CAMBRIDGE BIOLOGICAL SERIES
FOSSIL PLANTS
CAMBRIDGE UNIVERSITY PRESS
C. F. CLAY, +Manager+
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[Illustration]
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[Illustration: CHARLES RENÉ ZEILLER
Membre de l’Institut
Inspecteur général des Mines
Professeur à l’École Natˡᵉ Supérieure des Mines
(1847–1915)]
FOSSIL PLANTS
A TEXT-BOOK FOR STUDENTS
OF BOTANY AND GEOLOGY
BY
A. C. SEWARD
M.A., F.R.S., +Hon. Sc.D. Dublin+
PROFESSOR OF BOTANY IN THE UNIVERSITY;
MASTER OF DOWNING COLLEGE AND HONORARY
FELLOW OF EMMANUEL COLLEGE, CAMBRIDGE
WITH 253 ILLUSTRATIONS
VOLUME III
PTERIDOSPERMEAE, CYCADOFILICES, CORDAITALES,
CYCADOPHYTA
CAMBRIDGE:
AT THE UNIVERSITY PRESS
1917
TO THE MEMORY OF MY FRIEND
CHARLES RENÉ ZEILLER
ILLUSTRIOUS AS A MAN OF SCIENCE
AND A NOBLE-HEARTED GENTLEMAN
WHOM TO KNOW WAS TO REVERE
PREFACE
In the Preface to Volume II published in 1910 I rashly stated that
it was my intention “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,” also that Volume III would be completed with as little delay as
possible. Though nearly seven years have elapsed since the publication
of the second volume it may fairly be said that the delay is not
entirely due to causes which it was in my power to control. The subject
of geographical distribution receives no connected treatment in Volumes
III and IV for the simple reason that I underestimated the space
required for the description of the Gymnosperms. The alternatives were
either to insert a greatly compressed survey of the successive floras
of the world at the end of Volume IV or to attempt a fuller and less
technical treatment of the subject in a separate book. In choosing the
latter course I am conscious that a further obligation is undertaken
which it may not be possible to fulfil; but the risk is deliberately
taken. Volume IV is in the press and will, it is hoped, be published
before the end of 1917.
It is a pleasant duty to repeat my thanks to many friends who have
helped me in various ways. Dr Kidston generously and without reserve
allowed me access to his splendid collection of Palaeozoic plants,
and the frequent occurrence of his name in the list of illustrations
shows how freely I have availed myself of his kindness. He has read
some of the chapters and greatly assisted me by his friendly criticism
and encouragement. By reading the proofs of this volume Dr Scott has
further increased my already large debt to him. It is impossible to
thank him adequately; he not only corrected many careless mistakes but
by wise counsel and advice he rendered me a service which I greatly
appreciate.
The exchange of views with Prof. Zeiller has been a constant source of
profit and enjoyment, and it is hard to realise that the completed book
will not receive his kindly criticism. He was a singularly unselfish
and generous colleague, always ready to help fellow workers, and he
had the faculty in an unusual degree of influencing those who had the
privilege of his friendship by his sound advice and lovable personality.
The death of Count Solms-Laubach has deprived Palaeobotany of one of
its most learned and strongest supporters. In common with all students
of fossil plants I owe much to the critical treatment of the subject
in the _Einleitung in die Paläophytologie_. Prof. Jeffrey has very
kindly given me several photographs and sections which have been of
great service, and I am similarly indebted to Prof. Zalessky. To Prof.
Nathorst my thanks are due for the great interest he has taken in my
work and for his generosity in providing drawings and showing to me
many of the treasures in the famous Stockholm Museum. Prof. Bertrand
and Prof. Lignier freely supplied photographs and drawings of specimens
in their possession, and I am particularly grateful to them for the
willingness with which they always responded to my requests.
Through the death of Prof. Lignier in March 1916 Palaeobotany has
been deprived of another original thinker who devoted himself with
whole-hearted enthusiasm to botanical research and for many years
faithfully served the University of Caen: he was a generous friend to
whom one never appealed in vain for assistance. Through the kindness
of the Director of the Indian Geological Survey I have been able to
examine several fossils from the Calcutta Museum described by Oldham
and Morris and by Feistmantel. With the Director’s permission several
photographs and drawings made for a forthcoming paper to be published
by the Indian Survey are reproduced in this volume. I take this
opportunity of thanking friends in Australia who recently afforded me
facilities for examining fossil plants in their charge, and I would
especially thank Mr A. B. Walkom of the University of Brisbane, who
has recently undertaken an investigation of the rich plant-beds in the
Ipswich district, for all that he did to enable me to make the most of
a very short time available for palaeobotanical work.
For the loan of specimens and for other help I am indebted to Prof.
Bayly Balfour, Prof. Bower, Prof. Margaret Benson, Prof. Oliver, Sir
David Prain, Dr Smith Woodward, Prof. Weiss, the Director of the
Geological Survey, Dr A. H. Church, Dr Arber, and other friends. I
would also acknowledge a debt, by no means inconsiderable, to my
Colleague Mr Hamshaw Thomas. Among younger friends in the Cambridge
Botany School to whom I am indebted I wish particularly to thank Miss
Ruth Holden, Miss Bancroft, Mr Sayers, Mr Dutt and others who have
rendered me willing help.
In the List of Illustrations mention is made of Corporate Bodies and
individuals from whom blocks have been obtained, and I am grateful to
them for readily responding to my applications.
My Wife, though prevented by more urgent calls in the later stages of
my task from giving as much time to the illustrations as in the two
former volumes, has contributed several drawings, and my daughter
Phyllis Seward has also given me much help in preparing drawings from
previously published figures.
In spite of the vigilance and wise counsel of many friends numerous
blemishes remain and for these the author is alone responsible.
A. C. SEWARD.
+Downing College Lodge+,
_February 10, 1917_.
* * * * *
+Note.+ The letters A and B added to references in the footnotes
indicate that the works will be found in the Bibliographies at the
end of Volumes I and II.
TABLE OF CONTENTS
CHAPTER XXVIII
CYCADALES (Recent). Pp. 1–34.
CHAPTER XXIX
PTERIDOSPERMEAE (continued from Volume II). Pp. 35–85.
PAGE
I. =LYGINOPTERIDEAE= 35–85
=Lyginopteris= 35–70
_Telangium_ 54, 55; _Lagenostoma_ 55–64; _Lagenospermum_
64–66; _Pterispermostrobus_ 66, 67.
=Heterangium= 70–85
_Sphaerostoma_ 78–81.
CHAPTER XXX
II. =MEDULLOSEAE= 86–165
i. _Medullosa_ 86–109, 156–163
_Myeloxylon_ 106–110; _Neuropteris_ 110–117;
_Alethopteris_ and _Linopteris_ 113; _Trigonocarpus_
117–124; _Codonotheca_ 124–126; _Schützia_ 126–128;
_Whittleseya_ 128–131; _Dolerophyllum_ 132–139;
_Ottokaria_ 139–141; _Strobilites_ 141, 142.
ii. =Colpoxylon= 142–145
iii. =Rhexoxylon= 146–149
iv. =Sutcliffia= 149–156
_General considerations suggested by the anatomical
features of Medullosa_ 156–163
II. =A. STELOXYLEAE= 163–165
=Steloxylon= 163–165
CHAPTER XXXI
PTERIDOSPERMEAE. (Foliage and seeds.) Pp. 166–174.
_Pecopteris Pluckeneti_ 166–168; _Eremopteris artemisaefolia_
169–172; =Wardia= 172, 173; _Adiantites bellidulus_ and
_Lagenospermum Arberi_ 173, 174.
CHAPTER XXXII
CYCADOFILICES. Pp. 175–213.
I. =MEGALOXYLEAE= 175–180
=Megaloxylon= 175–180
II. =RHETINANGIEAE= 181–183
=Rhetinangium= 181–183
III. =STENOMYELEAE= 183–185
=Stenomyelon= 183–185
IV. =CYCADOXYLEAE= 185–190
=Cycadoxylon= 185–187
=Ptychoxylon= 187–190
V. =CALAMOPITYEAE= 190–200
=Calamopitys= 190–196
_Kalymma_ 194–196
=Eristophyton= 197–200
VI. =CLADOXYLEAE= 200–210
=Cladoxylon= 201–207
=Völkelia= 208–210
VII. =PROTOPITYEAE= 210–213
=Protopitys= 210–213
CHAPTER XXXIII
CORDAITALES. Pp. 214–299.
A. =POROXYLEAE= 214–219
=Poroxylon= 214–219
B. =CORDAITEAE= 219–284
=Cordaites= 219–265
_Noeggerathiopsis_ 238–243; _Rhiptozamites_ 244,
245; _Phylladoderma_ 244; _Euryphyllum_ 245;
_Artisia_ 246–248; _Dadoxylon_ 248–260;
_Metacordaites_ 260, 261; _Cordaianthus_ 264–270;
=Mesoxylon= 270–275; =Pelourdea= 277–281;
=Niponophyllum= 282, 283; =Titanophyllum= 283, 284.
CHAPTER XXXIV
C. =PITYEAE= 285–299
=Pitys= 285–289
=Archaeopitys= 290
=Callixylon= 291–293
=Coenoxylon= 293, 294
=Parapitys= 294, 295
=Mesopitys= 295, 296
=Antarcticoxylon= 296–299
CHAPTER XXXV
PALAEOZOIC GYMNOSPERMOUS SEEDS. Pp. 300–365.
I. +Lagenostomales+ 308–318
=Physostoma= 309–312; =Conostoma= 313–316;
=Sphaerostoma= 316; =Lagenostoma= 316; =Gnetopsis=
317, 318.
II. +Trigonocarpales+ 318–332
=Trigonocarpus= 319–321; =Tripterospermum= 321;
=Ptychotesta= 321; =Hexapterospermum= 321–323;
=Polypterospermum= 323; =Pachytesta= 323–326;
=Stephanospermum= 326–329; =Polylophospermum= 329,
330; =Codonospermum= 330, 331; =Aetheotesta= 331,
332; =Eriotesta= 332; =Gaudrya= 332.
III. +Cardiocarpales+ 332–356
=Cardiocarpus= 338–340; =Cyclospermum= 340,
341; =Cycadinocarpus= 341; =Rhabdocarpus= and
=Rhabdospermum= 341–345; =Mitrospermum= 345,
346; =Diplotesta= 346; =Leptocaryon= 346, 347;
=Taxospermum= 347; =Compsotesta= 347, 348;
=Samaropsis= 348–354; =Cordaicarpus= 354–356.
IV. +Miscellaneous Seeds+ 356–365
i. =Hexagonocarpus= 356,357; =Decagonocarpus= 357;
=Polypterocarpus= 357, 358; =Rhynchogonium=
358–360; =Boroviczia= 360; =Diplopterotesta= 360,
361; =Musocarpus= 361; =Holcospermum= 361–363.
ii. =Malacotesta= 363; =Thysanotesta= 364;
=Carpolithus= 364, 365; _Microspermum_ 365.
CHAPTER XXXVI
CYCADOPHYTA (+Fossil+). Pp. 366–420.
=BENNETTITALES= 367–420
=Cycadeoidea= 367–417
=Cycadella= 417, 418
=Amphibennettites= 418
=Vectia= 419, 420
CHAPTER XXXVII
=BENNETTITALES= (_continued_) 421–477
=Williamsonia= 421–463
=Wielandiella= 463–467
=Williamsoniella= 467–473
=Cycadocephalus= 473–475
=Weltrichia= 475–477
CHAPTER XXXVIII
CYCADOPHYTA. Pp. 478–506.
i. =Bucklandia= 480–490; =Cycadeomyelon= 490, 491;
=Colymbetes= 491–494; =Cycadeolepis= 494–496.
ii. =Carpolithus= 497–500; =Cycadospadix= 500, 501;
=Beania= 502; =Zamiostrobus=, =Cycadeostrobus=
503–505; =Androstrobus= 505, 506.
CHAPTER XXXIX
CYCADOPHYTA (+Fronds+). Pp. 507–591.
I. +Bennettitales+ 512–566
=Ptilophyllum= 512–529; =Zamites= 529–537;
=Otozamites= 537–545; =Dictyozamites= 546–548;
=Pterophyllum= 548–558; =Cycadites= and
=Pseudocycas= 558–566.
II. +Nilssoniales+ 566–587
=Nilssonia= 566–578; =Ctenis= 578–583; =Pseudoctenis=
584–587.
III. +Incertae sedis+ 587–591
=Sphenozamites= 587–589; =Plagiozamites= 589, 590;
=Cycadorachis= 590, 591.
+List of Works referred to in the Text+ (Vols. III & IV). 592–639
+Index+ 640–656
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.
The names of donors of photographs or drawings are added after the
descriptions of the figures.
+Frontispiece.+ Charles René Zeiller. From a photograph given to me by
Madame Zeiller.
FIG. PAGE
377. _Cycas circinalis_. A. Malins Smith 2
378. _Cycas revoluta_. [G. R. Wieland.] 3
379. _Encephalartos horridus_ 3
380. _Cycas circinalis_. [Encyclopaedia Britannica.] 4
381. _Cycas revoluta_ and _Zamia Loddigesii_ 5
382. _Encephalartos Ghellinckii_. [Camb. Phil. Soc.] 11
383. _Cycas siamensis_. [Encyclopaedia Britannica.] 12
384. _Cycas circinalis_ 13
385. _Cycas Micholitzii_ and _Zamia angustifolia_ 14
386. _Encephalartos Altensteinii_; _Dioon edule_. S. M. Wadham. 15
387. Cycadean Fronds 16
388. _Zamia Wallisii_ 17
389. _Zamia integrifolia_. [Camb. Univ. Press.] 18
390. _Zamia Loddigesii_ 18
391. _Bowenia spectabilis_. [Encyclopaedia Britannica.] 20
392. _Cycas pectinata_, _C. Riuminiana_, _C. angulata_,
_Encephalartos_, and _Stangeria_ 21
393. _Stangeria_, _Encephalartos_, and _Ceratozamia_ 22
394. _Macrozamia Preissii_. [Camb. Univ. Press.] 23
395. _Zamia floridana_. [G. R. Wieland.] 24
396. _Dioon edule_, _Cycas circinalis_, etc., _Encephalartos_,
_Bowenia_, _Macrozamia_, _Microcycas_ 26
397. _Stangeria paradoxa_. [New Phytologist; A. G. Tansley.] 29
398. _Macrozamia_ 29
399. Cycadean foliar bundles 31
400. _Cycas Micholitzii_. [Camb. Phil. Soc.] 33
401. _Lyginodendron Landsburgii_. R. Kidston 37
402. _Lyginopteris oldhamia_. [Camb. Phil Soc.] 39
403–405. _Lyginopteris oldhamia_ 41, 44, 48
406. _Lyginopteris oldhamia_. F. W. Oliver 49
407. _Crossotheca Hoeninghausi_. R. Kidston and other sources 53
408. _Lagenospermum Sinclairi_; _Lagenostoma_; _Calymmatotheca
Stangeri_; _Crossotheca Hoeninghausi_ 57
409. _Lagenostoma_ 58
410. _Lyginopteris oldhamia_ 69
411, 412. _Heterangium Grievii_ 73, 76
413. _Sphenopteris elegans_ 78
414. _Sphaerostoma ovale_ 79
415. _Heterangium Grievii_; _H. tiliaeoides_; _Lyginopteris_ root 82
416. _Medullosa_ (stem-anatomy) 92
417. _Medullosa centrofilis_ 96
418. _Myeloxylon radiatum_; _Medullosa stellata_; _M. Leuckarti_ 103
419. _Medullosa Leuckarti_ 104
420. _Myeloxylon radiatum_; _Medullosa anglica_, and _Medullosa_ sp. 107
421. _Potoniea adiantiformis_; _Linopteris obliqua_; _Neuropteris
heterophylla_ 111
422. _Neuropterocarpus Kidstoni_. [Edinburgh Royal Society.] 114
423–426. _Trigonocarpus Parkinsoni_ 118, 120, 121
427. _Codonotheca caduca_. [New Phytologist.] 125
428. _Whittleseya elegans_; _W. brevifolia_ 128
429. _Whittleseya elegans_ 130
430–432. _Dolerophyllum Goepperti_ 133, 134, 137
433. _Ottokaria bengalensis_. [Indian Geol. Survey.] 140
434. _Strobilites Milleryensis_ 141
435, 436. _Colpoxylon aeduense_ 143
437, 438. _Rhexoxylon africanum_ 146, 148
439, 440. _Sutcliffia insignis_ 150, 151
441. _Steloxylon Ludwigii_ 163
442. _Pecopteris Pluckeneti_ 167
443. _Eremopteris artemisaefolia_; _Samaropsis acuta_ 170
444. _Samaropsis acuta_. R. Kidston 171
445. _Wardia fertilis_ 172
446–448. _Megaloxylon Scotti_. [Camb. Phil. Soc.] 176–178
449, 450. _Rhetinangium Arberi_. W. T. Gordon 182
451. _Stenomyelon tuedianum_ 183
452. _Stenomyelon tuedianum_. R. Kidston 185
453. _Ptychoxylon Levyi_; _Cycadoxylon Fremyi_; _C. robustum_ 188
454, 455. _Calamopitys Saturni_. M. Zalessky 191, 192
456. _Kalymma grandis_ 195
457. _Eristophyton fasciculare_ 197
458. _Eristophyton Beinertianum_. M. Zalessky 199
459. _Cladoxylon mirabile_; _C. dubium_; _C. taeniatum_; _Syncardia
pusilla_ 202
460. _Cladoxylon Kidstoni_; _C. mirabile_ 206
461. _Völkelia refracta_ 209
462. _Protopitys Buchiana_ 211
463. _Poroxylon Edwardsii_. C. E. Bertrand and F. W. Oliver 216
464. _Poroxylon Edwardsii_; _P. Boysseti_. C. E. Bertrand 218
465. _Cordaites_ leaf. (_C. Felicis._) R. Kidston 228
466. _Cordaites principalis_; _Artisia transversa_. R. Kidston 231
467. _Cordaites lingulatus_ 234
468. _Cordaites_ (_Rhizo-Cordaites_); _Cordaites circularis_; _Cordaites_
sp. cf. _C. Lacoei_; _C. crassifolius_ 237
469. _Cordaites aequalis_; _C. Clerci_. M. Zalessky 239
470. _Cordaites_ (_Noeggerathiopsis_) _Hislopi_. G. R. Wieland. 241
471. _Cordaites_ (_Noeggerathiopsis_) _Hislopi_. [Geological
Society.] 241
472. _Cordaites_ (_Noeggerathiopsis_) _Hislopi_. [Geol. Surv.
India.] 242
473. _Cordaites_ stem 246
474, 475. _Dadoxylon materiarum_ 257
476. _Dadoxylon Pedroi_ 259
477. _Cordaites_ root 262
478. _Cordaites?_ root. T. N. Leslie 263
479. _Cordaianthus_. F. E. Weiss 265
480. _Cordaianthus Pitcairniae_; _C. Volkmanni_ 266
481. _Cordaianthus Grand’Euryi_; _C. Williamsoni_; _C. Zeilleri._
C. E. Bertrand 268
482. _Cordaianthus microsporangia_ 270
483. _Mesoxylon Sutcliffii_ 272
484. _Pelourdea vogesiaca_. [Geologists’ Assoc.] 279
485. _Titanophyllum Grand’Euryi_ 284
486, 487. _Pitys antiqua_ 286, 287
488. _Pitys primaeva_ 288
489. _Callixylon Trifilievi_. M. Zalessky 292
490. _Mesopitys Tchihatcheffi_ 296
491. _Antarcticoxylon Priestleyi_ 298
492. Diagram of a synthetic type of seed 303
493. _Lagenostoma ovoides_; _L. Lomaxi_; _Physostoma elegans_;
_Telangium Scotti_; _Stephanospermum akenioides_ 311
494. _Stephanospermum akenioides_; _Conostoma oblonga_; _Gnetopsis
elliptica_; _Physostoma elegans_; _Mitrospermum compressum_ 314
495. _Polypterospermum Renaultii_; _Ptychotesta tenuis_;
_Polylophospermum stephanense_; _Hexapterospermum
stenopterum_; _Diplotesta avellana_; _D. Grand’Euryana_;
_Taxospermum Grüneri_ 322
496. _Pachytesta incrassata_; _Polypterocarpus anglicus_ 324
497. _Pachytesta_ 325
498. _Codonospermum olivaeforme_; _Aetheotesta elliptica_ 330
499. _Samaropsis emarginata_ 337
500. _Cardiocarpus drupaceus_ var. _expansus_ 339
501. _Cardiocarpus sclerotesta_; _Rhabdocarpus cyclocaryon_ 340
502. _Samaropsis fluitans_; _S. emarginata_; _S. bicaudata_; _S.
Seixasi_; _S. barcellosa_; _S. Newberryi_; _Cordaicarpus
Cordai_ 350
503. _Samaropsis Leslii_ 352
504. _Samaropsis Milleri_. [Geol. Surv. India.] 353
505. _Cordaicarpus Cordai_ 355
506. _Holcospermum sulcatum_; _Codonospermum anomalum_;
_Diplopterotesta spitzbergensis_; _Gnetopsis elliptica_;
_Thysanotesta sagittula_; _Rhynchogonium costatum_;
_Boroviczia Karpinskii_; _Hexagonocarpus Noeggerathi_;
_Rhabdospermum tunicatum_ 359
507. _Cycadeoidea marylandica_. [G. R. Wieland.] 373
508, 509. _Cycadeoidea Wielandi_ [G. R. Wieland.] 375, 376
510. _Cycadeoidea_ sp. 377
511. _Cycadeoidea Gibsoniana_ 377
512. _Cycadeoidea ingens_. [G. R. Wieland.] 378
513–515. _Cycadeoidea_. [G. R. Wieland.] 380–383
516. _Cycadeoidea Dartoni_ 384
517–523. _Cycadeoidea Gibsoniana_ 387–394
524–527. _Cycadeoidea_ (_Bennettites_) _Morierei_. [O. Lignier.] 397–402
528–532. _Cycadeoidea dacotensis_. [G. R. Wieland.] 404–408
533. _Cycadeoidea colossalis_. [G. R. Wieland.] 410
534. _Cycadeoidea Reichenbachiana_. [A. Rothpletz.] 411
535–537. _Cycadeoidea gigantea_. [Geological Soc.] 413, 414
538. _Cycadeoidea micromyela_ 415
539. _Cycadeoidea Jenneyana_ (_?_) [G. R. Wieland.] 416
540. _Vectia luccombensis_. [Trustees of the British Museum.] 419
541–543. _Williamsonia gigas_ 424–427
544. _Williamsonia gigas_. [Yorkshire Nat. Union.] 428
545. _Williamsonia gigas_. A. G. Nathorst. 429
546, 547. _Williamsonia gigas_ 430, 431
548. _Williamsonia gigas_. O. Lignier. 432
549, 550. _Williamsonia gigas_. [Cambridge Phil. Soc.] 435, 436
551. _Williamsonia spectabilis_. A. G. Nathorst. 437
552. _Williamsonia spectabilis_. [Geological Soc.] 438
553, 554. _Williamsonia Leckenbyi_. A. G. Nathorst. 439, 440
555, 556. _Williamsonia whitbiensis_. A. G. Nathorst. 441
557. _Williamsonia_ sp. [Indian Geol. Survey.] 444
558. _Williamsonia Blandfordi_. [Indian Geol. Survey.] 446
559. _Williamsonia Carruthersi_ 447
560. _Williamsonia Bucklandi_ 449
561. _Williamsonia scotica_ 450
562–564. _Williamsonia scotica_. [Royal Society.] 451–453
565. _Williamsonia spectabilis_; _W. whitbiensis_; _W. mexicana_ 459
566, 567. _Wielandiella angustifolia_ 463, 464
568. _Wielandiella angustifolia_. A. G. Nathorst. 466
569–573. _Williamsoniella coronata_. [Royal Society.] 468–471
574. _Cycadocephalus Sewardi_. A. G. Nathorst. 474
575. _Bucklandia anomala_ 482
576. _Bucklandia Milleriana_ 484
577. _Bucklandia Yatesii_ 485
578. _Bucklandia buzzardensis_. [Trustees of the British Museum.] 486
579. _Bucklandia indica_. [Trustees of the British Museum.] 488
580, 581. _Colymbetes Edwardsi_ 492, 493
[Trustees of the British Museum.]
582, 583. _Cycadolepis_ sp. 495
584, 585. _Carpolithus conicus_ 498
[Trustees of the British Museum.]
586. _Beania gracilis_. [W. G. Carruthers.] 502
587. _Ptilophyllum pecten_. [Trustees of the British Museum.] 513
588, 589. _Ptilophyllum pecten_ 514, 516
[Geological Surv. India.]
590. _Ptilophyllum pecten_ and _Williamsonia Blandfordi_ 517
[Geological Surv. India.]
591. _Ptilophyllum cutchense_. [Geological Society.] 518
592. _Ptilophyllum pecten_ 519
593. _Ptilophyllum pecten_. [Geological Society.] 519
594. _Ptilophyllum pecten_ 520
595. _Ptilophyllum pecten_ 523
596. _Ptilophyllum pecten_. [Trustees of the British Museum.] 523
597. _Ptilophyllum boreale_. A. G. Nathorst. 526
598. _Ptilophyllum antarcticum_; _P. Anderssoni_ 527
599. _Zamites gigas_. [Encyclopaedia Britannica.] 533
600. _Zamites recta_ 534
601. _Zamites Buchianus_; _Z. Carruthersi_; _Z. Zitteli_ 535
602. _Zamites Buchianus_ 536
603. _Otozamites Goeppertianus_; _O. Bechei_ 538
604. _Otozamites Bechei_ 539
605. _Otozamites Bechei_ 541
606. _Otozamites Beani; O. Bunburyanus_ [Encyclopaedia Britannica.] 542
607. _Otozamites bengalensis._ [Geological Surv. India.] 542
608. _Otozamites Kliptsteini._ [Geological Society.] 545
609. _Dictyozamites Hawelli_ 548
610. _Pterophyllum Jaegeri_ 549
611. _Pterophyllum Nilssoni; Nilssonia mediana_ 551
612. _Pterophyllum Fayoli_ 552
613. _Pterophyllum Braunianum_ 554
614. _Pterophyllum Nathorsti; Nilssonia tenuicaulis_ 556
[Royal Society of Scotland.]
615. _Pterophyllum Nilssoni_ [Trustees of the British Museum.] 557
616. _Pterophyllum Lyellianum_ [Trustees of the British Museum.] 557
617. _Pseudocycas insignis_ 562
618. _Pseudocycas Saportae._ [Encyclopaedia Britannica.] 564
619. _Nilssonia pterophylloides; N. brevis; N. polymorpha_ 567
620. _Nilssonia brevis; N. saighensis_ 570
621. _Nilssonia rajmahalensis._ [Geological Surv. India.] 571
622. _Nilssonia compta._ [Trustees of the British Museum.] 574
623. _Nilssonia princeps._ [Geological Surv. India.] 577
624, 625. _Ctenis_ sp. [Manchester Phil. Lit. Society.] 579
626. _Ctenis sulcicaulis_ 583
627. _Pseudoctenis eathiensis_ [Trustees of the British Museum.] 584
628. _Sphenozamites Rochei_ 588
629. _Sphenozamites Belli._ [Trustees of the British Museum.] 588
CHAPTER XXVIII.
CYCADALES (+recent+).
Among the fossil genera described in the last chapter of the second
volume some were spoken of as true Ferns though most of them, it
was added, ‘may safely be regarded as plants which will ultimately
be shown to belong to some other group, in most cases that of the
Pteridosperms.’ Since this was written additional evidence has
been obtained in favour of the inclusion of certain genera in the
Pteridosperms. In the case of _Taeniopteris_, one of the genera already
described, there is reason to believe that at least one species is a
member of the Cycadales and not a true Fern as formerly supposed.
The Pteridosperms so far described are represented for the most part
by sterile leaves preserved as impressions, the genera founded on
more satisfactory material having been reserved for treatment in this
volume. As these genera are founded to a large extent on anatomical
characters oscillating in their essential features between recent Ferns
and Cycads, it is important that the student should be in possession of
the anatomical characteristics of both of these classes; and for this
reason a general account of recent Cycads is intercalated between the
Pteridosperms already described and those reserved for treatment in
this volume.
* * * * *
The section of the Gymnosperms known as the Cycadales, represented
by nine recent genera and less than 100 species, is of exceptional
importance phylogenetically and demands special attention from
palaeobotanical students. Familiarity with the morphology of recent
forms is essential not only in relation to extinct cycadean plants
but also to types which, though not sufficiently close to surviving
species to be included with them in one class, exhibit features
regarded by many botanists as indications of an affinity either to true
Cycads or to some generalised stock of which they are an offshoot.
The Cycads of to-day may fairly be spoken of as anachronisms, plants
appropriate to a former age but out of harmony with the present. They
are confined to tropical and sub-tropical regions in both the old
and new world. In habit many of them resemble tree-ferns, but the
columnar stem, which may live to a great age and attain a height of
20 metres, differs from that of ferns in its gradually tapered form
consequent on the presence of one or more cambial cylinders. Though
often unbranched (fig. 377) branching of the main trunk is by no means
unusual (fig. 378; fig. 381, B). Many Cycads are geophilous and
have short tuberous stems (figs. 383, 395, 1_a_; 396, E): the genus
_Zamia_ includes a few epiphytic forms[1]. The typical cycadean stem
is covered with persistent petiole-bases with or without an admixture
of smaller scale-leaf bases (figs. 379, 380), while in several species
a transversely wrinkled or irregularly fissured periderm forms the
superficial tissue (figs. 381, B; 383). The foliage-leaves are
relatively large and, with the exception of the bipinnate fronds of
_Bowenia_ (fig. 391), they are always pinnate. The fronds usually form
a terminal crown (figs. 377, 379) and as many as 100 may be produced
from one bud. In _Zamia pygmaea_[2] the fronds are only 10–12 cm. long,
but in some cycads they reach a length of several metres. On both
young foliage-leaves and scale-leaves long and very rarely branched[3]
unicellular hairs (fig. 396, N) form a characteristic feature and take
the place of the ramental scales of the majority of ferns. The apex of
the stem shown in fig. 386, A is covered with a mass of woolly hairs
and several scale-leaves are seen on the lower part of the bud.
[Illustration: Fig. 377. _Cycas circinalis._ From a photograph taken
by Mr A. Malins Smith at Teldeniya (Ceylon).]
[Illustration: Fig. 378. _Cycas revoluta_, as grown by Japanese
horticulturalists. (After Wieland.)]
[Illustration: Fig. 379. _Encephalartos horridus._]
[Illustration: Fig. 380. _Cycas circinalis._ Stem showing alternate
zones of leaf-bases (F) and scale-leaf bases (S). (From the
_Encyclopaedia Britannica_.)]
[Illustration: Fig. 381. A. _Cycas revoluta_, megasporophylls. B.
_Zamia Loddigesii_, branched stem.]
All recent Cycads are dioecious. The reproductive shoots, except the
megasporophylls of _Cycas_—which have departed to a less extent than
those of other genera from the foliage-leaf plan (fig. 381, A; fig.
392, A–C) and are borne in a terminal cluster through which the stem
subsequently pushes its way—consist of a varying number of micro-
or mega-sporophylls in dense spirals on the axis of an elongated or
oval strobilus (figs. 386, B, 393, 394). The microsporophylls are
occasionally verticillate[4]. The strobili are sometimes though rarely
branched[5] and generally but by no means invariably[6] terminal on
the main stem which branches sympodially[7]. A striking example of
lateral strobili has recently been described by Chamberlain[8] who
figures a stem of _Macrozamia Moorei_ with fertile shoots wedged among
the persistent petiole-bases, a condition very similar to that in
the Mesozoic Bennettitales. Pearson has also described clear cases
of laterally-borne cones in _Encephalartos._ _Cycas_ exhibits two
kinds of branching, the female plants being monopodial while in the
male the branching is sympodial. The microspores are produced in
sporangia grouped in more or less well defined sori (figs. 389, A; 392,
E–G). There is no definite annulus, but in the occurrence of groups
of thick-walled cells some microsporangia recall those of certain
ferns[9]. The ovules vary considerably in size, sometimes exceeding
5 cm. in diameter: there are usually two on each megasporophyll
(figs. 393, C; 394; 395, 1_d_) but in most species of _Cycas_ (fig.
392, B) and occasionally in other genera the number is larger[10]. A
thick integument encloses the nucellus with which it is fused except
in the apical region (fig. 396, A, B). Below the comparatively long
micropylar tube is a well-developed pollen-chamber (fig. 396, B′, _p_),
a striking feature of Cycadean ovules, immediately above the megaspore;
the latter is filled with prothallus-tissue and bears a small apical
group of archegonia on the floor of a depression (fig. 396, A–B′).
In _Microcycas_[11] as many as 200 archegonia are recorded—a very
exceptional case—and these are not confined to the apical region,
though only the apical archegonia are functional. Each archegonium
is characterised by a very large oval egg-cell and a much reduced
neck[12]. The microspores usually produce a single prothallus-cell, a
stalk-cell, and body-cell, and from the body-cell are developed two
spirally ciliated spermatozoids (fig. 396, M). In this respect also
the monotypic genus _Microcycas_ is peculiar: it may have as many as
8 body-cells and 16 male gametes in a single pollen-tube (fig. 396,
G), while in _Ceratozamia_[13] 4 gametes have been seen in one tube.
The pollen-tube grows like a fungal mycelium into the nucellar tissue
and the male gametes are formed in the distended proximal end which
on bursting liberates the motile sperms with the watery cell-sap.
Fertilisation is succeeded by the development of a homogeneous
proembryo partially or completely filling the zygote (fertilised
egg): by the formation of long suspensors the embryo is brought into
contact with the food-store of the prothallus. In some Cycads, _e.g._
_Encephalartos_, the embryogeny exhibits a close resemblance to that of
_Ginkgo_[14]. The embryo is dicotyledonous[15].
The single stele of the stem is characterised by a large pith which
in some genera (_e.g._ _Encephalartos_, _Macrozamia_) contains an
anastomosing system of collateral bundles. The vascular tissue of a
cycadean stem forms a cylinder of secondary xylem and phloem, the
primary xylem being represented only by a few, usually crushed,
protoxylem elements on the inner margin of the reticulately pitted
or scalariform tracheids. Both xylem and phloem are traversed by
numerous broad and deep medullary rays[16]. The looser texture and
more parenchymatous structure of Cycadean wood afford a ready means
of distinguishing it from the wood of Conifers: for the Cycadean
type the term _manoxylic_ is proposed and _pycnoxylic_ for the more
compact coniferous wood[17]. Rims (or ‘bars’) of Sanio, of which
much has been said in discussions on the phylogeny of Conifers, have
recently been described in the petiolar xylem of _Cycas revoluta_:
the rims are short and ‘cling closely to the borders of the pits,’
features which also characterise the rims found in the cones of the
Araucarineae and in the root- and cone-wood of certain Pines[18]. In
some Cycads the secondary xylem and phloem form a single cylinder,
but in others (_Cycas_, _Encephalartos_, _Macrozamia_, _Bowenia_) the
cambium is succeeded by one or several concentric cylinders of meristem
which have their origin in the pericycle. The spasmodic occurrence
of separate arcs of inversely orientated secondary xylem and phloem
between the normal cylinders is a feature of importance from the
point of view of comparison with the Palaeozoic Medulloseae[19]. The
occurrence of concentric cauline strands in the cortex of _Cycas_ is
also a peculiarity worthy of notice. Successive bands of periderm, and
occasionally a considerable amount of phelloderm[20], are formed in the
peripheral region of the stem.
The leaf-traces in an adult stem exhibit a striking feature in their
indirect or girdle-like course to the leaves (fig. 396, H, _g_) and
in the gradual change from an endarch (fig. 396, O) to an apparently
mesarch structure (fig. 400) as they pass from the perimedullary zone
to the petiole: except at the base of the petiole the vascular bundles
of the frond-axis consist of (i) centripetally developed xylem with a
median protoxylem and a much smaller amount of centrifugal xylem (fig.
400) separated by a few parenchymatous elements from the centripetal
xylem, (ii) an external arc of protophloem and within this metaphloem
and parenchyma[21]. In the slender petiole of _Bowenia_ there are a few
collateral bundles arranged in the form of a circle or ellipse[22];
in _Cycas_ and some other genera the more numerous bundles form a
pattern like an inverted U, and in some species of _Encephalartos_ the
number is greater and the strands more irregularly scattered[23]. In
the vegetative stems there is no centripetal xylem in the stele, but
scattered centripetal tracheids occasionally occur internal to the
protoxylem in the steles of the peduncles[24].
* * * * *
=Cycadeae.= Megasporophylls each bearing 2–8 ovules, borne separately
like foliage-leaves and not in strobili. Pinnae have a midrib but no
lateral veins (figs. 384, 387, A). _Cycas_ (fig. 377).
=Zamieae.= Both kinds of sporophylls form strobili. Pinnae have
several dichotomously branched, more or less parallel veins. _Zamia_
(figs. 388–390), _Macrozamia_, _Encephalartos_ (figs. 379, 386, C),
_Ceratozamia_, _Dioon_ (fig. 386, B), _Microcycas_.
=Stangerieae.= Strobili as in Zamieae. Pinnae fern-like, numerous
dichotomously branched lateral veins given off from a midrib.
_Stangeria._
=Bowenieae.= Leaves bipinnate (fig. 391), strobili as in Zamieae.
_Bowenia._
_Distribution._ The most widely spread genus, _Cycas_, occurs in Siam,
India, the Nicobar Islands, Ceylon, Madagascar, and Australia, in
many of the islands in the Indian and Pacific oceans, in New Guinea,
Borneo, New Caledonia, New Britain, China and Japan[25]. _Zamia_, the
most northerly genus, extends from North Mexico and Florida through
Central America and some of the West Indian islands to Ecuador,
Bolivia, Chile, and Peru. _Dioon_ and _Ceratozamia_ are confined to
South Mexico, and _Microcycas_ flourishes on the Cuban mountains. The
continent of Africa possesses two endemic genera _Encephalartos_ and
_Stangeria._ _Encephalartos_ extends from Cape Colony through Natal and
Zululand to Zanzibar and Mombasa[26]: a specimen in the Kew Herbarium
(probably _E. Hildebrandti_) is said to have been collected as far
north as the Soudan. Two species are recorded from the Congo[27] and
_E. Barteri_, discovered by Barter in Central Africa, is recorded from
the Gold Coast[28]. _Stangeria_ has a much more limited range in S.E.
Africa[29]; Australia possesses _Macrozamia_, represented by several
species in Western Australia, New South Wales and Queensland, _Cycas_
in Queensland and the Northern territory and the Queensland genus
_Bowenia_. There are no Cycads in New Zealand. As a whole Cycads have
a limited range and with the exception of _Cycas_ and _Zamia_ none of
them extend beyond the limits of a single continent. They are as a rule
not gregarious plants and play a subordinate part in the facies of the
vegetation. _Macrozamia_ forms dense thickets[30] in some districts
and occurs both in exposed situations and in association with Palms
in damp Queensland forests. Chamberlain[31] speaks of 100 plants
of _Dioon edule_ as visible in one view in South Mexico where the
species forms a mountain forest. In Florida _Zamia pumila_[32] grows
in dense moist woods, a habitat in contrast to that of many Cycads.
The Mexican _Ceratozamia_ is associated with luxuriant vegetation,
while its compatriot _Dioon_[33] lives in blazing sunshine. Sir
Joseph Hooker[34] speaks of _Cycas_ living in the deepest and hottest
valleys in Sikkim. _Encephalartos_ is essentially a xerophilous genus.
_Stangeria paradoxa_ is said to be confined to forests in Cape Colony,
and another species grows among the grass of the Park-lands in open
country[35]. While it is true that many Cycads are characteristic of
dry regions some species flourish in places where shade and moisture
are abundant.
Though it is impossible in many cases to form an estimate of the age
of individual plants, there are clear indications that some specimens
afford notable instances of longevity. Chamberlain estimates the age of
some plants of _Dioon spinulosum_ as exceeding 400 years and mentions
an example of _D. edule_ that is probably 1000 years old. An unusually
tall plant of _Encephalartos_ in the Botanic Garden of Amsterdam
is believed by Prof. de Vries to have reached the venerable age of
2000 years[36]. The restricted range and in many cases the solitary
existence of recent Cycads, with their tall stems clothed with the
persistent cork-covered stumps of thousands of fronds, deepens the
impression of antiquity derived from a study of the geological history
of this dwindling race.
_Stems._ The tall columnar stems of some species of _Cycas_, often
branched or bearing numerous ovoid buds like enlarged bulbils[37],
are characterised by the regular alternation of large and small
leaf-bases as seen in the stem of _C. circinalis_ reproduced in fig.
380. In older stems of this species the leaf-bases are exfoliated and
the stem is covered with wrinkled and fissured cork; but in _Cycas
revoluta_ the leaf-bases are even more persistent. The columnar but
relatively stout stems of _Encephalartos_ (figs. 379, 382, 386, A) and
_Ceratozamia_ are similarly encased in a covering of petiole-bases, but
in these genera the differences between foliage-leaves and bud-scales
is much less obvious and there is no zonal alternation. On the stems
of _Macrozamia_ the rhomboidal leaf-bases are more uniform in size
and there are no scale-leaves. The tall and often palm-like stems of
_Microcycas_ sometimes show transverse rings on the bark marking
the position of former terminal buds, and in older trunks these may
disappear, leaving a fissured bark[38]. In _Cycas siamensis_ the
tuberous stem is similarly covered with a rough bark (fig. 383) and the
stems of _Zamia_ are also characterised by an absence of persistent
leaf-bases (figs. 381, B; 395, I_a_, _a_). It is pertinent to remind
the palaeobotanical student of the occurrence of flowering plants
with stems closely simulating those of some Cycads. Prof. Bower[39] in
describing _Rhynchopetalum montanum_, an Abyssinian Lobeliaceous plant,
drew attention to the similarity in surface-features and to some extent
in anatomical structure to cycadean stems. The resemblances are further
emphasised in a more recently published account of the same species
under a different name, _Lobelia Rhynchopetalum_[40].
[Illustration: Fig. 382. _Encephalartos Ghellinckii._ (¹⁄₁₁ nat.
size.)]
[Illustration: Fig. 383. _Cycas siamensis._ (From the _Encyclopaedia
Britannica_.)]
_Fronds._ A general acquaintance with the various types of fronds
illustrated by recent Cycads is important to the student of fossils
not only to enable him to compare existing and extinct forms but
as affording safeguards against possible sources of error in the
description and identification of impressions[41]. The vernation
exhibits less uniformity than in Ferns: in _Cycas_ the rachis is
straight and the pinnae circinately coiled (fig. 220, B, vol. +ii.+
p. 283); in _Zamia_ and _Stangeria_ the rachis is bent and the pinnae
straight, while in _Ceratozamia_ and other genera both the axis and
leaflets are straight. As Braun pointed out, there is as a rule no
terminal leaflet, or it may be pushed to one side giving a forked
appearance to the frond apex[42].
[Illustration: Fig. 384. _Cycas circinalis_, abnormal frond. (From a
specimen in the British Museum.)]
_Cycas._ The presence of a strong midrib and the absence of lateral
veins are distinguishing features: the lower margin of the lamina is
frequently decurrent (fig. 387, A). In _C. circinalis_ the pinnae
may reach 40 cm. in length with a fairly uniform breadth of 2 cm. A
frond of this species in the British Museum, not quite complete, has
a length of 112 cm.: on the lower part of the rachis strong spines
replace the leaflets and near the apex of the leaf concrescent pinnae
form a continuous lamina traversed by seven ribs and dissected at the
margin into acuminate teeth (fig. 384): some of the pinnae are forked
as in _Cycas Micholitzii_[43] (fig. 385). Several years ago I noticed
a similar instance of concrescence in a small plant of _C. circinalis_
in the Royal Gardens, Kew (fig. 387, I). In _Cycas Micholitzii_
the pinnae, reaching a length of 20 cm., are repeatedly and deeply
forked (fig. 385, A, B; fig. 400): the pinnae of _C. Rumphii_ var.
_bifida_[44] are also deeply dissected. _Cycas Beddomei_ has very
narrow pinnae (15 cm. × 2 mm.) similar to those of the Wealden species
_Cycadites Saportae_, and it is noteworthy that narrow leaflets with
a strongly revolute lamina would produce casts with two parallel ribs
(the grooves between the midrib and the edge of the lamina) simulating
the double midrib of the fossil genus _Pseudocycas_. In some fronds,
_e.g._ _C. Cairnsiana_, the midrib is hardly visible on the upper
face of a dried pinna which shows a longitudinal wrinkling simulating
parallel venation.
[Illustration: Fig. 385. A, B, _Cycas Micholitzii._ (After
Thiselton-Dyer.) C, _Zamia angustifolia._]
_Encephalartos._ The fronds of this genus, in _Encephalartos
Laurentianus_[45] reaching the exceptional length of 7 metres, bear
alternate pinnae exhibiting a considerable range in form and breadth.
In _E. longifolius_, _E. Altensteinii_ (fig. 386, C), _E. Lehmanni_,
etc., the pinnae are for the most part linear, reaching a length of
20 cm. and a breadth of 2 cm.: in _E. caffer_ (fig. 387, D), _E.
latifolius_, and others the pinnae are broader and shorter and often
spinous. A frond of _E. longifolius_ or _E. Altensteinii_ may bear both
entire and lobed, spinous pinnae. In _E. Frederici-Guilielmi_ (fig.
387, G) and _E. Ghellinckii_[46] (fig. 382) the pinnae are very narrow
and almost filiform, with revolute edges. The thick and leathery pinnae
of some species are attached obliquely to the edge or to the upper
sloping sides of the rachis which forms a prominent ridge between the
rows of leaflets, and characteristic oval scars are left on the fall
of the pinnae (fig. 387, D, G′). The lamina in most species contains
several veins more or less parallel to the margins and often much more
prominent on the lower than on the upper surface.
[Illustration: Fig. 386.
A. _Encephalartos Altensteinii_, apex of stem.
B. _Dioon edule_,megastrobilus. (From a photograph by Mr S. M. Wadham.)
C. _Encephalartos Altensteinii_, frond.]
[Illustration: Fig. 387. Cycadean fronds. A, _Cycas circinalis_;
B, _Macrozamia Fraseri_; C, _Macrozamia Denisoni_; D, _Encephalartos
caffer_; E, F, _Dioon edule_ from below and above; G, _Encephalartos
Frederici-Guilielmi_, G′, side-view; H, _Ceratozamia mexicana_; I,
_Cycas circinalis_, lower part of young frond.]
_Zamia._ In _Zamia angustifolia_ (fig. 385, C) and _Z. linifolia_ the
pinnae are long and very narrow: the other extreme is represented by
_Z. Wallisii_[47] (fig. 388) with broad ovate segments reaching a
length of nearly ·5 metre and attached to the rachis by a short stalk;
the veins are prominent and dichotomously branched. Other forms of
pinnae are represented by _Z. integrifolia_, _Z. floridana_, and _Z.
Loddigesii_ (figs. 389, 390, 395). The broad and short pinnae of
_Z. furfuracea_[48] bear a close resemblance, except in the absence
of an auriculate base, to those of some species of the fossil genus
_Otozamites_. The broadly linear pinnae of _Z. pseudoparasitica_ (45
cm. × 3 cm.) often show longitudinal wrinklings on drying which suggest
comparison with the corrugated lamina of the fossil species _Nilssonia
brevis_. A basal pad or callosity on the slender bases of the pinnae is
characteristic of many _Zamia_ fronds.
[Illustration: Fig. 388. Pinna of _Zamia Wallisii_. From a drawing
after A. Braun in the Kew Herbarium. (⅓ nat. size.)]
[Illustration: Fig. 389. _Zamia integrifolia_ bearing a megastrobilus
and showing foliage-leaves and scale-leaves. A, microsporophyll; B,
megasporophyll. (After Rendle, from Jacquin.)]
[Illustration: Fig. 390. Small frond of _Zamia Loddigesii_. (⅔ nat.
size.)]
_Ceratozamia._ The fronds bear a fairly close resemblance to those
of _Macrozamia_: in _Ceratozamia mexicana_ the linear pinnae reach a
length of over 30 cm. and a breadth of 2–3 cm.; the lamina tapers to a
narrow apex and is more abruptly contracted at the base (fig. 387, H).
The veins in _Ceratozamia_ are sub-parallel and dichotomy occurs up to
the middle of the lamina[49]. A striking feature is the occurrence of
two opposite stipule-like projections a short distance above the base
of the petiole.
_Macrozamia._ A noteworthy feature in some species is the attachment of
the linear pinnae along the middle line of the rachis (fig. 387, C); in
others (fig. 387, B) the leaflets are attached laterally and may have
a basal callosity. The parallel veins, which branch dichotomously near
the base of the lamina, are often much more prominent on the lower than
on the upper face. In _M. heteromera_[50] (fig. 396, F, F′) the narrow
pinnae are deeply forked and strongly revolute. The spirally twisted
rachis of _M. spiralis_, _M. heteromera_, etc., is a striking feature
recalling the Rhaetic fern _Camptopteris spiralis_ Nath[51].
_Dioon._ The arrangement of the linear pinnae of _D. edule_ (fig. 386,
B), _D. spinulosum_, and _D. Purpusii_[52] forms a ready means of
distinguishing the fronds of this genus: the pinnae, often contiguous
and at right-angles to the rachis, are attached in a lateral groove
by an expanded and slightly decurrent base. The difference between
the lower and upper face of a frond (fig. 387, E, F) affords a good
illustration of a common source of error in the identification of
fossil specimens. The leaflets of _D. spinulosum_, which except in
their spinous margin are very similar to those of _D. edule_, may
reach a length of 15 cm. and a breadth of 8 mm. The parallel veins are
unbranched[53].
_Microcycas[54]._ The pinnae of this genus, very like those of the
Wealden species _Zamites Buchianus_, reach a length of 20 cm. and a
breadth of 8 mm.: on falling they leave oblong scars resembling those
on the rachis of _Encephalartos_.
_Stangeria._ This genus is particularly interesting because of its
fern-like habit and venation. The large fronds of _S. paradoxa_[55]
bear broadly linear acuminate pinnae with entire, unevenly lobed,
serrate, or pinnatifid margins. Some leaflets are so deeply dissected
as almost to justify the appellation pinnate. Both entire and dissected
leaflets may occur on one frond and the lower ones may be stalked while
the upper pinnae are sessile. The venation agrees closely with that of
the genus _Taeniopteris_[56].
_Bowenia._ The large fronds of this genus (fig. 391) are peculiar in
being bipinnate; they may reach a length of 2 metres and have a long
slender petiole: the asymmetrical lamina of the segments, entire or
deeply serrate, is attached by a very short stalk; the veins branch
dichotomously[57] and diverge slightly. Both entire and serrate pinnae
may occur on the same plant, but Chamberlain has revived André’s
specific term _serrulata_ in preference to the generally adopted
designation for the serrate forms, _B. spectabilis_ var. _serrata_[58].
[Illustration: Fig. 391. _Bowenia spectabilis_, frond. (From the
_Encyclopaedia Britannica_.)]
_Reproductive shoots_[59]. In _Cycas circinalis_, _C. Rumphii_, and
other species the megasporophylls reach a considerable length and bear
several lateral ovules each of which may be as large as a goose’s
egg: the sterile distal end has the form of a spear-point with an
irregularly serrate edge. In _C. revoluta_, _C. pectinata_, etc., the
sterile part is deeply dissected and may break off (fig. 392, A) from
the fertile portion of the sporophyll. The megasporophylls of _C.
Riuminiana_ exhibit a striking variation in form (fig. 392, B, C);
some are 15 cm. long with several ovules, while others, reduced to 8
cm., bear only two ovules and resemble the sporophylls of _Dioon_.
In all other genera the megasporophylls are aggregated into cones,
but in _Dioon_ the strobili are characterised by their more ovoid
form and by the looser arrangement of the sporophylls (fig. 386, B),
each of which consists of a horizontal stalk expanded distally into
a broadly lanceolate upturned end covered with a thick felt of hairs
and bearing at its base usually 2, rarely 5–6, ovules on cushion-like
swellings. In _Dioon spinulosum_ the cones may be 50 cm. long. Between
the cones of _Microcycas_, over 90 cm. long, and those of some Zamias,
a few centimetres long, there are many intermediate forms. The large
strobilus of an _Encephalartos_ reproduced in fig. 393, D, shows the
convex ends of the sporophylls with a jagged edge, and in monstrous
cones the marginal lobes may be abnormally developed and assume the
appearance of pinnae[60]. Each megasporophyll bears two large ovules
(fig. 393, B). In certain species of _Encephalartos_ the swollen ends
of the sporophylls have a truncate centre like the flattened umbo of
some Pines (fig. 392, D). The presence of two divergent spines is a
peculiarity of the megasporophylls of _Ceratozamia_ (fig. 393, C):
in _Macrozamia_ (fig. 394) the distal ends are prolonged as tapered
processes. The surface of the strobilus of _Stangeria_ is formed by
imbricate and rounded ends of sporophylls (fig. 392, H) not unlike the
cone-scales of _Pinus excelsa_ or _P. cembra_. The megasporophylls of
_Zamia_ are expanded into regular cushion-like hexagons with a flat
central area (figs. 389, B; 395, I_b_).
[Illustration: Fig. 392.
A. _Cycas pectinata_, apex of megasporophyll. (¾ nat. size.)
B, C. _Cycas Riuminiana_, megasporophyll. (¾ nat. size.)
D. _Encephalartos Altensteinii._ Distal end of megasporophylls. (From
the _Gardeners’ Chronicle_.)
E, F. _Cycas angulata_, microsporophyll and sorus.
G, I. _Ceratozamia mexicana_, I, microsporophyll with scars of sori
(_s_); G, sorus. (After Thibout.)
H. _Stangeria paradoxa_, megastrobilus.]
[Illustration: Fig. 393.
A. _Stangeria paradoxa_, part of microstrobilus.
B, D. _Encephalartos villosus_, megastrobilus in surface-view and in
section. (¼ nat. size.)
C. _Ceratozamia mexicana_, single megasporophyll.]
[Illustration: Fig. 394. _Macrozamia Preissii_, megastrobilus and (A)
single megasporophyll; _a_, axis of cone; _p_, stalk of megasporophyll;
_s_, unripe seeds. (After Rendle.)]
[Illustration: Fig. 395. _Zamia floridana._ I_a_, complete plant;
_a_, main trunk; _b_, branch-scar; _c_, secondary root; _d_, primary
tap-root. (⅛ nat. size.) I_b_, I_c_, megastrobilus. (¼ nat. size.)
I_d_, megasporophyll. (½ nat. size.) I_e_, pinna. (¾ nat. size. After
Wieland.)]
The microsporophylls (figs. 389, A; 392, E) are in all genera
aggregated into strobili which often bear a close resemblance to
seed-cones (fig. 393, A). On a single sporophyll of _Cycas circinalis_
there may be as many as 700 sporangia while in _Zamia floridana_ there
are only two microsporangia. The spore-output is large and in extreme
cases, _e.g._ in _Dioon spinulosum_, the average number of spores in a
sporangium is said to be 30,000[61].
_Seeds._ In the great majority of recent species the seeds may be
described as large and afford a striking contrast to the small seeds
of the Mesozoic Bennettitales. A feature of interest from the point
of view of comparison with Palaeozoic seeds is the absence of a
resting stage, germination in some cases following seed-fall without
an interval. As Warming pointed out, the embryo is often undeveloped
when the seeds are shed. An interesting fact is recorded by Capt.
Dorrien-Smith[62] with regard to seed-dispersal: he describes the
heavy pebble-like seeds of a _Macrozamia_ as being hurled from the
ripe cones a distance of 12 ft. The seeds of _Cycas_ are platyspermic;
the woody shell exposed on removal of the outer flesh is slightly
flattened and has two prominent angles, but three-angled seeds may
occur as in _Ginkgo biloba_ (fig. 631, C). In other genera the seeds
are radiospermic. The seed of _Encephalartos Altensteinii_[63] (fig.
396, D) has a square-cut distal end with a small papilla at the
summit of the unusually long micropylar canal (17 mm.). The stone of
this seed (fig. 396, C) shows parallel curved ridges which mark the
position of vascular strands in the inner region of the outer flesh.
The large ovules of _Cycas circinalis_[64] have an integument 1 cm.
thick consisting of an outer and inner flesh and an intervening stony
layer which reaches its greatest development at the base and apex.
Three vascular strands enter the base of the seed, the concentric
strand breaks up in the broad inner flesh into a group of bundles which
embrace but do not penetrate the lower end of the nucellus. Each of
the two lateral strands branches in the outer flesh near its entrance
into the seed; the outer and larger collateral and mesarch bundle
passes up close to the surface of the shell to the seed-apex, while the
inner branch penetrates the shell and, occasionally branching, passes
up the inner region of the inner flesh as far as the micropyle.
In other seeds the tracheal supply of the outer flesh consists of
several bundles and not two as in _Cycas_. The inner flesh abuts on
the nucellus and is connected with it except at the apex (fig. 396,
B). In ripe seeds the nucellus is reduced to a thin membrane enclosing
the large megaspore at the upper end of which is a depression (fig.
396, B′) or sometimes two depressions (fig. 396, I) in the prothallus
containing the archegonia. In the seed of _Dioon edule_[65] (fig. 396,
A) the position of the absciss-layer (_s_) is indicated by a slight
transverse constriction. In the seeds of _Bowenia_, constructed on the
same plan, the inner series of vascular strands appears to be nucellar
in position, thus differing from the strands in _Dioon_, _Cycas_, and
other genera which are confined to the integument. Miss Kershaw[66] in
describing _Bowenia_ speaks of an upper and a lower pollen-chamber; the
former serves as a storage-place for the microspores prior to their
further development in the lower chamber. Dr Stopes[67] regards the
integument as double in origin, a view suggested by Griffith[68] in
1835, and as homologous with the single integument _plus_ the cupule
of _Lagenostoma_. This view is supported by Mrs Thoday[69]: on the
other hand Miss Kershaw’s investigation of _Bowenia_ seeds leads her
to regard the integument as single. Although there would seem to be a
_prima facie_ case in favour of the dual nature of the integument, the
arguments on the other side have greater weight[70].
[Illustration: Fig. 396.]
[Illustration: Fig. 396.
A. Seed of _Dioon edule_ in longitudinal section; _a_, integument;
_v_, vascular tissue; _m_, prothallus; _n_, nucellus; _p_,
pollen-chamber; _s_, absciss-layer; _ar_, archegonia. (After
Chamberlain.)
B, B′. Seed of _Cycas circinalis_; _a_, _v_, integument (sarcotesta)
and vascular tissue; _b_, sclerotesta; _c_, inner sarcotesta; _m_,
_n_, prothallus and nucellus. (After Stopes.)
B′. Apex of nucellus; _p_, pollen-chamber; _i_, integument; _n_,
nucellus; _ch_, archegonial chamber; _ar_, archegonia.
C, D. Seed of _Encephalartos Altensteinii_; C, surface of stone.
(After Stopes.)
E. Stem of _Bowenia serrulata_; _g_, level of ground. (After
Chamberlain.)
F, F′. Pinnae of _Macrozamia heteromera_.
G. Pollen-tube of _Microcycas Calocoma_. (After Caldwell.)
H. Transverse section of stem of _Encephalartos horridus_; _s_, stele;
_g_, girdle-bundles. (After Mettenius.)
I. Apical view of prothallus of _Cycas_ showing two archegonial
chambers (_ch_). (After Treub.)
K. _Encephalartos Barteri._ Transverse section of stem; _x_, xylem;
_p_, phloem. (After Matte.)
L. _Cycas siamensis._ Transverse section of vascular tissue of young
stem. (After Matte.)
M. _Cycas revoluta_; two motile sperms. (After Miyake.)
N. Long hair with short basal cell from the petiole of _Macrozamia
heteromera_. (After Robertson.)
O. Vascular bundle of _Dioon edule_ from base of petiole; _p_, phloem;
_c_, cambium. (After Mettenius.)]
Recent observations point to the probability that insects play a part
in the pollination of cycadean ovules. Kraus[71] drew attention to the
strong smell emitted by the microstrobili of _Dioon edule_ and noticed
that small bees were attracted to the ripe strobili of _Macrozamia_,
while odourless cones of a neighbouring _Ceratozamia_ received no
attention. Pearson[72] and Rattray[73] have obtained evidence that
beetles and weevils act as pollinators to species of _Encephalartos_.
_Anatomical features._ Allusion has already been made to some of the
more striking anatomical features; the large pith, the occasional
occurrence of medullary vascular bundles, the presence of one or more
cambiums, the large size of the medullary rays, etc. It is worthy of
remark that the occurrence of an anastomosing system of medullary
bundles is not a constant feature within a genus; in _Macrozamia
Fraseri_ such a system is present, but absent in _M. Denisoni_[74]. In
the pith of stems with no medullary bundles cylinders of collateral
bundles may occur in connexion with a fertile shoot. These bundles
arise from the inner face of the main cylinder and pass upwards as
a domical system into the base of the terminal strobilus which is
eventually pushed to one side by the growth of a lateral bud[75].
The secondary xylem tracheids are usually provided with several
rows of bordered pits on the radial walls and resemble those of the
Araucarieae[76], but in Cycads the pits are often not contiguous
and less compact in their distribution. The wood of _Stangeria_
is peculiar in consisting of scalariform tracheids[77] (fig. 397).
Chamberlain describes growth-rings in the wood of _Dioon_; but this is
exceptional. In tangential sections of the stele leaf-trace bundles
are constantly seen passing horizontally through the broad and deep
medullary rays. The pith-cast of a cycadean stem reproduced in fig. 398
shows the wide meshes in the reticulum of tracheal tissue originally
occupied by parenchyma, which on decay left lenticular depressions
represented on the cast by tapered convex areas occasionally bearing
the impress of an outgoing trace in the form of a narrow groove.
The secondary phloem often rivals the xylem in breadth and is not
always easily distinguishable from it; it consists of sieve-tubes,
parenchyma, and fibres. The secondary cambial cylinders characteristic
of _Cycas_, _Encephalartos_, _Macrozamia_, and _Bowenia_, to which
reference was made in the summary of anatomical features, arise in the
pericycle, and a few layers of pericyclic parenchyma occur between
adjacent extrafascicular cylinders of xylem and phloem. In a stem of
_Cycas media_ 35 cm. in diameter examined by Worsdell there were 12
concentric cylinders. Matte[78] and Miss Dorety[79] have described
partially flattened arcs of extrafascicular xylem and phloem in the
hypocotyl of _Ceratozamia mexicana_. Worsdell[80] first drew attention
to the occasional occurrence of short tracheids on the inner edge of
the secondary wood and to the spasmodic development of cambial arcs in
the tissue between the extrafascicular cylinders forming strands of
inversely orientated xylem and phloem. More recent work by Matte gives
support to Worsdell’s comparison between Medullosan stems and those of
recent Cycads with inversely orientated arcs or concentric vascular
cylinders. The French author draws attention to the close resemblance
between the seedling stems of such species as _Encephalartos Barteri_
(fig. 396, K) and _Cycas siamensis_ (fig. 396, L) with their polystelic
type of structure and the adult stems of _Medullosa_[81]. In the stems
of _Dioon_, _Microcycas_, _Stangeria_, and _Zamia_ no extrafascicular
cylinders are recorded. Two main vascular bundles enter the cortex
from each leaf-base and in most stems these diverge right and left
and more or less completely encircle the stele before passing through
the medullary rays and joining the inner portion of the xylem of
the stele either as double or single bundles. These girdle-bundles
(fig. 396, H) first described by Karsten and Mettenius form a very
characteristic cycadean feature[82]. Adjacent girdles are joined
by connecting cortical bundles and, in addition, there are cauline
collateral bundles in the cortex which form an anastomosing system.
In some cases, _e.g._ species of _Macrozamia_ and occasionally in
_Stangeria_, the female peduncle of a _Ceratozamia_, and in seedlings
of _Bowenia_ and _Cycas revoluta_[83], the leaf-traces pursue a direct
course from petiole to stele as in stems of Bennettitales. It is
noteworthy that in seedlings of _Microcycas_[84], a genus characterised
by a large number of male gametes—presumably a primitive feature—the
leaf-traces are of the girdle-type. The two bundles at the base of a
petiole by repeated subdivision give rise to the numerous collateral
strands of the rachis. A leaf-trace in its passage to the leaf is like
that of a Conifer in having the protoxylem on its inner edge, whereas
in the petiole and elsewhere in the frond it is characterised by an
arrangement of the xylem that has usually been described as mesarch. A
typical vascular bundle from a cycadean frond is seen in fig. 399, C;
by far the greater part of the xylem is centripetal, the centrifugal
xylem being confined to an arc of scattered tracheids or a small strand
separated by a few parenchymatous cells from the protoxylem.
[Illustration: Fig. 397. Tracheids from the stem of _Stangeria
paradoxa_. (After Marsh.)]
[Illustration: Fig. 398. Pith-cast of a _Macrozamia_ stem, (⅖ nat.
size.)]
[Illustration: Fig. 399. Sketches illustrating the changes in the
structure of Cycadean vascular bundles in their course from stem to
leaf: _cp_, _cf_, centripetal and centrifugal xylem; _p_, phloem; _px_,
protoxylem. (After Marsh.)]
As considerable stress has been laid on the anatomical features of the
cycadean foliar bundles in discussions on the affinities and phylogeny
of certain Palaeozoic genera, it is important to consider the facts
more closely[85]. French anatomists described the cycadean bundle as
diploxylic on the ground that the centripetal and centrifugal xylems
are distinctly different things, the centripetal xylem being primary—a
relic of a former organisation—and the centrifugal xylem secondary
and homologous with the normal wood of the cauline bundle. The term
mesarch has in recent years been applied to the cycadean type of
bundle. A mesarch bundle is, however, one in which centripetal and
centrifugal xylem are alike in origin, both being primary structures
derived from a desmogen strand. Typical mesarch bundles occur in
several recent ferns; in the stele of the Osmundaceae, _Gleichenia_,
and other genera; but in these plants the xylem is all produced
directly from one primary desmogen region and there is no question of
‘primary’ and ‘secondary’ as in the two portions of the xylem of a
cycadean bundle. Recent researches into the development of cycadean
foliar bundles show that they do not conform to the mesarch type as
generally understood. A leaf-trace at the base of a petiole (fig. 399,
A) comprises centrifugal xylem only, and this consists of regular rows
of tracheids separated by medullary rays: in the lower part of the
petiole the structure is gradually modified, the centrifugal xylem
is reduced and the formation of centripetal xylem is initiated. At a
higher level (fig. 399, B) the centripetal xylem is in excess of the
centrifugal and the latter, for a time connected with the former,
eventually becomes separated by a few parenchymatous cells from the
protoxylem and persists as a small strand or arc of tracheids. Fig.
399 illustrates stages in the transformation of a typical collateral
bundle, at the base of a _Stangeria_ petiole, into one in which the
xylem is almost wholly centripetal at a higher level in the axis of
the frond. A cambium is present in all: in B the centrifugal xylem
is more or less clearly differentiated into two portions, loosely
arranged tracheids near the phloem, and the more compact groups
abutting on the centripetal xylem: figs. C–E show a further reduction
in the centrifugal tracheids. The conclusion drawn from developmental
study is that the two xylem portions of the bundle are independent
in origin[86]. Marsh has, however, shown that in _Stangeria_ bundles
near the base of the petiole the centrifugal xylem consists of rows of
secondary tracheids and an inner portion not in rows which connects the
centrifugal with the centripetal elements; this connecting portion, he
adds, is ‘probably primary and connects up the Cycadean foliar bundle
with the truly mesarch bundle of the Cycadofilices.’
[Illustration: Fig. 400. _Cycas Micholitzii_. Vascular bundles in
a forked pinna; _px_, protoxylem; _s_, sheath of thick-walled cells;
_cf_, _cp_, centrifugal and centripetal xylem.]
In the xylem portion of the bundle from the midrib of a forked pinna
of _Cycas Micholitzii_ shown in fig. 400 the centrifugal xylem
elements are unusually numerous: the space between the two xylems
is occupied by parenchyma and the whole strand is enclosed by a
sheath of crystal-containing cells, _s_, with thick inner walls.
Fig. 400, 1–4, illustrates the gradual change in the form of the
bundle in the region of dichotomy[87]. The ground-tissue of the
petiole is abundantly supplied with secretory canals and in the
hypodermal region is a cylinder of stereome. In some petioles, _e.g._
_Macrozamia heteromera_[88], the ground-tissue cells are lignified
and reticulately pitted, a feature met with in some Mesozoic cycadean
leaves[89]. In _Cycas media_ Worsdell noticed a tendency of the
leaf-trace bundles towards a concentric arrangement and similar
vascular strands are recorded in the peduncle of _Dioon edule_, in
various sporophylls[90] and in other cases. It is possible, as Worsdell
believes, that the fairly frequent occurrence of concentric bundles
in plants characterised by collateral bundles may have a phylogenetic
significance.
The pinnae are dorsiventral and the veins exarch or pseudomesarch:
secretory canals occur between (_Encephalartos_), above, or below the
veins. The mesophyll of _Cycas_ is characterised by the presence of
isolated xylem-elements passing from the midrib to the edge of the
lamina and, as Lignier[91] suggests, these may be regarded as a reduced
system of lateral conducting strands.
The epidermal cells of the leaflets have straight or slightly curved
walls except in _Stangeria_ where they are undulate and fern-like[92].
The stomata, with few exceptions confined to the lower epidermis, are
larger than in other gymnosperms (on the average ·075 × ·034 mm.) and
are more or less depressed below the surface; the guard-cells are
usually surrounded by 4–6 subsidiary cells.
The roots exhibit no feature to which attention need be called: the
pericycle is several cells broad and as in the stem there may be
extrafascicular cylinders of xylem and phloem.