_, Cyclopteroid pinnules occur on
the petioles of _Linopteris_, but the veins form a fine reticulum.
Grand’Eury[1560] records the association of _Linopteris Brongniarti_
with seeds belonging to the genus _Hexagonocarpon_, a fact which points
to the Pteridosperm nature of the foliage.

Some fertile pinnules of _Linopteris Schutzei_ (Roemer) are described
by Zeiller[1561] from Autun as bearing on the under surface of the
lamina two rows of long and pointed sporangia, probably united in
groups. The presumption is that these are microsporangia.

Fig. 374 is a reproduction of a careful drawing, originally published
by Zeiller[1562], of a pinnule of the type-specimen of Gutbier’s
species _Linopteris neuropteroides_. This species differs from
_Linopteris obliqua_, instituted by Bunbury[1563] for specimens
obtained by Lyell[1564] from the Coal-Measures of Nova Scotia, in
the smaller size of the meshes. _Linopteris obliqua_ occurs in the
Upper and Middle Coal-Measures of Britain; it is recorded by Zeiller
from Asia Minor, by Lesquereux[1565] from Pennsylvania, and by other
authors from several European localities. The pinnules frequently occur
detached from the frond and like those of some species of _Neuropteris_
were caducous. _Linopteris_ is rare in British strata.

[Illustration: FIG. 374. _Linopteris neuropteroides_, Gutb. (Pinnule of
  type-specimen. Enlarged. After Zeiller.)]


                             Alethopteris.

The name _Alethopteris_, instituted by Sternberg[1566], is applied to
compound fronds often reaching a considerable size, exhibiting the
following features:

  The linear pinnules are attached by the whole breadth of the base,
  with the lower edge of the lamina decurrent and usually continuous
  with that of the next pinnule (figs. 290, A, p. 399; 375). The
  ultimate segments are entire, with an acute or rounded apex and
  often characterised by a fairly thick lamina convex on the upper
  surface. From a prominent midrib, continued to the apex of the
  pinnule, numerous simple and forked secondary veins are given
  off at a wide angle, the decurrent portion of the lamina being
  supplied by veins direct from the axis of the pinna. In the upper
  part of a frond or primary pinna the pinnules may be replaced by
  a continuous, lobed, or entire simple lamina. The main rachis
  occasionally exhibits dichotomous branching, but the fronds are for
  the most part constructed on the pinnate plan. Single Cyclopteroid
  pinnules[1567] occur on the petiole of some species of the genus.

In certain species of _Alethopteris_ the pinnules appear to have been
deciduous as in _Didymochlaena_ among recent ferns[1568]. A piece of
cuticle from the upper surface of a pinnule of _Alethopteris Grandini_
(Brongn.) figured by Zeiller[1569] shows very clearly the polygonal
form and straight walls of most of the epidermal cells, those above the
veins being almost rectangular. The position of the sunken stomata is
revealed by small circular spaces surrounded by a circle of cells.

The absence of fertile specimens of this common genus of Upper
Carboniferous plants led Stur[1570] to exclude it from the ferns.
Although no seeds have so far been found in organic connexion with an
Alethopteris frond, it is certain that some species, probably all,
represent the foliage of Pteridosperms. Renault was the first to
describe petrified specimens of _Alethopteris_ fronds exhibiting the
anatomical structure of _Myeloxylon_ (leaf-axis of _Medullosa_). The
calcareous nodules from English Coal-seams contain numerous fragments
of the Myeloxylon type of rachis bearing Alethopteroid pinnules.

The constant association of the fronds of _Alethopteris lonchitica_
and _Trigonocarpon_ seeds noticed by Mr Hemingway in the Coal-Measures
of Yorkshire led him to regard the species as seed-bearing: it has
since been recognised as the foliage of the Pteridosperm _Medullosa
anglica_[1571].

Grand’Eury[1572] has recorded the association in French Coal-fields of
species of _Alethopteris_ with _Trigonocarpon_ and _Pachytesta_ seeds.


_Alethopteris lonchitica_ (Schlotheim)[1573]. Figs. 364, A; 290, A.

This species, described by Schlotheim in 1820 as _Filicites
lonchiticus_ and previously figured by Scheuchzer[1574], is abundant
in the Middle and Lower Coal-Measures of Britain[1575]. It is
characterised by large tripinnate fronds, probably quadripinnate in the
lower part, bearing primary pinnae of a more or less triangular form
divided into pinnate branches replaced in the apical region by linear
segments. The pinnules, 8–30 mm. long and 3–5 broad, are linear- or
oval-lanceolate with an obtuse apex; the upper margin of the lamina is
slightly contracted at the base, while the lower edge is decurrent.

[Illustration: FIG. 375. _Alethopteris Serlii_ (Brongn.). From a
  specimen in the York Museum. ¾ nat. size.]


_Alethopteris Serlii_ (Brongniart)[1576]. Fig. 375.

This species, figured by Parkinson in 1811, closely resembles _A.
lonchitica_, but is distinguished by the more crowded and relatively
longer pinnules which are joined to one another by a narrow connecting
lamina (Fig. 375). The secondary veins in _A. Serlii_ are rather finer
and more numerous. Grand’Eury[1577] records the association of the seed
_Pachytesta_ with fronds of this species in the Coal-Measures of St
Étienne.

_A. Serlii_ is very abundant in the Upper Coal-Measures but rare in
the Middle Coal-Measures of Britain[1578].


                             Lonchopteris.

This name was proposed by Brongniart[1579] for sterile fronds from
Upper Carboniferous rocks which are practically identical with
species of _Alethopteris_, but differ in the reticulate venation of
the pinnules. It has been pointed out in a previous chapter[1580]
that _Lonchopteris_ is usually used for Palaeozoic species, the
Wealden leaves, which were placed in this genus by Brongniart, being
transferred to _Weichselia_.

There can be little doubt as to the close relationship of
_Lonchopteris_ with _Alethopteris_: both may be referred to the
Pteridosperms. _Lonchopteris rugosa_ Brongn.[1581] (fig. 290, B, p.
399) and _L. Bricei_ Brongn., both British species, are fairly common
in Upper Carboniferous strata. In _L. rugosa_, a Middle Coal-Measures
species, the anastomosing secondary veins form polygonal meshes (fig.
290, B, p. 399) smaller than those of _L. Bricei_.


                              Pecopteris.

Reference has already been made to this genus in the chapter on
Marattiales, so far as regards certain species of fertile fronds the
sporangia of which resemble those of recent Marattiaceae. It is,
however, by no means safe to assume that such Pecopteris fronds were
borne on stems having the anatomical characters of ferns. The sporangia
in some at least of the species may have contained microspores. In
one Upper Carboniferous species usually referred to Pecopteris, _P.
Pluckeneti_, Schlot., Grand’Eury[1582] has recorded the occurrence of
seeds on the pinnules of the ordinary fronds. This species will be
referred to in Volume III. The substitution of such generic names as
_Ptychocarpus_, _Asterotheca_, _Hawlea_, _Dactylotheca_ and others
for the purely provisional designation _Pecopteris_ indicates a step
towards a conclusion as to natural affinity. The probability is that
_Pecopteris_, as applied to Palaeozoic species, in many cases stands
for the compound fronds of true ferns, but the possibility of the
inclusion of those of Pteridosperms in the same category is by no means
excluded. The designation _Pecopteris_ may conveniently be retained for
sterile bipinnate, tripinnate, or quadripinnate fronds bearing pinnules
having the following characteristics:

  Lamina short, attached to the rachis by the whole of the base and
  at a wide angle, with the edges parallel or slightly converging
  towards the usually blunt apex; adjacent pinnules may be continuous
  basally by a narrow lamina. A well-marked midrib extends to the
  apex and gives off simple or forked lateral veins almost at right
  angles (fig. 352, D, p. 529).

  Hydathodes like those on the leaflets of _Polypodium vulgare_ and
  other recent ferns[1583] are occasionally seen at the ends of the
  lateral veins of Pecopteris pinnules.

In addition to the examples of Palaeozoic fronds with the _Pecopteris_
form of pinnule referred to in chapter XXII., the species _Pecopteris
arborescens_ may be briefly described.


_Pecopteris arborescens_ (Schlotheim)[1584]. Figs. 352, D: 376.

The species named by Schlotheim _Filicites arborescens_ in 1804 is
characteristic of the Upper Coal-Measures and is recorded also from
Permian strata[1585].

  Fronds large; the rachis, which may reach a breadth of 3 cm.[1586],
  gives off long ovoid-lanceolate pinnae in two alternate rows
  (fig. 376); pinnules small, 1·5–4mm. long and 1–2mm. broad,
  contiguous, with rounded apex, attached approximately at right
  angles; the upper surface of the lamina is slightly convex and may
  be hairy[1587]. The fertile pinnules, identical in shape with the
  sterile, bear groups of ovoid exannulate sporangia (synangia). The
  midrib extends to the apex of the pinnule and gives off simple
  veins at a wide angle (fig. 352, D).

Our knowledge of the reproductive organs is very meagre. Grand’Eury
described the synangia as consisting of 3–5 sporangia borne on a
central receptacle; sporangia have been described also by Stur[1588],
Renault and Zeiller[1589], and Potonié[1590], but no fertile British
specimens are recorded. Stur places this species in the genus
_Scolecopteris_, and Potonié regards the sporangia found by him on
Permian fronds, which may be identical with _Pecopteris arborescens_,
as conforming to those of the _Asterotheca_ type. It is impossible to
decide on the evidence available whether this species is a Pteridosperm
or a fern, but there is a natural inclination in doubtful cases to give
preference to the first of these two choices.

[Illustration: FIG. 376. _Pecopteris arborescens_ (Schloth.). From
  the Upper Coal-Measures of Radstock. From a photograph by Dr
  Kidston. Reduced.]

The numerous fronds from Carboniferous and Permian rocks described
as species of _Pecopteris_ exhibit a considerable range of variation
in the form of the pinnules. In many species the pinnules are of the
type represented in fig. 352, D; in others the lamina of the ultimate
segments is slightly contracted at the base and the secondary veins
are given off at a more acute angle, as in _Pecopteris polymorpha_,
Brongn.[1591] In _Pecopteris unita_, Brongn., already described as
_Ptychocarpus unita_[1592], the pinnules are joined together except
in the apical region. Some fronds included in _Pecopteris_ possess
pinnules in which Pecopteroid and Sphenopteroid features are combined;
_P. Sterzeli_, Zeill.[1593] and _P. Pluckeneti_, Schlot. are examples
of fronds in which the pinnules are lobed as in _Sphenopteris_, but the
base of the lamina is only slightly contracted and the venation is not
that of typical Sphenopteris species.

The species to which Potonié has applied the generic name
_Alloiopteris_[1594] also illustrates the impossibility of drawing a
sharp line between _Pecopteris_ and _Sphenopteris_. The fronds already
described in chapter XXV. under the designation _Corynepteris_ bear
pinnules with a contracted base; in some species the lamina is lobed,
but in others (fig. 354, G) it is entire with a midrib nearer one edge
than the other. The species which Potonié assigns to _Alloiopteris_,
like many other Sphenopteroid and Pecopteroid fronds, are characterised
by the occurrence of an abnormal pinnule (aphlebia) at the base of
each pinna (fig. 354, G, p. 535). Young fronds of _Pecopteris_ are
occasionally met with showing very clearly the circinate vernation of
the pinnae as in the leaves of _Cycas_ and _Angiopteris_ represented in
fig. 220, p. 283. The genus _Spiropteris_ was created by Schimper[1595]
for coiled unexpanded fronds of fossil ferns; it is however superfluous
to apply a distinctive term to specimens of this kind.

The designation _Pecopteris_ is employed chiefly for leaves of
Palaeozoic age which are unknown in the fertile state, or do not afford
sufficient evidence as to the nature of the sporangia to justify the
substitution of a special generic name. Many Mesozoic species have also
been referred to _Pecopteris_, but most of these are more appropriately
included in Brongniart’s later genus _Cladophlebis_. The pinnules of
_Cladophlebis_, as Brongniart pointed out, are intermediate between
_Pecopteris_ and _Neuropteris_; they are usually attached by the whole
breadth of the base, as in _Pecopteris_, but the more acute origin,
more arched form, and more frequent dichotomy of the lateral veins
are features shared by _Neuropteris_. As a rule, Mesozoic sterile
fronds with straight or folded, entire or dentate pinnules are of the
Cladophlebis type: this genus is especially characteristic of Rhaetic
and Jurassic floras. Examples of _Cladophlebis_ pinnules are shown in
figs. 256, 257 (pp. 340, 342). It is to be regretted that authors do
not make more use of the generic name _Cladophlebis_ in describing
sterile fronds, instead of following the misleading and unscientific
practice of employing such genera as _Pteris_, _Asplenites_, and others
on wholly insufficient grounds.




                LIST OF WORKS REFERRED TO IN THE TEXT.


  =Amalitzky, W.= (01) Sur la découverte, dans les dépôts permiens
        supérieurs du Nord de la Russie, d’une flore Glossoptérienne
        &c. _Compt. Rend._ vol. CXXXII. p. 591.

  =Arber, E. A. N.= (02) On the distribution of the Glossopteris Flora.
        _Geol. Mag._ vol. IX. p. 346.

   ——  (02²) The Clarke collection of fossil plants from New South
        Wales. _Quart. Journ. Geol. Soc._ vol. LVIII. p. 1.

   ——  (03) Notes on some fossil plants collected by Mr Molyneux in
        Rhodesia. _Quart. Journ. Geol. Soc._ vol. LIX. p. 288.

   ——  (05) Catalogue of the fossil plants of the Glossopteris Flora
        in the British Museum. A monograph of the Permo-Carboniferous
        Flora of India and the Southern Hemisphere. _London._

   ——  (05²) The Sporangium-like organs of _Glossopteris Browniana_,
        Brongn. _Quart. Journ. Geol. Soc._ vol. LXI. p. 324

   ——  (05³) The fossil flora of the Culm-measures of N. W. Devon &c.
        _Phil. Trans. R. Soc._ vol. CXCVII. p. 291.

   ——  (06) On the past history of Ferns. _Annals Bot._ vol. XX. p.
        215.

  =Arber, E. A. N.= and =H. H. Thomas.= (08) On the structure of
        _Sigillaria scutellata_, Brongn. and other Eusigillarian stems,
        in comparison with those of other Palaeozoic Lycopods. _Phil.
        Trans. R. Soc._ vol. CC. p. 133.

  =Armour, H. M.= (07) On the Sorus of Dipteris. _New Phytologist_,
        vol. VI. p. 238.

  =Atkinson, G. F.= (94) The study of the biology of Ferns, by the
        collodion method. _New York._

  =Auerbach, J.= and =H. Trautschold.= (60) Ueber die Kohlen von
        Central Russland. _Nouv. Mém., Soc. Imp. Naturalistes Moscou_,
        vol. XIII.

  =Bäsecke, P.= (08) Beiträge zur Kenntnis der physiologischen Scheiden
        der Achsen und Wedel der Filicinen &c. _Bot. Zeit._ Heft
        II.–IV. Abt. I.

  =Baily, W. H.= (59) On the fructification of _Cyclopteris hibernica_
        (Forbes), from the Upper Devonian or Lower Carboniferous strata
        at Kiltorkan Hill, County Kilkenny. _Brit. Assoc. Rep. London_,
        1859, p. 75. (_Leeds meeting_, 1858.)

   ——  (60) On _Corynepteris_, a new generic form of fossil fern.
        _Journ. Geol. Soc. Dublin_, vol. VIII. p. 237.

   ——  (75) Figures of characteristic British fossils. _London._

  =Baker, J. G.= (67) Descriptions of six new species of simple fronded
        Hymenophyllaceae. _Journ. Linn. Soc._ vol. IX. p. 335.

   ——  (68) On the geographical distribution of Ferns. _Trans. Linn.
        Soc._ vol. XXVI. p. 305.

   ——  (68) See Hooker, Sir W. J. and J. G. Baker.

   ——  (88) On a further collection of ferns from West Borneo. _Journ.
        Linn. Soc._ vol. XXIV. p. 256.

  =Balfour, J. H.= (57) On the occurrence in coal of peculiar vegetable
        organisms resembling the Sporangia of _Lycopodium. Trans. R.
        Soc. Edin._ vol. XXI. p. 187.

  =Barber, C. A.= (89) On the structure and development of the bulb in
        _Laminaria bulbosa_, Lamour. _Annals Bot._ vol. III. p. 41.

  =Barrois, C.= (04) Sur les Spirorbes du Terrain Houiller de Bruay.
        (Pas de Calais.) _Ann. Soc. Geol. Nord_, vol. XXXIII. p. 50.

  =Bartholin, C. T.= (92) Nogle i den bornholmske Juraformation
        forekommende Planteforsteninger. _Bot. Tidsk. Kjövenhaven_,
        vol. XVIII. Heft 1.

  =Bather, F. A.= (07) Nathorst’s use of Collodion imprints in the
        study of fossil plants. _Geol. Mag._ vol. IV. p. 437.

   ——  (08) Nathorst’s method of studying cutinised portions of fossil
        plants. _Geol. Mag._ vol. V. p. 454.

  =Bayer, G.= (99) Einige neue Pflanzen der Perucer Kreideschichten in
        Böhmen. _Sitz. K. böhm. Ges. Wiss. Prag._

  =Bennie, J.= and =R. Kidston.= (88) On the occurrence of Spores in
        the Carboniferous formation of Scotland. _Proc. R. Physc. Soc.
        Edin._ vol. IX. p. 82, 1885–88.

  =Benson, Margaret.= (04) _Telangium Scotti_, a new species of
        Telangium (Calymmatotheca) showing structure. _Ann. Bot._ vol.
        XVIII. p. 161.

   ——  (08) _Miadesmia membranacea_, Bertrand; a new Palaeozoic
        Lycopod with a seed-like structure. _Phil. Trans. R. Soc._ vol.
        CXCIX. p. 409.

   ——  (08²) The Sporangiophore—a unit of structure in the
        Pteridophyta. _New Phytologist_, vol. VII. p. 143.

  =Bernard, C.= (04) Le bois centripète dans les feuilles de Conifères.
        _Bot. Cent._ Beiheft, vol. XVII. p. 241.

  =Berridge, E. M.= (05) On two new specimens of _Spencerites insignis.
        Ann. Bot._ vol. XIX. p. 273.

  =Berry, E. W.= (03) The American species referred to _Thinnfeldia.
        Bull. Torrey Bot. Club_, vol. XXX. p. 438.

  =Bertrand, C. E.= (81) Recherches sur les Tmésiptéridées. _Arch. Bot.
        Nord de la France_, vol. I. p. 252.

   ——  (82) Phylloglossum. _Arch. Bot. Nord France_, vol. II. p. 70.

   ——  (91) Remarques sur le _Lepidodendron Harcourtii_ de Witham.
        _Trav. Mém. Fac. Lille_, vol. II. Mém. 6.

   ——  (94) Sur une nouvelle Centradesmide. _Assoc. Franç. pour
        l’Avancement des Sciences_.

   ——  (99) On the structure of the stem of a ribbed _Sigillaria_.
        _Ann. Bot._ vol. XIII.

   ——  and =F. Cornaille.= (02) Études sur quelques caractéristiques
        de la structure des Filicinées actuelles. _Trav. Mem. L’Univ.
        Lille_, tome X. Mém. 29.

  =Bertrand, P.= (09) Études sur la Fronde des Zygoptéridées. _Lille_.

  =Binney, E. W.= (44) On the remarkable fossil trees lately discovered
        near St Helen’s. _Phil. Mag._ vol. XXIV. p. 165.

   ——  (46) Description of the Dukinfield _Sigillaria. Quart. Journ.
        Geol. Soc._ vol. II. p. 390.

   ——  (48) On the origin of coal. _Manchester Phil. Soc. Mem._ vol.
        VIII. p. 148.

   ——  (62) On some plants showing structure from the Lower
        Coal-Measures of Lancashire. _Proc. Geol. Soc._ vol. XXVIII. p.
        106.

   ——  (65) A description of some fossil plants showing structure,
        found in the Lower Coal-Seams of Lancashire and Yorkshire.
        _Phil. Trans. R. Soc._ vol. CLV. pt. ii. p. 579.

   ——  (71) Observations on the structure of fossil plants found in
        the Carboniferous Strata. _Palaeont. Soc. London_.

   ——  (72) Observations &c. Pt. III. _Lepidodendron. Palaeont. Soc._

  =Bischof=, — (53) Sigillarien aus dem bunten Sandstein Bernburgs.
        _Zeit. Gesammt. Naturwiss._ Bd. I.

  =Blanckenhorn, M.= (85) Die Fossile Flora des Buntsandsteins und des
        Muschelkalkes der Umgegend von Commern. _Palaeontographica_,
        vol. XXXII. p. 117.

  =Bommer, C.= (03) Les causes d’erreur dans l’étude des empreintes
        végétales. _Nouv. Mém. Soc. Belg. Geol._ &c. Fasc. I.

  =Boodle, L. A.= (00) Comparative anatomy of the Hymenophyllaceae,
        Schizaeaceae, and Gleicheniaceae. _Annals Bot._ vol. XIV. p.
        455.

   ——  (01) Comparative anatomy of the Hymenophyllaceae, Schizaeaceae,
        and Gleicheniaceae. _Annals Bot._ vol. XIV. p. 359.

   ——  (04) On the occurrence of Secondary Xylem in _Psilotum_. _Ann.
        Bot._ vol. XVIII. p. 505.

   ——  (04²) The structure of the leaves of the bracken (_Pteris
        aquilina_, L.) in relation to environment. _Journ. Linn. Soc.
        London_, vol. XXXV. p. 659.

   ——  (08) On the production of dwarf male prothalli in sporangia of
        _Todea. Ann. Bot._ vol. XXII. p. 231.

  =Boulay, N.= (76) Le Terrain Houiller du Nord de la France et les
        Végétaux Fossiles. _Lille_.

  =Bower, F. O.= (91) Is the Eusporangiate or the Leptosporangiate the
        more primitive type in the ferns? _Annals Bot._ vol. V. p. 109.

   ——  (93) On the structure of _Lepidostrobus Brownii_, Schmpr.
        _Annals Bot._ vol. VII. p. 329.

   ——  (94) Studies in the Morphology of Spore-producing Members.
        Equisetaceae and Lycopodineae. _Phil. Trans. R. Soc._ vol.
        CLXXXV. p. 473.

   ——  (96) Studies &c. II. Ophioglossaceae. _London_.

   ——  (97) Studies &c. III. Marattiaceae. _Phil. Trans. R. Soc._
        vol. CLXXXIX. p. 35.

   ——  (00) Studies &c. IV. The Leptosporangiate Ferns. _Phil. Trans.
        R. Soc._ vol. CXCII. p. 29.

   ——  (04) Studies &c. V. General Comparisons and Conclusions.
        _Ibid._ vol. CXCVI. p. 191.

   ——  (08) The origin of a Land Flora. _London_.

  =Bowman, J. E.= (41) Observations on the characters of the fossil
        trees lately discovered on the line of the Bolton railway.
        _Trans. Manchester Geol. Soc._ vol. I. p. 112.

  =Braun, A.= (63) Ueber die Isoetes Arten der Insel Sardinien.
        _Monatsber. k. Preuss. Akad. Wiss. Berlin_.

  =Braun, F.= (75) Die Frage nach der Gymnospermie der Cycadeen.
        _Monatsber. k. Preuss. Akad. Wiss._ p. 241.

  =Brebner, G.= (02) The anatomy of Danaea and other Marattiaceae.
        _Ann. Bot._ vol. XVI.

  =Brodie, P. B.= (42) On the discovery of insects in the Lower Beds of
        the Lias of Gloucestershire. _Brit. Assoc. Rep._ 1842, p. 58.

   ——  (45) A history of fossil insects in the Secondary Rocks of
        England, _London_.

  =Brongniart, A.= (25) Note sur les végétaux fossiles de l’Oolite à
        fougères de Mamers. _Ann. Sci. Nat._ tome IV. p. 417.

   ——  (37) Histoire des Végétaux Fossiles, vol. II. _Paris_.

   ——  (45) See Murchison, R., de Verneuil, and Count Keyserling.

   ——  (68) Notice sur un Fruit de Lycopodiacées Fossiles. _Compt.
        Rend._ vol. LXVII. [Aug. 17th].

  =Brown, R.= (45) On the geology of Cape Breton. _Quart. Journ. Geol.
        Soc._ vol. I. p. 207.

   ——  (46) On a group of erect trees in the Sydney coalfield of Cape
        Breton. _Quart. Journ. Geol. Soc._ vol. II. p. 393.

   ——  (47) Upright _Lepidodendron_ with _Stigmaria_ roots, in the
        roof of Sydney Main Coal. _Quart. Journ. Geol. Soc._ vol. IV.
        p. 46.

   ——  (49) Description of erect Sigillariae with conical tap-roots,
        found in the roof of the Sydney Main Coal, in the island of
        Cape Breton. _Proc. Geol. Soc._ (_March_ 21), p. 354.

   ——  (51) Some account of an undescribed fossil fruit
        (_Triplosporites_). _Trans. Linn. Soc._ vol. XX. p. 469.

  =Browne, Lady Isabel.= (09) The phylogeny and inter-relationships
        of the Pteridophyta. _New Phytologist_ (_Reprint_, No. 3).
        _Cambridge_.

  =Bruchmann, H.= (74) Ueber Anlage und Wachsthum der Wurzeln von
        _Lycopodium_ und _Isoetes. Jen. Zeit. Naturwiss._ vol. VIII. p.
        522.

   ——  (97) Untersuchungen über _Selaginella spinulosa_, A. Br.
        _Gotha._

   ——  (98) Ueber die Prothallien und die Keimpflanzen mehrerer
        Europäischer Lycopodien. _Gotha_.

  =Buckman, J.= (45) See Murchison, R. I.

   ——  (50) On some fossil plants from the Lower Lias. _Quart. Journ.
        Geol. Soc._ vol. VI. p. 413.

  =Bunbury, C. J. F.= (47) On fossil plants from the coal
        formation of Cape Breton. _Quart. Journ. Geol. Soc._ vol. III.
        p. 423.

   ——  (61) Notes on a collection of fossil plants from Nagpur,
        Central India. _Quart. Journ. Geol. Soc._ vol. XVII. p. 325.

  =Butterworth, J.= (00) Further research on the structure of
        _Psaronius_, a tree-fern of the Coal-Measures. _Mem. Proc.
        Manchester Lit. Phil. Soc._ vol. XLIII.

  =Campbell, D. H.= (04) The affinities of the Ophioglossaceae and
        Marsiliaceae. _Amer. Naturalist_, vol. XXVIII. no. 454.

   ——  (05) The structure and development of Mosses and Ferns. _New
        York_.

   ——  (07) On the distribution of the Hepaticae and its significance.
        _New Phytol._ vol. VI. p. 203.

  =Carruthers, W.= (65) On _Caulopteris punctata_, Göpp., a tree-fern
        from the Upper Greensand of Shaftesbury in Dorsetshire. _Geol.
        Mag._ vol. II. p. 484.

   ——  (69) On the structure of the stems of arborescent Lycopodiaceae
        of the Coal-Measures. _Month. Micr. Journ._ p. 177.

   ——  (69²) On the plant-remains from the Brazilian coal-beds, with
        remarks on the genus _Flemingites_. _Geol. Mag._ vol. VI. p. 5.

   ——  (70) On the nature of the scars in the stems of _Ulodendron_,
        _Bothrodendron_, and _Megaphytum_. _Monthly Micr. Journ._ p.
        144.

   ——  (72) On the structure of the stems of the arborescent
        Lycopodiaceae of the Coal-Measures. _Monthly Micr. Journ._ p.
        50.

   ——  (72²) Notes on fossil plants from Queensland, Australia.
        _Quart. Journ. Geol. Soc._ vol. XXVIII.

   ——  (72³) Notes on some fossil plants. _Geol. Mag._ vol. IX.

   ——  (73) On some Lycopodiaceous plants from the Old Red Sandstone
        of the North of Scotland. _Journ. Bot._, November, 1873.

   ——  (73²) On _Halonia_ of Lindley and Hutton and _Cyclocladia_ of
        Goldenberg. _Geol. Mag._ vol. X. p. 145.

  =Cash, W.= and =J. Lomax.= (90) On _Lepidophloios_ and
        _Lepidodendron_. _Brit. Ass. Rep._ (_Leeds_), p. 810.

  =Challenger Reports.= (85) Reports on the scientific results of
        the voyage of H. M. S. Challenger during the years 1873–76.
        _Narrative_, vol. I. pts. 1 and 2. _London_.

   ——  (85²) _Ibid._ Botany, vol. I.

  =Chick, Edith.= (01) See Tansley, A. G. and Edith Chick.

  =Chodat, R.= (08) Les Ptéridopsides des temps Paléozoïques. _Arch.
        Soc. Phys. Nat._ [4], vol. XXVI. Genoa.

  =Christ, H.= (96) Zur Farn-Flora der Sunda Inseln. _Ann. Jard.
        Buitenzorg_, vol. XIII. p. 90.

   ——  (97) Die Farnkräuter der Erde. _Jena_.

   ——  (04) _Loxsomopsis costaricensis_ nov. gen. et spec. _Bull.
        Herb. Boissier_ [2] vol. IV. No. 5.

   ——  and =K. Giesenhagen.= (99) Pteridographische Notizen, I.
        _Archangiopteris_ nov. gen. _Flora_, Bd. LXXXVI. p. 72.

  =Chrysler, M. A.= (08) Tyloses in tracheids of Conifers. _New
        Phytologist_, vol. VII.

  =Compton, R. H.= (09) The anatomy of _Matonia sarmentosa_. _New
        Phyt._ vol. VIII. p. 299.

  =Copeland, E. B.= (08) New genera and species of Bornean ferns. _The
        Philippine Journ. Sci._ vol. III. (C. Botany) p. 343.

   ——  (09) The ferns of the Malay Asiatic region. _Ibid._ vol. IV.
        No. 1.

  =Corda, A. J.= (46) See Reuss, A. E.

   ——  (52) See Germar, E. F.

  =Cornaille, F.= (02) See Bertrand, C. E. and F. Cornaille.

  =Cotta, C. B.= (32) Die Dendrolithen in Beziehung auf ihren inneren
        Bau. _Dresden._

  =Coward, K. H.= (07) On the structure of _Syringodendron_, the bark
        of _Sigillaria_. _Mem. Proc. Manchester Lit. Phil. Soc._ vol.
        LI., pt. ii.

  =Crépin, F.= (74) Description de quelques plantes fossiles de l’étage
        des Psammites de Condroz. _Bull. Acad. Roy. Belg._ [2] vol.
        XXXVIII.

   ——  (75) Observations sur quelques plantes fossiles des dépôts
        Dévoniens. _Soc. Roy. bot. Belg._ vol. XIV. p. 214.

  =Dale, E.= (01) See Seward, A. C. and E. Dale.

  =Dangeard, P. A.= (91) Mémoire sur la morphologie et l’anatomie des
        _Tmesipteris_. _Le Botaniste_ [1] Fasc. VI. p. 163.

  =Darwin, C.= (03) More letters of Charles Darwin, edited by F. Darwin
        and A. C. Seward (vol. II.). _London._

  =David, W. E.= and =E. F. Pittman=. (93) On the occurrence of
        _Lepidodendron australe_ (?) in the Devonian rocks of N. S.
        Wales. _Rec. Geol. Surv. N. S. Wales_, vol. III. pt. iv. p. 194.

  =Davy, E. W.= (07) Summer in British Central Africa. _Gard. Chron._
        vol. XLI. [3] p. 263.

  =Dawes, J. S.= (48) Remarks upon the internal structure of _Halonia_.
        _Quart. Journ. Geol. Soc._ vol. IV. p. 289.

  =Dawson, Sir J. W.= (61) On an undescribed fossil fern from the Lower
        Coal-Measures of Nova Scotia. _Quart. Journ. Geol. Soc._ vol.
        XVII. p. 5.

   ——  (66) Acadian Geology. _London._

   ——  (82) The fossil plants of the Erian and Upper Silurian
        Formations of Canada. Pt. II. _Geol. Surv. Canada._

   ——  (86) On Rhizocarps in the Erian (Devonian) period in America.
        _Bull. Chicago Acad. Sci._ vol. I. no. 9.

  =Debey, M. H.= and =C. von Ettingshausen=. (59) Die urweltlichen
        Acrobryen des Kreidegebirges von Aachen und Maestricht.
        _Denksch. k. Akad. Wiss. Wien_, vol. XVII.

  =Diels, L.= (02) Filicales. _Die Natürlichen Pflanzenfamilien._
        Engler and Prantl, Teil I. Abt. 4.

  =Eichwald, E.= (60) Lethaea Rossica. Vol. I. _Stuttgart._

  =Engler, A.= (09) Syllabus der Pflanzenfamilien. _Berlin._

   ——  and =K. Prantl=. (02) Die Natürlichen Pflanzenfamilien.
        _Leipzig._

  =Ernst, A.= (08) The new flora of the volcanic island of Krakatau.
        (Trans. by A. C. Seward.) _Cambridge._

  =Etheridge, R.= (80) A contribution to the study of British
        Carboniferous Tubicolar Annelida. _Geol. Mag._ vol. VII. p. 109.

   ——  _Lepidodendron australe_, McCoy.—Its synonyms and range in
        Eastern Australia. _Rec. Geol. Surv. N. S. Wales_, vol. II. pt.
        3, p. 119.

   ——  (92) See Jack, R. L. and R. Etheridge.

   ——  (94) On the mode of attachment of the leaves or fronds to the
        caudex in _Glossopteris_. _Proc. Linn. Soc. N. S. Wales_, vol.
        IX. p. 228.

   ——  (94²) On the occurrence of _Oleandridium_ in the Hawkesbury
        Sandstone series. _Rec. Geol. Surv. N. S. Wales_, vol. IV. pt.
        2, p. 49.

   ——  (99) On a fern (_Blechnoxylon talbragarense_) with secondary
        wood, forming a new genus, from the Coal-Measures of the
        Talbragar District, N. S. Wales. _Rec. Australian Mus._ vol.
        III. pt. 6.

  =Ettingshausen, C. von=. (52) Begründung einiger neuen oder nicht
        genau bekannten Arten der Lias- und der Oolithflora. _Abt. K.
        K. Geol. Reichs_, vol. I. Abth. 3.

   ——  (59) See Debey, M. H. and C. von Ettingshausen.

   ——  (66) Die Fossile Flora des mährisch-schlesischen Dachschiefers.
        _Denksch. K. K. Akad. Wien_, vol. XXV. p. 77.

   ——  (82) See Gardner, J. S. and C. von Ettingshausen.

  =Farmer, J. B.= (90) On _Isoetes lacustris_, L. _Annals Bot._ vol. V.
        p. 37.

  =Farmer, J. B.= and =W. G. Freeman=. (99) On the structure and
        affinities of _Helminthostachys zeylanica_. _Annals Bot._ vol.
        XIII. p. 421.

  =Farmer, J. B.= and =T. G. Hill=. (02) On the arrangement and
        structure of the vascular strands in _Angiopteris evecta_ &c.
        _Annals Bot._ vol. XVI. p. 371.

  =Faull, J. H.= (01) The anatomy of the Osmundaceae. _Bot. Gaz._, vol.
        XXXII. p. 381.

  =Feistmantel, C.= (79) Ueber die Nöggerathien. _Sitz. K. böhm. Ges.
        Wiss._

  =Feistmantel, O.= (72) Ueber Baumfarrenreste der böhmischen
        Steinkohlen. Perm. und Kreideformation. _Abt. k. böhm. Ges.
        Wiss._ vol. VI. [5].

   ——  (75) Die Versteinerungen der böhmischen Kohlenablagerungen.
        _Palaeontograph._ vol. XXIII. 1875–76.

   ——  (75²) Ueber das Vorkommen von _Noggerathia foliosa_, Stbg., in
        dem Steinkohlengebirge von Oberschlesien. _Zeit. Deutsch. Geol.
        Ges._

   ——  (77) Jurassic (Liassic) Flora of the Rajmahal group from
        Golapili (near Ellore), S. Godaveri District. _Mem. Geol. Surv.
        India_, vol. I. pt. iii.

   ——  (79) The Flora of the Talchir-Karharbári Beds. _Mem. Geol.
        Surv. India. Foss. Flor. Lower Gondwanas_, I.

   ——  (80) The Flora of the Damuda and Panchet Divisions. _Mem. Geol.
        Surv. India_. _Ibid._ vol. III.

   ——  (82) The Fossil Flora of the South Rewah Gondwana Basin.
        _Ibid._ vol. IV. pt. i.

  =Fischer, F.= (04) Zur Nomenclatur von _Lepidodendron_ und zur
        Artkritik dieser Gattung. _Abh. k. Preuss. Geol. Landes._
        [N.F.] Heft XXXIX.

  =Fitting, H.= (07) Sporen im Buntsandstein. Die Makrosporen von
        _Pleuromeia_. _Ber. Deutsch. Bot. Ges._ vol. XXV. p. 434.

  =Fliche, P.= (03) Sur les Lycopodinées des Trias en Lorraine. _Compt.
        Rend._ 1903 (_April 6th_).

   ——  (09) Sur une fructification de Lycopodinée trouvée dans le
        Trias. _Compt. Rend._ tome CXLVIII. p. 259.

  =Fontaine, W. M.= (83) Contributions to the knowledge of the Older
        Mesozoic Flora of Virginia. _Monographs U. S. Geol. Surv._ Vol.
        VI.

   ——  (89) The Potomac or younger Mesozoic Flora of Virginia. _U. S.
        Geol. Surv. Monographs_, VI.

   ——  (00) See Ward, L. F.

   ——  (05) See Ward, L. F.

  =Fontaine, W. M.= and =I. C. White.= (80) The Permian or
        Upper-Carboniferous Flora of W. Virginia and Pennsylvania.
        _Second Geol. Surv. Report of Progress._

  =Forbes, E.= (51) Note on fossil leaves represented in Plates II.–IV.
        in the Duke of Argyll’s paper on Tertiary Leaf-beds in the Isle
        of Mull. _Quart. Journ. Geol. Soc._ Vol. VII. p. 103.

   ——  (53) On the fossils of the Yellow Sandstone of the South of
        Ireland. _British Assoc. Rep. London_, 1853, p. 43 (_Belfast
        meeting_, 1852).

  =Ford, S. O.= (02) On the anatomy of _Ceratopteris thalictroides_ L.,
        _Annals Bot._ vol. XVI. p. 95.

   ——  (03) See Seward, A. C. and S. O. Ford.

   ——  (04) The anatomy of _Psilotum triquetrum_. _Annals Bot._ vol.
        XVIII. p. 589.

   ——  (06) See Seward, A. C. and S. O. Ford.

  =Freeman, W. G.= (99) See Farmer, J. B. and W. G. Freeman.

  =Frič, A.= and =E. Bayer=. (01) Studien im Gebiete der Böhmischen
        Kreideformation. _Arch. Naturwiss. Landes. Böhmen_, Bd. XI.

  =Fritel, P. H.= (08) Sur une espèce fossile nouvelle du genre
        Salvinia. _Journ. Bot._ Ann. XXI. No. 8, p. 190.

  =Fritsch, F. E.= (05) See Tansley, A. G. and F. E. Fritsch.

  =Fritsch, K. von=. (97) Pflanzenreste aus Thüringer Culm
        Dachschiefer. _Zeitsch. Naturwiss._ Bd. LXX.

  =Gardeners’ Chronicle=. (82) [_Selaginella grandis_ n. sp.] Vol.
        XVII. p. 40 (July 8).

  =Gardner, J. S.= and =C. von Ettingshausen=. (82) A monograph of the
        British Eocene Flora. Vol. I. Filices. _Palaeont. Soc. London._

  =Geikie, Sir Archibald=. (03) Text-book of Geology. 2 vols. _London._

  =Geinitz, E.= (73) Versteinerungen aus dem Brandschiefer der unteren
        Dyas von Weissing bei Pillaritz in Sachsen. _Neues Jahrb. Min._
        p. 691.

  =Geinitz, H. B.= (72) Fossile Myriopoden in dem Rothliegenden bei
        Chemnitz. _Sitzb. Naturwiss. Ges. Isis_, p. 128.

   ——  (76) Ueber rhaetische Pflanzen- und Thierreste in den
        Argentinischen Provinzen La Rioja &c. _Palaeontograph._ Suppl.
        iii.



  =Germar, E. F.= (52) _Sigillaria Sternbergi_ Münster, aus dem bunten
        Sandstein. _Zeit. deutsch. Geol. Ges._ p. 183.

   ——  (44–53) Die Versteinerungen des Steinkohlengebirges von Wettin
        und Löbejün im Saalkreise. _Halle._

  =Geyler, H. T.= (77) Ueber fossile Pflanzen aus der Juraformation
        Japans. _Palaeont._ vol. XXIV. p. 221.

  =Giesenhagen, C.= (90) Die Hymenophyllaceen. _Flora_, p. 411.

   ——  (92) Ueber Hygrophile Farne. _Flora_, Bd. 76 (Ergänz. Band).

  =Gilkinet, A.= (75) Sur quelques plantes de l’étage du poudingue de
        Burnot. _Acad. Roy. Belg._ [2] vol. XL. No. 8.

  =Goebel, K.= (91) Pflanzenbiologische Schilderungen. Teil 2.
        _Marburg._

   ——  (05) Organography of Plants. Vol. II. (Trans. by J. B.
        Balfour.) _Oxford._

  =Goeppert, H. R.= (41) Die Gattungen der fossilen Pflanzen. _Bonn._

   ——  (32) Fossile Flora des Uebergangsgebirges. _Nov. Act. Caes.
        Leop.-Carol._ Vol. XIV. (_Supplt._).

   ——  (54) See Roemer, F. A.

  =Goldenberg, F.= (55–62) Flora Saraepontana Fossilis. _Saarbrücken._

  =Gordon, W. T.= (08) On the Prothallus of _Lepidodendron
        Veltheimianum_. _Trans. Bot. Soc. Edinburgh_, vol. XXIII. p.
        330.

   ——  (09) On the structure of a new _Zygopteris_. _Nature._ (Botany
        at the British Association.) Vol. LXXXI. p. 537.

  =Grand’Eury, C.= (75) See Renault, B. and C. Grand’Eury.

   ——  (04) Sur les graines des Neuroptéridées. _Compt. Rend._ CXXXIX.
        p. 782.

   ——  (05) Sur les graines trouvées attachées au _Pecopteris
        Pluckeneti_, Schlot. _Compt. Rend._ vol. CXL. p. 920.

   ——  (05²) Sur les graines de Sphenopteris &c. _Compt. Rend._ CXLI.
        p. 812.

   ——  (06) Sur les graines et inflorescences des _Callipteris_.
        _Compt. Rend._ CXLIII. p. 664.

   ——  (08) Sur les organes et la mode de végétation des
        Neuroptéridées et autres Ptéridospermes. _Compt. Rend._ CLXVI.
        p. 1241.

  =Gresley, W. S.= (89) Note on further discoveries of _Stigmaria_
        (? _ficoides_) and their bearing upon the question of the
        formation of Coal-Beds. _Midland Naturalist_, vol. XII. p. 25.

  =Greville, R. K.= (31) See Hooker, W. J. and R. K. Greville.

  =Grigoriew, N.= (98) Sur la flore paléozoique supérieure recueillie
        aux environs des villages Troitskoie et Longanskoie dans le
        bassin du Donetz. _Bull. Com. Géol. St. Pétersbourg_, tome XVII.

  =Gwynne-Vaughan, D. T.= (01) Observations on the anatomy of
        solenostelic ferns. _Annals Bot._ vol. XIV. p. 71.

   ——  (03) Observations &c. _Ibid._ vol. XVII. p. 689.

   ——  (05) On the anatomy of _Archangiopteris Henryi_ and other
        Marattiaceae. _Annals Bot._ vol. XIX. p. 259.

   ——  (07–09) See Kidston, R. and D. T. Gwynne-Vaughan.

   ——  (08) On the real nature of the Tracheae in the ferns.
        _Annals Bot._ vol. XXII. p. 517.

   ——  and =R. Kidston=. (08) On the origin of the adaxially curved
        leaf-trace in the Filicales. _Proc. R. Soc. Edinb._ vol.
        XXVIII. pt. vi. p. 433.

  =Hall, Kate M.= (91) See Jennings, A. Vaughan, and Kate M. Hall.

  =Halle, T. G.= (07) Einige krautartige Lycopodiaceen Paläozoischen
        und Mesozoischen Alters. _Arkiv Bot._ Bd. VII. No. 5.

  =Hannig, E.= (98) Ueber die Staubgrübchen auf den Stämmen und
        Blattstielen der Cyathaeaceen und Marattiaceen. _Bot. Zeit._ p.
        9.

  =Harvey-Gibson, R. J.= (94) Contributions towards a knowledge of the
        anatomy of the genus _Selaginella_, Spr. _Annals Bot._ vol.
        VIII. p. 133.

   ——  (96) Contributions &c. _Ibid._ vol. X. p. 77.

   ——  (97) Contributions &c. _Ibid._ vol. XI. p. 123.

   ——  (02) Contributions &c. _Ibid._ vol. XVI. p. 449.

  =Haughton, S.= (59) On _Cyclostigma_, a new genus of fossil plants
        from the Old Red Sandstone of Kiltorkan, W. Kilkenny. _Journ.
        Roy. Dublin Soc._ vol. II. p. 407.

  =Hawkshaw, J.= (42) Description of the fossil trees found in the
        excavations for the Manchester and Bolton railway. _Trans.
        Geol. Soc._ [2] vol. VI. p. 173.

  =Hayden, H. H.= (07) The stratigraphical position of the
        Gangamopteris beds of Kashmir. _Rec. Geol. Surv. India_, vol.
        XXXVI. pt. i.

  =Heer, O.= (71) Fossile Flora der Bären Inseln. _Flor. Foss. Arct._
        vol. II.

   ——  (74) Die Kreideflora der Arctischen Zone. _K. Svensk.
        Vetenskaps-Akad. Hand._ Bd. XII. [_Flor. Foss. Arct._ vol. III.
        1875.]

   ——  (75) _Flora Fossilis Arctica_, vol. III.

   ——  (76) Jura-Flora Ostsibiriens und des Amurlandes. _Ibid._ vol.
        IV. [ii].

   ——  (80) Nachträge zur fossilen Flora Grönlands. _K. Svensk.
        Vetenskaps-Akad. Hand._ Bd. XVIII. [_Flor. Foss. Arct._ vol.
        VI. 1882.]

   ——  (82) Die Fossile-Flora Grönlands. _Flor. Foss. Arct._ vol. VI.

  =Hegelmaier, F.= (72) Zur Morphologie der Gattung _Lycopodium_. _Bot.
        Zeit._ 1872, p. 773.

  =Hick, T.= (93) On a new fossil plant from the Lower Coal-Measures.
        _Journ. Linn. Soc._ vol. XXIX. p. 86.

   ——  (93²) Supplementary note on a new fossil plant. _Ibid._ p. 216.

   ——  (96) On _Rachiopteris cylindrica_. _Mem. Proc. Manchester Lit.
        Phil. Soc._ vol. XLI. pt. i.

  =Hieronymus, G.= (02) Selaginellaceae. _Die Natürlichen
        Pflanzenfamilien._ Engler and Prantl, Teil I. Abt. 4, p. 621.

  =Hill, T. G.= (00) See Scott, D. H. and T. G. Hill.

   ——  (02) See Farmer, J. B. and T. G. Hill.

   ——  (04) On the presence of a parichnos in recent plants. _Annals
        Bot._ vol. XVIII. p. 654.

   ——  (06) On the presence of a parichnos in recent plants. _Ibid._
        vol. XX. p. 267.

   =Hofmeister, W.= (62) On the germination, development, and
        fructification of the Higher Cryptogamia, and on the
        fructification of the Coniferae. _Ray Soc._ 1862.

  =Hollick, A.= (94) Fossil Salvinias, including description of a new
        species. _Torrey Bot. Club_, vol. XXI. No. 6, p. 253.

   ——  (04) Additions to the Palaeobotany of the Cretaceous Formation
        on Long Island. _Bull. New York Bot. Gard._ vol. III. p. 403.

   ——  and =E. C. Jeffrey=. (09) Studies of Cretaceous coniferous
        remains from Kreischerville, New York. _Mem. New York Bot.
        Gard._ vol. III.

  =Hooker, Sir J. D.= (48) On the vegetation of the Carboniferous
        Period, as compared with that of the present day. _Mem. Geol.
        Soc. Great Britain_, vol. II. pt. ii. p. 387.

   ——  (48²) Remarks on the structure and affinities of some
        _Lepidostrobi_. _Ibid._ p. 440.

   ——  (59) Stangeria paradoxa. _Bot. Mag._ Tab. 5121.

  =Hooker, Sir W. J.= and =J. G. Baker=. (68) Synopsis Filicum.
        _London._

  =Hooker, Sir W. J.= and =R. K. Greville=. (31) Icones Filicum. Vol.
        II. _London._

  =Hosius= and =von der Marck=. (80) Die Flora der Westfälischen
        Kreideformation. _Palaeont._ Bd. XXVI. p. 127.

  =Hovelacque, M.= (92) Recherches sur le _Lepidodendron selaginoides_,
        Sternb. _Mém. Soc. Linn. Normandie_, vol. XVII.

  =Hudson, W. H.= (92) The Naturalist in La Plata. _London._

  =Jack, R. L.= and =R. Etheridge=. (92) The geology and palæontology
        of Queensland and New Guinea. _Brisbane._

  =Jahn, J. J.= (03) Ueber die Étage H. im mittelböhmischen Devon.
        _Verh. Reichsanst. Wien_, No. 4, p. 73.

  =Jeffrey, E. C.= (98) The morphology of the central cylinder in
        vascular plants. _Brit. Assoc. Rep._ (_Toronto Meeting_), p.
        869.

   ——  (98²) The Gametophyte of _Botrychium virginianum_. _Trans.
        Canad. Inst._ vol. V. p. 265.

   ——  (00) The morphology of the central cylinder in the Angiosperms.
        _Ibid._ vol. VI. p. 599.

   ——  (03) The structure and development of the stem in the
        Pteridophyta and Gymnosperms. _Phil. Trans. R. Soc._ vol. CXCV.
        p. 119.

   ——  (09) See Hollick, A. and E. C. Jeffrey.

  =Jennings, A. Vaughan= and =Kate M. Hall=. (91) Notes on the
        structure of _Tmesipteris_. _Proc. R. Irish Acad._ [3] vol. II.
        p. 1.

  =Jones, C. E.= (05) The morphology and anatomy of the stem of the
        genus _Lycopodium_. _Trans. Linn. Soc._ vol. VII. p. 15.

  =Jordan, Rose=. (03) On some peculiar tyloses in _Cucumis sativus_.
        _New Phytologist_, vol. II. p. 208.

  =Karsten, G.= (95) Morphologische und biologische Untersuchungen über
        einige Epiphytenformen der Molukken. _Ann. Jard. Buitenzorg_,
        vol. XII. p. 117.

  =Kidston, R.= (82) On the fructification of _Eusphenopteris tenella_
        and _Sphenopteris microcarpa_. _R. Physc. Soc. Edinb._ vol. VII.

   ——  (83) Report on the fossil plants collected by the Geological
        Survey of Scotland in Eskdale and Liddesdale. _Trans. R. Soc.
        Edinburgh_, vol. XXX. p. 531.

   ——  (84) On a new species of _Lycopodites_, Goldenberg (_L.
        Stockii_), from the Calciferous Sandstone Series of Scotland.
        _Ann. Mag. Nat. Hist._ [5] vol. XIV. p. 111.

   ——  (84²) On the fructification of _Zeilleria_ (_Sphenopteris_)
        _delicatula_, Sternb. sp.; with remarks on _Urnatopteris_
        (_Sphenopteris_) _tenella_, Brongnt., and _Hymenophyllites_
        (_Sphenopteris_) _quadridactylites_, Gutbier sp. _Quart. Journ.
        Geol. Soc._ vol. XL. p. 590.

   ——  (85) On the relationship of _Ulodendron_, Lindley and Hutton,
        to _Lepidodendron_, Sternberg; _Bothrodendron_, Lindley and
        Hutton; _Sigillaria_, Brongniart; and _Rhytidodendron_, Boulay.
        _Ann. Mag. Nat. Hist._ vol. XVI. p. 123.

   ——  (86²) On a new species of _Psilotites_ from the Lanarkshire
        Coal-field. _Ann. Mag. Nat. Hist._ 1886, p. 494.

   ——  (86³) On the occurrence of _Lycopodites Vanuxemi_, Göppert, in
        Britain, with remarks on its affinities. _Journ. Linn. Soc._
        vol. XXI. p. 560.

   ——  (86⁴) Notes on some fossil plants collected by Mr R. Dunlop,
        Airdrie, from the Lanarkshire Coal-field. _Trans. Geol. Soc.
        Glasgow_, vol. VIII. p. 47.

   ——  (87) On the fructification of some ferns from the Carboniferous
        formation. _Trans. R. Soc. Edinb._ vol. XXXIII. pt. i.

   ——  (88) See Bennie, J. and R. Kidston.

   ——  (88) On the fossil flora of the Radstock series of the Somerset
        and Bristol Coal-field (Upper Coal-Measures). Part I. _Trans.
        R. Soc. Edinb._ vol. XXXIII. pt. 2.

   ——  (88²) On the fructification and affinities of _Archaeopteris
        hibernica_, Forbes sp. _Ann. Mag. Nat. Hist._ [6] vol. II.

   ——  (89) On the fossil plants in the Ravenhead Collection in the
        Free Library and Museum, Liverpool. _Trans. R. Soc. Edinb._
        vol. XXXV. pt. ii.

   ——  (89²) Additional notes on some British Carboniferous Lycopods.
        _Ann. Mag. Nat. Hist._ vol. IV. p. 60.

   ——  (89³) On some fossil plants from Teilia quarry, Gwaenysgor,
        near Prestatyn, Flintshire. _Trans. R. Soc. Edinb._ vol. XXXV.
        pt. ii.

   ——  (91) On the fructification of _Sphenophyllum trichomatosum_,
        Stern. from the Yorkshire Coal-field. _Proc. R. Soc. Edinb._
        vol. XI. p. 56.

   ——  (91²) On the fructification and internal structure of
        Carboniferous ferns in their relation to those of existing
        genera. _Trans. Geol. Soc. Glasgow_, vol. IX. pt. i.

   ——  (91³) On the Fossil Flora of the Staffordshire Coal-fields.
        II. _Trans. R. Soc. Edinb._ vol. XXXVI. p. 63.

   ——  (93) On _Lepidophloios_, and on the British species of the
        genus. _Trans. R. Soc. Edinb._ vol. XXXVII. pt. iii. p. 529.

   ——  (94) On the various divisions of British Carboniferous rocks as
        determined by their fossil flora. _R. Physc. Soc. Edinb._ vol.
        XII. p. 183.

   ——  (96) On the Fossil Flora of the Yorkshire Coal-fields. I.
        _Trans. R. Soc. Edinb._ vol. XXXVIII. p. 203.

   ——  (97) On the Fossil Flora of the Yorkshire Coal-fields. II.
        _Trans. R. Soc. Edinb._ vol. XXXIX. pt. i. p. 33.

   ——  (01) Carboniferous Lycopods and Sphenophylls. _Trans. Nat.
        Hist. Soc. Glasgow_, vol. VI. pt. i. p. 25.

   ——  (01²) The flora of the Carboniferous Period. _Proc. Yorks.
        Geol. Polyt. Soc._ vol. XIV. pt. ii.

   ——  (02) The flora &c. Second Paper. _Ibid._ vol. XIV. pt. iii. p.
        344.

   ——  (03) The fossil plants of the Carboniferous rocks of Canonbie,
        Dumfriesshire, and of parts of Cumberland and Northumberland.
        _Trans. R. Soc. Edinb._ vol. XL. pt. iv. p. 741.

   ——  (05) On the internal structure of _Sigillaria elegans_ of
        Brongniart’s “Histoire des Végétaux Fossiles.” _Ibid._ vol.
        XLI. pt. iii. p. 533.

   ——  (05²) On the fructification of _Neuropteris heterophylla_.
        _Trans. R. Soc. London_, vol. CXCVII. p. 1.

   ——  (06) On the microsporangia of the Pteridospermeae, with remarks
        on their relationship to existing Ferns. _Phil. Trans. R. Soc._
        vol. CXCVIII. p. 413.

   ——  (07) Note on a new species of _Lepidodendron_ from Pettycur
        (_L. Pettycurense_). _Proc. R. Soc. Edinb._ 1906–07, p. 207.

   ——  (07²) Preliminary note on the internal structure of
        _Sigillaria mammillaris_ Brongniart and _S. scutellata_
        Brongniart. _Ibid._ vol. XXVII. p. 203.

   ——  (08) On a new species of _Dineuron_ and of _Botryopteris_ from
        Pettycur, Fife. _Trans. R. Soc. Edinb._ vol. XLVI. pt. ii. p.
        361.

   ——  (08) See Gwynne-Vaughan, D. T. and R. Kidston.

  =Kidston, R.= and =D. T. Gwynne-Vaughan=. (07) On the fossil
        _Osmundaceae_. Pt. I. _Trans. R. Soc. Edinb._ vol. XLV. pt.
        iii. p. 759.

   ——  (08) _Ibid._ pt. II. _loc. cit._ vol. XLVI. pt. ii. p. 213.

   ——  (09) _Ibid._ pt. III. _loc. cit._ vol. XLVI. pt. iii. p. 651.

  =Kitchin, F. L.= (08) The invertebrate fauna and palaeontological
        relations of the Uitenhage series. _Ann. S. African Mus._ vol.
        VII. pt. ii.

  =Knowlton, F. H.= (98) A catalogue of the Cretaceous and Tertiary
        plants of North America. _Bull. U. S. Geol. Surv._ No. 152.

   ——  (99) Fossil flora of the Yellowstone National Park. _U. S.
        Geol. Surv. Mem._ XXXIII. pt. ii.

   ——  (02) Report on a small collection of fossil plants from the
        vicinity of Porcupine Butte, Montana. _Bull. Torrey Bot. Club_,
        vol. XXIX.

  =Kny, L.= (75) Die Entwickelung der Parkeriaceen dargestellt an
        _Ceratopteris thalictroides_, Brongniart. _Nova Acta K.
        Leop.-Car. Deutsch. Akad. Naturf._ vol. XXXVII.

   =Koehne, W.= (04) Sigillarienstämme, Unterscheidungsmerkmale,
        Arten, Geologische Verbreitung &c. _Abh. K. Preuss. Geol.
        Landes._ [N. F.], Heft XLIII.

  =Krasser, F.= (95) Kreidepflanzen von Lesina. _Jahrb. K.-K. Geol.
        Reichs._ Bd. XLV. p. 37.

   ——  (96) Beiträge zur Kenntniss der Fossilen Kreideflora von
        Kunstadt in Mähren. _Beit. Paläont. Geol. Österreich.-Ung. und
        des Orients_, Bd. X. Heft 3.

   ——  (00) Die von W. A. Obrutschew in China und Centralasien 1893–94
        gesammelten fossilen Pflanzen. _Denksch. K. Akad. Wiss. Wien_,
        Bd. LXX.

   ——  (06) Ueber die fossile Kreideflora von Grünbach in
        Niederösterreich. _Sitzb. K. Akad. Wiss. Wien_ (Anz. iii.).

   ——  (09) Die Diagnosen der von D. Stur in der obertriadischen Flora
        der Lunzerschichten als Marattiaceenarten unterschiedenen
        Farne. _Sitz. Kais. Akad. Wiss. Wien_, Bd. CXVIII. Abt. i.

  =Kubart, B.= (09) Untersuchungen über die Flora des Ostrau-Karwiner
        Kohlenbeckens. I. Die Spore von _Spencerites membranaceus_ n.
        sp. _Denksch. K. Akad. Wiss. Wien_, Bd. LXXXV.

  =Kühn, R.= (90) Untersuchungen über die Anatomie der Marattiaceen.
        _Flora._

  =Kurr, J. G.= (45) Beiträge zur fossilen Flora der Juraformation.
        _Stuttgart._

  =Kurtz, F.= (94) Contribuciones a la Palaeophytologia Argentina.
        _Revist. Mus. de la Plata_, vol. VI.

  =Lang, W. H.= (99) The prothallus of _Lycopodium clavatum_ L. _Annals
        Bot._ vol. XIII. p. 279.

   ——  (08) Preliminary statement on the morphology of the cone of
        _Lycopodium cernuum_ and its bearing on the affinities of
        _Spencerites_. _Proc. Roy. Soc. Edinb._ vol. XXVIII. pt. V. p.
        356.

  =Leclerc du Schlon=. (85) Recherches sur la dissemination des Spores
        dans les Cryptogames vasculaires. _Ann. Sci. nat._ [7], vol.
        II. p. 5.

  =Leslie, T. N.= (06) See Mellor, E. T. and T. N. Leslie.

  =Lesquereux, L.= (78) Contributions to the fossil flora of the
        Western Territories. Pt. II. The Tertiary floras. _U. S. Geol.
        Surv. Report_.

  =Leuthardt, F.= (04) Die Keuperflora von Neuewelt bei Basel. Teil II.
        _Abh. Schweiz. Pal. Ges._ Bd. XXXI. p. 25.

  =Lignier, O.= (03) Equisétales et Sphénophyllales. Leur origine
        filicinéenne commune. _Bull. Soc. Linn. Normandie_ [5], vol.
        VII. p. 93.

   ——  (08) Sur l’origine des Sphénophyllées. _Bull. Soc. Bot. France_
        [4], vol. VIII. p. 278.

  =Lindman, C. A. M.= (04) _Regnellidium_ novum genus Marsiliacearum.
        _Arkiv Bot. K. Svensk. Vetenskaps-Akad. Stockholm._

  =Lloyd, E.= and =L. M. Underwood.= (00) A review of the species of
        _Lycopodium_ of North America. _Bull. Torrey Bot. Club_, vol.
        XXVII. p. 147.

  =Logan, W. E.= (42) On the character of the beds of clay immediately
        below the coal-seams of S. Wales. _Trans. Geol. Soc. London_,
        vol. VI. p. 491.

   =Lomax, J.= (90) See Cash, W. and J. Lomax.

   ——  (00) See Wild, G. and J. Lomax.

   ——  (05) See Weiss, F. E. and J. Lomax.

  =Luerssen, C.= (89) Die Farnpflanzen. _Rabenhorst’s Kryptogamen
        Flora_, Bd. III. _Leipzig._

  =Lulham, R. B. J.= (05) See Tansley, A. G. and R. B. J. Lulham.

  =Lyon, F. M.= (01) A study of the sporangia and gametophytes of
        _Selaginella apus_ and _S. rupestris_. _Bot. Gaz._ vol. XXXII.
        p. 125.

  =McCoy, Sir F.= (47) On the fossil botany and zoology of the rocks
        associated with the coal of Australia. _Ann. Mag. Nat. Hist._
        [1], vol. XX. p. 151.

   ——  (60) A commentary on “A communication made by the Rev. W. B.
        Clarke” &c. _Trans. R. Soc. Victoria_, vol. V. p. 96.

   ——  (74) Prodromus of the Palaeontology of Victoria. _Geol. Surv.
        Vict., Decades_ I–V.

  =McNicol, Mary=. (08) On Cavity Parenchyma and Tyloses in Ferns.
        _Ann. Bot._ vol. XXII. p. 401.

  =Marion, A. F.= (90) Sur le _Gomphostrobus heterophylla_. _Compt.
        Rend._ p. 892.

  =Maslen, A. J.= (99) The structure of _Lepidostrobus_. _Trans. Linn.
        Soc._ vol. V. p. 357.

   ——  (06) See Scott, D. H. and A. J. Maslen.

  =Mellor, E. T.= and =T. N. Leslie=. (06) On a fossil forest recently
        exposed in the bed of the Vaal River at Vereeniging. _Trans.
        Geol. Soc. S. Africa_, vol. IX. p. 125.

  =Mettenius, G.= (60) Beiträge zur Anatomie der Cycadeen. _Abh. K.
        Sächs. Ges. Wiss._ Bd. VII. p. 567.

   ——  (63) Ueber den Bau von _Angiopteris_. _Abh. K. Sächs. Ges.
        Wiss._ Bd. IX.

  =Miller, H.= (57) The testimony of the rocks. _Edinburgh._

  =Möller, H.= (02) Bidrag till Barnholms Fossila Flora. Pteridofyter.
        _Lunds Univ. Årsskrift_, Bd. XXXVIII. No. 5.

  =Mohl, H. von=. (40) Ueber den Bau des Stammes von _Isoetes
        lacustris_. _Linnaea_, vol. XIV.

  =Morris, J.= (40) _Ex_ Prestwich’s, J., Memoir on the Geology of
        Coalbrook Dale. _Trans. Geol. Soc._ vol. V. p. 413.

   ——  (45) See Strzelecki, Count.

   ——  (63) See Oldham, T. and J. Morris.

  =Motelay, L.= and =Vendryès=. (82) Monographie der Isoetaceae. _Actes
        Soc. Linn. Bordeaux_, Tom. XXXVI. p. 309.

  =Münster, G. Graf zu=. (42) Beiträge zur Petrefacten-Kunde. Heft 5.
        _Bayreuth._

  =Murchison, R. I.=, =J. Buchman=, and =H. E. Strickland=. (45)
        Outline of the Geology of the neighbourhood of Cheltenham.
        _London._

  =Murchison, R.=, =E. de Verneuil=, and =Count A. Keyserling=. (45)
        Géologie de la Russie d’Europe. Vol. II. _London and Paris._

   =Nathorst, A. G.= (78) Beiträge zur fossilen Flora Schwedens.
        Ueber einige Rhätische Pflanzen von Pålsjö in Schonen.
        _Stuttgart._

   ——  (78²) Om Floran i Skånes kolförande Bildningar. _Sver. Geol.
        Unders._ Ser. C.

   ——  (90) Ueber das angebliche Vorkommen von Geschieben des
        Hörsandsteins in den norddeutschen Diluvialablagerungen. _Arch.
        Ver. Freund. Nat. Mecklenb._, Jahr. XLIV.

   ——  (02) Zur fossilen Flora der Polarländer. I. Zur Oberdevonischen
        Flora der Bären-Insel. _K. Svensk. Vetenskaps-Akad. Hand._ Bd.
        XXXVI. No. 3.

   ——  (02²) Beiträge zur Kenntniss Mesozoischen Cycadophyten.
        _Ibid._ Bd. XXXVI. No. 4.

   ——  (04) Die Oberdevonische Flora des Ellesmere Landes. _Rep.
        Second Norwegian Arctic Exp. in the Fram_ (1898–02), No. 1.

   ——  (04²) Sur la flore fossile antarctique. _Compt. Rend._ (June
        6.)

   ——  (06) Om Några Ginkgoväxter från Kolgrufvorna vid Stabbarp i
        Skåne. _Lunds Univ. Årsskrift_, N.F. Bd. II. No. 8.

   ——  (06²) Bemerkungen über _Clathropteris meniscoides_,
        Brongn., und _Rhizomopteris cruciata_, Nath. _K. Svensk.
        Vetenskaps-Akad. Hand._ Bd. XLI. No. 2.

   ——  (06³) Ueber _Dictyophyllum_ und _Camptopteris spiralis_.
        _Ibid._ No. 5.

   ——  (07) Ueber die Anwendung von Kollodium-Abdrücken bei der
        Untersuchung fossiler Pflanzen. _Arkiv Bot., Stockholm_, Bd.
        VII. No. 4.

   ——  (07²) Ueber _Thaumatopteris Schenki_. _K. Svensk.
        Vetenskaps-Akad. Hand._ Bd. XLII. No. 3.

   ——  (08) Paläobotanisch. Mitteilungen, III. _Ibid._ Bd. XLIII. No.
        3.

  =Newberry, J. S.= (91) The Flora of the Great Falls Coal-Field,
        Montana. _Amer. Journ. Sci._ vol. XLI. p. 191.

  =Newton, R. Bullen.= (09) Fossils from the Nubian Sandstone of Egypt.
        _Geol. Mag._ vol. VI. p. 352.

  =Oldham, R. D.= (97) On a plant of _Glossopteris_ with part of the
        rhizome attached, and on the structure of _Vertebraria_. Rec.
        _Geol. Surv. India_, vol. XXX. pt. i. p. 45.

  =Oldham, T.= and =J. Morris=. (63) Fossil Flora of the Gondwana
        system. Vol. I. pt. i. Fossil Flora of the Rajmahal series in
        the Rajmahal Hills. Mem. _Geol. Surv. India_ [2], _Calcutta._

  =Oliver, F. W.= (02) A vascular Sporangium. _New Phytologist_, vol.
        I. p. 60.

   ——  (04) On the structure and affinities of _Stephanospermum_,
        Brongn., a genus of fossil Gymnosperm seeds. _Trans. Linn.
        Soc._ vol. VI. pt. 8.

  =Peach, C. W.= (78) On the circinate vernation, fructification, and
        varieties of _Sphenopteris affinis_ and on _Staphylopteris_ (?)
        _Peachii_ of Etheridge and Balfour, a genus of plants new to
        British rocks. _Quart. Journ. Geol. Soc._ vol. XXXIV. p. 131.

  =Pelourde, F.= (08) Recherches sur la position systématique des
        plantes fossiles dont les tiges out été appelées _Psaronius_,
        _Psaroniocaulon_, _Caulopteris_. _Bull. Soc. bot. France_ [4],
        tome VIII.

   ——  (08²) Recherches comparatives sur la structure de la racine
        chez un certain nombre de _Psaronius_. _Ibid_. p. 352.

   ——  (09) Recherches comparatives sur la structure des fougères
        fossiles et vivants. _Ann. Sci. nat._ vol. X. p. 115.

   ——  (09²) Observations sur un nouveau type de pétiole fossile, le
        _Flicheia esnostensis_. _Mém. Soc. d’hist. nat. d’Autun_, tome
        XXI.

  Penhallow, D. P. (92) Additional notes on Devonian plants from
        Scotland. _Canadian Rec. Sci._ vol. V. no. 1.

   ——  (02) _Osmundites skidegatensis. Trans. R. Soc. Canada_ [2],
        vol. VIII. sect. 4.

  Phillips, J. (75) Illustrations of the Geology of Yorkshire, pt. I.
        The Yorkshire Coast (edit. 3). _London_.

  Pittman, E. F. (93) See David, E. and E. F. Pittman.

  Potonié, H. (89) Der im Lichthof der Königlichen Geologischen
        Landesanstalt und Bergakademie aufgestellte Baumstumpf mit
        Wurzel aus dem Carbon des Piesberges. _Jahrb. K. Preuss. Geol.
        Landes_, p. 246.

   ——  (91) _Bericht. Deutsch. bot. Ges._ vol. IX. p. 256.

   ——  (92) Ueber einige Carbonfarne. _Jahrb. K. Preuss. Geol.
        Landes._ 1891.

   ——  (92²) Die den Wasserspalten physiologischentsprechenden Organe
        bei fossilen und recenten Farnarten. _Sitz.-Ber. Ges.
        naturforsch. Freunde zu Berlin. July_ 19, 1892.

   ——  (93²) Anatomie der beiden “Male” auf dem unteren Wangenpaar
        und der beiden Seitennärbchen der Blattnarbe des
        Lepidodendron-Blattpolsters. _Ber. deutsch. Bot. Ges._ Bd. XI.
        Heft 5, p. 319.

   ——  (93³) Eine gewöhnliche Art der Erhaltung von _Stigmaria_ als
        Beweis für die Autochthonie von Carbon-Pflanzen. _Zeits.
        Deutsch. Geol. Ges._

   ——  (95) Die Beziehung zwischen dem echt-gabeligen und dem
        fiederigen Wedel-Aufbau der Farne. _Ber. Deutsch. Bot. Ges._
        Bd. XIII. Heft 6.

   ——  (99) Lehrbuch der Pflanzenpalaeontologie. _Berlin._

   ——  (00) Fossile Pflanzen aus Deutsch- und
        Portugiesisch-Ost-Afrika. _Deutsch-Ost-Afrika_, Bd. VII.

   ——  (01) Fossile Lycopodiaceae und Selaginellaceae. Engler and
        Prantl: _Die natürlichen Pflanzenfamilien_, Teil I. Abt. IV. p.
        715.

   ——  (01²) Die Silur- und die Culm-Flora. _Abh. K. Preuss. Geol.
        Landes._ Heft XXXVI.

   ——  (02) Ueber die fossilen Filicales &c. Engler and Prantl: _Die
        natürlichen Pflanzenfamilien_, Teil I. Abt. IV. p. 473.

   ——  (03) Zur Physiologie und Morphologie der fossilen
        Farn-Aphlebien. _Ber. Deutsch. Bot. Ges._ Bd. XXI. Heft 3.

   ——  (04) Abbildungen und Beschreibungen fossilen Pflanzen-Reste der
        Palaeozoischen und Mesozoischen Formationen. Lief. II. _K.
        Preuss. Geol. Landes- und Bergakad._

   ——  (05) _Ibid._ Lief. III.

   ——  (06) _Ibid._ Lief. III.

   ——  (07) Abbildungen und Beschreibungen &c. Lief. V.

  =Prantl, K.= (81) Untersuchungen zur Morphologie der
        Gefässkryptogamen. Heft II. _Leipzig._

   ——  (02) See Engler, A. and K. Prantl.

  =Pritzel, E.= (02) Lycopodiales. Engler and Prantl: _Die natürlichen
        Pflanzenfamilien_, Teil I. Abt. IV. p. 563.

  =Raciborski, M.= (91) Ueber die Osmundaceen und Schizaeaceen der
        Juraformation. _Engler’s Bot. Jahrb._ vol. XIII. p. 1.

  =Reid, C.= (99) The Origin of the British Flora. _London._

  =Reinecke, F.= (97) Die Flora der Samoa-Inseln. _Engler’s Bot.
        Jahrb._ Bd. XXIII. p. 237.

  =Renault, B.= (69) Étude sur quelques végétaux silicifiés des
        environs d’Autun. _Ann. Sci. nat._ [5], vol. XII. p. 161.

   ——  (76) Étude du genre _Botryopteris_. _Ann. Sci. nat._ [6], vol.
        I. p. 220.

   ——  (76) Étude du genre _Myelopteris_. _Mém. Acad. Sci. l’Instit.
        France_, Tome XXII.

   ——  (79) Structure comparée de quelques tiges de la Flore
        Carbonifère. _Nouv. Arch. Mus. Paris._

   ——  (81) Étude sur les _Stigmaria_. _Ann. Sci. Géol._ tome XII.

   ——  (90) Sur une nouvelle Lycopodiacée houillère (_Lycopodiopsis
        Derbyi_). _Compt. Rend._, _April 14_.

  =Renault, B.= and =C. Grand’Eury.= (75) Recherches sur les végétaux
        silicifiés d’Autun. _Mém. Acad. Paris_, vol. XXII.

  =Renault, B.= and =A. Roche.= (97) Sur une nouveau Diploxylée. _Bull.
        Soc. d’hist. nat. d’Autun._

  =Renier, A.= (08) Origine raméale des cicatrices Ulodendroides du
        _Bothrodendron punctatum_, Lind. et Hutt. _Compt. Rend., June
        29._

  =Reuss, A. E.= (46) Die Versteinerungen der Böhmischen
        Kreideformation. _Stuttgart_, 1845–46.

  =Rhode, J. G.= (20) Beiträge zur Pflanzenkunde der Vorwelt. _Breslau._

  =Richter, P. B.= (06) Beiträge zur Flora der unteren Kreide
        Quedlinburgs. Teil I. Die Gattung _Hausmannia_, Dunker, und
        einige seltenere Pflanzenarten. _Leipzig._

  =Richter, R.= (56) See Unger, F. and R. Richter.

  =Roche, A.= (97) See Renault, B. and A. Roche.

  =Roehl, Major von.= (69) Fossile Flora der Steinkohlen Formation
        Westphalens. _Palaeont._ Bd. XVIII. p. 1.

  =Roemer, F. A.= (54) Beiträge zur geologischen Kenntniss des
        nordwestlichen Harzgebirges. _Palaeont._ Bd. III.

  =Royle, J. F.= (33) Illustrations of the Botany and other branches of
        natural history of the Himalayan Mountains. _London_, 1833–39.

  =Rudolph, K.= (05) Psaronien und Marattiaceen. _Denksch. Kais. Akad.
        Wiss. Wien_, Bd. LXXVIII.

  =Sadebeck, H.= (02) See Engler, A. and K. Prantl.

   =Salfeld, H.= (07) Fossile Landpflanzen der Rät.- und
        Juraformation Südwestdeutschlands. _Palaeont._ Bd. LIV.

   ——  (09) Beiträge zur Kenntniss jurassischer Pflanzenreste aus
        Norddeutschland. _Palaeont_. Bd. LVI.

  =Salter, J. W.= (58) On some remains of terrestrial plants in the Old
        Red Sandstone of Caithness. _Quart. Journ. Geol. Soc. Proc._
        vol. XIV. p. 77.

  =Saporta, le Marquis de.= (88) Dernières adjonctions à la flore
        fossile d’Aix-en-Provence. _Ann. Sci. nat._ [7], vol. VII.

   ——  (94) Flore fossile du Portugal. _Direct. Trav. Géol. Portugal.
        Lisbon._

  =Saxelby, E. M.= (08) The origin of the roots in _Lycopodium Selago_.
        _Annals Bot_. vol. XXII. p. 21.

  =Schenck, H.= (93) Beiträge zur Biologie und Anatomie der Lianen. Th.
        II. _Jena_.

  =Schenk, A.= (71) Beiträge zur Flora der Vorwelt. Die Flora der
        Nordwestdeutschen Wealdenformation. _Palaeont_. Bd. XIX. p. 203.

   ——  (76) Zur Flora der Nordwestdeutschen Wealdenformation.
        _Palaeont_. Bd. XXVIII. p. 157.

   ——  (85) Die während der Reise des Grafen Bela Széchenyi in China
        gesammelten fossilen Pflanzen. _Palaeont_. Bd. XXXI. p. 165.

   ——  (87) Fossile Pflanzen aus der Albourskette. _Bibl. bot_.
        (_Uhlworm und Haenlein_), Heft VI.

  =Schmalhausen, J=. (77) Die Pflanzenreste aus der Ursa-Stufe im
        Fluss-Geschiebe des Ogur in Ost-Sibirien. _Bull. Acad. Imp.
        Sci. St Petersburg_. Tome XXII. p. 278.

   ——  (94) Ueber Devonische Pflanzen aus dem Donetz-Becken. _Mém.
        Com. Géol_. vol. VIII. _St Petersburg_.

  =Schuster, J.= (08) Zur Kenntniss der Flora der Saarbrücker Schichten
        und des pfälzischen Oberrotliegenden. _Geognost. Jahresheft_,
        XX. 1907.

  =Scott, D. H.= (96) An introduction to structural botany. Pt. II.
        _London_.

   ——  (97) On the structure and affinities of fossil plants from the
        Palaeozoic rocks. On _Cheirostrobus_, a new type of fossil cone
        from the Lower Carboniferous strata (Calciferous Sandstone
        series). _Phil. Trans. R. Soc_. vol. CLXXXIX. p. 1.

   ——  (98) On the structure and affinities &c. II. On _Spencerites_,
        a new genus of Lycopodiaceous cones from the Coal-Measures
        founded on the _Lepidodendron Spenceri_ of Williamson. _Ibid._
        vol. CLXXXIX. p. 83.

   ——  (00) Studies in fossil botany. _London._

   ——  (01) On the structure and affinities &c. IV. The seed-like
        fructification of _Lepidocarpon_, a genus of Lycopodiaceous
        cones from the Carboniferous formation. _Phil. Trans. R. Soc_.
        vol. CXCIV. p. 291.

   ——  (02) The Old Wood and the New. _New Phytologist_, vol. I. p. 25.

   ——  (04) Germinating spores in a fossil fern Sporangium. _Ibid_.
        vol. III. p. 18.

   ——  (04²) On the occurrence of _Sigillariopsis_ in the Lower
        Coal-Measures of Britain. _Annals Bot._ vol. XVIII. p. 519.

   ——  (05) On the structure and affinities &c. v. On a new type of
        Sphenophyllaceous cone (_Sphenophyllum fertile_) from the Lower
        Coal-Measures. _Phil Trans. R. Soc._ vol. CXCVIII. p. 17.

   ——  (05²) What were the Carboniferous ferns? _Journ. R. Micr.
        Soc._ p. 137.

   ——  (05³) The Sporangia of _Stauropteris oldhamia._ _New Phyt._
        vol. IV. p. 114.

   ——  (06) On the structure of some Carboniferous ferns. _Journ. R.
        Micr. Soc._ p. 518.

   ——  (06²) The occurrence of germinating spores in _Stauropteris
        oldhamia._ _New Phyt._ vol. V. p. 170.

   ——  (06³) The structure of _Lepidodendron obovatum_, Sternberg.
        _Annals Bot._ vol. XX. p. 317.

   ——  (07) The present position of Palaeozoic botany. _Progressus Rei
        Botanicae_, Bd. I. p. 139.

   ——  (08) Studies in fossil botany (edit. II). Vol. I. _London._

   ——  (09) _Ibid._ Vol. II.

   ——  (09²) Dr Paul Bertrand on the Zygopterideae. _New Phyt._ vol.
        VIII. p. 266.

  =Scott, D. H.= and =T. G. Hill.= (00) The structure of _Isoetes
        Hystrix_. _Annals Bot._ vol. XIV. p. 413.

  =Scott, D. H.= and =A. J. Maslen=. (06) On the structure of
        _Trigonocarpon olivaeforme_. _Ann. Bot._ vol. XX. p. 109.

  =Scott, J.= (74) Notes on the tree ferns of British Sikkim. _Trans.
        Linn. Soc._ vol. XXX. p. 1.

  =Scott, Rina.= (06) On the megaspore of _Lepidostrobus foliaceus_.
        _New Phyt._ vol. V. p. 116.

   ——  (08) On _Bensonites fusiformis_, sp. nov., a fossil associated
        with _Stauropteris burntislandica_, P. Bertrand, and on the
        sporangia of the latter. _Annals Bot._ vol. XXII. p. 683.

  =Sellards, E. H.= (00) A new genus of ferns from the Permian of
        Kansas. _Kansas Univ. Quart._ vol. IX.

   ——  (01) Permian plants. _Taeniopteris_ of the Permian of Kansas.
        _Ibid._ vol. X. no. 1.

  =Seward, A. C.= (88) On a specimen of _Cyclopteris_ (Brongniart).
        _Geol. Mag._ vol. V. p. 344.

   ——  (90) Notes on _Lomatophloios macrolepidotus_ (Gold.). _Proc.
        Camb. Phil. Soc._ vol. VII. pt. ii.

   ——  (90²) Specific variation in Sigillarieae. _Geol. Mag._ vol.
        VII. p. 213.

   ——  (91) On an erect tree stump with roots, from the coal of
        Piesberg near Osnabrück. _Ibid._ vol. VIII.

   ——  (92) Fossil plants as tests of climate. _London._

   ——  (94) Coal: its structure and formation. _Sci. Progr._ vol.
        II. pp. 355–431.

   ——  (99) Notes on the Binney collection of Coal-Measure plants.
        _Proc. Phil. Soc. Camb._ vol. X. p. 137.

   ——  (99²) On the structure and affinities of _Matonia pectinata_,
        R. Br. with notes on the geological history of the Matonineae.
        _Phil. Trans. R. Soc._ vol. CXCI. p. 171.

   ——  (00) Catalogue of the Mesozoic plants in the Department of
        Geology, British Museum. The Jurassic Flora. I. The Yorkshire
        Coast. _London._

   ——  (03) Fossil floras of Cape Colony. _Ann. S. African Museum_,
        vol. IV. pt. i.

   ——  (04) The Jurassic Flora. II. Liassic and Oolitic floras of
        England. _Cat. Mesoz. Plants, British Museum. London._

   ——  (04²) On a collection of Jurassic plants from Victoria. _Rec.
        Geol. Surv. Victoria_, vol. I. pt. iii.

   ——  (04³) Presidential address. _Report of the 73rd meeting of the
        Brit. Assoc._ (Southport) p. 824.

   ——  (06) The anatomy of _Lepidodendron aculeatum_, Sternberg.
        _Annals Bot._ vol. XX. p. 371.

   ——  (07) Fossil plants from Egypt. _Geol. Mag._ vol. IV. [V] p. 253.

   ——  (07²) On a collection of Permo-Carboniferous plants from the
        St Lucia (Somkale) coalfield, Zululand, and from the Newcastle
        district, Natal. _Trans. Geol. Soc. S. Africa_, vol. X. p. 65.

   ——  (07³) Notes on fossil plants from South Africa. _Geol. Mag._
        vol. IV. p. 481.

   ——  (07⁴) Jurassic Plants from Caucasia and Turkestan. _Mém. Com.
        Géol. St Pétersbourg_, Livr. 38.

   ——  (07⁵) Permo-Carboniferous Plants from Kashmir. _Rec. Geol.
        Surv. India_, vol. XXXVI. pt. i.

   ——  (08) On a collection of fossil plants from South Africa.
        _Quart. Journ. Geol. Soc._ vol. LXIV. p. 83.

   ——  (09) Fossil plants from the Witteberg series of Cape Colony.
        _Geol. Mag._ vol. VI. p. 482.

  =Seward, A. C.= and =E. Dale=. (01) On the structure and affinities
        of _Dipteris_, with notes on the geological history of the
        Dipteridinae. _Phil. Trans. R. Soc._ vol. CXCIV. p. 487.

  =Seward, A. C.= and =S. O. Ford=. (03) The anatomy of _Todea_,
        with notes on the geological history and affinities of the
        Osmundaceae. _Trans. Linn. Soc._ vol. VI. pt. v.

   ——  (06) The Araucarieae, recent and extinct. _Phil. Trans. R.
        Soc._ vol. CXCVIII. p. 305.

  =Seward, A. C.= and =J. Gowan=. (00) The Maidenhair Tree. (_Ginkgo
        biloba_, L.) _Ann. Bot._ vol. XIV. p. 109.

  =Seward, A. C.= and =A. W. Hill=. (00) On the structure and
        affinities of a Lepidodendroid stem from the Calciferous
        Sandstone of Dalmeny, Scotland. _Trans. R. Soc. Edinb._ vol.
        XXXIX. pt. iv. p. 907.

   =Seward, A. C.= and =T. N. Leslie=. (08) Permo-Carboniferous
        plants from Vereeniging. _Quart. Journ. Geol. Soc._ vol. LXIV.
        p. 109.

  =Seward, A. C.= and =A. Smith Woodward=. (05) Permo-Carboniferous
        Plants and Vertebrates from Kashmir. _Mem. Geol. Surv. India_,
        vol. V. Mem. 2.

  =Shattock, S. G.= (88) On the scars occurring on the stem of _Dammara
        robusta_, Moore. _Journ. Linn. Soc._ vol. XXIX. p. 441.

  =Shove, Rosamund=. (00) On the structure of the stem of _Angiopteris
        erecta_. _Annals Bot._ vol. XIV.

  =Smith, G. O.= and =D. White=. (05) The geology of the Perry basin in
        South Eastern Maine. _U. S. Geol. Surv._ No. 35.

  =Sollas, Igerna B. J.= (01) Fossils in the Oxford Museum. On the
        structure and affinities of the Rhaetic plant _Naiadita. Quart.
        Journ. Geol. Soc._ vol. LVII. p. 307.

  =Solms-Laubach, H. Graf zu=. (83) Zur Geschichte der _Scolecopteris_,
        Zenker. _Nachr. K. Ges. Wise. Univ. Göttingen_, p. 26.

   ——  (92) Ueber die in den Kalksteinen des Kulm von
        Glätzisch-Falkenberg in Schlesien erhaltenen Structurbietenden
        Pflanzenreste. _Bot. Zeit._ p. 49.

   ——  (94) Ueber _Stigmariopsis_, Grand’Eury. _Palaeont. Abh._
        (_Dames and Kayser_) [N. F.] Bd. II. _Jena._

   ——  (96) Ueber die seinerzeit von Unger beschriebenen
        Strukturbietenden Pflanzenreste des Unterculm von Saalfeld in
        Thüringen. _Abh. K. Preuss. Geol. Landes._ Heft XXIII.

   ——  (99) Ueber das Genus _Pleuromeia_. _Bot. Zeit._ p. 227.

   ——  (99²) Beiträge zur Geologie und Palaeontologie von Südamerika.
        _Neues Jahrb. Min._, Beilageband XII. p. 593.

   ——  (02) _Isoetes lacustris_, seine Verzweigung und sein Vorkommen
        in den Seen des Schwarzwaldes und der Vogesen. _Bot. Zeit._ p.
        179.

   ——  (04) Ueber die Schicksale der als _Psaronius brasiliensis_
        beschriebenen Fossilreste unserer Museen. _Festsch. P.
        Ascherson’s Siebzigstem Geburtstage._ _Berlin._

   ——  (06) Die Bedeutung der Palaeophytologie für die systematische
        Botanik. _Mitt. Philo-math. Ges. Elsass-Loth._ Bd. III. p. 353.

  =Spieker, T.= (53) Zur _Sigillaria Sternbergi_ Münster, des bunten
        Sandsteins zu Bernburg. _Zeits. Gesammt. Naturw._ Bd. II.
        _Halle._

  =Sprengel, A.= (28) Commentatio de Psarolithis. _Halle._

  =Spruce, R.= (08) Notes of a botanist on the Amazon and Andes (Edited
        by A. R. Wallace). _London._

  =Staub, M.= (87) Die Aquitanische Flora des Zsilthales im comitate
        Hunyad. _Mitt. Jahrb. K. Ungar. Geol. Anst._ Bd. VII. Heft vi.

  =Stenzel, C. G.= (54) Ueber die Staarsteine. _Nova Acta Leop. Carol._
        Bd. XXIV.

   ——  (86) _Rhizodendron Oppoliense_, Göpp. _Jahresber. Schles. Ges.
        Vaterl. Cultur._ Ergänzungsheft LXIII.

   ——  (89) Die Gattung _Tubicaulis_. _Bibl. Bot._ Heft XII.

   ——  (97) Verkieselte Farne von Kamenz in Sachsen. _Mitt. K.
        Mineralog. Geol. und prähistorisch. Mus. Dresden._ Heft XIII.

   ——  (06) Die Psaronien, Beobachtungen und Betrachtungen. _Beit.
        Paläont. Geol. Öst.-Ung._ Bd. XIX.

  =Sterzel, J. T.= (78) Ueber _Palaeojulus dyadicus_ Geinitz und
        _Scolecopteris elegans_ Zenker. _Zeitsch. Deutsch. Geol. Ges._
        p. 417.

   ——  (80) Ueber _Scolecopteris elegans_ Zenker und andere fossile
        Reste. _Zeitschr. Deutsch. Geol. Ges._

   ——  (86) Die Flora des Rothliegenden im Plauenschen Grunde. _Abh.
        K. Sächs. Ges. Wiss._ Bd. XIX.

   ——  (86²) Neue Beitrag zur Kenntniss von _Dicksonites Pluckeneti_
        Brongn. sp. _Zeitschr. Deutsch. Geol. Ges._ p. 773.

   ——  (96) Gruppe verkieselten Araucariten Stämme. _Ber. Naturwiss.
        Ges. Chemnitz_, 1896–99.

   ——  (96²) See Weber, O. and J. T. Sterzel.

  =Stiehler, A. W.= (58) Beiträge zur Kenntniss der vorweltlichen Flora
        des Kreidegebirges im Harze. _Palaeont._ Bd. V.

   ——  (59) Zu _Pleuromeia._ _Zeit. Gesammt. Nat. Halle_, Bd. III. p.
        190.

  =Stokey, A. G.= (07) The roots of _Lycopodium pithyoides_. _Bot.
        Gaz._ vol. XLIV. p. 57.

   ——  (09) The anatomy of _Isoetes_. _Bot. Gaz._ vol. XLVII. p. 311.

  =Stopes, Marie C.= (06) A new fern from the Coal-Measures:
        _Tubicaulis Sutcliffii_, spec. nov. _Mem. Proc. Manch. Lit.
        Phil. Soc._ vol. L.

  =Strasburger, E.= (73) Einige Bemerkungen über Lycopodiaceen. _Bot.
        Zeit._ p. 81.

   ——  (74) Ueber _Scolecopteris elegans_, Zenk. _Jen. Zeitsch.
        Naturwiss._ vol. VIII. p. 88.

  =Strzelecki, Count.= (45) Physical description of New South Wales &c.
        _London._

  =Stur, D.= (81) Die Silur-Flora der Étage H-h in Böhmen. _Sitzb.
        Akad. Wiss. Wien_, 1 Abth. Bd. LXXXIV. p. 330.

   ——  (84) Zur Morphologie und Systematik der Culm- und Carbonfarne.
        _Sitzb. Akad. Wiss. Wien_, Bd. LXXXVIII.

   ——  (85) Die Carbon-Flora der Schatzlarer Schichten. _Abh. K. K.
        Geol. Reichs._ Bd. XI. Abth. I.

  =Sykes, M. Gladys.= (08) The anatomy and morphology of _Tmesipteris_.
        _Annals Bot._ vol. XXII. p. 63.

   ——  (08²) Note on an abnormality found in _Psilotum triquetrum_.
        _Ibid._ vol. XXII. p. 525.

   ——  (08³) Notes on the morphology of the Sporangium-bearing organs
        of the Lycopodiaceae. _New Phyt._ vol. VII. p. 41.

   ——  (09) Note on the Sporophyll of _Lycopodium inundatum_. _Ibid._
        vol. VIII. p. 143.

  =Szajnocha, L.= (88) Ueber fossile Pflanzenreste aus Cacheuta in der
        Argentinischen Republik. _Sitzb. K. Akad. Wiss. Wien_, Bd.
        XCVII. Abth. I. p. 219.

   ——  (91) Ueber einige Carbone Pflanzenreste aus der Argentinischen
        Republik. _Sitzb. K. Akad. Wiss. Wien_, Bd. C. Abth. I. p. 203.

  =Tansley, A. G.= (08) Lectures on the evolution of the filicinean
        vascular system. (Reprinted from the _New Phytologist_.)
        _Cambridge._

   ——  and =Edith Chick.= (01) Notes on the conducting
        tissue-system in Bryophyta. _Annals Bot._ vol. XV. p. 1.

   ——  and =F. E. Fritsch.= (05) The flora of the Ceylon littoral.
        _New Phyt._ vol. IV. p. 1.

   ——  and =R. B. J. Lulham=. (05) A study of the vascular system of
        _Matonia pectinata_. _Annals Bot._ vol. XIX. p. 475.

  =Thiselton-Dyer, Sir W. T.= (05) _Cycas Micholitzii_, Dyer. _Gard.
        Chron._ Aug. 19, p. 142.

  =Thoday, D.= (06) On a suggestion of heterospory in _Sphenophyllum
        Dawsoni_. _New Phyt._ vol. V. p. 91.

  =Thomas, A. P. W.= (02) The affinity of _Tmesipteris_ with the
        Sphenophyllales. _Proc. R. Soc._ vol. LXIX. p. 343.

  =Thomas, Ethel N.= (05) Some points in the anatomy of _Acrostichum
        aureum_. _New Phyt._ vol. IV. p. 175.

  =Thomas, H. H.= (08) See Arber, E. A. N. and H. H. Thomas.

  =Thompson, D’Arcy W.= (80) Notes on _Ulodendron_ and _Halonia_.
        _Edinb. Geol. Soc._

  =Trautschold, H.= (60) See Auerbach, J. and H. Trautschold.

  =Treub, M.= (84–90) Études sur les Lycopodiacées. _Ann. Jard. Bot.
        Buitenzorg_, vol. IV. V. VII. VIII.

  =Underwood, L. E.= (00) See Lloyd, E. and L. M. Underwood.

   ——  (07) A preliminary review of the North American Gleicheniaceae.
        _Bull. Torrey Bot. Club_, vol. XXXIV. p. 243.

  =Unger, F.= and =R. Richter=. (56) Beitrag zur Paläontologie des
        Thüringer Waldes. _Denksch. Wien. Akad._ Bd. XI.

  =Velenovský, J.= (85) Die Gymnospermen der böhmischen
        Kreideformation. _Prag._

   ——  (88) Die Farne der böhmischen Kreideformation. _Prag._

  =Vines, S.= (88) On the systematic position of _Isoetes_, L. _Annals
        Bot._ vol. II. pp. 117, 223.

  =Wanklyn, A.= (69) Description of some new species of fossil ferns
        from the Bournemouth leaf-beds. _Ann. Mag. Nat. Hist._ vol.
        III. p. 10.

  =Ward, L. F.= (99) The Cretaceous Formation of the Black Hills as
        indicated by the fossil plants. _U. S. Geol. Surv._, _19th Ann.
        Rep._ pl. II.

   ——  (00) Status of the Mesozoic Floras of the United States, I. _U.
        S. Geol. Surv._, _20th, Ann. Rep._

   ——  (04) Palaeozoic seed-plants. _Science_, Aug. 26, p. 279.

   ——  (05) Status of the Mesozoic Floras of the United States, II.
        _U. S. Geol. Surv. Monographs_, vol. XLVIII.

  =Watson, D. M. S.= (06) On a “fern” synangium from the Lower
        Coal-Measures of Shore, Lancashire. _Journ. R. Micr. Soc._ p. 1.

   ——  (07) On a confusion of two species (_Lepidodendron Harcourtii_,
        Witham, and _L. Hickii_, sp. nov.) under _Lepidodendron
        Harcourtii_, With. in Williamson’s XIX. Memoir, with a
        description of _L. Hickii_ sp. nov. _Mem. Proc. Manch. Lit.
        Phil. Soc._ vol. LI.

   ——  (08) On the Ulodendron Scar. _Ibid._ vol. LII.

   ——  (08²) The cone of _Bothrodendron mundum_. _Ibid._ vol. LII.

   ——  (09) On _Mesostrobus_, a new genus of Lycopodiaceous cones from
        the Lower Coal-Measures &c. _Annals Bot._ vol. XXIII. p. 379.

  =Weber, O.= and =J. T. Sterzel=. (96) Beiträge zur Kenntniss der
        Medulloseae. _Ber. Naturwiss. Ges. Chemnitz_, 1893–96.

  =Weiss, C. E.= (69) Fossile Flora der jüngsten Steinkohlenformation
        und des Rothliegenden im Saar-Rhein-Gebiete. _Bonn_, 1869–72.

   ——  (70) Studien über Odontopteriden. _Zeitsch. Deutsch. Geol. Ges._

   ——  (79) Bemerkungen zur Fructification von _Nöggerathia. Zeitsch.
        Deutsch. Geol. Ges._

   ——  (84) Zur Flora der ältesten Schichten des Harzes. _Jahrb. K.
        Preuss. Geol. Landes. Berlin_.

   ——  (86) Ueber eine Buntsandstein _Sigillaria_ und deren nächste
        Verwandte. _Ibid._ 1885.

   ——  (88) Ueber neue Funde von Sigillarien in der Wettiner
        Steinkohlengrube. _Zeitsch. Deutsch. Geol. Ges._

   ——  (89) Beobachtungen an Sigillarien von Wettin und Umgegend.
        _Neues Jahrb._ Bd. XLI. p. 376.

   ——  and =J. Sterzel.= (93) Die Sigillarien der Preussischen
        Steinkohlen und Rothliegenden Gebiete. _K. Preuss. Geol.
        Landes._ [N.F.], Heft 2.

  =Weiss, F. E.= (02) On _Xenophyton radiculosum_ (Hick), and on
        a Stigmarian rootlet probably related to _Lepidophloios
        fuliginosus_ (Will.). _Mem. Proc. Manch. Lit. Phil. Soc._ vol.
        XLVI. pt. 3.

   ——  (03) A biseriate Halonial branch of _Lepidophloios fuliginosus.
        Trans. Linn. Soc._ vol. VII. pt. 4.

   ——  (04) A probable parasite of Stigmarian rootlets. _New Phyt._
        vol. III. p. 63.

   ——  (06) On the tyloses of _Rachiopteris corrugata_. _New Phyt._
        vol. V. p. 82.

   ——  (07) The Parichnos in Lepidodendraceae. _Mem. Proc. Manch. Lit.
        Phil. Soc._ vol. LI. pt. ii.

   ——  (08) A Stigmaria with centripetal wood. _Annals Bot._ vol.
        XXII. p. 221.

  =Weiss, F. E.= and =J. Lomax=. (05) The stem and branches of
        _Lepidodendron selaginoides_. _Mem. Proc. Manch. Lit. Phil.
        Soc._ vol. XLIX.

  =White, D.= (93) A new Taeniopteroid Fern and its allies. _Bull.
        Geol. Soc. America_, vol. IV. p. 119.

   ——  (95) The Pottsville series along New River, West Virginia.
        _Bull. Geol. Soc. America_, vol. VI. p. 305.

   ——  (98) _Omphalophloios_, a new Lepidodendroid type. _Ibid._ vol.
        IX. p. 329.

   ——  (99) Fossil flora of the Lower Coal-Measures of Missouri. _U.
        S. Geol. Surv. Mon._ XXXVII.

   ——  (02) Description of a fossil alga from the Chemung of New York.
        _Rep. New York State Palaeontologist_, 1901.

   ——  (04) The seeds of _Aneimites_. _Smithsonian Miscell. Coll._
        vol. XLVII. pt. iii. p. 322.

   ——  (05) See Smith, G. O. and D. White.

   ——  (05²) Fossil plants of the group Cycadofilices. _Smiths. Misc.
        Coll._ vol. XLVIII. pt. iii.

   ——  (07) Permo-Carboniferous changes in South America. _Journ.
        Geol._ vol. XV. p. 615.

   ——  (07²) A remarkable fossil tree trunk from the Middle Devonic
        of New York. _New York State Mus. Bull._ 107. _Albany_.

   ——  (08) Fossil flora of the Coal-Measures of Brazil. _Rio de
        Janeiro_.

  =White, I. C.= (80) See Fontaine, W. M. and I. C. White.

  =Wickes, W. H.= (00) A new Rhaetic section at Bristol. _Proc. Geol.
        Assoc._ vol. XVI. p. 421.

  =Wigglesworth, Grace=. (02) Notes on the rhizome of _Matonia
        pectinata_. _New Phyt._ vol. I. p. 157.

  =Wild, G. and J. Lomax.= (00) A new Cardiocarpon-bearing strobilus.
        _Annals Bot._ vol. XIV. p. 160.

  =Williamson, W. C.= (72) On the organization of the fossil plants of
        the Coal-Measures. III. Lycopodiaceae. _Phil. Trans. R. Soc._
        vol. CLXII. p. 283.

   ——  (76) _Ibid._ pt. vii. _Phil. Trans. R. Soc._ vol. CLXVI. p. 1.

   ——  (77) _Ibid._ pt. viii. _Phil. Trans. R. Soc._ vol. CLXVII. p.
        213.

   ——  (83) Presidential address. _Brit. Assoc._

   ——  (87) Note on _Lepidodendron Harcourtii_ and _L. fuliginosum_.
        _Proc. R. Soc._ vol. XLII. p. 6.

   ——  (92) _Sigillaria_ and _Stigmaria_. _Nat. Science_, p. 214.

   ——  (93) On the organization &c. pt. xix. _Phil. Trans. R. Soc._
        vol. CLXXXIV. p. 1.

   ——  (93²) General morphological and histological index to the
        author’s collective memoirs on the fossil plants of the
        Coal-Measures, pt. ii. _Mem. Proc. Manch. Lit. Phil. Soc._ [7]
        vol. VII.

   ——  (95) On the light thrown upon the question of growth and
        development of the Carboniferous arborescent Lepidodendra by a
        study of the details of their organisation. _Ibid._ vol. IX. p.
        31.

   ——  (96) Reminiscences of a Yorkshire Naturalist. (Edited by Mrs
        Crawford Williamson.) _London_.

  =Woodward, A. Smith=. (05) See Seward, A. C. and A. Smith Woodward.

  =Worsdell, W. C.= (95) On transfusion-tissue; its origin and function
        in the leaves of Gymnospermous plants. _Trans. Linn. Soc._ vol.
        V. p. 301.

  =Wünsch, E. A.= (67) Discovery of erect stems of fossil trees in
        trappean ash in Arran. _Trans. Geol. Soc. Glasgow_, vol. II. p.
        97.

  =Yabe, H.= (05) Mesozoic plants from Korea. _Journ. Colt. Sci. Imp.
        Univ. Japan_, vol. XX.

  =Yapp, R. H.= (02) Two Malayan ‘Myrmecophilous’ ferns, _Polypodium_
        (_Lecanopteris_) _carnosum_ (Blume), and _P. sinuosum_. _Annals
        Bot._ vol. XVI. p. 185.

   ——  (08) Sketches of vegetation at home and abroad. IV. Wicken
        Fen. _New Phyt._ vol. VII. p. 61.

  =Yokoyama, M.= (89) Jurassic plants from Kaga, Hida, and Echizen.
        _Journ. Coll. Sci. Imp. Univ. Japan_, vol. III.

   ——  (06) Mesozoic plants from China. _Ibid._ vol. XXI.

  =Zalessky, M.= (04) Végétaux fossiles du Terrain Carbonifère du
        Bassin du Donetz. _Mém. Com. Géol. St Pétersbourg_. Livr. XIII.

   ——  (07) Sur la présence de _Mixoneura neuropteroides_, Göpp. avec
        _Neuropteris Scheuchzeri_, Hoffmann, et _N. rarinervis_,
        Bunbury &c. _Bull. Com. Géol. St Pétersbourg_, tome XXVI.

   ——  (08) Végétaux fossiles du Terrain Carbonifère du bassin
        du Donetz. II. Étude sur la structure anatomique d’un
        Lepidostrobus. _Mém. Com. Géol._, Livr. XLVI.

  =Zeiller, R.= (79) Note sur quelques fossiles du terrain permien de
        la Corrèze. _Bull. Soc. Géol. France_, tome VIII. p. 196.

   ——  (79²) Note sur le genre _Mariopteris_. _Bull. Soc. Géol.
        France_ [3], tome VII. p. 92.

   ——  (83) Fructifications de Fougères houillères. _Ann. Sci. nat._
        [6], vol. XVI.

   ——  (84) Cônes de fructification des Sigillaires. _Ibid._ vol. XIX.
        p. 256.

   ——  (85) Sur les affinités du genre _Laccopteris_. _Bull. Soc. Bot.
        France_, tome XXXII. p. 21.

   ——  (86) Présentation d’une brochure de M. Kidston sur les
        _Ulodendron_ et observations sur les genus _Ulodendron_ et
        _Bothrodendron_. _Bull. Soc. Géol. France_ [3], tome XIV. p.
        168.

   ——  (89) Sur les variations de formes du _Sigillaria Brardi_,
        Brongn. _Ibid._ [3], tome XVII. p. 603.

   ——  (90) Bassin Houiller et Permien d’Autun et d’Épinac. _Études
        des Gîtes Min. France_.

   ——  (94) Notes sur la flore des Couches Permiennes de Trienbach
        (Alsace). _Bull. Soc. Geol. France_ [3], tome XXII. p. 163.

   ——  (95) Note sur la flore fossile des Gisements houillers de Rio
        Grande do Sul. _Bull. Soc. Géol. France_ [3], tome XXIII. p.
        601.

   ——  (97) Observations sur quelques fougères des Dépôts houillers
        d’Asie Mineure. _Bull. Soc. Bot. France_ [3], tome XLIV. p. 195.

   ——  (97²) The reference of the genus _Vertebraria_. (Translation
        from the _Compt. Rend_, tome CXXII. p. 744.) _Rec. Geol. Surv.
        India_, vol. XXX. pt. i.

   ——  (97³) Les Provinces botaniques de la fin des temps primaires.
        _Rev. Gén. Sci._ (_Jan._ 15).

   ——  (97⁴) Revue des travaux de paléontologie végétale. _Rev. Gén.
        Bot._ tome IX.

   ——  (98) Sur un Lepidodendron silicifié du Brésil. _Compt. Rend._
        (_July_ 25).

   ——  (98²) Sur la découverte, par M. Amalitzky, de Glossopteris
        dans le Permien supérieur de Russie. _Bull. Soc. Bot. France_,
        tome XLV. p. 392.

   ——  (98³) Contribution à l’étude de la flore ptéridologique des
        schistes permiens de Lodève. _Bull. Mus. de Marseille_, tome I.
        Fasc. II. p. 9.

   ——  (99) Étude sur la flore fossile du Bassin houiller d’Héraclée.
        _Mém. Soc. Géol. France_ (_Paléont._), _Mém._ 21.

   ——  (00) Sur une Sélaginellée du terrain houiller de Blanzy.
        _Compt. Rend._ vol. CXXV. p. 1077.

   ——  (00²) Éléments de Paléobotanique. _Paris._

   ——  (02) Observations sur quelques plantes fossiles des Lower
        Gondwanas. _Mem. Geol. Surv. India_ [New Series], vol. II.

   ——  (03) Flore fossile des Gîtes de Charbon du Tonkin. _Études des
        Gîtes Min. France. Paris._

   ——  (03²) Revue des travaux de Paléontologie végétale. _Rev. Gén.
        Bot._ vol. XV.

   ——  (05) Une nouvelle classe de Gymnospermes: les Ptéridospermées.
        _Rev. Gén. Sci._ p. 718.

   ——  (06) Bassin houiller et Permien de Blanzy et du Creusot (Fasc.
        ii). _Études Gîtes Min. France._

   ——  (09) Observations sur le _Lepidostrobus Brownii_. _Compt.
        Rend._ vol. CXLVIII. p. 890.

   ——  (09²) Revue des travaux de Paléontologie végétale (1901–06).
        _Rev. Gén. Bot._, vols. XXI, XXII.

   =Zenker, J. C.= (37) _Scolecopteris elegans_ Zenk. Ein neues
        fossiles Farrngewächs mit Fructificationen. _Linnaea_, vol. XI.
        p. 509.




                                 INDEX


The Index includes the names of Authors and plants mentioned in this
volume. No references are, however, given to the following Authors,
whose names occur too frequently to render special reference of use
to the reader: A. Brongniart, R. Kidston, A. G. Nathorst, H. Potonié,
B. Renault, D. H. Scott, H. Graf zu Solms-Laubach, D. Stur, W. C.
Williamson, K. Zeiller.

  _Abies pectinata_, 217

  _Acrostichites Goeppertianus_, 340, 341

  _A. linnaeaefolius_, 340

  _A. rhombifolius_, 340

  _A. tenuifolius_, 332

  _A. Williamsonis_, 339

  _Acrostichum_, 499, 500

  _A. aureum_, 309, 379

  _A._ (_Lomariopsis_) _sorbifolium_, 301

  _Adiantites_, 376, 560

  _A. antiquus_, 376, 377

  _A. lindsayoides_, 376, 377

  _A. Sewardi_, 377

  _Adiantum pedatum_, 300

  _A. apalophyllum_, 380

  _Agathis_, 131, 195

  _A. australis_, 95

  _Alethopteris_, 485, 516, 557, 572–576

  _A. Grandini_, 574

  _A. lonchitica_, 399, 553, 574, 575

  _A. Roesserti_, 346

  _A. Serlii_, 575, 576

  _Alloiopteris_, 470, 579

  _A. Essinghii_, 535

  _Alsophila_, 295

  _A. excelsa_, 294

  _A. tahitiensis_, 309

  _Alsophilina_, 372

  Amalitzky, W., 498, 513

  _Anachoropteris Decaisnii_, 462

  Anachoropteroides, 455

  Andrae, K. J., 390

  _Androstrobus_, 88

  _Aneimia_, 287, 288, 346, 350

  _A. flexuosa_, 289

  _A. phyllitidis_, 289

  _A. rotundifolia_, 288, 307

  _Aneimites_, 346

  _Angiopteridium_, 485

  _A. californicum_, 409

  _Angiopteris_, 172, 317, 417, 425, 455, 527

  _A. evecta_, 283, 317–319

  _A. Richthofeni_, 409

  _Ankyropteris_, 365, 450–462, 465

  _A. bibractensis_, 453–456, 471

  _A. corrugata_, 436, 453, 455–462, 471

  _A. scandens_, 450–452, 456, 461, 462, 471

  _Anomopteris Mougeotii_, 329

  _A. Schlectendalii_, 329

  _Anomozamites_, 489

  _Antrophyum_, 499

  _Aphlebia_ 525–529, 533–536, 555

  _A. crispa_, 526, 528

  _A. Germari_, 526

  _Aphyllum cristatum_, 127

  _Araucaria_, 25

  _A. Balansae_, 36

  _A. excelsa_, 36

  _A. imbricata_, 93, 211

  _Araucarieae_, 44, 275

  _Araucarites Cordai_, 187

  _A. gracilis_, 84

  Arber, E. A. N., 178, 395, 420, 433, 497, 500, 507, 508, 512, 513

  Arber, E. A. N. and H. H. Thomas, 214, 222

  _Arberia_, 516

  _A. minasica_, 516

  _Arberia_ sp., 517

  Archaeopterideae, 565

  _Archaeopteris_, 15, 526, 560–565

  _A. archetypus_, 563–565

  _A. Dawsoni_, 564

  _A. fimbriata_, 563–565

  _A. fissilis_, 563, 564

  _A. gaspiensis_, 563

  _A. hibernica_, 561–565

  _A. Jacksoni_, 563

  _A. Roemeriana_, 563

  _A. Tschermaki_, 564

  _Archaeosigillaria_, 78, 267, 268

  _A. primaeva_, 201, 268

  _Archangiopteris_, 318, 319

  _Arctopodium insigne_, 456

  Artis, F. T., 127, 196, 229, 231, 422

  _Aspidiaria_, 124, 127, 128

  _Aspidites caudatus_, 404

  _Asplenites_, 580

  _A. macrocarpus_, 346

  _A. ottonis_, 346

  _Asplenium Johnstrupi_, 369

  _A. multilineatum_, 301

  _A. nebbense_, 344

  _A. nidus_, 485

  _A. resectum_, 300

  _A. whitbiense_, 344

  _Asterochlaena duplex_, 448

  _A. laxa_, 462, 471, 472

  _A. ramosa_, 471

  _Asterotheca_, 398, 409, 426, 576

  _A. Sternbergii_, 398, 400

  _Aulacopteris_, 567

  _Azolla_, 192, 274, 475


  _Baiera_, 307, 390

  Baily, W. H., 469, 537, 560, 562

  Baker, J. G., 33, 307

  Balfour, J. H., 191

  Barrois, C., 103

  Bartholin, C. T., 392

  Bates, H. W., 309

  Bennettitales, 396

  Bennie, J., 7

  Bennie, J. and R. Kidston, 85

  Benson, Margaret, 277, 532

  _Bensonites fusiformis_, 469

  _Bergeria_, 124, 126, 127, 174, 181

  _Bernouillia_, 409, 410, 541

  Berridge, E. M., 194

  Berry, E. W., 543

  Bertrand, C. E., 163, 213, 214, 222, 275, 277

  Bertrand, C. E. and F. Cornaille, 316

  Bertrand, P., 432, 434, 435, 443, 447, 449–452, 462, 467, 468

  Binney, E. W., 103, 110, 137, 153, 164, 171, 188, 232, 238, 462, 465

  Bischof, — 69

  Blanckenhorn, M., 72, 522, 523

  _Blechnoxylon talbragarense_, 509–511

  Bommer, C., 40, 353, 361

  Boodle, L. A., 20, 21, 24, 304, 311, 468

  Bothrodendreae, 248–266

  _Bothrodendron_, 75, 128, 130–133, 137, 188, 209, 234, 240, 248–268,
    276

  _B. kiltorkense_, 252, 255, 257–259

  _B. Leslei_, 258

  _B. minutifolium_, 251–256, 262

  _B. mundum_, 256, 262, 263

  _B. punctatum_, 135, 248, 250, 252, 254, 260

  _B. tenerrimum_, 264

  _Bothrostrobus_, 192, 262–264, 278

  _Botrychioxylon_, 459

  _Botrychium_, 169, 427, 438, 459, 510

  _B. Lunaria_, 322

  _B. virginianum_, 322

  Botryoptereae, 434–443

  Botryopterideae, 325, 365, 375, 427, 432–472

  _Botryopteris_, 436–443

  _Botryopteris antiqua_, 436, 442, 443, 470, 471

  _B. cylindrica_, 436, 438

  _B. forensis_, 437, 438, 442–445, 463, 470

  _B. hirsuta_, 436, 438

  _B. ramosa_, 436, 438, 440, 441, 470

  Boulay, N., 251

  _Bowenia_, 549

  _B. spectabilis_, 438

  Bower, F. O., 13, 14, 17, 44, 46, 53, 78, 191, 264, 268, 282, 284,
    296, 298, 300, 307, 325

  Bowman, J. E., 232

  Brabenec, — 476

  _Brainea_, 299

  _Brittsia_, 464

  _B. problematica_, 464

  Brodie, P. B., 82

  Brongniart, A. See note, page 609

  Brown, Richard, 232, 233, 237, 239

  Brown, Robert, 160, 190

  Browne, Lady Isabel, 267, 269

  Bruchmann, H., 64

  Bunbury, Sir Charles, 348, 352, 481, 570, 572

  Butterworth, J., 171, 413


  _Calamites_, 6, 11, 73, 207, 208

  _C. radiatus_, 11, 265, 256

  _Calamodendron_, 73

  _Calamostachys_, 9

  _Callipteridium_, 560

  _C. gigas_, 557

  _C. pteridium_, 560

  _Callipteris_, 556–560

  _C. Bergeroni_, 558

  _C. conferta_, 558–560

  _C. conferta_ var. _polymorpha_, 559

  _C. flabellifera_, 568

  _C. lyratifolia_, 557, 558

  _Calymmatotheca_, 407, 531, 532

  _C. affinis_, 532

  _C. Stangeri_, 531

  Campbell, D. H., 68, 192, 308

  Camptopteridinae, 385

  _Camptopteris_, 389, 390

  _C. exilis_, 381

  _C. lunzensis_, 385

  _C. Phillipsii_, 383

  _C. spiralis_, 382, 389, 390

  Cancellatae, 203

  _Canna_, 517

  _Cannophyllites_, 517

  _Cardiocarpon_, 271

  _C. anomalum_, 271

  _Cardiopteris_, 519, 523–525

  _C. frondosa_, 523–526

  _C. Hochstetterii var. franconica_, 524

  _C. Zuberi_, 540

  _Carica sp._, 202, 203

  _Carolopteris_, 360

  Carruthers, W., 27, 130, 137, 163, 171, 175–181, 271, 339, 374, 491,
    514, 562, 565

  Cash, W. and J. Lomax, 154

  _Castilloa_, 131

  _Caulopteris_, 372, 413, 421, 422

  _C. anglica_, 421

  _C. gigantea_, 424

  _C. peltigera_, 419–422

  _C. Saportae_, 421

  _C. tessellata_, 90

  _Cephalotheca_, 29, 537

  _C. mirabilis_, 536, 537

  _Ceratopteris_, 303

  _C. thalictroides_, 297

  _Ceratozamia_, 565

  _Cheirolepis_, 84

  _Cheiropteris palmatopedata_, 300

  Cheirostrobeae, 12

  _Cheirostrobus_, 7–12, 14, 15, 21, 24

  _C. pettycurensis_, 8

  _Chiropteris_, 431

  _C. spatulata_, 431

  _C. Williamsii_, 431

  _C. Zeilleri_, 430

  Chodat, R., 280, 281, 316

  _Chorionopteris gleichenoides_, 476

  Christ, H., 293

  Christ, H. and K. Giesenhagen, 319

  _Chrysodium lanzaeanum_, 350, 378

  _Cladophlebis_, 343–346, 579, 580

  _C. Albertsii_, 344

  _C. Brownii_, 349

  _C. denticulata_, 332, 335, 340–346

  _C. Dunkeri_, 349

  _C. koraiensis_, 349

  _C. lobifolia_, 529

  _C. Roesserti_, 343

  _C. virginiensis_, 340

  _Clathraria_, 203

  _C. Brardi_, 198, 224

  _Clathropteris_, 385–389

  _C. egyptiaca_, 388, 389

  _C. meniscoides_, 386, 387

  _C. platyphylla_, 387

  _C. whitbyensis_, 383

  _Clepsydropsis_, 448–450

  _C. antiqua_, 444, 446, 449

  Coenopterideae, 365, 432–472, 526

  _Coniopteris_, 367, 368, 409

  _C. arguta_, 370, 371

  _C. hymenophylloides_, 366–370, 528

  _C. lunzensis_, 367

  _C. Murrayana_, 367

  _C. quinqueloba_, 370

  Corda, A. J., 68, 69, 105, 346, 347, 354, 373, 422, 443, 476

  _Corynepteris_, 469, 470, 578

  _C. coralloides_, 445

  _C. stellata_, 469

  Cotta, C. B., 412, 443

  Coward, K. H., 221

  _Crematopteris_, 523

  Crépin, F., 27, 537, 563

  _Crossotheca_, 396

  _Cryptomeria_, 36

  _Ctenis Leckenbyi_, 549

  _Ctenopteris_, 548–550

  _C. cycadea_, 548, 549

  _C. Sarrani_, 541, 549

  _Ctenozamites_, 548

  _Cyathea_, 295, 313

  _C. dealbata_, 344

  _C. Imrayana_, 313

  _Cyathea sinuata_, 295

  _C. spinulosa_, 294

  Cyatheaceae, 294–296, 365–375, 403

  _Cyatheites_, 366

  _Cyathocarpus dentatus_, 404

  _Cyathotrachus altus_, 398

  Cycadophyta, 484

  _Cycadopteris_, 544, 546

  _Cycas_, 133

  _C. Micholitzii_, 307

  _Cyclopteris_, 560, 561, 566, 571–572

  _C. angustifolia_, 512

  _C. hibernica_, 560

  _C. Roemeriana_, 563

  _Cyclostigma_, 251

  _C. australe_, 259

  _C. densifolium_, 257

  _C. Griffithsi_, 251, 255

  _C. hercynium_, 257

  _C. kiltorkense_, 251, 255, 257

  _C. minutum_, 251, 255

  _Cyparissidium_, 39

  _Cyperus papyrus_, 230

  _Czekanowskia_, 67


  _Dacrydium_, 36

  _D. cupressinum_, 75

  _D. Kirkii_, 75

  _Dactylotheca_, 396, 404–406, 527, 565, 576

  _D. dentata_, 404

  _D. plumosa_, 399, 400, 404–406

  _Danaea_, 321, 398

  _D. microphylla_, 410

  _D. trichomanoides_, 300

  _Danaeites_, 398, 485

  _D. Heeri_, 410

  _D. sarepontanus_, 398, 400

  _Danaeopsis_, 407

  _D. Hughesi_, 409

  _D. marantacea_, 408

  _D. Storrsii_, 345

  Darwin, C., 103, 301, 514

  _Davallia_, 28, 293, 296, 366

  _D. aculeata_, 299, 300, 355, 533

  _D. concinna_, 294

  Dawes, J. S., 130, 137, 153

  Dawson, Sir J. W., 26–29, 177, 257, 346, 476, 563

  Debey, M. H. and C. von Ettingshausen, 355, 360

  _Dechenia Roemeriana_, 257

  Dennstaedtiinae, 296

  _Derbyella_, 516

  _D. aurita_, 517

  _Dichopteris_, 550–552

  _D. lanceolata_, 551

  _D. visianica_, 550, 551

  _Dicksonia_, 293, 366, 374

  _D. antarctica_, 424

  _D. Bertervana_, 295

  _Dicksonia coniifolia_, 294

  _D. culcita_, 294

  _D. Johnstrupi_, 369, 370

  _D. lobifolia_, 529

  _Dicksonites Pluckeneti_, 366

  _Dictophyllum_, 380–385

  _D. acutilobum_, 381

  _D. exile_, 381–383, 386

  _D. Fuchsi_, 385

  _D. Nathorsti_, 383, 385, 387

  _D. Nilssoni_, 382

  _D. rugosum_, 380, 383–385

  _Dictyopteris_, 571, 572

  _Dictyoxylon_, 220

  _Didymochlaena_, 574

  _Didymophyllum Schollini_, 124

  _Didymosorus comptonifolius_, 355

  _Diplolabis_, 433, 434, 446–449, 465

  _D. esnostensis_, 447, 448

  _D. forensis_, 444–446

  _Diplotmema_, 351, 530, 533–537

  _D. furcatum_, 529, 536

  _D. Zeilleri_, 535, 536

  Dipteridinae, 298, 380–394

  _Dipteris_, 308, 312, 381, 390, 393, 394, 533

  _D. bifurcata_, 298

  _D. conjugata_, 297, 298, 384

  _D. Lobbiana_, 298

  _D. quinquefurcata_, 297

  _D. Wallichii_, 297, 298

  _Discopteris_, 402, 403

  _D. cristata_, 402, 403

  _D. karwinensis_, 402, 403

  _D. Rallii_, 340, 500

  _D. Schumanni_, 402

  _Drymoglossum carnosum_, 304

  _Drynaria fascia_, 411

  Dunker, W., 390


  Eichwald, E. d’, 326, 329

  _Endogenites_, 412

  Engler, A., 282

  Equisetales, 10, 15

  _Etapteris_, 435, 465

  _E. Scotti_, 444, 462, 463

  Etheridge, R., 505, 510

  Ettingshausen, C. von, 25, 364, 376, 537, 542

  Eufilicineae, 283–316

  _Euphorbia_, 196, 231

  _Euphorbites vulgaris_, 196, 198

  Eu-Sigillariae, 203

  _Eusphenopteris tenella_, 407


  Farmer, J. B. and T. G. Hill, 318, 418

  _Favularia_, 198, 203

  Fée, A. L. A., 301

  Feistmantel, C., 84, 126, 136, 137, 346, 372, 409, 430, 489, 513,
    540, 541

  Feistmantel, O., 430

  Felix, J., 438

  Ferns, fossil, 324–472

   —— recent, 280–323

  _Ficoidites verrucosus_, 231

  Filicales, 280–472

  _Filicites arborescens_, 577

  _F. cycadea_, 548

  _F. dubius_, 181, 496

  _F. lineatus_, 537

  _F. lonchiticus_, 574

  _F. meniscoides_, 386

  _F. Miltoni_, 399

  _F. Nilssoniana_, 482

  _F. plumosus_, 404

  _F. pteridius_, 560

  Fitting, H., 72, 73

  _Flemingites_, 181

  _F. Pedroanus_, 177

  Fliche, P., 73, 90, 91

  _Flicheia esnostensis_, 448

  Fontaine, W. M., 342, 343, 345, 352, 362, 363, 368, 378, 543

  Fontaine, W. M. and I. C. White, 424, 487, 570

  Frič, A. and E. Bayer, 375, 474

  Fritel, P. H., 476

  Fritsch, K. von, 524

  Forbes, E., 380, 560

  _Fucoides_, 525


  _Gangamopteris_, 512–517

  _G. cyclopteroides_, 514–516

  _G. kashmirensis_, 516, 517

  Gangamopteris flora, 181, 513

  Gardiner, Stanley, 43

  Gardner, J. S., 82

  Gardner, J. S. and C. von Ettingshausen, 339, 350, 380, 394

  Geinitz, H. B., 26, 79, 130, 174, 233, 402, 491, 540, 561

  Germar, E. F., 69, 201, 265

  Geyler, H. T., 378

  Gilkinet, A., 28, 537

  _Ginkgo_, 307

  _G. digitata_, 376

  _Gleichenia_, 83, 311, 312, 351, 446, 526, 533

  _G. circinata_, 289

  _G. Cunninghami_, 300

  _G. dicarpa_, 290, 310, 351, 354

  _G. dichotoma_, 290, 291

  _G. dubia_, 344

  _G. hantonensis_, 355

  _G. linearis_, 291

  _G. lineata_, 540

  _G. moniliformis_, 291

  Gleicheniaceae, 288–291, 351–355

  _Gleichenites_, 351

  _G. elegans_, 353

  _G. gracilis_, 353

  _G. hantonensis_, 356

  _G. longipennis_, 354

  _G. microphyllus_, 353

  _G. neuropteroides_, 351

  _G. Nordenskioldii_, 354

  _G. Rostafinskii_, 290, 353

  _G. Zippei_, 354, 355

  _Glenopteris_, 538

  _Glossopteris_, 309, 496–512

  _G. angustifolia_, 507, 508, 509

  _G. angustifolia_ var. _taeniopteroides_, 508

  _G. Browniana_, 496–507

  _G. conspicua_, 512

  Glossopteris flora, 181, 513, 514

  _G. indica_, 505–508, 512

  _G. longifolia_, 482

  _G. Phillipsi_, 480

  _G. retifera_, 511, 512

  _G. Tatei_, 512

  Goebel, K., 301, 526

  Goeppert, H. R., 124, 228, 233, 235, 351, 366, 385, 398

  Goldenberg, F., 76, 77, 79, 86, 87, 126, 198, 208, 217, 231

  _Gomphostrobus_, 25, 26

  _Gonatosorus Nathorsti_, 366

  _Goniopteris unita_, 397

  Gordon, W. T., 177, 447, 448, 471

  Gradatae, 285, 298

  _Grammatopteris_, 434–436, 443, 471

  _G. Rigolloti_, 434

  Grand’Eury, C., 137, 200, 204, 205, 226, 234–238, 352, 366, 398, 414,
    426, 464, 532, 534, 555–557, 565, 567, 572, 575, 576

  Gresley, W. S., 228

  Grigoriew, N., 524

  Gunn, Marcus, 361, 392

  _Gunnera_, 528

  _G. manicata_, 527

  Gutbier, A. von, 525, 572

  Gwynne-Vaughan, D. T., 113, 314, 327, 375, 461

  _Gymnogramme reniformis_, 300


  _Haliserites Dechianus_, 27

  Halle, T. G., 76–80, 83, 87

  _Halonia_, 128, 135–139, 148, 150, 153, 154

  _H. regularis_, 141, 153

  _H. tortuosa_, 136

  _Hapalopteris_, 406

  Harcourt, C. G. V. V., 160

  Harvey, W. H., 303

  Harvey-Gibson, R. J., 51, 54, 55

  Haughton, S., 251, 255

  _Hausmannia_, 390–394

  _H. dichotoma_, 391, 392

  _H. Forchammeri_, 392

  _H. Kohlmanni_, 374, 392

  _H. Richteri_, 393

  _H. Sewardi_, 374, 393

  Hawkshaw, J., 232, 238

  _Hawlea_, 398, 400, 401, 576

  _H. Miltoni_, 399, 400

  _H. pulcherrima_, 399, 400

  Hayden, H. H., 514

  Heer, O., 11, 25, 84, 257, 351, 354, 355, 368, 369, 375, 407, 410,
    411, 474

  Hegelmaier, F., 43

  _Helminthostachys_, 322, 434, 436, 438

  Hemingway, W., 79, 253, 571, 574

  _Hemitelia capensis_, 302, 304, 528

  _Hemitelites_, 366

  Henry, A., 319

  Hepaticae, 308

  _Heterangium_, 77, 351, 532

  _Hexagonocarpon_, 572

  Hick, T., 157–159, 438

  Hill, A. W., 42, 164, 286

  Hill, T. G., 61, 65

  Hofmeister, W., 56, 63

  Hollick, A., 25, 474, 475

  Hooker, Sir Joseph, 40, 130, 246, 309

  Hooker, Sir J. and E. W. Binney, 185

  Hooker, Sir William, 291

  Hose, C., 291

  _Hostinella_, 28

  Hovelacque, M., 111

  Hutton, W., 255

  Hydropterideae, 280, 284, 473–483

  Hymenophyllaceae, 294, 301, 363–365, 434, 465

  _Hymenophyllites_, 363

  _H. patentissima_, 364

  _H. Phillipsi_, 367

  _H. quadridactylites_, 365

  _Hymenophyllum dilatatum_, 289

  _H. tunbridgense_, 294, 300, 315

  _H. waldenburgense_, 363

  _H. Weissi_, 364

  _H. Wilsoni_, 294

  _Hymenopteris psilotoides_, 378


  Inversicatenales, 432

  Isoetaceae, 33, 58–66

  _Isoetes_, 30–33, 46, 58–68, 72, 88–91, 103, 175, 184, 191, 208, 217,
    246, 269, 274, 277, 278

  _Isoetes Boryana_, 60

  _I. Braunii_, 68

  _I. Choffati_, 66

  _I. echinospora_, 58, 59

  _I. hystrix_, 33, 60, 61, 65, 66

  _I. lacustris_, 33, 58, 59, 61, 62, 66

  _I. Scheuzeri_, 68

  _I. setacea_, 68

  _Isoetites_, 67, 68

  _I. Choffati_, 67

  _I. crociformis_, 67

  _Isoetopsis_, 68

  _I. subaphylla_, 68


  Jack, R. L. and R. Etheridge, 509

  Jahn, J. J., 28

  _Jamesonia_, 304, 312

  Jeffrey, E. C., 113, 310, 312, 315

  Jordan, R., 461

  _Juncus_, 58


  Karsten, G., 301

  _Kaulfussia_, 321, 434

  Kerr, T., 164

  Kidston, B. See note, page 609

  Kidston, B. and J. Bennie, 191

  Kidston, B. and D. T. Gwynne-Vaughan, 267, 314, 326, 329, 334, 338,
    346, 377, 461, 472

  _Kidstonia heracleensis_, 325, 340

  _Klukia_, 348

  _K. exilis_, 347–349, 370

  Knorr, G. W., 124

  _Knorria_, 124–127, 174

  _K. imbricata_, 255

  _K. mirabilis_, 125

  Knowlton, F. H., 350, 380

  Kolbe, — 335

  König, C., 209

  Krasser, F., 181, 361, 409, 410, 474, 550, 552, 563

  Kubart, B., 195

  Kunze, — 307

  Kurr, J. G., 431, 544


  _Laccopteris_, 355–361, 411

  _L. Dunkeri_, 361

  _L. elegans_, 357

  _L. Goepperti_, 357, 358

  _L. Muensteri_, 374

  _L. polypodioides_, 358–361, 374

  _L. Woodwardi_, 360

  _Laminaria bulbosa_, 71

  Lamouroux, J., 572

  Lang, W. H., 47, 49, 194, 195

  _Lavoisiera lycopodioides_, 40, 75

  Leckenby, J., 549

  _Leckenbya_, 353

  _Leiodermaria_, 198

  Leiodermariae, 203

  Leitgeb, H., 55

  _Lepidocarpon_, 58, 92, 271–279

  _L. Lomaxi_, 272–275

  _L. Wildianum_, 274

  _Lepidodendron_, 7–10, 27, 28, 34, 40–43, 55, 60–63, 71–77, 90–192,
    196, 199–201, 207–211, 217–225, 230–249, 267–270, 312, 331

  _L. aculeatum_, 142, 155, 156

  _L. anglicum_, 264

  _L. australe_, 178–181

  _L. brevifolium_, 175, 176, 222

  _L. cyclostigma_, 264

  _L. dichotomum_, 178

  _L. discophorum_, 209

  _L. esnostense_, 99, 113, 139, 140, 266

  _L. fuliginosum_, 21, 139, 141–162, 169, 175, 177, 191, 246, 262

  _L. gaspianum_, 27

  _L. Harcourtii_, 113, 139, 141, 143, 160–163, 170–178, 182, 189, 191,
    262, 266, 275, 333

  _L. Hickii_, 101, 166, 161

  _L. longifolium_, 97

  _L. Losseni_, 253

  _L. macrophyllum_, 171, 176

  _L. mammillatum_, 266

  _L. mundum_, 241, 260–263

  _L. nothum_, 180

  _L. obovatum_, 139, 142, 154, 156

  _L. ottonis_, 224

  _L. Peachii_, 201

  _L. Pedroanum_, 177, 178

  _L. punctatum_, 371

  _L. rhodumnense_, 140, 266, 333

  _L. saalfeldense_, 141

  _L. selaginoides_, 110

  _L. Spenceri_, 192

  _L. Sternbergii_, 97, 98, 110

  _L. tenerrimum_, 260

  _L. vasculare_, 109–123, 139, 145, 148, 152, 163, 166, 169, 189, 266,
    334

  _L. Veltheimi_, 172

  _L. Veltheimianum_, 94, 99, 101, 125–129, 134, 141, 171–178, 187,
    188, 209, 222, 223, 245, 249, 255

  _L. vereenigense_, 105

  _L. volkmannianum_, 105

  _L. Williamsoni_, 141, 142

  _L. Wortheni_, 200, 201

  _L. Wükianum_, 257

  _L. Wünschianum_, 142, 152, 161–171, 187, 222, 223, 245

  _Lepidophloios_, 104–109, 138, 139, 142, 153, 154, 157, 170, 171

  _L. Dessorti_, 106

  _L. fuliginosus_, 141

  _L. laricinus_, 137

  _L. scoticus_, 106, 135, 136, 185

  _Lepidophyllum_, 181

  Lepidospermae, 278

  _Lepidostrobus_, 9, 39, 46, 60, 175, 181–192, 209, 248, 263, 272,
    274, 496

  _L. Bailyanus_, 257

  _L. Brownii_, 189–191

  _L. fimbriatus_, 46

  _L. foliaceus_, 192, 193

  _L. insignis_, 192, 193

  _L. oldhamius_, 188

  _L. Olryi_, 248–253

  _L. ornatus_, 181, 187, 188

  _L. variabilis_, 187, 188

  _L. Veltheimianus_, 175

  _L. Wünschianus_, 171

  _L. Zeilleri_, 264

  _Leptophloeum rhombicum_, 180

  Leptosporangiate Filicales, 283–316, 324–394

  _Lesleya_, 510, 517–519

  _L. Delafondi_, 487, 518

  _L. ensis_, 518

  _L. grandis_, 518

  _L. simplicinervis_, 518, 519

  Leslie, T. N., 105, 178, 258, 508

  Lesquereux, L., 77, 201, 419, 510, 517, 563, 570, 571, 573

  Leuthardt, F., 332, 343, 353, 408, 410

  Lhywd, E., 570

  Lignier, O., 15, 23

  Lindley, J., 67, 82, 84

  Lindley, J. and W. Hutton, 128, 130, 135, 160, 209, 210, 221, 239,
    249, 405, 421, 431, 481, 494, 530, 571

  Lindman, C. A. M., 473

  _Lindsaya_, 311–313, 377

  _Linopteris_, 567, 572, 573

  _L. Brongniarti_, 572

  _L. neuropteroides_, 572, 573

  _L. obliqua_, 572, 573

  _L. Schutzei_, 572

  _Lithosmunda minor_, 570

  Logan, W. E., 228, 232

  _Lomatophloios macrolepidotus_, 182

  _Lomatophloyos Wünschianus_, 163

  _Lomatopteris_, 544–546

  _L. jurensis_, 544, 545

  _L. Schimperi_, 546

  Lomax, J., 4, 240, 260

  Lomax, J. and F. E. Weiss, 110

  _Lonchopteris_, 494, 576

  _L. Bricei_, 576

  _L. Mantelli_, 494

  _L. rugosa_, 576

  _L. virginiensis_, 331, 332

  _Loxsoma_, 293, 298, 312

  Loxsomaceae, 293

  _Loxsomopsis costaricensis_, 293

  Lycopodiaceae, 33–49

  Lycopodiales, 7, 10, 14, 30–279

  _Lycopodites_, 28, 74–84

  _L. carbonaceus_, 251

  _Lycopodiopsis Derbyi_, 178

  _Lycopodites ciliatus_, 79

  _L. elongatus_, 79, 87

  _L. falcatus_, 39, 76, 83, 84

  _L. Gutbieri_, 79

  _L. lanceolatus_, 81–83

  _L. macrophyllus_, 79, 80, 85, 171

  _L. Milleri_, 28

  _L. Reidii_, 78, 79

  _L. scanicus_, 83

  _L. squamatus_, 76

  _L. Stockii_, 78

  _L. suissei_, 85

  _L. tenerrimus_, 84

  _L. Vanuxemi_, 78

  _L. victoriae_, 84

  _L. Zeilleri_, 80

  _Lycopodium_, 17, 24, 30–51, 56, 60, 63–66, 74–78, 82, 88, 96, 194,
    195, 215, 251, 253, 263, 417

  _L. alopecuroides_, 32, 82

  _L. alpinum_, 32, 41

  _L. annotinum_, 32

  _L. arboreum_, 76

  _L. casuarinoides_, 35, 39

  _L. cernuum_, 31, 37, 39, 41–49, 93, 185, 194, 217

  _L. clavatum_, 32, 40, 41, 46

  _L. complanatum_, 87

  _L. cruentum_, 32

  _L. Dalhousianum_, 35, 38, 42

  _L. densum_, 40

  _L. dichotomum_, 34, 35, 41, 44, 46, 106

  _L. elongatum_, 87

  _L. eryithraeum_, 36

  _L. falcatum_, 83

  _L. inundatum_, 32, 43, 44

  _L. nummularifolium_, 35, 38

  _L. obscurum_, 38, 39, 93

  _L. Phlegmaria_, 39, 44, 45, 78

  _L. primaevum_, 86

  _L. rufescens_, 34–36

  _L. saururus_, 41, 42

  _L. selaginoides_, 33

  _L. Selago_, 4, 32, 34, 44, 87, 133, 256

  _L. serratum_, 42

  _L. squarrosum_, 36, 38, 39

  _L. tetragonum_, 35, 39, 76

  _L. verticillatum_, 39

  _L. volubile_, 35, 39

  Lycopsida, 312

  _Lycostrobus_, 88–91

  _L. Scotti_, 88–91

  _Lyginodendron_, 140, 221, 270, 460, 510, 532, 565

  _Lygodium_, 42, 287, 311, 446, 533, 534, 537

  _L. dichotomum_, 337

  _L. Kaulfussi_, 350

  Lyon, F. M., 57, 58


  McCoy, Sir F., 180, 491, 500, 512

  McNicol, Mary, 461

  _Macroglossum alidae_, 321

  _Macrotaeniopteris_, 486

  _M. Feddeni_, 489

  _M. Wianamattae_, 489

  _Macrozamia corallipes_, 382

  _M. Fawcettiae_, 382

  Malaquin, M., 103

  _Marattia_, 320, 408, 409, 417, 455, 485, 527

  _M. fraxinea_, 317, 320, 528

  _M. Hookeri_, 350, 411

  _M. Kaulfussii_, 320, 397, 401, 411

  Marattiaceae, 316–321, 351, 352, 395, 411, 434, 447, 565, 576

  Marattiales, 316–321, 395–411

  _Marattiopsis_, 407–409

  _Marattiopsis marantacea_, 358, 408, 409

  _M. Muensteri_, 320, 408, 409

  Marion, A. F., 25, 26

  _Mariopteris_, 351, 533–536

  _M. muricata_, 534, 553

  _Marsilia_, 473, 477–479

  _M. Andersoni_, 474

  _M. cretacea_, 474

  _M. Drummondi_, 474

  _Marsilia elata_, 474

  _M. Nathorsti_, 474

  _M. perucensis_, 474

  _M. quadrifoliata_, 473

  Marsiliaceae, 473–475

  _Marsilidium_, 474

  _M. speciosum_, 474

  Martin, W., 229

  Martius, K. F. P. von, 420

  Maslen, A. J., 187, 189, 190

  _Matonia_, 291, 292, 298, 308, 316, 381, 420, 533

  _M. pectinata_, 289–293, 300, 310, 314, 356, 357, 362, 363, 383

  _M. sarmentosa_, 291, 310

  _Matonidium_, 63, 310, 355, 359, 361–363

  _M. Althausii_, 362, 363

  _M. Goepperti_, 362

  _M. Wiesneri_, 358, 363

  Matonineae, 291–293, 355–363

  _Medullosa_, 558, 567

  _M. anglica_, 574

  _Megalopteris_, 509

  _Megaloxylon_, 331

  _Megaphyton_, 413–415, 422

  _M. frondosum_, 422

  _M. insigne_, 421

  _M. McLayi_, 422

  Mellor, E. T. and T. N. Leslie, 233

  _Mertensides_, 352

  _Mesostrobus_, 195

  _Metaclepsydropsis_, 447–450

  _M. duplex_, 448–450

  Mettenius, G., 223, 424, 425

  _Miadesmia_, 92, 275–279

  _M. membranacea_, 275, 276

  _Microcachrys tetragona_, 76

  _Microdictyon_, 360

  Miller, H., 27, 28, 532

  _Mixoneura_, 555

  Mixtae, 285

  Mohl, H. von, 63

  Mohlengraaff, G. A. F., 505

  _Mohria_, 287

  Möller, H., 392, 481

  _Monogramme_, 306

  Morris, J., 185, 191, 539

  Münster, G. Graf zu, 24, 67–69

  _Muscites falcatus_, 83

  _Myeloxylon_, 556, 574


  Nägeli, K. W. von, 55

  Naiadaceae, 82

  _Naiadea acuminata_, 81

  _N. lanceolata_, 81

  _N. petiolata_, 81

  _Naiadita_, 82, 83

  _N. lanceolata_, 81

  _Naiadites acuminatus_, 81

  Nathorst, A. G. See note, page 609

  _Nathorstia_, 361, 410, 411

  _N. angustifolia_, 410

  _N. latifolia_, 410

  _Nephrodium filix-mas_, 313

  _Nerium oleander_, 567

  _Neuropteridium_, 519–523, 525

  _N. grandifolium_, 519, 522

  _N. intermedium_, 521–523

  _N. Plantianum_, 521

  _N. validum_, 519–523, 525, 559

  _N. Voltzii_, 523

  _Neuropteris_, 398, 516, 526, 528, 552, 553, 556, 557, 565–572, 579,
    580

  _N. cordata_, var. _angustifolia_, 570

  _N. cordata_, var. _densineura_, 524

  _N. conferta_, 559

  _N. Goeppertiana_, 340

  _N. Grangeri_, 567

  _N. heterophylla_, 351, 535, 568

  _N. hirsuta_, 570

  _N. horrida_, 571

  _N. macrophylla_, 535, 569

  _N. pseudogigantea_, 567

  _N. recentior_, 339

  _N. Scheuchzeri_, 535, 569–571

  _N. valida_, 520

  Newberry, J. S., 431

  _Nilssonia_, 485

  _Nipa_, 309

  _Noeggerathia_, 428–431, 560

  _N. acuminifissa_, 563

  _N. flabellata_, 431

  _N. foliosa_, 429

  _N. obovata_, 514

  _Noeggerathiopsis_, 233, 516

  Northampton, Marquis of, 190


  _Odontopteris_, 516, 526, 528, 552–558, 560, 567, 571

  _O. cf. alpina_, 555

  _O. Browni_, 556

  _O. cycadea_, 548

  _O. Fischeri_, 556

  _O. genuina_, 556, 557

  _O. jurensis_, 544

  _O. macrophylla_, 540

  _O. minor_, 554, 555

  _O. osmundaeformis_, 554

  _O. Plantiana_, 519, 521

  _O. Reichiana_, 555

  _O. Wortheni_, 555

  Oldham, R. D., 497, 501, 503, 505, 510

  Oldham, T. and J. Morris, 84

  _Oleandra_, 301

  _O. neriiformis_, 485, 492

  _Oleandridium_, 485, 486

  _O. lentriculiforme_, 492

  _Oligocarpia_, 409

  _O. Brongniarti_, 352, 364

  _O. Gutbieri_, 352

  Oliver, F. W., 437, 443, 532

  _Omphalophloios_, 264–266

  _O. anglicus_, 197, 264

  _Oncopteris_, 372, 373

  _O. Nettvalli_, 373

  _Onoclea hebraidica_, 380

  _O. sensibilis_, 380

  _O. struthiopteris_, 303, 344, 502, 503

  _Onychiopsis_, 369, 377–380

  _O. elongata_, 378

  _O. Mantelli_, 374, 378, 379

  _O. psilotoides_, 378

  Ophioglossaceae, 321–323, 434

  Ophioglossales, 427–431

  _Ophioglossites antiqua_, 428

  _Ophioglossum_, 12, 321, 428

  _O. palmatum_, 322

  _O. pendulum_, 321

  _O. vulgatum_, 321, 322

  _Osmunda_, 267, 341, 567

  _O. cinnamomea_, 286, 333, 339

  _O. Claytoniana_, 314, 315, 333, 338

  _O. lignitum_, 339

  _O. regalis_, 285, 286, 331, 338, 342

  _O. Sturii_, 339

  Osmundaceae, 285, 286, 308, 314, 315, 324–346, 403, 409, 434, 443,
    448, 461, 472

  _Osmundites Dowkeri_, 338, 339

  _O. Dunlopi_, 331–334, 337, 346

  _O. Gibbiana_, 335, 339

  _O. Kolbei_, 334–337

  _O. skidegatensis_, 337, 338

  _O. Sturii_, 339

  _Otopteris cuneata_, 481

  _Otozamites Beani_, 307

  _Ottokaria bengalensis_, 498

  _O. ovalis_, 498


  _Pachyphloeus tetragonus_, 171

  _Pachypteris_, 550, 552

  _P. dalmatica_, 550

  _P. lanceolata_, 550

  _Pachytesta_, 574, 575

  _Palaeojulus dyadieus_, 401, 402

  _Palaeopteris_, 560, 561

  _P. hibernica var. minor_, 563

  _Palmatopteris_, 533, 535, 537

  _P. furcata_, 537

  _Parapecopteris_, 398

  _P. neuropteroides_, 398, 399

  Parkeriaceae, 297

  Parkinson, J., 181, 231, 413, 575

  _Paullinia thalictrifolia_, 307

  Peach, C. W., 530

  _Pecopteris_, 298, 398, 494, 532, 541, 557, 576–580

  _P. abbreviata_, 399

  _P. arborescens_, 422, 529, 577, 578

  _P. bullatus_, 352

  _P. caespitosa_, 359

  _P. crenifolia_, 359

  _P. cristata_, 402

  _P. curtata_, 339

  _P. cyathea_, 422

  _P. dentata_, 339, 404

  _P. denticulata_, 343

  _P. exilis_, 348

  _P. Huttoniana_, 340

  _P. ligata_, 359

  _P. Miltoni_, 399

  _P. Phillipsii_, 343

  _P. Pluckeneti_, 419, 426, 576, 579

  _P. plumosa_, 399, 404

  _P. polymorpha_, 579

  _P. recentior_, 339

  _P. reticulata_, 494

  _P. Rutimeyeri_, 343

  _P. serra_, 404

  _P. Sterzeli_, 419, 426, 579

  _P. tenuis_, 339

  _P. undans_, 345

  _P. unita_, 397, 579

  _P. whitbiensis_, 339, 343, 344

  _P. Williamsonis_, 339

  _P. Zippei_, 354

  Pelourde, F., 448

  Penhallow, D. P., 28, 78, 337

  Petver, — 231

  _Phanerosorus_, 292

  Phillips, J., 67, 348

  _Phlebopteris Phillipsi_, 383

  _P. polypodioides_, 358

  _P. propinqua_, 358

  _P. Woodwardi_, 360

  _Phragmites_, 206

  _Phyllachne clavigera_, 40

  _Phyllites nervulosis_, 383

  _Phyllocladus_, 542, 543

  _Phylloglossum_, 30, 31, 33

  _P. Drummondi_, 33

  _Phytolithus cancellatus_, 126

  _P. parmatus_, 129

  _P. verrucosus_, 231

  _Picea excelsa_, 94

  _Pilularia_, 67, 473

  _P. globulifera_, 473

  _P. minuta_, 473

  _P. pedunculata_, 475

  _Pinakodendron_, 264

  _P. musivum_, 268

  _Pinus_, 194

  _P. attenuata_, 134

  _P. clausa_, 134

  _P. excelsa_, 174, 182

  _P. longifolia_, 95, 98

  _Plagiogyria_, 297

  Plant, N., 177

  _Platyzoma_, 291

  _P. microphylla_, 312

  _Pleuromeia_, 66–73, 91, 141

  _P. oculina_, 69

  _P. Sternbergii_, 68–70

  _Podocarpus_, 210

  _P. dacrydioides_, 75

  _Podoloma polypodioides_, 394

  _Poecilitostachys_, 91

  _P. Hangi_, 91

  _Polypodiaceae_, 296, 375–380

  _Polypodium_, 344

  _P. Billardieri_, 302

  _P. carnosum_, 301

  _P. heracleifolius_, 383

  _P. oregonense_, 377

  _P. quercifolium_, 297, 298, 302, 303, 392, 528

  _P. vulgare_, 301, 313, 577

  Potonié, H. See p. 609

  Prantl, K., 296

  Presl, C. B., 127, 356, 390, 407, 477, 525, 572

  Prestwick. J., 229

  Primofilices, 433

  _Protophyllocladus_, 543

  _Protopteris_, 370–374, 390

  _P. punctata_, 373–375

  _P. Sternbergii_, 371

  _P. Witteana_, 374, 375

  _Protorhipis asarifolius_, 390

  _Protosalvinia_, 476

  Psaronieae, 412–426

  _Psaronius_, 309, 372, 396, 412–426, 452

  _P. asterolithus_, 416

  _P. brasiliensis_, 420

  _P. coalescens_, 416, 420

  _P. Cottai_, 415

  _P. Cromptonensis_, 413, 425

  _P. infarctus_, 415–421, 424

  _P. musaeformis_, 416, 420

  _P. Renaulti_, 413, 418, 420, 425

  _P. Sterzeli_, 419, 420

  _Pseudobornia_, 11

  _P. ursina_, 8

  _Psilophyton_, 26–29

  _P. Dechianum_, 27

  _P. filiformis_, 24

  _P. princeps_, 26–29

  _P. robustius_, 27, 29

  Psilotaceae, 12–15

  Psilotales, 17–29

  _Psilotiphyllum_, 26

  _Psilotites_, 24, 25

  _P. filiformis_, 24

  _P. lithranthracis_, 25

  _P. unilateralis_, 25

  _Psilotum_, 12–24, 26, 29, 237

  _P. complanatum_, 18

  _P. triquetrum_, 17, 18, 20

  _Psygmophyllum_, 431

  Pteridospermaphyta, 278

  Pteridosperms, 282, 395, 396, 403, 407, 426, 484–580

  _Pteridotheca_, 325, 375

  _P. Butterworthi_, 325

  _Pteris_, 312, 580

  _P. aquilina_, 305–309

  _P. arguta_, 344

  Pteropsida, 312

  _Ptilozamites_, 539, 546, 547, 550

  _P. Heeri_, 546–548

  _Ptychocarpus_, 397, 411, 576, 578

  _P. oblongus_, 397

  _P. unita_, 397, 400, 578

  _Ptychopteris_, 413, 414, 422–424


  _Rachiopteris antiqua_, 449

  _R. corrugata_, 450, 455, 460

  _R. cylindrica_, 438

  _R. duplex_, 447, 448

  _R. hirsuta_, 436, 438, 442

  _R. inaequalis_, 453, 454

  _R. insignis_, 456

  _R. irregularis_, 453, 454

  _R. ramosa_, 436, 440

  _R. tridentata_, 438

  Raciborski, M., 339, 341, 348, 353, 543

  _Regnellidium_, 473, 479

  _R. diphyllum_, 474, 479

  Reinecke, F., 301

  Reinsch, P. F., 192

  Renault, B. See note, p. 609

  Renault, B. and C. Grand’Eury, 219

  Renault, B. and A. Roche, 204

  Renault, B. and R. Zeiller, 510, 555,
  560, 571, 577

  _Renaultia_, 394, 406

  Renier, A., 133

  _Rhacophyllum_, 525

  _R. crispum_, 526

  _Rhaciopterideae_, 449

  _Rhacophyton condrusorum_, 537

  _Rhacopteris_, 426, 430, 431, 525, 563, 564

  _R. flabellata_, 428

  _R. paniculifera_, 428

  _Rhizodendron oppoliense_, 375

  _Rhizomopteris_, 381

  _R. cruciata_, 388

  _R. major_, 383

  _R. Schenki_, 382

  _Rhodea_, 27, 129, 196, 251

  _R. moravica_, 364

  _R. patentissima_, 364

  _Rhytidodendron_, 251

  _R. minutifolium_, 251

  _Rhytidolepis_, 198, 203, 222, 237

  Richter, P. B., 390, 392, 393

  Rodway, J., 93

  Roehl, von, 571

  Roemer, F., 571

  _Rotularia cuneifolia_, 1

  Royle, J. F., 501

  Rudolph, K., 414, 417, 418

  _Ruffordia_, 350

  _R. Goepperti_, 349, 350


  _Saccoloma_, 420

  _S. adiantoides_, 424

  _Sadleria_, 344

  Salfeld, H., 545, 546

  _Sagenaria Bischofi_, 69

  _S. Veltheimiana_, 171

  _Sagenopteris_, 431, 477–483

  _S. angustifolia_, 478, 482

  _S. bilobata_, 481

  _S. cuneata_, 481

  _S. grandifolia_, 482

  _S. longifolia_, 482

  _S. Mantelli_, 431, 482

  _S. Nathorsti_, 482

  _S. Nilssoniana_, 478

  _S. Phillipsi_, 431, 478–482

  _S. Phillipsi_, f. _pusilla_, 482

  _S. rhoifolia_, 479–482

  _Salvinia_, 475

  _S. Alleni_, 25

  _S. auriculata_, 476

  _S. elliptica_, 475

  _S. formosa_, 476

  _S. natans_, 475

  _S. reticulata_, 25

  _S. Zeilleri_, 476

  Salviniaceae, 475–477

  _Samaropsis_, 517

  Saporta, le Marquis de, 66–68, 351, 360, 380, 545, 546, 548, 552

  Schenk, A., 341, 352, 356, 358, 361, 363, 474, 482, 492, 544, 545,
    549

  Scheuchzer, J. T., 570, 574

  Schimper, W. P., 25, 190, 257, 364, 376, 477, 486, 496, 523, 544,
    546, 560, 579

  Schimper, W. P. and A. Mougeot, 90, 519

  _Schizaea_, 312

  _S. dichotoma_, 307

  _S. elegans_, 287, 307

  _S. pusilla_, 287

  Schizaeaceae, 286, 287, 346–351

  _Schizoneura_, 523

  _Schizopteris_, 525

  _S. adnascens_, 404

  _S. pinnata_, 445, 464

  _S. lactuca_, 526

  _Schizostachys frondosus_, 464

  Schlotheim, E. F. von, 413, 560, 574, 577

  Schmalhausen, J., 257, 563

  Schuster, J., 559

  Schwarz, E. H. L., 259

  _Scleropteris_, 552, 578

  _S. Pomelii_, 552

  _Scolecopteris_, 401, 402, 426

  _S. elegans_, 400, 401

  _S. polymorpha_, 401

  _Scolopendrium nigripes_, 300, 513

  _S. vulgare_, 513

  Scott, D. H. See note, p. 609

  Scott, Mrs D. H., 192, 469

  _Selaginella_, 17, 30–33, 39, 49–58, 74–77, 85, 87, 88, 184, 215,
    217, 263, 274–278

  _S. apus_, 57

  _S. arabica_, 80

  _S. Berthoudi_, 84

  _S. caulescens_, 85

  _S. erythropus_, 53

  _S. grandis_, 50–53, 75, 84

  _S. inaequalifolia_, 54

  _S. laevigata_, 54

  _S. lepidophylla_, 33

  _S. Martensii_, 51, 53

  _S. revoluta_, 80

  _S. rupestris_, 52, 56, 57

  _S. spinosa_, 31, 33, 50, 52, 53, 55, 278, 440

  _S. spinulosa_, 23

  _S. Willdenowii_, 52, 53

  Selaginellaceae, 32, 33

  _Selaginellites_, 74–77, 85–88

  _S. elongatus_, 80, 87, 88

  _S. primaevus_, 80, 86–88

  _S. suissei_, 79, 85–88

  Sellards, E. H., 486, 488, 538

  _Senftenbergia_, 347, 404

  _S. elegans_, 346, 364

  _S. plumosa_, 404

  Shattock, S. G., 131

  _Sigillaria_, 39, 43, 44, 55, 61, 66, 69–75, 92, 98, 99, 105, 109,
    110, 128, 140, 170, 196–226, 230, 231, 234, 238–240, 248, 266–269,
    421

  _S. Brardi_, 179, 180, 198, 200–203, 207, 210, 212, 213, 219,
    224–226, 241, 261, 265–267

  _S. denudata_, 203

  _S. discophora_, 139, 209, 249

  _S. elegans_, 160, 197, 217–224

  _S. elongata_, 221, 222, 224

  _S. Eugenii_, 198

  _S. laevigata_, 198, 200, 202

  _S. lepidodendrifolia_, 200

  _S. McMurtriei_, 199

  _S. mammillaris_, 198, 199

  _S. Menardi_, 224

  _S. minutifolia_, 251

  _S. mutans_, 224

  _S. oculina_, 69–73

  _S. pachyderma_, 198

  _S. rimosa_, 248

  _S. rhomboidea_, 203

  _S. rugosa_, 197, 198, 200

  _S. scutellata_, 196, 198, 212, 221, 222

  _S. spinulosa_, 201, 212, 219, 224

  _S. Sternbergii_, 69

  _S. Taylori_, 209

  _S. tessellata_, 197

  _S. vascularis_, 110

  _S. Vanuxemi_, 78

  _S. xylina_, 221

  _Sigillariophyllum_, 200

  _Sigillariopsis_, 213, 214

  _S. Decaisnei_, 213

  _S. sulcata_, 214

  _Sigillariostrobus_, 200, 215–217

  _S. bifidus_, 26

  _S. ciliatus_, 216

  _S. major_, 217, 226

  _S. nobilis_, 215

  _S. rhombibracteatus_, 216

  _S. Teighemi_, 215, 216

  Simplices, 284, 298

  Smith, G. O. and D. White, 28, 563

  _Solenites Murrayana_, 67

  Sollas, Igerna B. J., 82, 83

  Solms-Laubach, H. Graf zu. See note, p. 609

  _Speirocarpus_, 409

  _S. tenuifolius_, 332

  _S. virginiensis_, 332

  _Spencerites_, 47, 49, 192–195, 263

  _S. insignis_, 192–195

  _S. membranaceus_, 195

  _Sphenolepidium_, 39

  Sphenophyllales, 1–16

  _Sphenophyllostachys_, 7, 9

  _S. Dawsoni_, 1, 2, 6, 14

  _S. fertilis_, 4, 5, 12

  _S. Roemeri_, 1–3, 14

  _Sphenophyllum_, 1–7, 10–17, 21, 430

  _S. cuneifolium_, 2

  _S. fertile_, 4

  _S. majus_, 2, 3, 14

  _S. myriophyllum_, 2

  _S. plurifoliatum_, 2, 4

  _S. trichomatosum_, 3, 4

  _Sphenopteris_, 529–578

  _S. affinis_, 530–532

  _S. arguta_, 367, 368

  _S. caudata_, 404

  _S. condrusorum_, 537

  _S. coralloides_, 470

  _S. cristata_, 402, 366

  _S. dissecta_, 532

  _S. elegans_, 532

  _S. furcata_, 529, 530, 535

  _S. Hoeninghausi_, 532

  _S. hymenophylloides_, 367, 368

  _S. Linkii_, 532

  _S. Mantelli_, 378

  _S. Matheti_, 526

  _S. nephrocarpa_, 367

  _S. obtusiloba_, 529, 530

  _S. petiolata_, 446

  _S. quinqueloba_, 370

  _S. Rallii_, 325, 402

  _S. stipata_, 367

  Spieker, T., 69

  _Spiropteris_, 579

  _Spirorbis_, 102–104

  Sprengel, A., 412

  _Stangeria paradoxa_, 307

  _Staphylopteris Peachii_, 531

  _Stauropteris_, 433, 434, 465–469

  _S. burntislandica_, 468, 469

  _S. oldhamia_, 444, 450, 465–468

  _Steffensia silesiaca_, 404

  Steinhauer, H., 126–128, 228, 229

  Stenzel, C. G., 375, 417, 418, 435, 450–453

  Sternberg, C. von, 105, 110, 124, 126, 198, 413, 573

  Sterzel, J. T., 366, 402, 412, 413

  Stiehler, A. W., 494

  _Stigmaria_, 66, 141, 153, 158, 226–247, 256, 261, 265

  _S. anabathra_, 231

  _S. ficoides_, 158, 159, 174, 226–232, 236–239, 246, 247, 256, 261

  _S. ficoides minuta_, 255

  _S. flexuosa_, 239

  _S. inaequalis_, 174

  _S. radiculosa_, 157–160

  _S. rimosa_, 226

  _S. stellata_, 247

  _Stigmariopsis_, 205, 208, 233–239

  _S. anglica_, 235

  Stokes and Webb, 494

  Stopes, Marie C., 436

  Strasburger, E., 398

  _Stromatopteris_, 291

  Stur, D. See note, p. 609

  _Sturiella_, 324

  Sub-Sigillariae, 203

  Sudworth, G. B., 134

  Sykes, M. Gladys, 23, 47

  _Syringodendron_, 198, 204, 205, 221, 226, 233, 238

  _S. esnostense_, 204

  _S. striatum_, 198

  Szajnocha, L., 540


  _Taeniopteris_, 485–494, 508, 509

  _T. Beyrichii_, 494

  _T. Carnoti_, 485, 488, 490

  _T. Carruthersi_, 491

  _T. coriacea_, 488, 490

  _T. Daintreei_, 490, 491

  _T. gigantea_, 489

  _T. immersa_, 492

  _T. jejunata_, 485, 488

  _T. Jourdyi_, 489

  _T. lata_, 489

  _T. Lescuriana_, 487

  _T. major_, 494

  _T. marantacea_, 407, 408

  _T. mareyiaca_, 491

  _T. missouriensis_, 485

  _T. multinervis_, 486–488

  _T. Newberriana_, 488

  _T. spatulata_, 489, 490

  _T. superba_, 489

  _T. tenuinervis_, 489, 492

  _T. virgulata_, 492

  _T. vittata_, 485, 489, 492–494

  _Tafalla graveolens_, 40, 75

  Tansley, A. G., 16, 280, 310, 440, 446

  _Telangium_, 532

  _T. Scotti_, 532

  _Teratophyllum aculeatum_, 301, 405

  _Thamnocladus_, 27

  _Thamnopteris_, 326, 329–331, 334, 337, 338

  _T. Schlechtendalii_, 329, 330, 448, 453

  _Thaumatopteris_, 385

  _T. Brauniana_, 385

  _T. Muensteri_, 386

  _T. Schenki_, 385

  _Theobroma_, 209

  _Thinnfeldia_, 537–552, 556

  _T. falcata_, 540

  _T. Fontainei_, 543

  _T. lancifolia_, 539

  _T. odontopteroides_, 538, 541–543, 546

  _T. rhomboidalis_, 542–545

  _T. tenuinervis_, 540

  _T. variabilis_, 482, 543

  Thoday, D., 6

  Thomas, A. P. W., 12, 13, 17, 19, 23

  Thomas, Ethel N., 239

  Thompson, D’Arcy W., 131, 209

  _Thyrsopteris_, 295, 296, 369

  _T. elegans_, 289, 294, 308, 368

  _T. elongata_, 378

  _T. Murrayana_, 367

  _T. rarinervis_, 369

  _T. schistorum_, 366

  _Tmesipteris_, 4, 12–25

  _T. tannensis_, 17

  _Todea_, 267, 337, 341, 468

  _T. australis_, 346

  _T. barbara_, 285, 286, 299, 314, 333, 339

  _T. hymenophylloides_, 325

  _T. Lipoldi_, 329

  _T. superba_, 333

  _T. Wilkesiana_, 286

  _Todeopsis primaeva_, 324, 340

  _Todites_, 339–343, 550

  _T. Roesserti_, 346

  _T. Williamsoni_, 332, 339–343, 352

  _Tracheotheca_, 437, 443

  Trautschold, H. and J. Auerbach, 260

  Treub, M., 307, 308

  _Trichomanes_, 293, 294, 303, 365, 452

  _T. Goebelianum_, 300

  _T. radicans_, 294, 315, 470

  _T. reniforme_, 300, 310, 311, 315, 440, 571

  _T. scandens_, 311

  _Trigonocarpon_, 574

  _Triletes_, 192, 215

  _Triplosporites_, 190

  _Tubicaulis_, 434–436, 443, 471

  _T. primarius_, 443

  _T. solenites_, 435

  _T. Sutcliffi_, 436

  _Tylophora radiculosa_, 157

  _Tympanophora racemosa_, 367

  _T. simplex_, 367


  _Ulodendron_, 95, 128–135, 137, 138, 185, 209, 210, 251, 254, 255

  _U. minus_, 209

  Unger, F., 180, 412, 446, 449

  _Urnatopteris_, 396, 407

  _Urophlyctites stigmariae_, 247


  _Variolaria ficoides_, 231

  Velenovský, J., 369, 372, 482, 543

  _Veronica_, 75

  _Vertebraria_, 497, 501–505

  _V. indica_, 502, 503

  _Vittaria_, 306

  Volkmann, G. A., 124, 231


  _Walchia_, 25

  Wanklyn, A., 355

  Ward, L. F., 278, 369

  Watson, D. M. S., 131, 156, 161, 195, 261, 263, 278, 397

  Weber, O. and J. T. Sterzel, 558

  _Weichselia_, 494–496, 576

  _W. erratica_, 495

  _W. Mantelli_, 494–496

  _W. reticulata_, 494

  Weiss, C. E., 73, 107, 203, 253, 257, 264, 324, 429, 430, 486,
    555–560

  Weiss, F. E., 98, 101, 102, 138, 139, 151, 154, 157, 182, 240–242,
    245–247, 261, 461

  _Welwitschia_, 278

  White, D., 27, 29, 201, 264, 265, 346, 377, 464, 485, 498, 513, 516,
    560

  Wickes, W. H., 82

  _Widdringtonites_, 39

  Wild, G. and J. Lomax, 271

  Williamson, W. C. See note, p. 609

  Williamson, W. C. and D. H. Scott, 6

  Witham, H., 160

  _Woodwardia_, 359

  _Woodwardites_, 377

  Wünsch, E. A., 163


  _Xenophyton radiculosum_, 158

  _Xenopteris_, 555


  Yabe, H., 377, 481

  Yokoyama, M., 349, 377

  Young, G. and J. Bird, 83


  Zalessky, M., 571

  _Zalesskya_, 326–330, 332, 337, 338, 461

  _Z. diploxylon_, 326–331

  _Z. gracilis_, 326–331

  Zeiller, R. See note, p. 609

  _Zeilleria_, 407

  _Z. avoldensis_, 407

  _Z. delicatula_, 407

  Zenker, J. C., 401

  Zigno, A. de, 353, 390, 410, 478, 482, 546–550

  Zygoptereae, 443–465

  _Zygopteris_, 418, 449

  _Z. bibractensis_, 453, 455

  _Z. Brongniarti_, 450

  _Z. Lacattii_, 463

  _Z. pettycurensis_, 447

  _Z. primaria_, 443, 444, 446, 451

  _Z. Roemeri_, 447, 448

  _Z. scandens_, 450





+----------------------------------------------------------------------+
|                             FOOTNOTES:                               |
|                                                                      |
| [1] The full titles of books and papers referred to in footnotes     |
| distinguished by the addition of A after the date are given in the   |
| Bibliography at the end of Volume I.                                 |
|                                                                      |
| [2] Chap. XI.                                                        |
|                                                                      |
| [3] _ibid_. p. 405.                                                  |
|                                                                      |
| [4] Sternberg (23) A. p. 33, Pl. XXVI. figs. 4 _a_, 4 _b_.           |
|                                                                      |
| [5] Scott (05) p. 34.                                                |
|                                                                      |
| [6] Zeiller (88) A. Pl. LXII. figs. 2—4.                             |
|                                                                      |
| [7] Vol. I., p. 397.                                                 |
|                                                                      |
| [8] Kidston (01) p. 128, fig. 25; (02) p. 361, fig. 13.              |
|                                                                      |
| [9] Bower (08) p. 404, fig. 221.                                     |
|                                                                      |
| [10] Kidston (91) p. 59, Pl. I.; (01) p. 123, fig. 22.               |
|                                                                      |
| [11] Scott (05).                                                     |
|                                                                      |
| [12] See also Browne, Lady Isabel (09) p. 4.                         |
|                                                                      |
| [13] Williamson and Scott (94) A. p. 911.                            |
|                                                                      |
| [14] Thoday (06).                                                    |
|                                                                      |
| [15] Scott (97) A.; see also Scott (00) p. 106.                      |
|                                                                      |
| [16] The term metaxylem may be conveniently applied to the primary   |
| xylem other than protoxylem; the latter is usually but by no means   |
| invariably characterised by spiral thickening bands.                 |
|                                                                      |
| [17] Scott (05) p. 21 (footnote).                                    |
|                                                                      |
| [18] Vol. I. p. 354, fig. 95, C.                                     |
|                                                                      |
| [19] Williamson (72) Pl. XLIV. p. 297, figs. 29, 30.                 |
|                                                                      |
| [20] ‘Exarch’ denotes that the protoxylem is on the outside of       |
| the primary xylem; ‘endarch’ that it is on the inner edge or in a    |
| central position; ‘mesarch’ that it is internal, either near the     |
| inner or the outer edge of the metaxylem.                            |
|                                                                      |
| [21] Nathorst (02) p. 24.                                            |
|                                                                      |
| [22] Heer (71) p. 32, Pls. I—VI.                                     |
|                                                                      |
| [23] Scott (07) p. 155.                                              |
|                                                                      |
| [24] Thomas, A. P. W. (02) p. 350.                                   |
|                                                                      |
| [25] Bower (04) p. 227; (08) p. 424.                                 |
|                                                                      |
| [26] See p. 19.                                                      |
|                                                                      |
| [27] Scott (00) p. 499.                                              |
|                                                                      |
| [28] Bower (94) p. 545.                                              |
|                                                                      |
| [29] Thomas (02). See also Sykes (08).                               |
|                                                                      |
| [30] Sykes (08).                                                     |
|                                                                      |
| [31] Boodle (04); see _postea_ p. 21.                                |
|                                                                      |
| [32] Bower (08) p. 426.                                              |
|                                                                      |
| [33] Lignier (03); (08).                                             |
|                                                                      |
| [34] Tansley (08) p. 26, who refers to similar views held by         |
| Potonié and by Hallier.                                              |
|                                                                      |
| [35] On the morphology of Sporangiophores, see also Benson (08²)     |
| and Scott, D. H. (09) p. 623.                                        |
|                                                                      |
| [36] Scott (00).                                                     |
|                                                                      |
| [37] Thomas (02).                                                    |
|                                                                      |
| [38] Bower (08) p. 398.                                              |
|                                                                      |
| [39] Dangeard (91) and Bertrand, C. E. (81) recognise other species  |
| of _Tmesipteris_, but it is doubtful how far such differences as     |
| exist are worthy of specific recognition.                            |
|                                                                      |
| [40] Baker (87) A. p. 30.                                            |
|                                                                      |
| [41] Thomas (02) p. 349.                                             |
|                                                                      |
| [42] Another form of abnormality in the sporophylls of _Psilotum_    |
| has recently been described by Miss Sykes. Sykes (08²).              |
|                                                                      |
| [43] Bertrand, C. E. (81); Ford (04).                                |
|                                                                      |
| [44] Boodle (04).                                                    |
|                                                                      |
| [45] See p. 150.                                                     |
|                                                                      |
| [46] Bertrand (81); Jennings and Hall (91).                          |
|                                                                      |
| [47] Sykes (08).                                                     |
|                                                                      |
| [48] _ibid._ (08).                                                   |
|                                                                      |
| [49] Lignier (08).                                                   |
|                                                                      |
| [50] Bower (94); (08).                                               |
|                                                                      |
| [51] Bertrand (81) p. 254.                                           |
|                                                                      |
| [52] Münster (42) p. 108, Pl. XIII. fig. 11; Pl. XV. fig. 20.        |
|                                                                      |
| [53] Schimper (70) A. p. 75.                                         |
|                                                                      |
| [54] Goldenberg (55) p. 13, Pl. II. fig 7.                           |
|                                                                      |
| [55] Kidston (86²).                                                  |
|                                                                      |
| [56] Hollick (94) p. 255, figs. 12, 13.                              |
|                                                                      |
| [57] Lesquereux (78) Pl. V. fig. 11.                                 |
|                                                                      |
| [58] Since this was written I have had an opportunity of seeing      |
| a leaf labelled _Tmesipteris_ from the Tertiary plant-beds of        |
| Florissant in a collection recently acquired by the British Museum:  |
| the specimen bears no resemblance to a leaf of the recent genus.     |
|                                                                      |
| [59] Marion (90).                                                    |
|                                                                      |
| [60] Potonié (93) A. p. 197, Pls. XXVII., XXVIII., XXXIII.           |
|                                                                      |
| [61] Potonié (91); (93) A. p. 197.                                   |
|                                                                      |
| [62] Geinitz (73) p. 700, Pl. III. figs. 5–7.                        |
|                                                                      |
| [63] Seward and Gowan (00) p. 137; Seward and Ford (06) p. 374.      |
|                                                                      |
| [64] Dawson (59) A. p. 478, fig. 1.                                  |
|                                                                      |
| [65] _ibid._ (71) A. p. 38.                                          |
|                                                                      |
| [66] Solms-Laubach (95) A.                                           |
|                                                                      |
| [67] Dawson (71) A. Cf. Pl. XI. figs. 131, 134, etc.                 |
|                                                                      |
| [68] Carruthers (73).                                                |
|                                                                      |
| [69] Goeppert (52) A.                                                |
|                                                                      |
| [70] Carruthers (73).                                                |
|                                                                      |
| [71] White (02).                                                     |
|                                                                      |
| [72] Crépin (75).                                                    |
|                                                                      |
| [73] Stur (75) A. p. 33.                                             |
|                                                                      |
| [74] Carruthers (73).                                                |
|                                                                      |
| [75] Gilkinet (75) figs. 2–5.                                        |
|                                                                      |
| [76] Penhallow (92) p. 8.                                            |
|                                                                      |
| [77] Smith and White (05) p. 58, Pls. V. VI.                         |
|                                                                      |
| [78] Kidston (86²) p. 232.                                           |
|                                                                      |
| [79] Stur (81) Pls. III. IV.                                         |
|                                                                      |
| [80] Jahn (03) p. 77.                                                |
|                                                                      |
| [81] Smith and White (05) p. 63.                                     |
|                                                                      |
| [82] Nathorst (02) p. 15, Pl. I. figs. 18–35.                        |
|                                                                      |
| [83] For a general account of recent Lycopodiales see Pritzel (02);  |
| Campbell (05); Bower (08).                                           |
|                                                                      |
| [84] Bruchmann (97).                                                 |
|                                                                      |
| [85] Treub (84–90); see also Lang (99) and Bruchmann (98).           |
|                                                                      |
| [86] See Baker (87) A.                                               |
|                                                                      |
| [87] The Rose of Jericho is _Anastatica Hierochuntina_ L. a          |
| Cruciferous plant.                                                   |
|                                                                      |
| [88] Baker (87) A. p. 34.                                            |
|                                                                      |
| [89] Vines (88).                                                     |
|                                                                      |
| [90] Scott and Hill (00).                                            |
|                                                                      |
| [91] For _Phylloglossum_, see Bertrand (82); Bower (94), (08);       |
| Campbell (05).                                                       |
|                                                                      |
| [92] Treub (84–90); Bruchmann (98); Lang (99).                       |
|                                                                      |
| [93] Sykes (08³).                                                    |
|                                                                      |
| [94] Bommer (03) Pl. IX. figs. 140, 141.                             |
|                                                                      |
| [95] Hooker (48) p. 423, figs. 12–14.                                |
|                                                                      |
| [96] Jones (05).                                                     |
|                                                                      |
| [97] Boodle (01) Pl. XIX.                                            |
|                                                                      |
| [98] This species is figured under the name _Lycopodium crassum_ by  |
| Hooker and Greville (31) Pl. 224. See also Brongniart (37) Pl. I.    |
| fig. 1.                                                              |
|                                                                      |
| [99] Hegelmaier (72). See also Hill, T.G. (06) p. 269; this author   |
| draws attention to the fact that in some species of _Lycopodium_     |
| the mucilage canals are confined to the sporophylls.                 |
|                                                                      |
| [100] Professor Yapp has drawn my attention to the very close        |
| anatomical resemblance between a specimen of _Lycopodium salakense_  |
| obtained by him from Gunong Inas in the Malay Peninsula and _L.      |
| cernuum_ as represented in fig. 125, H and I.                        |
|                                                                      |
| [101] Jones (05).                                                    |
|                                                                      |
| [102] Strasburger (73) p. 109; Brongniart (37) Pl. 8; (39) A. Pl.    |
| 32: Brongniart figures stems of _L. Phlegmaria_ and other species    |
| showing roots in the cortex. See also Goldenberg (55); Bruchmann     |
| (74); Saxelby (08).                                                  |
|                                                                      |
| [103] Since this was written a comparative account of the            |
| sporophylls of _Lycopodium_ has been published by Miss Sykes.        |
| [Sykes (08³).]                                                       |
|                                                                      |
| [104] Bower (94) p. 514; (08).                                       |
|                                                                      |
| [105] Seward and Ford (06).                                          |
|                                                                      |
| [106] Goebel (05) p. 579.                                            |
|                                                                      |
| [107] Bower (94).                                                    |
|                                                                      |
| [108] _ibid._ (94) Pl. XLVIII.                                       |
|                                                                      |
| [109] Kidston (83) Pl. XXXI. figs. 2–4.                              |
|                                                                      |
| [110] Lang (08).                                                     |
|                                                                      |
| [111] See page 192, and Watson (09).                                 |
|                                                                      |
| [112] Lang (08) p. 357.                                              |
|                                                                      |
| [113] Bruchmann (97).                                                |
|                                                                      |
| [114] Gard. Chron. (82).                                             |
|                                                                      |
| [115] Harvey-Gibson (02).                                            |
|                                                                      |
| [116] _ibid._ (94) (97) (02).                                        |
|                                                                      |
| [117] Bower (93).                                                    |
|                                                                      |
| [118] Harvey-Gibson (94) p. 152.                                     |
|                                                                      |
| [119] _ibid._ (94) p. 194; Scott (96) p. 9.                          |
|                                                                      |
| [120] Bruchmann (97).                                                |
|                                                                      |
| [121] The term solenostele, first used by Van Tieghem and revived    |
| by Gwynne-Vaughan, may be applied to a stem in which the vascular    |
| tissue has the form of a hollow cylinder with phloem and endodermis  |
| on each side of the xylem. As each leaf-trace is given off the       |
| continuity of the vascular tube is interrupted. See Gwynne-Vaughan   |
| (01) p. 73.                                                          |
|                                                                      |
| [122] Harvey-Gibson (94) Pl. XII, fig. 93.                           |
|                                                                      |
| [123] Harvey-Gibson (02).                                            |
|                                                                      |
| [124] _ibid._ (97).                                                  |
|                                                                      |
| [125] _ibid._ (96).                                                  |
|                                                                      |
| [126] Bower (08) p. 315.                                             |
|                                                                      |
| [127] Hieronymus (02).                                               |
|                                                                      |
| [128] Goebel (05) p. 581.                                            |
|                                                                      |
| [129] Lyon (01) p. 135.                                              |
|                                                                      |
| [130] See p. 271.                                                    |
|                                                                      |
| [131] Campbell (05) p. 522.                                          |
|                                                                      |
| [132] Motelay and Vendryès (82).                                     |
|                                                                      |
| [133] Campbell (05) p. 561.                                          |
|                                                                      |
| [134] Scott and Hill (00).                                           |
|                                                                      |
| [135] Motelay and Vendryès (82) Pls. XVI, XVII.                      |
|                                                                      |
| [136] Braun (63).                                                    |
|                                                                      |
| [137] Hill, T. G. (04) (06).                                         |
|                                                                      |
| [138] For figures, see Motelay and Vendryès (82); Bennie and         |
| Kidston (88) Pl. VI.                                                 |
|                                                                      |
| [139] Solms-Laubach (02).                                            |
|                                                                      |
| [140] See Von Mohl (40); Farmer (90).                                |
|                                                                      |
| [141] Von Mohl (40).                                                 |
|                                                                      |
| [142] Hofmeister (62).                                               |
|                                                                      |
| [143] Farmer (90); Scott and Hill (00).                              |
|                                                                      |
| [144] Miss Stokey (09), in a paper which appeared since this         |
| account was written, criticises the conclusions of Scott and Hill    |
| (00).                                                                |
|                                                                      |
| [145] Von Mohl (40).                                                 |
|                                                                      |
| [146] Saporta (94) p. 134, Pls. XXIV. XXV. XXVII.                    |
|                                                                      |
| [147] Münster (42) p. 107, Pl. IV. fig. 4.                           |
|                                                                      |
| [148] Phillips (29) A Pl X. fig. 12.                                 |
|                                                                      |
| [149] Lindley and Hutton A (34) Pl. CXXI.                            |
|                                                                      |
| [150] Nathorst (06); Seward (00) p. 278.                             |
|                                                                      |
| [151] Saporta (88) p. 28, Pl. II. pp. 16–20.                         |
|                                                                      |
| [152] Heer (76) A.                                                   |
|                                                                      |
| [153] Corda, in Germar (52).                                         |
|                                                                      |
| [154] Münster (42) A.                                                |
|                                                                      |
| [155] Solms-Laubach (99).                                            |
|                                                                      |
| [156] Germar (52).                                                   |
|                                                                      |
| [157] Bischof (53).                                                  |
|                                                                      |
| [158] Potonié (01) p. 754; (04) Lief ii.                             |
|                                                                      |
| [159] Goeppert, in Römer (54) Pl. XV. fig. 7.                        |
|                                                                      |
| [160] Spieker (53).                                                  |
|                                                                      |
| [161] Potonié (_loc. cit._).                                         |
|                                                                      |
| [162] Barber (89) Pls. V. VI.                                        |
|                                                                      |
| [163] Fitting (07).                                                  |
|                                                                      |
| [164] Potonié (04) Lief ii.                                          |
|                                                                      |
| [165] Weiss, C. E. (86).                                             |
|                                                                      |
| [166] Fliche (03).                                                   |
|                                                                      |
| [167] Vol. I, p. 300.                                                |
|                                                                      |
| [168] Halle (07) p. 1.                                               |
|                                                                      |
| [169] Feistmantel (75) A. p. 183, Pl. XXX. pp. 1 and 2.              |
|                                                                      |
| [170] Germar (49) Pl. XXVI; Geinitz (55) A. Pl. I. pp. 5, 6.         |
|                                                                      |
| [171] Bommer (03) p. 29, Pl. IX, figs. 138–141.                      |
|                                                                      |
| [172] Solms-Laubach (91) A. p. 137.                                  |
|                                                                      |
| [173] Zeiller (06) p. 140.                                           |
|                                                                      |
| [174] Halle (07).                                                    |
|                                                                      |
| [175] Brongniart (22) A. p. 304, Pl. VI, fig. 1.                     |
|                                                                      |
| [176] Brongniart (28) A. p. 83.                                      |
|                                                                      |
| [177] Brongniart (49) A. p. 40.                                      |
|                                                                      |
| [178] Goldenberg (55) p. 9.                                          |
|                                                                      |
| [179] Lesquereux (84) A. p. 777.                                     |
|                                                                      |
| [180] Kidston (86³) p. 561.                                          |
|                                                                      |
| [181] Halle (07).                                                    |
|                                                                      |
| [182] Renault (69) p. 178, Pls. XII–XIV.                             |
|                                                                      |
| [183] Renault (96) A. p. 249.                                        |
|                                                                      |
| [184] Kidston (86³).                                                 |
|                                                                      |
| [185] Goeppert (52) A.                                               |
|                                                                      |
| [186] Kidston (01) p. 38.                                            |
|                                                                      |
| [187] Kidston (84) Pl. V; (01) p. 37.                                |
|                                                                      |
| [188] Bower (08) p. 298, fig. 147.                                   |
|                                                                      |
| [189] Solms-Laubach (91) A. p. 186.                                  |
|                                                                      |
| [190] Penhallow (92) Pl. I. fig. 2, p. 8.                            |
|                                                                      |
| [191] Goeppert (52) p. 440.                                          |
|                                                                      |
| [192] Kidston (94) A. p. 254.                                        |
|                                                                      |
| [193] Geinitz (55) A. p. 32, Pl. I. fig. 1.                          |
|                                                                      |
| [194] Page 88.                                                       |
|                                                                      |
| [195] Kidston (01) p. 36, fig. 2, B.                                 |
|                                                                      |
| [196] Kidston (01) p. 37, fig. 2, A.                                 |
|                                                                      |
| [197] Goldenberg (55) Pl. I. fig. 5.                                 |
|                                                                      |
| [198] Halle (07) Pl. I. fig. 5.                                      |
|                                                                      |
| [199] Page 89.                                                       |
|                                                                      |
| [200] Halle (07).                                                    |
|                                                                      |
| [201] Brodie (45) p. 93.                                             |
|                                                                      |
| [202] Buckman in Murchison (45) p. 6.                                |
|                                                                      |
| [203] Buckman (50) p. 415, fig. 2.                                   |
|                                                                      |
| [204] Buckman (50) p. 415, fig. 4.                                   |
|                                                                      |
| [205] Wickes (00) p. 422.                                            |
|                                                                      |
| [206] Sollas (01).                                                   |
|                                                                      |
| [207] Seward (04) p. 14, Pl. II. figs. 2, 3.                         |
|                                                                      |
| [208] Vol. I. p. 240.                                                |
|                                                                      |
| [209] Sollas (01) p. 311.                                            |
|                                                                      |
| [210] Seward (04) p. 14.                                             |
|                                                                      |
| [211] Halle (07) p. 14, Pl. III. figs. 6–12.                         |
|                                                                      |
| [212] Lindley and Hutton (31) A. Pl. LXI.                            |
|                                                                      |
| [213] Sternberg (38) A. p. 38.                                       |
|                                                                      |
| [214] Schimper (70) A. p. 9.                                         |
|                                                                      |
| [215] Young and Bird (22) A. Pl. II. fig. 7.                         |
|                                                                      |
| [216] No. 39314, Brit. Mus.                                          |
|                                                                      |
| [217] Möller (02) Pl. VI. fig. 21.                                   |
|                                                                      |
| [218] Seward (04²) p. 161, Pl. VIII. figs. 2–4. The drawing is       |
| reproduced twice natural size.                                       |
|                                                                      |
| [219] Oldham and Morris (63) Pls. XXXIII. XXXV.                      |
|                                                                      |
| [220] Feistmantel (77) p. 87.                                        |
|                                                                      |
| [221] Heer (76) Pl. XV. figs. 1–8.                                   |
|                                                                      |
| [222] Nathorst (90) A. Pl. II. fig. 3. Saporta (94) Pls.             |
| XXIII.–XXVI. Knowlton (98) p. 136.                                   |
|                                                                      |
| [223] Lesquereux (78) Pl. V. fig. 12. See also Knowlton _loc. cit._  |
|                                                                      |
| [224] Zeiller (06) p. 141, Pls. XXXIX. XLI.                          |
|                                                                      |
| [225] Zeiller (00) p. 1077.                                          |
|                                                                      |
| [226] Bennie and Kidston (88) Pl. VI. fig. 22.                       |
|                                                                      |
| [227] Goldenberg (55) Pl. I. fig. 3.                                 |
|                                                                      |
| [228] Schimper (70) A. Pl. LVII. fig. 2.                             |
|                                                                      |
| [229] Halle (07).                                                    |
|                                                                      |
| [230] Goldenberg (55) Pl. I. fig. 2.                                 |
|                                                                      |
| [231] Schimper (70) A. p. 10.                                        |
|                                                                      |
| [232] Nathorst (08).                                                 |
|                                                                      |
| [233] Nathorst (02²) p. 5, Pl. I. fig. 1.                            |
|                                                                      |
| [234] Fliche (03).                                                   |
|                                                                      |
| [235] Fliche (09).                                                   |
|                                                                      |
| [236] Scott (01).                                                    |
|                                                                      |
| [237] Rodway (95) A. p. 153.                                         |
|                                                                      |
| [238] A good example of an old _Lepidodendron_ stem (_L.             |
| aculeatum_) is figured by Zalessky (04) Pl. I. fig. 3.               |
|                                                                      |
| [239] Seward and Ford (06) Pl. XXIII. fig. C.                        |
|                                                                      |
| [240] See Fischer (04).                                              |
|                                                                      |
| [241] Bertrand, C. E. (91) p. 84: derived from παρά, by the side     |
| of, and ἴχνος, trace or foot-print.                                  |
|                                                                      |
| [242] Renault (96) A. Pls. XXXIII. XXXIV. p. 178. For a good         |
| section of another Lepidodendron leaf, see Scott (08) p. 160, figs.  |
| 64, 65.                                                              |
|                                                                      |
| [243] Weiss, F. E. (07).                                             |
|                                                                      |
| [244] For a fuller account of the parichnos, see Hill, T. G. (06)    |
| and other papers quoted by F. E. Weiss (07).                         |
|                                                                      |
| [245] Barrois (04). See also Etheridge (80); Geikie (03) p. 1049.    |
|                                                                      |
| [246] Binney (48).                                                   |
|                                                                      |
| [247] Darwin (03) vol. II. pp. 217, 220.                             |
|                                                                      |
| [248] Solms-Laubach (92) Pl. II. figs. 2, 4.                         |
|                                                                      |
| [249] Williamson (93) p. 10.                                         |
|                                                                      |
| [250] Potonié (05) Lief, iii., p. 41.                                |
|                                                                      |
| [251] Stur (75) A. Heft II. p. 277.                                  |
|                                                                      |
| [252] Potonié (05) fig. 4.                                           |
|                                                                      |
| [253] Seward and Leslie (08) Pl. X. figs. 1 and 2.                   |
|                                                                      |
| [254] Sternberg (26) A. Pl. XI. figs. 2–4; (02) p. 23.               |
|                                                                      |
| [255] Corda (45) A. Pls. I.–IV.                                      |
|                                                                      |
| [256] Zeiller (92) A.                                                |
|                                                                      |
| [257] Kidston (93) p. 561, Pls. I. and II.                           |
|                                                                      |
| [258] Seward (90).                                                   |
|                                                                      |
| [259] Williamson (93) Pl. IV. figs. 30–32.                           |
|                                                                      |
| [260] Binney (62).                                                   |
|                                                                      |
| [261] Binney (65); see also Binney (72).                             |
|                                                                      |
| [262] Williamson (72).                                               |
|                                                                      |
| [263] Weiss, F. E. and Lomax (05).                                   |
|                                                                      |
| [264] Binney (62).                                                   |
|                                                                      |
| [265] Carruthers (69) p. 179.                                        |
|                                                                      |
| [266] Kidston (86) A. p. 151.                                        |
|                                                                      |
| [267] Seward (06) p. 372.                                            |
|                                                                      |
| [268] Hovelacque (92).                                               |
|                                                                      |
| [269] Solms-Laubach (92) Pl. II. fig. 6; Seward and Hill (00) Pl.    |
| IV. fig. 26. See p. 910 of the latter paper for other references.    |
|                                                                      |
| [270] Gwynne-Vaughan (08).                                           |
|                                                                      |
| [271] Jeffrey (98). See also Tansley (08) p. 37.                     |
|                                                                      |
| [272] Seward (99) p. 144.                                            |
|                                                                      |
| [273] Steinberg (26) A.                                              |
|                                                                      |
| [274] Goeppert (52) A. p. 196. See also Kidston (01) p. 50.          |
|                                                                      |
| [275] _ibid._ (52) A. p. 44. Pls. XXX. XXXI. Lief. i and ii.         |
|                                                                      |
| [276] Balfour (72) A.                                                |
|                                                                      |
| [277] Good examples are given by Schmalhausen (77) Pl. III.          |
|                                                                      |
| [278] Steinhauer (18) A. Pl. IV. fig. 5.                             |
|                                                                      |
| [279] Brongniart (49) A. p. 42.                                      |
|                                                                      |
| [280] Goldenberg (55).                                               |
|                                                                      |
| [281] Carruthers (73²) p. 6.                                         |
|                                                                      |
| [282] Feistmantel (75) A.                                            |
|                                                                      |
| [283] Potonié (05) Lief. III. 42–44.                                 |
|                                                                      |
| [284] Artis (25) A. Pls. XVI. XXIII.                                 |
|                                                                      |
| [285] Steinberg (38) A.                                              |
|                                                                      |
| [286] Stur (75) A. Heft II. p. 229.                                  |
|                                                                      |
| [287] Lindley and Hutton (31) A. Pls. V. and VI.                     |
|                                                                      |
| [288] Kidston (85). In this important paper Dr Kidston gives a full  |
| account of the history of our knowledge of _Ulodendron_.             |
|                                                                      |
| [289] Steinhauer (18) A. p. 286, Pl. VII. fig. 1.                    |
|                                                                      |
| [290] Rhode (20) Pl. III.                                            |
|                                                                      |
| [291] Lindley and Hutton (31) A.                                     |
|                                                                      |
| [292] Hooker (48), p. 427.                                           |
|                                                                      |
| [293] Geinitz (55) A.                                                |
|                                                                      |
| [294] Carruthers (70).                                               |
|                                                                      |
| [295] Williamson (72).                                               |
|                                                                      |
| [296] Thompson, D’Arcy (80).                                         |
|                                                                      |
| [297] Kidston (85).                                                  |
|                                                                      |
| [298] Seward and Ford (06) Pl. XXIII. fig. C.                        |
|                                                                      |
| [299] Shattock (88).                                                 |
|                                                                      |
| [300] Watson (08).                                                   |
|                                                                      |
| [301] Watson (08) p. 10.                                             |
|                                                                      |
| [302] Renier (08).                                                   |
|                                                                      |
| [303] Stur (75) A. Heft II.                                          |
|                                                                      |
| [304] _Garden and Forest_, vol. v., pp. 160–162, fig. 24 (April 6,   |
| 1902).                                                               |
|                                                                      |
| [305] Lindley and Hutton (35) A.                                     |
|                                                                      |
| [306] Kidston (93) Pl. II. fig. 6.                                   |
|                                                                      |
| [307] _ibid._ (02) Pl. LIII. fig. 2.                                 |
|                                                                      |
| [308] Williamson (83²) A. Pl. 34.                                    |
|                                                                      |
| [309] Feistmantel (75) A. p. 193, Pls. XXXIV.–XXXVII.                |
|                                                                      |
| [310] Feistmantel _loc. cit._ Pl. XLVII.                             |
|                                                                      |
| [311] Grand’Eury (90) A.                                             |
|                                                                      |
| [312] Dawes (48).                                                    |
|                                                                      |
| [313] Binney (72); see also Seward (99).                             |
|                                                                      |
| [314] Carruthers (73²).                                              |
|                                                                      |
| [315] Williamson (72).                                               |
|                                                                      |
| [316] _ibid._ (93).                                                  |
|                                                                      |
| [317] Weiss, F. E. (03).                                             |
|                                                                      |
| [318] Kidston (05).                                                  |
|                                                                      |
| [319] Renault (96) A. p. 175, Pls. XXXIII. XXXIV.                    |
|                                                                      |
| [320] For description of the leaf-anatomy, see pp. 98, 99.           |
|                                                                      |
| [321] Renault (79) p. 249, Pl. X.                                    |
|                                                                      |
| [322] Solms-Laubach (96) p. 18, Pl. X. figs. 7–11.                   |
|                                                                      |
| [323] They are regarded as identical by Fischer (04).                |
|                                                                      |
| [324] Binney (72) Pl. XIII. fig. 1.                                  |
|                                                                      |
| [325] Seward (99).                                                   |
|                                                                      |
| [326] As Miss Stokey (09) points out the production of parenchyma    |
| internal to the cambium of _L. fuliginosum_ is a feature shared by   |
| _Isoetes_. See also Scott and Hill (00), p. 424.                     |
|                                                                      |
| [327] Williamson (81) A. Pl. LII. p. 288. (Will. Coll. No. 379.)     |
|                                                                      |
| [328] Binney (72).                                                   |
|                                                                      |
| [329] Cash and Lomax (90).                                           |
|                                                                      |
| [330] Kidston (93) p. 547.                                           |
|                                                                      |
| [331] Weiss, F. E. (03) p. 218.                                      |
|                                                                      |
| [332] Scott, D. H. (06³).                                            |
|                                                                      |
| [333] Watson (07) p. 18.                                             |
|                                                                      |
| [334] Seward (06) p. 378.                                            |
|                                                                      |
| [335] Weiss, F. E. (02).                                             |
|                                                                      |
| [336] Hick (93).                                                     |
|                                                                      |
| [337] Hick (93²).                                                    |
|                                                                      |
| [338] See p. 240.                                                    |
|                                                                      |
| [339] Hick (93) Pl. XVI. fig. 1.                                     |
|                                                                      |
| [340] Witham (31) A.                                                 |
|                                                                      |
| [341] Witham (33) A. Pls. XII. XIII.                                 |
|                                                                      |
| [342] Lindley and Hutton (35) A. Pls. 98, 99.                        |
|                                                                      |
| [343] Brongniart (39) A.                                             |
|                                                                      |
| [344] Kidston (03) p. 822.                                           |
|                                                                      |
| [345] Williamson (87).                                               |
|                                                                      |
| [346] Kidston (03) p. 822; Watson (07).                              |
|                                                                      |
| [347] Bertrand, C. E. (91).                                          |
|                                                                      |
| [348] Williamson (80) A.                                             |
|                                                                      |
| [349] Williamson (93) Pl. I. fig. 3.                                 |
|                                                                      |
| [350] Volume I. p. 89. For other references to these stems, see      |
| Seward and Hill (00) p. 918.                                         |
|                                                                      |
| [351] Wünsch (67).                                                   |
|                                                                      |
| [352] Carruthers (69²) p. 6.                                         |
|                                                                      |
| [353] Williamson (80) A.; (93); (95).                                |
|                                                                      |
| [354] Wünsch _loc. cit._                                             |
|                                                                      |
| [355] Binney (71) p. 56.                                             |
|                                                                      |
| [356] Carruthers (69).                                               |
|                                                                      |
| [357] Seward and Hill (00).                                          |
|                                                                      |
| [358] Williamson (96) p. 175.                                        |
|                                                                      |
| [359] The term meristematic zone is used because some of the cells   |
| in this region are in a state of active division, though the inner   |
| portion may consist of permanent tissue.                             |
|                                                                      |
| [360] Scott (00) p. 131; (08) p. 142.                                |
|                                                                      |
| [361] Seward and Hill (00) Pl. II. fig. 14.                          |
|                                                                      |
| [362] Worsdell (95); Bernard (04).                                   |
|                                                                      |
| [363] No. 52, 625.                                                   |
|                                                                      |
| [364] Seward and Hill (00) p. 922.                                   |
|                                                                      |
| [365] Binney (71) p. 56, Pl. XI. figs. 2_a_-2_c_.                    |
|                                                                      |
| [366] Williamson (72) p. 298, pl. XLV. fig. 35.                      |
|                                                                      |
| [367] Carruthers (72).                                               |
|                                                                      |
| [368] Williamson (93) p. 30.                                         |
|                                                                      |
| [369] Goldenberg (55) p. 12.                                         |
|                                                                      |
| [370] See also Kidston (94), (86) A. p. 160; Potonié (05) Lief.      |
| III. 50.                                                             |
|                                                                      |
| [371] Stur (75) A. II. p. 330, fig. 34.                              |
|                                                                      |
| [372] Hannig (98).                                                   |
|                                                                      |
| [373] Young and Kidston (88) A.                                      |
|                                                                      |
| [374] Potonié (01²) fig. 72, p. 117.                                 |
|                                                                      |
| [375] Stur (75) II. A. Pl. XXXVI. fig. 9.                            |
|                                                                      |
| [376] See Chap. XVII.                                                |
|                                                                      |
| [377] Williamson (72) Pl. XLIV. p. 294: (93) (93²).                  |
|                                                                      |
| [378] Kidston (01) p. 60. See also Scott (00) p. 170, figs. 67, 68.  |
|                                                                      |
| [379] Williamson (93), Pl. VIII. figs. 51, 52. See also figs. 67–69  |
| given by Scott (00).                                                 |
|                                                                      |
| [380] Scott (00) p. 173.                                             |
|                                                                      |
| [381] Scott [(08) p. 187] suggests that the projection may have      |
| formed a passage for the admission of the microspores, or of the     |
| spermatozoids which they produced.                                   |
|                                                                      |
| [382] Bennie and Kidston (88) Pl. VI. figs. 20, _a–s_.               |
|                                                                      |
| [383] Gordon (08).                                                   |
|                                                                      |
| [384] Williamson (72).                                               |
|                                                                      |
| [385] Carruthers (69²).                                              |
|                                                                      |
| [386] Zeiller (95). See also White (08) p. 447.                      |
|                                                                      |
| [387] Arber (05) Pl. I. fig. 2.                                      |
|                                                                      |
| [388] Seward and Leslie (08).                                        |
|                                                                      |
| [389] Zeiller (98).                                                  |
|                                                                      |
| [390] Renault (90).                                                  |
|                                                                      |
| [391] Seward (07³).                                                  |
|                                                                      |
| [392] Nathorst (07); Bather (07); (08).                              |
|                                                                      |
| [393] Seward (97²) A. p. 326, Pl. XXIII.                             |
|                                                                      |
| [394] Carruthers (72²).                                              |
|                                                                      |
| [395] Unger and Richter (56).                                        |
|                                                                      |
| [396] Dawson (71) A. Pl. VIII. See also Smith and White (05).        |
|                                                                      |
| [397] M’Coy (74). See also Feistmantel (90) A.                       |
|                                                                      |
| [398] Kidston (86) A. p. 231.                                        |
|                                                                      |
| [399] Krasser (00) Pl. II. fig. 1.                                   |
|                                                                      |
| [400] Nathorst (94) A. Pl. II. fig. 8.                               |
|                                                                      |
| [401] Szajnocha (91) p. 203.                                         |
|                                                                      |
| [402] See Etheridge (90); David and Pittman (93).                    |
|                                                                      |
| [403] White (08).                                                    |
|                                                                      |
| [404] Brongniart (28) A. p. 87.                                      |
|                                                                      |
| [405] Parkinson (11) A. Pl. IX. fig. 1, p. 428.                      |
|                                                                      |
| [406] Carruthers (69²).                                              |
|                                                                      |
| [407] Brongniart (22) A. Pl. II. fig. 4.                             |
|                                                                      |
| [408] Bower (08) p. 305.                                             |
|                                                                      |
| [409] Seward (90); Potonié (93²).                                    |
|                                                                      |
| [410] Brongniart (37) Pl. XXIV.                                      |
|                                                                      |
| [411] Morris (40) Pl. XXXVIII. fig. 10.                              |
|                                                                      |
| [412] Williamson (93) Pl. VI. fig. 26, A.                            |
|                                                                      |
| [413] Kidston (01) p. 62.                                            |
|                                                                      |
| [414] Renault and Zeiller (88) A. Pl. LXI. fig. 4.                   |
|                                                                      |
| [415] Hooker (48²).                                                  |
|                                                                      |
| [416] Binney (71).                                                   |
|                                                                      |
| [417] Williamson (93) p. 26.                                         |
|                                                                      |
| [418] Maslen (99).                                                   |
|                                                                      |
| [419] Lindley and Hutton (37) A. Pl. 163.                            |
|                                                                      |
| [420] For a detailed account of this type, see Maslen (99).          |
|                                                                      |
| [421] Williamson (93) p. 28.                                         |
|                                                                      |
| [422] Binney (71).                                                   |
|                                                                      |
| [423] Binney (71) Pl. VIII. figs. 2, 4.                              |
|                                                                      |
| [424] Maslen (99) Pl. XXXVI fig. 11.                                 |
|                                                                      |
| [425] Brown, R. (51).                                                |
|                                                                      |
| [426] Brongniart (68).                                               |
|                                                                      |
| [427] Schimper (70) A. p. 67, Pl. LXII. figs. 13–29.                 |
|                                                                      |
| [428] Bower (93).                                                    |
|                                                                      |
| [429] Bower (94) Pl. XLVIII. fig. 93.                                |
|                                                                      |
| [430] Zeiller (09).                                                  |
|                                                                      |
| [431] Zalessky has recently (08) described a large species of cone,  |
| _Lepidostrobus Bertrandi_, 5 cm. in diameter.                        |
|                                                                      |
| [432] Morris (40).                                                   |
|                                                                      |
| [433] Balfour (57).                                                  |
|                                                                      |
| [434] Kidston and Bennie (88).                                       |
|                                                                      |
| [435] Reinsch (81) A.                                                |
|                                                                      |
| [436] Scott, R. (06).                                                |
|                                                                      |
| [437] Maslen (99) p. 373; Scott, R. (06) p. 117.                     |
|                                                                      |
| [438] Campbell (05) p. 414.                                          |
|                                                                      |
| [439] Williamson (78) A. p. 340, Pl. XXII. See also the drawings in  |
| Williamson’s later papers quoted in the synonymy.                    |
|                                                                      |
| [440] Williamson (93²).                                              |
|                                                                      |
| [441] Scott, D. H. (98).                                             |
|                                                                      |
| [442] Berridge (05).                                                 |
|                                                                      |
| [443] Lang (08).                                                     |
|                                                                      |
| [444] Lang (08) p. 364.                                              |
|                                                                      |
| [445] Williamson (78) A. Pl. XXII. fig. 53.                          |
|                                                                      |
| [446] Lang (08) p. 367. Since this was written a paper has been      |
| published by Mr Watson on a new type of Lycopodiaceous cone          |
| from the Lower Coal-Measures (_Mesostrobus_): in an appendix he      |
| criticises Dr Lang’s views in regard to _Spencerites_. [Watson,      |
| _Annals of Botany_, Vol. XXIII. p. 379, 1909.                        |
|                                                                      |
| [447] Seward and Ford (06) p. 395.                                   |
|                                                                      |
| [448] Artis (25) A. Pl. XV.                                          |
|                                                                      |
| [449] Rhode (20).                                                    |
|                                                                      |
| [450] Brongniart (22) A. Pl. XII. fig. 4.                            |
|                                                                      |
| [451] For generic names wholly or in part synonymous with            |
| _Sigillaria_, see White (99) p. 230.                                 |
|                                                                      |
| [452] Kidston (86) A. p. 186.                                        |
|                                                                      |
| [453] Brongniart (37) Pl. CL. fig. 1.                                |
|                                                                      |
| [454] Brongniart (22) A. Pl. XII. fig. 3.                            |
|                                                                      |
| [455] Sternberg (23) A.                                              |
|                                                                      |
| [456] Goldenberg (55).                                               |
|                                                                      |
| [457] Zeiller (88) A. (_S. elegans_).                                |
|                                                                      |
| [458] Goldenberg (55).                                               |
|                                                                      |
| [459] Renault (96) A. Pl. XXXV.                                      |
|                                                                      |
| [460] Stur (75) II. A. Pl. XLII.                                     |
|                                                                      |
| [461] For an account of the various external features made use of    |
| in the classification of Sigillarias, see Koehne (04).               |
|                                                                      |
| [462] Grand’Eury (90) A.                                             |
|                                                                      |
| [463] Germar (53).                                                   |
|                                                                      |
| [464] Cf. _Lepidodendron Zeilleri_, Zalessky (04) Pl. IV. fig. 1.    |
|                                                                      |
| [465] Lesquereux (79) A. Pl. LXIV.                                   |
|                                                                      |
| [466] Zeiller (88) A. Pl. LXXI.                                      |
|                                                                      |
| [467] Kidston (01) p. 46.                                            |
|                                                                      |
| [468] Kidston (85).                                                  |
|                                                                      |
| [469] White, D. (07²).                                               |
|                                                                      |
| [470] Weiss, C. E. (88).                                             |
|                                                                      |
| [471] Zeiller (89).                                                  |
|                                                                      |
| [472] Kidston (01) p. 94.                                            |
|                                                                      |
| [473] Seward (90²).                                                  |
|                                                                      |
| [474] Weiss, C. E. (89).                                             |
|                                                                      |
| [475] Grand’Eury (90) A.                                             |
|                                                                      |
| [476] Kidston (97) p. 46.                                            |
|                                                                      |
| [477] Grand’Eury (90) A. Pl. XIII. fig. 8.                           |
|                                                                      |
| [478] Renault and Roche (97).                                        |
|                                                                      |
| [479] Coward (07); Renault (96) A.                                   |
|                                                                      |
| [480] Grand’Eury (90) A. Pl. III.                                    |
|                                                                      |
| [481] Cf. Prof. Yapp’s account (08) of Fen vegetation.               |
|                                                                      |
| [482] Zeiller (88) A. Pl. LXXXV.                                     |
|                                                                      |
| [483] Brongniart (28) A. p. 63.                                      |
|                                                                      |
| [484] Brongniart (39) A.; (49) A. p. 55.                             |
|                                                                      |
| [485] Williamson (83).                                               |
|                                                                      |
| [486] Williamson (72) p. 228.                                        |
|                                                                      |
| [487] Renault (79).                                                  |
|                                                                      |
| [488] Goldenberg (55) p. 24.                                         |
|                                                                      |
| [489] Schimper (70) A. p. 105.                                       |
|                                                                      |
| [490] Zeiller (84).                                                  |
|                                                                      |
| [491] Zeiller (88) A.                                                |
|                                                                      |
| [492] Kidston (97).                                                  |
|                                                                      |
| [493] Grand’Eury (90) A. Vol. II.                                    |
|                                                                      |
| [494] Kidston (97).                                                  |
|                                                                      |
| [495] Renault (96) A.                                                |
|                                                                      |
| [496] Kidston (85).                                                  |
|                                                                      |
| [497] Lindley and Hutton (31) A. Pl. VI.                             |
|                                                                      |
| [498] Thompson (80).                                                 |
|                                                                      |
| [499] Kidston (85) Pl. VI. fig. 10.                                  |
|                                                                      |
| [500] Kidston (89²) p. 61; Pl. VI. fig. 1.                           |
|                                                                      |
| [501] Zeiller (88) A. p. 483, Pls. LXXIII. LXXIV.                    |
|                                                                      |
| [502] Zeiller (06) Pl. XLII.                                         |
|                                                                      |
| [503] Kidston (07²).                                                 |
|                                                                      |
| [504] Renault (96) A. Pl. XXXVII. fig. 3.                            |
|                                                                      |
| [505] Renault (79) Pls. XII. XIII. p. 270; (96) A. p. 245.           |
|                                                                      |
| [506] Scott, D. H. (04²).                                            |
|                                                                      |
| [507] Scott (08) p 230, fig. 95.                                     |
|                                                                      |
| [508] Kidston (07²).                                                 |
|                                                                      |
| [509] Arber and Thomas (08).                                         |
|                                                                      |
| [510] Goldenberg (55); Kidston (97).                                 |
|                                                                      |
| [511] Zeiller (88) A. Pl. XC. 1, p. 598.                             |
|                                                                      |
| [512] Zeiller (84); (88) A. Pl. LXXXIX.                              |
|                                                                      |
| [513] Kidston (97) Pls. I. II. p. 50.                                |
|                                                                      |
| [514] Goldenberg (55).                                               |
|                                                                      |
| [515] Kidston (05) Pl. III. figs. 23, 25, 26, 27.                    |
|                                                                      |
| [516] Zeiller (06) p. 160.                                           |
|                                                                      |
| [517] Brongniart (39); Renault (96) A.                               |
|                                                                      |
| [518] Zeiller (88) A. p. 586; Kidston (05) p. 534.                   |
|                                                                      |
| [519] Renault and Grand’Eury (75); Renault (96) A.                   |
|                                                                      |
| [520] Germar (44) A.                                                 |
|                                                                      |
| [521] Scott (08) p. 219.                                             |
|                                                                      |
| [522] Solms-Laubach (91) A. p. 253.                                  |
|                                                                      |
| [523] Renault and Grand’Eury (75) Pl. I. fig. 5.                     |
|                                                                      |
| [524] Coward (07).                                                   |
|                                                                      |
| [525] Renault (96) A. p. 237, Pl. XXXVIII. figs. 1–4.                |
|                                                                      |
| [526] Kidston (05).                                                  |
|                                                                      |
| [527] Brongniart (28) A. Pls. CXLVI. CLV. CLVIII.                    |
|                                                                      |
| [528] Bertrand (99).                                                 |
|                                                                      |
| [529] Scott (08) p. 227, fig. 93.                                    |
|                                                                      |
| [530] Kidston (07²).                                                 |
|                                                                      |
| [531] Arber and Thomas (07).                                         |
|                                                                      |
| [532] Williamson (72).                                               |
|                                                                      |
| [533] Scott (08) p. 227.                                             |
|                                                                      |
| [534] Mettenius (60).                                                |
|                                                                      |
| [535] e.g. _L. Wünschianum_ (fig. 181, B, _lt_).                     |
|                                                                      |
| [536] Kidston (05) p. 547.                                           |
|                                                                      |
| [537] Scott, D. H. (02).                                             |
|                                                                      |
| [538] For fuller synonymy, see Kidston (86) A. p. 179; and Zeiller   |
| (06) p 160; Koehne (04) p. 62.                                       |
|                                                                      |
| [539] Renault (96) A. Pl. XXXV.; Zeiller (06) Pl. XLII.              |
|                                                                      |
| [540] Grand’Eury (90) A.                                             |
|                                                                      |
| [541] Zeiller (06) Pl. XLII.                                         |
|                                                                      |
| [542] Renault (96) A. Pls. XXXVII. XLI.                              |
|                                                                      |
| [543] Grand’Eury (90) A. Pl. XI.                                     |
|                                                                      |
| [544] Zeiller (06) p. 176.                                           |
|                                                                      |
| [545] Goldenberg (55) Pl. XII.                                       |
|                                                                      |
| [546] Renault (96) A. Pl. XXXIX.                                     |
|                                                                      |
| [547] Zeiller (92) A.; (06).                                         |
|                                                                      |
| [548] Potonié (96) A.                                                |
|                                                                      |
| [549] Fontaine and White (80).                                       |
|                                                                      |
| [550] Kidston (94) p. 252.                                           |
|                                                                      |
| [551] Seward (97²) A.                                                |
|                                                                      |
| [552] White (08) p. 450, Pl. V. fig. 12.                             |
|                                                                      |
| [553] Potonié (01²).                                                 |
|                                                                      |
| [554] Goeppert (64) A.                                               |
|                                                                      |
| [555] Goeppert, _loc. cit._                                          |
|                                                                      |
| [556] Gresley (89) Pl. II.                                           |
|                                                                      |
| [557] Steinhauer (18) A.                                             |
|                                                                      |
| [558] Logan (42).                                                    |
|                                                                      |
| [559] Potonié (93³).                                                 |
|                                                                      |
| [560] Williamson (87) A.                                             |
|                                                                      |
| [561] A similar example, now in the Bergakademie of Berlin, has      |
| been described by Potonié (90) A.; see also a note on the German     |
| specimen by Seward (91).                                             |
|                                                                      |
| [562] Martin (09) A. Pl. XII.                                        |
|                                                                      |
| [563] Artis (25) A.                                                  |
|                                                                      |
| [564] Lindley and Hutton (38) A. Pl. CLXVI.                          |
|                                                                      |
| [565] For a fuller synonymy, see Kidston (03) p. 757.                |
|                                                                      |
| [566] Goldenberg (55) p. 6.                                          |
|                                                                      |
| [567] Binney (44) p. 165.                                            |
|                                                                      |
| [568] Brongniart (22) A. p. 228.                                     |
|                                                                      |
| [569] _ibid._ (49) A. p. 456.                                        |
|                                                                      |
| [570] Artis (25) A. Pl. X.                                           |
|                                                                      |
| [571] Lindley and Hutton (31) A. Pl. XXXI.                           |
|                                                                      |
| [572] Goldenberg (55).                                               |
|                                                                      |
| [573] Logan (42) p. 492.                                             |
|                                                                      |
| [574] Binney (44); (46).                                             |
|                                                                      |
| [575] Bowman (41).                                                   |
|                                                                      |
| [576] Brown (45); (46); (47); (49). See also Dawson (66).            |
|                                                                      |
| [577] Hawkshaw (42).                                                 |
|                                                                      |
| [578] Binney (46) p. 393.                                            |
|                                                                      |
| [579] Brown (49). This figure is reproduced by Williamson (87) A.    |
| p. 16.                                                               |
|                                                                      |
| [580] Williamson (87) A. p. 3. Solms-Laubach (91) A. p. 284.         |
|                                                                      |
| [581] Mellor and Leslie (06).                                        |
|                                                                      |
| [582] Goeppert (64) A. p. 197, Pls. 34–36.                           |
|                                                                      |
| [583] Renault (81).                                                  |
|                                                                      |
| [584] Grand’Eury (90) A.                                             |
|                                                                      |
| [585] Solms-Laubach (94).                                            |
|                                                                      |
| [586] Grand’Eury (77) A. p. 171.                                     |
|                                                                      |
| [587] For figures see Grand’Eury (87) A.; (90) A.                    |
|                                                                      |
| [588] Kidston (02) Pl. LI. fig. 4.                                   |
|                                                                      |
| [589] British Museum, No. 870 F.                                     |
|                                                                      |
| [590] Grand’Eury (90) A.                                             |
|                                                                      |
| [591] Solms-Laubach (94).                                            |
|                                                                      |
| [592] Williamson (92).                                               |
|                                                                      |
| [593] Thomas, E. N. (05) p. 187.                                     |
|                                                                      |
| [594] Williamson (87) A.                                             |
|                                                                      |
| [595] Solms-Laubach (92).                                            |
|                                                                      |
| [596] Renault (96) A. Pl. XL. fig. 5.                                |
|                                                                      |
| [597] Weiss, F. E. (08).                                             |
|                                                                      |
| [598] Williamson (89) A.                                             |
|                                                                      |
| [599] Renault (96) A.                                                |
|                                                                      |
| [600] Williamson (87) A. Pl. IV. fig. 20.                            |
|                                                                      |
| [601] Weiss, F. E. (02).                                             |
|                                                                      |
| [602] Hooker (48²) Pls. I. II. The sections of _Stigmaria_ figured   |
| by Hooker are in the British Museum (V. 8754).                       |
|                                                                      |
| [603] Williamson (87) A. Pl. XII.                                    |
|                                                                      |
| [604] Solms-Laubach (91) A.                                          |
|                                                                      |
| [605] Weiss, F. E. (02).                                             |
|                                                                      |
| [606] Weiss, F. E. (04).                                             |
|                                                                      |
| [607] Goeppert (41) Pl. X. Lief. I. II.; Williamson (87) A. Pl.      |
| XIII. fig. 78; Eichwald (60) Pl. XV.; Kidston (94) p. 254.           |
|                                                                      |
| [608] Goldenberg (55) Pl. VI. figs. 1–4.                             |
|                                                                      |
| [609] Nathorst (94) A. Pl. XVI. fig. 9.                              |
|                                                                      |
| [610] Watson (08).                                                   |
|                                                                      |
| [611] Zeiller (88) A. Pl. LXXVII. fig. 1.                            |
|                                                                      |
| [612] Cf. Lindley and Hutton (35) A. Pls. 80, 81.                    |
|                                                                      |
| [613] Kidston (86) A. p. 175.                                        |
|                                                                      |
| [614] _ibid._ (86⁴) p. 65.                                           |
|                                                                      |
| [615] Haughton (59).                                                 |
|                                                                      |
| [616] Weiss, C. E. (84) Pl. VI. figs. 6, 7.                          |
|                                                                      |
| [617] Lindley and Hutton (35) A. Pls. 80, 81. For synonymy, see      |
| Kidston (93) p. 344.                                                 |
|                                                                      |
| [618] Zeiller (86) Pl. _IX._ figs. 1–3.                              |
|                                                                      |
| [619] No. 52524.                                                     |
|                                                                      |
| [620] Nathorst (02) Pl. X. figs. 4, 5.                               |
|                                                                      |
| [621] Weiss, F. E. (08).                                             |
|                                                                      |
| [622] Schimper (70) A. p. 71.                                        |
|                                                                      |
| [623] Heer (71) Pl. VI. fig. 11; Pl. IX. fig. 1.                     |
|                                                                      |
| [624] Nathorst (94) A. p. 67, Pl. XV. figs. 14, 15.                  |
|                                                                      |
| [625] Schmalhausen (77) p. 281, Pl. I. fig. 5.                       |
|                                                                      |
| [626] Kidston (89²) Pl. IV. figs. 2–4, p. 65.                        |
|                                                                      |
| [627] Weiss and Sterzel (93) p. 56.                                  |
|                                                                      |
| [628] Kidston (03) p. 823.                                           |
|                                                                      |
| [629] Schmalhausen (77) p. 290, Pl. I. figs. 7–12.                   |
|                                                                      |
| [630] Dawson (71) A. Pl. VIII.                                       |
|                                                                      |
| [631] Weiss, C. E. (84) Pl. VII.                                     |
|                                                                      |
| [632] Potonié (01²) figs. 25–27.                                     |
|                                                                      |
| [633] Nathorst (02) p. 35.                                           |
|                                                                      |
| [634] Seward (03) Pl. XI. figs. 1–6, p. 87; Arber (05) p. 166.       |
|                                                                      |
| [635] Seward (09).                                                   |
|                                                                      |
| [636] Feistmantel (90) A.                                            |
|                                                                      |
| [637] Zeiller (80²) A.                                               |
|                                                                      |
| [638] Trautschold and Auerbach (60) Pl. III.                         |
|                                                                      |
| [639] Zeiller (82) A.; (86).                                         |
|                                                                      |
| [640] Nathorst (94) A. Pls. X. XI.                                   |
|                                                                      |
| [641] Volume I. p. 134.                                              |
|                                                                      |
| [642] Williamson (89) A. p. 197.                                     |
|                                                                      |
| [643] I am indebted to Mr Lomax for photographs of his specimens.    |
| For former references to Mr Lomax’s discovery, see Kidston (05);     |
| Weiss, F. E. (08); Scott D. H. (08) p. 200.                          |
|                                                                      |
| [644] Williamson (89) A.                                             |
|                                                                      |
| [645] Weiss, F. E. (08).                                             |
|                                                                      |
| [646] Nathorst (94) A. p. 42.                                        |
|                                                                      |
| [647] Williamson (80) A. p. 500, Pl. XV. 8.                          |
|                                                                      |
| [648] Watson (08²) p. 12.                                            |
|                                                                      |
| [649] Nathorst (94) A. p. 42, Pl. XII. figs. 8–10.                   |
|                                                                      |
| [650] Kidston (03) p. 797.                                           |
|                                                                      |
| [651] White (98); (99) p. 218, Pls. LXV.–LXVIII.                     |
|                                                                      |
| [652] Kidston (02) pp. 358, 359.                                     |
|                                                                      |
| [653] Tansley and Chick (01) p. 36.                                  |
|                                                                      |
| [654] Kidston (05) p. 547.                                           |
|                                                                      |
| [655] Renault (96) A.                                                |
|                                                                      |
| [656] Weiss, F. E. (08).                                             |
|                                                                      |
| [657] Browne (09) p. 25.                                             |
|                                                                      |
| [658] Scott (02) uses the terms old and new wood in discussing the   |
| evolutionary sequence in plant steles.                               |
|                                                                      |
| [659] White (07).                                                    |
|                                                                      |
| [660] Bower (08) p. 305.                                             |
|                                                                      |
| [661] Browne (09) p. 37.                                             |
|                                                                      |
| [662] Williamson (77) and (80) A.                                    |
|                                                                      |
| [663] Brongniart (28) A. p. 87.                                      |
|                                                                      |
| [664] Carruthers (72³).                                              |
|                                                                      |
| [665] Wild and Lomax (00).                                           |
|                                                                      |
| [666] Scott (01).                                                    |
|                                                                      |
| [667] Letter from D. H. Scott (March 30, 1908).                      |
|                                                                      |
| [668] Scott (01) 314.                                                |
|                                                                      |
| [669] Seward and Ford (06).                                          |
|                                                                      |
| [670] For a contrary opinion, see Scott (09) p. 656.                 |
|                                                                      |
| [671] Bertrand, E. (94).                                             |
|                                                                      |
| [672] Benson (08).                                                   |
|                                                                      |
| [673] Watson (08²) p. 12.                                            |
|                                                                      |
| [674] Ward (04).                                                     |
|                                                                      |
| [675] Tansley (08) p. 3. Cf. Braun (75) p. 267.                      |
|                                                                      |
| [676] Chodat (08).                                                   |
|                                                                      |
| [677] Hudson (92) p. 29.                                             |
|                                                                      |
| [678] Hardy, _Return of the Native_, II. p. 153.                     |
|                                                                      |
| [679] Bower (08).                                                    |
|                                                                      |
| [680] Zeiller (06) p. 8.                                             |
|                                                                      |
| [681] Engler (09).                                                   |
|                                                                      |
| [682] Bower (00).                                                    |
|                                                                      |
| [683] For an account of the mechanism of spore-dispersal, see        |
| Goebel (05) p. 587; Atkinson (94); Leclerc du Sablon (85); and       |
| Bower (00).                                                          |
|                                                                      |
| [684] For a fuller account of recent ferns, see Engler and Prantl    |
| (02), Christ (97), Hooker and Baker (68), and Bower (00) (08).       |
|                                                                      |
| [685] Prantl (81) Pl. VII. fig. 104, C; Zeiller (97) p. 215, figs.   |
| 7–10.                                                                |
|                                                                      |
| [686] Underwood (07), p. 243, has adopted Bernhardi’s genus          |
| _Dicranopteris_ in place of _Mertensia_ on the ground that the       |
| latter was used as early as 1793 for a Boraginaceous plant.          |
|                                                                      |
| [687] Goebel (05) p. 318.                                            |
|                                                                      |
| [688] Baker (88).                                                    |
|                                                                      |
| [689] Diels, in Engler and Prantl (02) pp. 343, 344.                 |
|                                                                      |
| [690] Compton (09).                                                  |
|                                                                      |
| [691] Copeland (08) p. 344.                                          |
|                                                                      |
| [692] Bower (00) p. 47; Gwynne-Vaughan (01).                         |
|                                                                      |
| [693] Christ (04).                                                   |
|                                                                      |
| [694] Scott, J. (74); Hannig (98).                                   |
|                                                                      |
| [695] _Challenger Reports_ (85) p. 827. (Narrative, Pl. II.)         |
|                                                                      |
| [696] Bower (00) p. 68.                                              |
|                                                                      |
| [697] Diels (02) p. 117.                                             |
|                                                                      |
| [698] Seward (92) p. 45.                                             |
|                                                                      |
| [699] Bower (00) p. 80.                                              |
|                                                                      |
| [700] Prof. Bower informs me that he is now at work on               |
| _Plagiogyria_ and other Polypodiaceae.                               |
|                                                                      |
| [701] Kny (75); Ford (02); Goebel (91).                              |
|                                                                      |
| [702] Seward and Dale (01).                                          |
|                                                                      |
| [703] Armour (07).                                                   |
|                                                                      |
| [704] Diels (02) fig. 98, p. 188.                                    |
|                                                                      |
| [705] Giesenhagen (92) p. 179, fig. 3.                               |
|                                                                      |
| [706] Bäsecke (08).                                                  |
|                                                                      |
| [707] Boodle (00).                                                   |
|                                                                      |
| [708] Yapp (02).                                                     |
|                                                                      |
| [709] Darwin (03) II. p. 381.                                        |
|                                                                      |
| [710] Reinecke (97).                                                 |
|                                                                      |
| [711] Karsten (95); Christ (96); Bommer (03).                        |
|                                                                      |
| [712] Goebel (05) p. 347.                                            |
|                                                                      |
| [713] A striking example of these so-called Aphlebiae of             |
| _Hemitelia_ may be seen at the Royal Gardens, Kew.                   |
|                                                                      |
| [714] Luerssen, in Rabenhorst (89) A. p. 483, fig. 164.              |
|                                                                      |
| [715] Goebel (01) Pl. XIII.                                          |
|                                                                      |
| [716] Spruce (08) II. p. 232.                                        |
|                                                                      |
| [717] Boodle (04).                                                   |
|                                                                      |
| [718] Goebel (05); Baker (67).                                       |
|                                                                      |
| [719] Seward and Gowan (00).                                         |
|                                                                      |
| [720] Hooker (59).                                                   |
|                                                                      |
| [721] Thiselton-Dyer (05).                                           |
|                                                                      |
| [722] Baker (68) p. 305.                                             |
|                                                                      |
| [723] Bower (08) p. 18.                                              |
|                                                                      |
| [724] Treub (88) A.; Ernst (08).                                     |
|                                                                      |
| [725] Campbell (07).                                                 |
|                                                                      |
| [726] Davy (07) p. 263.                                              |
|                                                                      |
| [727] Bates (63) A. p. 30.                                           |
|                                                                      |
| [728] _Challenger Reports_ (85) p. 785.                              |
|                                                                      |
| [729] Tansley and Fritsch (05) p. 43; Thomas, E. N. (05).            |
|                                                                      |
| [730] Tansley (08) p. 27.                                            |
|                                                                      |
| [731] Jeffrey (98).                                                  |
|                                                                      |
| [732] Boodle (00).                                                   |
|                                                                      |
| [733] Tansley and Lulham (02).                                       |
|                                                                      |
| [734] Gwynne-Vaughan (01); (03).                                     |
|                                                                      |
| [735] Boodle (01) p. 735.                                            |
|                                                                      |
| [736] Jeffrey (00); (03).                                            |
|                                                                      |
| [737] For an account of the probable methods by which this has been  |
| effected and of the factors concerned, see Tansley (08).             |
|                                                                      |
| [738] Gwynne-Vaughan (03).                                           |
|                                                                      |
| [739] Seward (99²); Wigglesworth (02).                               |
|                                                                      |
| [740] Seward and Ford (03); Jeffrey (03); Faull (01).                |
|                                                                      |
| [741] Kidston and Gwynne-Vaughan (07); (08); (09).                   |
|                                                                      |
| [742] Gwynne-Vaughan (08).                                           |
|                                                                      |
| [743] Bertrand and Cornaille (02).                                   |
|                                                                      |
| [744] Chodat (08) p. 15.                                             |
|                                                                      |
| [745] See also Pelourde (09) for an account of the anatomy of fern   |
| petioles.                                                            |
|                                                                      |
| [746] Observed in plants in the Botanic Gardens of Brussels and      |
| Leipzig. A.C.S.                                                      |
|                                                                      |
| [747] For an account of the spore-producing members of the           |
| Marattiaceae, see Bower (97).                                        |
|                                                                      |
| [748] Zeiller (90) p. 19.                                            |
|                                                                      |
| [749] Shove (00); Tansley (08).                                      |
|                                                                      |
| [750] Farmer and Hill (02) Pl. XVIII. figs. 26, 28.                  |
|                                                                      |
| [751] Christ and Giesenhagen (99).                                   |
|                                                                      |
| [752] Gwynne-Vaughan (05).                                           |
|                                                                      |
| [753] Hooker and Baker (68) p. 440.                                  |
|                                                                      |
| [754] The term synangium is applied to sporangia more or less        |
| completely united with one another and producing spores in groups    |
| separated by walls of sterile cells. A synangium may be regarded     |
| as a spore-forming organ produced by partial sterilization of        |
| sporogenous tissue or as a group of coalescent sporangia.            |
|                                                                      |
| [755] Brebner (02); Rudolph (05).                                    |
|                                                                      |
| [756] Tansley (08) p. 90; Kühn (90).                                 |
|                                                                      |
| [757] Pelourde (08) has recently dealt with the anatomy of recent    |
| and fossil Marattiaceous ferns.                                      |
|                                                                      |
| [758] Copeland (08) Pl. I. (09) Pl. V.                               |
|                                                                      |
| [759] Bower (96).                                                    |
|                                                                      |
| [760] Jeffrey (98). For an account of the anatomy of                 |
| _Helminthostachys_, see Farmer and Freeman (99).                     |
|                                                                      |
| [761] Stur (75) A. p. 77, Pl. XI. fig. 8.                            |
|                                                                      |
| [762] Renault (96) A. p. 21.                                         |
|                                                                      |
| [763] Zeiller (90) p. 16.                                            |
|                                                                      |
| [764] Zeiller (90) p. 48.                                            |
|                                                                      |
| [765] Scott, D. H. (08) p. 292.                                      |
|                                                                      |
| [766] Scott (04) p. 18.                                              |
|                                                                      |
| [767] Boodle (00) p. 484.                                            |
|                                                                      |
| [768] Zeiller (99) Pl. II. figs. 5, 6.                               |
|                                                                      |
| [769] _Ibid._ Pl. II. fig. 10.                                       |
|                                                                      |
| [770] See p. 402.                                                    |
|                                                                      |
| [771] Bower (91) Pl. VII.                                            |
|                                                                      |
| [772] Scott, D. H. (09).                                             |
|                                                                      |
| [773] Kidston and Gwynne-Vaughan (08).                               |
|                                                                      |
| [774] Eichwald (60).                                                 |
|                                                                      |
| [775] Gwynne-Vaughan (08).                                           |
|                                                                      |
| [776] Kidston and Gwynne-Vaughan (08) p. 226.                        |
|                                                                      |
| [777] Brongniart (49) A. p. 35.                                      |
|                                                                      |
| [778] Brongniart (28) A. Pl. LXXX.                                   |
|                                                                      |
| [779] Kidston and Gwynne-Vaughan (09).                               |
|                                                                      |
| [780] Seward (99).                                                   |
|                                                                      |
| [781] Krasser (09) p. 10.                                            |
|                                                                      |
| [782] Fontaine (83) Pls. XXVIII. XXIX.                               |
|                                                                      |
| [783] Leuthardt (04) Pl. XVIII.                                      |
|                                                                      |
| [784] Kidston and Gwynne-Vaughan (07).                               |
|                                                                      |
| [785] See p. 343.                                                    |
|                                                                      |
| [786] Seward and Ford (03).                                          |
|                                                                      |
| [787] Kidston and Gwynne-Vaughan (07).                               |
|                                                                      |
| [788] Seward (07³) p. 482, Pls. XX. XXI.                             |
|                                                                      |
| [789] Seward (03); Kitchin (08).                                     |
|                                                                      |
| [790] Cf. _Todea Wilkesiana_ (p. 286).                               |
|                                                                      |
| [791] Penhallow (02).                                                |
|                                                                      |
| [792] Kidston and Gwynne-Vaughan (07).                               |
|                                                                      |
| [793] See p. 314. Also Jeffrey (03); Faull (01); Seward and Ford     |
| (03).                                                                |
|                                                                      |
| [794] Raciborski (94) A. p. 19, Pls. VI. XI.                         |
|                                                                      |
| [795] Carruthers (70) A.; Kidston and Gwynne-Vaughan (07) p. 768;    |
| see also Seward, Vol. I. p. 212.                                     |
|                                                                      |
| [796] Gardner and Ettingshausen (82) pp. 22, 48, Pl. IV. figs. 1–3.  |
|                                                                      |
| [797] Seward (00) p. 86.                                             |
|                                                                      |
| [798] Seward and Ford (03) p. 251.                                   |
|                                                                      |
| [799] For a more complete list, see Seward (00) p. 87.               |
|                                                                      |
| [800] Schenk (85) Pl. III. fig. 3.                                   |
|                                                                      |
| [801] Raciborski (94) A. Pl. VI.                                     |
|                                                                      |
| [802] Nathorst (08) Pl. I. fig. 7.                                   |
|                                                                      |
| [803] Schenk (67) A.                                                 |
|                                                                      |
| [804] Fontaine (83).                                                 |
|                                                                      |
| [805] The geographical distribution of _Todites_ and other genera    |
| will be dealt with in Volume III.                                    |
|                                                                      |
| [806] Carruthers (70) A. p. 350.                                     |
|                                                                      |
| [807] Reid (99).                                                     |
|                                                                      |
| [808] Seward (08) Pl. VIII. p. 98.                                   |
|                                                                      |
| [809] Zeiller (03) Pls. II. IV.                                      |
|                                                                      |
| [810] Leuthardt (04) Pl. XV.                                         |
|                                                                      |
| [811] Fontaine (83) Pls. XI.–XIV.                                    |
|                                                                      |
| [812] For synonymy and figures, see Seward (00) p. 134; (04) p. 134. |
|                                                                      |
| [813] E.g. by Yokoyama (06) who identifies specimens of              |
| _Cladophlebis denticulata_ from Jurassic rocks of China as _Todites  |
| Williamsoni_.                                                        |
|                                                                      |
| [814] Lindley and Hutton (34) A. Pl. CXXXIV.                         |
|                                                                      |
| [815] Seward (94²) A. p. 91.                                         |
|                                                                      |
| [816] Nathorst (78).                                                 |
|                                                                      |
| [817] Lindley and Hutton (34) A. Pl. CXX.                            |
|                                                                      |
| [818] Fontaine, in Ward (05) Pl. XV. figs. 6–9).                     |
|                                                                      |
| [819] Feistmantel (77) Pls. XXXVI. XXXVII.                           |
|                                                                      |
| [820] Morris (45) Pl. VII.                                           |
|                                                                      |
| [821] Renault (83) p. 81, Pl. XI.                                    |
|                                                                      |
| [822] Dawson (61).                                                   |
|                                                                      |
| [823] White (04).                                                    |
|                                                                      |
| [824] Corda (45) A. Pl. LVII.                                        |
|                                                                      |
| [825] Zeiller (83) p. 188, Pl. X. figs. 1–5.                         |
|                                                                      |
| [826] Stur (85) A. p. 64.                                            |
|                                                                      |
| [827] Zeiller (88) A. p. 50.                                         |
|                                                                      |
| [828] Solms-Laubach (91) A. p. 147.                                  |
|                                                                      |
| [829] For synonymy, see Seward (00) p. 130.                          |
|                                                                      |
| [830] Raciborski (91).                                               |
|                                                                      |
| [831] Phillips (29) A. p. 148.                                       |
|                                                                      |
| [832] Bunbury (51) A.                                                |
|                                                                      |
| [833] Seward (94²) A.                                                |
|                                                                      |
| [834] Raciborski (94) A.                                             |
|                                                                      |
| [835] Yokoyama (89).                                                 |
|                                                                      |
| [836] Seward (94²) A.                                                |
|                                                                      |
| [837] Yabe (05) Pl. III.                                             |
|                                                                      |
| [838] Seward (07⁴) Pls. I. III.                                      |
|                                                                      |
| [839] Seward (94²) A. p. 75.                                         |
|                                                                      |
| [840] Gardner and Ettingshausen (82) p. 47, Pls. VII. X.; Heer (55)  |
| A. Pl. III. p. 41.                                                   |
|                                                                      |
| [841] Knowlton (99). Pl. LXXX.                                       |
|                                                                      |
| [842] Heer (55) A. Pl. XIII.                                         |
|                                                                      |
| [843] Saporta (72) A. Pl. I. figs. 13, 14.                           |
|                                                                      |
| [844] Goeppert (36²) A. Pls. IV. V.                                  |
|                                                                      |
| [845] Zeiller (88) A. p. 261.                                        |
|                                                                      |
| [846] Williamson (77) Pl. VII.                                       |
|                                                                      |
| [847] See Ch. XXVII.                                                 |
|                                                                      |
| [848] Goeppert (41) Pl. IV. figs. 1, 2.                              |
|                                                                      |
| [849] Zeiller (88) A. Pl. XI. figs. 3–5.                             |
|                                                                      |
| [850] Stur (85) A. p. 128.                                           |
|                                                                      |
| [851] Solms-Laubach (91) A. p. 146.                                  |
|                                                                      |
| [852] Schenk (88) A. p. 30.                                          |
|                                                                      |
| [853] Dr Scott tells me that an examination of Dr Zeiller’s          |
| specimens led him to agree with the latter’s description of the      |
| annulus of _Oligocarpia_. (A. C. S.)                                 |
|                                                                      |
| [854] Fontaine (83) Pls. XV.–XIX.                                    |
|                                                                      |
| [855] Bunbury (47) Pl. II. fig. 1; Seward (94²) A. p. 189.           |
|                                                                      |
| [856] Krasser (09) p. 16.                                            |
|                                                                      |
| [857] Leuthardt (04) p. 40, Pl. XVIII. fig. 3.                       |
|                                                                      |
| [858] Schenk (67) A. p. 86, Pl. XXII. figs. 7, 8.                    |
|                                                                      |
| [859] Zigno (56) A. Pl. X.                                           |
|                                                                      |
| [860] Raciborski (94) A. p. 43, Pl. XIII. figs. 15–20.               |
|                                                                      |
| [861] Seward (95) A. p. 225.                                         |
|                                                                      |
| [862] Seward (00) Pl. IV.                                            |
|                                                                      |
| [863] Schenk (71).                                                   |
|                                                                      |
| [864] Corda, in Reuss (46) p. 95, Pl. XLIX.                          |
|                                                                      |
| [865] Heer (75), p. 44, Pls. IV.–VII.                                |
|                                                                      |
| [866] Debey and Ettingshausen (59) Pl. I.                            |
|                                                                      |
| [867] Gardner and Ettingshausen (82), pp. 43, 59, Pls. VI. X.        |
|                                                                      |
| [868] Wanklyn (69).                                                  |
|                                                                      |
| [869] Presl, in Sternberg (38) A. p. 115.                            |
|                                                                      |
| [870] Schenk (67) A.                                                 |
|                                                                      |
| [871] Zeiller (85).                                                  |
|                                                                      |
| [872] Seward (99²) p. 194.                                           |
|                                                                      |
| [873] Schenk (67) A. Pls. XXIII. XXIV.                               |
|                                                                      |
| [874] For a more complete list, see Seward (00) p. 78.               |
|                                                                      |
| [875] Leckenby (64) A. p. 81, Pl. VIII. fig. 6. (Type-specimen in    |
| the Sedgwick Museum, Cambridge.)                                     |
|                                                                      |
| [876] Saporta (73) A. p. 306.                                        |
|                                                                      |
| [877] Debey and Ettingshausen (59) Pl. III.                          |
|                                                                      |
| [878] See Seward (94²) A. and (00) for an account of this fern.      |
|                                                                      |
| [879] Schenk (71) p. 219.                                            |
|                                                                      |
| [880] Zeiller (85).                                                  |
|                                                                      |
| [881] Ettingshausen (52) p. 16, Pl. V. For synonymy, see Seward      |
| (94²) A; (00).                                                       |
|                                                                      |
| [882] Fontaine, in Ward (05) p. 230.                                 |
|                                                                      |
| [883] Schenk (71) p. 19.                                             |
|                                                                      |
| [884] Fontaine, _loc. cit._ Pl. LXV. figs. 22, 23.                   |
|                                                                      |
| [885] Krasser (96) p. 119, Pls. XI. XII. XIV.                        |
|                                                                      |
| [886] Stur (75) A. p. 284, Pl. XXXIII. fig. 15.                      |
|                                                                      |
| [887] Renault (96) A. p. 19.                                         |
|                                                                      |
| [888] Ettingshausen (66) Pl. VII. fig. 4.                            |
|                                                                      |
| [889] Stur (75) A. p. 36, Pl. IX. figs. 1–9.                         |
|                                                                      |
| [890] Schimper (74) A. Pl. XXVIII. fig. 4–7.                         |
|                                                                      |
| [891] Solms-Laubach (91) A. p. 153.                                  |
|                                                                      |
| [892] Zeiller (83) p. 155; (88) A. Pl. VIII. figs. 1–3.              |
|                                                                      |
| [893] Kidston (84²) p. 593.                                          |
|                                                                      |
| [894] See p. 450.                                                    |
|                                                                      |
| [895] Scott (08) p. 343.                                             |
|                                                                      |
| [896] Stur (75) A. p. 19, Pl. X. figs. 1, 2.                         |
|                                                                      |
| [897] Goeppert (36²) A. pp. 319, 320, 329.                           |
|                                                                      |
| [898] Sterzel (86).                                                  |
|                                                                      |
| [899] Grand’Eury (05).                                               |
|                                                                      |
| [900] Zeiller (06) Pls. II. III.                                     |
|                                                                      |
| [901] Raciborski (94) A. Pl. IX.                                     |
|                                                                      |
| [902] Brongniart (49) A. p. 26.                                      |
|                                                                      |
| [903] Krasser (09).                                                  |
|                                                                      |
| [904] For fuller synonymy see Seward (00) p. 97.                     |
|                                                                      |
| [905] Heer (76).                                                     |
|                                                                      |
| [906] Fontaine (89).                                                 |
|                                                                      |
| [907] Fontaine (89) p. 123, Pls. XXVI. XLIII. etc.                   |
|                                                                      |
| [908] Ward (99) Pl. CLXI.                                            |
|                                                                      |
| [909] Velenovský (88).                                               |
|                                                                      |
| [910] Heer (75) A. Pl. I. figs. 6, 7.                                |
|                                                                      |
| [911] Heer (82) A. Pl. II. fig. 2.                                   |
|                                                                      |
| [912] Phillips (75) A. p. 215.                                       |
|                                                                      |
| [913] Seward (00).                                                   |
|                                                                      |
| [914] Sternberg (38) A. p. 169.                                      |
|                                                                      |
| [915] Sternberg (20) A. Pl. IV.                                      |
|                                                                      |
| [916] Corda (45) A. Pl. II. fig. 5.                                  |
|                                                                      |
| [917] Brongniart (28) A. Pl. XLI.                                    |
|                                                                      |
| [918] Feistmantel (72).                                              |
|                                                                      |
| [919] Velenovský (88).                                               |
|                                                                      |
| [920] Carruthers (65) Pl. XIII.                                      |
|                                                                      |
| [921] Heer (75).                                                     |
|                                                                      |
| [922] Heer (82) Pl. XLVII.                                           |
|                                                                      |
| [923] Frič and Bayer (01) p. 76.                                     |
|                                                                      |
| [924] Stenzel (86). See also Stenzel (97).                           |
|                                                                      |
| [925] Gwynne-Vaughan (08).                                           |
|                                                                      |
| [926] Schenk (71) Pl. XXX.; Seward (94²) A. Pl. XI.                  |
|                                                                      |
| [927] Scott (08) p. 293.                                             |
|                                                                      |
| [928] Goeppert (30) A. p. 217.                                       |
|                                                                      |
| [929] Schimper (69) A. p. 424.                                       |
|                                                                      |
| [930] Ettingshausen (66).                                            |
|                                                                      |
| [931] Kidston (89³) Pl. I.                                           |
|                                                                      |
| [932] White (04).                                                    |
|                                                                      |
| [933] Schenk (67) A. Pl. XIII.; Zeiller (03) p. 91, Pl. XVII.        |
|                                                                      |
| [934] Seward (04²) p. 162, Pl. VIII. fig. 5.                         |
|                                                                      |
| [935] Yabe (05) p. 39, Pl. I. figs. 1–8.                             |
|                                                                      |
| [936] Fontaine, in Ward (05) p. 64.                                  |
|                                                                      |
| [937] Yokoyama (89), p. 26.                                          |
|                                                                      |
| [938] Geyler (77) Pl. XXXI. fig. 4.                                  |
|                                                                      |
| [939] For synonymy, see Fontaine, in Ward (05) p. 155; Richter (06)  |
| p. 6; Seward (94) A. p. 41; (03) p. 5.                               |
|                                                                      |
| [940] Seward (94) A. p. 52.                                          |
|                                                                      |
| [941] Gardner and Ettingshausen (82) Pls. I. II.                     |
|                                                                      |
| [942] Forbes (51); Gardner and Ettingshausen (82).                   |
|                                                                      |
| [943] Knowlton (02) Pl. XXVI.                                        |
|                                                                      |
| [944] Saporta (68) A.; Gardner and Ettingshausen (82) Pl. X. fig. 1. |
|                                                                      |
| [945] Gardner and Ettingshausen (82) p. 21.                          |
|                                                                      |
| [946] Lindley and Hutton (34) A. Pl. CIV.                            |
|                                                                      |
| [947] Nathorst (06³).                                                |
|                                                                      |
| [948] Seward and Dale (01) p. 505.                                   |
|                                                                      |
| [949] Zeiller (03) p. 109, Pls. XXIII.–XXVIII.                       |
|                                                                      |
| [950] Seward (00) p. 122.                                            |
|                                                                      |
| [951] Nathorst (06³).                                                |
|                                                                      |
| [952] Krasser (09) p. 111.                                           |
|                                                                      |
| [953] Goeppert (41).                                                 |
|                                                                      |
| [954] Seward and Dale (01) p. 503.                                   |
|                                                                      |
| [955] Nathorst (07²).                                                |
|                                                                      |
| [956] Schenk (67) A. Pl. XVIII.                                      |
|                                                                      |
| [957] Zeiller (03).                                                  |
|                                                                      |
| [958] Brongniart (25).                                               |
|                                                                      |
| [959] Brongniart (25).                                               |
|                                                                      |
| [960] Zeiller (03).                                                  |
|                                                                      |
| [961] Seward (04) pp. 18, 164.                                       |
|                                                                      |
| [962] Seward (07).                                                   |
|                                                                      |
| [963] The evidence of the shells is stated by Mr R. B. Newton (09)   |
| to be in favour of the Cretaceous age of the Nubian Sandstone.       |
|                                                                      |
| [964] Nathorst (78) p. 33.                                           |
|                                                                      |
| [965] Nathorst (06²) p. 15.                                          |
|                                                                      |
| [966] Richter (06).                                                  |
|                                                                      |
| [967] Dunker (46) A. p. 12.                                          |
|                                                                      |
| [968] Andrae (53) A.                                                 |
|                                                                      |
| [969] Zigno (56) A. IX. fig. 2.                                      |
|                                                                      |
| [970] Nathorst (78²) Pl. IX. fig. 2.                                 |
|                                                                      |
| [971] Zeiller (97⁴) p. 51.                                           |
|                                                                      |
| [972] Seward and Dale (01).                                          |
|                                                                      |
| [973] Dunker (46) A., Pl. V. fig. 1.                                 |
|                                                                      |
| [974] Bartholin (92) Pls. XI. XII.                                   |
|                                                                      |
| [975] Moeller (02) Pls. IV.–VI.                                      |
|                                                                      |
| [976] Richter (06) p. 21.                                            |
|                                                                      |
| [977] Richter (06) p. 22.                                            |
|                                                                      |
| [978] Andrae (53) A.                                                 |
|                                                                      |
| [979] Moeller (02) Pls. IV.–VI.                                      |
|                                                                      |
| [980] Nathorst (78²) Pl. IX. fig. 2.                                 |
|                                                                      |
| [981] Zeiller (79).                                                  |
|                                                                      |
| [982] Gardner and Ettingshausen (82) p. 29, Pl. III. fig. 6.         |
|                                                                      |
| [983] Arber (06) p. 227.                                             |
|                                                                      |
| [984] Scott (06) p. 189.                                             |
|                                                                      |
| [985] Zeiller (05).                                                  |
|                                                                      |
| [986] Kidston (06).                                                  |
|                                                                      |
| [987] Kidston (06) p. 429.                                           |
|                                                                      |
| [988] Weiss, C. E. (69) p. 94, Pl. XI. fig. 2. The specimens         |
| figured by Weiss bear a somewhat remote resemblance to that          |
| described by Renault (96) A, under the same generic name.            |
|                                                                      |
| [989] Kidston (91²) p. 23.                                           |
|                                                                      |
| [990] Kidston (88) p. 350.                                           |
|                                                                      |
| [991] Renault (96) A. p. 9; Zeiller (88) A. p. 162; Grand’Eury (77)  |
| A. Pl. VIII. fig. 13.                                                |
|                                                                      |
| [992] Watson (06).                                                   |
|                                                                      |
| [993] Goeppert (36²) A. p. 380.                                      |
|                                                                      |
| [994] Stur (85) A. p. 221, Pl. LXI.; Zeiller (88) A. p. 41.          |
|                                                                      |
| [995] Grand’Eury (90) A. p. 288, Pl. VI. fig. 26.                    |
|                                                                      |
| [996] For an account of these genera, see Chap. XXVII.               |
|                                                                      |
| [997] Strasburger (74).                                              |
|                                                                      |
| [998] Stur (85) A. p. 183.                                           |
|                                                                      |
| [999] Corda (45) A. Pl. LVII.                                        |
|                                                                      |
| [1000] Kidston (91²) p. 20; Stur (85) A. Pl. LIX.                     |
|                                                                      |
| [1001] See Chap. XXVII.                                               |
|                                                                      |
| [1002] Stur (85) A. p. 106.                                           |
|                                                                      |
| [1003] Zenker (37).                                                   |
|                                                                      |
| [1004] Strasburger (74).                                             |
|                                                                      |
| [1005] Kidston (91²) p. 20.                                          |
|                                                                      |
| [1006] Geinitz (72). See Solms-Laubach (83), who gives in full the   |
| early history of the genus _Scolecopteris_.                          |
|                                                                      |
| [1007] Sterzel (78); (80).                                           |
|                                                                      |
| [1008] Stur (85) p. 140.                                             |
|                                                                      |
| [1009] Zeiller (99) p. 17.                                           |
|                                                                      |
| [1010] Zeiller (06) p. 10.                                           |
|                                                                      |
| [1011] Brongniart (28) A. Pl. CXXV. fig. 4.                          |
|                                                                      |
| [1012] Renault and Zeiller (88) A. Pl. XXIV.                         |
|                                                                      |
| [1013] Page 325.                                                     |
|                                                                      |
| [1014] Zeiller (83) p. 184; (88) A. p. 30.                           |
|                                                                      |
| [1015] Artis (25) A.                                                 |
|                                                                      |
| [1016] Stur (75) A.                                                  |
|                                                                      |
| [1017] Kidston (96) p. 205.                                          |
|                                                                      |
| [1018] Zeiller (83) p. 185.                                          |
|                                                                      |
| [1019] Kidston (82).                                                 |
|                                                                      |
| [1020] Stur (85).                                                    |
|                                                                      |
| [1021] Kidston (84²).                                                |
|                                                                      |
| [1022] Kidston (87).                                                 |
|                                                                      |
| [1023] Kidston (82) p. 32.                                           |
|                                                                      |
| [1024] Kidston (84²) p. 594.                                         |
|                                                                      |
| [1025] Williamson (83) A.                                            |
|                                                                      |
| [1026] Kidston (06).                                                 |
|                                                                      |
| [1027] Heer (76) A. p. 71, Pl. XXIV. fig. 1.                         |
|                                                                      |
| [1028] Schimper (74) A. Pl. 38; see also Schenk (88) A. p. 31.       |
|                                                                      |
| [1029] Leuthardt (04) p. 29, Pl. XIII. figs. 1, 2.                   |
|                                                                      |
| [1030] Goeppert (36²) A. Lief. I. and II. Pl. IV.                    |
|                                                                      |
| [1031] Schimper (69) A. p. 607.                                      |
|                                                                      |
| [1032] Schenk (83) A. p. 260.                                        |
|                                                                      |
| [1033] Zeiller (03) Pl. IX.                                          |
|                                                                      |
| [1034] Fontaine, in Ward (00) Pl. LV. figs. 3–5.                     |
|                                                                      |
| [1035] Bartholin (92) Pl. IX.                                        |
|                                                                      |
| [1036] Moeller (02).                                                 |
|                                                                      |
| [1037] Schenk (83) A.                                                |
|                                                                      |
| [1038] Seward (07⁴) Pl. II. figs. 16–18.                             |
|                                                                      |
| [1039] Nathorst (08).                                                |
|                                                                      |
| [1040] Krasser (09).                                                 |
|                                                                      |
| [1041] Feistmantel (82) Pls. IV.–X.                                  |
|                                                                      |
| [1042] Seward (08) p. 95.                                            |
|                                                                      |
| [1043] Krasser (00) Pl. II.                                          |
|                                                                      |
| [1044] Zeiller (03) Pl. IX.                                          |
|                                                                      |
| [1045] Krasser (09) p. 21.                                           |
|                                                                      |
| [1046] Leuthardt (04) Pls. XIX. XX.                                  |
|                                                                      |
| [1047] Zigno (56) A. Pl. XXV.                                        |
|                                                                      |
| [1048] Raciborski (94) A. Pl. VI.                                    |
|                                                                      |
| [1049] Heer (80).                                                    |
|                                                                      |
| [1050] Nathorst (08).                                                |
|                                                                      |
| [1051] Bayer (99).                                                   |
|                                                                      |
| [1052] Gardner and Ettingshausen (82) Pl. XII. figs. 1–7.            |
|                                                                      |
| [1053] Stenzel (54) p. 803.                                          |
|                                                                      |
| [1054] Cotta (32).                                                   |
|                                                                      |
| [1055] Sprengel (28).                                                |
|                                                                      |
| [1056] Stenzel (54) p. 753.                                          |
|                                                                      |
| [1057] Parkinson (11) A.                                             |
|                                                                      |
| [1058] Williamson (76).                                              |
|                                                                      |
| [1059] Scott (08).                                                   |
|                                                                      |
| [1060] Butterworth (00).                                             |
|                                                                      |
| [1061] Grand’Eury (77) A.                                            |
|                                                                      |
| [1062] Grand’Eury (77) A; (90) A.                                    |
|                                                                      |
| [1063] Rudolph (05).                                                 |
|                                                                      |
| [1064] Scott (08) p. 302.                                            |
|                                                                      |
| [1065] Butterworth (00). Pelourde (08²) has recently described the   |
| structure of the roots of several species of _Psaronius_.            |
|                                                                      |
| [1066] Stenzel (06).                                                 |
|                                                                      |
| [1067] Farmer and Hill (02).                                         |
|                                                                      |
| [1068] Williamson (76) Pl. III.                                      |
|                                                                      |
| [1069] Stenzel (89) Pl. VI.                                          |
|                                                                      |
| [1070] Zeiller (90) p. 204, Pls. XVI. XVII.; see also Rudolph (05).  |
|                                                                      |
| [1071] Renault and Zeiller (88) A. Pls. V.–VIII.                     |
|                                                                      |
| [1072] Solms-Laubach (04).                                           |
|                                                                      |
| [1073] Arber (05) Pl. VII.                                           |
|                                                                      |
| [1074] Scott (08) fig. 113; Zeiller (90) p. 246, Pl. XXI. fig. 1.    |
|                                                                      |
| [1075] Pelourde (08²).                                               |
|                                                                      |
| [1076] Stenzel (06) Pl. VI.; Goeppert (64) A.; Stenzel (06).         |
|                                                                      |
| [1077] Zeiller (90) Pl. XXIII.                                       |
|                                                                      |
| [1078] Scott (08) p. 301.                                            |
|                                                                      |
| [1079] Lindley and Hutton (33) A. Pl. XLII.                          |
|                                                                      |
| [1080] Kidston (88) Pl. XXVI.                                        |
|                                                                      |
| [1081] Renault and Zeiller (88) A. Pl. XXXV. fig. 6.                 |
|                                                                      |
| [1082] Kidston (86) A. p. 113.                                       |
|                                                                      |
| [1083] Artis (25) A. Pl. XX.                                         |
|                                                                      |
| [1084] Lesquereux (66) A.                                            |
|                                                                      |
| [1085] Renault and Zeiller (88) A. Pl. XL.; Grand’Eury (90) A.       |
|                                                                      |
| [1086] Corda (45) A.; see also Grand’Eury (90) A.; Renault and       |
| Zeiller (88) A. Pls. XXXVIII.–XL.                                    |
|                                                                      |
| [1087] Fontaine and White (80) Pl. XXXVI.; Zeiller (90) Pl. XIV.     |
|                                                                      |
| [1088] Mettenius (65); Tansley (08) p. 85.                           |
|                                                                      |
| [1089] Rudolph (05).                                                 |
|                                                                      |
| [1090] Scott, D. H. (08).                                            |
|                                                                      |
| [1091] Shove (00).                                                   |
|                                                                      |
| [1092] Butterworth (00).                                             |
|                                                                      |
| [1093] Farmer and Hill (02).                                         |
|                                                                      |
| [1094] Grand’Eury (77) A. p. 98.                                     |
|                                                                      |
| [1095] Stur (75) A. Pl. VIII.                                        |
|                                                                      |
| [1096] Zeiller (00) p. 55.                                           |
|                                                                      |
| [1097] Kidston (89³), Pls. I. II. For other figures of               |
| _Rhacopteris_ see also Stur (75) A.                                  |
|                                                                      |
| [1098] Renault (96) A. p. 30, Pl. LXXXII. figs. 7–9.                 |
|                                                                      |
| [1099] Stur (75) A.                                                  |
|                                                                      |
| [1100] Weiss, C. E. (79).                                            |
|                                                                      |
| [1101] Solms-Laubach (91) A. p. 141.                                 |
|                                                                      |
| [1102] O. Feistmantel (75).                                          |
|                                                                      |
| [1103] C. Feistmantel (79).                                          |
|                                                                      |
| [1104] C. E. Weiss (79).                                             |
|                                                                      |
| [1105] Potonié (99) p. 167.                                          |
|                                                                      |
| [1106] Seward (03) p. 63.                                            |
|                                                                      |
| [1107] Carruthers (72²) Pl. XXVII. fig. 5; Seward (03) p. 62.        |
|                                                                      |
| [1108] Newberry (91) Pl. XIV.                                        |
|                                                                      |
| [1109] D. H. Scott (08).                                             |
|                                                                      |
| [1110] P. Bertrand (09).                                             |
|                                                                      |
| [1111] Scott (09²).                                                  |
|                                                                      |
| [1112] Williamson (83²) A, p. 478.                                   |
|                                                                      |
| [1113] κοινός = Lat. _communis_, common or general. I am indebted    |
| to my friend Mr L. H. G. Greenwood, Fellow of Emmanuel College, for  |
| supplying me with a name to express the idea of the generalized      |
| nature of these Palaeozoic ferns.                                    |
|                                                                      |
| [1114] Arber (06).                                                   |
|                                                                      |
| [1115] Renault (96) A. p. 46, Pls. XXX. XXXI. See also Tansley (08)  |
| fig. 2, p. 13.                                                       |
|                                                                      |
| [1116] Cotta (32) p. 15.                                             |
|                                                                      |
| [1117] Stenzel (89) Pls. I. II.                                      |
|                                                                      |
| [1118] Stopes (06).                                                  |
|                                                                      |
| [1119] Williamson (89) A. p. 162. The term _Rachiopteris_ was        |
| adopted by Williamson for petrified petioles from the Coal-Measures  |
| which he believed to be filicinean.                                  |
|                                                                      |
| [1120] Renault (75); (96) A. p. 47, Pl. XXXII.                       |
|                                                                      |
| [1121] Oliver (02).                                                  |
|                                                                      |
| [1122] Oliver (04) p. 395 (footnote).                                |
|                                                                      |
| [1123] Scott, D. H. (08).                                            |
|                                                                      |
| [1124] Felix (86) A.                                                 |
|                                                                      |
| [1125] Williamson (78) A. p. 351.                                    |
|                                                                      |
| [1126] Hick (96).                                                    |
|                                                                      |
| [1127] Scott (08).                                                   |
|                                                                      |
| [1128] Williamson (91²) A. p. 261. The two species described by      |
| Williamson as _Rachiopteris hirsuta_ and _R. ramosa_ were first      |
| identified as _Botryopteris_ by Scott in 1898 (_British Assoc.       |
| Report_, Bristol Meeting, p. 1050).                                  |
|                                                                      |
| [1129] Tansley (08) p. 15.                                           |
|                                                                      |
| [1130] Kidston (08).                                                 |
|                                                                      |
| [1131] Oliver (02).                                                  |
|                                                                      |
| [1132] Corda (45) A.; see also Stenzel (89) p. 26.                   |
|                                                                      |
| [1133] P. Bertrand (09) pp. 136, 212.                                |
|                                                                      |
| [1134] Tansley (08) p. 22.                                           |
|                                                                      |
| [1135] Unger and Richter (56) Pl. VI. fig. 19.                       |
|                                                                      |
| [1136] Renault (96) A. p. 11.                                        |
|                                                                      |
| [1137] The _Diplolabis_ type of strand is very similar in the form   |
| of the metaxylem to the conducting strand of a lateral vein in       |
| _Scolopendrium officinarum_ [cf. Pelourde (09) fig. 3, p. 117].      |
|                                                                      |
| [1138] Solms-Laubach (92).                                           |
|                                                                      |
| [1139] Williamson (74) A. Pls. LIV. LV.                              |
|                                                                      |
| [1140] Gordon (09). Mr Gordon’s more complete account of this plant  |
| will shortly be published. I am indebted to him for furnishing me    |
| with the main facts in regard to the anatomical features.            |
|                                                                      |
| [1141] Solms-Laubach (92) Pl. II. fig. 13.                           |
|                                                                      |
| [1142] Bertrand, P. (09) p. 211.                                     |
|                                                                      |
| [1143] Pelourde (09).                                                |
|                                                                      |
| [1144] Kidston and Gwynne-Vaughan (08) p. 230.                       |
|                                                                      |
| [1145] _Ibid._ (09) p. 664.                                          |
|                                                                      |
| [1146] A Culm species _Rachiopteris aphyllus_ (Unger) is closely     |
| allied to _Metaclepsydropsis duplex_. [See Solms-Laubach (96) p. 30. |
|                                                                      |
| [1147] Unger and Richter (56) p. 165.                                |
|                                                                      |
| [1148] Corda (45) A. p. 83.                                          |
|                                                                      |
| [1149] κλεψύδρα, water-clock.                                        |
|                                                                      |
| [1150] P. Bertrand (09) p. 127.                                      |
|                                                                      |
| [1151] Stenzel (89) p. 25.                                           |
|                                                                      |
| [1152] Dr Scott points out to me that recent observations, which     |
| have not yet been published, both by Dr Kidston and himself show     |
| that Bertrand’s terminology requires modification. There are many    |
| points to be cleared up before we can hope to obtain a satisfactory  |
| classification of the Zygoptereae.                                   |
|                                                                      |
| [1153] Stenzel (89) p. 31, Pls. VI. VII.                             |
|                                                                      |
| [1154] Williamson (89) A. p. 158.                                    |
|                                                                      |
| [1155] _Ibid._; see also Scott (08).                                 |
|                                                                      |
| [1156] Scott (07) p. 180.                                            |
|                                                                      |
| [1157] Renault (69); Williamson (74) A. p. 697.                      |
|                                                                      |
| [1158] Williamson (77) Pls. V.–VII.                                  |
|                                                                      |
| [1159] Williamson (89) A. Pl. VIII. fig. 28.                         |
|                                                                      |
| [1160] Scott (08) p. 322.                                            |
|                                                                      |
| [1161] No. 245.                                                      |
|                                                                      |
| [1162] Williamson (80) A. p. 507.                                    |
|                                                                      |
| [1163] Scott (06).                                                   |
|                                                                      |
| [1164] Solms-Laubach (96).                                           |
|                                                                      |
| [1165] Scott, D. H. (06) p. 519.                                     |
|                                                                      |
| [1166] British Museum, section No. 245. Cf. figures by Williamson    |
| and Bertrand: Williamson (77) Pl. V. fig. 19; Bertrand, P. (09) Pl.  |
| XII. fig. 87.                                                        |
|                                                                      |
| [1167] Scott (07) p. 182; (08) p. 318.                               |
|                                                                      |
| [1168] Weiss, F. E. (06).                                            |
|                                                                      |
| [1169] Williamson (77).                                              |
|                                                                      |
| [1170] Williamson (88) A.                                            |
|                                                                      |
| [1171] Jordan (03).                                                  |
|                                                                      |
| [1172] McNicol (08).                                                 |
|                                                                      |
| [1173] Gwynne-Vaughan (09).                                          |
|                                                                      |
| [1174] Compare figures of the vascular cylinders of climbing         |
| Dicotyledons given by Schenck (93).                                  |
|                                                                      |
| [1175] For a figure of the stele see Tansley (08) p. 25, fig. 20.    |
|                                                                      |
| [1176] Stenzel (89) Pls. III. and IV.                                |
|                                                                      |
| [1177] Binney (72).                                                  |
|                                                                      |
| [1178] Williamson (74) A.                                            |
|                                                                      |
| [1179] Bertrand, P. (09).                                            |
|                                                                      |
| [1180] Felix (86) A.                                                 |
|                                                                      |
| [1181] Renault (69).                                                 |
|                                                                      |
| [1182] Grand’Eury (77) A. Pl. XVII.                                  |
|                                                                      |
| [1183] Renault and Zeiller (88) A.                                   |
|                                                                      |
| [1184] White (99) p. 97.                                             |
|                                                                      |
| [1185] Binney (72); Williamson (74) A. p. 685.                       |
|                                                                      |
| [1186] Williamson (74) A. p. 685.                                    |
|                                                                      |
| [1187] Bertrand, P. (09) Pl. VII. fig. 48.                           |
|                                                                      |
| [1188] Scott (05³) p. 115.                                           |
|                                                                      |
| [1189] Bertrand, P. (09) Pl. VII.                                    |
|                                                                      |
| [1190] Scott (04); (05³).                                            |
|                                                                      |
| [1191] Scott (06²).                                                  |
|                                                                      |
| [1192] Boodle (08).                                                  |
|                                                                      |
| [1193] Scott, R. (08) Pl. XXXIV. figs. 1, 2.                         |
|                                                                      |
| [1194] Baily (60) Pl. XXI. κορύνη, a club or mace.                   |
|                                                                      |
| [1195] Zeiller (83).                                                 |
|                                                                      |
| [1196] Kidston (94).                                                 |
|                                                                      |
| [1197] Potonié (02) p. 492.                                          |
|                                                                      |
| [1198] Zeiller (88) A. Pl. X.                                        |
|                                                                      |
| [1199] Tansley (08).                                                 |
|                                                                      |
| [1200] See p. 447.                                                   |
|                                                                      |
| [1201] Stenzel (89) p. 15, Pls. III. IV.                             |
|                                                                      |
| [1202] Lindman (04).                                                 |
|                                                                      |
| [1203] Baker (87) A.; Sadebeck, in Engler and Prantl (02).           |
|                                                                      |
| [1204] Campbell (04); Bower (08) p. 551.                             |
|                                                                      |
| [1205] Schenk (71) p. 225.                                           |
|                                                                      |
| [1206] Hollick (94) Pl. LXXI.                                        |
|                                                                      |
| [1207] Mentioned by Krasser (06) in a preliminary note.              |
|                                                                      |
| [1208] Frič and Bayer (01) p. 86, fig. 34.                           |
|                                                                      |
| [1209] Heer (82) Pl. XVI.                                            |
|                                                                      |
| [1210] Heer (55) A. Vol. III. p. 156, Pl. CXLV. fig. 35.             |
|                                                                      |
| [1211] Goebel (05).                                                  |
|                                                                      |
| [1212] See Seward (94) p. 441, for a description of the floating     |
| plants on the lagunas of Gran Chaco (S. America) by Prof. Graham     |
| Kerr.                                                                |
|                                                                      |
| [1213] Bower (08) p. 611.                                            |
|                                                                      |
| [1214] Hollick (94).                                                 |
|                                                                      |
| [1215] E.g. Lesquereux (78) Pl. LXIV. fig. 14; Pl. V. fig. 10.       |
| Staub (87) Pl. XIX. fig. 2.                                          |
|                                                                      |
| [1216] Zeiller (03) Pl. LI. figs. 2, 3.                              |
|                                                                      |
| [1217] Heer (55) A. Vol. III. p. 156, Pl. CXLV. figs. 1–315.         |
|                                                                      |
| [1218] Zeiller (09²) p. 95.                                          |
|                                                                      |
| [1219] Fritel (08).                                                  |
|                                                                      |
| [1220] See also Arber (06) p. 228.                                   |
|                                                                      |
| [1221] Solms-Laubach (91) A. p. 183.                                 |
|                                                                      |
| [1222] Dawson (86).                                                  |
|                                                                      |
| [1223] Zeiller (88) A. p. 58.                                        |
|                                                                      |
| [1224] Corda (45) A. Pl. LIV.                                        |
|                                                                      |
| [1225] Presl, in Sternberg (38) A.                                   |
|                                                                      |
| [1226] Schimper (69) A.                                              |
|                                                                      |
| [1227] Nathorst (78) p. 17.                                          |
|                                                                      |
| [1228] Zigno (56) A. Pl. XX.                                         |
|                                                                      |
| [1229] Salfeld (09) p. 17.                                           |
|                                                                      |
| [1230] In a footnote to Fontaine’s description of Jurassic plants    |
| of Oregon, Lester Ward writes:—“Seward treats _Sagenopteris_ as a    |
| fern, classing it now (_Jur. Fl. Yorkshire Coast_, 1900, p. 161) in  |
| the family Polypodiaceae, although in his _Wealden Flora_, 1894, p.  |
| 129, he placed it in the Schizaeaceae.” [Ward (05) p. 83, note _b_.  |
| My words are “I am disposed to regard _Sagenopteris_ as probably a   |
| genus of ferns” (_loc. cit._ 1900, p. 161). I have never referred    |
| this plant to the Polypodiaceae or Schizaeaceae or to any other      |
| family.                                                              |
|                                                                      |
| [1231] Solms-Laubach (91) A. p. 182.                                 |
|                                                                      |
| [1232] I am indebted to my friend Dr Nathorst for calling my         |
| attention to Lindman’s paper.                                        |
|                                                                      |
| [1233] For a fuller synonymy, see Seward (00) p. 162.                |
|                                                                      |
| [1234] Nathorst (04²).                                               |
|                                                                      |
| [1235] Bunbury (51) A.                                               |
|                                                                      |
| [1236] Lindley and Hutton (35) A. Pl. CLV.                           |
|                                                                      |
| [1237] Yabe (05) Pl. III. fig. 16.                                   |
|                                                                      |
| [1238] Moeller (02) Pl. VI. fig. 10.                                 |
|                                                                      |
| [1239] Lindley and Hutton (33) A. Pl. LXIII. fig. 2.                 |
|                                                                      |
| [1240] Seward (00) p. 169, fig. 26.                                  |
|                                                                      |
| [1241] Zigno (56) A. Pl. XXI.                                        |
|                                                                      |
| [1242] Moeller (02) Pl. VI. figs. 8, 9.                              |
|                                                                      |
| [1243] Ward (05) Pl. XV. fig. 5.                                     |
|                                                                      |
| [1244] Bartholin (92) Pl. V. fig. 9.                                 |
|                                                                      |
| [1245] Presl, in Sternberg (38).                                     |
|                                                                      |
| [1246] Zigno (56) A. Pls. XXI. XXII.; Raciborski (94) A. Pl. XX.     |
| figs. 13–18.                                                         |
|                                                                      |
| [1247] Brongniart (25) Pl. XII. fig. 1.                              |
|                                                                      |
| [1248] Fontaine, in Ward (05); Salfeld (09) Pl. I.                   |
|                                                                      |
| [1249] Schenk (67) A. Pl. XIII.                                      |
|                                                                      |
| [1250] Arber (05) p. 75.                                             |
|                                                                      |
| [1251] Seward (94²) A. p. 130.                                       |
|                                                                      |
| [1252] Velenovský (85) Pl. II.                                       |
|                                                                      |
| [1253] Fontaine, in Ward (05) Pl. LXV. Newberry’s _Chiropteris       |
| spatulata_ from Montana may be founded on leaflets of _Sagenopteris  |
| Mantelli_. Newberry (91).                                            |
|                                                                      |
| [1254] Brongniart (28) A. p. 61.                                     |
|                                                                      |
| [1255] White (93).                                                   |
|                                                                      |
| [1256] White (99) p. 143.                                            |
|                                                                      |
| [1257] Schimper (69) A. p. 610.                                      |
|                                                                      |
| [1258] Sellards (01).                                                |
|                                                                      |
| [1259] Weiss, C. E. (69) p. 98, Pl. VI. fig. 13.                     |
|                                                                      |
| [1260] Zeiller (94) p. 169.                                          |
|                                                                      |
| [1261] Renault (96) A. p. 1.                                         |
|                                                                      |
| [1262] Zeiller (90) Pls. XII. XIII.                                  |
|                                                                      |
| [1263] Fontaine and White (80) Pl. XXXIV.                            |
|                                                                      |
| [1264] Fontaine and White (80) Pl. XXXIV. figs. 1–8.                 |
|                                                                      |
| [1265] Sellards (01).                                                |
|                                                                      |
| [1266] Grand’Eury (77) A. p. 171.                                    |
|                                                                      |
| [1267] Renault and Zeiller (88) A.                                   |
|                                                                      |
| [1268] Potonié (93) A. p. 145, Pl. XVII. fig. 3.                     |
|                                                                      |
| [1269] Renault and Zeiller (88) A. p. 282, Pl. XXII. fig. 10.        |
|                                                                      |
| [1270] Feistmantel (81) A. Pls. XXI. A. XXII. A.                     |
|                                                                      |
| [1271] Oldham and Morris (63) p. 41.                                 |
|                                                                      |
| [1272] Schenk (67) A. Pl. XXVIII. fig. 12.                           |
|                                                                      |
| [1273] Nathorst (78) Pl. IX.                                         |
|                                                                      |
| [1274] Feistmantel (90) A. Pl. XXVII.                                |
|                                                                      |
| [1275] Saporta (73) A. Pls. LXI. LXII.                               |
|                                                                      |
| [1276] Zeiller (02) Pls. X.–XIV. p. 66.                              |
|                                                                      |
| [1277] Zeiller (02) Pl. XI. fig. 4.                                  |
|                                                                      |
| [1278] Zeiller (02) Pl. XIII. For synonymy, see also Arber (05) p.   |
| 124.                                                                 |
|                                                                      |
| [1279] Seward (04) figs. 18–22.                                      |
|                                                                      |
| [1280] Seward (08) p. 98.                                            |
|                                                                      |
| [1281] Geinitz (76) Pl. II. figs. 1–3.                               |
|                                                                      |
| [1282] Nathorst (78) Pl. XIX.                                        |
|                                                                      |
| [1283] Zeiller (02) Pl. XIV.                                         |
|                                                                      |
| [1284] For synonymy and distribution, see Seward (00) pp. 159, 304.  |
|                                                                      |
| [1285] Schenk (67) A. Pl. XXV. See also Bartholin (92) Pl. IX. fig.  |
| 7.                                                                   |
|                                                                      |
| [1286] Etheridge (94²).                                              |
|                                                                      |
| [1287] Lindley and Hutton (33) A. Pl. XCII.                          |
|                                                                      |
| [1288] Seward (00) p. 14.                                            |
|                                                                      |
| [1289] Schenk (71) Pl. XXIX.; Seward (94²) A. p. 125.                |
|                                                                      |
| [1290] Stiehler (58) Pls. XII. XIII.                                 |
|                                                                      |
| [1291] See p. 576.                                                   |
|                                                                      |
| [1292] Nathorst (90).                                                |
|                                                                      |
| [1293] For figures, see Stiehler _loc. cit._ and Hosius and Von der  |
| Marck (80) Pls. XLIII. XLIV.                                         |
|                                                                      |
| [1294] For synonymy, see Fontaine, in Ward (99) p. 651; Seward       |
| (94²) A. p. 114; Seward (00) p. 20.                                  |
|                                                                      |
| [1295] Brongniart (22) A. Pl. II. fig. 4.                            |
|                                                                      |
| [1296] Brongniart (28²) A. Pls. LXII. LXIII.                         |
|                                                                      |
| [1297] Schimper (69) A. p. 645.                                      |
|                                                                      |
| [1298] Seward (97²) A. p. 317.                                       |
|                                                                      |
| [1299] For figures see Zeiller (96) A.; Zeiller (02), (03); Arber    |
| (05); Seward (97) A.                                                 |
|                                                                      |
| [1300] Arber (05²); Seward (07²).                                    |
|                                                                      |
| [1301] Bunbury (61) Pl. XI.                                          |
|                                                                      |
| [1302] Zeiller (96) A.                                               |
|                                                                      |
| [1303] Oldham (97); Zeiller (97²).                                   |
|                                                                      |
| [1304] Seward (97) A. (07²); Arber (02²) p. 20; Zeiller (96) A. p.   |
| 374.                                                                 |
|                                                                      |
| [1305] White (08) p. 535.                                            |
|                                                                      |
| [1306] Zeiller (02).                                                 |
|                                                                      |
| [1307] Potonié (00).                                                 |
|                                                                      |
| [1308] Seward (04³); Zeiller (97³); Arber (05) p. 17; D. White (07). |
|                                                                      |
| [1309] Amalitzky (01); Zeiller (98²).                                |
|                                                                      |
| [1310] Zeiller (02).                                                 |
|                                                                      |
| [1311] D. White (07) p. 617 (footnote 2).                            |
|                                                                      |
| [1312] For synonymy, see Arber (05) p. 48.                           |
|                                                                      |
| [1313] Zeiller (96) A.                                               |
|                                                                      |
| [1314] McCoy (47).                                                   |
|                                                                      |
| [1315] Zeiller (96) A.                                               |
|                                                                      |
| [1316] Arber (05); (05²).                                            |
|                                                                      |
| [1317] Seward (97) A; (07).                                          |
|                                                                      |
| [1318] Royle (33).                                                   |
|                                                                      |
| [1319] Zeiller (96) A.                                               |
|                                                                      |
| [1320] Zeiller (96) A.                                               |
|                                                                      |
| [1321] Oldham (97).                                                  |
|                                                                      |
| [1322] Zeiller (02).                                                 |
|                                                                      |
| [1323] Zeiller (02) Pl. V. fig. 7.                                   |
|                                                                      |
| [1324] Etheridge (94).                                               |
|                                                                      |
| [1325] Arber (05) p. 47.                                             |
|                                                                      |
| [1326] Zeiller (96) A. p. 368, fig. 13.                              |
|                                                                      |
| [1327] Zeiller (02); (03).                                           |
|                                                                      |
| [1328] Oldham (97).                                                  |
|                                                                      |
| [1329] Amalitzky (01).                                               |
|                                                                      |
| [1330] Zeiller (03) Pl. XVI.                                         |
|                                                                      |
| [1331] Zeiller (02).                                                 |
|                                                                      |
| [1332] Seward and Leslie (08) p. 113.                                |
|                                                                      |
| [1333] Dawson (71) A. Pl. XVII.; Fontaine and White (80) p. 11;      |
| White (95) p. 315; Arber (05³) p. 307, Pl. XX.                       |
|                                                                      |
| [1334] Jack and Etheridge (92).                                      |
|                                                                      |
| [1335] Lesquereux (79) A. Pl. XXV.; Renault and Zeiller (88) A. Pl.  |
| XXIII. See p. 517.                                                   |
|                                                                      |
| [1336] Etheridge (99).                                               |
|                                                                      |
| [1337] Feistmantel (80) Pls. XXVIII. A., XLI. A.                     |
|                                                                      |
| [1338] Seward (07).                                                  |
|                                                                      |
| [1339] McCoy (47).                                                   |
|                                                                      |
| [1340] Arber (02²).                                                  |
|                                                                      |
| [1341] McCoy (60) p. 107 (footnote).                                 |
|                                                                      |
| [1342] McCoy (75).                                                   |
|                                                                      |
| [1343] Feistmantel (79).                                             |
|                                                                      |
| [1344] Seward and Woodward (05) p. 2.                                |
|                                                                      |
| [1345] Arber (02²) p. 14.                                            |
|                                                                      |
| [1346] White, D. (07).                                               |
|                                                                      |
| [1347] Arber (05).                                                   |
|                                                                      |
| [1348] Carruthers (69²) p. 9, Pl. VI. fig. 1.                        |
|                                                                      |
| [1349] Seward (03) p. 83.                                            |
|                                                                      |
| [1350] Hayden (07); Seward (07⁵).                                    |
|                                                                      |
| [1351] Darwin (87) A. Vol. III. p. 248.                              |
|                                                                      |
| [1352] For synonymy, see Arber (05) p. 104.                          |
|                                                                      |
| [1353] Seward and Smith Woodward (05); (07⁵).                        |
|                                                                      |
| [1354] White (08) pp. 473, 483.                                      |
|                                                                      |
| [1355] Stur (84) p. 638.                                             |
|                                                                      |
| [1356] White (08) p. 537, Pl. VIII. figs. 8–10.                      |
|                                                                      |
| [1357] _Ibid._ p. 543, Pl. IX. figs. 1–3.                            |
|                                                                      |
| [1358] Feistmantel (80) Pl. XXVII. fig. 5.                           |
|                                                                      |
| [1359] Lesquereux (80) A. p. 142; Pl. XXV.                           |
|                                                                      |
| [1360] Brongniart (28) A. p. 129.                                    |
|                                                                      |
| [1361] Grand’Eury (90) A. Pl. VIII. fig. 5.                          |
|                                                                      |
| [1362] Zeiller (90) p. 166, Pl. XIII. fig. 2.                        |
|                                                                      |
| [1363] Renault and Zeiller (88) A. Pl. XXIII. fig. 6.                |
|                                                                      |
| [1364] Lesquereux, _loc. cit._                                       |
|                                                                      |
| [1365] White (05²) p. 381.                                           |
|                                                                      |
| [1366] Grand’Eury (90) A. p. 305.                                    |
|                                                                      |
| [1367] Schimper and Mougeot (44) A.                                  |
|                                                                      |
| [1368] Schimper (69) A. p. 447.                                      |
|                                                                      |
| [1369] Carruthers (69²).                                             |
|                                                                      |
| [1370] See Arber (05) p. 116; Seward (03) p. 85.                     |
|                                                                      |
| [1371] White (08) p. 483.                                            |
|                                                                      |
| [1372] Seward (03) p. 83.                                            |
|                                                                      |
| [1373] Zeiller (95) p. 616.                                          |
|                                                                      |
| [1374] Feistmantel (79).                                             |
|                                                                      |
| [1375] Kurtz (94).                                                   |
|                                                                      |
| [1376] Schimper and Mougeot (44) A. Pl. XXXVIII.                     |
|                                                                      |
| [1377] Blanckenhorn (85) p. 127, Pls. XVII.–XIX.                     |
|                                                                      |
| [1378] Vol. I. p. 292.                                               |
|                                                                      |
| [1379] Zeiller (00²).                                                |
|                                                                      |
| [1380] Blanckenhorn (85) p. 129, Pl. XXI.                            |
|                                                                      |
| [1381] Blanckenhorn _loc. cit._ The specimens figured by this        |
| author are in the Strassburg Museum, as are also some of those       |
| figured by Schimper and Mougeot.                                     |
|                                                                      |
| [1382] Schimper (69) A. p. 452.                                      |
|                                                                      |
| [1383] Schimper and Koechlin-Schlumberger (62) A.                    |
|                                                                      |
| [1384] _Ibid._                                                       |
|                                                                      |
| [1385] Fritsch, K. (97).                                             |
|                                                                      |
| [1386] Stur (75) A. Pl. XIV. fig. 1.                                 |
|                                                                      |
| [1387] Grigoriew (98) Pl. IV.                                        |
|                                                                      |
| [1388] Schuster (08) p. 184.                                         |
|                                                                      |
| [1389] Presl, in Sternberg (38) A.                                   |
|                                                                      |
| [1390] For synonymy, see Zeiller (88) A. p. 301.                     |
|                                                                      |
| [1391] Page 406.                                                     |
|                                                                      |
| [1392] Potonié (03) p. 162.                                          |
|                                                                      |
| [1393] Zeiller (06) Pls. VI. VII.                                    |
|                                                                      |
| [1394] Arber (06).                                                   |
|                                                                      |
| [1395] Renault and Zeiller (88) A.; Zeiller (88) A. Pl. LI.          |
|                                                                      |
| [1396] Renault and Zeiller (88) A. Pl. XXIV.                         |
|                                                                      |
| [1397] Grand’Eury (90) A. Pl. XIX.                                   |
|                                                                      |
| [1398] Kidston (91) Pl. XXXV.                                        |
|                                                                      |
| [1399] Goebel (05) p. 318.                                           |
|                                                                      |
| [1400] See p. 406, fig. 293; Potonié (03) also figures a young       |
| frond of _Dactylotheca plumosa_ partially covered by Aphlebiae.      |
|                                                                      |
| [1401] Seward (00) Pl. XXI. fig. 1.                                  |
|                                                                      |
| [1402] _Ibid._ p. 145.                                               |
|                                                                      |
| [1403] Raciborski (94) A. Pl. XI.                                    |
|                                                                      |
| [1404] Brongniart (22) A.                                            |
|                                                                      |
| [1405] For synonymy, see Kidston (86) p. 68.                         |
|                                                                      |
| [1406] Kidston (94) p. 298.                                          |
|                                                                      |
| [1407] Zeiller (88) A. p. 147, Pls. IV. V.; Kidston (86) p. 80.      |
|                                                                      |
| [1408] See p. 535.                                                   |
|                                                                      |
| [1409] Lindley and Hutton (31) A. Pl. XLV.                           |
|                                                                      |
| [1410] Peach (78).                                                   |
|                                                                      |
| [1411] Kidston (87) p. 145.                                          |
|                                                                      |
| [1412] This species will be described in Vol. III.                   |
|                                                                      |
| [1413] Benson (04).                                                  |
|                                                                      |
| [1414] Miller (57), Frontispiece.                                    |
|                                                                      |
| [1415] Scott (05²) p. 144.                                           |
|                                                                      |
| [1416] Grand’Eury (05²).                                             |
|                                                                      |
| [1417] Kidston (01²) p. 191.                                         |
|                                                                      |
| [1418] Potonié (95); (99).                                           |
|                                                                      |
| [1419] Zeiller (79²).                                                |
|                                                                      |
| [1420] Kidston (01²) p. 195.                                         |
|                                                                      |
| [1421] For synonymy, see Kidston (03) p. 771.                        |
|                                                                      |
| [1422] Grand’Eury (08).                                              |
|                                                                      |
| [1423] Stur (75) A. p. 120.                                          |
|                                                                      |
| [1424] Zeiller (79²); (88) A. p. 142.                                |
|                                                                      |
| [1425] Kidston (94) p. 240.                                          |
|                                                                      |
| [1426] Zeiller (88) A. p. 147.                                       |
|                                                                      |
| [1427] _Ibid._ Pl. XVI.                                              |
|                                                                      |
| [1428] Potonié (92).                                                 |
|                                                                      |
| [1429] Nathorst (02) p. 15.                                          |
|                                                                      |
| [1430] Crépin (75). Previously described by Crépin (74) as           |
| _Psilophyton_.                                                       |
|                                                                      |
| [1431] Gilkinet (75).                                                |
|                                                                      |
| [1432] Nathorst (02).                                                |
|                                                                      |
| [1433] Zeiller (09²) p. 20.                                          |
|                                                                      |
| [1434] Ettingshausen (52).                                           |
|                                                                      |
| [1435] Sellards (00).                                                |
|                                                                      |
| [1436] For synonymy, see Seward (03) p. 52.                          |
|                                                                      |
| [1437] Solms-Laubach and Steinmann (99) Pl. XIV. fig. 2; Szajnocha   |
| (88).                                                                |
|                                                                      |
| [1438] Geinitz (76) Pl. I.                                           |
|                                                                      |
| [1439] Seward (08) p. 95.                                            |
|                                                                      |
| [1440] Feistmantel (90) A. Pl. XXIV.                                 |
|                                                                      |
| [1441] Zeiller (03).                                                 |
|                                                                      |
| [1442] For references, see Seward (04) p. 31.                        |
|                                                                      |
| [1443] Berry (03).                                                   |
|                                                                      |
| [1444] Seward (04) p. 31.                                            |
|                                                                      |
| [1445] Hollick and Jeffrey (09) p. 24.                               |
|                                                                      |
| [1446] Raciborski (94) A. Pl. XX. figs. 1, 2; Zeiller (00²) p. 98.   |
|                                                                      |
| [1447] v. 5950.                                                      |
|                                                                      |
| [1448] Fontaine (89) Pls. XVII. XVIII.                               |
|                                                                      |
| [1449] Solms-Laubach (91) A. p. 141.                                 |
|                                                                      |
| [1450] Schimper (69) A. p. 472.                                      |
|                                                                      |
| [1451] Kurr (45) Pl. II. fig. 1.                                     |
|                                                                      |
| [1452] Seward (04) p. 30.                                            |
|                                                                      |
| [1453] Saporta (73) A.                                               |
|                                                                      |
| [1454] Schenk (67) A.                                                |
|                                                                      |
| [1455] Salfeld (07) p. 192.                                          |
|                                                                      |
| [1456] Seward (04) p. 34, fig. 2, Pl. IV.                            |
|                                                                      |
| [1457] Salfeld (09).                                                 |
|                                                                      |
| [1458] Schenk (76) Pl. XXVI. fig. 7.                                 |
|                                                                      |
| [1459] Salfeld (09) p. 34.                                           |
|                                                                      |
| [1460] Zigno (56) A.                                                 |
|                                                                      |
| [1461] Solms-Laubach (91) A. p. 114.                                 |
|                                                                      |
| [1462] Nathorst (78).                                                |
|                                                                      |
| [1463] Saporta (73) A. p. 352.                                       |
|                                                                      |
| [1464] Nathorst (78) p. 122.                                         |
|                                                                      |
| [1465] Zeiller (03) p. 52.                                           |
|                                                                      |
| [1466] Leckenby (64) A. Pl. X. fig. 1; Seward (04) p. 36.            |
|                                                                      |
| [1467] Schenk (87).                                                  |
|                                                                      |
| [1468] Zeiller (03) Pls. VI.–VIII.                                   |
|                                                                      |
| [1469] Zigno (56) A. Pls. XII. XIII.                                 |
|                                                                      |
| [1470] Seward (00) p. 170.                                           |
|                                                                      |
| [1471] Brongniart (28) A. p. 49.                                     |
|                                                                      |
| [1472] Seward (00) p. 171.                                           |
|                                                                      |
| [1473] Saporta (73) A. p. 368.                                       |
|                                                                      |
| [1474] Krasser (95).                                                 |
|                                                                      |
| [1475] Saporta (73) A. Pl. XLVII.                                    |
|                                                                      |
| [1476] Brongniart (28) A. p. 60.                                     |
|                                                                      |
| [1477] Kidston (01²) p. 196.                                         |
|                                                                      |
| [1478] Potonié (93) A. Pl. XV.                                       |
|                                                                      |
| [1479] Kidston (89) p. 409.                                          |
|                                                                      |
| [1480] Zeiller (06) Pls. XIX.–XXII.; (00²) p. 100, fig. 73.          |
|                                                                      |
| [1481] Weiss, C. E. (70).                                            |
|                                                                      |
| [1482] Zeiller (06) p. 90.                                           |
|                                                                      |
| [1483] Lesquereux (80) A. p. 131; Weiss (70).                        |
|                                                                      |
| [1484] Weiss (69) p. 37.                                             |
|                                                                      |
| [1485] Grand’Eury (77) A. Pl. A.                                     |
|                                                                      |
| [1486] Renault and Zeiller (88) A. p. 219.                           |
|                                                                      |
| [1487] Stur (84).                                                    |
|                                                                      |
| [1488] Grand’Eury (77) A. Pl. XIII.                                  |
|                                                                      |
| [1489] Grand’Eury (08).                                              |
|                                                                      |
| [1490] Renault and Zeiller (88) A. Pl. XXIV.                         |
|                                                                      |
| [1491] Weiss, C. E. (69); Goeppert (64) A.; Potonié (93) A, (04);    |
| Lesquereux (80) A., p. 124; White (99) p. 125.                       |
|                                                                      |
| [1492] Seward (08) p. 97, Pl. VIII.                                  |
|                                                                      |
| [1493] Brongniart, in Murchison, Verneuil, and Keyserling (45) Pl.   |
| A.                                                                   |
|                                                                      |
| [1494] Weiss, C. E. (70) p. 871.                                     |
|                                                                      |
| [1495] Brongniart (49) A. p. 24.                                     |
|                                                                      |
| [1496] Grand’Eury (06).                                              |
|                                                                      |
| [1497] Weiss (69) Pls. VI. VII.                                      |
|                                                                      |
| [1498] Potonié (93) A. Pl. I. figs. 1, 2.                            |
|                                                                      |
| [1499] Weber and Sterzel (96) p. 99.                                 |
|                                                                      |
| [1500] Zeiller (90) p. 84.                                           |
|                                                                      |
| [1501] Zeiller (98³).                                                |
|                                                                      |
| [1502] For figures of this and other species, see Potonié (07).      |
|                                                                      |
| [1503] For synonymy, see Zeiller (90) p. 87 and Potonié (07) p. 2.   |
|                                                                      |
| [1504] Schuster (08) Pl. VIII. fig. 7.                               |
|                                                                      |
| [1505] Weiss, C. E. (70).                                            |
|                                                                      |
| [1506] Schlotheim (20) A. p. 406.                                    |
|                                                                      |
| [1507] Renault and Zeiller (88) A. Pl. XIX.                          |
|                                                                      |
| [1508] White (05²) p. 388.                                           |
|                                                                      |
| [1509] Forbes (53) p. 43.                                            |
|                                                                      |
| [1510] Baily (59) p. 75.                                             |
|                                                                      |
| [1511] Schimper (69) A. p. 473.                                      |
|                                                                      |
| [1512] Dawson (71) A. p. 48; (82).                                   |
|                                                                      |
| [1513] Kidston (91²) p. 30, Pl. III.; (06) p. 434.                   |
|                                                                      |
| [1514] Baily (75) Pl. XXVIII.                                        |
|                                                                      |
| [1515] Carruthers (72²) Pl. II.                                      |
|                                                                      |
| [1516] Dawson (71) A.                                                |
|                                                                      |
| [1517] Smith and White (05) p. 39.                                   |
|                                                                      |
| [1518] Lesquereux (80) A.                                            |
|                                                                      |
| [1519] Crépin (74).                                                  |
|                                                                      |
| [1520] Nathorst (02).                                                |
|                                                                      |
| [1521] Schmalhausen (94).                                            |
|                                                                      |
| [1522] Nathorst (04).                                                |
|                                                                      |
| [1523] Krasser (00) Pl. I. figs. 3–7.                                |
|                                                                      |
| [1524] Zeiller (03²) p. 27.                                          |
|                                                                      |
| [1525] Stur (75) A. Pls. VIII. XII. XVI.                             |
|                                                                      |
| [1526] Kidston (88²).                                                |
|                                                                      |
| [1527] Grand’Eury (08).                                              |
|                                                                      |
| [1528] Brongniart (22) A.                                            |
|                                                                      |
| [1529] Kidston (05²).                                                |
|                                                                      |
| [1530] Renault (76).                                                 |
|                                                                      |
| [1531] Grand’Eury (08).                                              |
|                                                                      |
| [1532] White (99) p. 128.                                            |
|                                                                      |
| [1533] Grand’Eury (77) A. p. 122.                                    |
|                                                                      |
| [1534] Zeiller (90) Pl. XI. fig. 6.                                  |
|                                                                      |
| [1535] Potonié (99) p. 113.                                          |
|                                                                      |
| [1536] Renault (82) A. Vol. III.; Zeiller (90) p. 139.               |
|                                                                      |
| [1537] Grand’Eury (77) A. p. 105.                                    |
|                                                                      |
| [1538] Brongniart (22) A. Pl. II. fig. 6. For synonymy, see Kidston  |
| (03) p. 773; Zeiller (88) A. p. 261.                                 |
|                                                                      |
| [1539] For synonymy, see Kidston (88) p. 354.                        |
|                                                                      |
| [1540] Scheuchzer (1723) A. p. 129, Pl. X. fig. 3.                   |
|                                                                      |
| [1541] Lhywd (1760) A. Pl. V. fig. 190.                              |
|                                                                      |
| [1542] Lesquereux (79) A. Pl. VIII.                                  |
|                                                                      |
| [1543] Fontaine and White (80) p. 47.                                |
|                                                                      |
| [1544] Bunbury (47) Pl. XXI.                                         |
|                                                                      |
| [1545] Kidston (94) p. 357; (03) p. 806.                             |
|                                                                      |
| [1546] White (99) p. 132.                                            |
|                                                                      |
| [1547] Zeiller (88) A. p. 251.                                       |
|                                                                      |
| [1548] See Vol. I. p. 45.                                            |
|                                                                      |
| [1549] Zalessky (07) Pl. XXIV. fig. 5.                               |
|                                                                      |
| [1550] Zeiller (88) A. p. 251.                                       |
|                                                                      |
| [1551] Renault and Zeiller (88) A. p. 251, Pl. XXXII.                |
|                                                                      |
| [1552] Brongniart (28) A. p. 51.                                     |
|                                                                      |
| [1553] Lindley and Hutton (33) A. p. 28.                             |
|                                                                      |
| [1554] Lesquereux (66) A.                                            |
|                                                                      |
| [1555] Roehl (69).                                                   |
|                                                                      |
| [1556] Seward (88).                                                  |
|                                                                      |
| [1557] Potonié (99) p. 153 (note).                                   |
|                                                                      |
| [1558] Gutbier (35).                                                 |
|                                                                      |
| [1559] Presl, in Sternberg (38) A.                                   |
|                                                                      |
| [1560] Grand’Eury (04).                                              |
|                                                                      |
| [1561] Zeiller (90) Pl. XI. fig. 9.                                  |
|                                                                      |
| [1562] Zeiller (99) p. 46.                                           |
|                                                                      |
| [1563] Bunbury (47) A. p. 427.                                       |
|                                                                      |
| [1564] Lyell (45) A. Vol. II. p. 202.                                |
|                                                                      |
| [1565] Lesquereux (80) A. p. 146.                                    |
|                                                                      |
| [1566] Sternberg (26) A.                                             |
|                                                                      |
| [1567] Grand’Eury (04).                                              |
|                                                                      |
| [1568] Grand’Eury (90) A.                                            |
|                                                                      |
| [1569] Zeiller (90) Pl. IX. fig. 6, A.                               |
|                                                                      |
| [1570] Stur (83).                                                    |
|                                                                      |
| [1571] Scott (07) p. 206; Scott and Maslen (06) p. 112.              |
|                                                                      |
| [1572] Grand’Eury (04).                                              |
|                                                                      |
| [1573] For synonymy, see Kidston (03) p. 772: Zeiller (88) A.        |
|                                                                      |
| [1574] Scheuchzer (1723) A. Pl. I. fig. 4.                           |
|                                                                      |
| [1575] Kidston (94) p. 245.                                          |
|                                                                      |
| [1576] For synonymy, see Kidston (94) p. 596; (03) p. 806; White     |
| (99) p. 117.                                                         |
|                                                                      |
| [1577] Grand’Eury (04).                                              |
|                                                                      |
| [1578] Kidston (94) p. 245.                                          |
|                                                                      |
| [1579] Brongniart (28) A. p. 59.                                     |
|                                                                      |
| [1580] Page 494.                                                     |
|                                                                      |
| [1581] Kidston (94) p. 596.                                          |
|                                                                      |
| [1582] Grand’Eury (05).                                              |
|                                                                      |
| [1583] Potonié (92²); (93) p. 54.                                    |
|                                                                      |
| [1584] For synonymy, see Kidston (88) p. 366.                        |
|                                                                      |
| [1585] Zeiller (90) p. 45; Potonié (93) A. p. 57.                    |
|                                                                      |
| [1586] Germar (44) Pls. XXXV. XXXVI.                                 |
|                                                                      |
| [1587] Kidston (88) p. 366.                                          |
|                                                                      |
| [1588] Stur (83).                                                    |
|                                                                      |
| [1589] Renault and Zeiller (88) A. p. 196.                           |
|                                                                      |
| [1590] Potonié (93) A. p. 48.                                        |
|                                                                      |
| [1591] Zeiller (00²) p. 88.                                          |
|                                                                      |
| [1592] Page 397.                                                     |
|                                                                      |
| [1593] Renault and Zeiller (88) A. p. 178, Pls. V.–VIII. _Ante_, p.  |
| 419.                                                                 |
|                                                                      |
| [1594] Potonié (02).                                                 |
|                                                                      |
| [1595] Schimper (69) A. p. 688.                                      |
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