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BY THE SAME AGLHOR.
AN INTRODUCTION TO STRUCTURAL BOTANY.
Parr I.—FLOWERING PLANTS (Tenth Edition). Crown
8vo. Cloth. Illustrated with 118 Figures. Price 5/- net.
Part II].—FLOWERLESS PLANTS (Eighth Edition).
Crown 8vo. Cloth. Illustrated with r2o Figures. Price 5/-.
** An introduction to the study of structural botany has long
been a desideratum in this country. . . . Dr. Scott’s little book
supplies this need in a most admirable manner, and he has
thoroughly earned the gratitude both of teacher and student
alike for the freshness and clearness with which he has presented
his subject.” —WVature.
STUDIES IN FOSSIL BOTANY.
VotumeE I.—PTERIDOPHYTA.
Third Edition. Containing 1go IIlustrations.
Demy 8vo. Cloth. Price 21/- net.
“It is a great gain to botanists to have in our language
so admirable a presentation of the important facts connected
with the structure and crganisation of the Palaeozoic plants.” —
Journal of Botany.
PUBLISHED BY
A. & C. BLACK, LTpD., 4 SOHO SQUARE, LONDON, W.1.
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Restoration.
ginopteris oldhamia,
Ly,
Fic. 1.—
Frontispiece.
STUDIES -
POSSIL BOWAN ¥
BY
DUKINFIELD HENRY SCOTT
LATELY HONORARY KEEPER OF THE JODRELL LABORATORY, ROYAL BOTANIC
GARDENS, KEW
AUTHOR OF ‘AN INTRODUCTION TO STRUCTURAL BOTANY,’ ‘THE EVOLUTION
OF PLANTS,’ ETC.
“* Nous devons donc envisager l'état présent de l’univers, comme l’effet
de son état antérieur.”—Lafgéace.
THIRD EDITION
VOR “11
SPERMOPHYTA
CONTAINING 136 ILLUSTRATIONS
mak BLACK MrT Dp,
4,5, & 6 SOHO SQUARE, LONDON wW.1
1923
—
Furst Edition, in one volume, published 1g00. ;
Vol. I. of Second Edition fublished 1908, Vol. Il. 1909.
Vol. I. of Third Edition published in 1920.
Vol. Ll. of Third Edition published in 1923.
7
*
s
Printed in Great Britain by R. & R. Ciark, Limitep, £ din urgh.
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Per ace LO LHikD EDITION
VOU UMA
In the present volume the account of the so-called “‘ Seed
Ferns ”’ (Pteridosperms ; Chapters I.-III.) has been com-
pletely rearranged, and for the most part rewritten.
Since the previous edition appeared, the author’s
views as to the relationships of the Pteridosperms have
changed. The theory that they were derived from Ferns
no longer appears tenable. The Seed Plants, of which
the Pteridosperms seem to be the most “ primitive ”’
representatives known, are now regarded as an inde-
pendent phylum, running back as far as any of the
recognised lines of the Higher Cryptogams.
Chapter I. (Lyginopterideae) now begins with Heter-
angium, which, on anatomical grounds, is taken before
the type-genus Lyginopteris (the old Lyginodendron).
The account of the seeds referred to this family has been
considerably extended.
Chapter II. is practically new, and illustrated almost
entirely by new Figures. The families considered are
now dealt with fully, and their mutual relations discussed.
In Chapter III. we return to those Pteridosperms in
which there is direct evidence for the mode of reproduc-
tion. Various outlying groups are also considered.
In Chapter IV. (Cordaitales) the more advanced
families of Palaeozoic Gymnosperms are considered. Prof.
Gordon’s important discoveries in the early group of the
Pitys trees are recorded in his own words and illustrated
Vv
v1 STUDIES. IN FOSSIL BOTANY
from photographs which he has supplied. Under the
family Cordaiteae several additional genera (notably the
new genus Mesoxylon) are now included.
In Chapter V. (Mesozoic Gymnosperms) much greater
stress is now laid on the Williamsonian Tribe, the older,
and, as Dr. Wieland has taught us, the more important
line of the great Cycadeoid phylum. A number of new
discoveries are recorded, among which Dr. Marie Stopes’s
extraordinary Cycadeoid fruit from the Gault deserves
special mention.
The final chapter (General Results) has again been
completely recast. The discovery of the early Devonian
land plants, described in Volume I., has profoundly
affected the whole aspect of plant-evolution ; we have
learnt much more, but the effect has been rather to open
up new questions than to solve the old.
The following Figures (52 in number) appear for the
first time in this-edition: Figs. 8, 10, 17, 20, 2%, 26am
41-53, 50-67, 75, 76, 84, 94-97, 100, 103, 104, I12, 114,
TF5e 129.1024 132-130:
The author is much indebted to the skill of Mr. e a,
Gwilliam, F.R.A.S., in drawing or re-drawing a number
of the new illustrations.
Among those to whom special thanks are due for the
loan of Figures and other kind help may be mentioned:
Dr, Agnes Arber, Prof. Paul Bertrand, Prof. Vv
Gordon,. Dr. R. Kidston, F.R.S., Prof. Be kiaame
Prof. F. W. Oliver, F-R.S., Prof. -A. C, Sewarndsaiieees
Dr. Marie C. Stopes, and. Mr. H. Hamshaw Thomas.
Mrs. D. H. Scott, F.L.S., has again undertaken the
preparation of the Index. .
It may be of interest to some readers to know that
the Scott Collection of fossil slides, like the Williamson
Collection, is now at the British Museum (Natural
History) and open to consultation by students.
D. H. SCOT
April 10, 1923.
CONTENTS OF VOLUME II
PAGE
- PREFACE TO VOLUME II ‘ , ; ; Vv
CHAPTER I
PTERIDOSPERMEAE
Lyginopterideae
Introductory Remarks : } ; ‘ : I
LYGINOPTERIDEAE 2
Heterangium g
H. Grievii as
The Stem : : ’ ‘copa
The Leaf-trace and Leaf ‘ : , : : 8
The Root : 2 : ; ; : II
Other Species of Heterangium : : : re
Lyginopteris 19
L. oldhamia 21
The Stem : : : : : : 22
Young and Small Stems ; 34
Branching of the Stem : : ; 36
Anomalies of the Stem : 40
The Leaf - : , : 42
The Glandular Spines . ; : 47
The Roots : Se ve , : : 49
Hiawit \ . : : : : ‘ : 55
Vil
Vill STUDIES IN FOSSIL BOTAN
LYGINORACHIS
Lyginorachis Papilio, Kidston
Other Species of Lyginopteris .
THE ANATOMICAL CHARACTERS OF THE LYGINOPTERIDEAE
THE FRUCTIFICATION OF THE LYGINOPTERIDEAE
The Reproduction of Lyginopteris oldhamia
The Seed
Other Species
The Microsporangia of Lyginopteris
Sphaerostoma, the probable Seed of Heterangium Grievii
Other Seeds, probably referable to Lyginopterideae
AFFINITIES OF THE LYGINOPTERIDEAE
CHAP TERA
PTERIDOSPERMEAE—continued
PAGE
oT
a7
60
60
63
63
63
Fp
74
80
84
88
Rhetinangieae ; Megaloxyleae ; Calamopityeae ; Stenomyeleae ;
Protopityeae ; Cladoxyleae
Introductory Remarks
RHETINANGIEAE
Rhetinangium, Gordon
MEGALOXYLEAE
Megaloxylon, Seward ,
CALAMOPITYEAE
Calamopitys, Unger
Calamopitys (Eu-Calamopitys) americana
Calamopitys (Eu-Calamopitys) annularis
Calamopitys (Eu-Calamopitys) Saturnt
The Sub-genus Evistophyton
Calamopitys (Evistophyton) fascicularis
Calamopitys (Evistophyton) Beinertiana
94
95
O5
Io!
Io!
107
108
109g
rH
118
122
422
126
CONTENTS OF VOLUME II 1X
SYNOPSIS 128
Affinities of Calamopitys 129
NEW CALAMOPITYEAE 132
1. Calamopitys zonata, Kidston " ; ; 133
2. Calamopitys vadiata, sp. nov. . : . 133
| 3. Bilignea solida, Kidston . . ; yas ee
4. Bilignea resinosa, sp. nov. ‘ ; : 134
STENOMYELEAE 135
Stenomvyelon, Kidston 135
Stenomyelon tuedianum, Kidston i : ‘ : 135
Stenomyelon tripartitum, Kidston : , : ; AS
Diagnosis of the Two Species 143
Affinities of Stenomyelon 143
PROTOPITYEAE 145
Protopitys, Goeppert 145
Protopitys Buchiana, Goeppert 145
Protopitys vadicans, Kidston 153
Affinities of Protopityeae 153
THE CLADOXYLEAE 150
Cladoxylon, Unger 158
Vélkelia, Solms 105
Affinities of the Cladoxyleae 166
eee, She FEY OE Eid Soom BR
PTERIDOSPERMEAE—continued
Medulloseae ; Aneimiteae ; Seed-bearing Pecopterideae ;
Dolerophylium ; Steloxylon ; Rhexoxylon ; Cycadoxyleae ; Summary
MEDULLOSEAE 170
manir : , : ; ; : ; 170
ANATOMY—WMedullosa . : : : : 173
Colpoxylon 45 : : Lee
Sutcliffia : : : : : 196
x STUDIES IN, FOSSIL BOTANY
FRUCTIFICATION OF MEDULLOSEAE
AFFINITIES OF MEDULLOSEAE
ANEIMITEAE
SEED-BEARING PECOPTERIDEAE
DOLEROPHYLLUM
COMPLEX STEMS OF UNCERTAIN AFFINITY
Steloxylon, Solms
Rhexoxylon, Bancroft
CYCADOXYLEAE
SUMMARY OF THE PTERIDOSPERMS
CHAPTER TY.
THE CORDAITALES
Poroxyleae ; Pityeae ; Cordaiteae
I. THE POROXYLEAE
IL. THe PIirvexe
III. THE CORDAITEAE
I. External Characters
2. The Stem, Cordaites
Mesoxylon .
Mesoxylopsis
Parapitys
Caenoxylon
Mesopitys
Metacordaites
Hapaloxylon
3. The Root
4. The Leaves
CONTENTS OF VOLUME II
5. The Fructifications
A. The Male Fructification
B. The Female Fructification
Mesoxylon .
Morphology
6. The Seeds .
7. Affinities
CHAPTER V
THE MESOZOIC GYMNOSPERMS
I, CyCADOPHYTA
1. Bennettitales
A. Bennettiteae .
B. Williamsonieae
2. Cycadales
3. Affinities of Mesozoic Cycadophyta
II. CONIFERAE
III. GINKGOALES
COAPIER Vi
GENERAL RESULTS
Introductory Remarks
THE PSILOPHYTALES
LYCOPSIDA
SPHENOPSIDA
PTEROPSIDA
Filicales
- Spermophyta
INDEX TO VOLUME II. .
316
320
320
353
366
309
EY at
383
386
387
398
404
411
411
414
433
| MST OR LUSL RA TIONS
FIGURE PAGE.
1. Lyginopteris oldhamia. Restoration : : : . Frontispiece
2. Sphenopteris elegans. Ribbed stem 4
3 As ae Part of frond 5
4. Heterangium Grievit. Restoration of stem 3 ; ; ; 6
5 * S Transverse section of stem 74
6. A fe Transverse section of outer part of tai 9
7 “ ys Corresponding longitudinal section . . 10
8. Heterangium Schustert. Transverse section of stem . ; : 13
9. Heterangium tiliaeoitdes. Radial section . ; : 15
10. Heterangium shorense. Transverse section of ee bike ; é 16
11. Lyginopteris oldhamia. Transverse section of stem . ; 3 23
12. 3 % Transverse section of stem and foliage . 25
13. 5 * Transverse section of xylem-strand : 26
tA. _ 5 Transverse section of leaf-trace . : 27
15. Stangeria paradoxa. ‘Transverse section of double bundle : 27
16. Lyginopteris oldhamia. Transverse section from outer part of stele 29
17. BS “3 Diagram of course of leaf-traces . : 31
18. 5 - Transverse section of young stem . : 35
19. 5 5 Transverse section of branching stem. 37
20. : 3 Five transverse sections of branching stem 39
21. Sphenopteris Honinghausi. Frond . ; : , f , 43
22. Lyginopteris oldhamia. Radial section of stem : : 4 44
25. “4 . Transverse section of rachis . ; : 45
24. - a} Vertical section of leaflet : ; ‘ 46
25. “4 23 Gland ; = : : 48
26. BS 3 Radial section of stem, showing root . 50
27. mi sg Transverse section of root . y E 51
28. a Me Tangential section of root . J f 53
29. Lagenostoma Lomaxi. Longitudinal section of seed . , : 64
30. ae a Restoration of seed : P E . 64
Bi. Es + Capitate gland on cupule ; ; , 65
32. Lyginopteris oldhamia. Capitate gland on petiole : ' : 65
33. Lagenostoma Lomaxt, Apex of seed : A 66
34. = = Diagram of seed in ioneatuaiaad Brian A 67
Ose “e 5: Diagrammatic transverse sections , : 68
36. = + Transverse sections, showing prothallus_ , 70
a7. a Sinclairi. Rachis bearing seeds . 72
38. x >: Two seeds in cupules_ . : : : 73
xlll
X1V
STUDIES IN FOSSIL BOTANY
FIGURE
79+
. Crossotheca Héninghaust. Fertile pinna
a Ae Fertile, in connection with sterile pinnae
Telangium, sp. Transverse section of synangium
- Cer iarasions ovale. Diagrammatic longitudinal section of seed. ¢
. Physostoma elegans. Diagrammatic sections of seed
. Rhetinangium Arbert. Transverse section of stem
Transverse section of stele
a oy Transverse section of leaf-trace
Megaloxylon Scotti. A. Transverse section of stem. B. Radial
section of stem. C. Transverse section of wood :
Megaloxylon Scotti, A. Transverse section of primary wood.
B. Radial of same : : : ‘ : :
Calamopitys americana. ‘Transverse section of xylem-strand
Longitudinal section showing tracheides
>? )
99 be)
in pith
. Calamopitys americana. Transverse section of leaf-trace
. Kalymma, Transverse section : ;
. Calamopitys annularis. Transverse section of stem
. Calamopitys Saturni. Transverse section of stem
. Calamopitys fascicularis. Transverse section of stem
. Stenomyelon tuedianum. ‘Transverse section of stem .
Transverse section of stele
5 Transverse section of leaf-trace
Protopitys Buchiana. ‘Transverse section of stem
Transverse section of primary wood
Other end of primary wood
Three diagrams of transverse sections
9 9
. Cladoxylon taeniatum, ‘Transverse section of stem
Arctopodium radiatum. Transverse section of stem and teahpeee
. Cladoxylon, sp. Diagram of stem in transverse section
. Hierogramma mysticum. Transverse section of petiole
A. Cladoxylon Kidstont. Transverse section, =5, Vélkelia
vefracta. Transverse section
. Neuropteris heterophylla. Part of frond
. Alethopteris lonchitica. Part of frond
Medullosa anglica. External view of stem
Transverse section of stem
Transverse section of steles ,
Transverse section of leaf-trace bundles
a — A. Transverse section of petiole. B. Vertical
section of leaflet
. Medullosa, stems. Diagrammatic sections of various species
Colpoxylon aeduense. Transverse sections and external surface
oi stem
. Sutcliffia insignis. Transverse section of stem .
Neuropteris heterophylla. Seed attached to rachis
Trigonocarpus Parkinsoni, Diagrammatic median section of sai
Diagrammatic transverse section
Section through micropyle
> ?
” 9
PAGE
yas
79
79
82
85
96
97
99
103
105
Lor
LE
II3
II5
bs Og
II9g
123
136
139
140
146
147
149
150
157
162
163
164
167
r97T
172
174
175
177
179
181
IgI
T95
197
202
205
206
207
LIST OF ILLUSTRATIONS
FIGURE
82. Stephanospermum akenioides. Upper part of pollen-chamber
83. “4 a Multicellular pollen-grains
84. Neuropterid lructifications : ; ;
85. Pecopteris Pluckeneti, Vertile pinna with seeds
86. Cycadoxylon robustum. Part of transverse section
87. Ptychoxylon Levyi. Transverse section of stem
88. Cycadospadix milleryensts
89, A. Poroxylon Edwardsit. Transverse section of stem. B.
Boysetii. Transverse section of young stem .
90. Poroxylon Edwardsii. Transverse section of xylem-strands
gi. Poroxylon Boysettt, Transverse section of petiole
g2. Rhabdocarpus subtunicatus. Transverse section of seed
93. Pitys antiqua. Transverse section of xylem-strand
94. Pitys Dayi. Transverse section of stem
“ ee i Transverse section of stele
oo. |, ~ Transverse section of leaf P
97. Callixylon Trifilievi. Part of transverse section of stem
98. Dorycordaites, sp. Restoration
99. Cordaites laevis. Branch with catkins
100. Cordaites, sp. Transverse section of branch
tor. Cordaites Brandlingii. A. Radial section of stem. B. Radial
section, inner part of wood . : ,
102. Mesoxylon Sutcliffi. Transverse section of stem
103. Mesoxylon multirame. Diagrammatic transverse section of stem .
104. Mesoxylon poroxyloides. Transverse section of xylem-strand
105. Amyelon radicans. Transverse section of root
106. Cordaites. Leaves in tramsverse section. A. C. angulosostriatus.
B. C. rhombinervis. C. C. lingulatus
107. Cordaianthus Penjoni. A. Longitudinal section of male catkin.
B. Stamens
108. Cordatanthus Willcamsoni. A. Tangential section of female cat-
kin. B. Ovule
109. Cordaianthus Grand Euryt. A. Longitudinal section showing
ovule. B. Canal of pollen-chamber
110. Cycas, sp. Longitudinal section of ovule
fcr , sp. Pollen-chamber
112. Mesoxylon multirame. Fertile shoot
113. Cycadinocarpus augustodunensis. Upper part e seeds
114. Mitrospermum compressum. Diagrammatic sections of seed
II5. ” 2 Two seeds in transverse section
116. Cycadeoidea marylandica
117. Bennettites Gibsonianus. A. Stemin transverse section. B. Stem
in tangential section ; : ‘ ;
118. Bennettites Saxbyanus. Transverse section of stem
119. Bennettites Gibsonianus. Longitudinal section of fructification .
220. a - A. Diagram of fruit in radial section.
B. Ramenta. C. Transverse section of seed. D. Section
through micropyle d ; ; :
121. Bennettites Gibsonianus. Transverse section of fruit .
330
332
Xvl1
STUDIES IN FOSSEE BOFANS
FIGURE
122. Bennettites Gibsonianus. Longitudinal section of seed, showing
embryo
. Bennettites albianus. Transverse section through micropyle
= 3 A. Restoration of seed. B. Restoration,
in longitudinal section, of seed and scales
25. Cycadeoidea dacotensis. Longitudinal section of flower
. 3 Longitudinal section through summit of
flower
. Cycadeoidea ingens. Restoration of expanded flower
a ‘ Plan of expanded flower
. Cycadeoidea dacotensis. Transverse section of synangia
. 3 Longitudinal section of synangium
. Williamsonia gigas. Restoration ;
. Williamsonia spectabilis. Restoration of ale few er
. Williamsoniella coronata. Mature flower
Restoration of plant .
9 9
< Restorations of Rhynie plants. 1. Rhynia Gwynne- Vance
2. R. major
. Restorations of Rhynie ales 3. Hornea Ligniert. 4. Aster-
oxylon Macktet
PAGE
334
336
339
343
344
346
347
348
349
354
357
361
362
388
389
a7 UODIES IN“ FOSSIL BOTANY
VOL. II—SPERMOPHYTA
CHAPTER I
PTERIDOSPERMEAE
Lyginopterideae
WE now leave the Cryptogams, and pass on to the Pterido-
spermeae, a series of forms which are among the most
interesting made known to us by fossil botany, for they
appear to unite in their organisation the characters of
two of the main divisions of the Vegetable Kingdom—
the Seed-plants and the Ferns.
It had been recognised many years ago that some of
the fronds from the Carboniferous strata, commonly de-
scribed as those of Ferns, were subject to grave suspicion
of not having really belonged to the class Filicineae.
Such suspicions attached not only to the so-called genera
Alethopteris and Neuropteris, and to a large part of
Sphenopteris, but to an actual majority of the Fern-like
fronds. The plants in question had never been found
with recognisable fructifications of a Fern-type, whereas
in the accepted fossil Ferns, specimens with sori occurred
in a fairly large proportion of cases. It was on such
negative evidence as this (which is not without its value,
if drawn from sufficiently numerous instances) that Stur
in 1883 based his exclusion of certain of these genera
from Ferns and their reference to Cycads. Subsequently,
a large body of well-ascertained positive data accumu-
I I
2 STUDIES IN FOSSIL BOTAN
lated, derived mainly from anatomical investigation,
on which, indeed, we then had to depend, for in none of
the plants concerned were the organs of reproduction
known with certainty up to the year 1903. The anatomi-
cal characters observed indicated a position intermediate,
at least in certain respects, between Ferns and Gymno-
sperms, the particular class of Gymnosperms approached
being that of the Cycadophyta. Hence the convenient
name Cycadofilices was applied by Prof. Potonié to the
group, and generally adopted.
The remarkable progress made from 1903 onwards
left no doubt that most, if not all, the members of this
intermediate group, which embraces the majority of the
Fern-like plants of the Palaeozoic, bore seeds. They
thus proved to be much nearer Gymnosperms than
appeared before, but on account of vegetative and other .
characters they retained an intermediate position, and
are now associated under the name Pteridospermeae.
This class may be provisionally defined as :
Plants resembling Ferns in habit and occasionally in
anatomical characters, bearing seeds of a Cycadean type ;
seeds and microsporangia borne on fronds only slightly
modified as compared with the vegetative leaves.
The Pteridosperms were thus, as Van Tieghem has
said, ‘‘ Phanerogams without flowers.”
We begin with the family Lyginopterideae (formerly
Lyginodendreae ; see below, p. 21); the genus Heter-
angium is taken first, on account of its age and anatomical
characters.
LYGINOPTERIDEAT
HETERANGIUM
The genus Heterangium was founded by Corda in
1845, on fragmentary specimens from the coal-balls of
1 Corda, “‘ Flora Protogaea’’—Beitrdge zur Flora der Vorwelt,
Prag, 1845 (2nd ed. Berlin, 1867).
HETERANGIUM 2
Bohemia, of Middle Coal-measure age. Corda examined
the anatomy as well as he was able, and his generic
name indicates his view that the wood was composed
of two kinds of vessels, large and small. The larger
elements were the tracheides of the primary wood, but
the smaller were confused with the intermingled cells,
which have no claim to the name of vessels. Corda
called his species H. faradoxum, which is thus the type-
species of the genus. But, though better specimens
have since come under observation,! it is still one of the
most imperfectly known species, and our description
will, in the first instance, be based on a form described
by Williamson in 1873 from the Pettycur deposit,? and
named by him, first Dictyoxylon and then, on recognising
its affinity with Corda’s specimens, Heterangium Gnievit.
This is at present the best known of all the species ; it
is also the oldest, for it is the only one of Lower Carbon-
iferous age of which the structure has been investigated ;
anatomically, it is one of the simplest forms. This
species may therefore best serve as our starting-point.
H. Gnievit
The stem of Heterangium Grievit was of considerable
height and slender form, reaching a diameter of about
2 cm.; as Williamson said, it “‘ always appears in the
form of straight, slender, unbranched stems.’’ Its pro-
portions are shown both in the larger petrified fragments
and in impressions, such as those named Sphenopteris
elegans, which there is good reason to believe belonged
to this plant (Fig. 2). The outline of the stem is angular,
owing to the rapid succession and decurrent attachment
of the leaf-stalks (Fig. 4). The leaves, as shown in these
impressions (Fig. 3), were of considerable size and highly
* Habart, 1911 (see p. 12). —
* Williamson, “‘ On the Organisation of the Fossil Plants of the
Coal-measures, Part iv., Dictyoxylon, Lyginodendron and Heterangium,”’
Phil. Trans. Royal Soc. 1873, pp. 377-408.
4 STUDIES IN FOSSIL BOTANY
compound, like the fronds of such recent Ferns as some
species of Davallia.
The Stem.—The anatomy of the stem, though simple,
Fic. 2.—Sphenopteris elegans (probably = Heterangium
Grievit). Ribbed stem, bearing several petioles. Note
the transverse marks on the surface, where the inner
cortex is exposed, corresponding to the sclerotic bands
of H. Grievii, as shown, for example, in Fig. 4. 4 nat.
size. After Stur.
is highly charac-
teristic. There is
a single, large vas-
cular cylinder, of
the type called a
pfrotostele, for no
pith is present, the
wood extending to
thexgéntre of -the
stele. The:trache-
ides are in groups,
intermingled
throughout with
cellular’ tissue,
forming an irregu-
lar network (Figs.
4, 5).-- inal ine
inner part of the
wood the tracheides
are of one kind,
large elongated ele-
ments, with several
rows of bordered
pits on each wall,
whichever way it
may face. The
cellular tissue be-
tween the tracheal
groups is thin-
walled.
At the outer border of the primary wood, with which
alone we are concerned at the moment, the xylem-
strands have a more differentiated structure. It is here
that the spiral elements, the protoxylem, from which the
HETERANGIUM 5
development of the wood started, are placed. They lie
in the interior of each of the peripheral xylem-strands,
Fic. 3.—Sphenopteris elegans (probably foliage of Heterangium Grievii). Part of frond,
Note the transverse bands on the rachis, as in Fig. 2. 32 nat.size. After Stur.
accompanied by a few thin-walled cells. The strand
thus has a mesarch structure, the xylem being developed
6 STUDIES IN FOSSIL BOTANY
partly in a centripetal and partly in a centrifugal direc-
tion (Fig. 6). The centrifugal portion is relatively small,
only a few layers of tracheides lying outside the proto-
xylem. The centrifugal elements are in immediate
contact with the protoxylem, and have a spiral or scalari-
form sculpture on their walls; the inner or centripetal
part of the xylem-strand, separated from the protoxylem
|peszexs
| seas
ee
) ee
a)
Lt
| Sause saiteat pet 4
Fic. 4.—Heterangium Grievii. Restoration of a portion of the stem, showing transverse
and longitudinal section, and part of the external surface. %, primary wood of stele ;
x*, secondary wood; pc, phloem and pericycle (left blank); c, cortex, with horizontal
sclerotic bands; hy, hypoderma of stem and petioles; 1.t., leaf-traces, one of which is
entering a petiole; 7, adventitious root. The bases of several petioles are shown.
Enlarged. After Williamson, Phil. Trans.
by the little island of cellular tissue, is composed, like
the rest of the wood, of pitted tracheides (Fig. 7). Hence
we may infer that the small, centrifugal portion was the
first to be formed after the protoxylem. The peripheral
xylem-strands, while easily recognisable from _ their
structure and position, are not sharply delimited from
the rest of the primary wood (Figs. 5, 6). A certain
number of them form the direct downward prolongation
of the leaf-traces, while others appear to be of the nature
HETERANGIUM
of ‘“‘reparatory strands,’
leaf-traces as they pass out.
7
which take the place of the
The whole mass of primary wood is surrounded by a
zone of phloem, usually ill-preserved, and by a well-
marked pericycle of rather large cells.
r
saat
“
wi
' use
TAs
a
\\n\
A
iy
NY
Sa
ay:
‘s ft, iby,
CO oh fF,
: aa Vis
%
& Lf
Ge llLtY, ype
uc.
Fic. 5.—Heterangium Grievii. Transverse section of stem. 4%, central mass of primary
wood, consisting of tracheides and parenchyma; +x”, secondary wood, beginning to
form ; next come phloem and pericycle; 1.c., inner cortex (x in this zone is a sclerotic
group); L.t., leaf-traces; 7, base of an adventitious root; 0.c., outer cortex or hypo-
derma (only present in places) ; pet, base of petiole, partly detached.
Coll396:,, (G.. TG.)
So much for the primary structure of the stele; in
most specimens secondary growth in thickness had taken
place. The primary xylem is then surrounded by a
zone of radially arranged, secondary wood, not, as a
rule, attaining any very great breadth (Fig. 6).
secondary tracheides are generally small compared with
those of the primary wood; the bordered pits are for
S.
The
8 STUDIES IN FOSSIL BOTANY
the most part restricted by the radial walls; medullary
rays, often several cells in width, traverse the wood ; in
this species there is no definite distinction between
principal and secondary rays, though some of them are
continuous with the network of cellular tissue in the
primary wood. The cambium is sometimes preserved ;
it lies on the outer border of the wood which it had formed,
and produced secondary phloem towards the exterior.
The process of secondary growth was, in fact, altogether
a normal one, anticipating the scheme familiar to us in
the higher plants. It is interesting to find this typical
mode of growth in thickness already established in a
plant, which, in its primary structure, is on a level with
one of the lower Ferns.* :
The cortex presents some characteristic features.
The inner cortex contains, embedded in the cellular
tissue, numerous horizontal plates of thick-walled cells,
which may be called stone-cells; the plates succeed
one another in regular vertical series (Fig. 4). Within
each plate, the cells have a regular arrangement in short
vertical rows, indicating that the plate was formed by
a special meristem. These horizontal stiffening plates
are conspicuous even to the naked eye, and enable us
to recognise the plant at a glance when seen in longi-
tudinal section or on the surface of a fracture (cf. Fig. 2).
The outer cortex consists of alternating radial bands
of thick-walled fibres and cellular tissue, the former
serving to give mechanical strength to the stem, while
the latter were in communication with the stomata of
the epidermis. The fibrous bands run parallel and are
not usually united into a network (Figs. 4, 5).
The Leaf-trace and Leaf.—We have now to consider
1 There is a fairly close analogy in the structure of the stele
between a Heterangium such as .H. Grievii and one of the simpler
species of Gleichenia. In both, the vascular cylinder is a protostele,
the wood consisting of intermixed tracheides and parenchyma, and
in both the structure is mesarch, the protoxylem-groups lying some
little distance within the periphery of the wood.
HETERANGIUM 9
the leaf-trace and its connection with the leaf. In this
species the leaf-trace is always a single bundle through-
out its course, only dividing in the rachis to supply the
successive subdivisions of the compound frond. Where
it first leaves the stele (cf. Fig. 6), the leaf-trace usually
has a single protoxylem-group, which soon splits into
two as the strand moves outwards. The trace passes
Fic. 6.—Heterangium Grievit. Part of transverse section, from outer part of stele, showing
a primary xylem-strand and adjacent tissues. x, protoxylem of strand; +, centri-
petal, x1, centrifugal, primary wood; mx, metaxylem, c.p., conjunctive parenchyma ;
x*, secondary wood; cb, cambium; ph?, phloem. x 135.. Phil. Trans., W. and S.
Will. Coll. 1293.
through the phloem and pericycle, and then very gradu-
ally traverses the cortex, so that the traces of a number
of the leaves are seen in the same transverse section
(Fig. 5). The structure of the trace-bundle is at first
collateral, 7.e. with the phloem on the outer side only,
but by the time it enters the leaf-stalk it becomes con-
centric, the phloem here extending all round the xylem,
as in the main foliar bundles of most Ferns. Though
the bundle never divides, it becomes somewhat bilobed
10 STUDIES IN FOSSIL BOTANY
in the outer part of its course, and the two halves of the
xylem are sometimes separated by a narrow radial band
of cells; this fact is of some interest, as faintly fore-
shadowing the divided leaf-trace characteristic of other
species.
The leaves are arranged in a spiral order, the phyllo-
taxis being 2 in the larger
and 2 in some of the smaller
stems. The petioles are rather
small compared with the stem
which bore them; thus in a
stem about 2 cm. in diameter
the width of the leaf-base is
only about 4 mm.
The structure of the foliar
bundle remains essentially
the same as when it left the
stem; it is concentric and
mesarch, . The cortex ar eae
petiole and rachis contains
the same horizontal plates
of stone-cells as that of the
stem, a fact which has aided
in the identification of the
Fic. 7.—Corresponding longitudinal section, foliage when preserved in the
showing the structure of the tracheides. form of impressions (Fig. 2).
x*y, parenchyma at the commencement
of a medullary ray. Other lettering as The fibrous bands of the
in) Bigs6, 295. “Pal. Trans: W. Pc
and S. Will. Coll. 1266. outer cortex are also similar
in both organs.
The highly compound frond, now identified as belong-
ing to Heterangium Grievi1, was long previously known
under the name Sphenopteris elegans, Brongn. (Fig. 3).*
1 This identification was originally due to Dr. Kidston, “ Fructi-
fication and Internal Structure of Carboniferous Ferns,’’ Tvans. Geol.
Soc. Glasgow, 1889, p. 49. When first discovered by Volkmann in
1720 the present Sphenopteris elegans was named Lumaria officinalis,
which is thus a synonym for Heterangium Grievii—a strange freak of
nomenclature |
HETERANGIUM II
This was referred by Stur to his genus Diflotmema,
characterised by the forking of the rachis of the primary
pinnae. Sections of the rachis of H. Grievii are some-
times met with in which the vascular bundle has divided
into two equal strands ; this may represent the bifurca-
tion of the pinna, as described by Stur. It is, however,
possible that the main rachis may have also forked, as
was the case in the allied genus Lyginopteris. The
structure of the ultimate leaflets, borne on the rachis,
is not known in detail, owing to defects of preservation.
The Root.—The roots of Heterangium Grievit were
first identified by Dr. Margaret Benson, F.L.S., who
found them in connection with the stem, on which they
were borne in vertical rows. The larger roots, attaining
a diameter of about 4 mm., are almost invariably triarch,
that is to say, the central, primary wood has three groups
of spiral elements, protoxylem, from which the develop-
ment started. The smaller roots and rootiets are often
diarch. Secondary growth took place in the manner
typical of recent roots, 7.e. the arcs of secondary wood
were first formed in the spaces between the protoxylem
groups. Opposite each protoxylem there is thus a broad
ray, which, however, becomes broken up by the inter-
calation of a few radial rows of tracheides, usually smaller
than those of the woody wedges. The cortex consists
of loosely packed cells, and is bounded on the outside
by a rather small-celled epidermis.
It will be noticed that these roots are in all respects
comparable to those of a recent plant of Gymnospermous
affinities. The comparison might equally well be extended
to Dicotyledons, if it were not for the absence of vessels,
as distinguished from tracheides. True vessels, arising
by cell-fusion, have not yet been demonstrated in the
wood of any Palaeozoic plant.
12 STUDIES IN FOSSIL BOTANY
Other Species of Heterangium
Heterangium Grievit represents the simplest type of
the genus, characterised especially by the leaf-trace con-
sisting of a single vascular strand, while the central
cylinder is of a strictly protostelic type, the peripheral
strands not being sharply marked off from the rest of
the primary wood. The name Fu-heterangium has been
given to a sub-genus, of which H. Gmevii is the type.
One or two other species of this sub-genus merit a brief
mention.
Several species of Heterangium, from the Ostrau beds
of Upper Silesia, have recently been described by Dr.
Kubart.1. The horizon is Upper Carboniferous, but older
than that of our Lower Coal-measures, corresponding to
the upper part of the Millstone Grit. Several of these
species are referable to the sub-genus Eu-heterangium.
The simplest is H. Sturi1, Kubart, a form-in which the
peripheral strands of the primary wood are even less
differentiated than in H. Grvievi1, only becoming distinct
when they are given off as leaf-traces. Their structure
is nearly exarch, the primary centrifugal xylem being
much reduced. This, however, is a character subject to
much variation throughout the genus. The leaf-traces
appear to be quite undivided. In H. alatum, Kubart,
the leaf-traces are somewhat more clearly delimited at
the border of the stele, and they are again typically
mesarch, as in H. Grvievii. The number of leaf-traces is
considerable, as many as ten appearing in the transverse
section ; they remain undivided. The stem bore crowded
leaves, the small winged petioles surrounding the axis.
H. polystichum is a nearly allied species, in which the
1 B. Kubart, “ Pflanzenversteinerungen enthaltende Knollen,”’ etc.,
Sitzungsber. d. K. Akad. d. Wiss. in Wien, Math.-Naturwiss. Klasse,
Bd. cxvii. 1908. ‘‘ Corda’s Sphaerosiderite,” etc., 1bid. Bd. cxx.
rg11. ‘‘ Uber die Cycadofilicineen Heterangium und Lyginodendron,”
etc., Osterreichische bot. Zeitschrift, Jahrgang 1914.
HETERANGIUM 13
leaf-traces are still more numerous, the number in the
transverse section being thirteen, probably indicating a
;y phyllotaxis. |
H. Schusteri has a stele only a little more differentiated
than in H. Sturit, but there is the interesting difference
that the leaf-traces, which are few and large, divide into
Fic. 8.—Heterangium Schusteri. Transverse section of stem, showing primary and secondary
wood and cortex, with three leaf-traces (I—3), the two outer dividing. x about 8.
After a photograph by Dr. Kubart. (G. T. G.)
two after leaving the stele (Fig. 8). There is a British
species, H. minimum (Scott, 1917), which agrees with
H. Schusteri in this respect. It is convenient to include
in the sub-genus Eu-heterangium, forms in which the
trace leaves the wood as a single strand, even though it
may divide once on its outward course.
From the simple type of Eu-heterangium other members
14 STUDIES IN? FOSSIL BOTA Y
of the genus diverge in two directions. On the one hand
we have a series of species in which the leaf-trace, from
its first starting-point, is double, consisting of two separate
strands, which further subdivide in the cortex or base
of the leaf. At the same time the peripheral strands of
the primary wood are somewhat sharply differentiated.
Such forms have been grouped in the sub-genus Poly-
angium.*
On the other hand there are certain species in which
the central part of the stele has undergone a change:
a pith has begun to develop, the cellular tissue of the
primary wood increasing at the expense of the tracheal
groups. These forms constitute a clear transition to the
next genus, Lyginopteris, and it is proposed to include
them under a third sub-genus, Lyginangium. We will
take the sub-genus Polyangium first.
Three closely allied species are known from the British
Lower Coal-measures, and others, from the Upper Coal-
measures of France,-seem to belong here also.” The
most interesting species is H. tiliaeoides, described by
Williamson in 1887, for the specimens are in many
respects exceptionally well preserved.? The structure of
the primary wood is somewhat more regular than in
H. Gnievit, consisting of a number of fairly definite groups
or packets of tracheides, separated by a network of
cellular tissue. The peripheral xylem-groups are some-
what sharply delimited, and where secondary wood had
developed, it is traversed by large, principal rays,
corresponding to and in connection with the cellular
tracts separating the primary peripheral strands. The
1 D. H. Scott, ‘““ The Heterangiums of the British Coal-measures,”’’
Linnean Society’s Journal, Botany, vol. xliv. 1917.
* Renault, “ Bassin houiller et permien d’Autun et d’Epinac,”’
Flore fossile, ii. pp. 248-260, 1896, and the earlier papers there cited.
3 Williamson, Part xiii., ‘‘ Heterangium tiliaeoides,” etc., Phil.
Trans. Royal Soc. 1887, B; Williamson and Scott, “‘ Further Observa-
tions, etc., Part iii., Lyginodendyron and Heterangium,”’ ibid. vol. 186, B
(1895).
HETERANGIUM 15
centrifugal portion of the primary xylem in these strands
is little developed, the structure approaching the exarch
condition more nearly than in H. Grievit.
To form the trace of each leaf, two perfectly distinct
strands depart from the stele. Thus the leaf-trace, from
its first origin, is |
double. The two
strands subdivide in
passing through the
cortex, and there are
thus four separate
bundles in the petiole.
The pericycle is very
wide and often con-
tains groups of stone-
cells, like those in the
cortical plates. But
the most remarkable
feature of the species
is the great develop-
ment of the phloem,
which in several cases
equals the secondary
wood in thickness.
The rays, where they Fic. 9.— Heterangium tiliaeoides. Radial section
through part of secondary wood and phloem.
pass throu <4 h the x2, secondary wood; tr’, fully developed pitted
: tracheides ; #r, tracheides with pits beginning to
phloem-zone, are di- form; cb, cambium; ph?, secondary phloem ;
lated outwards, like sv, sieve-tubes; sv.p., sieve-plate; 7, phloem-
‘ ray. X 112. Phil. Trans., W. and S. Will.
those of the Lime tree, Coll. 1628.
a fact to which the
species owes its name. The sieve-tubes are often wonder-
fully preserved, the numerous sieve-plates on the radial
walls appearing as clearly as in the tissues of a recent
plant (Fig. 9). This is a rare though not unprecedented
case among fossil plants. The sieve-tubes have very much
the same structure as in recent Cycads. The cortex is
similar to that of the species already considered.
16 STUDIES*IN FOSSIL BOTANY
The adventitious roots of H. tiliaeoides are known ; .
they do not differ essentially from those of H. Grievit, but
appear to be usually tetrarch or pentarch, whereas in that
species triarch structure prevails.
The great feature in which H. tzliaeoides differs from
Eu-heterangium is the compound leaf-trace, the char-
acter of the sub-genus Polyangium. This is even more
Fic. 10.—Heterangium shorense. ‘Transverse section of leaf-base, attached to cortex of stem
v.b., the four vascular bundles ; sc, sclerenchyma delimiting the leaf-base on either side ;
s.p., sclerotic plate. x6. S. Coll. 2787. (G. T. G.)
strikingly shown in another species, H. shorense.1 Here,
as in H. tiliaeoides, the trace is double on first leaving
the stele; in passing through the cortex each strand
divides into two, so that the leaf-base contains four
bundles (Fig. 10); a further subdivision then takes
place, the petiole containing as many as eight bundles
—a wide departure from the simple structure of H.
Grievi. |
The third British representative of the sub-genus
1 This is from Shore, Littleborough, Lancs, while H. tiliaeoides is
a Yorkshire species, from the Halifax Hard Bed.
HETERANGIUM 17
Polyangium, H. Lomaxii,’ agrees in the behaviour of the
leaf-trace with H. tiliaeoides, but is remarkable for the
frequent wide separation of the two bundles of the trace,
owing to the presence of a vertical series of adventitious
roots between them. This species, of which several
forms are known, is also interesting from the fact that
the stem, in one instance, has been observed to branch,
the only case in which branching of the stem has so far
been recorded in the genus Heterangium. The branch
is of small size compared with the parent stem, but
agrees with it essentially in structure.” The stone-cells
of the inner cortex are remarkably well developed in
some specimens of H. Lomaxi1; they form massive
groups, many cells thick, differing from the compara-
tively thin sclerotic plates of H. Grievit.
All the three species just described are characterised,
apart from the compound leaf-trace and polydesmic
petiole, by the well-marked delimitation of the peripheral
xylem-strands, and by the tendency to exarch structure
in the vascular bundles. The former character indicates
a slight departure from the pure protostelic type, owing
to a progressive downward differentiation of the leaf-
trace system. The exarch condition is never completely
attained, for a little primary centrifugal wood always
persists, so far as hitherto observed.
Four species described by Renault from the Upper
Coal-measures of Autun appear to be referable to the
sub-genus Polyangium. Three of them, H. punctatum,
Ren., H. Renault, Brong., and H. Duchartrei, Ren., are
so similar that they may perhaps all be forms of one
species. They have a general resemblance to the British
H. tiliaeoides. Nenault’s fourth species, H. bibractense,
is remarkable for the small size of the primary, and the
great development of the secondary wood; while the
1 From Dulesgate, Lancs. All the known specimens came from a
single coal-ball.
2 Williamson and Scott, /.c. 1895.
18 STUDIES IN FOSSIL BOTANY
former is only from I to I-5 mm. in diameter, the latter
attains a thickness of nearly a centimetre.
It will be noticed that the Polyangium species are
generally of later geological age than those of the simpler,
Eu-heterangium, type. Of the latter, one, H. Grievit, is
Lower Carboniferous, the four Ostrau species are from a
low horizon (Millstone Grit) of the Upper Carboniferous,
while only one species (H. minimum) is as late as our
Lower Coal-measures. On the other hand, the species
referred to Polyangium are all of Lower or Upper Coal-
measure age.
The sub-genus is interesting as showing a marked
advance on the simple organisation which was once
supposed to be characteristic of Heterangium. Poly-
angium, however, does not appear to lead to anything
higher than itself. It presents interesting analogies, as
regards leaf-trace and petiole, with groups, such as
Calamopityeae and Medulloseae, to be later described,
but there is no evidence of any direct evolutionary con-
nection.
It is very different with the third group of species,
to which it is proposed to assign the sub-generic name
Lyginangium, for they appear to lead directly to the
next genus, Lyginopteris. To anticipate a little here,
we may point out that Lyginopteris, in its typical form
(e.g. in a full-sized stem of L. oldhamia), is characterised
by possessing a large pith, the central part of the primary
wood having wholly disappeared, being replaced by
cellular tissue, leaving only the peripheral strands to
represent the original protostele. At the same time the
peripheral xylem-strands are themselves reduced in
number, those only persisting which are either themselves
leaf-traces or are in immediate connection with them.
The forms connecting Heterangium with Lyginopteris
were all discovered by Dr. ' Kubart.'. Heterangium
Andrei is one of the Ostrau species. The stem may
1 Kubart, /.c. 1914.
HETERANGIUM 19
still be called protostelic, for the xylem extends to the
centre, but the more central tracheides are scattered,
the cellular tissue beginning to predominate. The
peripheral xylem-strands are very distinct and few in
number. If we compare a section of H. Andrei with that
of a typical Lyginopteris, such as L. oldhamia, the general
similarity at once strikes the eye ; the resemblance even
extends to the presence of peculiar stalked glands on
stem and petiole. In H. Andrei a single leaf-trace starts
from the stele, divides into two on its outward course,
and subdivides into four on entering the leaf-stalk.
In this species we have a combination of the characters
of Heterangium and Lyginopteris, though the former
are still predominant. In another species, H. inter-
medium, from a different locality (Westphalia) and a
somewhat higher horizon (Middle Coal-measures), Dr.
Kubart finds an even nearer approach to Lyginopteris,
but details are still unpublished.
To complete the story of the transition, we must pass
on at once to the next genus, for there is no real break
in the series.*
LYGINOPTERIS
Lyginopteris heterangioides, Kubart, another of the
Ostrau species, is, in all respects save one, a typical
Lyginopteris. There is an extensive pith around which
the few xylem-strands, only six in number, and all
forming part of the leaf-trace system, are ranged. But
in the middle of the pith a few tracheides are constantly
present, an evident vestige of the central primary wood
of Heterangium, already becoming more and more reduced
in H. Andrei and H. intermedium. As Dr. Kubart, the
discoverer of the transitional forms, says: ‘‘ We have
before us a continuous series, in which the protostele
1 For the sake of continuity the vegetative structure is treated
consecutively. The reproductive organs of the family are described
later (p. 63).
20 STUDIES “IN - FOSSIL BOTANY
slowly becomes a siphonostele.”” The latter, a tubular
stele with a pith, is the form of vascular cylinder char-
acteristic of the higher plants.
We may also look at the transition from a somewhat
different point of view. The protostele, with its solid
axis of primary wood, is clearly a primitive form of
vascular organisation. It is found among the simpler
and more ancient Ferns and Lycopods, throughout the
extinct Palaeozoic group of the Sphenophylls and in
the oldest known phylum, the Devonian Psilophytales.
Where this type of structure prevails, the leaf-traces
(where they exist) play a subordinate part—they are in
connection with the stele, but do not build it up. Now,
in the higher plants, both Gymnosperms and Angio-
sperms, the whole vascular system of the stem has come
to be a leaf-trace system; all the vascular strands of
the stele can be accounted for as the downward pro-.
longations, variously fusing, of the bundles which pass
in from the leaves.
In Eu-heterangium we have the more primitive condi-
tion; the leaf-traces contribute only a subordinate part to
the stele, and when they have once entered it, soon lose
their individuality. In the sub-genus Polyangium, they
show a little more independence, but the central wood per-
sists, and is still predominant. In the sub-genus Lyginan-
gium, while the peripheral strands increase in distinctness
and show a more direct relation to the leaves, the central
xylem begins to dwindle. In Lyginopteris heterangioides
it is reduced to a mere vestige, and the primary wood is
represented almost wholly by the leaf-trace system. In
the rest of the genus the central xylem has disappeared
altogether. It is entirely replaced by pith, and. only
the leaf-traces remain; 1.e. that part of the vascular
system which is in direct communication with the leaves
alone persists. That the rest of the primary xylem
can be dispensed with, is explained by the increasing
development of the secondary wood, which replaces, in
LYGINOPTERIS 2
a more adaptable form, the non-leaf-trace xylem of the
protostele.
Having briefly traced the transition from Helerangium
to Lyginopteris, it will now be most profitable to study
the structure of the latter genus in its type-species,
Lyginopteris oldhamia, Binney, in which the anatomy
of all the organs is known.
L. oldhamia
Lyginopteris oldhamia is a plant of the Lower and
Middle Coal-measures, extremely common in the coal-
balls of Lancashire and Yorkshire, and also occurring in
those of Westphalia at a somewhat higher horizon. It is
quite possible, and even probable, that under the specific
name more than one species is embraced, the name thus
representing a type of structure rather than a single
plant, but the forms included under it have not yet been
specifically discriminated. On the other hand, the species
described by Dr. Kubart from the Ostrau beds seem to
be quite distinct from ours.
Lyginopteris oldhamia was discovered and _ briefly
described by Binney in 1866 under the name Dadoxylon
oldhamium.+ Our full knowledge of its structure is due
to Williamson, who described the stem in 1873, first calling
it Dictyoxylon oldhamium and then placing it in Gourlie’s
genus Lyginodendron, based on cortical impressions,
with which Williamson identified his structural specimens.
It has turned out, however, that Gourlie’s type-specimens
belonged to quite a different group of plants (Lepido-
dendreae) ; his name Lyginodendyon is still used in its
original sense for reticulate cortical impressions, which,
as a rule, have nothing to do with the plant described
1 E. W. Binney, Proc. Lit. and Phil. Soc. Manchester, 1866; E. A.N.
Arber, ‘“‘ Notes on the Binney Collection of Coal-measure Plants, iii.
The type-specimens of Lyginodendron oldhamium (Binney),”’ Proc.
Cambridge Phil, Soc. vol: xi. 1902.
22 STUDIES IN FOSSIL BOTANY
by Binney and Williamson. Hence the name Lygino-
dendron for the latter type has been abandoned, and we
now use the generic name Lyginopteris, proposed by
Potonié in 1899.1
All the vegetative parts of Lyginopteris oldhamuia are
known, not to mention the reproductive organs, which
will be dealt with later. The history of our knowledge
of the species may be said to go back to 1829, when
Brongniart described and figured the external characters
of the foliage in Sphenopteris Hoeninghaust, which there
are strong grounds for identifying with the petrified
specimens of L. oldhamia, discovered nearly forty years
later. The restoration in the frontispiece will serve to
give an idea of ithe general habit of the plant.
The Stem.—The dimensions of the stem are very
variable, the largest specimens having a diameter of
about 4 cm. and the smallest of about 2mm. The stem
is known to have frequently branched, at least in some
forms of the plant. Our description will, in the first
instance, be based on the larger stems, which best show
the structure which we may regard as typical.
In all specimens of L. oldhamia, as in other species
of the genus, there is a well-developed pith, usually of
large size relatively to the stem as a whole (Fig. 11).
Around the pith a number (5—10) of scattered xylem-
strands, belonging to the leaf-trace system, are disposed
inaring. Outside this, in all but the youngest specimens,
we find a zone of secondary wood; then follows the
phloem, secondary and primary. Beyond the phloem
is a well-marked pericycle, usually with a zone of peri-
derm; this completes the stele... We mext reach the
inner cortex, of parenchymatous structure, and then the
very characteristic outer cortex, consisting of a network
of radial fibrous bands, with cellular tissue in the meshes.
In favourable cases a few external layers of cortex, with
1 Potonié, Lehrbuch der Pflanzenpaldontologie, p. 170, Berlin, 1899 ;
Seward, fossil Plants, vol. iii. pp. 36-38, Cambridge, 1917.
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LYGINOPTERIS
24 STUDIES IN FOSS SOTARY
the epidermis, may be preserved. The bases of the
leaves are frequently found in connection with the stem ;
the usual phyllotaxis was 2. In all the tissues of the
stem, from the wood outwards, leaf-traces are met with
on their way out to the leaves.
We will now consider the various tissues more in
detail. The pith consists of a matrix of large, short
cells, among which very characteristic groups of dark,
thick-walled elements are embedded (Fig. 11); these
are known as the “‘sclerotic nests.” The cell-walls are
sometimes extremely thickened and _ stratified. The
cells of each nest are usually ranged in vertical rows,
and the whole body is comparable to one of the plates
of stone-cells in Hetevangium, though the distribution
of the groups is different.
Passing on to the vascular tissues, we find that the
primary wood of the stele consists solely of the isolated
xylem-strands surrounding the pith. Each strand has
mesarch structure, and closely resembles a peripheral
xylem-strand of Hetervangium Grievit (Fig. 6). The
protoxylem lies nearer the outer than the inner edge of
the strand, but is so placed that there is quite an appre-
ciable amount of primary centrifugal xylem (Fig. 13).
Here, as in Heterangium, an island of cellular tissue
adjoins the protoxylem, which is in contact with the
centrifugal part of the strand; the elements of this part
are spiral or scalariform, while those of the centripetal
xylem are pitted (cf. Fig. 7). The pitting is multiseriate,
as in Heterangium, and in the case of the primary
tracheides is present on all the walls alike.
We see, then, that not only has the whole of the central
wood of Heterangium disappeared, having been replaced
by pith, but that only a few of the peripheral xylem-
strands remain, namely, those which are in the most
direct connection with the leaves. But those strands
which still persist are identical with the corresponding
parts of the primary wood of Heterangium. Williamson
LYGINOPTERIS 25
recognised from the first the close affinity of the two
genera, and this has been confirmed by all subsequent
research.
When secondary growth begins, the spaces between
the primary xylem-strands are at once bridged over by
the activity of the interfascicular cambium, so that the
secondary wood forms a practically continuous zone,
interrupted only by the outgoing leaf-traces (Figs. II, 12).
Fic. 12.—Lyginopieris oldhamia. ‘Transverse section of stem (structure as in Fig. 11),
surrounded by a mass of foliage, showing rachis and leaflets cut in various directions.
On the left, the stem is giving off an adventitious root. x 4. From a photograph by
Mr. L. A. Boodle. S. Coll. 636.
It has, however, a lax structure, due to the presence of
numerous, and often wide, medullary rays. As growth
goes on, new rays are added between the old. The
structure of the secondary wood is the same as in Heter-
angium ; the multiseriate bordered pits, of which there
may be as many as seven rows on the wall, are, as a rule,
limited to the radial faces of the tracheides. Where
the preservation is good, it can be seen that the pore of
the pit has the form of an inclined slit. The rays, as
is usually the case, consist of muriform cellular tissue.
26 SPFUDIES IN FOSSIL BOLANY
The cambium itself is often well preserved (Fig. 16).
Where a ray is being formed, the tangential divisions
are few, and the cambial cells are therefore longer in the
radial direction than elsewhere.
In good sections a group of primary phloem can be
clearly recognised opposite each of the primary xylem-
strands (Fig. 16). The cambium adds a considerable
thickness of secondary phloem, distinguished by the
Fic. 13.—Lyginopteris oldhamia. Part of transverse section of stem, showing a primary
xylem-strand, and adjacent tissues. px, protoxylem; ¥%, centripetal primary wood ;
x}, centrifugal primary wood; x*, secondary wood; 7, medullary rays; p, pith; s.s.,
secretory sac. »X 100. Phil. Trans.,W.andS. Will. Coll. 1884.
radial seriation of its elements. It is broken up into
narrow groups by the numerous phloem-rays, and consists
of larger and smaller elements, in tangential layers ; the
former appear to have been the sieve-tubes.
The pericycle, outside the phloem, is a well-marked
zone of short cells, among which many sclerotic nests,
like those of the pith, are embedded. In the outer
layers of the pericycle, a phellogen arises, which forms,
on its outer side, a conspicuous internal periderm (Figs.
14, 16). We have not, however, observed any case in
LYGINOPTERIS 27
which the cortex outside the periderm had been ex-
Fic. 14.—Lyginopteris oldhamia. Part of transverse section of stem, showing a double leaf-
trace, and adjacent tissues. px, protoxylem of bundles; %, centripetal, x1, centri-
fugal, part of xylem; pf!, phloem of leaf-trace; ph?, phloem of stele; s.s., secretory
sacs; pd, periderm. x about 40. Phil. Trans.,W.andS. Will. Coll. 1884.
Oa 4
ard gare
eu
¥
oy
am
ces
2,
ee
e
plangEeria fara Aoxa.
Fic. 15.—Stangeria paradoxa. Part of transverse section of petiole, showing a double bundle
to compare with Fig.14. sc, stone-cell. Other lettering asin Fig. 14. x 95. Froma
drawing by Mr. G. Brebner.
foliated, though the imperfect preservation of the inner
28 SPUDIES IN FOSSIL BOTANY
cortex may perhaps be an indication that it was
beginning to die off.
The inner cortex consists of a large-celled tissue, and
is usually the worst preserved part of the stem. The
outer cortex has a strong mechanical construction, and
was no doubt of much greater importance in supporting
the plant than the loosely built wood. The deep fibrous
bands differ from those of Heterangium in being united,
in the tangential direction, into a regular network, with
the meshes filled with a cellular tissue which becomes
much dilated in stems which have undergone considerable
growth in thickness (Fig. 11). This type of construction
is often called “‘ Dictyoxylon”’ cortex, and is distinguished
from the ‘‘ Sparganum ’’? cortex found in Heterangium,
in which the fibrous strands run parallel and are seldom
connected. Both forms are very common among Palaeo-
zoic plants of various affinities, and the distinction
between them is not always constant. The presence of
a few layers beyond the Dictyoxylon zone has already
been noticed. A conspicuous feature of the external
surface of the plant is the occurrence of large and massive
spines or outgrowths, which are not hairs but deep-
seated emergences. They are also present on the leaves,
-and will be described in connection with these organs.
The Leaf-traces—We have now to consider the course
of the leaf-traces, and the changes of structure which
they exhibit during their passage outwards. We will
first describe the arrangement of the strands as they
appear in a transverse section of the stem (Fig. 11). It
is a very general rule that in the larger stems with which
we are now concerned there are five leaf-traces outside
the wood, in any transverse section. All five may still
lie within the limits of the pericycle, the most external
trace perhaps bulging it outwards. Or this trace may
already be traversing the cortex on its way to enter the
1 These terms are taken from the names of obsolete genera, once
characterised by the features in question.
LYGINOPTERIS 29
base of a leaf. The fact that the traces of five successive
leaves are seen at once, shows that each leaf-trace must
have traversed about five internodes between leaving the
wood and passing out into a leaf. As the traces are all,
or all but one, still within the pericycle, it follows that
the outward course of the trace was at first extremely
gradual, while finally it bent out somewhat sharply, to
pass through the cortex and enter the leaf-base.
. pa
6
yO)
Ab
‘>
Fic. 16.—Lyginopteris oldhamia. Part of transverse section, from outer part of stele. +?,
secondary wood; 7, medullary rays; cb, cambium; ph*, secondary, ph, primary,
phloem; s.s., secretory sac; pd, periderm. X52. Phil. Trans.,W.andS. Will. Coll.
1640,
The circum-medullary xylem-strands already described
are sometimes five in number like the leaf-traces outside
the wood. Usually they are more numerous, some of
the strands having divided to form a pair (Fig. Ir).
Where they are only five they alternate regularly with
the external leaf-traces ; where they are more numerous
the same general arrangement is maintained, each pair
corresponding approximately in position to an undivided
strand.
Strands are often met with in the zone of secondary
30 STUDIES"IN BPOSSIE BOTANY
wood, on their way out from pith to pericycle (Fig. 11, /.t.*).
It is thus manifest that the circum-medullary strands are
of the same nature as the external leaf-traces, represent-
ing them, so far as the xylem is concerned, in the lower
part of their course. As the circum-medullary and the
external strands are continuous, the alternation of the
former with the latter requires explanation. This is
afforded by the comparison of successive transverse
sections, enabling us to follow the exact course of a given
leaf-trace.
We have seen that the phyllotaxis is normally 2. In
a good transverse section we can determine the direc-
tion of the spiral by the relative positions and changes
of structure of the leaf-traces; the outermost leaf-trace
is evidently destined for the next leaf above, the second
outermost for the next higher leaf, and so on, the inner-
most trace thus belonging to the highest leaf of the five.
The direction from the outermost to the next inner trace
(at a divergence from it of 2) will thus be in the ascending
or anodic direction of the leaf-spiral ; conversely, a line
from an inner to the next outer trace will be in the descend-
ing or kathodic direction (see Fig. II).
If we choose any one of the external leaf-traces and
follow its downward course in successive transverse
sections, we find that at a certain point, namely, about
five internodes below its entry into the stem from a leaf,
it begins to pass inwards, through the zone of secondary
wood, leaving its phloem behind.t. The xylem-strand of
the trace soon reaches the edge of the pith, and, con-
tinuing its downward course, bends somewhat in the
kathodic direction, until it meets the circum-medullary
strand, lying in the interval between the trace in question
and the adjacent one on the kathodic side (Fig. 11 and
diagram, Fig. 17). The two strands then unite into one.
Thus every leaf-trace on reaching the margin of the pith
1 This is due simply to the occurrence of secondary thickening
which intercalates secondary wood between the xylem and phloem.
LYGINOPTERIS 31
fuses with the nearest circum-medullary strand in the
kathodic direction. Conversely, if we take a circum-
medullary strand lying midway between two of the
external leaf-traces, and follow it upwards, we find that
it divides into two; the larger of the two daughter-
strands, which is that on the anodic side, curves away
Kath —— —> An
8k (8) dk (5) 2k (2) dk (4.)_ 4
—
Brees é
i Pe
ies
‘\
Hf
Fic. 17.—Lyginopteris oldhamia. Diagram of the course of the leaf-traces, showing the
cylinder of bundles spread out in a vertical plane. The arrows, Kath and An, indicate
the kathodic and anodic directions of the leaf-spiral. Phyllotaxis ?. The dots 1—5 and
1X—5* indicate the points of exit of the leaf-traces; the numbers (1)—(5) at the top, the
orthostichies. 31k—5k mark the reparatory strands on the kathodic side of each leaf-
trace. The bundles belonging to the upper cycle (I—5) are dotted ; those of the lower
cycle (1X—5*) are shown as full lines. The Roman numerals mark the nodes. Cf. the
transverse section, Fig. 11. (G. T. G.)
from the other in the anodic direction and passes out to
become a leaf-trace. The other, namely, the kathodic
branch of the original strand, continues its course straight
up the stem, until the point is reached (five nodes higher)
where it has to divide again and give off another leaf-
trace, lying vertically above the former. The strands
32 STUDIES "IN FOSSIL-BOTANY
which thus divide to give off the successive leaf-traces
may be called the veparatory strands, as they repair the
gaps left by the outgoing traces. In other words, each
reparatory strand constitutes a sympodium, built up of
the bases of successive leaf-traces which always diverge
from the vertical in the anodic direction. (Diagram,
Fig. 17.)
The point at which a reparatory strand divides to give
off a new leaf-trace varies in different specimens, and this
is why the number of circum-medullary strands in a
transverse section varies. For if the division takes place
relatively low down, 7.e. some distance below the point
where the new trace begins to pass out, several of the
strands will be represented by pairs and the total number
may rise to eight or more (see Fig. 11, where three out of
the five circum-medullary strands have divided). This
is usually the case in large stems. If the division only
takes place high up, t.e. just below the emission of a new
trace, the strands as seen in transverse section will either
be all undivided, numbering five only, or one may have
just divided, making six in all.
The significance of these details lies in the proof they
afford that the entire vascular organisation of Lyginopteris
is a leaf-trace system comparable to that of the higher
plants. The special case of L. oldhamia is similar to that
of Iberis, familiar to readers of De Bary’s Comparative
Anatomy, if we allow for the difference in phyllotaxis,
which is ,°, in Zbevis and 2 in our fossil. It is one of the
simplest forms of leaf-trace system in plants with a
spiral arrangement of the leaves, and a single bundle
entering the stele from each leaf.
We have next to consider the changes of structure
which a leaf-trace undergoes in its course, and here it will
be most convenient to follow it from below upwards, 7.e.
from within outwards. Where a xylem-strand diverges
1 De Bary, Comp. Anatomy of the Phanerogams and Ferns, Oxford,
1884, p. 237.
LYGINOPTERIS 33
from its kathodic neighbour and begins to pass out, it
has a single protoxylem-group, which becomes doubled
as it leaves the pith (Figs. 13 and 14). Secondary
thickening affects the outgoing trace, as it does the rest
of the vascular ring, and in all but the youngest stems
we find that the trace, on its way between pith and
pericycle, has an arc of secondary wood and bast on its
outer side (Fig. 11, /.¢.1 and 1.t.2). When it reaches the
pericycle, the zone of secondary wood closes in behind it,
but for a time the trace retains its own arc of secondary
tissue (Fig. 11, /.t.2). This gradually dies out, only the
primary tissues remaining, and at the same time another
change takes place, the trace dividing into two strands,
side by side (Fig. 14). These changes are usually gone
through in about the length of an internode, but occasion-
ally the secondary wood and bast persist for a certain
distance after the bundle has divided.
While the leaf-trace is slowly passing out through the
pericycle, little further change takes place, beyond a
gradual separation of the two-strands. Throughout this
part of its course the structure of the trace remains
collateral, the phloem being limited to the external side
of the xylem.. Ultimately the trace begins to leave the
pericycle, which for a time follows its course by an out-
ward bulge, and then it passes rapidly through the cortex
to enter the leaf-base. In traversing the cortex the two
bundles of the trace are inclined to one another, con-
verging outwards, and each assumes a concentric structure,
the phloem extending all round the xylem. On entering
the base of the leaf the two bundles may wholly or
partially unite, or may remain distinct. In the mean-
‘time their protoxylem-groups have further subdivided,
so that in the leaf-base there are often three groups in
each strand.
The cortical tissues of the stem are continuous with
those of the leaf-base. There is commonly a great
development of sclerotic nests in the axillary region,
>
34 STUDIES TN-POSSIEY BOTANY
whereas in other parts of the stem they are mostly limited
to the pith and pericycle. At a certain level a tangential
band: of thick-walled tissue appears immediately below
the axil and is connected upwards with the Dictyoxylon
cortex on the inner side of the petiole as it becomes free
(Fig. 22). The leaf itself is described below (p. 42).
Young and Small Stems.—So far we have been con-
sidering the structure of a typical, full-grown stem.. We
otten meet with stems of quite normal structure and
dimensions, which are in a young condition, little or no
secondary tissue having as yet been developed. In these
cases there is little. distinction between the circum-
medullary strands and the more external leaf-traces,
for there has been no intercalation of secondary wood
and phloem. In such young stems the radial fibrous ©
bands of the Dictyoxylon cortex are crowded together,
for the cellular tissue between them has not yet under-
gone any dilatation (Fig. 18).
Apart from such examples of merely young stems, we
meet with other cases in which the stem, though mature,
is unusually small, and sometimes has a rather different
structure from the specimens which we have taken as
typical. In extreme cases such stems may be only
about 2mm.in diameter. In some of them the structure
is essentially normal, except that the phyllotaxis appears
to have sometimes been } instead of 2; sclerotic nests
are often absent from the pith. Other small specimens
are more remarkable, in so far that the primary xylem-
strands are to a considerable extent fused laterally, so
as to form a more or less continuous ring round the
pith.
In the smallest stem observed, about 2 mm. in diameter
when complete, the pith is obliterated, and must have
been small originally. There are six circum-medullary
strands close together, but not actually fused, and four
leaf-traces to the exterior. It is probable that the phyllo-
taxis was here of the usual 3 type. Five or six layers of
LYGINOPTERIS 35
secondary wood had been formed, and the structure in
all essentials is typical.
The stem of Lyginopteris oldhamia is now known to
have often been branched, as will be described in the
next section. It is possible that these minute stems
may, in certain cases, represent branches of a high order,
though some of them show the bases of roots, a fact
which seems inconsistent with this interpretation. It
Lt
Fic. 18.—Lyginopteris oldhamia. Transverse section of a very young stem, at the com-
mencement of secondary growth. x, one of the six primary xylem-strands surrounding
the pith, which is not preserved; %*, narrow zone of secondary wood; L.t., leaf-trace
bundles ; c, outer cortex; pet, base of petiole. % 11. Will. Coll. 1144 D. (G. T. G.)
has been suggested? that the specimens with an almost
continuous ring of primary xylem may represent the
basal part of the stem, which has a similar structure in
Osmunda, a fern presenting some anatomical analogies
with the primary condition of Lyginopteris. But at
present we do not possess the data for a positive con-
clusion as to the nature of the exceptionally small speci-
1 Williamson and Scott, 1895, p. 721.
36 STUDIES IN BOsslil Borin
mens; it is possible that several distinct species may
be involved.
Branching of the Stem.—Stems of L. oldhamia bearing
branches were first described by Mr. James Lomax in
1902; up to that time only unbranched specimens had
been met with. Since then a number of ramified stems
have come to light ; two such cases were described by
Miss Brenchley in 1913; they are of great interest, as
showing a number of branch-bearing nodes on the same
axis. For anatomical details the best specimen avail-
able is one of those originally described by Mr. Lomax,
from which a series of twenty-five transverse sections
was prepared by him.’
Miss Brenchley’s conclusions from the ‘ve she
investigated are:
1. That the branches were axillary.
2. That secondary and tertiary as well as wary
branches occurred.
3. That the direction of the phyllotaxis of a branch
was the reverse of that of the axis on which it was borne.
_ 4. That the branching disturbed the phyllotaxis, the
normal divergence of ; being lost in the appendages.’
It is a question whether the axillary position of the
branches was constant. It will be worth while to describe
the relations of branch and stem as shown in the most
perfect specimen (Fig. 19), which may serve as a type
of normal ramification; adventitious branching also
occurred.
The diagrams (Fig. 20, I.-V.) show five transverse
sections selected from the series of twenty-five, and
illustrate the separation of the branch and subsequent
changes. In the lowest section figured (Diagram I.)
the branch (Br) forms a scarcely noticeable protrusion,
chiefly indicated on the stele. Of the five leaf-traces,
1 Now slides 2072- ee in the Scott collection.
2W. E. B renchley, ‘On Branching Specimens of Lyginodendron
oldhamium, Will.,”’ Linnean Society’s Journal—Botany, vol. xli. 1913.
LYGINOPTERIS 37
No. TI is clearly the innermost and No. 5 the outermost.
The traces do not follow the regular =? arrangement,
for, while No. 5 is the first to pass out into a leaf, it is
followed (as shown in still higher sections) by No. 4, the
adjacent trace, the interval thus being } instead of 2. It
will be noticed that the centre line of the branch passes
Fic. 19.—Lyginopteris oldhamia. Transverse section of branching stem. On the left of the
figure is the base of a petiole containing two bundles (/.¢. 5 in Diagrams I. and II., Fig. 20).
The stele of the branch lies on the right of that of themainstem. xX about 4. S. Coll. 2077.
From a photograph by Mr. Tams. © Fig. 20, Diagram II., shows the section nest above this.
midway between the leaf-traces 2 and 3 ; it thus appears
not to have been axillary, for its position does not corre-
spond to that of a leaf, but, considering the irregularity of
the phyllotaxis, this conclusion may be open to some doubt.
The five leaf-traces, in spite of their irregular succes-
sion, appear to form a single cycle belonging to the
main stem. Yet we find that two of them (Nos. 2 and 3)
38 STUDIES IN- FOSSIL Bot Any
pass out with the branch, supplying its first two leaves.
This becomes evident in the second diagram ; the inter-
vening sections leave no doubt as to the identity of
the strands. This fact sufficiently accounts for the dis-
turbance in the phyllotaxis of the parent stem at the
point of branching.
The first two leaves of the branch are thus lateral,
and, judging from the similar phase of the two leaf-
traces, must have been borne almost at the same level.
The third leaf of the branch is abaxial and median, its
leaf-trace starting from the branch-stele (Diagrams III.,
IV., J.t.M). In other words, the first two leaves of the
branch are supplied by traces which pass down into the
main stem, and do not join the stele of the branch until
it has completely fused with that ot the parent axis.
The leaf-trace system of the latter undergoes a corre-
sponding interruption.
Simultaneously with and nearly opposite the branch,
a leaf (supplied by trace 5) is given off from the main
stem (Diagram II.). A second leaf (supplied by trace 4)
is borne at a higher level. In the meantime new leaf-
traces have left the main stele ; the first of these (/.¢.A)
almost corresponds in position with the original trace 3,
while the second (not figured) is on the same radius as
trace 5. Thus the divergence is now 2, and the normal °
phyllotaxis is being restored.
It must be specially noted that the branch receives
a certain number (here five) of circum-medullary xylem-
strands from the main stele, and is thus in direct con-
tinuity with the primary vascular system of the parent
axis. It is this point which distinguishes the normal
from the adventitious branching. Above the separation
of the branch from the stem, numerous roots are given
off from the latter (Diagram V.).
Several cases of adventitious branching have been
observed. The essential characteristic of this form of
branching is that all the primary xylem-strands remain
LYGINOPTERIS
39
Fic. 20.—Lyginopteris oldhamia.
from a series.
Five transverse sections from a branching stem, selected
l.t.1-l.t.5, the original leaf-traces—l.t.2 and 1.t.3 pass out into the branch
Br (see Diagrams II.-V.), and 1.t.5 into a petiole (Diagram II.) ; 1.t.A (Diagrams III.-V.),
new leaf-trace in main stem; /.t.M (Diagrams JII.-V.), new leaf-trace in branch; Rt
(Diagram V.), roots. For full description see text.
Diagram I., S. Coll. 2073; II., 2078;
Lif.,.2083'; 1V., 20873. V., 2090. (G. T. G.)
40 STUDIES IN FOSSIL. BOTANY
in the stele of the present stem ; none enter the stele of
the branch. The latter is thus left without any primary
xylem in its lower part, though the strands may reappear
at a higher level. In such cases the first leaf-traces of
the branch consist principally of secondary xylem. The
structure indicates that the branches in question were
somewhat late formations, perhaps due to some injury
to the stem, and therefore had no share in the primary
organisation of the parent axis.
The fact that for thirty-five years after the discovery
of L. oldhamia no branching specimens were met with
is significant, and may probably be an indication that
the branched habit was limited to certain species included
under the collective name L. oldhamia.
Anomalies of the Stem.—The stem of L. oldhamia is
subject to various anomalous anatomical developments,
due to the appearance of cambium in other than the
normal position. These peculiarities, some of which are
fairly common, are limited to individual stems, or to
parts of the stem, and have no systematic significance.
They are, however, of interest, as showing close analogies
with anomalous structures in the stems of certain recent
Dicotyledons. |
The most frequent anomaly in L. oldhanuia is the
formation of a medullary cambium, usually arising just
inside the primary xylem-strands and producing wood
and bast with inverted orientation, the bast facing the
middle of the pith. The medullary cambium is often
in continuity, through the leaf-gaps, with the normal
cambium, and probably this is usually the case at some
point or other. In extreme instances the wood may
thus become broken up into several distinct masses, each
with its own ring of cambium, forming new secondary
tissues all round it. Hence these isolated masses may
come to simulate so many distinct steles, but this appear-
ance is entirely due to the abnormal extension of the
cambium, and has nothing to do with the primary struc-
LYGINOPTERIS 41
ture. The presence of inverted medullary wood and
phloem finds its analogue, for example, in the recent
Bignoniaceous climber Tecoma, while the splitting up of
the vascular ring into a number of pseudo-steles is
paralleled in Acanthophyllum (Caryophyllaceae) and in
various Sapindaceous lianes.
It occasionally happens that the parenchyma accom-
panying the protoxylem of the primary strands takes
part in the new cambial development, and then the
centripetal part of the primary xylem is carried inwards
into the pith by the secondary growth. An analogous
process has been observed in the recent anomalous
Plumbagineous genus Acantholimon.
In some cases the anomalous extension of the cambium
is not limited to the stele, but affects the out-going leaf-
traces; one or both bundles of the divided trace may
become encircled by a cambium, giving rise to a zone of
secondary tissue, so that here also the whole strand
simulates a stele. When this anomaly coexists with
the medullary peculiarities above described, the stem
may acquire a remarkably complex pseudo-polystelic
structure. In addition, mere groups of sclerotic cells
may become the centres of new rings of secondary xylem
and phloem.
An attempt has been made to correlate these excep-
tional developments in Lyginopteris with the normal
polystely of Medullosa and allied genera, to be described
in a later chapter.t But the two phenomena really have
nothing in common, for the steles of Medullosa are laid
_ down as part of the primary structure of the stem, while
the occasional appearance of stele-like masses in individual
stems of Lyginopteris is entirely a secondary develop-
ment, owing its origin to an unusual distribution of
the cambium, probably called forth, in many cases, as
a response to injury of the stem.
1 W. C. Worsdell, “‘ The Structure and Origin of the Cycadaceae,”’
Ann. of Bot. vol. xx. 1906, pp. 139-143.
42 STUDIES IN POSSI Le BOrTANyY
As Miss Brenchley has pointed out,! a good deal of
medullary wood is frequently formed where a branch is
being given off; she suggests that the anomalous tissue
may help to close up the gap caused by the mass of
xylem passing out to supply the shoot. :
The real importance of the anomalous specimens of
the Lyginopteris stem lies in the demonstration they
afford of the wonderful plasticity which the acquirement
of cambium gives to the anatomical organisation of a
plant. Lyginopteris belonged to an early group of
Seed-plants, which still retained many analogies with a
Cryptogamic stock, yet it already shows, as occasional
peculiarities, several of the anomalies of secondary
structure which are otherwise known only among the
most highly modified Dicotyledons of the present day.
The Leaf.—The best information as to the form and
configuration of the leaf of L. oldhamua is afforded by the
impressions of Sphenopteris Hoeninghausi (Fig. 21); the
evidence of identification is given on p. 56. In sections
of the petrified material the leaf is necessarily met with
in a fragmentary condition; we cannot expect to find
any considerable portions of the frond lying flat in the
plane of section. Yet a vivid idea of the general character
of the foliage can often be gained from such preparations,
and all the main points are shown in them. The frond
was evidently a highly compound one ; all stages in its
ramification, from the main petiole to the ultimate
leaflets, are found. The connection between stem and
petiole is shown in Fig. 22. |
The impressions, as Potonié showed, prove that the
principal rachis of the frond was forked, the dichotomy
occurring at a point above the insertion of the lower
pinnae. Evidence of the bifurcation is also supplied
by the petrified specimens, some of which show, in
1 W. E. Brenchley, /.c. 1913, p. 355.
2 Potonié, ‘‘ Uber einige Carbonfarne,” ii. Jahrbuch d. Kk. Preuss.
Geol. Landesanstalt, Berlin, 1890, p. 16.
LYGINOPTERIS 43
transverse section, the separation of the two equal
vascular bundles destined to enter the two limbs of the
forked rachis. Both the primary pinnae and those of a
Fic. 21.—Sphenopteris Honinghausi (=Lyginopieris oldhamia). Frond, showing the pinna-
tion and the forking of the main rachis. Reduced to 2 nat. size. After Potonié.
From Jahrbuch d. Geolog. Landesanst. und Bergakademie, 1890.
higher order were inserted on the rachis at a wide angle,
approaching a right angle. The ultimate pinnules of the
rachis bore on their slender stalk two alternating series
44 STUDIES IN fOSSIE- BOTANY
of small, somewhat cuneate leaflets, lobed in a varying
degree. The venation of the leaflets is admirably shown
in sections parallel to their surface ; the veins separate
from each other at an acute angle. The leaflets, in their
MY FT
uf)
A
iy!)
RS
/ PF.
ripe y
4, x } y
f
= a |
ARGS Mi i
‘ A
Pe
caaeedll|
ie
Fic. 22.—Lyginopteris oldhamia, Radial section of stem, passing through the base of a
petiole. x*, wood of stem, enclosing pith; pc, pericycle; c, outer cortex ; pet, petiole ;
the vascular bundle extends from the petiole down into the pericycle of the stem;
é, cortical spines. «xX 3%. Will. Coll. 1982. (G. T. G.)
natural condition, are somewhat conchoid, convex above
and concave below (Fig. 24).
Turning now to the more strictly anatomical features,
we find that in the main petiole and rachis the bundle
has the form of a V or a W, with the arms pointing
upwards ; the W form is no doubt a preparation for the
LYGINOPTERIS 45
forking of the bundle. In some cases, however, as we
have seen, the two strands which enter the leaf-base
from the stem remain distinct from the first. In the
main branches of the rachis the V shape of the bundle
is retained (Fig. 23); its structure is always concentric ;
several protoxylem-groups are embedded in the wood
towards the convex (lower) side, which of course corre-
sponds to the outer side of the strand in the stem. The
Fic. 23.—Lyginopteris oldhamia. Transverse section of rachis. x, V-shaped xylem; ph,
phloem, completely surrounding xylem, forming the concentric bundle v.b.; hy, hypo-
derma. Xabout 35. Fromaphotograph. Phil. Trans.,W.andS. Will. Coll. 145.
tracheides are for the most part spiral or scalariform,
but some pitted elements occur in the centripetal (upper)
portion of the xylem. The Dictyoxvlon cortex is continued
from the stem into the petiole and principal branches
of the rachis; the inner cortex contains numerous plates
of stone-cells, not unlike those in the leaf of Heterangium
(Fig. 22). The rachis of the ultimate pinnules, which
immediately bear the leaflets, has a simpler structure ;
the bundle, still concentric, assumes a rounded outline,
the sclerotic plates disappear, the cortical cells are
46 STUDIES IN-FOSSIL; BOTANY
shortened, and the Dictyoxylon zone is reduced to a
single hypodermal layer.
The bundles are given off into the leaflets at an acute
angle, and immediately begin to branch. Both in the
ultimate rachis and in the leaflet itself, each bundle is
enclosed in a conspicuous sheath of relatively large cells.
In the leaflet the bundle at last loses its concentric
structure and becomes collateral ; the xylem may reach
the sheath on the upper side, and the phloem is limited
Fic. 24.—Lyginopteris oldhamia. Vertical section of a leaflet. ep, upper epidermis; hy,
hypoderma; p.p., palisade- parenchyma; s.p., spongy parenchyma; v.b., vascular
bundle; e, spine. ™ about 70. From a photograph. Phil. Trans., W. and S, Will.
Coll. 1196.
to the lower part. A similar change of structure is
familiar in the vascular system of the lamina in the fronds
of recent Ferns.
Where the bundles of the leaflets end, the xylem is
much enlarged, the tracheides becoming wider and at
the same time shorter. It is interesting to recall that
the same peculiarity of the bundle-endings was observed
by Schimper in the leaves of the Mangrove plants of
tropical seashores.1_ The leaflets are relatively thick, with
their lobes incurved towards the lower surface (I*ig. 24).
1A, F. W. Schimper, Die indo-malayische Strandflora, Jena, 1891,
p. 14, Plate iv. Fig, 3.
LYGINOPTERIS 47
Beneath the upper epidermis is a hypodermal layer of
rather thick-walled cells, a feature characteristic of
xerophytic or halophilous plants, and next comes a well-
marked palisade tissue, with cells vertically elongated,
as is usual in this position. Towards the lower surface
the cells of the mesophyll are shorter and less closely
packed, forming the spongy parenchyma. Stomata,
somewhat depressed beneath the surface, are found in
the lower epidermis.
The structural features of the frond of Lyginopteris
are on the whole those which characterise the leaves of
plants inhabiting either a dry situation or one in which
the roots are exposed to salt water.
All parts of the leaf are studded with spines or glands,
to which we will now turn our attention.
The Glandular Spines.—Spines are present on all the
organs of the plant except the roots. The stem, the
petioles, the rachis of all orders, and the leaflets, especi-
ally on their lower surface, are studded with these out-
growths. On the rachis they are remarkably conspicuous,
ranged in long parallel rows. They densely clothe the
youngest branches and leaves, forming a protection to
the bud. Such immature, spine-clad buds, perhaps
arrested in development, are sometimes found in the
axils of the leaves.
The spines are massive, deep-seated organs, and are
therefore not of the nature of hairs. They have no
vascular supply, and fall technically under the head of
“emergences.”’ In extreme cases they may reach a
length of something like 4 of an inch (3 mm.); they
frequently exceed 2 mm., but others are quite short.
The spine is usually flask-shaped, with a broad base
tapering to a narrow neck (Fig. 25), but the form is very
variable.
A well-developed spine consists of a_ thick-walled
epidermis (occasionally showing stomata) overlying a
few layers of fibrous elements, which enclose a core of
48 STUDIES IN FOSSIL BOTANY
thin-walled cellular tissue. A spine is commonly seated
astride of a parenchymatous band of the outer cortex,
the fibrous tissue of the spine joining on to the adjacent
fibrous ribs of the supporting organ and its cellular core
to the parenchyma between (Fig. 32).. In the smaller
spines the epidermis alone has
thickened cell-walls.
It appears that all the spines
terminated, when complete, in a
glandular head. At one time a
distinction was drawn between
spines and glands, but a re-
investigation has shown that
wherever the end of a spine is
completely “preserved, 21g
crowned by a glandular body.
The latter, it is true, has often
perished, perhaps normally, per-
haps as the effect of decay.
The glandular head is a round
or oval body, ranging from I20u
to 400% in diameter. The in-
terior’ is filled -by a mass of
small, angular, or rounded cells,
which no doubt constituted the
secretory tissue. The free outer
rea Saag tems aiee wall is composed of a layer of
the right of thestalkisastoma. thin, tabular cells, the wall
x Ghotcecph’ by te La, becoming thicker at thevemie-s
eae ye Trans. and passing over below into
the outer tissues of the spine
(Fig. 25). In some cases the secretory tissue has more
or less completely broken down, leaving the head nearly
or quite empty (Fig. 32).
The glandular bodies are borne on spines of all sizes,
and also sometimes occur in a sessile position. In some
cases the glandular head is large relatively to the stalk
Fic. 25. — Lyginopteris oldhamia.
Vegetative gland, showing well-
LYGINOPTERIS 49
or spine, in others the reverse is the case. Specially
large glands, often with a comparatively slender stalk,
appear to characterise particular forms of the plant,
possibly distinct species. In such cases, where the gland
is large in proportion to the stalk or actually sessile, one
may suppose that secretion was the sole function of the
organ. But where the spine is well developed and the
glandular body relatively small, it is evident that there
was a double function. The secretory activity may well
have been only transitory, while the spine persisted,
either as a protective organ or perhaps as an aid in
climbing, if such was the habit of the plant.
The glandular spines of Lyginopteris oldhamia have
twice played an important part in the reconstruction of
the plant from its fragmentary remains. The similar
“emergences’’ occurring on stem and leaf assisted
Williamson in recognising his “ Rachiopterts aspera’”’ as
the petiole of Lyginopteris.1 At a later date (1903) it
was by means of the glands on the cupule that the seed
of Lyginopteris was first identified (see p. 63).
In addition to the glands or spines, true hairs, com-
posed of a single row of cells, are also formed.
The Roots—The stem of L. oldhamia bore large
numbers of adventitious roots, once described as a
separate plant, under the name Kaloxylon Hookeri. It
seems that the roots must have been aerial,? for they are
borne on the stem among the bases of the foliage-leaves
and above the insertion of branches (see above, p. 38),
that is, on parts which could scarcely have been near the
base. They also grow out from the stem on all sides
equally ; it is therefore unlikely that the stem was a
creeping one, and indeed its obviously radial organisation
points to a more or less erect habit ; it is, however, not
unlikely that its lower part may have often been sub-
merged under the waters of the swamp.
1 Williamson, /.c., Part xvii. Phil. Trans. Royal Soc. 1890, B, p. 91.
* This suggestion was originally due to Mr. James Lomax.
4
50 STUDIES. IN "FOSSIL BOTANY
The roots branched freely, and many of the rootlets
must, it seems, also have been aerial, for they sometimes
arose from the base of the root, where it had scarcely
emerged from the parent stem (Fig. 26).
The position of the roots on the stem shows no direct
relation to that of the leaves, but there was an indirect
relation, for the primary wood of the roots is commonly
inserted on the xylem-strands round the pith, and we
Fic. 26.—Lyginopteris oldhamia. Part of radial section of stem, showing an adventitious
root, which is so curved as to be seen partly in longitudinal, partly in transverse section.
x*, secondary wood cf stem; pc, pericycle; 0.c., outer cortex; a, connection between
root and wood of stem; 7, root, in transverse section, showing tetrarch structure, and
giving off arootlet. x 9. S. Coll. 466. (G. T. G.)
have seen that the latter alternate with the leaf-traces
(p. 29). The roots are sometimes borne on the stem in
short vertical rows, and often several are inserted at
about the same level (see Fig. 20, Diagram V.). The
connection of a root with the stem is shown in Fig. 26.
The roots are among the best-preserved organs of the
plant, and almost every point in their structure and
development is clear. The main roots reach a diameter
of about 7 mm., while the ultimate rootlets are quite
minute, less than 0-3 mm. in thickness. The rootlets are
LYGINOPTERIS 51
extremely abundant in many coal-balls, penetrating into
all kinds of vegetable debris, and even into each other,
just like the Stigmarian rootlets.
All the larger roots were capable of secondary growth
in thickness, but the finer rootlets usually remained in
the primary condition. We will first consider the struc-
ture of a main root at the stage before secondary thicken-
he
rt
Fic. 27.—Lyginopteris oldhamia. Transverse section of root, somewhat diagrammatic. px,
one of the protoxylem-groups; x, the heptarch primary wood; +x?, secondary wood;
ph, phloem; 1.c., inner cortex; 0.c., outer cortex ; rt, rootlets, opposite two protoxylem-
groups. xX 24. Founded on S. Coll. 448. (G. T. G.)
ing had begun. Sucha root consists of a stele of moderate
size, surrounded by a wide cortex, bounded externally
by a conspicuous peripheral zone, usually two cells thick.
In the principal roots the stele ranges from tetrarch
to octarch structure. The specimen figured is heptarch
(Fig. 27). The structure is perfectly typical; the arms of
the xylem are prominent, each terminating on the outside
in the small elements of the protoxylem, which are seen
52 STUDIES IN FOSSIL. BOTANY
in longitudinal section to be spiral tracheides. The more
central elements of the wood are pitted like those of the
stem. There is no pith, but a certain amount of con-
junctive tissue is present among the tracheides. The
phloem-groups alternate regularly with the protoxylem-
angles of the wood, lying in the depressions between
them. The stele is bounded in the usual way, by a peri-
cycle and endodermis. Beyond the endodermis comes
the broad zone of cortex, consisting of rather large cells,
loosely packed, so as to leave considerable intercellular
spaces between them. Numerous “secretory sacs,”
with dark contents, are scattered through the cortex.
Lastly, we reach the peripheral zone, consisting of two
or three layers of large cells, more resistant than those of
the cortex. This zone has much the appearance of a
velamen, which is quite what one would expect to find
on an aerial root, but no markings on the walls have —
been detected. Nothing exterior to this zone appears
to have existed, so we may regard the outermost layer,
at any rate, as epidermal.
Such is the structure of a young root before secondary
thickening had set in. The cambium was first formed in
the conjunctive tissue lying on the inner side of each of the
phloem-groups, in the intervals between the prominent
protoxylem-angles. Subsequently the isolated secondary
arcs became united, by divisions taking place in the
pericycle outside the protoxylem- groups, so that the
cambium and secondary tissues formed a continuous
but wavy ring, which, as growth proceeded, became
filled out into a circle. In the thickened root
a principal ray lies opposite each protoxylem-angle,
dividing the secondary zone into wedges, corresponding
to the original phloem-masses (Fig. 27). These rays,
however, may become broken up by intercalated rows of
tracheides. It does not appear that the cortex was ever
cut off by periderm. It will be seen that the secondary
growth, like the primary structure, is altogether typical
LYGINOPTERIS 53
and comparable in every respect to that in the root of a
Gymnosperm or Dicotyledon.
The branching of the root is equally normal. The
rootlets arose exactly opposite the protoxylem-strands
of the parent root, and were manifestly endogenous in
origin (Fig. 27).
The finer rootlets FRY. > r
are commonly di- w “
arch. It will be
remembered _ that
van Tieghem
showed that there
is a constant dif-
ference between
Phanerogams and
Vascular Crypto-
gams in the orienta-
tion of the xylem-
plate of a diarch
rootlet; in the
former it is verti-
cal, in the latter
horizontal, with
reference to the
axis of the parent
Fic. 28.— Lyginopteris oldhamia. Tangential section
root. Prof. i Ee: through cortex of small root, bearing a diarch
: rootlet, which is cut transversely. The xylem-plate
Weiss has made the of the rootlet is vertical; it appears as a row of clear
interesting fie cells in the middle of the little stele. x about 200.
5 Manchester Coll., R. 1025, 1. From a photograph by
covery that in Mr. W. Tams.
Lyginopteris, the
plane of the xylem plate of the rootlet is vertical? (as
shown in Fig. 28), so that in this respect, as in the
fructification, Lyginopteris shows itself to have been a
Seed-plant and not a Cryptogam.
1 van Tieghem, Traité de botanique, Paris, 1891, pp. 702, 705.
2 Weiss, ‘“‘ The Root-apex and Young Root of Lyginodendron,’’
Manchester Memoirs, vol. lvii. 1913.
54 SFUDIES IN FOSSIL Bora
Even the smallest rootlets can be identified by means
of the secretory sacs in the cortex and the double peri-
pheral zone. The rootlet has a diarch xylem-plate, with
the phloem-groups on either side ; a single-layered peri-
cycle and endodermis are present. The latter consists
of cells, which generally fit on to those of the cortex
outside, but not to those of the pericycle within. Thus
the endodermis is, as it should be, the innermost layer
of the cortex ; the dark marks on some of its radial cell-
walls may indicate the ‘‘ Casparyan strips.”’ The cortex
was evidently a somewhat lacunar tissue; numerous
secretory sacs are present. The double peripheral layer
is conspicuous ; the cells of the two rows do not corre-
spond, so they may be of diverse morphological origin.
No root-hairs have been observed ; they would probably
be absent in a plant such as Lyginopteris, which almost
certainly lived in a watery habitat.
It is remarkable that, while the structure of the stem
is peculiar and unfamiliar among recent plants, that of
the root is perfectly typical, and indeed might be used to
illustrate the most ordinary features of root-organisation
in the higher plants. This fact bears out the opinion
that the root, in the chief outlines of its structure, is a
conservative organ, which has come down to us with
little change, from very early stages in the evolution of
vascular plants.
Not only are the finest details of the root-structure in
Lyginopteris often well preserved ; there are also several
good examples of the actual apex or growing point of the
root. Such specimens were first discovered by Dr.
Marie Stopes and Mr. Watson, and were more fully
investigated by Prof. F. E. Weiss.? The root-cap is
evident ; a section, which seems to be nearly median,
shows the plerome in the central region as well as the
1 Stopes and Watson, “‘On the Distribution and Origin of Coal-
balls,” etc., Phil. Trans. Royal Soc. Series B, vol. 200, 1908, p. 173.
2 Weiss, /.c. 1913.
LYGINOPTERIS 55
young cortex, further to the outside. The question
whether there was a single apical cell or an initial group
must, however, be left open ; Prof. Weiss inclines to the
former view.
Habit—We have already described the principal
features in the structure of all the vegetative organs of
Lyginopteris oldhamia. We may now attempt a recon-
struction of the plant, so as to gain some idea of its habit,
before going on to consider the subject of the organs of
reproduction (see below, p. 63).
The stem must have been a comparatively slender
one, of great length compared with its diameter. This
appears to be proved by the length of the internodes
(about an inch or so), and by the fact that every piece
of stem shows, on the average, the traces of ten success-
ive leaves (five traces outside the vascular ring and five
or more around the pith). As the great majority of the
specimens show no signs of any approach to the apex or
base, it seems clear that they represent fragments of very
long stems, bearing a large number of leaves. Although
the stem was well constructed mechanically, thanks
principally to the sclerenchymatous network of the outer
cortex, it may be doubted whether an axis of such length
and such slender proportions, bearing numerous leaves
of large size, could have supported itself unaided in the
vertical position. Yet the plant shows complete radial
symmetry, and could not well have been of prostrate
habit. It is not unlikely that Lyginopteris oldhamia was
a climbing plant of the “scrambler ’”’ type, a suggestion
which is confirmed by the presence of spines on the stem,
and on all parts of the compound leaves. These spines
may well have been organs of attachment, enabling the
plant to cling to the trees or shrubs which supported it,
just as we see in the recent Fern Davallia aculeata, where,
however, it is only the frond, and not the stem that climbs.
On the other hand, a comparison has been suggested with
the tall, erect species of Todea, such as T. australis.
56 STUDIES IN FOSSIL BOTANY
The evidence for the identification of the foliage of
our fossil with Sphenopteris Honinghaust is now con-
clusive. The agreement is exact in the venation, form,
and size of the leaflets, and in their conchoid curvature,
in the mode of branching of the rachis, the presence of
spines on all the parts, and the reticulated cortex of the
petiole. Further, casts were figured by Zeiller, which
agree closely with the stem of Lyginopteris, and at the
same time bear the foliage of Sphenopteris Héninghausi.*
The leaves of this species, which are very perfectly pre-
served as impressions, from the same horizon to which the
specimens of Lyginopteris oldhamia belong, were of large
size, and highly compound--tripinnate or more, with
the main rachis forked, as already mentioned (see Fig. 21).
There are various other species of Carboniferous Fern-
fronds of very similar habit, and it is quite possible, as
Zeiller 2 suggested, that all may have belonged to stems
of the Lyginopteris type.
The arrangement of the Sphenopteris leaves on He
Lyginopteris stem, in 2? phyllotaxis, has already been
mentioned, and appears to agree with that of the speci-
mens described by Zeiller. In the drawing *® reproduced
in the Frontispiece, an attempt has been made to give
a restoration of the plant, as it would have appeared in
nature. The slender stem (of which only the lower part
could be included in the figure) is shown somewhat
inclined, to indicate that it was probably supported by
other plants. Its surface bears the characteristic spines,
and shows traces of a reticulated cortical structure.
The arrangement and form of the large, highly compound
leaves are known, from the evidence given above, to be
1 Zeiller, Bassin houiller de Valenciennes, p. 84, Plate vi. Fig. 1, 1886.
See also Kidston, ‘‘ Microsporangia of Pteridospermeae,’”’ Phil. Tvans.
Roy. Soc. B, vol. 198, 1906.
2 Zeiller, ‘“‘ Obs. sur quelques fougéres des dépdts houillers d’Asie
Mineure,”’ Bull. Soc. Bot. de France, vol. xiv. p. 195, 1897.
% Prepared, according to my instructions, by Mr. J. Allen, a skilful
botanical artist.
LYGINOPTERIS 57
essentially true to nature, the lamina of the leaf having
been copied from that of Sphenopteris Honinghaust. The
forking of the main rachis, however, does not come out
in the figure. The position of the branching adventitious
roots on the stem is correct ; some of them were borne
on aerial parts of the stem, as shown in the figure, while
others were, no doubt, entirely buried in the soil. The
drawing was made before the discovery of the branching
of the stem, which we now know to have occurred freely
in many specimens (p. 36).
The pendulous, tufted bodies shown, in Fig. 1 (Fronti-
spiece), on parts of the foliage, are intended to represent
the lobed cupules, discovered by Stur in another species,
and now known to have enclosed the seeds.
LYGINORACHIS
This genus has been suggested by Dr. Kidston for
isolated petioles, showing a structure closely similar to
that of the petiole in Lyginopteris. In the absence of
any further evidence, we cannot refer them with certainty
to that genus, and the new provisional name Lyginorachis
thus serves a useful purpose. Two species are at present
known, both of Lower Carboniferous age.
Lyginorachis Papilio, Kidston
There is a certain amount of evidence for the occurrence
of the genus Lyginopteris in Lower Carboniferous rocks,
the strongest case, perhaps, being that of Calymmatotheca
Stangert, Stur (see p. 71), which was almost certainly
a Lyginopteris. In the absence, hitherto, of any evidence
from Lower Carboniferous specimens showing structure,
considerable interest attaches to a petiole, Lyginorachis
Papilio, discovered by Dr. Kidston in the Calciferous
Sandstones of the Tweed, for its characters are closely
similar to those of a typical Lyginopteris petiole, such as
that of L. oldhamia.
58 STUDIES IN FOSSIL BOTANY
The single specimen was found at Norham Bridge,
on the Tweed, in the Cement Stone group of the Calcifer-
ous Sandstone Series. It has hitherto been undescribed,
and the discoverer kindly permits me to give some account
of the fossil here.
The petiole measures about 8 by 6 mm. in diameter.
In form it is somewhat flattened on one side (no doubt
the upper surface) and convex on the other. It contains
a single, very large vascular bundle, U-shaped in trans-
verse section, with the concavity directed towards the
upper surface. The resemblance to the wings of a butter-
fly suggested the appropriate specific name. The inner
cortex contains sclerotic nests, and the outer zone prob-
ably has a Dictyoxylon structure.
The bundle was no doubt concentric, for such remains
of the phloem as are preserved occur on all sides. The
convex side of the xylem is irregularly indented, but this
appears to be due in part to decay, for the irregularity
varies in degree in different sections. Groups of small
elements, presumably the protoxylem, are embedded in
the wood near its convex side, just as in the petiolar
bundle of Lyginopteris oldhamia. In the present case,
however, they are more numerous than in the Coal-
measure species, the number in L. Papilio being about
ten. A small strand, with its protoxylem directed out-
wards, is being given off from each extremity of the main
bundle, just as in L. oldhamia, where similar strands pass
out from the rachis into the pinnae.
Longitudinal sections show that most of the tracheides
bear multiseriate bordered pits; scalariform elements
are few, and are probably limited to the neighbourhood
of the protoxylem-groups. In the petiole of L. oldhamia
the proportion of scalariform to pitted tracheides is
greater.
The inner cortex consists of a short-celled parenchyma,
in which the sclerotic nests are embedded. The latter
form somewhat flattened groups or plates, transversely
LYGINORACHIS 59
placed, and of no great extent. In all respects the
agreement with the corresponding zone of the petiole in
L. oldhamia is complete.
The outer cortex, so far as can be judged from the
somewhat imperfect tangential sections, 1s of the Dicty-
oxylon type, the fibrous strands forming a_ network,
as in Lyginopteris, and not running parallel, as in
Heterangium.
It will be observed that Lyginorachis Papilio, both
in general anatomical configuration and in the detailed
structure of the various tissues, agrees very closely with
the petiole of a Lyginopteris such as L. oldhamia. The
differences noticed, in the greater number of protoxylem-
groups and the smaller proportion of scalariform
tracheides, appear to be only of specific value. The
agreement with Heterangium is decidedly less close. In
H. Grievii, the only species which is readily comparable,
the form of the bundle in transverse section is much
simpler, the sclerotic nests are in the form of more ex-
tensive flat plates, and the outer cortex is of the
Sparganum, not of the Dictyoxylon type.
It may seem, then, that we should be justified in
referring the fossil to the genus Lyginopteris, as the
petiole of some unknown Lower Carboniferous species.
The genera Lyginopteris and Heterangium, however, are
so closely connected, especially through the intermediate
forms discovered by Dr. Kubart, that we cannot draw
any perfectly certain conclusion from the petiole alone.
It is therefore best to leave the Tweed specimen in the
provisional genus Lyginorachis, but it may safely be
stated that Lyginorachis Papilio has more in common
with the petiole of a Lyginopteris than with that of any
other known genus.
A second species, Lyginorachis Taitiana, Kidston,
from the Carboniferous Limestone Series of Lanarkshire,
and therefore somewhat younger than L. Papilio, differs
from that species in the form of the bundle and some
60 STUDIES IN FOSSIL BOTANY
other details, but is equally suggestive of the petiole
of a Lyginopterts.
Other Species of Lyginopterts
Additional species of the genus have been briefly
recorded by Dr. Kubart, from the Ostrau Beds of Upper
Silesia. While L. lacunosa appears to be essentially of
the L. oldhamia type, others, such as L. tristicha, are
peculiar in so far as the primary xylem-strands are
united to form a more or less continuous ring round the
pith. The ring is enlarged to form a distinct strand at
the points where a leaf-trace is to be given off. In
L. tristicha there are commonly three of these prominent
xylem-strands, in other species more.t' The species with
a fused primary xylem are described as more complex
than those with separate strands, but further details
must await the fuller investigation which Dr. Kubart
is undertaking.
THE ANATOMICAL CHARACTERS: OF THE
LYGINOPTERIDEAE
At present only the two genera, Heterangium and
Lyginopteris, are definitely referred to the Lygino-
pterideae ; the possible relation of Dr. Gordon’s genus
Rhetinangium to the family will be considered in the
next chapter.
Heterangium and Lyginopteris have the following
anatomical points in common :
Mesarch xylem-strands in stem, petiole and rachis.
Leaf-traces collateral in stem, concentric in petiole and rachis,
Normal secondary growth in thickness in stem and root
(apart from individual anomalies in certain stems of
L. oldhamia).
1 Kubart, /.c. 1914; also 1908 and 1911.
LYGINOPTERIDEAE 61
Tracheides (apart from the protoxylem-region) pitted with
multiseriate bordered pits.
Sclerenchyma much developed, both in the form of hypo-
dermal ribs, and of sclerotic plates or nests in the more
internal tissues.
Adventitious roots numerous; the relatively main roots
triarch to polyarch, the rootlets diarch.
As not strictly anatomical characters may be added
the radial symmetry of the stem, with spirally arranged
leaves, and the highly compound foliage, of the Spheno-
pteroid type, where its form is known.
The structure of the stem, as we have seen, ranges
through various intermediate stages, from the protostele
of Heterangium to the eustele! of Lyginopteris oldhamia.
That the latter is an approach to the structure of the
higher Seed-plants is obvious; the discussion of this
relation will be postponed to a later stage, when we have
gathered more data, but at this point a word may
be_ said on the question of the relation of Lygino-
pterideae to the Ferns. Heterangium, assuming that it
bore seeds (p. 80), is the best-authenticated case of a
Seed-plant with a protostele—a remarkable combination
of characters. As has already been mentioned (p. 8),
the stele of Heterangium has certain points in common
with that of the simpler Gleichenias. In lke manner,
the anatomy of Lyginopteris has been compared with
that of Osmunda, and so far as the primary structure of
the stem is concerned, there is no doubt a certain resem-
blance in the ring of collateral, in part mesarch, vascular
bundles.
But such comparisons with recent Ferns are at best
only analogies. Though both Gleicheniaceae and Osmun-
daceae have a fairly long geological history, we may say
with some confidence that neither group as we now
1 Eustele is the late Mr. Brebner’s term for a central cylinder with
a ring of collateral bundles surrounding a pith and surrounded by a
pericycle. It is more precise than siphonostele.
62 STUDIES *INEEFOSSIE BOTANY
know it had come into existence at the time when Heter-
angium and Lyginopteris flourished. The oldest known
Osmundaceae, of Permian age, had a stem-structure
quite different from that of Lyginopteris. It is impossible
to suppose that there was any affinity between the
Lyginopterideae and the late or recent Ferns which we
arbitrarily compare with them. It is more to the purpose
to inquire whether the family shows any relationship,
as indicated by the anatomy, with contemporary groups
of fossil Ferns. The answer must be in the negative.
The classes of Palaeozoic Ferns of which the structure
is known are the Primofilices! and the Psaroni. The
Primofilices include, for anatomical purposes, the Botryo-
pterideae and the Zygopterideae ;? the former have a
simple, solid protostele, the latter a protostele more or
less complicated by the differentiation of an internal
xylem distinct from the outer zone of wood. In neither
family is there any resemblance to the Heterangium type
of protostele, while the leaf-traces throughout are on a
totally different plan from those of the Lyginopterideae.
The Psaroni1, complex solenostelic or polystelic Ferns,
apparently of Marattiaceous affinities, have nothing in
common with Lyginopterideae beyond a certain similarity
in the polyarch roots, a point on which no great stress
can be laid.
There is, in fact, nothing in the anatomical evidence
to indicate a relationship between the Lyginopterideae
and any known family of Palaeozoic Ferns. It is true
that they resemble the Ferns more than any other class
of Vascular Cryptogams, but there is no proof, in the
present state of our knowledge, of any direct genetic
connection between the two groups. For the moment,
the Lyginopterideae, in some anatomical respects the
1 The name given them by the late Dr. Newell Arber, who in-
tended it to designate the Ferns most characteristic of the Primary
Rocks.
* Both families may be classed under the common name Botryo-
pteridaceae. See Vol. I. Chap. IX.
LYGINOPTERIDEAE 03
most primitive known representatives of the Seed-plants,
must stand by themselves.
THE FRUCTIFICATION OF THE LYGINOPTERIDEAE
In considering the important subject of the repro-
ductive organs of the family, it will be best to begin with
Lyginopteris oldhamia, the plant in which we have the
most direct evidence, both for the seeds and the pollen-
sacs.
The Reproduction of Lyginopteris oldhanua
The Seed.—Up to the year 1903 our knowledge of this
type was practically limited to the vegetative organs.
Any previous observations, bearing on the mode of
reproduction, were still of uncertain significance; there
was nothing to show whether Lvginofteris was a Fern
or a seed-bearing plant. Definite and decisive evidence
was first obtained when Prof. F. W. Oliver succeeded in
identifying an unassigned seed as belonging to Lygino-
pteris oldhamia, by means of the glands borne on its
outer envelope. The seed in question had been named
by Williamson (in MS.) Lagenostoma Lomaxi: the genus
Lagenostoma was founded by him, but he had left this
species undescribed.!
Lagenostoma Lomaxi is a barrel-shaped seed, of rather
small size compared with many other Palaeozoic seeds,
the extreme dimensions reaching 5:5 mm. in length by
4:25 mm. in maximum diameter. It is enclosed in an
outer husk or capsule, which completely enveloped the
seed when young (Fig. 29) though it was no doubt open
at maturity (see Fig. 30, from a model). In fortunate
1 Oliver and Scott, ‘‘ On Lagenostoma Lomaxi, the Seed of Lygino-
dendron,” Proc. Roy. Soc. vol. Ixxi. 1903; ‘“‘ On the Structure of the
Palaeozoic Seed Lagenostoma Lomaxi, with a statement of the evidence
upon which it is referred to Lyginodendron,”’ Phil. Trans. Roy. Soc. B,
vol. 197, 1904.
64 STUDIES IN’ POSSE BOTANY.
cases the cupulate seed is found still attached to its stalk
or pedicel: both pedicel and cupule are studded with
Fic. 29.—Lagenostoma Lomaxi. Longitudinal section of a small seed, invested by the lobed
cupule, which bears numerous glands. Micropyle and pollen-chamber well shown ;
chalazal tissue displaced. From a photograph by Mr. Boodle. Oliver and Scott, Phil.
Trans. X about 15. Will. Coll. 1931, A.
Fic, 30.—Restoration of the seed of Lyginopteris (Lagenostoma Lomaxi), from a model by
Mr. H. E. Smedley. The seed is shown surrounded by the open glandular cupule.
the capitate glands by the help of which the relation of
the seed to Lyginopteris was first established (Figs. 29
LAGENOSTOMA 05
and 30). The glands, though occasionally sessile, are
usually borne each on a stout, multicellular stalk. The
cavity of the head is, as a rule, empty, and the whole
structure is identical with that of the well-known glands
on the vegetative organs of Lyginopteris oldhamia, at a
stage when the secretory tissue had perished. (Compare
Fig. 3r from the cupule of Lagenostoma Lomaxi, with
Fic. 31.—Capitate gland on the cupule of Fic. 32.—Capitate gland on the petiole of
Lagenostoma Lomaxi. x 70. Oliver Lyginopteris oldhamia. xX 70. Oliver
and Scott, Phil. Trans. S. Coll. 558. and Scott, Phil. Trans. Univ. College
Coll. M rz, é.
Figs. 31 and 32 from photographs by Mr. Boodle.
Fig. 32 from a petiole of Lyginopteris oldhamua.) No
other fossil plant is known with glands of this kind, and,
considering the close and constant association of the
seed with the stem and foliage of L. oldhamua, we are well
justified in assigning the seed to this plant. The conclu-
sion drawn from the identity of the glands is supported
by further structural evidence, as will be seen below.
The cupule has been compared in its general form
to the husk of a hazel nut, and more especially to the
5
66 STUDIES IN-FOSSIE BOTANY
glandular husk of the Eastern species Corylus Colurna ; it
was ribbed in its lower, gamophyllous part, and divided
into free lobes above (see Figs. 30 and 35). The cupule
was borne on the pedicel immediately below the base of
the seed, which it surrounded without being in any way
attached to it (see diagram, Fig. 34).
The pedicel was traversed by a single vascular strand,
of concentric and mesarch structure. Before entering
the chalaza of the seed this strand gave off a number of
aa, Wom, nt
canoe a ASA QQ ah
tun, WARS eae
i
iy Hh Ny
th | Hy
At h
RM i ba ich
e/a \ yi —
YG Oy iV ty Vly
Ki
bh ww
will \
a! Mh nro
A wn i C
Wyatt yy
R Vag (QUIN
Whe
- it ~ el
A| Hest sa fy
}
Aa\s| he
Fic. 33.—Lagenosioma Lomaxi. Apex of seed in median longitudinal section through micro-
pyle. 7, palisade-layer; otf, outer; if, inner wall of canopy (integument); s, space
between canopy and nucellus; ~.c., cavity of pollen-chamber; 9, its orifice; c.c., central
column of pollen-chamber ; p.g., pollen-grains ; pl, part of nucellus supporting pollen-
chamber; mg, membrane of megaspore. Xx about 50. After Oliver. Univ. College
Coll. R r.
bundles (probably nine or ten) into the cupule; the
cupular bundles were branched and appear to have
been collateral and mesarch. There is, in fact, a detailed
agreement in structure between the strands of the pedicel
and cupule on the one hand and those of the rachis and
leaflet of Lyginopteris,on the other. Thus all the evidence
goes to show that the pedicel and cupule were of a foliar
nature. Multicellular hairs were borne on the young
cupule, as they were on young vegetative parts of
Lyginopterts.
LAGENOSTOMA 67
We now come to the seed itself, which was ortho-
tropous and, broadly speaking, of a Cycadean type ; its
symmetry is perfectly radial (Fig. 35). The single in-
tegument has a somewhat complex structure, and, while
entirely free from the cupule, is completely adherent to the
nucellus,except inthe
apical region (Fig. 34).
The central strand
of the pedicel, after
giving off the cupular
bundles, passes
straight up, and be-
comes the chalazal
bundle of the seed ;
in this region it is
embedded in a mass
of thick-walled
strengthening tissue.
The chalazal bundle
then breaks up into
about nine peripheral
Eecands, which Ay:
traverse the whole ; |
length of the in- ARS
tegument (Figs. 34 Vd
and 3 5). In its FIG. 34.—Lagenostoma Lomaxi. Diagram of seed in
median longitudinal section. c, cupule; v.b., vas-
upper part, where it cular bundles of pedicel, cupule, and integument ;
becomes free from cp; canopy of integument ; #.c., cavity of pollen-
chamber; c.c., central column; o.pc., orifice. A, B,
the nucellus and C, D, planes of the transverse sections in Fig. 35.
¥ ‘ After Oliver.
forms the micropyle,
the integument expands into a chambered “ canopy,” a
ring of nine loculi, separated from each other by thick
partitions, and originally filled by a delicate tissue, which
has usually perished (Fig. 35, A). Into each of these
loculi one of the nine vascular strands of the integument
enters, and there terminates. The canopy, with its
ample vascular supply, probably represents an apparatus
.
>
ey
S
WS
Sw ;
As Af:
yaa ee Par It Par / .
ead La .
—e
tiene he ele o*
anSre ws cecigh
“oe .
68 STUDIES INVPOSSE BOTAN
for water-storage, serving perhaps, as has been suggested,
to provide the necessary liquid for pollination by means
of a ‘“drop-mechanism.”” The outer layer of the in-
tegument has a col-
umnar or palisade-like
structure (Figs. 33 and
36) ; there is some evi-
dence that the secre-
tion of mucilage took
place from this layer,
as is so often the case
with the seeds of living
plants.
As in recent Cycads
and in the Maidenhair
Tree, the free apex aor
the nucellus contained
the pollen-chamber,
a cavity serving for
the reception Of (ile
pollen-grains (cf. Figs.
TIO, IDI, p.°209)9 ue
Lagenostoma, however,
the pollen-chamber is
peculiar and more com-
ms — —
Fic. 35.—Lagenostoma Lomaxi. Diagrammatic trans-
verse sections in the planes A, B, C, and D of
Fig. 34. A (through micropyle) shows pollen-
chamber, canopy of integument and free lobes
of cupule ; B (through body of seed) shows fused
nucellus and integument, with vascular bundles,
and cupule partly divided into lobes; C (through
chalaza) shows central bundle, chalazal tissue,
base of integument, and continuous, furrowed
cupule; D, section of the rachis-like pedicel.
After Oliver.
plex than in the recent
Gymnosperms referred
to; a solid columneat
tissue rises up in the
middle of the cavity,
leaving only a com-
paratively narrow,
annular space, available for the pollen-grains (see Figs. 33,
34, 35, A). The whole pollen-chamber or rather the apical
part of the nucellus containing it, is flask-shaped, and was
called, by Williamson, the lagenostome (flagon-mouth), a
useful name, still employed for this particular type of
LAGENOSTOMA 69
pollen-chamber. The neck projects a little through the
micropyle, as an open tube, and no doubt received the
pollen-grains directly, without their having first to traverse
a micropylar passage (Figs. 33,34). Pollen-grains are found
in the lower part of the cavity of the pollen-chamber ;
it has been suggested that the annular form of the cavity
was correlated with the arrangement of the archegonia.
The pollen-grains themselves appear to have been multi-
cellular, but this point is better shown in other plants
(see Figs. 82, 83, 109, B, pp. 210, 211, 208).
In the interior of the seed the contour of the mega-
spore or embryo-sac can usually be traced (Fig. 33),
but its membrane cannot always be distinguished from
the disorganised tapetal layer of the nucellus. In an
interesting specimen referred to L. Lomaxi and described
by Prof. McLean,’ a large part of the prothallus is excel-
lently preserved, as shown, in approximately transverse
section, in Fig. 36, A. It is retracted from the megaspore-
membrane. The central part of the prothallus (obscure
in the figure) consists of rounded cells; then comes a
broad zone of large, radially elongated elements, and
finally, at the periphery, there is a well-defined layer
of small, squarish cells (see Fig. 36, lower drawing).
The structure agrees closely with that of the prothallus
of recent Gymnosperms, both Cycads and Conifers. The
archegonia have not yet been observed.
The identification of the seed of Lyginopteris oldhamia
afforded, for the first time, the proof that a member
of the ‘“ Cycadofilices’’ was a seed-bearing plant, and
led, as further evidence came in, to the establishment
of the class Pteridospermeae.
The seed, as we have seen, is a remarkably complex
one, already far enough removed from a cryptogamic
megasporangium ; there is indeed little trace of any-
thing primitive about Lagenostoma, except perhaps the
1 R. C. McLean, ‘‘ Two Fossil Prothalli from the Lower Coal-
measures,’ New Phytologist, vol. xi. 1912, p. 3006.
70 STUDIES IN POSSIL* BOTANY
fact that the reception of the pollen was a function of
the nucellus—the sporangial part of the seed or ovule—
and had not been assumed by the integument. This
Fic. 36.—Lagenostoma Lomaxi. A, Transverse section of seed, showing the testa, remains of
nucellus and megaspore-membrane, enclosing the prothallus, the greater part of which
is preserved. » about 18. B, outer tissues of prothallus, enlarged. After R. C.
McLean, 1912. Reproduced from The New Phytologist by kind permission.
is an interesting peculiarity, but whether it was really
primitive is quite an open question. So far as the seed
itself is concerned, there is little to indicate any special
affinity to the Ferns.
LAGENOSTOMA 71
The absence of any trace of an embryo is a negative
character common to all known Palaeozoic seeds, though
there are many instances of the preservation of the
archegonia (see, e.g., Fig. 113, p. 307). Yet the seeds,
as a rule, are evidently mature and not mere ovules.
Neither, considering the frequent presence of pollen-
erains in the pollen-chamber, can we assume that all
the seeds found happened to be barren. It is possible
that, though pollinated, they were not yet fertilised,
the latter process perhaps taking place an appreciable
time after the seeds were shed ; or again, it may be that
a resting stage followed immediately on fertilisation,
before any marked development of the embryo had
started. In any case it appears that the period of rest
came much earlier with reference to the growth of the
embryo than in most of our recent seeds. We find a
relic of the old conditions in recent Cycads, in which
the embryo is often scarcely to be recognised when the
seed is ripe and ready for sowing. On the other hand
the Mesozoic Bennettites was completely modern in this
respect for there the embryo was far advanced, filling
the whole embryo-sac, before the seed was shed (see
e122, Pp. 334)-
Returning to the seed of Lyginopteris oldhamia, we
have seen that the structure of the pedicel and cupule
shows that the seed-bearing organ formed part of a leaf.
Evidence from allied species affords evidence that the
seeds were borne on compound fronds or pinnae, only
differing from the sterile foliage in the suppression of
the laminae of the leaflets, or rather, perhaps, in their
modification to form the cupules.
Other Species
Calymmatotheca Stangert, a fructification of Lower
Carboniferous age, described by Stur in 1877,’ consists
1 PD. Stur, “‘ Die Culmflora der Ostrauer und Waldenburger Schich-
ten,” Abhand. der K. K. Reichsanstalt zu Wien, Band viii. Heft i1.
72 STUDIES “IN "FOSS. SOTANY
of stellate, usually six-rayed bodies, borne, in the original
specimens, on the naked rachis of a fertile frond. They
are indicated in the restoration of Lyginopteris (Fig. I,
Frontispiece). A re-investigation of Stur’s specimens
confirmed his attribution of the fructification to a Spheno-
pteris closely similar to S. Héninghausi (the foliage of
Lyginopterts oldhamia) and also his interpretation of
the stellate bodies as foliaceous indusia, and not groups
of sporangia, as others had conjectured. There is, in
fact, little doubt that these organs are of the same nature
as the cupules of Lyginopteris
oldhamia, but, in Stur’s speci-
mens the seeds had! “been
shed, perhaps prematurely.
In a British specimen of
C. Stangert, from the Carboni-
ferous Limestone Series of
Yorkshire, kindly communi-
cated to me by Dr. Kidston,
Fic. 37.—Lagenostoma Sinclairi. Portion there: is a cupule, in scloge
clarence mtn ving capuete association and possible con-
nection with a frond of the
vegetative form of the species. This cupule is more
closed than in Stur’s examples, and may probably still
contain the seed.
Dr. Newell Arber * described, under the name Lageno-
stoma Sinclairt, seeds preserved as carbonaceous impres-
sions, of Lower Coal-measure age, which, in dimensions
and external characters, agree generally with a Lageno-
stoma of the type of L. Lomax. As in that species each
seed is invested by a lobed cupule (Figs. 37, 38). The
cupulate seeds are borne on the terminations of the finer
branches of a highly compound frond, with reduced
lamina, in all probability of the Sphenopteris form. The
, crenatures at the tip of the ribbed seed suggest the
1 E. A. N. Arber, “‘Some new Species of Lagenostoma, a Type of
Pteridospermous Seed,’’ Proc. Royal Soc. B, vol. Ixxvi. 1905.
LAGENOSTOMA 73
presence of a canopy. While the affinity of the seed
with Lagenostoma is undisputed, the absence of internal
structure has led to the employment of another generic
name (Radiospermum,
Arber ; Lagenospermum,
Nathorst) for seed-impres-
sions of thisnature. There
is some probability, on
grounds of association,
that Lagenostoma Sinclair
may have belonged to the
frond known as Sfheno-
pteris obtusiloba, Brongn.
In Sphenofteris
Dubuissonis, a Lower
Coal-measure species from
Brittany, allied to
S. Héninghausi, Grand’-
Eury observed six-lobed
cupules, in some cases still
containing theseeds, borne
on the ends of long, slender
Fic. 38.—Lagenostoma Sinclairi. Two seeds,
pedicels identical with the enclosed in lobed cupules, and borne ter-
; r : - minally on branches of the rachis. xX 5.
ultimate ramifications of After Arber.
the rachis.*
Other cases of cupulate seeds or cupules attached
to a rachis have since been recorded by Dr. Kidston,
the Abbé A. Carpentier and Dr. Marie C. Stopes.? All
1 C. Grand’Eury, “ Sur les graines de Sphenopieris, etc.,’’ Comptes
vendus, t. 141, p. 812, 1905.
2 R. Kidston, ‘‘ On the Fossil Flora of the Staffordshire Coal-
Fields,’ Part iii. Trans. Royal Soc. Edinburgh, vol. 1. Part 1. 1914,
p. 160; A. Carpentier, “‘ Fructifications et inflorescences du West-
phalien du Nord de la France,’’ Rev. Gén. de Botanique, t. xxiii. 1911 ;
‘Contribution a l’étude du carbonifére du nord de la France,’’ Mém.
de la Soc. géolog. du Nord, Lille, 1913, p. 390. M. C. Stopes, “ The
‘Fern Ledges,’ Carboniferous Flora of St. John, New Brunswick,”’
Canada Dept. of Mines, Mem. 41, 1914, p. 74.
74 STUDIES IN FOSSIL BOTANY
the specimens are preserved in the form of impressions
and in certain instances, as in Dr. Stopes’s Pterispermo-
strobus bifurcatus, we are left in some doubt whether
the fructification was a seed-bearing or pollen-bearing
organ. The clearer examples, however, in which the
seeds are evident, supplement in a satisfactory way the
evidence of the structural specimens, and confirm the
conclusion that the seeds of the Lyginopteris group were
borne on the rachis of the frond. The analogy of the
microsporangiate fructification, described below, estab-
lishes a certain presumption that the fertile rachis may
have formed part of the same frond which elsewhere
bore vegetative leaflets.
The well-known seed Lagenostoma ovoides, described
by Williamson and recently investigated more fully
by Miss Prankerd,1 has the structure very perfectly
preserved. No cupule has been detected with certainty,
but the agreement with L. Lomax: in all the important
characters of the seed itself is so close as to leave no
doubt that it belonged to some plant of the Lyginopteris
type, and very possibly to a species embraced under the
collective name of L. oldhamia. Other seeds, less closely
allied, but of the same general affinity, will be mentioned
below (pp. 80, 84).
The Microsporangia of Lvginopteris
Nothing definite was known of the male fructifica-
tion of Lyginopteris, or indeed of any Pteridosperm,
until Dr. Kidston in 1905 discovered a species of Cvos-
sotheca in organic connection with foliage, which he
identified with that of Sphenofteris Honinghausi, and
therefore with the frond of Lyginopteris oldhamia. The
1 JT, L. Prankerd, ‘‘ On the Structure of the Palaeozoic Seed Lageno-
stoma ovoides, Will.” Linnean Society Journal—Botany, vol. xl. 1912,
D. AOX,
CROSSOTHECA 75
Fic. 39.—Crossotheca Héninghausi (the microsporangiate fructification of Lyginopteris
oldhamia) Fertile pinna, contained in an ironstone nodule. On the ultimate branches
of the rachis are borne the somewhat peltate fertile pinnules, from the under surface of
which the long microsporangia hang down. x 3. Enlarged from a photograph lent by
Dr. R. Kidston, F.R.S.
70 STUDIES IN POSSIE” BOTANY
name employed by Dr. Kidston is Crossotheca Honing-
hausi.*
The genus Crossotheca was founded by Zeiller in 1883,
on a fructification found by him in connection with a
Sphenopieris* (see. Fig: z19,: F, Vol, “Lp. 255)¢ ae
genus is characterised by the arrangement of the sporangia,
hanging from the lower surface of the oval or spathulate
fertile segment, the whole resembling an epaulet with
its fringe. On account of the absence of an annulus
and the appearance of a slight fusion between the
sporangia, Zeiller referred Crossotheca to the Marattiaceae,
a view generally adopted up to the date of Dr. Kidston’s
discovery. In the meantime a number of other species
had been described, some with the Sphenopteroid and
others with the Pecopteroid type of foliage.
Dr. Kidston’s specimens were found in ironstone
nodules from the Dudley Coal-field (Westphalian Series)
(Fig. 39). The specimens are preserved in the form of
casts, but in some cases the cavities are infiltrated with
carbonate of lime and so retain their natural form and
something of the original structure of the organs. Though
most of the fertile specimens bear no sterile pinnules,
in several instances the two forms occur in organic |
connection (see Fig. 40). Dr. Kidston has no doubt
that the foliage is that of Sphenopteris Honinghaust,
and therefore of Lyvginopteris oldhamia.®
1 R. Kidston, ‘‘On the Occurrence of Microsporangia in organic
connection with the foliage of Lyginodendron,” Proc. Royal Soc. B,
vol. Ixxvi. p. 358, 1905; ‘‘On the Microsporangia of the Pterido-
spermeae,’’ Phil. Trans. Royal Soc. B, vol. 198, 1906.
2 R. Zeiller, ‘‘ Fructifications de fougéres du terrain houiller,”’
Ann. Sct. Nat. (Bot.), ser. vi. t. Xvi.
8 Dr. Kidston’s identification was accepted by Zeiller and is gener-
ally admitted. Prof. Chodat in 1908 endeavoured to show that the
true microsporangia of Lyginopteris are identical with the annulate
sporangia described under the name of Ptevidotheca Williamsonii (vol.
1. p. 265). This, however, is a mistake; the leaflets on: which the
Ptevidotheca sporangia are borne are quite different in structure from
those of Lyginopteris. Dr. Gothan, in 1913, expressed doubt as to
the specific identity of Dr. Kidston’s specimens with Sphenopteris
CROSSOTHECA 27
The general structure and arrangement of the fertile
pinnules are shown clearly in lig. 39 from one of Dr.
Kidston’s photographs ; the pinnules are oval in form,
about 2 to 2-5 mm. in length, and borne on stout pedicels,
the mode of insertion rendering them somewhat peltate.
They are rather thick, and each appears to be traversed
by a branched vein. “ Each-pinnule usually bore six,
rarely seven, bilocular microsporangia. They are fusi-
form and end ina sharp point ”’ (Kidston). When young,
the sporangia were convergent, but they opened out
later, assuming the fringe-
like arrangement. A sporan-
gium is about 3 mm. long
and 1:5 mm. in maximum
width, while each of the two
loculi is about 0-5 mm. in
diameter.
No evidence of cohesion
among the sporangia was
found; a bilocular spor-
angium may be interpreted
as a synangium, and Dr.
yy
Fic. 40.—Crossotheca Héninghausi. Fertile
Kidston considers it prob- pinna in connection with sterile pinnae
: - : of Sphenopteris Hoéninghausi (leaf of
able that it has arisen Lyginodendron). xX 2. R.S. Froma
through the coalescence sketch after a photograph lent by Dr.
; Kidston.
of two sporangia (l.c. p.
430). The nature of the preservation in the Dudley
specimens is such as to leave the detailed morphology
somewhat uncertain, but the occurrence of bilocular
sporangia has since been observed in petrified material
also (see Fig. 41). In Cvossotheca Héninghausi the
microspores are still contained in the cavities of the
Héninghausi. See R. Chodat, “‘ Les Ptéridopsides des temps paléo-
zoiques, étude critique,’’ Archives des sci. phys. et nat. t. xxvi. 1908,
p-. 22, Geneva; W. Gothan, “‘ Die oberschlesiche Steinkohlenfiora, I.
Teil, Farne und farnahnliche Gewachse,”’ Abhand. d. K. Preuss. Geol.
Landesanstalt, Neue Folge, Heft 75, 1913, p. 49.
78 STUDIES: TINSrOSSt eb Orainwy
sporangia. Each spore has a distinct triradiate ridge,
indicating tetrahedral arrangement, and the surface of
the outer wall is rough with minute points. The spores
vary from 50u to 70 in diameter.
Dr. Kidston finds that ‘“‘ the cleft by which dehiscence —
took place passed longitudinally down the centre of the
inner face of the microsporangium and thus the micro-
spores of both loculi would be liberated simultaneously.”’
Another species of Crossotheca, named C. Hughesiana
by Dr. Kidston, occurs.in the Dudley nodules; ) fie
fertile pinnules are cordate in form and twice the size
of those of C. Héninghausi, measuring about 5 x 5 mm.
In all other respects, including the bilocular structure
of the microsporangia, there is a close agreement with
the former species. The sterile foliage of C. Hughesiana
is unknown.
Shortly before Dr. Kidston’s discovery of Cvossotheca
Honinghaust, Dr. Margaret Benson had described a
fructification (Lelangium Scottr) with structure preserved,
from the coal-balls of Lancashire, and was inclined to
attribute it to Lyginopteris.1 The sporangia are long
and pointed, somewhat resembling those of Dr. Kidston’s
Crossotheca in shape and size, but they are not bilocular,
and are united in their lower part to form large synangia,
often with as many as eight members.
Dr. Benson described the synangia as borne terminally
on the ultimate ramifications of a rachis, without a limb,
this being a distinctive character of her genus Telangium.
As a matter of fact the synangia in T. Scott: are often
seated on a flat disc or lamina, which may be compared
to a fertile pinnule of Cvossotheca, so that the distinction
between the genera is not always as marked as it appears
at first sight. At present the relation of Telangium
Scotti to Lyginopterts or its allies is doubtful. An interest-
ing point emphasised by Dr. Benson is the resemblance
1 M. Benson, “ Telangium Scotti,” Ann. of Bot. vol. xviii. 1904. A
preliminary note was published two years earlier.
TELANGIUM 79
between the spores of her Yelangium and the pollen-
grains found in the pollen-chamber of Lagenostoma
ovoides.
Other species referred, more or less provisionally,
to Lelangium have been observed, both as impressions
and petrifications ; two of the former, of Lower Carboni-
ferous age, 7. affine and T. bifidum, are attached to the
fronds of definite species of SAhenopteris, while an Upper
Carboniferous species, 7°. nutans, Carpentier, is associated
with Sphenopteris obtusiloba, which it resembles in the
mode of branching of the rachis, the tufts of sporangia
appearing to correspond in position to the tertiary
pinnules of the sterile frond.
Fic. 41.—Telangium, sp. Transverse section of synangium, consisting of two coherent
sporangia, each of which is divided into two loculi, by a partition, p. Xx about 36.
Univ. College Collection, R. 99. (G. T. G.)
As regards the petrified specimens of Telangijim,
which are frequent in the coal-balls of the Lower Coal-
measures, there is no published information except in
the case of 7. Scotti, and the whole subject demands
investigation. The specimen figured, by kind permis-
sion of Prof. Oliver, F.R.S., is provisionally referred to
Telangium ; its interest lies in the fact that it affords
conclusive proof of the occurrence of bilocular sporangia,
as found by Dr. Kidston in his less favourably preserved
specimens of Cvossotheca. The section figured (Fig. 41)
is a transverse one of.a bisporangiate synangium ; the
two sporangia clearly have a common wall where they
1 See Carpentier’s memoirs, cited on p. 73.
So STUDIES “IN FOSSIL SOLAN
joi. Each sporangium is divided into two loculi by a
narrow septum at right angles to the common wall. The
sporangial wall is several cells thick, the outer layer
having conspicuous dark contents; the septa between
the loculi are continuous at either end with sterile tissue
in the interior of the sporangium ; the loculi are filled
with ill-preserved spores. There is no evidence at present
as to the plant to which this fructification belonged.
Other cases of bilocular sporangia have been observed
in the petrified material. It is, however, remarkable
that no petrified Crossotheca, as distinguished from a
Telangium, has yet been identified in association with
Lyginopteris, in the coal-balls.
Dr. Kidston’s discovery that a Crossotheca was borne
on a Sphenopteris of the same type as the frond of
Lyginopteris oldhamia establishes a strong presumption
that the Crossothecas generally, formerly regarded as
Fern-fructifications, constitute the pollen-bearing organs
of Pteridosperms. In bearing their microsporangia on
modified pinnules of the ordinary frond, these plants
show a lower degree of differentiation than any Spermo-
phytes previously known.
Sphaerostoma, the probable seed of Heterangium
Grievit
We have as yet no direct evidence as to the nature
of the seed in any species of Heterangium. A seed,
however, is frequently found in close association with
the stem and foliage of H. Grievit in the Pettycur beds,
and as there is no other plant present to which it is
likely to have belonged, there is a fairly strong pre-
sumption that the two were connected. Attempts,
however, to find actual continuity have proved uncon-
vincing. Sphaerostoma ovale, as this Lower Carboni-
ferous seed is now called, was originally described
by Williamson under the names Conostoma ovale and
SPHAEROSTOMA 81
C. intermedium. The two species are now merged in one,
and Dr. Margaret Benson, to whom we owe a full
investigation of the Pettycur seed, has shown that it is
generically distinct from Conostoma and has founded the
genus Sphaerostoma to receive it."
Sphaerostoma ovale is a seed of the general type of
Lagenostoma, a fact which agrees well with its attribu-
tion to Heterangium, an ally, as we have seen, of Lygino-
pteris. The seed is about 3-5 mm. in length, by 2-2 mm.
in maximum diameter. Dr. Benson’s restoration of the
longitudinal section is reproduced in Fig. 42. In some
of the specimens the seed is found enclosed in a cupule
(Fig. 42, c), a somewhat delicate structure, traversed
by vascular bundles (v.b.1) and surmounting the micro-
pyle. The presence of a cupule is an obvious point of
agreement with the type represented by Lagenostoma
Lomaxi. The cupule has been called an “ outer integu-
ment’’; it is, however, perfectly free from the seed within
(Fig. 42).
The seed is radially symmetrical; the transverse
section is circular in the middle region, becoming some-
what octagonal towards either end. The seed is built
on the same lines as a Lagenostoma, the differences being
in detail. The integument is fused with the nucellus,
except at the upper end, in the region of the micropyle
(Fig. 42, 7). The epidermis of the free surface, whether
external or within the micropyle, is papillate and was
probably mucilaginous. The most conspicuous feature
is the “frill”? (Fig. 42, f), a crest of large, vertically
elongated cells, surrounding the micropyle. Dr. Benson
finds that the frill was not continuous, but was composed
of about eight lobes with furrows between. Within the
1 W. C. Williamson, ‘“ Organisation of Fossil Plants of Coal-
measures,’ Part viii., Phil. Trans. Royal Soc. vol. 167, 1877, p. 244,
Figs. 82-87. M. Benson, “‘ Sphaerostoma ovale (Conostoma ovale et
intermedium, Williamson), a Lowér Carboniferous ovule from Pettycur,
Fifeshire, Scotland,’ Trans. Royal Soc. Edinburgh, vol. 1. Part 1.
1914.
6
82 STUDIES IN FOSSIL BOTANY
epidermis is a mechanical zone of fibres, which at the
chalazal end extends inwards, forming a sheath around
the supply-bundle (ch). The latter enters the seed as
a single strand, which branches repeatedly to form the
RAY
SA
hk
Tic. 42.—Sphaerostoma ovale. Diagrammatic, longitudinal section of seed, in its cupule.
c, cupule; 7, integument; f, frill of integument; p.c., pollen-chamber; c.c., central
column; a, probable position of archegonia ; m, megaspore-membrane ; v.b.', vascular
bundle of cupule; v.b.*, vascular bundle of integument; ch, chalazal strand. After
Dr. Margaret Benson, F.L.S.
vascular system of the integument. In the body of the
seed there are eight, or sometimes nine, bundles ranged
in a ring (v.).”)._ That the vascular system really belongs
to the integument and not to the nucellus is indicated
SPHAEROSTOMA 83
by the fact that the bundles extend up into the canopy,
far above the summit of the nucellus.
Little structure is preserved in the nucellus except
at its free, upper end. Here the outer layer is perfect,
forming the nearly horizontal plinth (to use Prof. Oliver's
term) from which the dome of the pollen-chamber rises
(Fig. 42, p.c.). The form and structure of the pollen-
chamber or lagenostome present the chief distinctions
from the genus Lagenostoma. The low squat dome,
which contains the pollen-chamber of Sphaerostoma, does
not even reach the micropylar passage, and is thus very
different from the long tubular lagenostome of the other
genus, which, as we have seen, extends through the
micropyle to the exterior. A low central column is
present in Sphaerostoma, and this again differs from the
corresponding structure in Lagenostoma, not only in
form but in the fact that the epidermis of the pollen-
chamber wall stretches right over it (Fig. 42, c.c.). Thus
the annular pollen-chamber appears to be closed, but
there is evidence that circumscissile dehiscence took
place, the wall splitting around the edge of the central
column, as is indicated in the diagram. Dr. Benson
supposes that there was a hygroscopic mechanism causing
the wall to erect itself, thus opening the circular crevice,
and then returning to its original position, effecting
closure after the pollen-grains had been admitted. The
epidermis forming the pollen-chamber wall has a different
structure from that which covers the central column
and also from that of the “plinth.” The cells of the
pollen-chamber wall are radially elongated and have their
vertical membranes thickened, the whole thus bearing
some resemblance to a multiseriate annulus. The rest
of the epidermis is formed of ordinary isodiametric cells.
The megaspore membrane is preserved, sometimes
accompanied by disorganised remains of nucellar tissue.
Only doubtful traces of the prothallus have been detected.
The seed is evidently of the Lagenostoma type, and
84 STUDIES IN FOSSIL Botany
there is every probability that it belonged to the closely
associated Heterangium Grievit, though proof is still
lacking. It may be pointed out that in the Lower
Carboniferous Sphaerostoma pollination must have taken
place in the ordinary Gymnospermous fashion, through
the micropyle. This fact casts doubt on the primitive
character of the peculiar mechanism of the later Lageno-
stoma, in which the pollen-chamber reached the exterior
and appears to have received the microspores directly.
Other seeds, probably referable to Lyginopterideae
There are several seeds, of which the structure is well
known, which appear to belong to the Lagenostoma
group, and may therefore be referred with some prob-
ability to the Lyginopterideae. But at present there is
no clue whatever to the particular plants which bore
the seeds, so only a brief notice is called for here.
Perhaps the most remarkable of these isolated seeds
is Physostoma elegans (Lagenostoma ~physoides), first
described by Williamson in 1875 and 1877, and more
recently investigated in detail by Prof. F. W. Oliver.*
This is an Upper Carboniferous seed from the coal-
balls of Lancashire and Yorkshire; an imperfectly pre-
served specimen from the Lower Carboniferous of Petty-
cur has been provisionally referred to the same genus
by Dr. Gordon.
Physostoma elegans is a Sree slender seed about
6 mm. in length by 2-25 mm. in maximum diameter.
Its most remarkable feature is the structure of the micro-
pylar region, for here the integument, instead of forming
a continuous tube, is divided up into a circlet of about
ten free tentacles (Fig. 43) surrounding and surmounting
1 Williamson, ‘‘ On the Organisation of the Fossil Plants of the
‘ Coal-measures,”’ Part viii., Phil. Trans. Royal Soc. vol. 167, 1877, p.
241; F. W. Oliver, “‘ On Physostoma elegans, Williamson,: an archaic
type of seed from the Palaeozoic Rocks,’’ Ann. of Bot. vol. xxiii. 1909.
PHYSOSTOMA 85
In the body of the seed, where
the apex of the nucellus.
the integument is continuous, the tentacles are repre-
sented by ribs (Fig. 43, B); each rib and tentacle is
The external
traversed by a delicate vascular bundle.
surface of ribs and tentacles is clothed by a dense growth
AN
WWars
Iv
AW
A
NY
NY
AWAY
9
989
Mi
|
Q :
18)
Cy
SSS
wy Z
GMM, thy
Zz.
MOY
MAA
WOOO
QUAN
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WAS
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SS
AS
Ss
Diagrammatic sections of seed. The longitudinal section
Fic. 43.—Physostoma elegans.
shows the integument with the quill-like hairs, and the vascular bundles; the nucellus
and megaspore. /.c., pollen-chamber, containing pollen-grains. The transverse sections
are taken at the levels B and C, B through the body of the seed, and C through the
A, chalaza, D, micropylar region. After Prof. F. W. Oliver, F.R.S.
pollen-chamber.
of large, overlapping, quill-like unicellular hairs, prob-
ably mucilaginous ; the seed thus has a highly peculiar
and characteristic appearance.
The nucellus is completely fused to the integument,
except in the upper region ; its tissues in the body of
the seed are preserved and include a secretory layer
At the free end
and a tapetum next the embryo-sac.
86 STUDIES IN FOSSIE BOTs Y.
is the pollen-chamber, which has an unusual form, owing
to its floor being bulged in by the growth of the apex
of the megaspore (Fig. 43). The most interesting feature
of the pollen-chamber, however, is the great number
of pollen-grains which it contains. In two successive
sections of the same pollen-chamber nearly fifty pollen-
grains were counted, so that the total number present
must have been very considerable. Their abundance has
raised questions as to the mode of pollination, whether
anemophilous or entomophilous, questions which un-
fortunately cannot be answered. The pollen-grains have
a multicellular structure, and in some cases had emitted
bodies which have been interpreted as spermatozoids.
The megaspore-membrane appears to have been thin ;
some remains of the prothallus have been observed.
The ring of free tentacles, replacing the micropylar
tube, has been regarded as a primitive character; the
chambers of the canopy in Lagenostoma may be con-
sidered as representing the tentacles in a fused and
possibly more advanced condition. In any case, it is
probable that the tentacles, though distinct, fitted closely
together with the aid of their interlocking hairs, and
thus formed an efficient corridor down which the micro-
spores were guided to their goal.
While Phvsostoma is regarded as a relatively primitive
type of seed, Conostoma as now understood seems to
have been an advanced genus of the group. For the
somewhat complicated structure reference must be made
to the original descriptions. Our present detailed know-
ledge is due to the elaborate investigations of Oliver
and Salisbury.1. As shown by the adherent integument,
the lagenostome and the canopy, Conostoma clearly
belongs to the Lagenostomales, of which together with
1 “On the Structure and the Affinities of the Palaeozoic Seeds of
the Conostoma group,” Ann. of Bot. vol. xxv. 1911. A valuable general
account of this genus and of other Palaeozoic seeds will be found in
Seward’s Fossil Plants, vol. iii. 1917, chaps. xxix. to xxxi, and chap.
XXXV.
CONOSTOMA. GNETOPSIS 87
_Gnetopsis, to be mentioned immediately, it seems to
represent the highest development. The cylindrical or
slightly flattened seeds are ribbed or angular, the in-
tegument somewhat lobed at the apex. The vascular
strands are equal to or fewer than the ribs or angles ;
the loculi of the canopy are nearly obliterated and equal
the vascular bundles in number; the epidermis was
mucilaginous. ;
The lagenostome is a minute, goblet-shaped organ,
fitting exactly into the base of the highly developed
micropyle. A cavity was formed in the plinth or upper
part of the nucellus, and it is in this lower cavity and
not in the lagenostome itself that the pollen-grains are
found. Two species are described, C. oblongum, William-
son, from the English coal-balls, and C. anglo-germanicum,
Oliver and Salisbury, which also occurs in the West-
phalian and Rhenish petrifications of Langendreer and
Duisburg.
In the second edition of this book the opinion was
expressed that Renault’s seed Gnetopsis elliptica was
probably related to Lagenostoma and the Lyginopterideae.
This view has now been fully confirmed by the investiga-
tions of Oliver and Salisbury. In the fructification
described by Renault ! (referred by him to the Gnetaceae)
four seeds (two of which are often abortive) are enclosed
within a common envelope or cupule, consisting of two
partly fused bracts, each of which is divided into about
five teeth above and traversed by the same number of
vascular bundles. The seeds or ovules are small (2-5 mm.
long) and have a somewhat complex structure, which
has been shown by Oliver and Salisbury to agree closely
with that of Conostoma. The integument of Guetopsis
is traversed by four vascular strands as in C. anglo-
germanicum, while thé seed is slightly flattened as in
C. oblongum. The lacunar region of the integument
1 Cours de bot. fossile, t. iv. 1885, p. 179; Pl. xx. Pl. xxi. Figs.
1-6, Pl. xxii. Figs. 2-4.
88 STUDIES IN FOSSIL BOTANY
near its apex, interpreted by Renault as a floating ap-
paratus for transport by water, is shown by Oliver and
Salisbury to correspond to the mucilaginous layer of
Conostoma. On the other hand the apical plumes sur-
rounding the micropyle, a conspicuous feature of Renault's
genus, have not been found in Conostoma. Renault
thought that they served first for guiding the pollen-
grains ‘to the micropyle and subsequently for effecting
dissemination by the wind.
The lagenostome and plinth-chamber (the latter
usually containing the pollen-grains) are essentially the
same in both genera; the division of the lagenostome
wall into lobes, observed in most specimens of Guetopsis,
is regarded by Oliver and Salisbury merely as an effect
of maceration.
The common cupule, enclosing several seeds, is a
striking feature which has so far only been observed in
Gnetopsis. Nothing certain is known of a cupule in
Conostoma. Oliver and Salisbury, however, point out
that the hairs lining the cupule of Guetopsis closely
resemble those found, chiefly at an early stage, on the
cupule of Lagenostoma Lomaxi. In Gnetopsis elliptica
the prothallus, with indications of the archegonia, is
preserved in several specimens.
Some other species referred to Gnetopsis have been
described. One of them, G. anglica, Kidston, with the
micropylar appendages more than 2 cm. long, is described
from the middle Coal-measures of Barnsley, Yorks.
The genus is of great interest, especially from the
light it throws on the nature of the cupule, which here,
at any rate, cannot be interpreted as an outer integument.
Renault called it an ovary.
AFFINITIES OF THE LYGINOPTERIDEAE
The anatomical characters of the family have already
been briefly discussed (p. 60), with special reference to
AFFINITIES OF LYGINOPTERIDEAE 89
the relation to Ferns. We found that this relation
was to a great extent a matter of analogy; while the
Lyginopterideae undoubtedly have more in common
with the Ferns than with any other Cryptogamic phylum,
there is no proof of genetic connection with any known
group recognised as Ferns. In fact, the early Seed-
plants, of which the Lyginopterideae are one family,
may, for all we know, be as ancient as the Ferns them-
selves. The most we can assume is a common ancestry
as yet unknown.
Now that we have considered such evidence as we
possess regarding the reproductive methods of the family,
we may take a more general view of its characters.
The seed clearly indicates affinity with Cycadophyta,
though probably not a close one with the existing Cyca-
daceae. The adherent integument, its vascular system,
and the pollen-chamber are all Cycadophytic characters.
While the definite attribution of the seed to a parti-
cular plant is still practically limited to the one case of
Lyginopteris oldhamia, there can be no reasonable doubt
that all the seeds grouped as Lagenostomales belonged
to the same family of plants, Sphaerostoma probably
being the seed of Heterangium. There is a considerable
variety among the seeds in question, but it cannot be
said that any of them are markedly primitive, or show
much trace of the Cryptogamic megasporangium from
which we assume that the seed was ultimately derived.
In certain cases a remote analogy between the lageno-
stome-wall and a multiseriate annulus has been detected,
but that is all. Any further consideration of the morpho-
logy of the seed may best be deferred till other types
have been dealt with.
As regards the pollen-bearing organs our knowledge
is still very limited. On the basis of Dr. Kidston’s
observations, we may be prepared to find that the Crosso-
thecas generally were the male fructifications of the
Lyginopterideae, though direct evidence is still confined
go STUDIES IN FOSSIL BSrany
to a single case. As the bodies in question were formerly
accepted as sporangial fructifications of Marattiaceae,
their transference to Lyginopterideae has been regarded
as indicating a certain affinity between the two families,
and thus between Ferns and Pteridosperms. If indeed
we might take the bilocular microsporangia of Cvosso-
theca Honinghaust as typical, the structure would be
very different from anything known in Marattiaceae or
other Ferns. It is, however, probable that synangia such
as those of Telangiwm Scotti, in which the sporangia are
unilocular, may also have belonged to Lyginopterideae ;
and in that case an analogy with Scolecopteris would
be evident; at present, however, our knowledge is too
imperfect to justify further speculation.
Where the foliage of the Lyginopterideae is known,
it is of the Sphenopteris form. If, however, we may
take the Crossotheca type of microsporangiate organ as
characteristic, the family was not limited to Spheno-
pteroid foliage, for various species of Crossotheca are known
to have been borne on Pecopteroid fronds. Three such
species are enumerated by Dr. Kidston,’ besides two
other Pecopterids which Prof. Zeiller regarded as prob-
ably belonging to Crcssotheca. One of the latter, Peco-
bteris exigua, is of special interest, as the structure of the
synangia is known and bears a considerable resemblance
to that of Telangium Scotti.”
Anatomically, Lyginopteris, as is well known, shows
a certain relation to the Cycads. The primary bundles
are isolated from one another and are disposed round
a large pith. The whole organisation of the vascular
zone, both primary and secondary, is, broadly speaking,
what that of a Cycad would be if the mesarch structure
of the foliar bundles were continued downwards from
the petiole into the stem (see above, p. 27, Figs. 14
and 15). We now know that this actually occurs in
1 ‘* The Microsporangia of the Pteridospermeae,”’ /.c. p. 432.
2 B. Renault, Cours de bot. fossile, t. iii. Pl. xix. Figs. 13-18.
AFFINITIES OF LYGINOPTERIDEAE gI
certain Cycadean peduncles, which are themselves portions
of the stem. The validity of a comparison between the
mesarch xylem of a Lyginopteris and that of a Cycad
has, however, been disputed by Prof. Chodat ; he points
out, quite correctly, that in the Cycadean foliar bundle
the protoxylem is in connection with the centripetal
xylem, while in Lyginopterts (and the same applies to
Heterangium) it abuts on the centrifugal portion. This
involves a different order of development of the meta-
xylem elements in the two cases. In Cycads the first
development is inwards from the protoxylem, to form
the centripetal wood; the centrifugal portion being
added later. In Lyginopteris, on the contrary, it may
be assumed that differentiation, starting from the proto-
xylem, first extended to the centrifugal metaxylem, sub-
sequently spreading round on both sides, to form the
centripetal portion. This is confirmed by the fact that
spiral and scalariform tracheides form the centrifugal
xylem (7.e. its primary part), while those of the centri-
petal wood present the definitive pitted structure. Prof.
Chodat therefore regards the Lyginopteris bundle as
forming a “closed divergent ’’ (Bertrand and Cornaille) of
a purely Filicinean type, as in Osmunda, and as quite
unrelated to the mesarch bundle of the Cycadean leaf.
There is no doubt that Chodat has called attention
to what, on the whole, is a real distinction. It is not,
however, quite constant. Thus in the mesarch bundles
occurring in the peduncle of some Cycads the protoxylem
is usually connected with the centrifugal part of the wood ;
in some foliar strands it is in contact with both parts.?
Mr. A. S. Marsh found that near the base of the
petiole in Stangeria there is some primary centrifugal
xylem in contact with the protoxylem, and internal to:
1 R. Chodat, “‘ Les Ptéridopsides des temps paléozoiques,”’ Archives
des sci. phys. et nat., Geneva, t. xxvi. 1908, pp. I0-20,
2 Scott, “‘ Anatomical characters presented by the Peduncle of
Cycadaceae,’”’ Ann. of Bot. vol. xi. 1897, p. 399.
Q2 SEUDIES IN FOSSIV Bartany
the secondary portion.’ For the most part, however,
and sometimes wholly, the centrifugal xylem of the
Cycadean bundle is no doubt secondary, as Dr. Le Goc
has rightly pointed out,’ criticising a former view of my
own. It is probably on this fact that the distinction
emphasised by Prof. Chodat depends. Wherever second-
ary growth takes place, there is always a tendency for
any primary centrifugal wood to become merged in the
secondary. The first-formed elements will then neces-
sarily belong to the only primary portion which remains
—the centripetal xylem.
In Poroxylon, with a stem-structure much like that
of Lyginopteris, the xylem-strands have become exarch,
the protoxylem thus being in connection with the centri-
petal wood, while all the centrifugal part is secondary.®
This case seems to be quite parallel to that of the foliar
bundles of Cycads.
Prof. Chodat’s distinction is an interesting one, but
a transition from one type to the other can quite well
be traced. Taking the seeds into consideration, it seems
that a certain affinity between Lyginopterideae and
Cycads must be admitted, though it is improbable that
the two groups have any direct genetic relation.
Our knowledge of the Lyginopterideae is still too
fragmentary for it to be possible to draw up the essential
characters of the family. The following points may,
however, ‘be mentioned, as likely to occur in plants of
this relationship :
Leaves filicoid (Sphenopteroid or Pecopteroid).
Stem monostelic; leaf-trace single or double, sometimes
undergoing further divisions ; vascular bundles collateral
in stem, becoming concentric in leaf-trace. Xylem
mesarch.
1 A. S. Marsh, ‘“‘ Notes on the anatomy of Stangeria paradoxa,”’
New Phytologist, vol. xiii. 1914, p. 18.
2M. J. Le Goc, ‘‘ Observations on the centripetal and centrifugal
xylems in the petiole of Cycads,’”’ Ann. of Bot. vol. xxviil. 1914, p. 183.
8 See p. 247, Fig. 90.
AFFINITIES OF LYGINOPTERIDEAE 93
Reproductive organs borne on somewhat modified pinnae of
the frond,
Microsporangiate organs of the Crossotheca or Telangium type.
Seeds with radial symmetry, of Cycadean type, enclosed in a
cupule. Integument adherent to nucellus, with a single
vascular system. Pollen-chamber (lagenostome) present.
The relations of the Lyginopterideae to other groups
will be further discussed at a later stage.
CHATTER i
PTERIDOSPERMEAE—continued
Rhetinangieae ; Megaloxyleae ; Calamopityeae ;
Stenomyeleae ; Protopitveae ; Cladoxyleae
WE now go on to consider a series of families, some of
which show a decided affinity with Lyginopterideae,
while others are of altogether doubtful position. In
none of them is there, as yet, any evidence as to the
fructification ; they are included under Pteridosperms
solely on the ground of anatomical characters. In the
following chapter we shall return to groups that are
known to have borne seeds, and are therefore Pterido-
sperms, in the strict sense.
In the last edition of this book, Potonié’s name
‘“‘ Cycadofilices ’? was retained for families only known
anatomically, while the newer name Pteridosperms was
restricted to those groups in which there was some
evidence, however partial, for reproduction by seeds.
The distinction, however, is in no way a natural one,
being based merely on our ignorance, and has proved
impossible to carry out in practice. It has therefore
been decided to employ the name Pteridospermeae in
the widest sense, to embrace the whole plexus of Palaeo-
zoic plants which show in their structure an analogy
with Ferns on the one hand, and an approach to Gymno-
sperms on the other. Within this plexus we know that
the seed-habit existed in members of two families (the
4
RHETINANGIUM 95
Lyginopterideae and the Medulloseae),’ widely diverse
in anatomical respects, as well as in other groups of
which the anatomy is unknown. There is thus evidence
that reproduction by seeds was widespread among [ern-
like plants of Palaeozoic age, and there is a certain
presumption, though of very unequal strength, that it
may have extended to all the families in question. These
considerations may justify the provisional use of the
class-name Pteridospermeae ? for the whole series.
The families described in the present chapter follow
most naturally on the Lyginopterideae. We begin with
a type which has much in common with Heterangium.
RHETINANGIEAE
Rhetinangium, Gordon
The only species, R. Arberi, was discovered by Dr.
W. T. Gordon in the Pettycur Beds of the Calciferous
Sandstone Series. It is thus of Lower Carboniferous
age, the contemporary and associate of Heterangium
Grievii. The two excellently preserved specimens have
been fully described by the discoverer.*
One of the fragments was as much as Io inches long :
the stem was presumably a tall one, perhaps of scrambling
habit, as Dr. Gordon suggests.
In its more obvious anatomical features the stem
is like that of a large Heterangium (Fig. 44) and the size
is about the same, the diameter being approximately
2cm. The central cylinder is a protostele, the primary
1 See.Chapter ITI.
2 The name Cycadofilices is also still employed as a synonym for
Pteridospermeae, as for example by Dr. Lotsy, in his well-known
Botanische Stammesgeschichte. This use of the name is quite unob-
jectionable, except, perhaps, on the ground that not all Pteridosperms
show an affinity to Cycads.
3 Gordon, “ On Rhetinangium Arberi, a new Genus of Cycadofilices
from the Calciferous Sandstone Series,’’ Trans. Royal Soc. Edinburgh,
vol. xlviii. Part iv. Ig1t2.
96 STUDIES IN FOSSIL BOTANY
wood forming a solid mass, consisting of groups of
tracheides in a network of cellular tissue, as in Heterangium
(Fig. 45). This is surrounded by a zone of secondary
wood and bast. The cortex has a strong mechanical
construction, with radially arranged fibrous bands of
great depth. Perhaps
the» most) striae
feature, if the section
happens to pass through
a node, is the enormous
size of the leaf - base,
almost equalling that
of the whole stem (Fig.
44). The arrangement
of the leaves was spiral,
but the phyllotaxis has
not been determined.
So far, however, no
fundamental difference
from the Heterangium
type of structure strikes
the eye. The individual
packets of tracheides
are, itis true, somewhat
larger in Ihetinangium,
and the _ intervening
Fic. 44.—Rhetinangium Arberi. Transverse sec. tracts of cellular tissue
tion of stem and petiole-base. The stem is somewhat broader, but
above: the enlarged petiole- base below.
x 2:3. From W. T. Gordon. these are trifling distinc-
tions. The tracheides
are just like those of Lyginopterideae, for they are long
elements with numerous rows of bordered pits on their
walls. The xylem-parenchyma and other cellular tissues
of the stem contain numbers of elongated secretory sacs
with dark contents and also shorter cells of a similar
nature, but such differentiated elements are frequent in
some species of Helerangium.
RHETINANGIUM 97
It is when we come to examine the outer border of
the primary wood that the first great difference from
Heterangium reveals itself. In Rhetinangium the peri-
pheral strands of xylem are not mesarch but exarch,
the small elements of the protoxylem lying on the extreme
outside of each strand, adjacent to the secondary wood.
Longitudinal sections show that the smallest tracheides
are spiral.
Fic. 45.—Rhetinangium Arberi. Transverse section of stele and adjacent tissues, showing
—s
primary and secondary wood, and inner and outer cortex. At three points leaf-traces
are passing out from the stele. x 8. From W. T. Gordon.
The pericycle, not always so sharply defined as in
Heterangium,' is a delicate tissue, in which the ‘‘secretory
sacs ’ are especially abundant. The cortex, in its inner
part, consists of a uniform tissue of short, rather thick-
walled cells: the sclerotic plates, so characteristic of
Heterangium, are absent. The outer cortex, with its
1 Dr. Gordon does not distinguish between pericycle and inner
cortex. From the analogy of the Lyginopterideae it seems preferable
to regard the whole thin-walled zone of tissue as pericycle.
“I
98 STUDIES. IN’ FOSSIL Sera
beautiful mechanical! system of strong, fibrous bands of
great radial depth, far exceeds in its development any-
thing that we find in Heterangium and is even more
elaborate than in Lyginopteris; it rather recalls the
corresponding region in the stem and leaf-stalk of the
Medulloseae, to be described in Chapter III. The fibrous
strands, viewed tangentially, unite with one another
at long intervals, forming a narrow-meshed network :
they are accompanied by long secretory sacs, and the
tissue between them is often dilated.
We have next to consider the leaf-trace and petiole.
The leaf-trace is the most characteristic feature of the
genus, and appears to be unlike that of any other plant
known. Three traces, at different stages of emission,
are usually seen in the transverse section (Fig. 45). The
trace, from its first differentiation, includes several of the
peripheral xylem-strands of the stele, and increases in
complexity as it passes outwards. An example is shown
in Fig. 46, where it is just separating from the wood.
The trace consists, as regards its xylem, of a number
of tracheal strands united by xylem-parenchyma, and
irregularly fusing on the inner side to form U-shaped
masses. The whole thus has a complex, corrugated
form, as seen in transverse section. The protoxylem-
groups are numerous (as many as nine or ten in some Cases)
and are placed at the extreme outer edge of the xylem-
strands constituting the massive trace (Fig. 46). Thus
the structure of the leaf-trace, like that of the stelar
xylem, is exarch. It has no secondary tissues of its
own.
The complex trace never breaks up into separate
bundles ; it passes out, with little change, into the leaf-
base and petiole, and retains its corrugated form even
in the branches of the rachis. It is thus equally different
from the single leaf-trace of the sub-genus E-u-heterangium
and from the completely divided trace of the Polyangium
species of Heterangium. It is essentially on account
RHETINANGIUM 99
of the exarch xylem and the complex, but not multiple
leaf-trace, that Rhetinangium is placed in a distinct
family from the Lyginopterideae. Owing to the imperfect
preservation of the phloem, it is difficult to decide whether
the trace was concentric or collateral. The appearances
point to its having been concentric after entering the
leaf-base, but we do not know at what point this structure
was acquired.
Where the leaf-trace enters the cortex from the
stele, the incipient leaf-base is marked off on either side
Fic. 46.—Rhetinangium Arberi. Transverse section of leaf-trace departing from stele; the
secondary wood of stele is seen on either side; the compound leaf-trace has numerous
external protoxylem-groups. x 30. From W. T. Gordon.
by an extension of the fibrous bands inwards, across
the inner cortical zone. A little higher up, as already
mentioned, the leaf-base becomes enormously swollen,
at the same time changing its structure. At a certain
level all the fibrous bands disappear, and the whole leaf-
base is merely a uniform mass of cellular tissue, with
the vascular bundle at its inner edge (Fig. 44). We
may conjecture from the analogy of recent leaves that
the leaf-base was of the nature of a pulvinus, adapted
perhaps to execute day and night or other movements,
with which the presence of rigid mechanical tissues
would have interfered.
100 STUDIES IN FOSSIL *BOrani
Higher up the petiole the ordinary structure 1s
assumed ; the fibrous bands reappear, beginning on the
adaxial surface; on the opposite side they first show
themselves in a deep-seated position, only resuming a
more external station at a higher level. Finally, the
free petiole acquires the same mechanical construction
as the stem, the diameter of the whole diminishes, and
the vascular bundle takes up a central position. The
leaf was, no doubt, a compound one, but no details of
its form are known.
Returning to the stem, the zone of secondary wood
and phloem is quite like that of a Heterangium. ‘The
principal ravs correspond to the cellular bands between
the primary xylem-strands, though the distinction be-
tween principal and secondary rays is not always con-
spicuous (Fig. 45). The rays, where they pass through
the phloem-zone, are often dilated.
In one or two cases, the bases of adventitious roots
have been observed on the stem, inserted either on the
leaf-trace or near its point of emission. They appear
to be tetrarch and possess secondary tissues. Nothing
certain is known as to the free roots.
Dr. Gordon considers that the affinities of Rhetinan-
gium are closest with the genus Megaloxylon, Seward,
which will be described in the next section. The chief
points in common are the exarch xylem and the large
leaf-trace with several abaxial protoxylem-groups. Some-
what similar grounds of comparison may be found with
Sutcliffia, one of the Medulloseae. These relations
will be best discussed when we have described the
genera in question. Both Megaloxylon and Sutcliffia are
Upper Carboniferous plants, much later geologically than
Rhetinangium.
In the meantime something more must be said as
to the relation of Rhetinangium to the Lyginopterideae
and especially to Hetervangium, the only comparable
genus of equal antiquity. In anatomical habit there is
RHETINANGIUM 101
undoubtedly a great similarity between the two genera.
The points of agreement have been sufficiently dwelt on
in the course of the description. Broadly speaking, the
general harmony in anatomical plan seems sufficient to
indicate a certain degree of real affinity. After all, Rhetin-
angium is more like Heterangium than anything else.
The important distinctions lie in the exarchy of the
xylem and the complexity of the leaf-trace. In Heter-
angium the degree of mesarchy varies, as we have seen,
in the different species, but the exarch condition is never
reached. Its complete attainment would involve, it
would seem, a somewhat important change, for the centri-
fugal portion of the xylem, small as it may be, appears
to have been the part first formed, as shown by its im-
mediate contact with the protoxylem and by the character
of its tracheides. Its disappearance would therefore
involve a change in the direction of the first differentia-
tion of the xylem (see above, p. 91).
The other important distinctive character of Ehetin-
angium—the complex leaf-trace—is quite different from
anything met with in Lyginopterideae, where the leaf-
trace, as it starts from the stele, always consists either
of one simple strand or of two such strands, separate
from one another. Dr. Gordon points out how the union
of a number of Hetevangium leaf-traces, with the loss
of their centrifugal xylem, might give rise to the /hetin-
angium type of trace, but, as he realises, no transition
between the two conditions is actually known.
In the present state of our knowledge we have no
other course open to us but to leave Rhetinangium in a
family by itself.
MEGALOXYLEAE
Megaloxvlon, Seward
Here again we have to do with a monotypic family,
containing a single genus with a single species, Megalo-
102 STUDIES IN FOSSIL BOTANY
xylon Scotti, Seward. In this case our knowledge is
further lmited to one incomplete specimen, of which
the wood only is known. The scanty material available
has, however, been so thoroughly worked out by Prof.
Seward ! as to put us in possession of data of considerable
interest and importance. The fragment, previously un-
described, was found in the Binney Collection at Cam-
bridge : it came from the Lower Coal-measures of Lanca-
shire, and is thus of Upper Carboniferous age. The
association of the specimen with Goniatite shells shows
that it was derived from a roof nodule: the Flora of
such nodules, probably representing drifted remains, is
often different from that of the ordinary coal-balls
occurring in the underlying seams of coal.
The specimen was part of a rather large stem, measur-
ing, in its incomplete condition, about 4:5 cm. in diameter.
The central axis of primary wood reaches a diameter
of I-g cm., the remainder of the fragment consisting of
a zone of secondary wood (Fig. 47, A and B).
The primary structure is that of a protostele, for the
wood extends to the centre, but it is a protostele of a
very peculiar kind. The primary wood is made up of
intermingled tracheides and cellular tissue ; the tracheides
throughout the greater part of the cylinder and the whole
of its central region are of large diameter, but extremely
short, the breadth commonly exceeding the length
(Fig. 48, B). Their walls bear numerous bordered pits.
In some places the short elements extend as far as the
inner edge of the secondary wood, but this is only the
case in the intervals between the leaf-traces, which have
a different structure (Fig. 48, B). The short, 4vige
tracheides are often arranged in transverse bands, the
parenchyma between the bands having contracted so as
to give rise to horizontal gaps recalling the discoid pith
1 A. C. Seward, ‘‘ Notes on the Binney Collection of Coal-measure
Plants, Part ii. Megaloxylon Gen. nov.,’’ Proc. Cambridge Phil. Soc.
vol. x. Part iil. p. 158, 1899.
MEGALOXYLON 103
of Cordaiteae (see p. 270). As Prof. Seward suggested,
the dilated tracheides of the primary xylem probably
served for the storage of water.
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Fic. 47.—Megaloxylon Scotti. A, Transverse section of stem (wood only). x1, primary
wood, surrounded by a broad secondary zone: 1.t., leaf-trace. Naturalsize. B, Radial
section of the same. +1, primary, x2, secondary wood; lL.t., leaf-trace, still compact ;
l.t.1, the same trace lower down, becoming merged in the metaxylem. Natural size.
C, Transverse section of secondary wood. x 24. From Seward’s Fossil Plants (Cam-
bridge Press), by kind permission of the author and publishers and of the Cambridge
Philosophical Society.
The large leaf-traces lie in the peripheral part of the
primary cylinder ; they are five in number in the trans-
verse section and are cut at different levels, the arrange-
ment implying a 2 phyllotaxis. The comparison of
104 STUDIES IN FOSSIL BOTANY
transverse and longitudinal sections has revealed the
changes which the leaf-trace undergoes as it passes
down the stele. When it first enters the primary cylinder
the trace forms a fairly compact, oval mass, as seen in
transverse section, consisting, as the longitudinal section
shows, of long, normal tracheides of moderate diameter,
interspersed with cellular tissue (Figs. 47, B and 48, B).
The protoxylem lies on the extreme outside of the strand,
next the secondary wood, and forms several groups,
usually about six (Fig. 48, A). Thus.the structure is
completely exarch. Followed downwards, the trace
gradually spreads out, the proportion of parenchyma
to tracheides increasing; at the same time the inner
tracheides of the trace become wider and shorter and
gradually become merged in the general metaxylem ! of
the cylinder. As the trace expands, the protoxylem-
groups on its outer margin become more widely spaced.
The outer part, adjacent to the protoxylem, is the last
to be affected by the change, but step by step the whole
trace loses itself in the general primary wood, and ulti-
mately the protoxylem itself dies out.
It is only the leaf-traces that possess protoxylem-
elements ; in the transverse section there are five traces
and about thirty protoxylem-groups altogether—six to
each trace. In the intervals, where the metaxylem abuts
directly on the secondary wood, no protoxylem exists.
The fan-like downward expansion of the leaf-trace and
its gradual merging in the metaxylem appear to be
peculiar to Megaloxylon.
The secondary wood has a somewhat compact structure
(Fig. 47, C); it consists of pitted tracheides of the usual
multiseriate type, with rather high medullary rays from
one to five cells in width. The wood presents no peculiari-
ties, but it is interesting to find that the large leaf-trace,
where it passes out through the secondary zone, is sur-
1 The word ‘‘ metaxylem ’”’ is here employed, somewhat loosely, for
all the primary wood apart from the leaf-traces.
Pt BN WI LN
MEGALOXYLON 105
rounded by a secondary ring of xylem of its own. No
division of the trace has been observed, but we must
Fic. 48.—Megaloxylon Scotti. A, Transverse section at the junction of the primary and
secondary wood (the latter above). px, px, protoxylem groups of the primary wood.
x 50. B, Radial section from the same region. %?, secondary wood ; 1.t., large leaf-
trace; m, metaxylem, showing discoid structure. x 16. _From Seward’s Fossil Plants
(Cambridge Press), by kind permission of the author and publishers and of the Cambridge
Philosophical Society. ;
remember that nothing is known of its course beyond
the limits of the secondary wood.
106 STUDIES IN FOSSIL BOTANY
In considering the relationships of Megaloxylon, the
first point to note is that the plant must have been
monostelic, for leaf-traces are given off on all sides of the
vascular cylinder alike. If the specimen had represented
a single stele of a polystelic stem, such as that of the
Medulloseae (see p. 175), the traces would have been
limited to one side.
The protostelic organisation and the character of
the pitting on the tracheides indicate that the genus
must be placed among the simpler Pteridosperms or
Cycadofilices. Among these, the nearest resemblance is
to Rhetinangium, as was pointed out by Dr. Gordon.
The two genera agree in the exarch xylem and the large
leaf-traces with numerous protoxylem-groups. In other
respects, however, they are very different. There seems
to be no analogy in Lthetinangium (or indeed elsewhere)
for the downward spreading-out and ultimate “ nirvana ”’
of the leaf-trace of Megaloxylon.
The sectional form of the trace 1s quite unlike ie
trace of Megaloxylon being a strand of simple compact
form, while that of Rhetinangium is corrugated and
evidently compound. Another point of difference is in
the distribution of the protoxylem-groups, which are
strictly limited to the leaf-traces in Megaloxylon, while
in Rhetinangium they appear to extend all round the
primary cylinder.
The peculiar structure of the metaxylem in Megalo-
xylon is of course quite different from anything in
Rhetinangium, though analogies are not wanting in other
genera. For example, in Zalesskya and Thamnopteris
among the Permian Osmundaceae, in Dziplolabis among
the Zygopterideae, and in Lepidodendron selaginoides the
differentiation of the central xylem in the form of short
tracheides is characteristic. This is an adaptive change,
which seems to have occurred in various distinct phyla,
where the central xylem had presumably become super-
fluous for conducting purposes, and found a use as an
7 “Ty a2
MEGALOXYLON 107
organ for water storage:' A more remote analogy is
found in a plant which we include in another family of
Pteridosperms, Calamopitys fascicularis, where the inner
secondary tracheides have undergone a similar modiifi-
cation. Some further newly discovered cases will be
mentioned below (see bilignea, p. 134).
It may be that Megaloxylon, so much later in geo-
logical age than Rhetinangium, represents an advanced
scion of the same stock, but this is a pure conjecture.
At present the genus remains isolated, like so many of
the plants grouped under the vague but useful name of
Pteridosperms.
CALAMOPITYEAE
It is an interesting fact that this family and the three
which follow, as well as the Rhetinangieae, already
described, are all of Lower Carboniferous age, while
some of their members may even go back to the Upper
Devonian. Heterangium, too, among the Lyginopteri-
deae, belongs in part to the Lower Carboniferous flora.
It is evident that at a comparatively early geological
period a considerable number of distinct types of Pterido-
sperms already existed ; at the same time most of these
forms are so isolated as to show that our knowledge
is still extremely fragmentary, and that only a few
chance examples of what must then have been a great
and varied class of plants have come down to us. Un-
fortunately, with the exception of Heterangium Grievit, we
have no evidence as to the fructification in any of these
Lower Carboniferous types. But on the anatomical data
it seems clear that this distinct phylum, uniting, to a
certain extent, fern-like characters with those of Gymno-
sperms, is among the oldest groups of the Vasculares.
The family Calamopityeae is better represented than
the two last considered, for five species have been de-
1 Scott, ‘“‘ The Old Wood and the New,” New Phytologist, vol. i.
Pp- 25, 1902.
108 SLUDIES IN EFOSSIE: BOTANY
scribed, and some authors group them in two distinct
genera, here adopted only as sub-genera. In addition,
there are at least four undescribed forms, which appear
to belong to this family ; they will be further mentioned
at the end of this section.
Calamopitys, Unger
Of the five published species of Calamopitys (in the
wider sense here maintained) two, C. Saturni, Unger and
C. annularis (Unger), Solms, come from Thuringia in
Central Germany, one, C. americana, Scott and Jeftrey,
from the State of Kentucky, one C. fascicularis, Scott,
from Scotland and North England, while the fifth, C.
Beinertiana (Goepp.), Scott, has been found both in
Silesia and in Scotland.
The two species last named, C. fascicularis and C.
Beinertiana, have been placed by Dr. Zalessky in a separate
genus, Evistophyton,! an arrangement which has been
adopted -by Prof. Seward.? Here we prefer to-streqe
Evnistophyton as a sub-genus. The three other species,
C. americana, C. annularis and C. Saturni, may constitute
another sub-genus and be distinguished as Eu-Calamopitys.
While the age generally accepted for all five species
is Lower Carboniferous, it is interesting to note that
Solms-Laubach, in his later years, believed that the
Thuringian beds, containing C. Saturm and C. annulans,
were of Upper Devonian age, while he suspected the same
of part at least of the Silesian Falkenberg remains.?
1M. D. Zalessky, ‘‘ Etude sur l’anatomie du Dadoxylon Tchiha-
tcheffi,’’ Mém. du Comité Géol., nouvelle sér. livr. 68, Petrograd, IgI1.
2 Seward, Fossil Plants, vol. lii. p. 197, 1917.
’ Whether this applied to C. Beinertiana we cannot say. In Scot-
land, at any rate, there is no doubt of its Lower Carboniferous age.
Solms, “‘ Die Bedeutung der Palaophytologie fiir die aaa
Botanik,” Mitt. der Philomath. Gesellsch. in Elsass-Lothringen, Bd.
1906. More recent work appears, however, to show that the Thuringian
specimens are not older than the passage beds of the two formations.
ee "eee aN oe eee a
CALAMOPITYS 109
Further, specimens of leaf-stalks apparently identical
with those of C. americana are reported from the Genessee
Shales, of Upper Devonian horizon, in Kentucky. It
is therefore possible that some of the species now to
be described may be even older than the base of the
Carboniferous formation.
Of the three species included in the sub-genus Eu-
Calamopitys, two, C. annularis and C. americana, are very
closely allied, so that it is difficult to find distinctive
characters, though, as they come from different con-
tinents, it is probable that they are really separate
species. C. Satuyni is somewhat different in structure,
and apparently more advanced ; it leads the way to the
two Evistophyton species, C. fascicularis and C. Beiner-
tirana, which certainly represent the highest type of the
group.
Our account will be based, in the first instance, on
C. americana, which is in some respects better known
than its Old World fellow, C. annularis.
Calamopitys (Eu-Calamopitys) americana
This species was among the petrified fossil plants
discovered by Prof. Charles Eastman at the base of the
Waverley Shale (Lower Carboniferous) in Boyle County,
Kentucky, U.S.A.1. The nodule layer, in which the
specimens occur, lies unconformably upon the Genessee
Black Shale, of Upper Devonian age, but, as already
mentioned, the same or a closely similar species is
reported to occur at the lower horizon also.
Several specimens of the stem, of various dimensions,
and also of the petioles are known; in one case leaf-base
and stem have been found in connection. The stems
observed range from a little over 2 cm. to about 4 cm.
1 Scott and Jeffrey, ‘‘ On Fossil Plants, showing Structure, from the
Base of the Waverley Shale of Kentucky,” Phil. Tvans. R.S. Ser. B,
vol. 205, p. 315, 1914.
Ilo STUDIES IN FOSSHS BOTANY
in diameter, but the large size of some of the associated
leaf-stalks shows that other stems must have attained
much more considerable dimensions. The stems must
have been of some height ; we have a fragment a foot
long and of comparatively uniform diameter.
In the smaller stems the pith is only 2-4 mm. in
diameter ; in the largest specimen observed it measures
13 mm. The word “ pith,’ however, is not properly
applicable, for it includes the primary wood, which may
even extend to the middle of the stele. Outside the
central region there is always a wide zone of secondary
wood, accompanied on the exterior by remains of the
phloem; the cortex, with an external belt of mechanical
tissue of the Sparganum type, is sometimes preserved
(cf. Fig. 52). Leaf-traces are met with, passing out
through the wood and cortex (Fig. 51).
We may now consider the various tissues more in
detail. The main part of the primary wood consists
of a ring of xylem-strands surrounding the mixed pith ; *
the strands form collectively an almost continuous zone,
and are only separated from each other, if at all, by quite
narrow bands of cellular tissue. The structure of each
xylem-strand is mesarch (Fig. 49), the protoxylem lying
nearer the outer than the inner margin, while the centri-
fugal portion is usually composed of smaller tracheides
than the centripetal. The tracheides, so far as the
somewhat imperfect preservation allows one to judge,
are for the most part of the usuai form, with multiseriate
bordered pits. So far, the structure appears much like
that of a Lyginopterts with almost confluent xylem-strands.
The comparison of transverse and longitudinal sections
shows, however, that the tissue within the xylem-zone
is not a true pith, for it contains tracheides intermixed
with the short-celled parenchyma. In the smaller
stems the medullary tracheides are numerous, in pro-
1 A “ mixed pith ”’ is a pith containing tracheides as well as paren-
chyma.
CALAMOPITYS . i
portion to the parenchyma; where the mixed pith is
larger, it is more parenchymatous, and the tracheides
more scattered, occurring either singly or in little groups ;
they are elongated and generally resemble those of the
peripheral xylem-strands ; sometimes they have _ hori-
zontal or slightly oblique transverse walls (lig. 50).
It is only the peripheral xylem-strands that are con-
cerned in the emission of the leaf-traces. It will be seen
that the structure so far described is comparable to that
5°)
Fic. 49.—Calamopitys americana. Primary, mesarch xylem-strand in transverse section.
px, protoxylem, x*, secondary wood. 73. S. Coll. 2862. (G. T. G. from Phil. Trans.
R.S.)
of a Heterangium with a considerable amount of xylem-
parenchyma, or of a Lyginopteris, such as L. heterangioides,
in which some of the central tracheides still persist. The
organisation may be called protostelic, in so far as xylem-
elements extend to the centre of the stele, but evidently
the metaxylem is becoming reduced and somewhat in-
constant in its development.
In the secondary wood the tracheides are smaller
than those of the primary region; the pits, where pre-
served, are found to be in five or six rows on the radial
i STUDIES IN FOSSIL? BOTANY
walls. The medullary rays are of considerable height,
and from two to eight cells in width. Portions of the
cambium, phloem and pericycle are sometimes preserved,
but no details of interest are shown. The secondary
thickening was clearly quite normal and presents no
peculiarities.
The inner cortex is a uniform tissue of short cells ;
the outer, mechanical zone shows the parallel bands of
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Fic. 50.—Calamopitys americana. Longitudinal section, showing tracheides embedded in the
pith, and part of a xylem-strand. ¢, medullary tracheides ; x, part of xylem-strand-
x about 27. S. Coll. 2867. (G. T.G., from Phil. Trans. R.S.)
fibres characteristic of the Sparganum cortex, and similar
to those of Heterangium; this part of the structure is
better exhibited in the petioles (lig. 52).
The course of the leaf-trace has been followed con-
tinuously, up to the point where it leaves the secondary
zone of wood. The traces succeed each other at some-
what short intervals. Where a trace is to be given off,
a preliminary division first takes place, separating the
xylem of the trace from a reparatory strand which remains
CALAMOPITYS a
3
in the stele. This is comparable to what has _ been
described in Lyginopteris. After this the trace begins
to pass slowly outwards. Its xylem is at first a single
strand, with one protoxylem-group, placed nearer the
outer than the inner surface. The trace is accompanied,
on its outer side, by a fan of secondary wood. As it
gradually moves out, the protoxylem first divides and
then the whole strand becomes gradually severed into
a 7Y
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Fic. 51.—Calamopitys americana. Transverse section of leaf-trace, passing out through the
secondary wood. The two strands are now separating, and each has a large fan of
secondary xylem, beginning to encroach on the inner side. _.t., 1.t., primary wood of the
leaf-trace strands. Cortex shown to the left. Xxabout 7. S. Coll. 2960. From a
photograph by Mr. W. Tams.
two, the corresponding arc of secondary wood also
resolving itself into two distinct arcs. By the time the
leaf-trace has reached the outer edge of the stelar wood,
it is completely divided into two bundles, each of which
is here surrounded by its special zone of secondary wood
and bast, which is thicker on the outer than on the inner
side (Fig. 51). Thus the leaf-trace enters the cortex
as two distinct strands, each with concentric structure
and secondary growth.
114 STUDIES “IN FOSS EBOrany
The further changes have not been followed in detail,
but it is known that the bundles of the trace soon lose
their secondary tissues and undergo further divisions,
so that in a leaf-base attached to the stem there are
several bundles (cf. Fig. 54). In this species, as well
as in C. annulans and C. Saturm, the structure of the
leaf-base has proved to be identical with that of the
separate petioles, formerly named Kalvmma by Unger,
now known to be leaf-stalks of various species of Calamo-
pitvs. It is only in the sub-genus Fu-Calamopitys
that the petioles are known.
The leaf-base is marked off from the cortex ~otjiie
stem by a band of fibrous tissue; it contains several
vascular bundles, radially elongated as seen in trans-
verse section. The structure is, however, best shown
in the free petioles associated withthe stems, and no
doubt of the same species.
A fine specimen of the petiole is shown in Fig. 52,
in transverse section. Its dimensions in the part figured
are about 4:5 x 3:°3cm. There is a main ring of seventeen
vascular bundles, deeply embedded in the ground tissue.
On one side the bundles are large and much elongated
radially ; on the opposite side they are smaller and less
elongated. The two bundles at the ends of the elliptical
section, and one other, are somewhat U-shaped, with
the concavity outwards, and are evidently in course of
division or fusion. Comparison with another transverse
section shows that both processes occurred at intervals.
In addition to the main vascular ring, three minute
strands are present, on the inner side of the aromas
large bundles, from which they have probably been
given off.
Though most of the tissues of the petiole are perfect,
the phloem of the bundles is so badly preserved in all
cases, that it has not been possible to decide whether
the structure was collateral or concentric ; the appear-
ances point to the latter alternative. The smallest
CALAMOPITYS II5
tracheides, presumably the protoxylem, occur in groups,
usually three in the larger bundles, lying embedded in
the xvlem near one edge. Their position is confirmed
by the longitudinal sections, which in favourable cases
show narrow, spiral elements not far from the edge of
the xylem-strand. In the case of the minute inner
bundles, there appears to be a single eccentric proto-
xylem. A much elongated bundle, from a still larger
petiole, at least 6 cm. in diameter, shows no less than
Fic. 52—Kalymma (petiole of a Calamopitys, probably C. americana). Transverse section.
x about 2. S. Coll. 3046. From a photograph by Mr. W. Tams.
five protoxylem-groups in a more or less median position.
The larger tracheides often have multiseriate bordered
pits, as in the stem, while others are scalariform. In
smaller specimens of the petiole fusion of the bundles
is more frequent.
The parenchyma consists of large, short cells, and is
very uniform, though the cells around the bundles are
smaller. The mechanical zone of the outer cortex is
beautifully developed; the radial bands of fibres are
deep, and often forked outwards (Fig. 52). We may
116 STUDIES IN FOSSIL corANt
call it a ““Sparganum ”’ cortex, for the fibrous bands
on the whole run parallel, but fusion frequently occurs.
Some parenchyma is present, outside the mechanical
zone, but the superficial layers are not preserved.
This is the first example we have had of a petiole
with very numerous bundles in a ring, a structure different
from anything found in the Lyginopterideae, and neces-
sitating the separation of the two families, though they
offer many analogies in the characters of the stem. The
petioles are known to have branched; in the European
specimens this has been directly observed, and in the
almost identical American form the specimens vary
much in dimensions, so that the smaller may probably
sometimes represent a secondary rachis. Kalymma was
evidently the petiole of a large, compound frond, but no
further details of its form are known. From the dimen-
sions of the larger petioles, it is clear that the plant to
which they belonged must have attained a very con-
siderable size. It may well have been a small tree.
Calamopitys (Eu-Calamopitys) annularis
This Thuringian species, first described by Unger in
1856 as a Stigmaria, but recognised by Solms-Laubach
in 1896 as belonging to Calamopitys, is so similar to
C. americana that a brief description will suffice.
In the more typical specimens (Fig. 53), the pith,
including the primary wood, has a diameter of from
7togmm. The primary xylem forms an almost con-
tinuous ring ; the numerous strands of which it is built
up are more or less eccentrically mesarch with the proto-
xylem towards the outer side; where the eccentricity
is marked, the smaller, centrifugal portion consists of
narrower tracheides than the more extensive centri-
petal region. In the pith, tubular elements are present,
which are in all probability medullary tracheides, though
the evidence is less conclusive in this case than in C,
CALAMOPITYS 117
americana! In the larger specimens, the secondary
wood is practically identical with that of the Kentucky
species; the rays are multiseriate. In a specimen,
however, from the Halle museum, referred by Solms-
Laubach to C. annularis, the structure is somewhat
different. The pith is very small (2:5 x 1-7 mm.) and
the medullary rays of the secondary wood are narrow ;
most of them are uniseriate, others, or other parts of
the same rays, are two cells thick, and only in one case
was a width of as much as four cells observed. This is
Fic. 53.—Calamopitys annularis. Transverse section of stem, showing primary and secondary
wood, with part of cortex, and, on the right, a leaf-base, containing three bundles. x 2}.
413 in the Solms Coll. From a photograph by Mr. W. Tams.
a point of some importance, for comparison with species
of the sub-genus ELv:stophyton, in which the rays are
constantly narrow.
The course of the leaf-trace through the wood has
not been followed in C. annularis, and we do not know
at what stage it divided. Outside the wood, however,
leaf-trace strands are present, with a wide secondary
zone which may extend almost uniformly all round the
bundle. So far the structure of the leaf-trace is essenti-
* Scott, “‘ Notes on Calamopitys, Unger,”’ Linnean Society's Journal
—Botany, vol. xliv. p. 205, 1918.
118 STUDIES IN FOSsii BOTANY
ally the same as in C. americana. Further out, in the
leaf-base, the agreement between the two species is
equally close; here also the large bundles give off, to-
wards the inner side, small subsidiary strands, each with
a single protoxylem. The cortical tissues also appear
to have been quite alike in the two species.
C. americana and C. annularis are evidently closely
allied species, and appear to represent the Calamopitys
type in its most primitive form, with an almost continu-
ous ring of primary xylem, and medullary tracheides,
indicating a protostelic structure. This last point, it
is true, has only been proved in the case of the Kentucky
plant, but there seems to be little doubt that thes mme-
in the pith of C. annularis are of the same nature.
Calamopitys (Eu-Calamopitys) Saturni
This is another Thuringian fossil and is the type-
species of Calamopitys, on which the genus was founded
by Unger in 1856. Our knowledge of its true structure
is, however, principally due to the work of Solms-Laubach,
fortv years later.
The stems recorded’ are small, only reaching about
I°5 cm. in diameter; the pith is even smaller in pro-
portion, about 1 to 2 mm., including the primary wood.
The latter was described by Solms-Laubach as “an
irregular tracheal zone, perhaps quite interrupted here
and there, which swells out in places into expanded nests,
projecting into the pith-parenchyma.”’? He pointed out
that in C. annularis the primary wood was more strongly
developed, forming a quite or almost closed ring.? To
judge from the stems of C. Saturni observed, the difference
between the two species is greater than this. It will be
1 Solms-Laubach, ‘‘ Pflanzereste des Unterculms von Saalfeld,”’
Abhandl. dey K. Preuss. Geol. Landesanstalt, neue Folge; Heft 23, p.
63, 1896.
2 Solms-Laubach, 1896, p. 65.
8 Solms-Laubach, 1896, p. 74.
a es
~ RELL Me eae
—
CALAMOPITYS 119
seen in Fig. 54 that, surrounding the pith, there are six
primary xylem-strands. Unlike the conditions in the
two previous species, all the six strands are perfectly
well defined and distinct from each other, just as much
so as in Lyginopteris oldhamia; there is no approach
to a continuous xylem-ring. Occasionally one of the
strands is slightly embedded in the pith.
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Fic. 54.—Calamopitys Saturni, Unger. Transverse section of stem. %, primary xylem-
strands ; x”, secondary wood ; o0.c., outer cortex, with fibrous strands ; I.t., double-leaf-
traces ; pet, petiole-base, containing six bundles ; sc, sclerenchyma at junction of petiole
with stem. x about 4. After Solms-Laubach.
Another point of difference from C. americana and
C. annularis is that in C. Saturni the xylem-strands are,
as a rule, centrally mesarch, the centrifugal and centri-
petal portions being equally developed, with the proto-
xylem in the middle. In the preceding species the
structure was eccentrically mesarch, with the centri-
fugal commonly less developed than the centripetal
xylem.
Neither is there any evidence for the presence of
120 STUDIES IN FOSSIL BOTANY
tracheides in the pith of C. Saturn: ; the parenchyma
appears to be practically uniform and continuous. In
a specimen of C. americana of corresponding dimensions
the “‘ pith’ would be full of tracheides. Tor ies
reasons it may be concluded that C. Saturni is not only
a perfectly distinct species, but that it stands somewhat
apart from those previously described, at least as regards
the primary structure of the stele.
The secondary wood, on the other hand, has essentially
the same organisation as in the former species; the
medullary rays are high and wide. The only difference
observed is that in C. Saturvni the rays are often dilated
outwards, a feature not met with in the other two species.
The phloem is sometimes preserved, and was found by
Solms-Laubach to contain bast-fibres as well as the
usual elements of the soft bast.
The outward course of the leaf-trace was followed by
Solms-Laubach with great accuracy. It differs from
that described in C. americana, for in C. Saturni, though
the outgoing strand doubles its protoxylem-group in
traversing the secondary wood, the trace itself remains
undivided, and enters the cortex as a single bundle. It
is only in the cortex that the division into two strands
takes place. On leaving the stele, the undivided trace
has secondary tissues of 1ts own, but they are limited
to the outer side. The two bundles resulting from the
first division of the leaf-trace divide again, and of the
four strands thus formed the two lateral ones repeat
the process, so that the leaf-base contains six bundles,
a number which, in the small specimens observed, is
still maintained in the free petiole (Fig. 54).
The bundles in the leaf-base have lost their secondary
tissues and acquired in all respects the same structure
as in the leaf-base and petiole of the species previously
described. From the arrangement of the successive
leaf-traces, which follow one another at short intervals,
so that five may appear in the’ same transverse section,
CALAMOPITYS I2I
Solms-Laubach determined the phyllotaxis as 3? or a
very similar higher fraction.
Besides the late division of the leaf-trace, we.have
seen that C. Saturni is characterised by the distinct
strands of primary xylem, by their centrally mesarch
structure, and probably by the absence of medullary
tracheides.
As regards the structure of the leaf-base and petiole:
all the three species of Eu-Calamopitys appear to be
essentially alike. In all, the petiole is a Kalymma, with
a Sparganum outer cortex and a single main ring of
bundles, each of which has internal protoxylem-groups.
We are not yet in a position to distinguish between the
petioles of the three species. Yet there can be no doubt
that under the name Kalymma several species are in-
cluded. The distinctions are not of sufficient moment
to be dwelt on here.
We may, however, call attention to certain petioles,
which have been provisionally placed in a separate
genus, Calamopteris, Unger. A Thuringian species, C.
debilis, Unger, differs but little from the smaller petioles
referred to Calamopitvs americana, except that the
indications point to a collateral structure of the bundles.*
The Kentucky species, C. Hippocrepis, Scott and Jeffrey,
is more distinct. Here the bundles are extensively fused,
though some remain separate, the ring having the form
of a kind of split horse-shoe, with a wide opening on one
side, and a narrower gap on the other. The arrange-
ment of the bundles remains fairly constant in different
transverse sections, though the narrower gap may close
up. The phloem is tolerably preserved, and seems to
be limited to the outer side of the vascular ring, the
structure thus being collateral. The xylem consists,
-cort and Jefirey, i.c. 1914, p. 330; R. Richter and: F.
Unger, “‘ Beitrag z. Palaontologie des Thiiringer Waldes’’; 2ter
Teil, von F. Unger, ‘“‘ Schiefer- u. Sandsteinflora,’’ Denkschriften der
K. Akai. d. Wiss., Wien, Bd. xi. 1856.
122 STUDIES IN POSSI, BOTANY
so far as observed, of scalariform tracheides, and has
mesarch structure, the protoxylem-groups lving towards
the outer surface. The ground-tissue is like that of
Kalymma, and the mechanical zone is strongly con-
structed, with the fibrous bands near together.
The fossil is evidently a: petiole, allied to: thatwes
Calamopitys, but differs sufficiently to be kept distinct.
It may probably have belonged to some unknown stem
of the family Calamopityeae.
The Sub-genus Evistophyton
We now come to the two species which were separated
by Dr. Zalessky from Calamopitys, under the name
Eristophyton, here adopted as a sub-genus. The system-
atic position will be discussed after the species have
been described. Unfortunately, in the case of both
species, the cortical tissues and leaf-base are unknown,
so that our data are much more restricted than in Fu-
Calamopitys, a fact which may account for the difference
of opinion as to the relations of these plants.
Calamopitys (Enstophyton) fascicularis
Two specimens of the plant are known. One was
derived from the Calciferous Sandstones of the Kilpatrick
Hills in Dumbartonshire, the other from the Carbon-
iferous Limestone of Haltwhistle in Northumberland ; }
thus both are of Lower Carboniferous age. The actual
specimens are from 2 to 3 cm. in diameter, but these
dimensions are of no significance, as even the wood is
incomplete.
The pith is small, from 2 to 3 mm. in diameter. It
is surrounded by a ring of eight or nine primary xylem-
1 Scott, ‘‘On the Primary Structure of certain Palaeozoic Stems
with the Dadoxylon Type of Wood,” Trans. Royal Soc. Edinburgh,
Vol, xli, Part 11. 1902:
CALAMOPITYS 123
strands, beyond which is the zone of dense secondary
wood (Fig. 55). The strands around the pith are of
very unequal size, the larger having a diameter of
o-8 — 1 mm., while the smallest measure less than 0-25 mm.
The comparison of successive transverse sections shows
Fic. 55.—Calamopitys fascicularis. Transverse section of central part of stem, showing the
pith (rather contracted), the primary xylem-strands, and part of the secondary wood.
A, large xylem-strand, about to pass out to a leaf; B, still larger strand, already on the
way out; px, protoxylem-groups; C (arrow), direction of another outgoing strand ;
a, b, c, reparatory strands of the bundles A, B, C. d, e, main and reparatory strands of
two other leaf-traces, lower down in their course. X20. Kidston Coll. 540a. (G. T.G.)
that the large bundles are those which are seen in the
upper part of their course, where they are about to pass
out as leaf-traces (Fig. 55, B) while the smaller strands
are those cut at a lower level. Traced downwards, the
strands rapidly diminish in size. Another feature which
will be noticed is that the largest xylem-strands are in
124 SLUDIES; IN “FOSSIL BOiANG
immediate contact with the secondary wood, while all
the others are more or less embedded in the pith, a few
layers of small-celled parenchyma intervening between
these strands and the inner edge of the woody zone
(Rigw55. 62.0.2);
The large, outgoing xylem-strands are almost circular
in section and centrally mesarch, agreeing exactly in
structure with those of Calamopitys Saturni. The central
protoxylem is accompanied by a little thin-walled tissue.
The larger primary tracheides are of the usual kind with
multiseriate pits, while the elements adjoining the proto-
xylem are smaller and scalariform.
The xylem-strands lower down in their course, as
they dwindle in size, change somewhat in structure ;
the protoxylem approaches the inner edge of the strand,
the centripetal xylem becoming reduced and even in-
terrupted (Fig. 55). There is thus, as the xylem-strand
is followed downwards, an approach to endarch structure ;
nothing of the kind is found in any species of Eu-Calamo-
pitys. The reduction of the centripetal xylem, though
here so local, marks a first step towards the structure
of the higher Gymnosperms, in which it ultimately dies
out. On the other hand, the great size of the outgoing
primary strands, often amounting to 2 of the pith-
diameter, is a character indicating that we are here still
among plants of Pteridosperm affinity.
The pith itself consists of short-celled tissue ; a few
of the cells have dark contents and may possibly have
been differentiated for some special function, such as
secretion. There is nowhere any indication of medullary
tracheides.
The secondary wood is very different from that of
any of the Eu-Calamopitys species, if we except the
peculiar specimen of C. annilaris described above (p. 117).
In C. fascicularis the wood is dense, with small tracheides
and narrow rays, usually one cell in width, but occasion-
ally biseriate in the middle. The rays are also low, seldom
CALAMOPITYS 125
exceeding about sixteen cells in height. The bordered
pits of the tracheides are excellently preserved ; they are
usually in three or four rows on the radial walls, and
their arrangement in vertical series is more regular than
in Eu-Calamopitys. In form they are more or less
hexagonal, owing to their close contact and alternate
position.
The most remarkable feature of the secondary wood
in this species is the structure of its inner layers, where
it borders on the pith and primary strands. In this
region the tracheides are short and wide, with more
numerous rows of pits on their walls ; their arrangement
is irregular and the medullary rays between them are,
correspondingly distorted. The structure of this inner
part of the secondary wood is comparable to that of the
primary xylem in Megaloxylon (p. 102) and may also
have served the purpose of water-storage. This function
may have been the more necessary, as the xylem-strands
dwindled so much in the lower part of their course that
a reserve of water may have been required to maintain
the supply.
The course of the leaf-traces has been followed, within
the narrow limits imposed by the incompleteness of the
specimens. From the succession of the leaf-traces it
is clear that the phyllotaxis was ?. From the rapid
succession of the leaf-traces it may be inferred that the
internodes were short. Otherwise the course of the
traces, and especially the union of each in turn with
the strand on its kathodic side, agree perfectly with the
conditions in Lyginopteris oldhamia (cf. p. 31).
As the trace passes out through the woody zone, its
protoxylem divides into two groups. No doubt this was
preparatory to the division of the trace as a whole, but
the loss of the outer. tissues prevents our following up
its further course.
The chief points to be noted in C. fascicularis are as
follows: The centrally mesarch structure and large
126 STUDIES IN FOSSLE BOTANY
size of the outgoing xylem-strands, resembling those
of C. Saturni; their rapid attenuation and approach
to endarch structure as they pass downwards, and their
becoming embedded in the pith; the course of the
bundles, agreeing, so far as can be determined, with that
in Lyginopteris oldhamia ; the structure of the secondary
wood, with its low and narrow rays, like the wood of
the Cordaiteae (see p. 273) and certain Conifers.
Calamopitys (Eristophyton) Beinertiana
This fossil is the Avaucarites Beinertianus of Goeppert,
who first recorded it as long ago as 1850. It was re-
described by Solms-Laubach in 1893, but the primary
structure was not observed till 1902.1 The original
specimens came from deposits, almost certainly of Lower
Carboniferous age, near Falkenberg in Silesia, and at
a later date the same species was identified by Dr. Kidston
in the Calciferous Sandstones of the Tweed. Subse-
quently specimens were observed in the neighbourhood
of the Balaton See in Hungary. Thus the species had
a wide distribution at the beginning of the Carboniferous
period.
The stem is larger than that of C. fascicularis ; in
the Scottish specimens, though incomplete, the diameter
is about 5 cm. With the exception of a fragment of
scale-bark, nothing beyond the pith and wood is _ pre-
served. The pith is considerably larger than in C.
fascicularis, the diameter being about 8 cm. in Solms-
Laubach’s Falkenberg specimen and 13-15 cm. in the
Tweed fossil. A remarkable feature in the structure
of the pith is the presence of large sclerotic nests, with
radiating cells around them, the whole strikingly like
the nests in the pith of Lyginopteris oldhanuia. This
cannot, however, be accepted as evidence of affinity,
for the character is only a specific one, the nests
t ‘Scott; 726, 1002,-p: 347,
CALAMOPITYS 127
being entirely absent even from the closely allied C.
fascicularis.
Surrounding the pith is a ring of numerous strands
of primary xylem, which may be locally confluent with
one another. The largest strands are those which are
about to pass out as leaf-traces; they have the same
centrally mesarch structure as in the preceding species ;
the dimensions also are nearly equal, the diameter amount-
ing to o-8 mm., but they appear less important owing to
the greater size of the pith. The smaller strands repre-
sent the same bundles lower down in their course. As
they pass downwards they gradually lose their centri-
petal xylem, and thus become endarch ; the change of
structure, which was only imperfectly carried out in
C. fascicularis, is here complete. The strands, in this
species, remain in contact with the woody zone and do
not become embedded in the pith.
The phyllotaxis has not been determined, but was
no doubt a complex spiral. Several leaf-traces may
appear in the same transverse section, as they pass out
through the wood, so we may infer that the internodes
were short. The traces, observed in their passage
through the secondary wood, do not clearly show any
division of the protoxylem, and nothing is known of
their ultimate fate.
The wood, as in C. fascicularis, has a dense structure,
like that of a Cordaitean or Araucarian stem. The
medullary rays are seldom more than one cell in width ;
they vary much in height. The bordered pits are usually
in two rows on the radial walls of the tracheides; in
places they may be reduced to a single series. The
secondary tracheides thus present a sharp contrast with
the large elements of the primary xylem-strands, in
which the rows of pits may be very numerous. The
short, inner, secondary tracheides, characteristic of C.
fascicularis, have not been observed in the present
species.
128 STUDIES*IN FOssilL borin,
We have scarcely any information about the roots
of Calamopitys. It is therefore of interest to note that
Solms-Laubach found, in the Falkenberg. material, frag-
ments of roots associated with C. Beinertiana, and agree-
ing with the stem sufficiently, in the structure of the
secondary wood, to be referred with some probability
to the same species. One of these associated roots had
a clearly pentarch primary xylem.
C. Beinertiana has much in common with C. /fascicu-
laris, both in its primary and secondary structure. The
former species, however, seems to be somewhat the more
advanced of the two, as shown especially by the fact
that the xylem-strands, as traced downwards in the
pith, actually assume an endarch condition, a structure
to which the corresponding strands of C. /ascicilaris
show only an approximation. The large size and peculiar
structure of the pith give the’ stem avery difierens
anatomical character from that of the allied species.
In general appearance the sections of C. Beinertiana sug-
gest the organisation of the higher Gymnosperms more
strongly than those of any other species so far referred to
Calamopitys.
SYNOPSIS 2
A concise synopsis of the chief characters of the five species
may be of service for reference.
1. Xylem-strands of fairly uniform size, all mesarch (E£u-
Calamopitys).
Rays usually multiseriate.
Petiole with Kalymma structure.
A. Xylem-strands usually eccentrically mesarch, with
protoxylem outwards, connected to form a nearly
continuous zone. Medullary tracheides present.*
C. americana (from Kentucky).
C. annularis * (from Central Germany).
L Solms;'}.2.: 0803; D.:208, 2 Scott, /.c. 1918, p..gom
%’ Proved for C. americana ; highly probable for C. annularis.
4 It would be premature to give distinctive characters at present. In
the meantime the localities prevent any confusion.
—E
CALAMOPITYS 129
B. Xylem-strands usually centrally mesarch ; quite
separate from one another. Medullary tracheides
probably absent. C. Saturni.
2. Xylem-strands of very unequal size; large and centrally
mesarch in the upper part of their course, becoming small
and nearly or quite endarch lower down (Evistophyton).
Rays usually uniseriate.
(Petiole unknown.)
a. C. fascicularis. Pith small, with no sclerotic nests.
Smaller xylem-strands embedded in the pith, with
their centripetal xylem much reduced.
B. C. Beinertiana. Pith large, with conspicuous sclerotic
nests.
All xylem-strands in contact with secondary wood.
Centripetal xylem dying out in the smaller strands,
which thus become endarch.
The course of the leaf-trace has not been included in the
synopsis as it is only adequately known in the two species
C. americana and C. Saturni; in the former the first division
of the trace takes place in the zone of thickening; in the
latter not till the trace has passed beyond this zone.
Affinities of Calamopitys
The question whether we regard Evistophyton as a
separate genus, or as a sub-genus under Calamopfitys is
of little importance. We have rather to consider how
far the five species described form a natural series and
what affinity they show to other groups.
The three species grouped under Eu-Calamofitys are
undoubtedly allied ; they agree in the constant mesarch
structure of the xylem-strands throughout their whole
course, in the organisation of the leaf-base and petiole,
in all cases of the Kalymma type, and in the general
character of the secondary wood, which if we except
the peculiar specimen of C. annularis referred to above
(p. 117) always has wide medullary rays.
Within this group, C. americana and C. annularis
present a closer agreement, shown in the prevailing
9
130 STUDIES IN FOSSIL BOTANY
eccentrically mesarch structure of the primary xylem,
the centrifugal portion being the less developed, in the
union of the primary strands to form an almost con-
tinuous zone, and probably in the presence of medullary
tracheides, rendering the structure protostelic. The last
character is as yet less certainly demonstrated in the
case of C. annularts than in that of its fellow species.
C. Saturni, on the other hand, appears to stand some-
what apart; here the xylem-strands are, as a rule, cen-
trally mesarch, and are also quite separate from one
another ; neither is there any evidence for the presence
of tracheides in the pith. In these respects C. Saturni
approaches the Evistophyton species.
The sub-genus Evistophyton is, however, distinguished
from Eu-Calamopitys by characters of considerable
importance. The gradual dwindling of the xylem-
strands as they pass down the pith, accompanied by the
reduction or even complete suppression of the centri-
petal portion, is a striking feature, peculiar to this sub-
genus. The latter character marks an approach, as far
as it goes, to the total loss of the centripetal wood, which
characterises the higher Gymnosperms. We find a
familiar intermediate stage in the recent Cycads, where
the centripetal xylem has wholly disappeared in the
main stem and even in the leaf-base, while it still per-
sists in the petiole and lamina, and occasionally in the
floral peduncle.
The characters of the primary xylem are those on
which the distinctness of the Evistophyton group seems
to me chiefly to depend. Another feature, also of im-
portance, on which Dr. Zalessky has laid the main stress,
is the structure of the secondary wood, which in E7sto-
phyton is constantly of the type found in Cordaiteae and
certain Conifers, with narrow and comparatively: low
rays, while in Eu-Calamopitys it is, as a rule, of a
more Lyginopteridean character, with the rays high
and wide. In this point also the. Eristophyton species
CALAMOPITYS 131
show an obvious approach to the organisation of the
higher Gymnosperms.
There is thus a considerable range of structure within
the genus Calamopitys, in the wide sense, and Dr. Zales-
sky's separation of Eristophyton as a distinct genus has
much in its favour. But on the whole I agree with
Solms-Laubach ! that, while our knowledge of the struc-
ture is so incomplete, it is wisest to avoid the multiplica-
tion of genera. The true relations of Evistophyton to
Eu-Calamopitys will only be determined, when we be-
come acquainted with the cortex and petiole of the
former, so as to be in a position to compare the whole
structure of the two groups. Until then, any arrange-
ment must be provisional.
In the meantime, judging from our present limited
knowledge, it seems clear that the five species form a
natural series, in which C. americana and C. annularis
are the most primitive members, and C. Saturn in some
respects intermediate, while C. fascicularis and C. Beiner-
tiana are decidedly the most advanced, the last-named
having made the maximum progress in a Gymnospermous
direction. The principal reason for still including the
Eristophvton species in Calamopfitys, and therefore in the
Pteridosperms or Cycadofilices,? is the structure of the
outgoing leaf-trace, which exactly resembles a xylem-
strand of C. Saturni and is unlike that of any other
known plant. The great relative size of the primary
strand, as it leaves the pith, so marked in C. /fascicularis,
is a feature peculiar to Pteridosperms (if we leave the
Ferns out of consideration) and is totally unlike anything
met with in the higher Gymnosperms. In C. Beinertiana,
where the pith is so much larger, this character is less
conspicuous, but the affinity of these two species is not
1 Solms-Laubach, Review of Zalessky, Zeitschrift f. Botanik, Band
iv. 1912, p. 291.
2 Dr. Zalessky expressed some doubts as to the relation of Eristo-
phyton to this class.
132 STUDIES IN FOSSIL’ BOTANG=:
disputed. We may presume that in Evistophyton, as in
Eu-Calamopitys, so massive a leaf-trace supplied a large,
and probably a compound leaf.
As regards the affinities of the genus and family as
a whole, it is fairly clear that the nearest relationship
is with the Lyginopterideae. C. Saturni admits of a
ready comparison with Lyginopteris, both having a ring
of distinct mesarch xylem-strands surrounding the pith.
The secondary wood is also very similar ; and the course
of the leaf-traces analogous. Now, however, that it
has been discovered that some species of Calamopitys
were protostelic, a comparison with Heterangium becomes
more apposite. There is evidently a somewhat close.
analogy between C. americana, for example, and H eteran-
gium, especially such species of the latter as had several
vascular bundles in the petiole. But there is nothing
to indicate a direct connection between the two families,
nor are there any grounds for deriving the one from the
other. The Calamopityeae and the Lyginopterideae are
parallel lines, so far as we can trace them ; if our know-
ledge ever extends further back, we may find that they
had a common origin in some earlier period.
There is no other group with which any near relation-
ship is shown. The more advanced species of Calamo-
pitys, forming the sub-genus Fvistophyton, make some
approach, as already mentioned, to the higher Palaeozoic
Gymnosperms, namely the Cordaitales. The significance
of this approximation will be better appreciated after we
have described some other forms.
NEW CALAMOPITYEAE
As already mentioned, there are four plants of Carboni-
ferous age still undescribed which appear to have a more
or less close affinity to the family Calamopityeae. [I am
indebted to my friend Dr. Kidston for the opportunity
of examining and describing these fossils, all of which
NEW CALAMOPITYEAE 133
are his discoveries. A full description with figures will
be given elsewhere—here it is only proposed to char-
acterise the new forms briefly.
1. Calamopitys zonata, Kidston.—This is a provisional
name which will probably require alteration as regards
the genus. The fossil is of Lower Carboniferous age,
coming from the Carboniferous Limestone Series of Ayr-
shire. The specimen, which was collected by the late
Dr. John Young, is part of a fairly large stem about
6 cm. in diameter, including the cortex. Around the
large pith a certain number of primary xylem-strands
are distributed ; their structure appears to be endarch
throughout. The secondary wood is dense, with un-
usually low, uniseriate, or locally biseriate rays. It is
remarkable for having distinct annual rings. The cortex,
as preserved, is mostly secondary, consisting of successive
zones of periderm.
The structure of the secondary wood removes the
plant from Eu-Calamopitys ; it might perhaps be referred
to the sub-genus Evistophyton, but if, as appears to be
the case, the xylem-strands are constantly endarch, an
affinity with Zalessky’s genus, Mesopitys, mentioned in
another connection (p. 283) may be indicated.
2. Calamopitys radiata, sp. nov.—The specimen is
derived from the Calciferous Sandstone Series of Dum-
bartonshire, and is thus somewhat older than C. zonata.
It presents quite different characters from that species.
The pith is small, and is surrounded by a ring of partly
confluent xylem-strands, which are either actually exarch,
or slightly mesarch, with the protoxylem very near the
outer edge. There appear to be tracheides scattered in the
pith, and in the case of a small branch borne on the main
stem the appearance suggests that such elements were
numerous, as in the smaller specimens of C. americana.
But in the absence of good longitudinal sections through
the pith, the presence of medullary tracheides cannot
be regarded as finally proved.
134 STUDIES UN FOSSIL BOTANY
The secondary wood is very parenchymatous, owing
to the enormous dilatation of some of the medullary
rays. These enlarged rays are crossed in various direc-
tions by strands of tracheides and present a fantastic
appearance in tangential section. No cortex is present.
There seems to be no objection to putting this species
in Calamopitys and in the sub-genus Eu-Calamopitys.
The xylem-strands in C. annularis are sometimes nearly
exarch, and it is with this species that the affinity seems
to be closest. The great size and peculiar structure of
certain of the medullary rays characterise the species
as a perfectly distinct one.
The two remaining forms are referred to a new genus,
Bilignea, Kidston, which is of great interest. Its essential
character lies in the fact that the pith is replaced by a
more or less solid column of short tracheides.
3. Bilignea solida, Kidston.—The fossil comes from
the Carboniferous of Ayrshire, but its horizon is not
further known. The cortex is absent, but the inner
tissues are remarkably perfect. The central column
consists exclusively of very short, rather wide tracheides,
with numerous bordered pits on their walls.
The central tracheal column is surrounded by a ring
of xylem-strands which pass out to form the leaf-traces.
These strands are mesarch in the upper part of their
course, the centripetal xylem being predominant ; lower
down, this portion is gradually reduced till the dwindling
strand becomes nearly or quite endarch, as in the E7sto-
phyton species of Calamopitys. The xylem strand begins
to divide into two before passing out. The internodes
are short and the phyllotaxis probably ;';. The second-
ary wood is dense, with low, uniseriate, or locally bi-
serlate rays. The specimen was collected by Mr. John
smith, Dalry.
4. Bilignea resinosa, sp. nov., from the Calciferous
Sandstone Series of Dumbartonshire. This Lower Car-
boniferous species differs in several respects from JB.
STENOMYELON 135
solida. In particular, the tracheides of the central
column are intermingled with large ‘‘ secretory sacs ”’ ;
the xylem-strands are smaller than in b. solida, and
show no sign of division; they are mesarch on entering
the wood, becoming apparently endarch and then dying
out, as traced downwards.
A Bilignea may be described as an Evistophyton in
which the pith-cells are replaced by short tracheides.
The new genus provides us with fresh examples of the
utilisation of the central column for the purpose of water
storage, but, whether in this case the storage-apparatus
was derived directly from a protostele, or by the trans-
formation of a pre-existing pith, must be left an open
question.
STENOMYELEAE
Stenomyelon, Kidston
This genus now contains two species, Stenomyelon
tuedianum, Kidston, and S. tripartitum, Kidston, both
of Lower Carboniferous age and derived from the Calci-
ferous Sandstone series of southern Scotland.
Stenomyvelon tuedianum, Kidston
This is the type-species, on which the genus was
founded by Dr. Kidston. The fossil, which is of great
interest, has a curious history. The original specimens
were discovered by Mr. Adam Matheson, of Jedburgh,
in the fifties of the last century, but no description was
published. Dr. Kidston, on examining the specimens,
suspected, from the character of the matrix, that they
came from the Norham Bridge locality,.on the Tweed
In 1901, together with Mr. Macconochie of the Scottish
Geological Survey, he carried out a careful search, which
was rewarded by the discovery of the material sought
13
+>
6
STUDIES IN FOSSIL BOTANY
for, in a cutting in the road at the north end of Norham
Fi
G.
536.—Stenomyelon tuedianum. Transverse
section of the stem, showing the cylindrical
stele, the cortex flattened into a thin wing,
and other fragments. The dividing leaf-
traces are seen at various points. x 2}.
Kidston Coll. 2068. From Kidston and
Gwynne-Vaughan.
Bridge. The block then
found yielded the beautiful
specimen on which the
memoir by Kidston and
Gwynne-Vaughan is
chiefly based, though sup-
plemented by a compara-
tive examination of the
original material.?
The cortex of the stem
is much flattened, giving
the fossil a winged ap-
pearance, which the plant
did not possess in the
natural condition; the
stele, however, retains its
approximately cylindrical
form (Fig. 56). In the
principal specimen, the
stele, measured to the
outside of the secondary
wood, is 8 to 9 mm. in
diameter, while the bluntly
triangular primary xylem
is fom 3to4mm. The
latter consists of three
masses or lobes, more or
less separated from one
another by narrow bands
of cellular tissue, meet-
ing at the centre, and
forming collectively the
“narrow pith” recorded
in the name of the
1 Kidston and Gwynne-Vaughan, “‘ On the Carboniferous Flora of
Berwickshire, Part I. Stenomyelon tuedianum, Kidston,” Trans. Royal
Soc. Edinburgh, vol. xlviii. part ii. 1912.
STENOMYELON 137
genus! (Fig. 57). The leaf-traces were given off from
the ends of the lobes, and it is inferred that the
leaves were borne in three vertical rows, for the lobes
retain their individuality throughout. The zone of
secondary wood is thickest opposite the bays of the
primary xylem, and thinnest at its prominent corners,
thus assuming a practically circular transverse section.
In the collapsed cortex, numerous leaf-trace bundles,
in various stages of subdivision, are met with; the
outer cortex is of the familiar Sparganum type (Fig. 56).
Portions of detached leaves accompany the stem.
Returning to the primary wood of the stem, we find
that the three xylem-lobes contain no parenchyma,
each lobe consisting of a solid mass of tracheides. The
cellular bands between the xylem-lobes are usually not
quite continuous, but often interrupted by bridges of
tracheides. Yet, on the whole, the lobes, though thus
connected locally, retain their independence. In addi-
tion to the bands between the lobes, there is often a
little parenchyma separating the primary wood from
the surrounding secondary zone.
The large tracheides of the primary xylem are elong-
ated elements, reaching 160 pw in diameter, with the
usual multiseriate bordered pits. The outermost elements
of each lobe, however, are scalariform, and diminish
in size. There appears to have been no protoxylem
proper to the stem, but where a leaf-trace is about to
depart from the distal end of a lobe, a pair of definite,
exarch protoxylem-groups appear. These groups are
decurrent from the leaf-trace, and unite to form a single
strand lower down in the’stem, ultimately disappearing
altogether. It will be remembered that in Megaloxylon
the protoxylem was limited to the leaf-traces (p. 104).
The structure of the secondary wood presents no
exceptional features. The medullary rays are as a rule
of considerable height, and from one to six cells in width ;
1 The nature of these bands is discussed below, p. 144.
138 STUDIES IN FOSSIE BOrANy
the tracheides are smaller than those of the primary
region, but vary in size in different zones; they have
from three to five rows of crowded bordered pits on their
radial walls only. Early stages of the development of
the secondary wood have been observed ; it began to
form in the bays of the primary xylem, and subsequently .
extended round the prominent angles.
No true phloem is preserved, but outside the wood a
radially seriated tissue 1s present, which, when seen in
transverse section, may simulate phloem (Fig. 57). That
it can hardly be of that nature is indicated by the fact
that its cells are quite short, and that no medullary rays
can be distinguished. Kidston and Gwynne-Vaughan
interpret this tissue as an internal periderm. A com-
parison also suggests itself with the sclerotic layers of
the phloem in Protopitvs Buchiana, described by Solms-
Laubach ; they also have short cells and show no medul-
lary rays (see below, p, 152). In Stenomyelon, however,
no trace of the intervening layers of soft bast is found.
Sclerotic nests, quite similar to those in the pith of
Calamopitys Beinertiana, are frequent in the inner cortex,
and are often found in close connection with the periderm
or hard bast. Otherwise little of the structure of the
inner cortex is preserved. The outer cortex is of the
usual Sparganum character, with parallel, vertical bands
of fibres, which seldom unite with one another. The
tissue between the fibrous bands is a rather firm-walled
parenchyma, containing cells with dark contents, possibly
representing resin-sacs.
“ The leaf-traces,’’ to quote from Kidston and Gwynne-
Vaughan, “‘ depart from the ends of the lobes of the
primary xylem in a perfectly protostelic manner ”’
(.c. p. 266). The traces are given off in regular succes-
sion from the three lobes. The extremity of one of the
lobes gradually becomes more prominent, and is then
nipped off as a fairly large, roundish leaf-trace (Fig. 57)
leaving no gap behind. The trace, with its two exarch
STENOMYELON 139
protoxylem-groups, passes slowly outwards, the secondary
wood at once closing in at the rear. When it first frees
itself from the stele, the trace has its own zone of second-
ary wood, extending all round, but considerably more
Fic. 57.—Stenomyelon tuedianum. Transverse section of stele and adjacent tissues, showing
a leaf-trace just free from the primary xylem. x 9g. Kidston Coll. 2095. From
Kidston and Gwynne-Vaughan.
developed on the outer than on the inner side (Fig. 57)
The double protoxylem may be regarded as a preparation
for the first division of the trace, which soon follows,
each of the resulting strands having a single protoxylem.
The secondary tissues persist, at least on the abaxial
140 STUDIES IN FOSSIL BOTANY
side of each strand, till after the first division, but sub-
sequently disappear. The subdivision of the trace con-
tinues, each successive division being preceded by a
bipartition of the protoxylem. The position of the
latter changes after the trace has left the stele. At
first, as-we have seen, it lies on the outer edge of the
xylem-strand, which is thus exarch, but soon it becomes
immersed, rendering the structure of the free trace-
bundles slightly
mesarch (Fig. 58).
The strands of the
subdivided trace
are much displaced,
but there is no
doubt that Yvule
protoxylem was
directed outwards
in all cases.
In the flattened
portions of petiole
and rachis associ-
ated with the stem
the bundles are
Fi. 58.—Stenomyelon tuedianum. Leaf-trace inthe cortex Very numerous.
suis of reenter the Soe ee They
From Kidston and Gwynne-Vaughan. structure already
described, but the
scalariform elements are relatively more abundant than
in the stem; they. may extend all round the strand,
but are chiefly concentrated in the side where the proto-
xylem is placed. The size of the largest leaf-stalk is
out of proportion to that of the associated stem ; prob-
ably it belonged to a larger specimen. The Sparganum
cortex is much more strongly developed on the petiole
than on the stem.
The size of the stems varied considerably ; in one
specimen the diameter of the stele, including a certain
STENOMYELON 141
amount of secondary wood, is only 2:5 mm. as against
8 or 9 mm. in the principal specimen. These variations
suggest that the stem may have branched.
Associated with the stem, sections of a midrib and
lamina have been observed. From their large size it
was conjectured by Kidston and Gwynne-Vaughan that
the leaf may probably have been a simple one.
Before considering the affinities of Stenomyelon it
will be desirable to give some account of the second
species, S. tvipartitum, which has not hitherto been
described.
Stenomyelon tripartitum, Kidston
This species is derived from the Calciferous Sand-
stones of the Langton Burn, near Duns, Berwickshire.
I am indebted to the discoverer, Dr. Kidston, for the
loan of the sections which he had cut, and for permission
to describe the plant. It is hoped to publish a fuller
account elsewhere.
There are three distinct specimens known, besides
some fragments; in none of them is anything shown
beyond the wood. The diameter ranges from I cm.
to 3mm. The size of the primary xylem varies greatly,
its diameter in the three stems being about 3 mm.,
I'25mm., and 0-7 mm. respectively. In the larger stems
the three lobes of the primary xylem are widely separated,
but this is no doubt partly due to accidental causes.
The primary tracheides are comparable in size to
those of S. tuedianum. The outer tracheides are some-
what smaller, but the protoxylem could not always
be detected, nor is the emission of a leaf-trace shown,
in any specimen. The secondary wood consists of
tracheides about 75 mw in diameter, with numerous
medullary rays of varying width.
Longitudinal sections show that the large primary
tracheides have four or five rows of bordered pits on
their walls, while the smaller peripheral elements are
142 STUDIES IN POSSIE BOTANY
scalariform or even spiral, with transitions to the pitted
form. The tracheides of the secondary wood have
three or four rows of pits on the radial walls, while the
rays present the usual muriform appearance. Tan-
gential sections show that they are in a large proportion
of cases uniseriate, and often of small height, even down
to a single cell.
The smallest specimen is a minute stem, the total
diameter of the wood barely reaching 3 mm., while the
maximum diameter of the primary region is only about
o-7mm. The most interesting feature is that the primary
xylem of this small stem or branch is quite undivided,
and consists, so far as can be judged from the transverse
section, of a continuous mass of tracheides. The tri-
partite xylem is therefore not a constant character of
the species. The primary xylem has no marked lobes,
but there are three angles, at one of which a protoxylem-
group is fairly evident.
There are five transverse sections in all, of the various
specimens, and in none of them is the emission of a leaf-
trace from the stele shown. This is, rather a striking
difference from S. tuedianum, in which, as Dr. Kidston
informs me, “‘it is almost impossible to get a section
without evidence of leaf-traces going off.’ It would
thus seem that the internodes of S. tmipartitum must
have been considerably longer than those of the type-
species.
Another definite distinction 1s to be found in the
medullary rays of the two species. In S. tuedianum, as
we have seen, the majority of the rays are multiseriate
and vertically high, though uniseriate rays, sometimes
of small height, also occur. In S. tripartitum a large
proportion of the rays are uniseriate and many are quite
low. This, though a difference of degree, gives quite a
distinct character to the tangential sections of the wood.
For these reasons we are justified in recognising
S. tripartitum as a distinct species of the genus.
STENOMYELON 143
Diagnosis of the two species
1. Stenomvelon tuedianum, IKidston.—Stem mono-
stelic, primary xylem without xylem-parenchyma, divided
more or less distinctly into three lobes by as many radi-
ating and interrupted bands of parenchyma. Primary
tracheides pitted on all walls. The protoxylems of the
leaf-trace decurrent as exarch strands on the extremities
of the lobes. Secondary thickening occurs. Secondary
tracheides with bordered pits on radial walls only. Medul-
lary rays numerous, one to six cells wide, usually high
and multiseriate. Stele closely invested by a zone of
sclerotic periderm or hard bast. Leaf-traces depart in
rapid succession from the extremities of the lobes and
repeatedly divide in the cortex. Leaf-trace protoxylems
become immersed. Outer cortex of the “ Sparganum ”’
type."
2. Stenomyelon tripartitum, Kidston.—Primary xylem
divided into three lobes, or, in smalJl stems, continuous.
Leaf-traces unknown, but apparently given off at long
intervals. Protoxylem exarch, at the extremities of
certain of the lobes. Medullary rays commonly uni-
seriate and often of small height. Cortex unknown.
It may be added that the primary xvlem, in two
of the known specimens, is considerably smaller than
in any stem of S. tuedianum which has come under
observation.
Affinities of Stenomyelon
In considering the affinities of the genus, the first
question to be decided is whether the primary structure
of the stem is to be interpreted as a protostele, or as a
leaf-trace system. As Kidston and Gwynne-Vaughan
point out, the leaf-traces depart from the stele in a
perfectly protostelic manner, 7.e. nothing of the nature
1 This diagnosis is slightly modified from that given by Kidston
and Gwynne-Vaughan, IQI2, p. 270.
144 STUDIES IN FOSSIL BOTANY
of a leaf-gap is left behind; the trace is simply nipped
off from a solid mass of xylem. The whole structure
certainly suggests a protostele, for the primary xylem
is nearly solid, and the narrow strips of parenchyma are
not even continuous. The fact that in the smallest
stem of S. tvipartitum the primary xylem is quite un-
divided, materially strengthens this view. Apart from
this, we might no doubt interpret the three lobes as a
triplice of reparatory strands enclosing a narrow pith,
and each lving immediately behind the leaf-trace which
it gives off. This would make the whole essentially a
leaf-trace system. But we have no analogy for such
a system occupying practically the entire stele; in all
other cases it forms a peripheral zone, and appears to
have been differentiated from the outer part only of the
stele (Lyginopterideae and Calamopityeae). It thus
seems most natural to adopt the protostelic hypothesis
and to regard the intrastelar bands of parenchyma (when
present) not as a pith, but as comparable rather to the
network of cellular tissue in the primary wood of Heteran-
gium or Rhetinangium, only in a simpler form.
On this view, Stenomyelon comes low down among
the Pteridosperms, for the leaf-trace is only differentiated
when it begins to pass out. Kidston and Gwynne-
Vaughan, to whom our knowledge of the genus is primarily
due, suggest no affinities, merely pointing out that it
differs essentially from Sutclifia (an aberrant genus of
Medulloseae ; see p. 196), with which the exarch proto-
xylem suggested a comparison, in the absence of meri-
steles intervening between the stele and the leaf-traces.
Stenomyelon is undoubtedly an isolated genus. The only,
or at least the nearest, analogy seems to be with the
Calamopityeae, with which it agrees in having numerous
bundles in the petiole, all of which arise from the sub-
division of a single original leaf-trace. There is no other
group of Pteridosperms known for which this holds good.
Another point of resemblance between the two families
STENOMYELON 145
is in the secondary thickening of the leaf-trace, persist-
ing even after its first division. On the whole there
seems to be more in common with Calamopityeae than
with any other group, though there are great differences,
for example, in the exarch xylem. The trace, however,
as it passes outwards, becomes somewhat mesarch, and
on the other hand there is some approach to exarchy in
the protostelic species of Calamopitys, and probably more
than an approach in the new species, C. radiata (p. 133).
If there is any real relation between the two families,
the connection no doubt lay very far back; in some
respects Stenomyelon, as we have interpreted its structure,
is more primitive than any member of the Calamopityeae.
PROTOPITYEAE
Protopitys, Goeppert
Our knowledge of this group has hitherto been con-
fined to the one species, Protopitys Buchiana, Goeppert,
the commonest fossil in the Falkenberg beds, of Lower
Carboniferous age. A similar plant has in more recent
years been discovered in the Yoredale Rocks of York-
shire, and will be referred to subsequently.
Protopitys Buchiana, Goeppert |
This species has long been known; the secondary
wood, which has a quite characteristic structure, was
well described by Goeppert in 1850, and again by Kraus
in 1887. The remarkable primary structure of the
stem was first elucidated by Solms-Laubach, who pub-
lished an admirable account of the fossil in 1893.
The stem attained a very large size. A specimen
observed by Solms-Laubach was almost a foot and a
half in diameter, though doubtless incomplete. Thus
the plant became a tree, and as its leaves were ranged
Io
146 STUDIES IN FOSSIL BOTANY
in two opposite vertical rows, like the Traveller’s Tree
of Madagascar, it must have presented a strange appear-
ance. The detailed structure has been chiefly investi-
gated in a stem or branch of moderate dimensions, about
3-5 cm. in diameter, measured to the outside of the
secondary wood.
The centre is occupied by an elliptical pith, which
in this specimen is well over 1 cm. long by, 4 mm. m
Fic. 59.—Protopitys Buchiana. ‘Transverse section of stem, showing the pith and the
primary, and part of the secondary wood. a and b, the ends sbown enlarged in Figs. 60
and 61. xX about 6. 239a in Solms Coll. From a photograph by Mr. W. Tams.
maximum width, including the primary wood. The
latter forms a continuous but very unequal zone, quite
narrow at the sides, but swelling into a massive strand
at each end of the elliptical transverse section (Fig. 59) ;
these strands constitute the leaf-traces. The broad zone
of secondary wood has a dense structure, resembling,
as seen in transverse section, that of a Conifer. Some
remains of the phloem and cortex are occasionally pre-
served.
PROTOPITYS 147
The details of the primary structure, as shown in the
transverse sections, vary according to the level at which
the section is cut, for they are much affected by the
successive emission and reparation of the large leaf-
traces; we may take the section illustrated in Figs.
59-61 and in the diagram (Fig. 62, III.) as our starting-
point.
The central tissue of the stele forms an extensive,
a ‘ ie
< = in >
_ Oe? J
a «A 4
Fic. 60.—Protopitys Buchiana. Transverse section showing part of the primary wood and
pith at the end a, in Fig. 59. The leaf-trace strand is just detaching itself from the
lateral bands of xylem. The reparatory swellings of the xylem-hands are seen to
the right of the trace. x 32. From a photograph by Mr. W. Tams.
true pith, consisting of uniform, somewhat elongated
cells, with no sign of medullary tracheides; some of
the cells are distinguished by their dark contents. The
primary xylem, as already mentioned, forms a practic-
ally continuous mantle round the pith. At the sides
of the elliptical pith the mantle is quite thin, for the most
part only from one to three tracheides in width. The
primary tracheides are somewhat smaller than the pith-
cells, but larger than the secondary elements abutting
148 STUDIES IN BOsSsiz-bOTANY
on them externally ; they thus constitute a fairly con-
spicuous band on either side (Fig. 59).
At each end of the ellipse we observe a massive
xylem-strand, about 1-5 mm.in diameter. The position of
the strands at the two ends is somewhat different. At
the end marked a (Figs. 59, 60) the strand is just detached
from the lateral xylem-bands, and is plunging into the
secondary wood. It has a rounded section, flattened on
the side towards the pith, and consists of rather large
tracheides, intermixed with some xylem-parenchyma,
often rendered more conspicuous by the dark contents
of the cells (Fig. 60). There is no evident protoxylem
at this level. This strand is the xylem of a leaf-trace,
just preparing to pass out.
A little behind the leaf-trace, the xvlem-band on either
side is enlarged to form a marked projection about
ten to twelve elements in depth (Fig. 60). These two
prominences, like the large strand, contain a little xylem-
parenchyma; the smallest tracheides, presumably con-
stituting the protoxylem-groups, lie on the side towards
the pith, indicating an endarch structure. These two
projections represent, as we shall see, the reparatory
strands of the leaf-trace (Fig. 59).
Turning now to the opposite end (0) (Fig. 59) of the
elliptical pith, we again find a large xylem-strand, but
of a somewhat different form, for it 1s concave, and has
a slight indentation, on the face adjoining the pith
(Fig. 61); it thus passes over somewhat gradually, on
either side, into the narrow lateral xylem-bands, with
which it is continuous. The general structure of the
strand is similar to that previously described, but there
is one important difference. Near the middle of the
inner face and on either side of the median indentation,
there are two definite groups of minute elements, no
doubt the protoxylem (Fig. 61). Their position in this
case is not endarch but mesarch, for they are separated
from the pith by two or three layers of larger tracheides.
PROTOPITYS 149
This xylem-strand is clearly a double one, though the
fusion of its two constituent parts is nearly complete
at the level shown. It represents a leaf-trace cut lower
down in its course than that at a, already described.
By the comparison of different transverse sections,
Solms-Laubach was able to explain the formation and
course of the leaf-traces. Three distinct phases (though
not a continuous series) are shown in the diagrams 1.-IILI.
aw nap tg ete ist pirat, She 4:
ai zy my ft Z he
> . > Ci 3
caer whe Mawes 8';
a i we, P. we
opi
r]
Fic. 61.—Protopitys Buchiana. Similar section at the end b in Fig. 59, showing a leaf-trace
strand lower down in its course. It is here continuous with the xylem-bands and has
two immersed protoxylem-groups. Xx 32. From a photograph by Mr. W. Tams.
(Fig. 62), the last of the three being identical with the
section already described and figured in detail. This
figure will therefore be readily understood. In all the
diagrams the dark points indicate the approximate
position of the protoxylem-groups. It will be observed
that in Diagram III. none are shown in the trace at a,
which is beginning to pass out. Behind this trace the
two lateral reparatory strands or prominences, with their
protoxylem points, are evident. At the end J, the com-
150 STUDIES IN POSSE Botany
position of the new trace from the two united reparatory
strands is indicated.
In Diagram II. trace a is shown at a level intermediate
between a and bd in the section just described ; it has
lost its protoxylem, but has not yet detached itself from
the xylem-mantle ; the reparatory strands, which will
appear behind it, are not yet differentiated. At the
end 0, the leaf-trace
is intersected high
up in its course ; it
is quite detached
from the xylem-
mantle and has
already divided
into two. strands,
which have no pro-
toxylem. The two
reparatory strands
which will replace
the outgoing trace
are already promi-
Fic. 62.—Protopitys Buchiana. ‘Three diagrams of trans-
verse sections of the primary wood, to show emission nent.
of leaf-traces. I. At a the double trace is passing Diagram 2 shows
out, at bit has already gone. Reparatory swellings
conspicuous at both ends. II. At a the trace is gq different phase
undivided and not yet detached. At b it is detached
and divided into two. Reparatory swellings only again, for it passes
developed at bend. III. At @ the trace is detached, above the point of
though not yet divided. At b it is cut low down in
its course. Reparatory swellings only formed ata exjt of both leaf-
end. This is the section shown in Figs. 59-61. The
black spots indicate protoxylem throughout. After traces. The trace
gale sas at a is still visible,
but cut obliquely; it is forking to form two strands.
The reparatory projections behind it are about to meet.
At the end 0b the trace has disappeared altogether,
leaving the pith open. Here also the reparatory strands
are very prominent.
It will be noticed that the two traces are never shown
in the same phase in any one section, for they were given
off alternately, the arrangement of the traces, and there-
t
%
'
i, ce
i
=
pane
PROTOPITYS 151
fore of the leaves which they supplied, thus being distich-
ous. Solms-Laubach obtained direct evidence of this
by means of a longitudinal section in the plane of the
major axis of the pith. It shows clearly how the three
traces met with were given off alternately on opposite
sides, each leaving a gap just above its exit.
This is the first example we have met with of a dis-
tichous phyllotaxis ; so far, it stands alone among plants
referred to Pteridosperms, though instances are well
known among fossil Tree-ferns (Megaphyton).
The mode of formation of the leaf-trace is also excep-
tional. We may sum up the process as follows: When
the previous trace has passed out, the parts of the xylem-
mantle near the edges of the gap become thickened,
forming two opposite prominences ; they then meet and
fuse into a solid strand to form the new leaf-trace, which
now detaches itself from the xylem-mantle and divides
into two as it moves outwards. The construction of
the trace by the fusion of two reparatory strands is quite
peculiar ; somewhat similar thickenings of the edges of
the leaf-gap have been observed in some recent Ferns
with a tubular stele, but the analogy seems remote.
As Solms-Laubach points out, the reparatory structures
are not properly described as “strands,” for they are
merely enlarged portions of a continuous xylem-ring,
and only become free when the new trace is constituted.
The behaviour of the protoxylem is also remarkable.
Endarch in the reparatory strands, it becomes mesarch
in the fused leaf-trace, owing probably to the mode of
fusion, and then dies out altogether. The change from
endarch to mesarch structure has a parallel in the xylem-
strands of the Evistophyton sub-genus of Calamopitys,
with which there is otherwise no analogy.
In the primary xylem, so far as Solms- Laubach
observed, the tracheides are typically scalariform; no
pitted elements are recorded. This again is an excep-
tional feature. The secondary wood is equally peculiar
152 STUDIES IN POSsSsthe ay TAM
and unlike that of any plant we have previously described.
In transverse section, as already mentioned, it has the
dense appearance of a Coniferous or Cordaitean wood
(Fig. 59); its special characters appear in the radial
and tangential aspects. The pits, limited as usual to
the radial walls, are transversely elongated, and for the
most part form a single vertical series; occasionally
the row is double and the pits shorter. The structure
is almost intermediate between the scalariform and the
ordinary pitted types. Where the preservation is ex-
ceptionally good, it can be seen that the pits are bordered,
with slits inclined, as usual, in opposite directions on
adjacent walls.
Prof. Seward has pointed out that a somewhat similar
form of pitting occurs in a Mesozoic Conifer, Xenoxylon
phyllocladoides.+
The medullary rays are narrow and for the most
part of extremely small height ; in fact, as often as not,
they are only one cell high, thus forming a single radial
line of cells. The greatest height observed was sixteen
cells, but this is quite exceptional. The rays are as a
rule uniseriate, but sometimes two, or very rarely three
cells wide in the middle. The general character of the
wood is thus quite peculiar and different from that of
the great majority of Pteridosperms.
In one case Solms-Laubach was able to examine the
structure of the phloem, which is seldom preserved. He
found that it consists of alternating concentric zones of
hard and soft bast ; the former has an unusual character,
for it consists of short stone-cells, and no medullary
rays can be distinguished. A comparison with the
corresponding region of Stenomyelon tuedianum was
suggested above (p. 138). The zones of soft bast
contain long tubular elements, presumably the sieve-
tubes.
Some fragments of tissue associated with the stem
1 Seward Fossil Plants, vol. 111. 1917, p. 213.
FROLGPITYS 153
seem to belong to the lamina of a leaf, rather than to
the cortex, for an apparent epidermis is present on both
sides ; the tissue is badly preserved, but small vascular
bundles, with scalariform tracheides, can be recognised.
Solms-Laubach observed the base of a branch in con-
nection with the main stem. The stele of the branch
has the same structure as that of the parent axis, on
which it is inserted obliquely. The size of the pith
diminishes, and the amount of primary xylem increases,
as the branch-stele is followed inwards to its junction
with the main axis.'
Protopitys radicans, Kidston
This species is derived from the Yoredale rocks of
Swarth Fell, Yorkshire, and thus belongs to the upper
part of the Lower Carboniferous. Our knowledge of
the plant is due to Dr. Kidston, who still has the speci-
mens under investigation. The characters of the second-
ary wood, namely the pitting of the tracheides and the
structure of the medullary rays, indicate the reference
of the species to Pvrotofitys. The cortex is preserved
and is traversed by a zone of embedded roots, a peculiar
feature, which suggested the specific name. Pending
further investigation especially of the primary tissues,
we can only record the occurrence of the species, which
promises to be of much interest.
Affinities of Protopityeae
Protopitys seems to be the most isolated of the genera
which are referred, on anatomical grounds, to the Pterido-
sperms or Cycadofilices. Its peculiarities have been
1 See Solms- Laubach, ‘‘ Uber die in den Kalksteinen des Kulms
von Glatzisch-Falkenberg in Schlesien enthaltenen structurbietenden
Pflanzenreste,”’ ii. Bot. Zeitung, Band li. 1893, p. 197. The older
references are given in this paper.
154 STUDIES IN FOSSIL BOTANY
pointed out in the course of the description of P. Buchiana,
but may be shortly recapitulated as follows :
. The distichous phyllotaxis.
. The continuous, but unequal ring of primary xylem.
. The union of two reparatory masses to form the leaf-
trace.
. The endarch structure in the reparatory region, becoming
mesarch in the leaf-trace, in which, however, the proto-
xylem is soon lost.
. The scalariform tracheides of the primary ia
The semi-scalariform pitting of the secondary wood.
. The narrow and usually very low medullary rays.
_ OO N H
NI NWN
The distichous phyllotaxis appears to be only
paralleled, among Palaeozoic plants, in the Fern
Megaphytum, which has otherwise nothing in common
with our fossil. The unequal xylem-ring may find a
partial analogy in certain species of Calamopitys and
Lyginopteris, but the vascular system is so different in
the two cases that no real resemblance can be traced.
The fusion of two equivalent reparatory units to form
the new leaf-trace, and their origin as swellings on the
xylem-ring, seem to be quite peculiar features; the
thickenings on the edge of the leaf-gap in some soleno-
stelic Ferns are not comparable, for they are cauline in
nature, and are not concerned in the formation of the
leaf-trace.*
The change from endarch to mesarch structure in
the ascending leaf-trace is of course familiar (e.g. Calamo-
pitys, sub-genus LEvistophyton, Bilignea, Mesoxylon), but
the dying out of the protoxylem in the upward direc-
tion seems to be without analogy, while the reverse is
often the case.
The scalariform sculpturing of the tracheides of the
1D. T. Gwynne- Vaughan, ‘ Observations on the anatomy of
solenostelic Ferns,” Part u., Ann. of Bot. vol. xvii. 1903, pp. 692,
COG.
PROTOPITYS 155
primary wood, while pitted elements are absent, is an
unusual feature in the stem of Pteridosperms ; analogies
among higher plants, such as the Cordaiteae, are too
remote to be significant. The nearest parallel is with
the primary xylem of the Cladoxyleae, another isolated
group, to be described in the next section.
The wood of Protopitys, in fact, is altogether peculiar,
for the secondary elements constantly show scalariform
or semi-scalariform pitting, very different from the usual
round, multi-seriate pits of other families. Here, also,
the Cladoxyleae present the closest analogies (see below,
p. 160).
The medullary rays of Protopitys are remarkable for
being, as a rule, uniseriate, with a large proportion of
‘““one-storied’’’ rays, 7.e. rays only one cell high. These
little rays are often strung together in moniliform rows.
Some similarity is shown here also by the secondary
wood of Cladoxyleae, in which the rays are usually
uniseriate and often one-storied.
The general result of our brief survey is to confirm
the impression that Protopfitvs is an isolated type; there
is, in fact, no agreement of a really suggestive kind with
any other group, except, perhaps the highly problematic
Cladoxyleae, with which the structure of the wood
shows a close analogy, though the general organisation
is totally different.
All the families previously considered have shown a
certain relationship, sufficient to justify us in classing
them as Pteridosperms, though it is only in the Lygino-
pterideae that we know the seeds. With the Proto-
pityeae the case is different, the type stands apart, and
we include it under the heading Pteridosperms or Cycado-
filices, because it is in some ways Fern-like, but is not a
Fern. Solms-Laubach, to whom we owe our knowledge
of the true structure of the plant, put Protopitys with
Lyginopteris and Heterangium, among plants which are
intermediate in their characters between Filicineae and
156 STUDIES IN FOSSIL BOTANY
Gymnosperms and may represent descendants in different
directions of a primitive group common to both.!
This was in 1893, when comparatively few such plants
were known. Solms first made Protopfitys into a distinct
family, and pointed out the absence of any Cycad-like
features, such as are found in Lyginopteris. Since that
time, in spite of many new discoveries, there has been
little to connect Pvotopitys. any more closely with the
other families now grouped under Pteridosperms.
THE CLADOXYLEAE
We now come to an interesting group of early Palaeo-
zoic plants, very different from any of those already
described and, in fact, remarkably isolated, so that its
affinities are open to much doubt. The Cladoxyleae
have been known for a long time ; a number of forms
were described by Unger in 1856; his specimens came
from Saalfeld in Thuringen, the same locality which
yielded Calamopitys Saturn, C. annularis, Clepsydropsis
antiqua and a number of other fossils of interest. Our
knowledge of the family was first placed on a scientific
basis by Solms-Laubach forty years after the date of
Unger’s discoveries; in recent years the investigation
has been taken up anew by Prof. P. Bertrand, whose
results are not yet published in full.
The stems referred to this family agree in the fact
that they all have a complex, polystelic structure, thus
differing completely from the families of “ Pteridosperms’’
already described, in which the vascular system of the
stem is always referable to a single central cylinder. In
the Cladoxyleae there is the further peculiarity that in
mature specimens each stele has its own secondary zone
of tissue, though in other cases the primary structure
has remained unaltered, thus presenting the general
appearance of a polystelic Iern-stem (cf. Figs. 63 and
1 Solms, /.c. 1893, p. 207.
CLADOXYLEAE 157
64). The petioles have now been recognised in some cases,
but we are still practically without information as to the
external habit, while the fructification is wholly unknown.
Dr. Bertrand recognises three genera in the family:
Fis. 63.—Cladoxylon taeniatum. Transverse section of stem, showing the numerous steles,
those of the outer zone radially elongated and those of the centre circular. The three
steles at the top of the figure are believed to be destined for a leaf-trace. Xx about 3.
From a photograph by Dr. Bertrand.
Cladoxylon, Unger, Volkelia, Solms, and Steloxylon, Solms ;
the last mentioned, however, is still a highly problematic
fossil. Cladoxylon and Vélkelia are of Lower Carboni-
ferous or possibly, as regards the Thuringian species,
of Upper Devonian age ; the horizon to which Steloxylon
158 STUDIES IN POSsSil BOTANY
belongs is open to question. We will begin with the
type genus Cladoxylon.*
Cladoxylon, Unger
This is the best-known genus of the family. Unger
described no less than eight species, and referred them
to five different genera; we may now, however, pro-
visionally adopt the simple view of Dr. Bertrand, who
assigns Unger’s forms to the one genus, with three
Saalfeld species, C. mivabile, Unger, C. taematum (Unger),
and C. Solmsi, P.B. To these we must add the Scottish
species C. Kidstont, discovered by Dr. Kidston and
described by Solms-Laubach in rg1o.
The larger specimens, reaching 4 cm. or more in dia-
meter, have the typical Cladoxvlon features and were
no doubt, the stems; others, usually smaller, and with
a somewhat different, though still polystelic structure,
have now been identified as the petiole or rachis. Taking
the stem first, we find the following characters common
to the genus. The numerous steles are for the most
part elongated in a radial direction, an unusual feature
in polystelic plants (Figs. 63, 64). Each stele has a
median band or mass of primary wood, in which the
tracheides are irregularly arranged ; at the distal end,
or about the middle if the stele is cylindrical, there is
a gap or loop containing the protoxylem elements.
Usually, but not always, the primary xylem is sur-
rounded completely or incompletely, as the case may
be, by a zone of radially seriated, secondary wood,
traversed by uniseriate, medullary rays. The pitting is
1 See Unger, in Richter and Unger, “‘ Beitrag zur Palaontologie des
Thiiringer Waldes,’ 2ter Theil, Denkschriften der K. Akad. d. Wiss.,
Wien,. Band xi. 1856; Solms-Laubach,. ‘‘ Uber die seinerzeit von
Unger beschriebenen struckturbietenden Pflanzenreste, etc.’’ Abhandl.
d. K. Preuss. Geol. Landesanstalt, 23, 1896; P. Bertrand, “ Etat actuel
de nos connaissances sur les genres Cladoxylon et Steloxylon,’’ Assoc.
Frang. pour l’ Avancement des Sciences, Congres de Havre, 1914, p. 446.
CLADOXYLON 159
generally scalariform, that of the secondary elements
being limited in all probability to the radial walls.
Externally the wood of each stele is enclosed in a layer
of phloem, usually ill-preserved. The surrounding tissue
is parenchymatous, but in the parts remote from the
steles a fibrous structure has been observed.
The two principal Saalfeld types are C. mirabile and
C. taeniatum. In C. mirabile the steles, as seen in trans-
verse section, are usually long and often forked or curved,
sometimes assuming a U form, with the concavity directed
outwards (Fig. 64). Where a curved stele abuts with
both ends on the periphery, each arm has its own peri-
pheral loop or protoxylem group. The steles in their
longitudinal course occasionally fused with one another.
The secondary thickening is not usually very pronounced ;
sometimes it is only present on one side of the stele,
while in other cases it is absent altogether, as in the
stem shown in Fig. 64. Such stems, no doubt represent-
ing the young condition, were in some cases separated
by Unger under the name Arctopodium radiatum.
. The second type, Cladoxylon taeniatum, is character-
ised by the usually straight steles; those of the outer
zone are radially directed and may be much elongated
or elliptical in section, the longer and shorter steles
irregularly alternating. There is also a central group of
steles (five in number in the case figured) which are
more or less circular in section. Similar round central
steles (“ star-rings ’’) occur in several of the Medulloseae,
another polystelic family, to be described in the next
chapter. In C. taeniatum there is a great development
of secondary tissues around each stele, as shown in Fig.
63.2
@ae thing species, .C.— Solms:, P.B., resembles C.
taemmatum, but without the central steles, while .the
occasional curvature of the steles recalls C. mirabile ;
1 C. dubium, Unger, often mentioned in the literature, seems to be
a form of C. taeniatum with shorter steles.
160 STUDIES IN FOSSIL BOTANY
this is the plant in which the petiole was first recognised
by Solms-Laubach.!
The secondary wood seems to be very uniform through-
out the genus; in some cases it is most developed on
the side of the steles directed towards the centre of the
stem, a peculiarity which recurs in some species of
Medullosa (see p. 176).
The narrow medullary rays are characteristic—they
are often only one cell high as well as one cell wide, thus
being reduced to a single radial row of cells.
As already mentioned, there is one British fossil
which has been placed in the genus Cladoxylon. The
specimen, discovered by Dr. Kidston, is of Lower Carboni-
ferous age and is derived from the Calciferous Sandstone
Series of Berwickshire. It was described and figured
by Solms-Laubach, who named it C. Kidstom.?
The species is a fragment of a rather large stem,
containing part of a ring of steles, ovate in transverse
section and but little elongated in the radial direction
(Fig. 67, A). In each there is a narrow band of primary
wood, surrounded by a broad secondary zone chiefly
developed on the side presumably facing the centre of
the stem, while on the opposite side it is limited to one
or two small wedges.
The pitting of the secondary tracheides is confined
to the radial walls. Prof. Seward, who has re-investi-
gated the specimen, finds that the pits are either “‘ uni-
serlate and transversely elongated, very like those of
Protopitvs, or biseriate and almost circular, like those
of Conifers.’? Sometimes there are three rows.?
1 Lc. 1896, p. 55, Taf. ii. Fig. 13, Taf. iii. Fig. 4. Solms called this
specimen ‘‘ C. mirabile ?’’ He also figured and described a probable
petiole in a specimen which he named Arctopodium radiatum (see our
Fig. 64).
2 Solms- Laubach, ‘‘ Uber die in den Kalksteinen von Gli&tzisch-
Falkenberg in Schlesien erhaltenen structurbietenden Pflanzenreste,”’
iv., Zeitschrift fiir Botanik, ii. 1910, p. 537, Figs. 5, 7, 11, 13.
8 Seward, Fossil Plants, vol. iii. pp. 205-207, Fig. 460, A, C, 1917.
CLADOXYLON 101
The numerous medullary rays are almost always
uniseriate ; the tangential section of the wood is a good
deal like that of Protopitys. The presence of rays favours
the reference of the plant to Cladoxylon, rather than the
next genus Vdlkelia, to which it otherwise bears some
resemblance (Fig. 67, A and B). Prof. Seward does not
accept the evidence for the attribution to Cladoxylon
as convincing, but no other affinities have been suggested,
beyond a certain analogy with the problematic South
African genus Rhexoxylon (see p. 228).
We now come to the question of the petiole and leaf-
trace of Cladoxylon. As already mentioned, the base
of a petiole was observed by Solms-Laubach in the form
named by Dr. Bertrand C. Solmsi, and also in a specimen
described under Unger’s name Arctopodium radiatum.
The latter case is shown in Fig. 64 from a photograph
by Dr. Bertrand, to whom our present knowledge of the
appendages of Cladoxylon is due.}
The specimen shown in Fig. 64 is very clear. The
stem is of the C. mirabile type, but without secondary
thickening, 7.e. it was still young, which no doubt accounts
for the petiole still being attached to it ; the two organs
are connected by parenchyma, though at this level the
vascular systems are already separated. The petiole
contains eight vascular strands, one of which seems
to be dividing. They are round or elliptical in section,
and quite different in form from the steles of the stem.
Each strand has a well-marked median band or group
of protoxylem. As might be expected, all the wood
appears to be primary. The ground-tissue is also well
preserved, and on the abaxial surface there is a layer
resembling a hairy covering.
The bodies, roundish in section, which accompany
the petiole are described by Dr. Bertrand as aphlebiae,
1 I am indebted to Dr. Bertrand for valuable information given in
correspondence, in addition to his preliminary notes already pub-
lished.
II
162 STUDIES IN FOSSIL BOTANY
each containing a single bundle, or sometimes two,
resembling those of the petiole. The aphlebiae were
finely divided.
The emission of the leaf-trace has been studied by
Dr. Bertrand ; an example is shown in Fig. 65, a diagram
aphlebiz
Fic. 64.—Arctopodium radiatum, probably a young stem of Cladoxylon mirabile. Below,
the stem is shown, with the curved and forked steles, without secondary thickening.
Connected with the stem above is a petiole containing several elliptical bundles. The
roundish structures on either side are the aphlebiae. x about 7. From a photograph
by Dr. P. Bertrand.
taken from one of Unger’s sections now in the Jermyn
Street Museum. The typical process is described as
follows :—The outgoing mass is formed at the expense
of four to six radiating plates of the stem. The four
median plates each give off two outgoing rings ; the end
Ras ye
CLADOXYLON 163
plates only one each; the latter pass out into the finely-
divided aphlebiae. The eight remaining rings arrange
themselves in a circle, first becoming flattened tangenti-
ally, and then elongating radially. They have not been
followed out into the petiole, but comparison suggests
that the latter organ assumes the structure of Hzevo-
gramma., |
The latter is one of Unger’s genera, which, as now
suggested, consists of the petioles of Cladoxylon. An
Petiole primaire
Aphlebia: -
Fic. 65.—Diagram of stem in transverse section, to show the emission of a leaf-trace entering
a petiole. JT, stem; F, base of petiole; I, IV, bundles destined for aphlebiae; II,
III, central strands of leaf-trace. Jermyn Street Coll., 15871. After Dr. P. Bertrand.
example of Hievogramma mysticum is shown in Fig. 66 ;
the great tangential elongation of the outer steles is an
indication of approaching dichotomy. A bilateral sym-
metry is characteristic of these organs and serves to
distinguish them from the stems. The picturesque name
given by Unger indicates the hieroglyphic-like pattern
of the transverse section.
It will be seen that the structure of Hierogramma is
very different from that of the attached petiole shown
in Fig. 64. The latter, however, is cut near the base,
164 STUDIES IN POSSIE' BOTANY
and the structure may have changed higher up; it is
possible, as Dr. Bertrand has suggested, that Hierogramma
may have been the petiole of the species C. taentatum.
In the leaf-base found by Solms-Laubach in connection
with the stem now named Cladoxylon Solmst, the single
bundle shown resembles that of a Hierogramma.
Syncardia, another of Unger’s genera, is described by
Dr. Bertrand as a reduced state of Hzerogramma with
from four to six xylem plates. Probably it represents
Fic. 66.—Hierogramma mysticum (petiole of a Cladoxylon). Transverse section, showing
the stelar system of a petiole about to dichotomise. x 8. From a photograph by
Dr. P Bertrand.
a secondary rachis of the same leaf, but the connection
has not been observed.
From the arrangement of the leaf-traces in C. mirabile
(Arctopodium radiatum) Dr. Bertrand finds that the
phyllotaxis was spiral and the divergence probably 3.
It will be seen that our knowledge of the genus Clad-
oxylon is still very incomplete, and that various points
need corroboration. We may hope for further light
from the extension of the important investigations which
Dr. Bertrand has initiated."
1 See, in addition to the paper above cited, P. Bertrand, ‘‘ Observa-
sions sur les Cladoxylées,’’ Comptes Rendus de l’ Association Frang. pour
VOLKELIA 165
VOLKELIA, Solms
This genus was founded by Solms-Laubach in Ig1o
on the Sphenopteris refracta of Goppert. The specimens
are derived from the Lower Carboniferous of Falkenberg
in Silesia.1 The plant was put in Sphenopteris by its
discoverer because some of the fragments include portions
of a compound frond, bearing finely divided leaflets.
But, as Solms-Laubach has pointed out, the fragments
showing the foliage do not show structure, and vice versa.
Hence there is no actual proof that the two kinds of
specimens belonged to the same plant, though there is
a certain probability that this may have been the case.
If it were so, this would be the only instance in which
we have any indication of the outward habit of a member
of the Cladoxyleae.
The stem, about 8-10 mm. in diameter, has the highly
polystelic structure usual in the family. In fact, the
general appearance of the transverse section is almost
identical with that of the Cladoxylon dubium of Unger,
who actually referred G6ppert’s specimens to that
species. In Vélkelia there are a dozen or more ovate
or angular steles, large and small; the larger steles
nearly meet at the centre, while the smaller ones are
wedged in between them, towards the periphery (Fig.
67, B). The main part of each stele is formed of large,
radially arranged scalariform tracheides, the inner layers
of which have often collapsed. This secondary zone is
thickest towards the centre of the stem, and sometimes
l Avancement des Sciences, Congrés de Dijon, 1911; ‘‘ L’Etude du stipe
de l’Asteropteris noveboracensis,”’ XII. Session du Congrés géologique
international, Ottawa, 1913. The latter paper contains diagrams of
the leaf-traces of Cladoxylon. The note of 191I was written at a time
when the author thought that Clepsydvopsis might be the petiole of
Cladoxylo, a view which he has since abandoned, having recognised the
true petioles belonging to the genus, as stated in the text.
1 See Solms-Laubach, 1910, above cited, and the earlier works
there referred to.
166 - STUDIES: IN- FOSSIL BOTANY
almost dies out on the peripheral side of the stele. In
the interior, eccentrically placed towards the peripheral
end, there is a well-preserved primary strand of smaller
elements. In this group the outer tracheides, like
those of the secondary wood, are scalariform, but about
the centre narrow, annular, and reticulate tracheides are
intermingled with long-celled parenchyma. This, then,
is the seat of the protoxylem.
The characteristic feature of V6lkelia lies in the
structure of the secondary wood; the tracheides are
pitted on all their walls, and there is no trace of any
medullary rays. So simple a structure of a secondary
zone of xylem is rarely met with, and at once distinguishes
the genus from its allies.
The steles are only slightly elongated (as seen in
transverse section) in the radial direction ; the phloem
is not preserved; the outer zone of the cortex has a
fibrous character, and approaches the Dictyoxylon type.
Thus Volkelia in its general construction betrays an
evident affinity with Cladoxylon, and can only be placed
in the same family ; in the structure of the wood it is
quite peculiar, and simpler than any other plant referred
to the Pteridosperms or Cycadofilices.
According to the views of Dr. Bertrand, Steloxylon
should be included in the Cladoxyleae, but in the present
state of our knowledge it will be more convenient to
take that doubtful genus after we have dealt with the
Medulloseae.
Affinities of the Cladoxyleae
It is sufficiently plain, from what has been said above,
that this family is a very isolated one and shows no
evident affinity with any of those previously described.
Certain points in common with Protopitys in the structure
of the wood have already been pointed out ; the general
structure, however, is so totally different that no near
relationship can be imagined. In the next chapter we
CLADOX YLEAE 167
shall make ourselves acquainted with an important
group, the Medulloseae, which, lke the Cladoxyleae,
Fic. 67.—A. Cladoxylon Kidstoni. Transverse section, showing several steles, with very
unequal secondary thickening. Slightly magnified. After Solms-Laubach. B. Volkelia
refracta. Transverse section of stem, somewhat diagrammatic, showing the numerous
steles. In each the primary wood is near the periphery.
Inner layers of secondary
wood collapsed—outer layers preserved. ™X about 6.
After Solms-Laubach, modified.
combine polystely with secondary growth. But here
too there are difficulties in the way of assuming a real
affinity.
168 SLPUDIES IN FOSSIL: BOTANY
The radially orientated steles, the peripheral loops,
the usually scalariform tracheides, the participation of
several steles in constituting the leaf-trace, the peculiar
stem-like structure of the petiole and the presence of
aphlebiae seem to be the chief characters of the Clado-
xyleae. .
How are we to class them? Dr. Bertrand in his
note of 1914 says that they appear to constitute a new
group of ancient Phanerogams. More recently, in a
letter dated August 3, 1920, he expresses the view that
the Cladoxyleae are very primitive types, and that it
is necessary to make them a class apart—one cannot
class them with complete certainty either among the
Ferns or among the Phanerogams, yet they surely be-
longed to one or other of these two groups and very
probably to the Phanerogams. He points out that in
them the distinction between the stems and the petioles
was still very slightly marked.
This discloses a very interesting position. We appear
to have in the Cladoxyleae a very primitive group, with
little differentiation between axis and appendages, and
yet there is a probability that they were already Phanero-
gams (7.e. Pteridosperms in a wide sense). Dr. Bertrand’s
remarks suggest the belief, which seems to be growing
stronger every day, that the Spermophyta may go back as
far as any of the recognised types of Pterodophyta, and
may have had their origin among quite early vascular
plants, on a level, perhaps, with the Psilophytales.
At the same time it must be recognised that the
evidence for referring the Cladoxyleae to Pteridosperms
is extremely indirect. As Dr. Bertrand remarks, the
only other group with which they can be compared is
the Ferns; they have something in common with the
latter, especially with the Zgyopterideae, in the peri-
pheral loops of the xylem and in the aphlebiae.*
1 Aphlebiae, however, appear to occur also on certain fronds re-
ferred to Pteridosperms.
CLADOXYLEAE 169
In other respects, especially the complex vascular
system of the petiole, the organisation is very different
from anything we find among Palaeozoic Ferns; the
analogies with some of the Pteridosperms, though still
remote, are somewhat closer. On the whole, therefore,
the opinion cautiously expressed by Dr. Bertrand, in
essential agreement with that of Solms-Laubach, appears
to be justified.
CHAPTER CMs
PTERIDOSPERMEAE—continued
Medulloseae ; Aneimiteae ; Seed-bearing Pecopterideae ;
Dolerophyllum ;_ Steloxylon; Rhexoxylon ; Cycad-
oxyleae ; Summary
MEDULLOSEAE
Hapit.—As long ago as 1883 the Austrian palaeobotanist
Stur, as already mentioned, proposed to exclude certain
of the principal genera of fossil Fern-like fronds from the
Ferns, on the ground that, in spite of all the research
devoted to them, they had never been found to bear
Filicinean fructifications. The genera which he specially
cited were Neuropteris, Alethopteris,: Odontopteris, and
Dictyopteris ; these genera, along with others, are now
1 In a new species referred to Alethopteris, A. Pfeilstickeri, from
the Coal-measures of Saxony, Prof. R. Beck recently described a sup-
posed Fern-like fructification. It consists of numerous round pustules,
interpreted as sori, arranged in rows on the lower side of certain leaflets.
The pustules lie between the veins and not over them, a position which
is unfavourable to the interpretation of these bodies as sori. The
supposed indications of sporangia appear to be of doubtful value. See
R. Beck, “‘ Alethopteris Pfeilstickerit, ein neuer Farn aus dem Ober-
karbon von Lugau-Olsnitz,”” Abhandl. d. naturwiss. Gesellschaft ISIS in
Dresden, 1917, p. 23. For a criticism see W. Gothan, “‘ Palaobota-
nische Verodffentlchungen aus den Jahren 1914-1918,” Zeitschrift fur
Botamik, Band 11, 1919, p. 192. The Abbé Carpentier has recently
found some scattered pollen-grains in cavities formed in the leaflets of
Alethopteris Grandini. ‘There seems, however, to be no proof that the
pollen-grains are in situ. Carpentier, ‘‘ Note sur quelques Végétaux a
structure conservée,”’ etc., Revue gén. de Botanique, t. xxxili. p. 684,
1921.
170
ay Ee Bee
NEUROPTERIDEAE 171]
often grouped in the family Neuropterideae, based on
external characters, corresponding in part, if not
altogether, to the Medulloseae as defined by structure.
Recent investigation has fully justified Stur’s conclusion
(though not accepted at the time), and, as we shall see,
there is now every reason to believe that the Neuro-
pterideae generally were seed-bearing plants (Pterido-
Fic. 68.—Neuropteris heterophylla. Part of vegetative frond, slightly enlarged.
From a photograph by Dr. R. Kidston, F.R.S.
sperms) and not Ferns. Among the genera in question
Neuropteris and Alethopteris are the most extensive and,
at present, the best investigated.
The leaves of Neuropteris are of a very large size,
bipinnate, tripinnate, or even quadripinnate in composi-
tion, with ovate or oblong leaflets somewhat cordate at
the base, and usually attached to the rachis by a short
stalk. The median nerve of the pinnule is distinct till
near the end, where it breaks up into smaller dichotomous
172 STUDIES IN POSsi ze BOTANY
nervules ; similar nervules are given off from the sides
of the median nerve throughout its length; they leave
the latter at an acute angle, and bend outwards to the
margin (Fig. 68). The fronds recall those of some recent
Osmundas.
In some cases, pinnae of a different form, without
a median nerve, and described under the name of Cyclo-
pteris, were attached directly to the rachis, and may
have been of a stipellar
nature. These organs.are
of the same kind as the
“aphlebiae’’ mentioned
in Vol. I., Chapters Vie
and IX., as occurring on
the fronds of Ferns.
In the genus Aletho-
pteris the leaves are
likewise large, and _ bi-
to tripinnate, but here
the thick, usually oblong
pinnules are inserted on
the rachis by a_ broad,
decurrent base, and are
in some cases confluent
with one another. The
Fic. 69.— Alethopteris lonchitica (foliage of a edges of each leaflet are
Munn, Fart of ina. Retwed. incurved on the lower
side. The median nerve
extends the whole length of the pinnule, and is prominent
on its under surface; the secondary nerves leave the
median one at a wide angle, and pass directly, with or
without dichotomy, to the margin (see Fig. 69). The
habit resembles that of the recent Marattiaceous Fern
Angiopteris.
In the case of both these so-called genera, founded
on the external characters of the leaf, there is now good
evidence that they belonged to stems of the family
MEDULLOSEAE 173
Medulloseae, of which the structural characters are known.
The nature of the proof will be given later, after describ-
ing the anatomy of the stem; but, while considering this,
it is necessary to bear in mind that we are dealing with
plants which possessed a highly compound Fern-like
foliage, and which, in some forms at any rate, must have
had a habit not unlike that of some of the existing Tree-
ferns. We will first describe the anatomy of various
representatives of the family, beginning with the type
genus Medullosa, and will then go on to the evidence
which we now possess as to the reproductive organs,
especially the seeds.
ANATOMY—WMedullosa.—The anatomical description
will be based, in the first instance, on a British species,
which is of greater geological antiquity than most other
known members of the genus, and is likewise simpler
in structure. As this form is now known with a con-
siderable degree of completeness, it will best serve to
give an idea of the essential anatomical characters of
the group.
Medullosa anglica is derived from the Lower Coal-
measures of Lancashire, at the same horizon to which
most of our British Coal-plants, with structure preserved,
belong. The original specimens were found in nodules
from the coal-seam at the Hough Hill Colliery, Staly-
bridge, at dates ranging from 1892 to 1808, by the late
Mr. G. Wild and Mr. Lomax.’ It is a curious fact that
these specimens were the first stems of a Medullosa to be
recognised in this country, though the petioles of plants
belonging to this genus had long been familiar among
the common objects of the calcareous nodules. Speci-
mens have since been found in other localities, and it
is interesting that at Shore, Littleborough, they occur in
1 For a fuller description, see my paper, “‘ Structure and Affinities
of Fossil Plants from the Palaeozoic Rocks: iii. Medullosa anglica, a
New Representative of the Cycadofilices,”’ Phil. Trans. vol. 191, B, 1899.
A
74 STUDIES IN FOSSIL BOTANY 7
the roof-nodules, which often show a distinct Flora from
that of the nodules in the seam below.?
The stems are of rather large size, having a mean
diameter of 7 or 8 cm., in the specimens at present known.
This dimension includes the leaf-bases, which were ad-
herent to the stem for a long distance before becoming
free ; in fact, practically the whole external surface was
formed by these leaf-bases, which were spirally arranged,
Fic. 70.—Medullosa anglica. External view of stem, showing two large leaf-bases, with a
furrow between them. The surface is ribbed, owing to the presence of hypodermal
strands of sclerenchyma. # nat. size. S. Coll. (G. T. G.)
the phyllotaxis, where it could be determined, having
followed the 2. arrangement. Fig. 70 will give an idea
of the external appearance of the fossil stem ; the surface
of the large adherent leaf-bases is marked by a longi-
tudinal striation, due to the hypodermal ribs of scler-
enchyma, which stand out prominently in the fossil,
1 Dr. Arber described in 1903 a specimen in the Binney Collection at
Cambridge. This must have been discovered many Years before the
type-specimens, but had apparently lain unnoticed. See Arb€r, “ On
the Roots of Medullosa anglica,”’ Ann. of Bot. vol. xvii. 1903.
MEDULLOSA 175
though during life they must have been nearly or quite
concealed from view by overlying tissue. The trans-
verse section, represented somewhat diagrammatically
in Fig. 71, shows the chief points in the organisation
of the stem. This section was cut near the bottom of
a piece of stem about a foot long. At this level, three
large leaf-bases are shown ; that marked c in the figure
is the nearest to its separation from the stem, and actually
became free an inch or two higher up. The next leaf
*
L.A.B.
Fic. 71.—Meduillosa anglica. ‘Transverse section of stem, showing three large leaf-bases,
a, b, and c. ab, bc, position of next leaf-bases above. st, the three steles; 1.t, leaf-
traces ; an, accessory rings cf wood and bast; fd, periderm, forming a ring round the
group of steles, and also enclosing one of the accessory strands ; 7, adventitious root ;
o.c, hypoderma; sc, sclerenchymatous band between leaf-base and stem. Slightly
reduced. Phil. Trans.,S. S. Coll. 737.
to become free is that marked 0b, while a remains in
connection with the stem for a vertical distance of 5 or
6 inches. At higher levels, two new leaf-bases make
their appearance, the first (bc) between b and c, and the
next (ab) between a and b. Thus the order of insertion
of the leaves from below upwards was c, b, a, bc, ab, an
arrangement which implies a 2 phyllotaxis. The habit
of the stem, clothed with its large adherent leaf-stalks,
may well have resembled that of some of the Tree-ferns.
Coming now to the internal structure of the stem, we
find that its organisation resembles that of the majority
176 STUDIES IN| FOssi. Beran
of the Ferns, in being of the so-called polystelic type.*
The number of the steles in MW. anglica is normally three
(see Fig. 71, st); each has a somewhat elongated and
irregular transverse section ; traced longitudinally, they
divide and again fuse with one another at long intervals.
The structure of the individual stele is almost identical
with that of the single vascular cylinder of a Heterangium.
The central part of each stele is completely occupied by
the primary wood, consisting of groups of tracheides
intermixed with conjunctive parenchyma. The primary
tracheides are for the most part pitted, just-as in Heter-
angium ; the spiral tracheides of the protoxylem, accom-
panied by a few scalariform or reticulated elements,
occur in several groups near the outer margin of the
primary wood (see Fig. 72, which includes parts of two
steles).
Each stele is surrounded separately by its own zone
of secondary wood and bast (Figs. 71 and 72, x, ph),
so that we have in this family a combination of polystelic
structure with normal secondary growth of the individual
stele. This is the great anatomical character of the
genus Medullosa, with its immediate allies, and separates
them at once from all plants now living, though, as we
have seen, there is one other fossil family (that of the
Cladoxyleae) which shares the peculiarity (see p. 156).
It will be noticed that in M. anglica, as in certain Clado-
xyleae, the development of secondary wood is commonly
greatest on the side towards the centre of the stem.
The secondary wood has the same structure as
in Heterangium or Lyginopteris (see Fig. 72). The
tracheides, which are in radial series, accompanied by
muriform medullary rays, are, as a rule, pitted on their
radial walls only. The pits are multiseriate and bordered,
1 I have adhered to the now familiar terms “ polystely ”’ and
‘“‘ polystelic,’’ but they are used in a purely descriptive sense, without
any implication that each of the several steles is to be regarded as
homologous with the single stele of a typical monostelic stem.
MEDULLOSA 177
just as in the genera last mentioned. Only slight
remnants of the cambium are preserved, but sufficient
to show that it was in the normal position, forming
wood internally and phloem externally, with reference
to each stele. The phloem itself is fairly preserved in
places (Fig. 72, ph), and consisted of strands of long
a as ,
Sts oF >
ne eh
%
ot
et
* ; *
4
*
oad
Fic. 72.—Medullosa anglica. Part of transverse section, showing portions of two steles, and
leaf-traces going off from them. 4%, primary wood of steles; x?, secondary wood ; ph,
phloem ; /.t., leaf-trace, just detached from its stele ; /.¢?., large leaf-trace, beginning to
divide. Other smaller bundles are shown. x 10. Phil. Trans., S. From a photo-
graph. S. Coll. 579.
tapering elements, clearly the sieve-tubes, forming a
network, the meshes of which were occupied by the
rather wide phloem-rays. In the Binney specimen,
described by Dr. Arber, the sieve-tubes are perfectly
preserved, and have conspicuous sieve-plates on their
lateral walls, just as in Heterangium tiliaeoides.1 There
1 Arber, loc. cit. Plate xx. Fig. 4.
I2
178 STUDIES: IN. FOSSIL BOTANY
appears to have been a pericycle around each stele, but
its structure is ill-preserved.
So far, the general organisation of Medullosa anglica
may be roughly described as that of a polystelic Heter-
angium. In the points which remain to be described,
the Heterangium type is departed from more widely ;
the differences are partly correlated with the polystely,
and partly depend on the greater size and complexity
of the plant as a whole.
The leaf-trace bundles were given off, for obvious
reasons, only from the free, peripheral side of the steles.
Where a leaf-trace first becomes free from the stele,
it is a large bundle, to all appearance truly concentric
in structure (see Fig. 72; 72.).. It consists ofa centrat
mass of primary wood, with one or more protoxylem-
groups near its external margin. This is surrounded
by a zone of secondary wood and phloem. The primary
wood of the leaf-trace is continuous with the outer part
of that of the stele from which it springs. As the leaf-
trace passes upwards and outwards through the cortex
it loses its secondary tissues, and divides up repeatedly
(Fig. 72, 1.2.2) to form a number of smaller bundles, each
of which eventually assumes a collateral structure.
These ultimate leaf-trace bundles have their protoxylem
directed outwards, adjoining the phloem (see Fig. 73,
in which two exceptionally well-preserved collateral
bundles are shown); their xylem usually consists of
spiral and finely scalariform elements only, the pitted
tracheides, which are abundant in the undivided leaf-
traces, disappearing as the ramification of the bundle
goes on.
The cortical tissues of the stem require no detailed
description ; they consist of short-celled parenchyma,
traversed by numerous secretory canals, much resembling
the gum-canals of recent Cycads.
A zone of internal periderm was formed around the
central part of the stem, enclosing the group of steles,
MEDULLOSA 179
and separating them from the outer cortex and _leaf-
bases (Fig. 71, pd). The periderm was morphologically
comparable to cork; it is extremely well preserved,
and was evidently formed wholly or chiefly on the external
side of the phellogen. How far the tissue was actually
suberised is doubtful; the good preservation of parts
lying outside the periderm suggests that true cork had
not yet been formed.
In one specimen, apparently forming part of an old
Fic. 73.—Medullosa anglica. Two leaf-trace bundles from the outer cortex of the stem, in
transverse section, showing collateral exarch structure. px, protoxylem; %, centripetal
xylem; ph, phloem. x 35. Phil. Trans.,S. Froma photograph. S. Coll. 579.
stem, the whole of the outer cortex, together with the
leaf-bases, had been exfoliated, leaving the periderm
exposed. It may be doubted, however, whether this
exfoliation was a normal process.
A point of some anatomical interest is the occasional
presence, in the cortex, of accessory vascular strands,
of concentric structure, and probably of wholly secondary
origin (Fig. 71, av). These formations recall the similar
cortical bundles occurring in the genus Cycas and some
other members of the Cycadaceae at the present day.
The petioles of Medullosa anglica were of large size,
180 STUDIES) IN TOSSREZB OT ANY
having a diameter of 4 cm. or more, at the point where
they became free from the stem. Each leaf-stalk received
a large number of vascular bundles, as many as seventy
or eighty in all, derived from the repeated ramification
of several of the principal leaf-traces. The supply of
bundles did not all enter the leaf-base from the stem at
the same level; they passed in successively, in groups
corresponding to the various principal leaf-traces from
which they were derived. Thus their number, in the
leaf-base, increased from ,below upwards. At a certain
height, however, the leaf-base was marked off from the
interior of the stem by a band of internal sclerenchyma,
and above this level no more bundles were received (see
Fig. 71; c).° The: petiole, where 1 first detachesai-em
from the stem, has the following structure (Fig. 74, A):
On the extreme outside we may find a layer or two of
palisade-like tissue (rarely preserved), which probably
served for assimilation. Within this is the broad hypo-
dermal zone (/y), consisting of numerous vertical strands
of fibres, interspersed with parenchyma, and accompanied
by secretory canals of the usual Cycadean type.
The whole interior of the leaf-stalk is occupied by
a short-celled ground-tissue, containing secretory canals
(mc), and traversed by the numerous vascular bundles
(v.b.), ranged more or less regularly in concentric circles.
The general structure was, in fact, much like that of
the petiole of a recent Cycad. The individual bundles
likewise resemble those of the recent family, differing
only in the fact that their xylem was entirely centri-
petal, while in a modern Cycad a small amount of
centrifugal wood is also present. This difference, how-
ever, does not seem to have been an absolutely con-
stant one, for in some of the Medulloseae the foliar
bundles are described as having precisely the Cycadean
structure.
Petioles of the kind described have long been known
under the generic name of Myeloxylon ; the particular
MEDULLOSA 181
form belonging to our Medullosa resembles that named
by M. Renault Myeloxylon Landriotii, distinguished
chiefly by the multiseriate arrangement and elliptical
transverse section of the fibrous hypodermal strands.
Fic. 74.—Medullosa anzlica. A. Transverse section of petiole, showing the numerous
vascular bundles, v.b.; m.c., mucilage-canals ; hy, hypoderma, with sclerenchymatous
ribs. The whole has the structure of ‘“‘ Myeloxylon Landriotit.’’ X about 8. S. Coll.
686. (G.T.G.) B. Vertical section of leaflet. v.b., vascular bundles of mid-rib, and
lamina; m.c., mucilage-canal. Palisade-tissue shown towards upper surface. xX 28.
Phil. Trans., S. S. Coll. 691.
The same petiolar structure, however, was no doubt
common to certain other species of Medullosa. The fact
that the fossils named Myeloxylon are nothing but the
petioles of Medullosa had previously been proved, by
182 STUDIES IN FOSSIL BOC Nx
Weber and others, for one of the Continental species.?
In the case of M. anglica the conclusion is perfectly
obvious, for the leaf-bases, still attached to the stem,
show in all respects the typical Myeloxylon structure.
The genus Myeloxylon is therefore one of those which
can now be dispensed with, or at most be retained, as
a matter of convenience, for those petioles which have
not yet been referred’ to their particular \speciessjan
Medullosa.
The petioles of Medullosa anglica were of great
length, and branched repeatedly, the successive branches
diminishing in size, and undergoing some simplification
in structure. The whole evidently constituted the rachis
of a highly compound, probably bi- or tripinnate leaf.
The final ramifications, which are no more than a milli-
metre in diameter, contain only a very few vascular
bundles, but these still retain the same collateral, exarch
structure as those of the main petiole. Gum-canals
occur throughout the rachis ; the hypodermal structure
becomes simplified in the finer branches, consisting of
an almost continuous zone of peripheral sclerenchyma.
Associated with the branched rachis, leaflets of
characteristic structure are found.’ As shown by trans-
verse sections, these leaflets are constantly revolute at
their margins (see Fig. 74, B) ; the parenchyma towards
the upper surface is of palisade-like structure, while the
lower portion of the mesophyll is more lacunar. The
lateral bundles, which traverse the lamina in an oblique
direction, are accompanied by fibrous elements. The
midrib is very prominent on the lower surface, and
shows the same structure as a small branch of the rachis.
From constant association and agreement in structural
details, there is no doubt that these pinnules formed
part of the Medullosa leaves. This conclusion is of
1 See Weber and Sterzel, Bettrage z. Kenntnis der Medulloseae,
Chemnitz, 1896. The original discovery was made by Weber about
the year 1880.
MEDULLOSA 183
great interest, because the pinnules in question agree
closely with certain leaflets described by M. Renault
in 1883, which, as shown by their external characters,
belonged to an Alethopteris.' The rachis and petiole of
M. Renault’s Alethopteris showed the anatomical structure
of “ Myeloxylon Landriotii.’’ Thus the French author’s
observations, taken in conjunction with Weber’s dis-
covery that “‘ Myeloxylon Landriotiu ’’ was the leaf-stalk
of a Medullosa, proved that the well-known Alethopteris
fronds were borne as foliage on certain of the Medullosa
stems.
From the organisation of the petioles and leaves in
Medullosa anglica, there can be little doubt that the
English species also bore foliage of the Alethopteris type,
an example of which is illustrated in Fig. 69 from
A.lonchitica, very probably the actual species concerned.
The roots of M. anglica have frequently been found
in connection with the stem, on which they were borne
in vertical series, between the leaf-bases. They have a
normal triarch structure, and, with increasing age,
formed a large amount of secondary wood and bast,
interrupted opposite the protoxylem-angles by large
medullary rays, just as in recent roots with secondary
growth. The detailed structure of the xylem agrees
with that of the corresponding tissue in the stem. Dr.
Arber found that the phloem much resembled that in
the stem of Heterangium tiliaeoides. The groups of sieve-
tubes are accompanied by phloem-parenchyma, and
separated by dilated parenchymatous rays. The sieve-
tubes show the lateral sieve-plates particularly well ; ?
this appears to be the only case in which this structure
has been recognised in the root of a fossil plant.
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Fic. 75.—Medullosa, stems. Reproduced from Seward’s Fossil Plants (Cambridge Univ.
Press) by permission. A-C. M. anglica. A. Transverse. a, b, accessory strands ;
c, periderm ; d, sclerenchyma (see Fig. 71). B. Part of secondary wood in tangential
section. C. Primary xylem. D. M. stellata, transverse; a, star-rings; p, “ partial
pith ”’ of solenostele (after Weber and Sterzel). E. M. Solmsti, transverse (after Weber
and Sterzel). F. M. stellata, with enormously thick outer wood of peripheral stele
(Brit. Museum Coll., No. 13767). G. M. stellata, var. corticata, showing some steles
and cortex. v, leaf-trace bundles (after Weber and Sterzel). H. I. M. Leuckarti.
H, transverse, showing central and peripheral steles. I. transverse from interior of a
stele, showing primary wood below and secondary above (after Weber and Sterzel and
Solms-Laubach). K. M. stellata, var. gigantea, transverse; star-rings below; a, part
of peripheral stele ; b-b, successive layers uf extra-fascicular wood (adapted from Weber
and Sterzel). L. M. Solmsii, var. lignosa, transverse, showing part of the double zone
of steles, and of two extra-fascicular layers. M. M. porosa, transverse, showing the two
kinds of central steles and the inner edge of the peripheral stele. (IL, M, after Weber
and Sterzel.) All from Seward. Block lent by the Cambridge University Press.
192 STUDIES IN FOSSIL BOTANY
by Sterzel and Weber as M. stellata, var. lignosa. In
the latter case we have the same condition as in the
British species, MW. centrofilis, so different in other respects.
In the largest stems, as already mentioned, the normal
secondary thickening of the steles may be supplemented
by the appearance of successive extra-fascicular zones of
wood and bast (Fig. 75, K).
The Medulloso gigas of Renault (Palaeoxylon, Brong-
niart), from the Permian of Autun in France, is founded
on fragments of large trunks, in which little but the
secondary wood is preserved. There is scarcely any
trace of the internal centripetal layer of wood, which
should be present if the structure were on Medullosean
lines, but in some specimens circular or elliptical strands
have been recognised in the pith recalling the “ star-
rings’ of other species. The stem, if correctly refered
to Medullosa, appears to be the largest known in the
genus.*
Medullosa porosa, Cotta, is a species closely allied to
M. stellata, with which it agrees in the structure of the
peripheral stelar zone. The difference lies in the internal
steles or “‘star-rings’’; they are numerous and differenti-
ated into two distinct zones (Fig. 75, M). The more
central “‘star-rings’’ are small and regular like those
of M. stellata; the outer ring, however, consists of larger
steles, often fused together, with the remarkable
peculiarity that their secondary thickening is chiefly
or even wholly limited to the zuner side. It will be
remembered that the same feature was: met with in the
steles of the British Lower Coal-measures species. An-
astomosis takes place, not only among the “ star-rings ”’
of the outer zone, but also between the latter and the
steles of the central group.
Medullosa Solmsu, Schenk, is a very different species
from those just described. The peripheral steles or
1 Renault, ‘‘ Bassin houillier et permien d’Autun et d’Epinac,”’ Flore
fossile, ii. p. 297, Pl. lxxi. 1893-1896.
MEDULLOSA 193
“ plate-rings ’’ are numerous and distinct, and are ranged
in two concentric circles, those of the outer circle being
the larger (Fig. 75, E). In the central pith of the stem
there are many minute cylindrical steles or “‘ star-rings ”’
of the usual structure ; these, however, are unimportant
compared with the main peripheral system. The
primary wood of the various steles seems to have been
-little developed, and the secondary wood is of denser
structure than in other species. As already mentioned,
it is from the inner of the two peripheral circles of steles
that the leaf-traces are given off; they pass outwards
through the gaps between the steles of the outer zone
(Fig: 75, E).
In the older stems the wood of the outer steles becomes
excessively thickened on the peripheral side, and, in
addition, successive extra-fascicular secondary zones may
be developed in the cortex (M. Solmsu, var. lignosa),
just as in the largest form of M. stellata (Fig. 75, L).
The species Medullosa Leuckarti, Goepp. and Stenz.,
already described, is again very distinct. Here the
peripheral vascular system of the stem consists of one
or two zones of large steles, few in number ; each stele,
as seen in transverse section, has an irregular, sinuous
form, which led the older writers to employ the express-
ive term “snake-rings’”’ (Fig. 75, H). The steles have
a wide “ partial pith,’ consisting of the primary wood,
intermingled with parenchyma; the secondary tissues
do not attain any great thickness. A portion of the
primary and secondary xylem of a stele is shown in
Fig. 75, I.
In the middle of the stem there are several large
“star-rings’’; they appear to be budded off from the
inner face of the peripheral steles. The leaf-trace strands
and the Myeloxylon leaf-bases borne on the stem have.
been mentioned above.
Of all the continental species M. Leuckarti bears the
nearest resemblance to the M. anglica type, with which
x3
194 STUDIES IN FOSSIL’ BOLANY
it agrees in many details; it might well be described
as an elaborated M. anglica, the species M. centrofilis
forming a. bridge between the two. The other Permian
species give the impression of belonging to a distinct
and more highly differentiated race within the genus
Medullosa.
Colpoxylon.—A curious fossil stem, I5 cm. or more
in didmeter, from the Permian of Autun, in France,
named by Brongniart Colpoxylon aeduense, and sub-
sequently fully described and illustrated by Renault,}
agrees in many respects with the simpler forms of Medut-
losa, but is peculiar in having, for a part of its length, a
single vascular cylinder only (Fig. 76, 1). The stele has
a very irregular outline, like the “snake-rings”’ of M..
Leuckarti, and is surrounded by secondary wood and bast
of the structure usual in Medulloseae. In the interior
there are scattered groups of tracheides, for the most
part running horizontally, and embedded in parenchy-
matous tissue.
Towards one end of the specimen the stele divides,
first into two (Fig. 76, 2) and then into six or seven parts,
so that the stem of Colpoxylon was monostelic in one
part and polystelic in another. Internal “ star-rings ”’
are entirely absent. The leaf-trace bundles are _pre-
served, and appear to agree essentially with those of
Medullosa (cf. Figs. 72, 73). Their ultimate branches
are collateral, and of the ‘‘ Myeloxylon’’ type; in some
of them, centrifugal as well as centripetal wood has been
found. The external surface of the stem bears a general
resemblance to that of Medullosa anglica; the leaves
(except for their scars) are unknown. There can be no
doubt that Colpoxylon belonged to the family Medul-
loseae ; possibly it may ultimately prove to have been
simply an aberrant representative of the genus Medullosa
itself. The local reduction of the vascular system of
the stem to a single stele is the point of chief interest.
1 Flore fossile d’Autun et d’Epinac, Part ii. p. 301, Pl. 66-68,
COLPOXYLON 195
Fic. 76.—Colpoxylon aeduense. 1. Transverse of stem, showing the single, sinuous stele
preparing to divide into two. a, a’, wood of stele; b, phloem, partially preserved ;
c, cortex, containing leaf-traces and sclerotic strands; d, stellate bundles, probably
undivided leaf-traces. 2. The same, where the stele has divided into two. a-d, as in
section I. ¢, primary xylem-groups in “ partial pith’’ of the steles. 3. Portion of
external surface, about # of natural size. From Renault.
196 STUDIES IN FOSSIL BOTANY
There is some evidence that Colpoxylon was the stem of
an Alethopteris,: though Renault thought that the gigantic
simple leaves known as Titanophyllum might belong to
it. Some original observations with new figures of
Colpoxylon will be found in Prof. Seward’s Fossil Plants,
VoL Wi, p: 1242:
Sutclifia.—Prof. Seward, in 1894, described, under
the name of Rachiopteris Williamsoni,? a petiole which
bears a great general resemblance to “‘ Myeloxylon,”’ but
differs from it (among other minor points) in the vascular
bundles having concentric instead of collateral structure.
Considering that in Medullosa the leaf-traces were, to
all appearance, concentric on first leaving the steles,
it was not surprising that in some forms they should
have retained this structure after entering the petiole,
and it thus appeared from the first highly probable that
Rachiopteris Williamsont represented the leaf-stalk of
some unknown member of the Medulloseae.
This conclusion has since been confirmed by the
discovery of a new Medullosean stem (Swtcliffia insignis,
Scott), first found by Mr. J. Lomax in material from
Mr. Sutcliffe’s colliery at Shore, Lancashire. Sutchfia
insignis, like Prof. Seward’s fossil, is derived from the
roof-nodules, where it is associated with Goniatite shells
(see Fig. 77). A second specimen has since been de-
scribed. The roof-nodule specimens no doubt represent
the drifted fragments of a distinct flora, flourishing at
some little distance from the coal-forming forests; to
the latter the ordinary seam-nodules owed their origin.
The stem is a large one, measuring, in the type speci-
men, 12 x6:5 cm. in diameter in its present somewhat
1 Grand’Eury, “‘ Sur les organes et le mode de végétation des Neuro-
ptéridées et autres Ptéridospermes,’’ Comptes vendus, t. cxlvi. p. 1243,
1908.
2 Annals of Botany, vol. vill. 1894, p. 287.
% Scott, ‘ On Sutcliffia insignis, a New Type of Medulloseae from the
Lower Coal-measures,’’ Tvans. Linn. Soc, London, 2nd ser. Bot. vol. vii.
Part iv. 1906.
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198 STUDIES “IN - FOSSIL ‘BOTANY
distorted condition. In a length of 9 inches, not more
than one petiole leaves the stem, so the plant was pre-
sumably of a tall stature. The stem is clothed by large,
spirally arranged leaf-bases, but detached petioles have
been found greatly exceeding in size those borne by the
stem, which must have been a comparatively small
specimen—probably from a young plant. The second
specimen, however, though older, is smaller.
The main feature of the anatomy, in which Swtcliffia
differs from any Medullosean stem previously known,
is the presence of a single central stele, of large size
(measuring 4:7 x 1-8 cm. in the section figured, Fig. 77).
There is no pith, and the wood has the same structure
as in a stele of Medullosa anglica, except that in Sutcliffia
the protoxylem-groups are peripheral, the xylem thus
being exarch. A zone of phloem, in which strands of
sieve-tubes can be recognised, surrounds the wood. In
the stem first investigated (the only specimen then dis-
covered) secondary growth was just beginning.
From the main stele, large, irregular strands, the
meristeles or subsidiary steles, were detached at intervals,
giving a remarkable and unique appearance to the trans-
verse sections (see Fig. 77, a, B, and 6). The meristeles
break up into smaller strands, but the main branches
of adjacent meristeles often fuse with one another. Thus
the large mass. 5, in Fig..77, is the product of sie
fusion, as shown by the comparison of serial sections.
The strands derived from the further subdivision of the
meristeles or their fused branches (Fig. 77, a, Bp’, B)
ultimately constitute the numerous bundles of the leaf-
trace (Fig. 77, d.r., v:b.). The vascular strands in the
leaf-bases and petioles always, however, retain a con-
centric structure, and their xylem contains parenchyma,
so that they preserve a more stele-like character than
the corresponding bundles in a Medullosa. The structure
of the petiole agrees in all essentials, though not in every
detail, with that of Seward’s Rachiopteris Williamsoni,
SUTCLIFFIA 199
which appears to be the petiole of another species of
Sutcliffia, now called S. Williamsont.
A second specimen of the stem, probably referable
to the species S. insignis, was discovered in IgI0 at
Dearnley, in a mine adjacent to that from which the
type-specimen was obtained. It was fully and admir-
ably described by Dr. Ethel de Fraine in 1912.1. This
also was a roof-nodule fossil. It is a smaller stem than
the type-specimen, measuring about 9:5 x 3:5 cm. in
transverse dimensions as against I2 x 6:5 cm. in the type.
It is true that the leaf-bases are lost in the Dearnley
specimen, but the dimensions of the primary wood of
the stele and meristeles are relatively small, and the
specimen owes much of its present proportions to second-
ary growth. This is one of the great differences from
the Shore stem; the latter was young, and secondary
thickening had only just started; the Dearnley plant
was almost in a senile condition, with an immense develop-
ment of secondary wood, leading to the crushing and
distortion of much of the primary xylem. The secondary
zone reaches a thickness of 9 mm. in the stele, and is
also predominant in the meristeles. In fact, one of the
latter had thus grown to such abnormal dimensions
that it might easily be taken for a second stele, if it were
not that at a higher level it partly breaks up into leaf-
traces.
Besides the great growth of the secondary tissues
there are some other points in which the Dearnley speci-
men differs from the Shore plant. The most striking
of these is the presence of a number of extra-fascicular
vascular strands outside the normal system of stele and
meristeles. These are arcs or concentric strands of
secondary wood and bast, and appear to have no con-
nection with the primary vascular system. The extra-
fascicular formations always start from a cluster of
1 E. de Fraine, “On the Structure and Affinities of Sutcliffia, in the
light of a newly discovered specimen,’’ Ann. of Bot. vol. xxvi. 1912.
200 STUDIES IN FOSSH) BOTANY
isodiametric reticulate tracheides of large diameter.
Such short tracheides, probably belonging to the peri-
cycle, also occur elsewhere, in places where no secondary
development had taken place.
The extra-fascicular strands of the Dearnley Swtcliffia
fuse with one another to form a network. In structure
they are practically identical with the accessory strands
and arcs sometimes found in Medullosa anglica,’ while
they present a less close analogy with the external zones
of thickening occurring in large stems of Medullosa
stellata and M. Solmsiu, and also have their parallel
among recent Cycads.
Another feature of the Dearnley specimen is the
presence of bands of periderm in the cortex. Dr. de
Fraine was inclined to refer the absence of leaf-traces and
outer cortex to this cause, the external tissues having
been normally exfoliated, owing to cork-formation.
In the type-specimen, indications of cortical meri-
stems, perhaps the precursors of periderm, have been
noticed.
The peculiarities so far mentioned may all be explained
by the more advanced age of Dr. de Fraine’s specimen.
One or two differences affecting the primary structure
are also noted in her memoir. In the type-specimen
fusions between distinct meristeles or their branches
occur, as their course is followed in the upward direction.
This was not observed in the second specimen, though
the branches of the same meristele may sometimes
reunite ; in one case a meristele fused again with the
main stele. ‘
Dr. de Fraine also came to the conclusion that the
meristeles were ultimately used up completely to form
leaf-trace strands; in the type-specimen, where fusion
took place, it seemed probable that a part of the meri-
stele persisted in the stem; these differences, if con-
firmed, might point to a specific distinction, though,
1 See D. H. Scott, ‘‘ On Medullosa anglica,’’ loc. cit. p. 98.
SUTCLIFFIA 201
on the other hand, there are so many details of structure
common to both specimens as strongly to suggest specific
identity.
Prof. Seward has judiciously solved the problem by
distinguishing the two specimens as forma a and forma [.'
Dr. de Fraine, while retaining the term “ meristeles ”’
for convenience, regarded these structures as essentially
identical with the main leaf-traces of Medullosa. They
are, however, so widely different in dimensions, form,
and behaviour from ordinary leaf-traces, that they seem
to demand a separate category, as subsidiary steles.
The vascular system of Swéclifia has no parallel
among any plants at present known, though a remote
_ analogy may be traced with the anomalous structure
of certain lianes belonging to the Sapindaceae. The
genus is referred to the Medulloseae on account of the
general organisation of the leaf-base and petiole, the
numerous leaf-trace bundles, the tendency to dialystely
shown in the formation of the subsidiary steles, and the
histology of the vascular and cortical tissues.
The stem, however, has not deviated far from the
monostelic condition, for the single central cylinder
forms the dominant feature of the vascular system,
while the meristeles serve to effect the transition to the
leaf-traces. The plant is of considerable interest, as
indicating the probable derivation of the Medullosean
stem from a simple protostelic type, such as exists in
Heterangium among the Lyginopterideae.
Further theoretical considerations will be postponed
(p. 219). »s
FRUCTIFICATION OF MEDULLOSEAE.—There are at
least two cases in which we have clear and direct proof
that a member of the Medulloseae, or, as we should rather
say, of the Neuropterideae, was a seed-bearing plant.
In the same year in which the seed of Lygonopteris was
1 Fossil Plants, vol. iii. p. 149, 1917.
202 STUDIES, IN- FOSSIL; BOTANY
first identified, Dr. Kidston was able to demonstrate
the presence of seeds in a species of Neuropteris, one of
the genera which Stur, twenty years before, had pro-
posed to exclude from the Ferns.
In the well-known species NV. heterophylla, the frond
of which is illustrated in
Fig. 68 (p. 171), bodies
considerably larger than
a hazel-nut, and rela-
tively longer, were dis-
covered by Dr. Kidston,
in nodules from the
Middle Coal- measures
of Dudley, attached to
a rachis bearing the
characteristic pinnules
of Neuropteris hetero-
bhylla* (Fig: 78)> eee
has since recorded other
and more perfect speci-
mens, . They are casi
not petrifactions, so no
detailed study of struc-
ture has been possible,
but the external char-
acters leave no doubt
that the organs in ques-
Fic. 78.—Newropteris heterophylla. Seed, attached tion are seeds. They
to a branch of the rachis bearing two char- are of the radially sym-
acteristic pinnules. Xx 2. After Kidston. 4
metrical type, and the
testa has a fibrous structure. Chiefly on account of
the latter character Dr. Kidston refers the seeds to
the genus Rhabdocarpus of Goppert and Berger.” The
1 R. Kidston, ‘ The Fructification of Neuropteris heterophylla,” Phil.
Tvans. Royal Soc. B, vol. cxcvii. 1904.
* Brongniart, however, limited the genus Rhabdocarpus to seeds with
bilateral symmetry (Platyspermeae of Oliver), see Fig. 92, p. 253.
FRUCTIFICATION OF MEDULLOSEAE = 203
seeds appear to be borne terminally on the fertile
branches of the rachis; it is a striking fact that the
seed-bearing frond or pinna should be so little modified
as to show the same form of pinnule as the vegetative
foliage ; the differentiation of the sporophyll had scarcely
even begun in a case like this.
The seed shown in Fig. 78 is incomplete at the top ;
more perfect specimens have a somewhat sharp point,
more or less oblique at the apex; this probably marks
the position of a micropylar tube (Fig. 84, A, p. 216;
cf. Tvigonocarpus, Fig. 79, p. 205).
The second case of continuity between a seed and the
frond of a Neuropteris was recorded by Kidston and
Jongmans in 1rog1I,1 in WN. obliqua, a species allied to
N. heterophylla. The specimen was derived from the
Westphalian Coal-measures of Limburg, Holland. Here
the seeds are borne 1n a pair on the ends of a forked rachis,
which also bears the pinnules characteristic of the species.
The seeds themselves are of the same type as those of
N. heterophylla, but are considerably larger, measuring at
least 4:5 cm. in length by 2-5 in maximum width.
A doubt has been suggested whether the bodies
described as seeds in these species of Neuvopteris may not
merely have been large vegetative bands, such as occur
among recent Ferns. The points of agreement with
undoubted seeds, and especially the indications of a
micropylar tube, seem, however, to be conclusive in
favour of their seed-nature.
The names Neuropterocarpus, Grand’ Eury, and Neuro-
spermum, P. Bertrand, have been proposed for the type
of seed just described ; such names may be required in
cases where it is not possible to refer the seed to a definite
species of frond. Some instances of association without
continuity will be mentioned later.
1 R. Kidston and W. J. Jongmans, “ Sur la fructification de Neuro-
pteris obliqua, Brongn.,’’ Archives néerlandaises des Sciences, Ser. iii.
B, tome i. p. 25, I9II.
204 SLUDIES IN FOSsiy BOTANY
Dr. Kidston was the first to observe direct continuity
between the seed and the frond in a Fern-like Palaeozoic
plant, and it was his discovery, in conjunction with the
equally strong though less direct evidence in the case of
Lyginopteris, which first suggested the institution of the
class Pteridospermeae.
There is at present no instance of a petrified seed,
showing structure, which can be referred to the Medul-
loseae or Neuropterideae with the same certainty as
the casts just described. One of the best-known Palaeo-
zoic seeds, however, Trigonocarpus Parkinsoni, Brongn.,
may be attributed with great probability, as we shall
see, to Alethopteris; we will therefore shortly describe
its structure.
Ivigonocarpus Parkinson is found in three distinct
states of preservation in the English Coal-measures :
(1) in the common condition of nut-like, somewhat
triangular casts which, as shown by Hooker and Binney
and by Williamson, are really internal casts of the seed
cavity ; (2) as external casts, showing the testa and the
true form of the seed; (3) as petrifactions, in which
the structure is more or less perfectly preserved. From
these various data a fairly complete knowledge of the
organisation of the seed has been gained; its more
important features are shown in the diagrammatic
figures 79-81.
The seed is a very large one, the length reaching
5 cm., of which quite half is accounted for by the
enormously long micropyle; the body of the seed has
a maximum diameter of over 2 cm. (Fig. 79). The testa
consists of two clearly distinct layers—the outer layer
or sarcotesta, composed of delicate, partly lacunar tissue,
bounded externally by a sharply differentiated hypo-
derma and epidermis, and the inner ribbed sclerotesta,
constructed, like the stone of a peach, of dense, thick-
walled tissue. The ribs show a very definite arrange-
ment. There are three principal ridges, corresponding
Ys
TRIGONOCARPUS 205
sa
SC.
woesnncen eed aonenaeeseee 22°98 0.6.
n.e.
met.
m.m.
ch.b.
Fic. 79.—Trigonocarpus Parkinsoni. Diagrammatic median section in the plane of the
“wing’’ (Fig. 81). sa, sarcotesta; 1, its limiting layers; sc, sclerotesta; mi, micropyle ;
1.t., remains of “‘ inner flesh’”’ ;.sa.b., sarcotestal bundles ; .c., pollen-chamber ; #.c.0.,
its beak ; s, septum at bottom of pollen-chamber ; .e., nucellar epidermis ; v.t., nucellar
tracheal system; m.m., membrane of megaspore ; t.d., tracheal disc at chalaza; ch.b.,
chalazal bundle. x about 3. From a drawing by Mr. A. J. Maslen, F.L.S.
206 STUDIES IN FOSSIL EOTANY
to sutures, in the sclerotesta, and usually three secondary
ridges in each space between the former, making twelve
ribs in all (Fig. 80); within the sclerotesta there are
some traces of an inner soft layer. The nucellus has a
definite epidermis, and appears to have been free from
the integument, from the chalaza upwards ; it terminates
at the apex in a dome-shaped pollen-chamber, provided
with a long, narrow beak (Fig. 79, p.c., p.c.b.), as in the
Fic. 80.—Diagrammatic transverse section through the body of the seed, at about the level
of the line m.m. in Fig. 79. ”, principal ridges ; 7?, secondary ridges. Other lettering
as in Fig. 79. ™ about 3. Froma drawing by Mr. A. J. Maslen.
seeds of the Cordaiteae, described in Chap. IV. The
membrane of the megaspore or embryo-sac is evident
but the prothallus has not yet been found preserved.
The vascular system of the seed is double. At the
base six bundles branch off from the common supply-
strand and pass upwards through the sarcotesta (Fig.
79), taking a definite position opposite certain of the
secondary ridges (Fig. 80). These bundles appear to
have been collateral, with external phloem, and there
is evidence that the xylem was mesarch. The inner
v ware, a
‘i . ant
® .
TRIGONOCARPUS 207
vascular zone formed a complex tracheal network in
the nucellus; near the chalaza the sheath of nucellar
tracheides is continuous ; farther up they range them-
selves in longitudinal strands connected by abundant
transverse anastomoses. The most remarkable feature
of the seed is the long micropylar tube, formed by an
extension of the ribbed sclerotesta, and enclosed in a
broad, wing-like prolongation of the sarcotesta (Ligs.
79, 81). It is not quite certain, however, to what extent
the flattened form of this part of the seed is natural.
The seed, with its fleshy and stony coats, double
vascular system, and pollen-chamber, is evidently very
Fic. 8r1.—Diagrammatic transverse section through the micropyle, at about the level of the
line p.c.b. in Fig. 79, showing the wing on one side. Lettering as in Fig. 79. From a
drawing by Mr. A. J. Maslen.
nearly akin to the seed of a recent Cycad, the chief
difference consisting in the free nucellus, whereas in the
modern family it is adherent to the integument.
The petrified specimens of Tvigonocarpus Parkinsoni
are, almost without exception, associated with the
leaflets, petioles, and other organs of Medullosa anglica,
while the casts very generally occur together with the
Alethopteris foliage, which no doubt belonged to that
plant and allied species of Medullosa. Histologically
there is a striking agreement in the tracheides, a peculiar,
finely scalariform type being characteristic both of the
Medullosa and the Trigonocarpus. There is also a certain
similarity between the limiting layers of the sarcotesta
208 STUDIES IN FOSSIy BOTANY
and those of the petiole. The evidence is of course far
from amounting to proof, but the presumption is entirely
in favour of this seed being the fructification of the
Alethopteris (probably A. lonchitica), which formed the
fohage of Medullosa anglica.}
The structure of another species of Tvigonocarpus
(I. shorensis, from the Lower Coal-measures of Shore,
Littleborough) has been fully investigated by Dr. Salis-
bury.* This is.a-large seed, over 4 cm: in lengiiiag
nearly 2:5 cm. in maximum breadth, and of a stouter
build than T. Parkinsont. The micropylar beak is short ;
there are three principal ribs on the hard -shell; the
secondary ribs die out below the middle of the seed,
and tertiary ribs are absent. The sclerotesta is thinner
and the sarcotesta thicker than in T. Parkinsoni ; there
is a well-marked transition from one to the other, indi-
cating that they were derived from a single integument.
The bulk of the sarcotesta has a lacunar structure, but
the external layers are somewhat complex, including a
system of radial sclerotic plates, comparable to the
hypoderma of a Medullosa, accompanied by numerous
secretory elements. The six mesarch vascular bundles
of the sarcotesta are distributed round its outer border.
The internal vascular system forms a tracheal cup at
the base of the nucellus, with numerous mesarch strands
lining its inner surface. The epidermis of the nucellus,
which is free from the testa, is even more pronounced
than in T. Parkinsom. Thus the two seeds show a
general agreement in their construction, while differing
in a number of definite specific characters.
1 On Trigonocarpus see Hooker and Binney, “ On the Structure of a
certain Limestone Nodules enclosed in seams of bituminous Coal, with
a description of some Trigonocarpons contained in them,’’ Phil. Trans.
Royal Soc. vol. cxlv. 1855. Williamson, ‘‘ On the Organisation of the
Fossil Plants of the Coal-measures,”’ Part viii. 7bid. vol. clxvii. 1877.
Scott and Maslen, “ The Structure of Tvigonocarpus,’’ Ann. of Bot. vol.
xx1. 1907. :
2 E. J. Salisbury, ‘“‘ On the Structure and Relationships of Trigono-
carpus shorensis, sp. nov.,’’ Ann. of Bot. vol. xxviii. 1914, p. 39.
OT Pk Oe ee
~ er:
STEPHANOSPERMUM 209
No pollen-grains have yet been observed in the pollen-
chamber of Tvigonocarpus,! but in another genus of the
same group, Stephanospermum, Brongn., reinvestigated
by Prof. F. W. Oliver, they have been found in perfect
preservation. The species to which Figs. 82 and 83
refer, Stephanospermum akenioides, Brongn., is one of
the numerous seeds, originally described by Brongniart,
from the Black Pebbles of St. Croix, near St. Etienne,
of Upper Coal-measure age. It is a comparatively small
seed (measuring about I0 x 4:5 mm.), and, though the
sarcotesta is not preserved, is evidently of the same
general type as Trigonocarpus, with which it agrees in
the radial symmetry, the prolonged micropyle, the beaked
pollen-chamber, and the apparently free nucellus, of
which the characteristic tracheal investment forms part.
The most striking peculiarities of the seed consist in
the presence of a prominent ring or collar of the sclero-
testa around the micropylar region, and in the nature
of the nucellar tracheal system, which forms a continuous
mantle of spiral or scalariform tracheides, extending as
far as the pollen-chamber and spreading over its floor.
In this seed the prothallus is sometimes well preserved ;
the archegonia appear to have been only two in number ;
in the egg-cell the nucleus has been recognised.
The apex of the pollen-chamber was prolonged into
a long beak or tube, engaging with the micropyle (cf.
Fig. 79, Tvigonocarpus).2 Through this beak the pollen-
grains entered the pollen-chamber, in which they are
found in almost every seed. They also occur loose in
the matrix, where they are of small size, averaging only
about 60 yw in length, while the average dimensions of
those in the pollen-chamber are 160 x 100 p» (210 p being
the extreme length observed), so that, as Renault first
1 Except in a minute seed, T. pusillus, Brongn. referred to that
genus.
2 In Fig. 82 the conical mass at the top of the figure represents the
funnel-shaped base of the tube, but the tube itself is missed.
14
210 STUDIES IN -POSSELSEOTANY
showed, the pollen-grains developed actively after enter-
ing the seed. The multicellular structure of the pollen-
grains, in this and other cases, was first demonstrated
by Renault, and fully confirmed by the more recent
observations of Oliver, who finds that there are about
twenty cells in each grain, so arranged that five radial
septa are seen when the grain is cut transversely (Fig.
83). Ultimately the internal cells appear to have be-
come retracted towards the periphery, leaving behind
Fic. 82.—Stephanospermum akenioides. Upper part of pollen-chamber, showing part of its
wall, with the base of the beak. In the chamber a large multicellular pollen-grain is
shown, also three small foreign pollen-grains, one of which partly overlies the large grain.
x go. Will. Coll. 1486a. From a photograph lent by Prof. F. W. Oliver, F.R.S.
them in the middle of the grain a framework of cell-
wall—the “‘ replum ”’ (see Fig. 83).
In the light of our present knowledge of the re-
production of Ginkgo and the Cycads, it is an obvious
suggestion that the internal cells of the pollen-grain
were antheridial cells, producing spermatozoids. Renault,
however, actually anticipated the discovery of Ikeno
and Hirase. In an allied seed, Aetheotesta, as well as
in Stebhanospermum itself, the cell-walls of the pollen-
grains which they contain are perforated, and Renault
STEPHANOSPERMUM 211
suggested, in 1887, “that the perforations served for
the passage of mobile bodies analogous to antherozoids.”’
He adds: ‘“ We do not regard as impossible the existence
in the past of pollen-grains, which, instead of effecting
fertilisation by means of a tube, discharged into the
pollen-chamber of the appropriate seeds antherozoids
capable of performing this function.”’ 4
Renault’s prescience has been fully justified by sub-
sequent discoveries; possibly even the direct proof of
Fic. 83.—Stephanospermum akenioides. Multicellular pollen-grains in pollen-chamber ; some
shreds of the wall extend into the cavity. The middle pollen-grain is in transverse
section, and shows the radiating septa dividing up the grain. The grain to the right is
in longitudinal section, and shows the peripheral cells and the ‘“‘ replum ”’ in the middle
(see text). xX 137. Univ. College Coll.S 74. From a photograph lent by Prof. Oliver.
the existence of spermatozoids in fossil Seed-plants may
yet be obtained.’
The presence of a pollen-tube in the case of Stephano-
spermum and other Palaeozoic Spermophytes is very
doubtful. Small papillae are occasionally observed (as
1 Renault, ‘“‘ Note sur le genre Aetheotesta,’’ Mém. de Soc. d’Hist.
nat. de Sadne-et-Lotre, pp. 156, 158, 1887. For Stephanospermum see
Brongniart, Graines fossiles silicifiées, 1881; Renault, Cours de bot.
fosstle, t. iv. p. 184, Plates xxi. and xxii. 1885; F. W. Oliver, “‘ Struc-
ture and Affinities of Stephanospermum,’’ Trans. Linn. Soc. London, 2nd
ser. Bot. vol. vi. Part viil. 1904.
* Evidence on this subject is adduced in Prof. F. W. Oliver’s memoir
«© On Physostoma elegans,’’ Ann. of Bot., January 1909.
212 SFUDIES IN FOSSIL, BOTANY
in the large pollen-grain shown in Fig. 82), but their
significance is still uncertain. Some further reference
to the question will be made in discussing the fertilisa-
tion of the Cordaiteae (Chap. IV. p. 300).
It is only in the cases of Neuropteris heterophylla and
obliqua that we have, as yet, the direct proof that Neuro-
pterideae bore seeds; as we have seen, there is strong,
though less conclusive, evidence that the seed Tvigono-
carpus Parkinson belonged to Medullosa anglica, which,
according to its foliage, was certainly an Alethopteris.
A considerable mass of evidence, mainly from associa-
tion, has further been accumulated through the extensive
investigations of M. Grand’Eury and others, both in the
Upper Coal-measures of Central France and in the more
ancient deposits of Belgium, Northern France, and the
Saar Valley. Grand’Eury, whose experience in such
researches was unrivalled, found that the vegetative
organs of Neuropterideae, wherever there was evidence
that they grew im situ, were constantly associated with
seeds of the radially symmetrical type, such as rarely
occur in company with plants of any other group; he
further found special types of seed in close association
with definite genera and species of frond. Considering
the wide field covered by Grand’Eury’s observations,
and the fact, which he established, of the social growth
of plants of the same group, there can be no doubt of
the value of the conclusions arrived at. Grand’Eury
was led to refer some fifteen genera or sub-genera of
seeds to the Neuropterideae, the general characters of
the seeds being that they are of radial symmetry and
striated, polygonal, or winged, the number of the angles
or wings being some multiple of three.
Among Grand’Eury’s special results we may mention
that he referred the huge seed Pachytesta gigantea (some-
times 4 inches long) to a species of Alethopteris (A.
Grandini), and smaller seeds of the same type to other
species of the genus. In the Northern Coal-fields, how-
SEEDS OF MEDULLOSEAE 213
ever, he found Tvigonocarpus seeds associated with
certain Alethopterids (in agreement with our conclusion
as to 7’. Parkinsoni), and pointed out the affinity between
Pachytesta and Tvrigonocarpus.
A considerable variety of seeds has been referred to
Neuropteris ; the seed attributed to N. flexuosa appears
to be of the same type as that of N. heterophylla, dis-
covered by Kidston.
Various seeds have also been referred (not to mention
other cases) to the genera Odontopteris and Linopteris
(=Dictyopteris), which are some of those which Stur
had already removed from the Ferns in 1883.
Grand’Eury in several cases detected the “ inflores-
cence ’’ or fertile rachis on which the seeds were borne.
He was of the opinion that, as a rule, the organs of repro-
duction of Neuropterideae and other Pteridosperms were
borne on “ special organs, separate from the leaves, 1.e.
on independent inflorescences.’’ In Neuropteris hetero-
phylia, however, and in other cases, to be subsequently
mentioned, the seeds were borne on a frond but slightly
modified, so there can be little doubt that the organ
supporting them, even when more specialised, was still
foliar in nature.
Some further cases of the association of seeds with
the foliage of various Neuropterideae have come to light
more recently. A ribbed seed (‘‘ Rhabdocarpus, cf.
tunicatus’’’) has been found both by Dr. Renier and
Dr. P. Bertrand, in close association with the fronds
of Neuropteris Schlehani, another species of the same
group as N. heterophylla. The specimens occur in the
Coal-measures of Belgium and Northern France.
Another type of seed, Hexapterosbermum, Brongn.,
occurs in similar localities, associated with Neuropteris
* C. Grand’Eury, “Sur les graines des Neuroptéridées,’’ Comptes
vendus, t. 139, pp. 23 and 782, 1904; ‘‘ Sur les inflorescences des
fougeres a graines du Culm et du terrain houiller,”’ Comptes rvendus,
t. 143, p. 761, 1906.
214 STUDIES, IN-FOSSTE- BOTANY
gigantea, a species representing a different group from
that of N. heterophylla. These seeds have a six-angled
sclerotesta, enclosed in what was probably a- fleshy outer
coat ; they thus bear some resemblance to T7igonocarpus.
Cup-like, fringed bodies, also associated with the seeds,
have been interpreted as their cupules, but the evidence
for the presence of a cupule in Neuropterideae is by no
means conclusive.
Another species of Hexapterospermum is associated
with fronds of Linopteris obliqua; in this case no
“cupules’”’ have been met with. Linofterrs is a genus
closely allied to Neuropteris, from which it chiefly differs
in the reticulate venation of the pinnules.
We thus see that while the direct proof of continuity
between seed and frond is still limited to two species of
Neuropteris, there is a considerable body of indirect evi-
dence which, as far as it goes, supports the opinion that
the Neuropterideae generally were seed-bearing plants.
We have still but little positive knowledge as to the
nature of the male organs in the Neuropterideae. In
1887 Dr. Kidston described a form of fructification in
Neuropteris heterophylla, the species in which he subse-
quently discovered the seed. The specimen? consists of
a forked rachis, bearing the normal vegetative pinnules
below, while the branches terminate in small four-lobed
bodies, which may be interpreted either as groups of
sporangia or as cupules (Fig. 84, B). As there is no
evidence for the presence of minute cupules of this kind
in Neuropterideae, the former interpretation is somewhat
the more probable, in which case the specimen would
no doubt represent the microsporangiate fructification.
M. Grand’Eury also observed a rachis bearing sporangium-
like bodies in Neurvopteris, and “ floral discs,’’ which he
regarded as male, in Linopteris.
1 The figure and description are reproduced in Dr. Kidston’s paper
on ‘“ The Fructification of Neuropteris heterophylla,”’ above cited.
MALE ORGANS OF MEDULLOSEAE 215
In later years our information has somewhat in-
creased, and here again the most definite advance is
due to Dr. Kidston.
A peculiar form of leaflet, apparently bearing sporangia
(cf. Fig. 84, C), had been observed both by the Abbé
Carpentier and Dr. P. Bertrand,! in association with
Neuropteris gigantea and similar species. The leaflets are
more or less orbicular, and large, reaching half an inch
or more in diameter. They appear to have been of a
fleshy consistency and are traversed by radiating and
forking veins. They resemble the “ cyclopteroid ’’ pin-
nules which occur on the fronds of Neuropteris gigantea
(see p. 172). The sporangia were found by Carpentier
to be embedded in the substance of the thick lamina.
Dr. Kidston has discovered similar pinnules in the
Westphalian of Coseley, near Dudley. They are borne
terminally on the branches of a stout rachis. The under
side of the rounded pinnules bears densely packed,
narrow, elongated sporangia, from which Dr. Kidston
obtained numerous spores by maceration; they are
from 45 to 60 uw in diameter and show a tri-radiate ridge.
Thus, the sporangia were no doubt the pollen-sacs of
the plant. Further, Dr. Kidston found on the same
rachis, sterile pinnules, which are clearly those of a
Neuropteris, though the species could not be identified.
The provisional name Neuroptevis Carpentiert, Kidston,
is therefore used for these specimens. As Dr. Kidston
says, “that the fossils just described are the micro-
sporangial organs of a Neuropteris can scarcely be
doubted.”
Somewhat similar fertile pinnae were described by
Zeiller under the name Potontea adiantiformis (Fig. 84,
C), and the French specimens described by Carpentier
and P. Bertrand have also been referred to the pro-
1 See the memoirs by Carpentier cited on p. 76. Also P. Bertrand,
“ Les Fructifications de Neuroptéridées,’”’ Ann. de la Soc. Géol. du Nord,
f xiiiip. 113, 1913.
216 SLUDIES. IN FOSSIL BOTANY
visional genus Potoniea, and even to the same species,
but, as Kidston has pointed out, they differ in certain
respects from Zeiller’s specimens, which, however, prob-
ably belonged to the same group.
Two types of supposed male organs have been attri-
buted to the genus Linopteris, but only on the evidence
of association. A fructification much resembling a large
=p
4
Se WIE
ae J Fa>
>
ss
>
SU PANS
Fic. 84.—Neuropterid Fructifications. A. Restoration of a seed-bearing pinna of N.
heterophylla, showing the micropylar beak of the seed; cu, supposed cupule. After
P. Bertrand. B. Fructification (probably g) of N. heterophylla. After Kidston.
C. Potoniea adiantiformis. 4 Fructification of a Neuropterid. The teeth on the pinnules
are believed to represent microsporangia. After P. Bertrand. All the figures are reduced.
Crossotheca (see p. 75, Fig. 39) from the Upper Coal-
measures of Commentry and Autun, was referred by
M. Zeiller to the species L. Germari; the case for this
attribution is a strong one, though continuity is lacking.
There is, however, some doubt whether the fringe,
1 R. Kidston, ‘“‘ On the Fossil Flora of the Staffordshire Coal Fields,’’
Part iii., Trans. Royal Soc. of Edinburgh, vol. 1. Part i. 1914, p. 112.
MALE ORGANS OF MEDULLOSEAE 217
which in true Crossothecas consists of microsporangia,
may not in this case represent mere expansions of the
pinnule, perhaps concealing the actual reproductive
organs. Our knowledge of the fructification cannot
therefore be regarded as satisfactory.
On the other hand, the “floral discs’’ attributed to
L. Brongmarti and L. obliqua are of the “ Potoniea”’
type, though more peltate and cupulate than the fertile
pinnules referred to Neuropteris gigantea. While the
evidence from exclusive association and resemblance to
sterile pinnules strongly supports the attribution of the
bodies in question to Linopfteris, little or nothing is known
of the actual pollen-sacs which they may be assumed
to have borne.
It may be pointed out that the fertile pinnules which
appear to have borne the microsporangia in the cases
last described are extremely different from the supposed
male fructification of N. heterophylla (Fig. 84, B and C).
Our knowledge, in fact, of these pollen-bearing organs
in the whole group is still very imperfect ; the clearest
case is that of N. Carpentiert, described by Dr. Kidston.
It is unnecessary to describe other fructifications, the
attribution of which to Neuropterideae is merely a matter
of conjecture.
M. Grand’Eury found evidence that various Neuro-
pterideae possessed stolons and other means of vegetative
propagation.
AFFINITIES OF _MEDULLOSEAE
We may provisionally treat the family names Medul-
loseae and Neuropterideae as synonymous, for though
there can as yet be no strict proof that the groups in-
dicated were coextensive, yet there is evidence that the
1 C. Grand’Eury, ‘“‘ Sur les organes et le mode de végétation des
Neuroptéridées, et autres Ptéridospermes,’’ Comptes vendus, t. 146,
p. 1241, 1908.
218 STUDIES IN*FOSSIL BOTANY
Medullosean type of structure existed in several of the
genera with Neuropteridean characters in the frond.
In the Medulloseae, as in the Lyginopterideae, we
find certain not unimportant structural characters, even
apart from the habit, which suggest an analogy with
the Ferns. So far as Medullosa itself is concerned, the
most Fern-like feature is the vascular system of the
stem, which in its primary “ polystelic’’ arrangement
recalls the higher Ferns, and was compared by Weber
and Sterzel in 1896 with that of Psaronimus. The fact
that this original ground-plan becomes more or less
obscured as secondary growth goes on does not affect
the nature of the primary structure, but a more de-
cisive difference from the Ferns consists in the absence
of leaf-gaps in Medullosa (see above, p. 188). The dis-
covery of the Sutcliffia type of vascular system, which
may be described as a modified protostele, renders it
probable that polystely arose within the family Medul-
loseae, and we must certainly regard this character as a
parallel development to the polystely of the Ferns and .
in no way as an inheritance from them. In Sutcliffia,
however, the anatomy of the stem, peculiar as it is,
might be compared, though remotely, with that of a
protostelic Fern, while the concentric foliar bundles
suggest some analogy. There is nothing to indicate
any real relation between Ferns or other Pteridophyta
and the Medulloseae, and the great complexity of the
seed shows clearly enough how remote any connection
with a cryptogamic phylum must have been. On
anatomical grounds it seems not unlikely that this family
may have had a common origin with the Lyginopterideae
from some unknown protostelic type.
On the whole, the Medulloseae or Neuropterideae _
strike one as a more advanced group than the Lygino-
pterideae. Their seeds, if we may take 77igonocarpus
as a type, perhaps approach nearer than any other
Palaeozoic seeds to those of recent Cycadaceae, as shown
AFFINITIES OF MEDULLOSEAE 219
by the differentiation of the integument into a sarcotesta
and a sclerotesta, the double vascular system and the
form of the pollen-chamber ; the chief difference lies in
the apparently free nucellus of the fossil seeds, a feature
with which other distinctions may be correlated. As
regards anatomical characters, the petiole and rachis of
Medullosa very closely resemble those of a Cycad in
structure; the same may be said of the root. The
stem-structure, however, throughout the Medulloseae is
essentially different, for neither in the almost protostelic
Sutclifia, nor in the more complex polystelic stems of
Meduillosa, do we find, as it seems to me, any fundamental
agreement with the stem either of recent Cycadaceae or
of Mesozoic Bennettiteae, though certain analogies can
be traced. On the whole of the evidence an affinity
between the Medulloseae and the Cycadophyta of later
periods appears well established, but we cannot assume
that the former were the direct ancestors of the latter.
Dr. Ethel de Fraine, in her paper on Sutcliffia, framed
an interesting hypothesis, which she stated as follows:
‘From such a type as Sutcliffia, which may be regarded
as the most primitive member of the Medulloseae at
present known, it is suggested that two divergent lines
may have arisen. The one advanced with increasing
complexity in the direction of multiplication of the
number of steles, through some such form as Medullosa
angzlica, and ended blindly in the more complex Medul-
loseae. . . . The other maintained the protostelic con-
dition, and advanced by further modification of the
single vascular cylinder, and perhaps by the elaboration
of the extra-fascicular arcs and accessory vascular strands
of the cortex, in the direction of the Cycadales.”’ ?
This 1s a perfectly tenable view, which reconciles the
affinity between Medulloseae and Cycads, with the
essentially monostelic stem-structure of the latter. Con-
‘necting links are of course wanting at present, and the
; 1 E. de Fraine, /.c. p. 1062.
220 SLUDIES IN POSS BOTAN:
suggestion therefore remains a pure hypothesis until
further evidence becomes available. We shall return to
the question in the final chapter.
ANEIMITEAE
The genus Anezmites,1 Dawson, may be mentioned
in connection with the Neuropterideae, to which it has
sometimes been referred on foliar characters, though, as
we shall see, the fructification shows that there can have
been no near affinity. The habit of the fronds is like
that of a Maiden-hair Fern (Adiantum), as the original
generic name Adiantites implied; the genus extends
from the Devonian to the Middle Coal-measures, and is
characteristic of the Lower Carboniferous. In a species
(Aneimites ? fertilis) from the Pottsville beds of West
Virginia, of an age corresponding to that of gounr
Millstone Grit, Dr. David White has demonstrated
the presence of seeds on the fronds. “They are bore
on the apices of branched, terminal extensions of the
peripheral pinnae ; the pinnules on the adjacent sterile
portions of the frond, though considerably reduced,
retain the characteristic cuneiform shape. The small
seeds (averaging 4-5 mm. in length) are rhomboidal in
form, lenticular in cross-section, and winged; it thus
appears that they were of the platyspermic (bilaterally
symmetrical) type, which was once supposed to char-
acterise the Cordaiteae. As the specimens are only
known in a carbonised condition, nothing certain can
be said as to the structure, though the discoverer believed
that he detected indications of the micropyle and pollen-
chamber. The isolated seeds were named Wardia fertilis
1 David White, ‘‘ The Seeds of Aneimites,’’ Smithsonian Miscel-
laneous Collection, vol. xxvii. Pp. 322, 1904.
2 The older and more familiar name, Adiantites, GOppert, is main-
tained by some authors. Aneimites is still used here, because the seeds
were originally described under that name.
ANEIMITEAE 221
before their connection with the frond was observed,
and this name is retained by Prof. Seward. Dr. White
has discovered different forms of the Wardia seeds in
the most intimate association with four other species
of the genus; in one of these, A. tenuifolius, Goppert,
they again occur in actual connection with the frond.
The author points out that the proof of the Pterido-
spermous nature of Aneimites throws suspicion on various
similar frond-genera, in one of which, Evemopteris, there
appears to be strong evidence from other sources for
the occurrence of seeds of a platyspermic type. The
specimens of the Coal-measure species, £. artemisiaefolia
(Sternberg), are almost constantly associated with the
platyspermic seed, Samaropsis acuta (L. and H.). The
seeds of Aneimites resemble some of those grouped under
the name Cardiocarpon, and it may be hoped that this
clue may eventually lead to the recognition of their
structure.
SEED-BEARING PECOPTERIDEAE
Up to the year 1905 the form-genus Pecopteris was
regarded as the stronghold of the true Ferns, no suspicion
of other alliances attaching to any of its members. In
that year, however, M. Grand’Eury made the striking
discovery that the species Pecopteris Pluckeneti, from the
Upper Coal-measures of St. Etienne, was a seed-bearing
plant. In twenty specimens he found the seeds attached
by hundreds to the fronds. Sometimes they occur on
pinnae of the usual vegetative form, but where they are
numerous the lamina is somewhat reduced. The seeds
are attached at the ends of the stout lateral veins of
the pinnules (see Fig. 85). They are described as
forming a wide angle, when in the natural condition,
with the plane of the lamina, so that they no doubt
hung down freely from the under side of the fertile
1 “Sur les graines trouvées attachées au Pecopteris Pluckeneti,
Schlot.,’’ Comptes rendus, t. cxl. p. 920, 1905. P
222 SLUDIES IN FOSS BOTANY
frond. The seeds, like those of Aneimites, are winged
(Fig. 85), and resemble Samaropsis, a seed of which other
species have been assigned to the Gymnosperm Dory-
cordaites (see p. 267) so
closely that the two may
easily be confused when
found isolated.
The species P. Pluche-
nett belongs to a section
of the genus characterised,
according to Prof. Zeiller,
Pe mie Reted Teen by. the large, lob aaae
the ends of the lobes. x 3. From nules, and the dichotom-
en not Grand Bunyls spec - ously branched frondseaeel
a bud, capable of further
growth, in the axil of each bifurcation. Though usually
included in Pecopteris, some authors have placed the
species in other genera, and notably Sterzel, in 1883,
founded a new genus, Dicksonites, for its reception,
because he observed, in some specimens, round disks at
the margins of the pinnules, which he compared to the
sori of Dicksoma.* The nature of these bodies appeared
to have been elucidated by a later observation of M.
Grand’Eury’s. He stated that he found “ stellate groups
of anthers in the place of the receptacles,’ and that they
were borne on different specimens from those showing
seeds. But there is also evidence suggesting that the
“receptacles ’’ may represent the scars of seeds.which
had been shed.
There is another species of Pecopteris, P. Sterzelt,
Zeiller, which so closely resembles P. Pluckeneti, in the
form and mode of branching of the frond, that Prof.
Zeiller had no doubt that this too was a Pteridosperm,
1 Zeiller, Eléments de paléobotanique, p. 89, 1900.
2“ Uber Dicksoniites Pluckeneti,’’ Bot. Centralblatt, Bd. xiii. 1883.
% See Grand’Eury, “‘ Sur les inflorescences des fougéres a graines,’’
etc., Comptes vendus, t. cxlili. p. 764, 1900.
SEEDS OF PECOPTERIS 223
though the seeds have not yet been observed. There
is evidence of considerable weight that the fronds of
P. Sterzeli were borne on a Caulopteris stem—Caulopteris,
as already stated, representing the casts of “ Tree-fern ”’
stems, the structure which, when known, is that of
Psaronius (Vol. I. p. 268). Although Prof. Zeiller ceased
to regard the connection between Pecopteris Sterzeli and
the Caulopteris as proved, it seems desirable to call
attention to the question. If the attribution should be
confirmed by future investigation,! the relation of the
Marattiaceous to the Pteridospermous Pecopterids will
need serious reconsideration.
It has already been mentioned (Vol. I. p. 262) that
additional evidence for the Pteridospermous nature of
certain Pecopterids is afforded by the fact that they
bore fructifications of the Crossotheca type. Dr. Kidston?
enumerates three species of Cvossotheca in which the
foliage is known to have been that of a Pecopteris, and
there are two other species in which this was probably
the case. As Dr. Kidston says: ‘“‘ Having shown that
the supposed sporangia of one species of the genus [Cvosso-
theca| are in reality the microsporangia of one of the
Pteridosperms, I think we are justified in provisionally
concluding that all the remaining species also belong to
the Pteridospermeae, even though we do not possess a
complete knowledge of the structure of their micro-
sporangia.’’ There is thus a presumption that a con-
siderable fraction of the old genus Pecopteris is made
up of seed-bearing plants.
One of the probable Pecopterid Crossothecas, Pecopteris
exigua, Ren.,? from the Permo-Carboniferous of Autun,
occurs in the silicified condition, with structure preserved,
1 For the history of this question see Zeiller, Flore fossile de Com-
mentry, Pt. i. 1888, p. 184, Plate viii.; Bassin houiller et permien de
Blanzy, flore fossile, 1906, p. 62.
* Microsporangia of the Pteridospermeae, p. 432.
3 Renault, Cours de bot. fossile, année 3, p. 115, Plate xix. Figs.
13-18, 1883.
224 STUDIES IN “FOSSIL; BOTANY
but only fertile portions of the frond appear to be known.
The little fertile pinnules, elliptical in form and about
I mm. long, are inserted on the rachis like the leaflets
of a Pecopteris. Each pinnule bears, on its lower surface,
two rows of ovoid, pointed sporangia, three or four in
each row; they appear to be free from each other, and
do not show the bilocular structure described by Dr.
Kidston in the Cvossotheca of Lyginopterts. There 1s,
of course, no proof that they were microsporangia, but
the general resemblance to a Cvossotheca tells in favour
of this supposition.
In Callipteris, a characteristic Permian genus of com-
paratively small bipinnate fronds, placed by M. Zeiller
in Pecopterideae, M. Grand’Eury found evidence that
seeds were present in at least two species. The seeds,
which appear to have been borne on a slender, branched
rachis, are of an elliptical or roundish shape, and from
5 to 10 mm. in length, and are described as resembling
berries, and as the simplest in form of any Pterido-
spermous seeds. Bodies resembling an enormous Cvosso-
theca, 2 to 3 cm. in length, and bearing marginal sporangia,
are regarded as possibly constituting the male organs
of the plant. M. Grand’Eury pointed out that Calh-
pteris differs widely from the Neuropterideae in its organs
of reproduction as well as in foliar characters.!
The common Coal-measure “ Fern,’ Manopteris
muricata, with forked primary pinnae and a Lygodium-
like habit, was found by M. Grand’Eury in close associa-
tion, if not in connection, with small seeds,” so it is prob-
able that this Pecopteroid form, in which no Fern-like
fructification has ever been observed, will likewise prove
to belong to the Pteridosperms. It has been suggested
1 Grand’Eury, “‘ Sur les graines et inflorescences des Callipteris,’’
Comptes vendus, t. cxhii. p. 664, 1906.
* Grand’Eury, “‘Sur les organes et le mode de végétation des
Neuroptéridées et autres Ptéridospermes,’’ Comptes vendus, t. cxlvi.
p. 1243, 1908.
PECOPTERIDEAE 225
by Dr. Gothan that Mariopteris may have belonged to
a Coal-measure Helerangium.
We see, then, that on present evidence there is every
reason to believe that a large proportion of the Fern-
like Palaeozoic plants with Pecopteroid foliage will find
their place, like Pecopterts Pluckeneti, among seed-bearing
plants. As we have already seen (Chap. VIII. Vol. I.),
there are still good grounds for the opinion that some
other Pecopterids were true Ferns; much further in-
vestigation will be necessary before we are able to
discriminate with certainty between the two classes of
plants represented among fossils of this habit.
DOLEROPHYLLUM
Some remarkable fossils, described under this name,
may be mentioned here ; they would be of great interest,
if it were certain that the various organs belonged to
the same plant or to the same genus; as, however, this
is not proved, a very brief notice must suffice.
The vegetative organs referred to Dolerophyllum,
Saporta, consist of large, circular, peltate leaves, borne
on an axis. In D. Berthiert, Ren., the leaves are 18
to 20 cm. in diameter; the numerous veins are forked.
This species was derived from the Permo-carboniferous
of France (Mont-Pelé, near Epinac). Other species have
been described ; D. Goepperti, Saporta, the first to be
recorded, came from the Permian of the Ural in Russia,
and is in the form of large buds, 3 inches long. The
young, convolute leaves resemble the mature leaves of
the French specimens, but the relation is uncertain.
The anatomical structure is partly preserved; there
are stomata on the upper surface of the leaves; the
numerous vascular bundles appear to be of the collateral
mesarch type, familiar in Cycadophyta.
Associated with the leaves of the Mont-Pelé species,
Renault found some carbonised discs, containing pollen-
15
226 STUDIES IN FOSSiE BOTANY
grains or spores, and attributed them to the Dolero-
phyllum. Petrified fragments of similar bodies were
discovered at another locality (Grand Croix) and are
probably of the same nature. The discs are 5-6 cm.
in diameter with a thickness of 15-20 mm. The thick
lamina is perforated by a number of vertical tubes, or
immersed sporangia, filled with large pollen-grains or
spores. Each grain measures about 460x330; 1
appears to have opened by an operculum in the outer
wall, and the interior is divided into 8 or Io cells, thus
resembling many other Palaeozoic pollen-grains.
The structure of the staminate discs, however, is
unique, and throws no light on the affinities of the plant.
A seed, Aetheotesta elliptica, Ren., of the Trigonocarpus
group, was attributed by Renault to Dolerophyllum, on
the ground of a certain similarity between the pollen-
grains found in its pollen-chamber and those of the
staminate discs. The evidence, however, is quite in-
decisive.
The affinities of the genus, supposing that the scattered
organs are rightly referred to one type of plant, are
wholly uncertain. Dolerophyllum, if a natural group,
probably belonged to some branch of the Pteridosperms,
somewhat remote from the better-known families, but
perhaps nearest to the Medulloseae.!
COMPLEX STEMS OF UNCERTAIN AFFINITY
Steloxylon, Solms.—This genus was founded by Solms-
Laubach on the Medullosa Ludwigii of Géppert and
Stenzel, a fossil discovered near Semipalatinsk, in Western
Siberia. It was found in a secondary deposit, and its
geological age is therefore doubtful ; it may be Permian
or older. Dr. P. Bertrand states that one of the Saalfeld
+ Hor Dolervophyllum see Renault, “‘ Bassin houiller et permien
d’Autun et Epinac,”’ Flore fossile, ii. 1896, p. 260, Pl. Ixxii. ; Seward,
Fossil Plants, vol. iii. 1917, p. 132.
STELOXYLON 227
specimens, attributed to Cladoxylon dubium, is really a
Steloxylon ; if this is the case, the genus goes back at
least to the Lower Carboniferous.
The original specimen formed part of a fairly large
stem, quite 5 inches in diameter. The structure differs
from that of both Medulloseae and Cladoxyleae. The
stem contains a great number of steles, some nearly
circular in transverse section, others elongated. In the
latter case, the longer diameter of the stele is radially
directed, as in the Cladoxyleae. The steles are every-
where connected by anastomosis, forming a complex
network. The exterior of the stem is clothed in an
armour of crowded, rather small petiole bases, spirally
arranged, and in this respect differs widely from either
of the families above mentioned. Further, each leaf-
base receives two or more branches from the external
steles of the stem. The leaf-trace strands retain their
stelar structure, and so far resemble the foliar strands
of Cladoxyleae rather than those of Medulloseae.
Each stele, as preserved, consists mainly of secondary
wood ; no doubt there was some primary xylem in the
middle, but it was little developed, and nothing is
known of its structure. The foliar steles, entering the
leaf-bases, have the same, largely secondary, structure.
The pitting of the tracheides is of the multiseriate, bor-
dered type, as in the Medulloseae. Medullary rays are
present ; they widen out towards the centre of the stele.
The most important differences from Medulloseae are,
first, the orientation of the steles, which are elongated
radially and not tangentially ; secondly, the structure
of the leaf-bases, with a few steles, instead of numerous,
relatively small bundles. From Cladoxyleae, Steloxylon
differs in the pitting of the tracheides. The dense
armour of small leaf-bases is a character equally foreign
to both groups. In his note of 1914 Dr. Bertrand goes
so far as to suggest that Steloxylon may simply represent
a special condition of Cladoxylon, but the differences
228 STUDIES IN FOSSiby BOTARY
just mentioned render this view difficult to accept. It
is much to be desired that Dr. Bertrand’s results, hitherto
only briefly indicated in preliminary notes, may soon
be published in full. In the meantime the position of
Steloxylon remains uncertain; it is a polystelic stem,
having some points in common both with the Medul-
loseae and the Cladoxyleae, but in other features very
different from either."
Rhexoxylon, Bancroft.— The, original species, AR.
africanum, was founded on a portion of a silicified stem
from the Karroo series of South Africa. As this series
of rocks ranges from Upper Carboniferous to Rhaetic or
Lower Jurassic age, the antiquity of the specimen was
uncertain, but the age was probably Triassic. The cortex
and outer part of the vascular system are missing; the
remaining central portion, about 7x5 cm. in diameter,
shows an inner ring of “steles,’”’ with portions of an
outer vascular zone. - The ““steles ” consist “im geaer
case of a smaller external and a larger internal mass
of secondary wood; the chink between the two was
supposed to contain the original primary xylem. The
surrounding phloem is still preserved. The outer
vascular ring consists of normally orientated masses of
secondary wood ; they have been called “ partial steles,”’
but in this region there was never any evidence of stelar
structure. The large stem-pith contains an irregular
vascular plate or elongated stele, as well as some sclerotic
nests and a few bands of periderm. The secondary wood
of the various vascular masses has a dense structure
like that of a Conifer, and is traversed by uniseriate
medullary rays. The tracheides bear from one to three
(usually two) rows of bordered pits on their radial walls,
and have an Araucarian character.
1 For Steloxylon see especially Solms-Laubach : ‘‘ Uber die in den
Kalksteinen des Kulms . . . Pflanzenreste, iv. Volkelia, Steloxylon,”’
Zeitschrift f. Botanik, ii. 1910; also the earlier literature there cited ;
also the note by P. Bertrand, cited above, on p. 158.
RHEXOXYLON 229
Rhexoxylon has recently been re-investigated by Mr.
John Walton of Cambridge, whose results will shortly
be published. He has had various important new
specimens at his disposal, and recognises more than
one species. He shows that no primary wood is present
in the supposed “ steles.’”’ Hence the structure is not
polystelic, for all the anomalies are secondary. The
affinity, once suggested, with Medulloseae must therefore
be given up. Mr. Walton interprets the very remarkable
structure as that of a climber or lane, of Dadoxylon
type.
CYCADOXYLEAE
We have now to consider a series of fossil forms of
which our knowledge is still imperfect, but which are of
great interest, as they appear to connect the Lygino-
pterideae with a more distinctly Cycad-like type of
structure.
A portion of a large stem, Cycadoxylon robustum,
regarded by Williamson as belonging to his Lygzno-
dendron, and subsequently named L. vobustum by Prof.
Seward, was discovered by Nield more than forty years
ago, in the Lower Coal-measures of the Oldham district.
Although the specimens are fragmentary, they show
some points of considerable interest. No cortical
tissues are preserved, and even the wood is probably
incomplete, but the remaining, central part of the stem
has a diameter of about I4 cm., so, in the natural condi-
tion, the plant must have reached the dimensions of a
small tree. The secondary wood, which, in its present
state, has a thickness of nearly 6 cm., resembles that
of Lyginopterts oldhamia (Fig. 86, x”). The medullary
rays are broad, and of great height, so that the whole
1 For Rhexoxylon see N: Bancroft, “ Rhexoxylon africanum, a new
Medullosean stem,’’ Trans. Linn. Soc. Botany, vol. vili. 1913 ; Seward,
Fossil Plants, vol. iii. 1917, p. 146. See also Mr. Walton’s paper, when
published.
230 STUDIES IN FOSSIL BOTANY
character of the wood was very parenchymatous, like
that of the recent Cycads. The tracheides, which have
a somewhat sinuous course, bear multiseriate bordered
pits on their radial walls.
The pith, which is almost 3 cm. in diameter, is
imperfectly preserved, but there are distinct remains of
neB >;
8B
2
ry
Fic. 86.—Cycadoxylon robustum. Part of transverse section, showing inner portion of normal
wood, with two anomalous zones of wood and bast. «?, normal secondary wood ; #°, ph,
first inverted band of medullary xylem and phloem; 4‘, ph*, second band of the same ;
PR, 263s sp Celli viszs, (Cr, Ake (C:,)
scattered, dark groups of sclerotic tissue, such as we
find in the pith of L. oldhamia.
The most characteristic feature of Lyginopteris, how-
ever, namely the strands of primary wood on the border
of the pith, cannot be recognised with certainty in Nield’s
specimen, and if present, must, it would seem, have
been much reduced. The remains of leaf-traces, passing
out through the secondary wood, are seen at several
CYCADOXYLON 231
ae
.
places, but even here the primary xylem of the outgoing
bundle has not been detected. It must therefore remain
an open question whether the primary structure of the
xylem was of the Lyginopleris type, or whether the whole
wood developed centrifugally, as in the stem of recent
Cycads or Conifers. On the other hand, the large stem
presents a peculiarity of structure which occurs in some
specimens of Lyginopteris oldhamia. It was mentioned
above (p. 40) that, in that plant, anomalous vascular
tissues are sometimes developed in the outer part of the
pith, immediately within the normal ring of bundles.
These tissues, when present, have inverted orientation,
the xylem facing outwards, towards the normal wood,
and the phloem inwards, towards the centre of the pith.
Precisely the same anomaly reappears, in a more striking
form, in Cycadoxylon robustum. There is a distinct zone
of secondary wood at the margin of the pith, reaching
in places a thickness of about sixteen tracheides in a
radial row, and on the inner side of the anomalous zone
a corresponding band of phloem can be recognised (Fig.
86, x°, ph*®). Thus, the medullary vascular tissues had
the same reversed orientation as in the corresponding
anomalous formations sometimes found in Lyginopteris
oldhanua. In Cycadoxylon robustum the anomalous
vascular zone is at some places double, the second band
of medullary wood and bast having the same orientation
as the first (see Fig. 86, x*, ph‘).
The structure as a whole leaves little doubt that
the fossil Cycadoxylon rvobustum really possessed some
affinity with Lyginopteris, but, as there is no proof that
the primary structure of the two was similar, we no
longer place them in the same family, but have trans-
ferred the species discovered by Nield to the type-genus
of the Cycadoxyleae, to which, as we shall now see, it
naturally belongs.*
1 On Cycadoxylon robustum see Williamson, ‘‘ Organisation of the
Fossil Plants of the Coal-measures,’’ Part iv. Phil. Trans. 1873,
232 STUDIES IN, FOSS BOLANT,
The interest of the fossil depends on two points.
The first is the thoroughly Cycadean character of the
secondary wood, a character shown much more evidently
in this large stem, which in its dimensions is comparable
to that of a recent Cycad, than in the smaller stems of
the Lyginopterideae. The second point is the marked
development of the anomalous medullary vascular tissues,
which we have already found, as an individual peculiarity,
in Lyginopteris oldhamia.
A small stem, from the Lower Permian ‘of Autun,
described by Renault, and named Cycadoxylon Fremyt,
shows still more perfectly the type of structure just
described. The stem is from 20 to 25 mm. in diameter ;
the cortex, which is fairly preserved, contains gum-
canals, and large pitted elements, probably with a
mechanical function. Within the cortex is a ring of
normal wood and bast, both well preserved, and exactly
resembling the vascular tissue of a modern Cycad. The
medullary rays are extremely wide, exceeding in extent
the tracheal bands between them. The tracheides are
for the most part pitted; the bordered pits are ranged
in numerous series on the radial walls. Towards the
interior of the normal zone of wood, scalariiorm
tracheides occur, and at its inner limit are the spiral
elements of the protoxylem. It would thus appear
that the whole normal wood was centrifugally developed,
as is usual in recent Cycads. Professor Seward, how-
ever, states that. at’ one place he detected a “distin
strand of primary xylem; this may indicate that some
trace of the mesarch structure of the Lyginopterideae
p. 386; Williamson and Scott, ‘‘ Further Observations,’’ etc. Part iii.
Phil. Trans. vol. 186, B, 1895, p. 742; Seward, ‘‘ A Contribution to
our Knowledge of Lyginodendron,’’ Annals of Botany, vol. ix. 1897,
Pp. 05.
As Professor Seward points out, the specimen described by M.
Renault in the Flore fossile d’Autun et d’Epinac, Part ii., under the
name of Medullosa gigas, appears to be almost identical with Nield’s
plant. (But see above, p. 192.)
CYCADOXYLON 233
still persisted in Cycadoxylon, though much reduced,
The wide phloem-zone consists of alternating concentric
bands of parenchyma and sieve-tubes.
Within the normal vascular ring are two or more
interrupted zones of anomalous wood and bast, with
inverted orientation, the phloem facing inwards. These
medullary vascular arcs are separated by parenchyma
from the normal centrifugal wood. The whole structure
is thus comparable to that of Cycadoxylon robustum,
except that the normal zone is much less developed,
which may simply be a matter of age.
Curiously enough, no leaf-trace bundles have so far
been found in Cycadoxylon Fremyi. The characters, as
at present known to us, strongly suggest Cycadean
affinities, though the characteristic anomaly of Cycado-
xylon, the formation of inverted zones of secondary
wood and bast in the pith, is not known in the same
form among recent Cycads. On the other hand, it is
identical with the most frequent anatomical variation
occurring in stems of Lyginopteris oldhamia.
Another silicified stem from the Permian of Autun,
the Ptychoxylon Levy: of Renault, presents a somewhat
similar combination of characters. In this fossil the
dimensions are greater than in Cycadoxylon Fremyi, the
stem of Ptychoxylon attaining a diameter of 5 or 6 cm.
The external surface bears the marks of spirally disposed
appendages. The character of the genus depends on
the arrangement of the vascular tissues. There is an
outer, more or less continuous cylinder of wood and
bast, surrounding a very large pith, within which are
several secondary vascular bands, with their wood
developed centripetally, while that of the normal outer
ring is centrifugal (Fig. 87). The traces of both leaves and
branches are present, and, as the two organs appear to
correspond in position, it is not improbable that the latter
were axillary. It seems that the phyllotaxis was 2.
Where the bundles of a leaf or branch pass out, the
234 STUDIES IN FOSSIL BOTANY
external vascular cylinder is interrupted, and its edges
are incurved, to unite with two of the internal vascular
bands (see Fig. 87, x’, ph’). The latter are thus always ~
continuous, at some point of their longitudinal course,
with the normal vascular ring. This, it will be remembered,
(=p
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Fic. 87.—Ptychoxylon Levyi. Transverse section of a decorticated stem. x, ph, normal
xylem and phloem; x’, ph’, first inverted medullary bands of xylem and phloem, con-
tinuous at the leaf-gaps with the normal zone; x”, ph”, second inverted zone; br, stele
of a branch. Slightly magnified. After Renault.
is precisely what happens in some specimens of Lygino-
pleris oldhamia, where the anomalous medullary wood
and bast are likewise connected, at the leaf-trace gaps,
with the normal vascular tissues (see p. 40). In Ptycho-
xylon, however, the conditions are more complicated,
for there are often two or three concentric systems of
PTYCHOXYLON 235
internal vascular arcs, joining on at different levels to
the external ring (see Fig. 87, x”, ph”). . The character
of the wood and bast of each ring is very parenchymatous,
like that of Cycadoxylon, or of a recent Cycad. The
phloem, which is external in the case of the normal zone,
but internal in each of the anomalous bands, is beauti-
fully preserved, and even the details of the sieve-tubes
have been made out. There appears to be no indication
in this genus of any primary centripetal wood in the
stem.
The leaf-traces, however, appear, from Renault’s
description and figures, to have essentially the same
structure as in Lyginopteris: the trace consists of two
bundles, side by side; in each bundle there is a large
arc of secondary wood on the outer side of the primary
strand ; the spiral elements lie near the limit of primary
and secondary wood, so it appears that the former was
wholly or mainly centripetal in its development.
The parenchymatous cortex, which contains secretory
sacs, or canals, is coated externally by periderm ; this
may account for the absence of any hypodermal fibres,
which had very probably been lost by exfoliation.
The branches, at their base, had a normal vascular
ring, but, as they became free, gradually assumed the
complex structure of the main stem.”
The stems just described, *Cycadoxylon robustum,
C. Fremyi, and Ptychoxylon Levyi, may be grouped
under the family-name of Cycadoxyleae, a designation
already used by Renault, but in a somewhat more ex-
tended sense.2 The interpretation of their structure
1 Compare the double anomalous zone in Cycadoxylon vobustum,
Fig. 86.
2 For a full description of Cycadoxylon and Ptychoxylon see Renault,
‘« Bassin houiller et permien d’Autun et d’Epinac,’’ Flore fossile, Part ii.
PP. 307-21, 1896.
3 Renault included Medullosa and Colpoxylon in the Cycadoxyleae.
On the view here taken, these two genera belong to a different, though
related, line of descent, as has already been shown.
23 STUDIES EIN FOSSIL BOTANY
which, in agreement with the views of Professor Seward,}
I desire to suggest is that they may have been derived
from some form resembling Lyginopteris oldhamia, from
which they have deviated in two principal respects.
On the one hand, they have gradually lost the primary
centripetal wood of the vascular bundles in the stem.
In Cycadoxylon robustum, this tissue has not been recog-
nised with certainty, and must at most have been
relatively unimportant ; in C. Fremyi it was certainly
on the verge of extinction ; in Ptychoxylon it had prob-
_ably disappeared altogether. This change is in a Cycado-
phytic direction, for the recent Cycads (as well as the
Mesozoic Bennettiteae) have wholly lost the centripetal
primary wood of their vegetative stems, while retaining
it in their leaves, and occasionally in the peduncles of
their cones. It is very interesting to find that the leaf-
trace bundles in the cortex of Ptychoxylon retain the
Lyginopteris structure: in a typical Cycad they would
not possess centripetal wood in this part of their course.
The extinction of the centripetal xylem wasaena
doubt, correlated with the advance of secondary growth.
As the centrifugal wood became more and more pre-
dominant with the increasing activity of the cambium,
the small centripetal portion (the ‘‘ Cryptogamic ’’ wood
of the French authors) became insignificant in com-
parison, and could be dispensed with, so far as the stem
is concerned. In the roots there was a special physio-
logical reason, connected with the absorptive function,
for its retention,” and here it has held its own all through :
in the leaves, where secondary tissue-formation is less
marked, it persisted in many cases, as in Cycads, Cor-
daiteae, and perhaps, in a modified form, in Coniferae,
'“ Contribution to our Knowledge of Lyginodendron,” Annals of
Botany, vol. xi. 1897; also Fossil Plants, vol. iii. 1917, p. 185.
* See Strasburger, Histologische Beitrége, iii. p. 140; also Chauveaud,
“ L’Appareil conducteur des plantes vasculaires,’’ Ann. des Sci. Nat.
Boy Ser. 0, ty-Xill. LOTT:
CYCADOXYLEAE 237
but in the highly modified sporophylls, even of Cycads, it
tends to disappear.!
On the other hand, the Cycadoxyleae had changed
in another direction, and one peculiar to themselves
among the allied groups. The anomalous formation of
inverted medullary wood and bast, which in Lyginopteris
only appears as an individual and comparatively un-
important peculiarity, had in the Cycadoxlyeae become
a constant and marked character. We regard this
structure as a new formation, due to the spreading in-
wards of cambial divisions through the leaf-trace gaps,
as is clearly shown in Lyginopteris itself, and in Ptycho-
xylon. There is no reason to suppose that the anomalous
centripetal wood thus formed had anything to do with
the primary and normal centripetal wood of the more
primitive forms: the example of Lyginopteris oldhamia
shows that the two structures were quite independent.
Neither does it seem practicable to derive the structure
of Cycadoxyleae from a system of Medullosean steles.
Scattered medullary bundles are a characteristic ana-
tomical feature in the recent genera Encephalartos and
Macrozamia,? but continuous zones or extensive arcs of
inverted wood and bast do not appear to be known in
the pith of normal Cycads. Such anomalies, however,
as shown by similar cases in many recent Dicotyledons,
are extremely variable, and the peculiarity in question
cannot hinder us from recognising the generally Cycado-
phytic character of the stems of Cycadoxyleae.
It must always be remembered that the Cycadophyta
were once an extensive and dominant class of plants,
and that the few, which have survived to our own time,
only give us a very imperfect and partial idea of the
1 See Worsdell, “‘ Vascular Structure of the Sporophylls of the
Cycadaceae,’’ Annals of Botany, vol. xii. 1808.
2 See Worsdell, ‘“ Anatomy of the stem of Macrozamia,”’ etc., Annals
of Botany, vol. x. 1896. ‘‘ The Structure and Origin of the Cyca-
dacea,”’ zbid. vol. xx. 1906.
7
>
238” STUDIES EN 2OSSID BOTANY
range of organisation which the group once exhibited.
The Cycadoxyleae’ present, as we have seen, marked
analogies with the later Cycadophytes, but it is improb-
able that they were on the direct
line of descent (see Chap. V.).
It is interesting to find that
the same Permian beds of Autun,
which have yielded the stems of
Cycadoxyleae, also contain both
leaves and fructifications which
may be of a Cycadophytic char-
acter. The leaves are referredae
the genera Pterophyllum and
Sphenozamites,, the former re-
calling the foliage of the recent
Dioon, and the latter that ar
some species of Zama. The
agreement, in form and venation,
with typical Cycadean leaves, is
sufficiently close to ‘Tenders
probable that the affinities of
these fossils were with the Cyca-
dophyta.
The fructification referred to
—Cycadospadix milleryensis, Ren.”
—is a very remarkable one, re-
Fic. 88.—Cycadospadix milleryensis, presented in Fig. 88. The sams
Fmuctification, consisting of an bears numerous fimbriated spore;
axis, bearing numerous laciniate
sporophylls (!), each of which phylls (/), concave on their lower
bears seeds (s) (probably two :
to each sporophyll) onitslower Surface, and on. the underssnee
tee Ok each’ Sporophyl) two -seecamn
were borne. lRenault, the dis-
coverer, stated that the sporophylls were spirally
arranged, and regarded the whole structure as con-
.
wa
?
'
‘
1 See Renault, Flore fossile d’Autun et d’ Epinac, Part ii.
2 Loc. cit. Prof. Seward uses the generic name Strobilites, as the
Cycad relation is doubtful.
CYCADOXYLEAE 239
stituting a lax cone. Some of the specimens are in-
serted, almost at right angles, on a branch little thicker
than the axis of the cone itself. Such an arrangement
is not found among true Cycads, but the comparatively
slender, branched stem of the Rhaetic Wielandiella (see
Chap. V.) offers an analogy; and as Ptychoxylon, at any
rate, is known to have branched pretty freely, it is quite
possible that Renault’s interpretation is the right one.
It seems not impossible, however, that the whole struc-
ture may represent a single compound leaf or sporo-
phyll, or even a _ single fertile pinna, the bodies
immediately bearing the seeds being of the nature of
leaflets. In the latter case, we should have a sporophyll
more complex than that of any recent Cycad, and its
affinities would probably be with the Pteridosperms ; on .
Renault’s interpretation, the fructification would repre-
sent a nearer approach to the cones of the Zamieae. In
any case the fossil is of the greatest interest, and it is
much to be hoped that specimens with structure pre-
served may yet be discovered.
Whether these leaves and fructifications belonged to
Cycadoxyleae or not, it is probable that the stems in
question (or some of them) were those of plants which
had already passed the boundary (at most a very in-
definite one) between Pteridosperms and Gymnosperms.
SUMMARY OF THE PTERIDOSPERMS
As explained above (p. 94), we have used the name
Pteridospermeae in the widest sense, to cover all the
families previously included under Cycadofilices, as well
as those in which there is direct evidence for the seed-
habit. The reason for this extension of the denotation
is the impossibility of carrying out in practice a dis-
tinction based only on the degree of strength or weakness
of the evidence. The name Cycadofilices may be and
has been employed in the same wide sense; the only
240 STUDIES IN TOSsShL EOIN
objection to this use of it is that it implies an affinity
with Cycadophyta, which is only indicated in certain
families and not throughout the whole group. Both
names may be criticised on the ground that they suggest
a Closer relation to Ferns than appears on a reconsidera-
tion of the data to be established.
The Pteridosperms, as now understood, constituted
a great and complex phylum, nearest, on the whole, to
the Ferns, but independent and perhaps running as far
back in geological time as any of the lines of the Vascular
Cryptogams. Possibly their origin may have to be
sought among plants of the Psilophytales Flora.
It is still only in very few cases that reproduction by
seeds has been definitely proved among Pteridosperms—
in Lyginopteris Oldhamia, a couple of species of Neuro-
pteris and of Aneimites, and in Pecopteris Pluckenets.
There is further a considerable body of collateral evidence,
varying in its degree of cogency, but sufficient to show
that the seed-habit was widespread.
All the same, there are still many groups, here in-
cluded under Pteridosperms, in which there is no evidence
at all as to the mode of reproduction. This is the case
with all the families described in Chap. II., which are
characterised throughout by their vegetative structure
only. Here we can judge of their systematic position
solely by comparison with the anatomy of families known
to include seed-bearing members, namely, the Lygino-
pterideae and Medulloseae, the only groups in which
the structure is known which at present fulfil this
condition.
The four families, KRhetinangieae, Megaloxyleae,
Calamopityeae, and Stenomyeleae, all have something
in common with the Lyginopterideae, as shown by the
well-developed primary wood, the large leaf-traces with
mesarch or exarch xylem, the secondary thickening and
the multiseriate bordered pits of the tracheides. The
degree of affinity indicated varies greatly ; the structure
SUMMARY OF THE PTERIDOSPERMS — 241
is monostelic throughout, but the frequent occurrence
of exarch xylem and the numerous petiolar strands in
Calamopityeae and Stenomyeleae suggest a _ certain
approach to a Medullosean type ; it will be remembered
that in Heterangium among Lyginopterideae there is
often some approximation to exarch structure, while the
petioles, in several species, are polydesmic.
In any case, the four families mentioned appear
clearly to belong to the same cycle of affinity with known
seed-bearing groups, and there is thus a strong presump-
tion that they too had reached the spermophytic stage.
The two families, Protopityeae and Cladoxyleae, are
more isolated ; their peculiarities have been sufficiently
emphasised above (pp. 153,166). We have also seen that
they have certain features in common, though the general
organisation of the two groups is on quite different lines.
In these families we may have the relics of some very
ancient stock, perhaps somewhat remote from the main
body of the Pteridosperms. They certainly show no
affinity to Cycadophyta, as Solms pointed out, in the
case of Protopitys, in 1893; still, we can find no place
for either family elsewhere than among Pteridosperms—a
wider and greater class than the old name Cycadofilices
implied. While some members of the Pteridosperm
phylum no doubt led on to Cycadophyta, and others
perhaps to Cordaitales, the majority in all probability
led nowhere, but simply died out. The Protopityeae and
Cladoxyleae were presumably among the latter.
It is unnecessary to discuss the problematic genera
Steloxylon and Rhexoxylon, still imperfectly known ; the
former seems to have some characters in common with
both Cladoxyleae and Medulloseae, but whether it really
forms a link between the two diverse groups is extremely
doubtful. Rhexoxylon no longer appears to be built on a
polystelic plan, and at- present stands quite by itself.
The Cycadoxyleae, as we have seen, are questionable
Pteridosperms, for the almost complete loss of primary
16
242 STUDIES IN “FOSSIL "BOTANY
xylem in the stem separates them from all the recognised
families of the phylum. They show closer analogies with
the Cycadophyta than do the Pteridosperms proper. On
the other hand, Dolerophyllum, if the connection of the
various organs described under this name were estab-
lished, might probably find its place as an aberrant
Pteridosperm.
It is obvious that, in the present state of our know-
ledge, it would still be premature to attempt to define
the limits of the Pteridospermeae, or to assign them
precise characters. A purely provisional diagnosis may,
however, be of use for the purpose of distinguishing the
class from other Palaeozoic Spermophyta. The follow-
ing characters may serve :
Plants megaphyllous.
Leaf-traces relatively large.
Primary xylem well developed, usually mesarch or exarch,
both in the stele and leaf-traces.
Secondary wood and bast formed.
Pits of the tracheides bordered, usually multiseriate.
Male and female sporophylls comparatively little differen-
tiated from the vegetative foliage.
No cones formed.
Seeds of a Cycadophytic type, with a pollen-chamber and a
highly developed vascular system.
The reproductive characters are taken from the few
cases in which the fructification is known, and thus
rest on a narrower basis than the anatomical part of the
diagnosis. We are not yet in a position to distinguish
the seeds from those of Cycadophyta or Cordaitales.
The microsporangia have not been included in the pro-
visional diagnosis, as our knowledge of these organs is
still too scanty.
ee
CHAPTER: IV
THE CORDAITALES
Poroxyleae ; Pityeae ; Cordaiteae
I. POROXYLEAE
WE now pass on to a group of fossil plants, which occupies
a somewhat different position from those which we have
just described. We are no longer concerned with Pterido-
sperms, but with a class of plants more typically Gymno-
spermous. The group first to be considered, that of
the Poroxyleae, while having much in common with
certain of the Pteridosperms, especially with the Lygino-
pterideae and Calamopityeae, shows affinities not directly
with the Cycadophyta but rather with a wholly extinct
order of Gymnosperms, the important Palaeozoic family
Cordaiteae. The three families, Poroxyleae, Pityeae, and
Cordaiteae, are, in fact, so far interrelated that they
may provisionally be grouped under the common class-
name Cordaitales.
The Poroxyleae are represented at present by the
one genus Porvoxylon (of which two or three species are
known). Poroxylon is a genus in which the available
data chiefly relate to the vegetative structure ; such
evidence as we possess concerning its organs of repro-
duction will be considered later on. Our present, very
complete, knowledge of the anatomical structure, which
is preserved in astonishing perfection, is due to the
243
244 STUDIES IN FOSSIL BOTANY
investigations of the two French palaeobotanists, Renault
and the elder Bertrand.
The genus was originally discovered in the Permo-
Carboniferous deposits of Grand Croix and Autun, in
France. The two best-known French forms, Poroxylon
Boyssetit (which includes the specimens first discovered,
and described by Renault in 1879) and P. Edwardsi,
only differ from each other in unimportant characters,
which may or may not be of specific value.
The stems of these plants were comparatively slender,
the specimens described not much exceeding half an
inch in diameter; they bore spirally arranged leaves,
separated from each other, for the most part, by rather
long internodes; the French authors worked out the
phyllotaxis from the course of the leaf-trace bundles,
and found the divergence between two successive leaves
to be 7. The leaves themselves were very different
in character from those of any of the Pteridosperms, as
at present known. They were broad, thick, simple
leaves, inserted on the stem by a definite petiole, and
tapering towards the opposite extremity. The lamina
was traversed by numerous parallel veins.2. This is
quite a different type of leaf from anything we have
met with among the groups already considered.
The structure of the stem, however, is of a type
already familiar to us. The transverse section of a
young stem is represented in Fig. 89, B. We Seeman
once that there is a well-marked pith, surrounded by a
ring of collateral vascular bundles. The primary xylem-
strands of these bundles, which border immediately on
1 B. Renault, Tiges de la flove carboniféve, 1879; C. E. Bertrand
et B. Renault, ‘ Les Poroxylons,”’ in Archives bot. du Nord de la France,
1886.
2 The leaves, or at least their laminae, do not appear to have been
found in connection with the stem, in these species; but, as Bertrand
and Renault pointed out, the close anatomical agreement between
stem and leaf established a strong presumption that the two organs
belonged to identical or closely related species.
ee
POROXYLON 245
Fic.
89.—A, Poroxylon Edwardsii. Transverse section of stem. c, cavity in pith; x, primary
wood of bundles, which are numbered in the order of the ,°; phyllotaxis, No. 1 belonging
to the lowest leaf of the series; the angle 1, c, 2, is that of the divergence between two
successive leaves; 1/ and 17, the two bundles constituting the outgoing leaf-trace; x°,
secondary wood; ph, phloem. Xx about 5. After Bertrand and Renault. B, P.
Boyssetii. Transverse section of young stem. ?, pith; x, primary wood of bundles;
x*, secondary wood; ph, phloem; gc, secretory (?) sacs or canals; g, mucilage-canal ;
c, cortex; h, hypoderma. x 7. After Renault.
246 STUDIES IN FOSSIL BOTANY
the pith, are clearly marked off from the surrounding
zone of radially arranged secondary wood, which is
succeeded externally by the well-preserved cambium
and phloem. The stem thus had secondary growth in
thickness, of a normal character. The pericycle, im-
mediately surrounding the phloem, and the inner primary
cortex, contain structures interpreted as gum-canals, and
similar organs are also present in the pith. The outer
cortex was strengthened by a system of hypodermal
strands of sclerenchyma, such as we have so often met
with in the stems of Palaeozoic plants.. The general
anatomy of the stem is thus strikingly similar to that of
a Lyginopteris, and a more detailed examination shows
that the resemblance is a real one. A general agreement
with Calamopitys is also evident.
The bundles surrounding the pith are rather more
numerous than in Lyginopteris, a fact which is correlated
with the more complex phyllotaxis of Poroxylon. Each
leaf-trace, on entering the stem from a leaf, runs down
through thirteen internodes before joining the trace of
a leaf vertically below. Hence, in any transverse section
of the stem, the traces of thirteen successive leaves are
met with (see A, Fig. 89).
The internodes are long, and, as the leaf-trace traverses
the cortex in about half the length of an internode, it
follows that in any transverse section of the stem not
more than one outgoing trace (if any) is shown (see
Fig. 89, A and B). Each leaf-trace, in the upper part
of its course, consists of a double bundle. It will be
remembered that in Lyginopteris also the leaf-trace is
a double one. In that genus, however, the two strands
of the trace unite, as we follow them inwards through
the pericycle (see Fig. I1, p. 23); 1n Calamopitys they
unite in the same region (Fig. 54, p. I19), or in the zone
of thickening, whereas in Poyvoxylon they remain distinct
for some distance below their entry into the interior
of the stele. Thus, the two strands of primary wood
POROXYLON 247
shown in Fig. 90 both belong to the same leaf-trace,
which (proceeding from the second leaf above) has already
taken up its position at the margin of the pith.
This figure also serves to illustrate the important
point that the development of the primary xylem of
the bundles was centripetal. At the level of the section
each of the twin-bundles has two protoxylem-groups (px),
separated by parenchyma from the secondary wood on
aie 4
4
e&
eat SS O
= A : 5Q ‘
2 Oy. ION ORR AR SE
SR A A ee
LEROY AOS BORER PD
Ly ae CNT ey OB
FSSA ISR. HRY
Ste a ala clan
Of WOR SA ALAN
MBAS
a mr 2 LAs £
ie
Fic. 90.—Poroxylon Edwardsii. Transverse section of the stem, showing two primary
xylem-strands, with adjacent tissues. , pith; gc, mucilage-canais; px, protoxylem ;
x, primary centripetal xylem; x”, secondary xylem; m.r., medullary rays. x 66.
After Bertrand and Renault.
their exterior side. The centripetal xylem of each strand
forms an arc, abutting, at its ends, on the secondary wood.
The whole structure is strikingly like that in Lyginopteris
(cf. Fig. 13, p. 26), except that, so far as has been observed,
there is no centrifugal primary xylem in the case of
Poroxylon.
The elements adjoining the spiral protoxylem are
scalariform, while the more internal parts of the centri-
petal wood consists of pitted elements ; we may compare
248 STUDIES IN-FOSSIL BOTANY
Lyginopteris or Heterangium (p. 91). Traced further down-
wards in the stem, the structure of the primary wood
becomes simplified ; the protoxylem-groups fuse with
each other, and ultimately die out. It is a fact well
known to anatomists that the spiral elements often
disappear in the lower part of the course of a bundle,
as is very clearly seen in the Fern Osmunda, the structure
of which is in some respects comparable to that of the
plants under consideration. Eight internodes below the
node the centripetal xylem also disappears, leaving only
the wedge of secondary wood to mark the position of
the trace (see Fig. 89, A, bundles 10-14; cf. Calamopitys
Beinertiana, p. 127). The communication between the
different leaf-traces was kept up by lateral fusions during
their passage down the stem.
The secondary wood presents no peculiarities; it
consists of regular, radial series of tracheides, with
medullary rays between them. The rays are of con-
siderable height, and two or three cells in thickness ;
the tracheides have several rows of round or hexagonal
bordered pits on their radial walls. The structure, in
fact, is identical with that of the wood in Lyginopters,
so that the two could scarcely be distinguished. There
is also a close resemblance to the wood of Eu-calamopitys.
The secondary phloem, which is extraordinarily well
preserved, is traversed by the medullary rays, and
made up of alternate tangential bands of sieve-tubes
and parenchyma. Poroxylon is one of the few fossil
plants in which the structure of the sieve-tubes can be
made out. A radial section of P. Edwards is figured
by Bertrand and Renault, in which the numerous com-
pound sieve-plates on the radial walls are perfectly plain,
just as in some recent Cycads. Heterangium tiliaeordes,
Medullosa anglica, and Stauropteris oldhamia, among
British fossil plants, sometimes rival Povoxylon in the
perfection with which the phloem is preserved.
The French authors state that there is no pericycle,
POROXYLON 249
distinct from the primary phloem. ‘That is a matter of
interpretation, but it is an interesting point that the
formation of periderm took place on the inner border
of the cortex, and immediately outside the “ primary
phloem ’’—in fact, in just the same position which it
occupied in Lyginopleris. In the older stems, the whole
of the cortex was thrown off as bark, a stage which has
not been observed in the latter genus, though Calamo-
pitvs may offer analogies.
The double leaf-trace, as it passes out through the
cortex, preserves its collateral structure, and is accom-
To oot
io 9 Se S “9° Oe
Fic. 91.—Poroxylon Boyssetit. Transverse section of petiole. x, primary xylem; 22,
secondary xylem; ph, phloem; hy, hypoderma. xX about 10. After Renault.
panied by secondary wood and bast on its outer side.
The same structure 1s maintained in the leaf itself.
Fig. gI represents a transverse section of the petiole of
P. Boyssetit. The vascular bundles, which have begun to
subdivide, are arranged in a transverse series, the phloem
facing downwards and the xylem upwards, as is usual
in leaves ; they present essentially the mesarch structure
of the bundles of Cycadean leaves (cf. Fig. 15, p. 27)
with all the centrifugal xylem secondary. The petiole,
like the stem, had a strong mechanical construction,
owing to the presence of hypodermal ribs of sclerenchyma
(Fig. 91, hy).
250 SFUDIES IN FOSSIL BOTANY
The petiole widened out gradually into the broad
simple lamina, which was traversed by numerous parallel
bundles, derived from the subdivision of those of the
petiole, and branching dichotomously. The larger
bundles, which are crowded together in the median
region of the lamina, have the same structure as those
in the petiole; the finer strands, toward the edges of
the leaf, are simplified, and no longer show any centri-
fugal wood. Just the same simplification of structure
occurs in the smaller bundles of the leaf, in recent Cycads.
The lamina was of considerable thickness, and was
stiffened by the usual hypodermal fibrous strands on
both surfaces. The dense mesophyll is said to show
some traces of palisade-like arrangement. The larger
bundles of the lamina were connected by transverse
bridges of thick-walled elements.
Grand’Eury? subsequently identified the leaves of
Poroxylon in the form of carbonaceous impressions. He
finds that they are of great size, reaching a length of a
metre, with a breadth of -15 to -20 metre, — Theyeare
narrowed at the base, passing insensibly into the petiole.
In these leaves we have a highly remarkable organisa-
tion, totally different from anything met with, either
in the Ferns or among the genera associated under the
Pteridospermeae. The detailed structure is, in fact, that
of a Cycad, but the leaf of Poroxylon was a simple not
a compound one, so that the whole leaf has been com-
pared to a single leaflet of a Cycad such as Bowenza.
In the fact that the vascular bundles retain collateral
structure throughout the leaf, Porvoxylon agrees with
Medullosa but differs strikingly from Lyginopteris, in
which, as described above (pp. 33 and 45), the structure
becomes concentric as the petiole is entered. We shall
see presently that the leaves of Poroxylon present the
closest analogies with those of the Cordaiteae.
1“ Sur les Rhabdocarpus, les graines et l’évolution des Cordaitées,’
Comptes vendus, t. cxl. p. 995, 1905.
POROXYLON 251
An interesting point in the morphology of the genus
Poroxylon is the fact that the stem bore axillary branches,
thus presenting a further analogy with some forms of
Lyginopteris. The vascular system of the branch was
inserted on the two bundles of the main axis, between
which the trace of the subtending leaf passed out. Thus,
in the section shown in.Iig. 89, A, the branch, if present,
would have been in vascular connection with the bundles
marked 6 and g. The first few internodes of the branch
were short, and the first leaves probably rudimentary,
judging from the small development of the leaf-traces
supplying them. In its upper part, the branch assumed
the same structure as the main stem.
Poroxylon appears to have possessed a complex
branch-system, for shoots are found of very different
calibre, independently of differences due to age.
Roots and rootlets, which have been found in associa-
tion with Poroxylon Boyssetii and Edwards, agree so
exactly, in the structure of their histological elements,
with the stems of those plants as to leave no reasonable
doubt that Bertrand and Renault were justified in re-
ferring them to the genus Poroxylon. The rootlets, in
particular, are perfectly preserved, and their anatomy
has been fully investigated. The structure is, as a rule,
diarch; in a few cases a tetrarch cylinder has been
observed. The anatomy of the roots and rootlets is,
in all respects, such as characterises Gymnospermous
roots at the present day. In the usual case of diarch
organisation, the secondary wood and bast form two
large masses, one on either side of the primary xylem-
plate, while a broad ray corresponds to each of the two
protoxylem-groups at the ends of the plate. In the
details of wood and phloem the roots agree precisely
with the stem. The whole cortex was thrown off at
an early stage by the formation of pericyclic periderm.
Thus the outer surface of the root was formed by a
layer of cork, just as in the roots of Medullosa anglica,
252 STUDIES IN FOSSIL BOTANY
described in the last chapter, or in those of recent
Gymnosperms.
Bertrand and Renault were able to observe the mode
of insertion of the rootlets on the main root, and to
determine that the plane of the diarch xylem-plate
coincided in the two organs. This is a point of interest,
for, as 1s well known from the researches of Prof. van
Tieghem and others, this arrangement is characteristic
of the roots of Gymnosperms and Phanerogams generally,
while, in the case of the diarch roots of Vascular Crypto-
gams, the plane of the xylem-plate of the rootlet lies
at right angles to that of the parent root. It will be
recalled that Lyginopteris agrees with Poroxylon in this.
respect also.
Our summary has been based on the discoveries of
Bertrand and Renault; the anatomy was worked out
in the most elaborate detail by the French investigators,
owing to whose labours this genus became one of the most
completely known, so far as the vegetative organs are
concerned, among fossil plants.
An English species, described in the second edition
of this book under the name Porvoxylon Sutcliffii, has now
been made the type of the new genus Mesoxylon,an account
of which will be found under Cordaiteae.
We have still no certain information as to the fructifi-
cation of Poroxylon. On grounds of association, however,
Grand’Eury* attributed the seeds known as Rhabdo-
carpus, Brongniart, to these plants, with which he also
found “floral axes, bearing large and long male and
female buds, without bracts.’’ Rhabdocarpus, as limited
by Brongniart, is a genus of seeds with bilateral sym-
metry, characterised by the presence of numerous fibrous
strands in the sarcotesta. The seeds are of the same
general type as those of the Cordaiteae, described below
(see p. 305). Fig. 92 shows a seed of this genus in trans-
verse section, displaying the characters of the platy-
1 See his paper above cited, ‘Sur les Ithabdocarpus,’’ etc,
POROXYLON 253
spermic type. The discovery, if confirmed, will con-
siderably strengthen the affinity otherwise indicated
between the Poroxyleae and Cordaiteae.
Bertrand and Renault regarded the genus as related,
on the one hand, to Svgillavia, and, on the other, to
Cordaiteae. The
affinity with the
Cordaiteae seems
indisputable, as will
appear when we
come to describe
that family ; the re-
lation to Sigillania,
however, though it
appeared tenable at
the time it was Fic. 92.—Rhabdocarpus subtunicatus, Grand’Eury. Trans-
verse section of seed, to show the platyspermic type
suggested, and was of structure. a, sclerotesta; opposite the ridge (v)
at each side is a vascular bundle; c, sarcotesta,
supported by the with numerous fibrous strands ; d, contracted nucellus,
Bias . within which is the embryo-sac. X about 3. After
case of Srgillariop- ease
sis, With its double
foliar bundle and occasionally pitted tracheides (see
Vol. I. p. 207), now seems to be excluded by the manifest
affinity between Povoxylon and the Pteridosperms of the
Lyginopteris group. As has been already pointed out,
and as the French observers recognised, the agreement
in structure between Poroxylon and Lyginopteris is in
many respects a close one, so much so that there can
_ scarcely be a doubt that the two genera are allied. The
same remark applies, to a great extent, to the Calamo-
pityeae also. The Pteridosperms, however, as is now
abundantly proved, were a distinct stock, showing certain
analogies with the Ferns, and the inference appears
justified that Poroxylon also, though more modified, was
derived from this independent phylum and not from a
Lycopodinean stock. The importance of this conclusion
will become evident when the Cordaiteae have been
considered.
254 STUDIES IN FOSSIL BOTANY
Il. THE PITYEAE
Before going on to the Cordaiteae we will shortly
consider a group of fossil plants which evidently con-
stitute a separate family, though they may be provision-
ally regarded as forming part of the wider group which
we call Cordaitales. Our knowledge of the group has
considerably increased of late years.
Most of the stems in question fall under the genus
Pitys of Witham,! as emended by Goppert.? There are
now four species of Pitys, all from the Lower Carbon-
iferous of Southern Scotland ; three of these were described
by Witham in his famous pioneer work of 1833. The
species are chiefly distinguished by the width of the
medullary rays, the principal rays being as much as
seven cells wide in P. frimaeva, five or six cells in P.
antiqua, and four cells in P. Withami. Pitys Withamii
is the well-known Craigleith tree, of which a trunk is
set up in the grounds of the Natural History Department
of the British Museum. A stem of this species found
at Craigleith, near Edinburgh, in 1830, was 47 feet in
length; at the top, the wood still had a diameter of
14 foot. The fourth species, P. Day, Gordon, will be
described below.
The pith and wood are the only parts preserved in
Witham’s species, as at present known. Our knowledge
of P. Dayi is more complete. The wood, except for the
greater width of the principal medullary rays, is of the
Araucarian type, and so far, as we shall see, agrees with
that of the Cordaiteae (cf. Fig. 101, p. 274) ; the secondary
tracheides have multiseriate bordered pits, confined for
the most part to their radial walls.
1 The Internal Structure of Fossil Vegetables found in the Carbon-
ifevous and Oolitic Deposits of Great Britain, described and illustrated,
Edinburgh, 1833, p. 71.
2 “ Revision meiner Arbeiten iiber die Stamme der fossilen Coni-
feren,” Bolan. Centralblatt, Bande v. and vi. 1881.
PITYs 255
A point of great interest is the presence, in all these
species, of a number of small strands of primary wood, dis-
posed around the pith.1_ This structure is well shown in
Pitys antiqua, the Lennel Braes tree, from which the
illustration in Fig. 93 is taken. The imperfectly discoid
pith is large, sometimes as much as 2 inches across; in
a specimen where the
pith measured only
22 mm. in diameter,
the number of xylem-
strands round the pith
was between forty and
fifty. The diameter of
each xylem-strand is
small, averaging about
-25 mm.; most of the
strands are embedded
in the pith at some
little distance from the
inner edge of the
woody zone (Fig. 93),
with which they only
come into contact
when about to make
their exit as_leaf-
traces. W her c a Fic. 93.—Pitys antigua. From a transverse section
xylem ~ strand passes of thestem. v.b., primary xylem-strand embedded
: in the pith; px, protoxylem; 22, inner part of
out into the zone of secondary wood; m.r., medullary rays. The cells
with black contents may be secretory sacs. X 73.
secondary wood, its Kidston Coll. 5984. (G. T. G.)
place is taken by a
reparatory strand lying behind it, deep in the pith.
The outgoing strand shows some sign of division into
two, but the two halves appear to reunite further out
in its course. Branching and anastomosis of the strands
are found at many places.
1 Scott, ‘“‘ Primary Structure of certain Palaeozoic Stems,”’ etc.,
Trans. Roy. Soc. Edinburgh, vol. xl. part il. 1902.
256 SLfUDIES IN: FOSSIL BOTA
In the great majority of the xylem-strands the struc-
ture is definitely mesarch, the spiral protoxylem-elements
lying in the interior (Fig. 93, #x). The primary tracheides
are accompanied by a little xylem-parenchyma.
No spiral elements could be detected at the inner
edge of the woody zone, so it would appear that the
primary wood is represented only by the medullary
strands. The considerable separation between the latter
and the main zone of wood is difficult to account for,
and suggests some specialisation of function, as, for
example, that the primary strands might have become
superfluous for the main work of water-conduction and
have served to supply the bulky parenchymatous pith.
The mesarch xylem-strands, in spite of their reduced
size and the peculiarities of their arrangement, are
evidently comparable to those of the Lyginopterideae
and Calamopityeae. On the other hand, the arboreal
habit has suggested an affinity with the Cordaiteae.
In the specimens originally observed, the primary
xylem-strands were found, as already described, to be
limited to the peripheral part of the pith. That they
were not necessarily restricted to this region has been
shown by the researches of Prof. W. T. Gordon, whose
work has in various points greatly extended our know-
ledge of the anatomy and morphology of the genus.
Prof. Gordon has kindly permitted me to insert an
account, in his own words, of his unpublished observa-
tions, iulustrated by photographs which he has supplied,
reproduced in Figs. 94-96. By way of preface to his
remarks it is necessary to mention that a new genus,
named Archaeopitys, Scott and Jeffrey, chiefly dis-
tinguished by the presence of xylem-strands throughout
the whole of the pith, had already been described, from
the Lower Carboniferous of Kentucky. We shall return
to this genus later. Prof. Gordon’s statement is as
follows :
‘The discovery of several small twigs of a new type
PITYS 257
of Pitys (P. Dayi) in Lower Carboniferous rocks at
Gullane, East Lothian, has thrown more light on the
structural features of this genus and has rendered its
correlation with the Cordaitales less probable than has
been supposed.
“The specimens vary from 1-5 to 2 inches in diameter,
and in many cases are still clothed in bark (Fig. 94),
Fic. 94.—Pitys Dayi. General transverse section of stem, showing pith, wood, and cortex.
Leaf-traces are seen, both in the wood and cortex ; the latter are dividing up into con-
centric strands. x3. From a photograph by Prof. W. T. Gordon.
while two examples terminated in buds with leaf-bases
and petioles still attached.
“In no case has any indication of the reproductive
members been discovered and therefore the affinities
must be based on purely vegetative characters.
“The axis in all the specimens consists of a wide,
parenchymatous non-discoidal pith surrounded by a
ring of xylem (Fig. 94). The primary strands are, as
usual in Pitys, separated from the secondary wood by
a zone of parenchyma, two or three cells deep. But there
17
258 STUDIES AN-FOSStE BOTANY
are other strands more deeply immersed in the pith, a
circumstance recalling the structure of Avrchaeopitys
Eastman, Scott and Jeffrey. These additional strands
are scattered through the whole pith, but are generally
Fic. 95.—Pitys Dayi. Transverse section of stem, showing pith, with part of secondary
wood and cortex. In the pith the medullary and circum-medullary xylem-strands can
be made out. A leaf-trace is passing out through the wood. X10. From a photograph
by Prof. W. T. Gordon.
smaller than the circum-medullary types (Fig. 95). So
far it has not been possible to follow the course of these
inner strands throughout their length.
“The circum-medullary bundles, on the other hand,
PITYS 259
have been traced out into the petioles. On its passage
outwards the bundle increases in size and then divides
into three, though exceptionally five bundles have been
noted (Figs. 94, 95). In every case actually traced into
a petiole there were only three strands, and these per-
sisted throughout the length of the leaf. It is interesting
Fic. 96.—Pitys Dayi. Transverse section of leaf, showing the sclerenchymatous cortex,
the ground -tissue, and the three vascular bundles. x18. From a photograph by
Prof. W. T. Gordon.
to note that in Avaucaria excelsa the bundle supplying
the leaf divides into three, though only the median of
these persists throughout the length of the leaf.
“The free petiole is a short fleshy member with a
marked hypoderma and three bundles clearly distinguish-
able in transverse section (Fig. 96). The length exceeds
260 SLUDIES IN - FOSSIL ‘Botany
I°5 inches and the whole tapers gradually to a sharp
point. No sign of a lamina occurs, and from the general
appearance of the end of the petiole it is practically
certain that no lamina ever existed. To compensate
for this the petiole has enlarged into a stout fleshy organ.
‘““ All these vegetative characters are strikingly similar
to corresponding characters in Avaucaria, especially A.
excelsa. The wide pith, the intimate characters of the
tracheides, the leaf-trace bundle with three branches,
the short fleshy petioles and absence of lamina are char-
acters common to both Pitvs and Avaucarnia, The
spatulate or Poa-like leaf of Cordartes is quite distinct
from this Pitys type.
‘Where branches have been observed passing out
from any of these new stems a group of the circum-
medullary bundles runs out from the main axis, but the
details of branch emission have not yet been ascertained.
“The new features exhibited by P. Dayi were so
interesting that the older species were re-examined, and
specimens of P. antigua and P. primaeva have also been
found to possess immersed bundles in addition to the
circum-medullary strands. Yet the sections, examined
by Dr. Scott in 1899, did not show these immersed bundles,
and the exact conditions under which such strands may
develop have not so far been determined. Further
search among the new specimens may throw some light
on this point.
“The new evidence then correlates Pitys more closely
with Archaeopitys and at the same time widens the gap
between these genera and the members of the Cordaitean
alliance. It also indicates Araucarian affinities, particu-
larly with these forms which possess uninerved leaves
like A. excelsa. Boyd Thomson’s case for the great
antiquity of the Araucarian alliance seems to get con-
siderable support from these new specimens.” 1
1 A brief summary of Prof. Gordon’s results was given in Seward’s
Fossil Plants, vol. iii. 1917, p. 288.
ARCHAEOPITYS 201
The great importance of Prof. Gordon's observations
is manifest. His new species, P. Dayi, is at present the
only member of the Pityeae in which the cortex and
leaves are known, and thus throws more light on the
position of the family than all the rest. Before entering
on any further discussion, however, it is desirable to
describe other forms referred to this group.
A new genus, Archaeopitys, was founded in 1914, on
a species, A. Eastmanii, one of the fossils from the base
of the Waverley Shale (Lower Carboniferous) of Kentucky.!
At the time the original description was written only
one specimen was available; the maximum diameter
of the incomplete fragment was 2-7 cm., and that of the
pith about 5-5 mm. Since then I have received a second
specimen from Prof. Jeffrey, forming part of a larger
stem, about 4:5 cm. in diameter as preserved, with a
large pith about 3 cm. diameter. Neither specimen
includes anything outside the secondary wood; _ the
second one, however, shows the exit of the leaf-traces,
which the former did not. Hence it has now been
possible to determine with certainty the upper and
lower ends of the specimen.’
The xylem-strands in the pith are the chief feature ;
about half of these strands lie at the margin of the pith,
while the rest are scattered all through its substance.
The former may be called circum-medullary, the latter
simply medullary strands. The structure of each xylem-
strand is mesarch, as in Pitys, and the dimensions of
the strands not very different from those of that genus.
Where a leaf-trace passes out, one of the circum-medullary
strands divides into two; the inner branch becomes a
reparatory strand and remains in the pith, while the
1D. H. Scott and E. C. Jeffrey, ‘‘ On Fossil Plants, showing Structure,
from the base of the Waverley Shale of Kentucky,’ Phil. Trans. R.
Soc. Series B, vol. 205, 1914, Pp. 345.
2 It turns out that this was done wrongly in the case of the original
specimen ; we have, therefore, to reverse the words ‘‘ downward ”’
and ‘“‘ upward ”’ in the description given in the Kentucky memoir.
262 STUDIES IN FOSSIL BOTANY
outer makes its exit through the wood, and constitutes
the leaf-trace, which is thus a single bundle at its origin.
It is interesting to find that, as the trace approaches the
outer border of the wood, it becomes completely sur-
rounded by its own secondary zone of xylem, like the
leaf-traces of Pitys Day, figured by Prof. Gordon (Fig. 94).
Some signs of division of the trace have been observed,
but could not be followed far enough for comparison
with the divisions in P. Dayt.
The secondary wood is dense, compared with that
of the Pitys species. The density is due, partly to the
small size of the tracheides, partly to the relatively small
number of the wider medullary rays, which may attain
a thickness of five or six cells. The rays are all rather
short and most of them comparatively narrow. The
pitting is badly preserved, but two or three rows of pits
on the radial tracheide-wall could be made out in places.
In the light of Prof. Gordon’s results it seems doubtful
whether the genus Archaeopitys can be kept up, for the
main character on which it was founded (the presence
of xylem-strands throughout the whole pith) proves to
be common to various species of Pitys, though not always
constant. It is better, however, to maintain the genus
provisionally, until the publication of Prof. Gordon’s
researches in full allows of a more exact comparison
with Pitys.
Another genus allied to Pitys is Callixylon, founded
by Dr. Zalessky! on a species, C. Trifilievi, discovered
by him in the Upper Devonian of the Donetz Basin in
South Russia. The plant is thus of special interest from
its age. The preservation of the specimens is excellent,
but does not extend beyond the wood.
Callixylon differs from Pitys and Archaeopitys in the
1 Zalessky, ‘‘ Communication prélim. sur un nouveau Dadoxylon
a faisceaux de bois primaire,” etc., Bull. de l’Acad. Imp. des Sciences
de St-Pétershourg, 1909, p. 1175; ‘‘ Etude sur l’anatomie du Dadoxylon
Tchihatcheffi,”’ Mém, Comité Géol. livr. 68, 1911, p. 28.
CALLIXYLON 263
fact that all the primary xylem-strands are circum-
medullary, and usually in contact with the secondary
wood, though occasionally a few cells may intervene
(Fig. 97). The strands are mesarch, and in all respects
similar to those of Pitys antigua, the resemblance extend-
ing to the radial elongation of the adjacent medullary
cells and to the detailed structure of the pith as a whole.
SS :
SS
bs
4
3 . SON
\.3y ‘ anew’ \s
pS: ~*
. ae % x!
Fic. 97.—Callixylon Trifilievi. Part of transverse section of stem, showing part of the
pith, and five primary mesarch xylem-strands, corresponding to the wedges of secondary
wood. One of the strands is double. Xx about 14. From a photograph supplied by
Dr. Zalessky.
The exit of the leaf-traces has not been described ; Prof.
Seward * suggests that the occurrence of twin-bundles (as
shown at one place in Fig. 97) may indicate that the trace
was double. This, of course, is not conclusive ; a some-
what similar approximation of two bundles has been
observed in Archaeopitys, where the leaf-trace was single.
The structure of the secondary wood presents some
points of interest. It is divided, towards the pith, into
wedges, each wedge corresponding to one of the circum-
medullary strands (Fig. 97). The inner ends of the
1 Fossil Plants, vol. iii. p. 291.
264 STUDIES IN FOSSIL BOTANY
medullary rays, between the wood-wedges, are much
dilated, but elsewhere the rays are narrow, usually only
one cell in width ; this is a striking difference from Pitys,
and even from Archaeopitys, in which wide rays also
occur. The pitting is of the usual multiseriate, bordered
type, but the distribution of the pits is remarkable.
They are not uniformly distributed on the radial walls,
but form definite pitted areas, separated by tracts of
unpitted cell-wall. The pitted areas of consecutive
tracheides are ranged in regular radial series, giving a
very characteristic appearance to the radial sections
Tangential pits occur, as in Pitys antiqua.
Two American species, Callixylon Newberry: and C.
Owent, of Upper Devonian age, have been placed in this
genus, on account of the well-marked characters of the
secondary wood ; the primary structure of these species
has not yet been observed.!
The genus Callixylon is of great interest, as the oldest
known representative of the family. That it really
belongs to the Pityeae seems to be proved by the agree-
ment of the primary structure (pith and xylem-strands)
with that of Pitys, if we choose for comparison specimens
(such as those originally described in P. antiqua) in which
~ the xylem-bundles are limited to the peripheral zone
of the pith. At the same time there are definite dis- -
tinctions both in the position of the primary strands and
in the secondary wood-structure, which fully justify
generic separation.
Dr. Zalessky also compared the structure of his
plant with that of Parapitys (formerly Dadoxylon) Spencer,
a fossil which was described under the heading Pityeae
in the second edition of these “ Studies.’”’ A relationship
is by no means out of the question, but 1t now seems
more natural to consider Parapitys in connection with
the Cordaiteae (see p. 282).
1 Elkins and Wieland, ‘‘ Cordaitean Wood from the Indiana Black
Shale,’’ American Journal of Science, vol. xxxvill. 1914.
PITYEAE 265
The discovery of the leaves of Pitys by Prof. Gordon
puts the affinities of the group in quite a new light. Such
leaves have nothing in common with those of the Cor-
daiteae (see p. 289), and seem rather to suggest an ap-
proach to the “needles ’’ of a Conifer. Prof. Gordon’s
comparison of his plants with certain Araucarias is of
great interest, and when further developed will, no
doubt, have an important bearing on the affinities of
the Coniferae. In the meantime it is already evident
that the Pityeae form a more independent family than
was realised before, as shown both by their anatomical
and morphological characters. We continue to include
them under the wide class Cordaitales on grounds of
convenience, but we can no longer say, as was said in
the second edition of this book, that they lead up to the
family Cordaiteae. It is a somewhat striking fact that
the most highly differentiated wood-structure in the
Pityeae is found in the oldest genus, the Devonian Calli-
xylon. This suggests a high antiquity for the family.
III. THE CORDAITEAE
We now pass on to a family which belongs beyond
question to the true Gymnosperms. The Poroxyleae
and Pityeae are at present chiefly or solely known to us
by their vegetative characters; we have now to deal
with a group in which our evidence is drawn from all
the organs of the plant—reproductive as well as vegeta-
tive. Though even here our knowledge is but limited
and urgently needs to be extended, the fact remains
that the family in question—that of the Cordaiteae—is
one of the best known, as it is also among the most
remarkable, of those which fossil botany has revealed
to us.
Among the vegetable remains from the Carboniferous
strata, specimens were long ago observed, such, for
example, as fragments of petrified wood, which presented
266 SPUDIES’ IN FOSSIL BOTANY
Coniferous characters, while others, such as the impres-
sions of large parallel-veined leaves, suggested at first
sight Monocotyledons of the Yucca type. Associated
with these remains, fossil catkin-like inflorescences
(Antholithus) were sometimes found, as well as a con-
siderable variety of seeds, of the bilateral type. The
piecing together, on sure evidence, of these remains,
apparently so diverse, and the revelation of their struc-
ture, was essentially the work of the two French in-
vestigators, Grand’Eury and Renault,! though valuable
contributions from other hands have not been wanting.
1. External Characters.—We may begin by stating the
general results of the reconstruction which has been
arrived at, and then go on to describe the organisation
of the various organs more in detail. The Cordaiteae
were tall; somewhat slender trees, with trunks rising
to a great height before branching, and bearing at the
top a dense crown, composed of branches of various
orders, on which simple leaves of large size were pro-
duced in great abundance (Fig. 98). The stumps of the
trees, with the roots attached, have often been found ;
the root system is said to have been rather feebly developed.
The stems, in their present state, attain a diameter of
a couple of feet or more, which is small in comparison
with the height of the trees, for Grand’Eury found that
in various specimens the shaft alone (below the crown)
reached a height of Io, 20, or even 30 metres. It must
be remembered, however, that the large specimens have
their wood reduced to coal, so that the total diameter
was no doubt considerably greater in the natural state
than appears from the fossil remains.
The leaves were borne in a spiral sequence, on the
ultimate branches; they were simple elongated leaves,
1 See especially Grand’Eury, Flore carbonifeve du Département de
la Loive, 1877, and Renault, Structure comparée de quelques tiges de la
flore carbonifere, 1879.
CORDAITES 267
varying considerably in form in different members of
the group; on these differences genera or sub-genera
Fic. 98.—Dorycordaites, sp. Restoration, showing roots, trunk, and crown, the latter
composed of branches bearing large lanceolate leaves and inflorescences. The trunk
is shown too short. After Grand’Eury. Modified.
have been founded. Thus, in the typical Cordaites (Eu-
Cordaites) the leaves are spatulate, with blunt ends ;
268 STUDIES IN FOSS. BorANy
they reached in some cases a length of a metre, and a
width of 15 cm. To this group the forms most fully
investigated belong (see Fig. 99). Then we have Dory-
cordaites, with leaves little inferior in length to those of
the last group, but lanceolate and sharply pointed. Our
Fig. 98 represents a restoration of a tree belonging to
this sub-genus. Finally there is Poacordaites, with grass-
like leaves, reaching half a metre in length, by only a
centimetre or so in breadth. The leaves of Cordaiteae,
whatever their form may have been, are all characterised
by parallel venation, giving them much the appearance
of Monocotyledonous leaves, such as those of a Yucca
or Dracaena ; consequently, the earlier writers on fossil
botany always placed these fossils in the class Mono-
cotyledons. The veins are repeatedly forked, except in
the narrow leaves referred to Poacordaites. In many
instances branches have been found, bearing the leaves
(cf. Fig. 99), or marked by the scars due to their fall.
The scars are usually transversely elongated, and some-
times bear the prints of the vascular bundles which
entered the leaf. The leaves were crowded in some
forms, more remote in others, but there was always a
free internodal surface between their insertions. In some
cases a lateral twig is found in an early stage, as a large
leaf-bud, as shown in Fig. goa.
The habit of the Cordaiteae must have been different
from that of any trees with which we are now familiar.
The species with comparatively short leaves may be
compared with such Coniferae as Agathis (e.g. the Kauri
Pine of New Zealand), or with certain forms of Podo-
carpus, and these trees may best serve to give us some
idea of the appearance of the extinct family. But the
longer-leaved species must have had a habit very different
from anything which we are accustomed to associate
with Gymnosperms at the present day.
Branches showing the characteristic marks! of Cor-
daites were found by Grand’Eury with structure pre-
CORDAITES 2609
served, and this important discovery enabled palaeo-
botanists to identify a large proportion of the apparently
Fic. 99.—Cordatites levis. Branch (restored) bearing the large spatulate ieaves, with
parallel venation, and the inflorescences, each with numerous catkins. A large bud
is also shown. Reduced. After Grand’Eury.
Coniferous woods of the Palaeozoic strata, named Avau-
carioxylon or Dadoxylon, as belonging to the Cordaiteae.
270 STUDIES IN FOSSIL BOTANY
The anatomical structure will be described below ; here
it is only necessary to say that the large size of the pith,
sometimes attaining a diameter of nearly 4 inches, is
characteristic of these plants, and at once distinguishes
their stems from those of the Coniferae.
Casts of the pith-cavity of Cordaites are well-known
and characteristic fossils, which used to be called Avtisia
or Sternbergia. They are cylindrical, or somewhat ribbed
casts, sometimes very slender, but usually an inch or
more, and sometimes approaching 4 inches, in diameter,
and marked by numerous transverse constrictions at very
short intervals, so that the whole resembles a pile of
coins. Williamson, in 1851,1 found a cast of this kind
still enclosed in wood, which proved on investigation to
have the structure of Avaucarioxylon. This was one of
the first steps made towards the reconstruction of these
fossils, for we now know that the wood in question,
resembling that of the recent Araucarias, belonged to
certain members of the Cordaiteae. The peculiar appear-
ance of the casts, as Williamson explained, is due to the
discoid structure of the pith, such as is found, not only
in the Walnut, and in some Jasmineae and Euphorbiaceae,
but also in certain species of Pinus, at the present day.
The pith undergoes transverse rupture in many places,
so as to leave numerous diaphragms separated by empty
spaces. The constrictions on the cast in the fossil speci-
mens mark the position of the diaphragms (cf. Fig. ror, A). »
The recognition of the true nature of Sternbergia has
proved important, for by this means the large, rooted
stumps, found in the Coal-measures of the Loire, con-
taining Sternbergia casts, have been identified as belonging
to Cordaiteae.
The fructifications of the Cordaiteae were known, so
far as their external characters are concerned, long before
1 ‘‘On the Structure and Affinities of the Plants hitherto known
as Sternbergiae,’”’ Mem. Manchester Lit. and Phil. Soc. ser. ii. vol. ix.
1851.
CORDAITES 271
their nature was recognised. These fossils, which were
at first placed in the provisional genus Antholithus, con-
sist of a simple or branched stalk, bearing laterally little
catkin-like bodies, not often exceeding a centimetre or
so in length. The male and female catkins cannot always
be distinguished externally ; in some forms, however,
the axis of the female inflorescence appears to have borne
solitary ovules, accompanied only by a few bracts.
Grand’Eury was so fortunate as to find inflorescences
such as these in connection with the leaf-bearing shoots
of Cordaites. An example (more or less restored) is
shown in Fig. 99, where we see a leafy branch bearing
several fertile peduncles, each of which in its turn bears
a number of catkins, probably female. The _ inflor-
escences appear to have been inserted a little above the
subtending leaves, and not immediately in their axils.
We see, then, that the connection of all the organs
—stems, roots, leaves, and catkins—has now been estab-
lished, at least for some species of the genus Cordaites.
The other genera or sub-genera are at present less com-
pletely known. We will now go on to consider the
internal organisation of the various parts, beginning
with that of the stem.
2. The Stem, Cordaites—The general type of structure
of the stem of Corvdaites was that of a Conifer, but the
pith, as we have seen, was far larger than we ever find it
in the Coniferae, and in its dimensions rather resembled
that of a Cycad. It has already been mentioned that,
in many cases (though probably not in all), the pith was
discoid, as shown in Fig. ror, A. This structure was
no doubt due to the fact that the more central part of
the pith was not able to follow the growth of the stem
in length, and consequently split across at short intervals,
leaving gaps between the persistent diaphragms. At the
outer edge, next the wood, the medullary tissue remained
continuous.
In those specimens which were originally referred to
272 STUDIES. IN FOSSIL BOTANY
Cordaiteae, the wood, unlike that of the Poroxyleae and
Pityeae, was wholly centrifugal in its development, the
first-formed spiral elements lying on the interior margin,
next the pith (Fig. 101, B, px); they are localised in
groups, often projecting somewhat into the pith, and
marking the position of the primary bundles. In the
genus Mesoxylon, however, to be described below, centri-
petal xylem was present.
Fic. 100.—Cordaites, sp. Part of transverse section of a young branch, showing outer
pith, wood, bast, and cortex. a, empty space between two diaphragms; 6, outer,
persistent zone of pith; c, inner zone of wood (cf. Fig. ror, B); d, outer zone of wood ;
f, vascular strand about to pass out; g, probable phloem; 4, commencement of peri-
derm; i, cortex, containing gum-canals, /, and fibrous strands, k; m, outgoing leaf-
trace, dividing ; m, epidermis. x 10. After Renault.
In Cordaiteae of the type described by Renault, the
elements of the wood are radially arranged throughout,
so that in transverse sections there is no marked distinc-
tion between primary and secondary xylem (see Fig. 100).
In radial sections, however, such as that from which
Fig. ror, B, was drawn, we find a regular progression,
from the pith outwards, in the structure of the walls of
the tracheides. The narrow spiral elements of the proto-
@poe~
CORDAITES 273
xylem are succeeded by wider spiral tracheides, and
these again by scalariform elements. It is not until
many rows have been passed that we come to the pitted
tracheides (b¢) which form the bulk of the wood. The
transitional region between primary and secondary xylem
was thus more extensive in these plants than in most
of the recent Conifers.
The secondary wood has essentially the structure of
that of Avaucaria, and was hence named Araucarioxylon
by Kraus, a name which is now superfluous in cases
where the connection with Cordaites has been established.
The bordered pits, which are limited to the radial walls,
are usually in two or more rows, and are densely crowded
in alternating series, the borders thus having a hexagonal
outline (Fig. ror, B, bt). In good material, the pore of
the pit can be recognised clearly, and has the form of
an inclined elliptical slit. Certain variations in the
diameter of the tracheides of successive zones were
regarded by Renault as indicating periods of growth,
but, generally speaking, annual rings cannot be dis-
tinguished.
The medullary rays are narrow; the principal rays,
between the original bundles, may be as much as three
cells in thickness, but the secondary rays are usually
one, or at most two cells thick. The narrow rays have
been used to distinguish the wood of Cordaites from that
of other families, such as Poroxyleae and Calamopityeae,
but the distinction does not always hold good.
We see, then, that, so far as the secondary wood is
concerned, the structure of Cordaites is indistinguishable
from that of a Conifer, of the family Araucarieae.
The phloem, when preserved, shows a radial arrange-
ment of its elements, corresponding to that in the wood.
1 The names Dadoxylon, of Endlicher, and Araucarites, of Goppert,
are often used in the same sense as Avaucarioxylon. Dadoxylon is
preferable in so far as it does not suggest any affinity with the Arau-
carieae.
58
i)
74 STUDIES IN FOSSIL BOTANY
Sieve-tubes and phloem-parenchyma have been distin-
guished, and in some forms bast-fibres are also present.
The parenchyma of the primary cortex was traversed
by secretory sacs, and strengthened by many radial bands
iia Naas
re)
8
va)
a ae
vA)
Q
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Gr
me a - OSX]
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; os PISeSH et! ee oO
) : ae oo Pies os’. oT
a SS es Stores RSS 4
ss 2 SRST IS OS SoSH ae,
. i SI X OQneaoe
”” ibid. vol. xXxxim,
of Mesoxylon multivame,’
Fertile Shoots of Mesoxylon and an Allied Genus,
TOlo; Pp, I.
MESOXYLON 277
and the protoxylem is accompanied by a few paren-
chymatous cells. The centrifugal portion is continuous
with the secondary wood (Fig. 104). The illustration,
from M. poroxyloides, shows a xylem-strand, after the
two bundles of the trace have already fused at the margin
11.
4
oe”
-“
an
-
|
on | Ae
/
Fic. 103.—Mesoxylon multirame. Somewhat diagrammatic transverse section of stem.
3-16, leaf-traces, or their axillary steles (in 12, 13, 14 and 16), numbered from within
outwards. Traces 1 and 2 had already disappeared at this level, and trace 15 was lost.
Xrabout a. s. Coll:2334. “(G..T.'G.)
of the pith. The centripetal xylem is very distinct,
though not so extensively developed as it would be
higher up in the course of the trace. The protoxylem,
as in the foliar bundles of the Cordaiteae and of Cycads,
is in contact with the centripetal wood. The latter
usually consists of spiral tracheides, closely wound,
278 STUDIES IN-FOSSID BOTANY
except in the protoxylem itself. The centrifugal xylem,
corresponding to the leaf-trace strands, consists of spiral,
scalariform, and transitional elements, continuing for
some distance before the typical pitted structure of the
secondary wood is assumed. In all these respects there
is a close agreement with Cordaites, except for the presence
of centripetal xylem. In the intermediate wood, lying be-
tween the leaf-traces, a region of scalariform elements may
be present or practically absent, according to the species.
There is a difference in the structure of the leaf-strand
from Povoxylon, in which pitted tracheides occur in the
centripetal xylem as well as throughout the centrifugal
portion.
A general section of M. Sutcliffit, a species in which
the stem is densely clothed with leaf-bases, is shown
in Fig. 102. The double leaf-traces, in passing out
through the cortex, subdivide, eight bundles entering
the leaf-base. In the petiole of M. Sutcliffi, Mr. Maslen
found as many as sixteen. Followed downwards into
the stem, the behaviour of the leaf-traces varies in the
different species. In M. Lomaxi and M. poroxyloides
the twin-bundles converge as they reach the pith and
almost immediately fuse, retaining their centripetal
xylem for some distance below the fusion (Fig. 104).
In M. Sutcliffii and M. multirame, on the other hand,
the two strands of the trace remain distinct at the edge
of the pith for a long distance before being merged ;
they retain their centripetal xylem about as far as they
remain independent. But, in all cases, this tissue dies
out gradually downwards, as in Poroxylon, Calamopitys
Beinertiana, and other cases. In M. flatypodium the
twin-strands are very far apart in the pith, and begin
to subdivide before the wood is passed. ‘This species
is peculiar, in so far as the leaf-trace bundles in the cortex
form two distinct rows of four each. All eight enter the
very broad leaf-base, from which the name of the species
was taken.
————
MESOXYLON 279
Axillary shoots have been found in three out of five
species, namely, in M. Sutcliffii, M. multirame, and M.
platypodium. In M. Suteliffii, where a shoot appears
to be present in the axil of every leaf, they take the form
of little leafy buds (lig. 102). Their leaves are of the
nature of scales and presumably the buds were resting.
In M. multivame the axillary shoots, though more localised,
Fic. 104.—Mesoxylon poroxyloides. Transverse section ot a xylem-strand at the edge of
the pith, below the union of the two strands of the leaf-trace. x, centripetal xylem ;
px, protoxylem ; %x*, secondary wood ; m.r., medullary ray. Xx about 200. S. Coll.
2354. After a drawing by Miss G. C. Harrison.
are almost equally common, but quite different in struc-
ture ; each is a perfectly leafless axis, with a stele much
flattened inthe tangential plane. As we shallsee presently,
these naked shoots were doubtless the stalks of the
inflorescences. :
In M. platypodium, only the steles of the axillary
branches have been observed. Two or more steles occur
280 STUDIES IN FOSSIL BOTANY
in the axil of the leaf, subtended by the eight bundles
of the double trace. In M. Sutcliffii and M. multivame
the axillary stele, traced inwards, sometimes divides in
the cortex or in the wood, but the steles of M. platypodium
are so far apart that it seems as if they must have belonged
to separate buds in the same axiul.
As regards the structure of the secondary wood of
Mesoxylon, there 1s a close agreement with that of Cor-
daites. The medullary rays are uniseriate, or may be
locally biseriate. Two features have been observed in
the wood of M. multirame, which are rare in Palaeozoic
stems: one is the occurrence at some places of tangential
pits on the tracheides, a character otherwise recorded
only in Pitys antigua and Callixylon Trifiievi among
Palaeozoic Gymnosperms. The other is the presence of
xylem-parenchyma, forming vertical strands in the wood ;
this, too, had been previously noticed in Pitys antiqua.
The phloem is very well preserved in some specimens,
especially those of M. multirame and M. Sutcliffi. It is
made up of approximately tangential bands of larger
and smaller elements. The larger appear to represent
resiniferous tubes ; the smaller are of two kinds, phloem-
parenchyma and sieve-tubes ; in favourable cases the
sieve-plates on the inclined walls of the latter have been
recognised. The pericycle contains large sacs, perhaps
of a secretory character. |
In most stems of Mesoxylon there is a zone of internal
periderm, usually starting on the outer edge of the peri-
cycle, but sometimes, as successive layers appeared,
cutting deeply into the underlying tissue. In the large
stems referred to WM. Lomax the periderm or secondary
cortex reaches a great thickness, while in WM. platypodium,
where the specimens are young, it had scarcely begun
to appear. In M. Sutchffi, Mr. Maslen found a well-
marked abscission-layer at the base of the leaf—a rare
feature in Palaeozoic plants.
The outer cortex is generally of the Dictyoxylon type,
MESOXYLON 281
with a network of hypodermal fibrous bands. In M.
platypodium the bands of fibres run vertically with
occasional connections.
In four out of the five species, the pith is known to
have been discoid, as in Cordaites ; while the outer zone
is persistent and continuous, the middle region has been
broken up into diaphragms with empty spaces between
them. In M. flatypodium alone, the structure of the
pith could not be determined, owing to the state of
preservation.
The genus Mesoxylon, while agreeing closely in
anatomical structure with Cordaites, provides an interest-
ing link between this group and the Poroxyleae, on
account of the presence of centripetal xylem in the
stem. The fertile shoots, which afford further evidence
-of the Cordaites connection, will be considered below.
It may be mentioned that two of the species, M.
Lomaxit and M. platypodium, occur in roof-nodules,
while the other three are found in the ordinary coal-balls
formed in the seam.
Dr. Zalessky kindly informs me that he has discovered
a new species of Mesoxylon, M. Demetrianum, Zal., in
coal-balls from the Coal-measures of the Donetz Basin
in South Russia. As he points out, his species, while
_ quite distinct from any of ours, has most in common,
as regards the course of the primary xylem-strands, with
M. Lomax and M. poroxvloides.
Mesoxylopsis—Another genus, named Mesoxylopsis,
with the one species, M. Arberae, has been founded for
stems from the same source as Mesoxylon, but differing
in the smaller size of the pith and more especially in the
fact that the leaf-trace departs from the stele as a single
and not a double bundle. In other respects the specimens
agree with the previous genus.!
Buds of Mesoxylopsis are known, with the young
leaves attached ; these leaves are broad and have many
1 See Scott, 1919, above cited.
282 STUDIES IN FOSSIL BOTANY
bundles ; they are clearly of the Cordaitean type. The
single leaf-trace divided repeatedly in traversing the
cortex to supply the vascular system of the leaf.
Parapitys—A stem described in the second edition
of ‘“‘ Studies,’ under the name Dadoxylon Spenceri, has
since been placed in the new genus Parapitys by Dr.
Zalessky.1. The structure of the plant indicates a place
among the Cordaiteae rather than the Pityeae, as was
previously suggested. Parapitvs Spencert is a_ fossil
found near Halifax: there has been some doubt as to
its horizon, which was probably low down in the Upper
Carboniferous.
The stem has a small, obtusely pentagonal pith,
apparently not discoid, and a very dense secondary wood
with the tracheides narrow and the medullary rays almost
always uniseriate. The leaf-traces are given off from
the angles of the pith in pairs; the comparison with
Ginkgo in this respect was already suggested by William-
son, who first described the fossil. At the edge of the
pith and in contact with the woody zone, there are pairs
of small, primary xylem-strands, corresponding to the
leaf-traces. Traced downwards the strands of each pair
fuse ; they are distinctly mesarch in the upper part of
their course, but at a lower level the centripetal xylem
appears to die out, as in Mesoxylon and other cases.
The mesarch structure is characteristic, for in Parapitys
the centrifugal part of the strand is evidently primary,
whereas in Mesoxylon it 1s merged in the secondary
wood.
The interest of Parvapitys thus lies in its combining
the wood-structure of the Cordaiteae with primary
xylem-strands like those of Lyginopteris or Calamopitys
in a reduced form.
1D. H. Scott, ‘‘ Primary Structure of certain Palaeozoic Stems,”’
etc., Trans. Royal Soc. Edinburgh, vol. xl. Part ii. 1902, p. 357; M.
Zalessky, ‘‘ Etude sur l’anatomie du Dadoxylon Tchihatcheffi,” Mém.
Com. Géol., St Pétersbourg, N.S., livr. 68, 1911, p. 28.
MESOPITYS 283
Caenoxylon.—This is one of Dr. Zalessky’s new genera,
and is founded on a stem of Upper Palaeozoic age (C.
Scotti, Zalessky), perhaps from the Permian of the Ural.
There is a large pith, 2 cm. in diameter, and surrounding
it are a number of strands of primary xylem, much
broken up, the pith intruding between them. All these
strands, though sharply marked off from the secondary
wood, are endarch in structure, no centripetal xylem
being present. The leaf-traces, running out from the
primary xylem, are double, traversing the secondary
zone almost horizontally. The secondary wood has the
usual Cordaitean structure, with medullary rays one cell
thick, but is interesting as showing distinct annual rings.
The chief peculiarity of the genus, however, is the ex-
tensive primary wood, consisting entirely of endarch
strands.
Mesopitys—This genus was also founded by Dr.
Zalessky and is based on the Avaucarites Tchihatcheff
of G6ppert. Like Caenoxylon, it is a Permian plant
from Siberia; as in that genus annual rings are well
marked. The pith is small (e.g. 3 mm. in diameter),
and here also there are definite strands of primary xylem,
though not so largely developed as in Caenoxylon. The
strands are described by Zalessky as endarch throughout,
but Seward, who has re-examined the specimens, is not
convinced that this is constant; ‘‘in a few cases there
may be a small amount of centripetal xylem present.”’
Observations of my own tend to confirm Seward’s state-
ment. The leaf-trace, unlike that of Caenoxylon, is a
single strand, where it passes through the secondary wood.
The plant resembles Calamopitys (Enstophyton) Beiner-
tiana in the presence of sclerotic nests in the pith, and
Zalessky suggests an affinity between the two plants.
1 On Caenoxylon and Mesopitys see Zalessky, ‘‘ Etudes paléo-
botaniques, Ire Partie, Note prélim. sur le Caenoxylon Scottt,’’ St-
Pétersbourg, I9gII, p. 13, and his paper on Dadoxylon Tchihatche ffi,
above cited ; also Seward, Fossil Plants, vol. iii. 1917, pp. 293 and 295.
284 So LUDIES: TIN FOSS’ BOTANY.
Antarcticoxylon is a genus founded by Prof. Seward
on a specimen from the Priestley glacier, in lat. 74° S.
The species is named A. Priesitleyi. The plant is of
interest from its occurrence so far south, where it was
discovered on Capt. Scott’s second Antarctic Expedition.
The age is probably Mesozoic and not earlier than the
Rhaetic ; the fossil was thus considerably later than
the others described in this chapter. The secondary
wood is of a Cordaitean or Araucarian type, with usually
uniseriate rays. There are distinct annual rings, as in
the two genera last mentioned. The pith is small, and
at its margin there is a fairly broad zone of small, delicate
tracheides, with spiral or scalariform markings. The
leaf-traces of Antarcticoxylon are single.!
Unpublished observations by Mr. Walton indicate
that Antarcticoxylon is really a species of Khexoxylon
(see above, p. 228).
The stems just considered agree, for the most part, in
possessing a distinct primary xylem, whether practically
exarch as in Mesoxylon, mesarch as in Parapitys, or
more or less completely endarch as in Caenoxylon and
Mesopitys. In the next genus this is not the case.
Metacordaites.—This genus was founded by Renault
in 1896 on a specimen from the Permo-carboniferous of
Autun. The pith is continuous, not discoid, and con-
tains large resin-canals near the outside. The wood is
radially seriated throughout as in Cordaites, and com-
pletely endarch, with no primary strands. The secondary
wood only differs from that of Cordaites in the fact that
most of the tracheides bear only a single row of bordered
pits. The phyllotaxis was 3; the leaf-trace, in traversing
the wood, consists of five bundles, arranged in a V, with
the strand of an axillary branch above. The multi-
fascicular trace in this region is a peculiarity, though
1 A full account of Antarcticoxylon will be found in Seward, Antarctic
Fossil Plants, British Museum (Natural History), 1914, p. 17. See
also his Fossil Plants, vol. iii. 1917, p. 296.
HAPALOXYLON 285
Prof. Boyd Thomson states that he has found six bundles
in the trace of Cordaites Brandlingti, also in the wood.
There are no annual rings. Renault regarded this stem
as transitional between the Cordaiteae and the Conifers,
but nearer the latter. The data are, however, insufficient
to establish this interesting hypothesis.!
Hapaloxylon.—This genus is of quite uncertain posi-
tion, but deserves mention on account of its unique
structure. The name means “ soft wood,’’ and the great
peculiarity of the stem is that its wood consists almost
wholly of cellular tissue, only quite a narrow zone, next
the pith, containing tracheides. Such a structure is
quite unknown among Gymnosperms, though paralleled
to a certain extent in floating woods of some Dicotyledons,
such as the Leguminosae Aeschynomene and Herminiera.
The pith is large (a Cordaitean character) ; on its outer
border there are two or three layers of spiral and pitted
tracheides. All the rest of the wide zone of wood is
formed of elongated, square-ended cells, without any
trace of pits. The parenchymatous mass is traversed
by uniseriate rays. Beyond the wood is a broad zone
of beautifully preserved phloem, the numerous sieve-
plates clearly shown on the radial walls of the sieve-
tubes. At the outer edge of the cortex there is a
periderm.
The external surface of the specimen bears numerous
small leaf-scars each containing the print of a single
leaf-trace strand.
The triarch roots are known. While the primary
xylem appears to be normal, the secondary wood, here,
as in the stem, consists exclusively of parenchyma.
The excellent preservation seems to preclude any
doubt as to the correct interpretation of this remarkable
structure. The genus was referred by Renault to the
Araucarian Conifers, but a relation to Cordaiteae seems
1 B. Renault, “‘ Note sur le genre Métacordaite,’’ Soc. d'Histoire
nat. d’Autun, 1896.
286 STUDIES EY POssie BOTANY
about equally probable. The one species, H. Rochei,
comes from the Permian of Autun.!
3. Ihe Root.—Mixed with the remains of leaves and
branches of Cordaites, silicified specimens of roots have
also been found ; they agree so well in histological struc-
ture with the stem, that there is no reason to doubt the
{} A
04) BETES
note ti: Sasi
ry fe
me Ses
tt
joe
138)
ni renepeseoree”
ste sgunaeseecsce!
“Ad LD
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ne =
gaite
a
Nis
\\
Fic. 105.—Amyelon radicans (probably a root of one of the Cordaiteae). +, triarch primary
xylem; %?, secondary xylem; ph, phloem; fd, periderm. X 23. S Coll. 450.
(Gals Ge)
correctness of Renault’s conclusion, that they belonged
to the same plants, though I am not aware that roots
showing structure have yet been found in actual connec-
tion with the stem. In the French specimens the roots
are diarch, with a broad zone of secondary wood. The
elements of the protoxylem are spiral, the rest of the
primary tracheides scalariform, while the surrounding
1 Renault, “ Bassin houiller et permien d’Autun et d’Epinac,”’
Flore fossile, ii. p. 360, pl. Ixxvi.
CORDAITES 287
secondary zone is made up of pitted tracheides and
medullary rays, and agrees in all essential respects with
the wood of the stem. The root is limited on the outside
by a broad zone of periderm, which, from Renault’s
description, would appear to have been derived from the
external cortex. This is unusual in Gymnospermous
roots, and the point seems to deserve further investiga-
tion.
Our Fig. 105 is taken from a root known as Amyelon
vadicans, frequent in the Lower Coal-measures of England,
which in all probability belonged to some member of
the Cordaiteae. All the tissues, both primary and
secondary, are well preserved. In this case the roots
are usually triarch—sometimes tetrarch; in other
respects there is sufficient agreement with the French
specimens, to leave little doubt as to the affinities of our
fossil. In Amyelon, at any rate, the origin of the periderm
was, no doubt, deep-seated, the cortex being exfoliated.
The same was the case in a diarch root associated with
a Cordaitean stem, provisionally named Cordaites shorensis,
from Shore.
4. The Leaves.—The leaves of Cordaites are fossils
of frequent occurrence, especially in the Upper Coal-
measures, as, for example, at Radstock in Somersetshire,
and in the coal-fields of Central France, where they
appear to have played an important part in the formation
of coal. At St. Etienne, certain beds of coal are said to
consist exclusively of dense masses of the carbonised
leaves of Cordaiteae. But in addition to the carbonised
remains and impressions, which are ill adapted for the
investigation of structure, petrified specimens also occur.
Thus, in the “ black flints’’ of Grand Croix, silicified
remains of Cordaitean leaves are packed together in
layers, “like damp Beech-leaves on the ground in our
forests.’’1 These silicified specimens are often in a
1 Solms-Laubach, Fossil Botany, English edition, p, 105.
288 STUDIES IN FOSSIE “BOTANY
state of exquisite preservation, and rendered it possible
for the French palaeontologists, notably Renault, to
work out the structure in great detail. The anatomical
specimens recorded from France are all referred to the
genus Cordaites, though there is often some doubt as to
the particular species (as determined from impressions)
to which they belonged.
Broadly speaking, the structure of the leaf of Cordaites
resembles that of a single pinna of the leaf of a Cycad,
such as Zamia, while thefe is a more general resemblance
to the leaf of A gathis, or one of the larger-leaved Araucarias.
There are, as might be expected, appreciable specific
differences among the various Cordaitean leaves examined.
For example, in the leaf shown in transverse section in
Fig. 106, A, referred provisionally to C. angulosostriatus,
each of the numerous parallel vascular bundles is enclosed
in a strong sheath, which abuts, above and below, on a
hypodermal strand of fibres. Smaller hypodermal ribs
are interposed between the vascular bundles. ~The
bundle-sheaths are connected together laterally by trans-
verse bridles of thickened cells, which may perhaps be
compared to the accessory transfusion - tissue which
occurs in the genus Cycas.1_ In this species of Cordaites,
the mesophyll shows little differentiation. The most
interesting point is the structure of the bundles them-
selves, which agree exactly with those in the leaves of
recent Cycads. The xylem is in two parts, with the
spiral elements (¢) between them. The larger portion
is towards the upper surface (centripetal, a), and the
smaller towards the lower surface (centrifugal, J).
Below this again is the phloem, usually ill preserved.
In a word, we have in these cases (Fig. 106, A and C)
the collateral, mesarch structure, characteristic of the
1 A reticulate system of thick-walled tracheides, which extends
from the midrib to the margin of the leaflet in this genus. See Worsdell,
‘On Transfusion-Tissue,”’ Trans. Linn. Soc. 2nd ser. (Bot.), vol. v.
1897, p. 308.
CORDAITES 2809
bundles of Cycadean leaves, and already familiar to us
in other fossil plants. Some other species show the
same structure of the bundles, but in several the centri-
fugal part of the xylem is absent, as in the petioles of
S
Ee KE
Ae iret ae
egeeaie Oe
14 abe
Fic. 166.—Cordaites. Leaves in transverse section. A. C. angulosostriatus (?). h, i, hypo-
dermal ribs of sclerenchyma; , mesophyll; d, bundle-sheath; a, centripetal xylem ;
t, protoxylem; 6, centrifugal xylem; c, phloem; f, tissue connecting the bundles.
x 60. B. C. rhombinervis. Here the ribs of sclerenchyma only occur in connection
with the bundles; palisade-tissue and spongy parenchyma are differentiated. » 50.
C. C. lingulatus. Ribs as in B; palisade-tissue well marked. x 50. Allafter Renault.
Medullosa, whereas it only dies out in the finer bundles
in the case of recent Cycadean leaves.!
1 See M. C. Stopes, ‘‘ On the Leaf-Structure of Cordaites,’’ New
Phytologist, vol. ii. 1903, p. QI.
1g
290 STUDIES IN’ FOSSIL BOTANY
In other anatomical points there is considerable
diversity of detail. The mesophyll is in some forms
clearly differentiated into an upper palisade layer, and
a lower lacunar portion (see Fig. 106, B and C). This
is beautifully shown in a species investigated by Dr.
Marie C. Stopes, and identified as C. principalis. In the
same species Dr. Stopes observed the very interesting
fact that both the inner and outer sheaths surrounding
each bundle consist of elements with bordered pits,
and may thus be regarded as forms of transfusion-tissue.
Otherwise, centrifugal xylem is absent in this leaf. In
certain cases the hypodermal ribs are limited to the
upper and lower surfaces of the bundles, not occurring
between them. In one form (C. crassus) the leaf had a
distinctly fleshy character, as if adapted to xerophytic
life. Numerous stomata, of normal structure, occur in
these leaves, on the epidermis of the lower surface, to
which they seem to be limited. The general conclusion
to which we are led is that, while the leaf, in its simple
form and general structure, approaches most nearly to
that of such Conifers as Agathis, in the details of internal
organisation it agrees more closely with a single leaflet
of a Cycad, thus showing a striking combination of char-
acters, such as we have aJready met with in the leaf of
Poroxylon.
In a large bud, referred to Cordaites lingulatus, Ren.
(cf. Fig. 99), Lignier was able to follow the differentiation
of the tissues in the successive young leaves, an observa-
tion rarely possible in a fossil plant. The phloem ap-
peared to be completed early, but the first definite differ-
entiation in the procambial strand is that of the proto-
xylem ; the rest of the centripetal wood follows, and this
may be completely formed before the arc of centrifugal
xylem becomes lignified. Thus the course of develop-
ment is quite normal. The bundle-sheath, which bears
somewhat irregular bordered-pits on its walls, becomes
marked out almost simultaneously with the protoxylem,
MESOXYLON 2gI
while the transfusion tracheides, lying between the
sheath and the xylem, are completed about the same
time as the centrifugal arc. A secretory gland, probably
cellular, not intercellular, is developed early, on each
side of the sheath, to which it belongs.
The fibrous bands of the leaf appear as early as the
procambial strands, and their cell-walls become thickened
concurrently with those of the xylem of the bundles.
_The differentiation of the palisade and spongy tissues of
the mesophyll takes place somewhat late in the develop-
ment.
It has already been mentioned that the leaves,
commonly attributed to Cordaites, which occur in the
Lower Coal-measures of England, probably belong to
the genus Mesoxylon, of which the stems are far commoner
at such horizons than those of the true Cordaites. Con-
siderable interest therefore attaches to Dr: Margaret
Benson's account of a type of leaf named by her Cordaites
Felicis, occurring frequently in the coal-balls which
yield the stems of certain species of Mesoxylon. It does
not differ in any essential respect from the well-known
leaves of Cordaites, but shows definite distinctive char-
acters. The chief feature is that the sclerenchymatous
bands placed midway between the bundles extend right
through the leaf from one surface to the other, forming
regular partitions as seen in transverse section. Addi-
tional fibrous bands are present in a hypodermal position.
The palisade and spongy tissues of the mesophyll are
not strongly differentiated. Each bundle is surrounded
by a thick sheath ; the walls of the sheath-cells are pitted.
As usual, the centripetal xylem forms the chief part of
the wood, but where the bundle is fully developed there :
is a well-marked band of centrifugal xylem. In addition,
there are some tracheides between the xylem and the
sheath, which may be called transfusion tissue and
* O. Lignier, “ Différentiation des tissus dans le bourgeon végétatif
du Cordaites lingulatus,’’ Ann. des Sci. nat. (Bot.), sér. 9, t. xvii. 1913.
292 STUDIES IN’ FOSSI Eo BOTAN Y
represent the inner sheath described by Dr. Stopes in
other species. Towards the edges the bundles are some-
what simplified, the centrifugal xylem disappearing,
though some transfusion tissue remains. In this, as in
other respects, there is a close agreement with the struc-
ture of the pinnae in recent Cycads.
Dr. Benson’s species agrees very nearly with C.
Wedekindi and other species described by Felix from the
Coal-measures of Westphalia. The nomenclature pre-
sents some difficulties, as we can hardly continue to use
the generic name Cordaites for leaves which in all prob-
ability belonged to another genus. At the same time,
it is not yet possible to refer Dr. Benson’s specimens to
a definite species of Mesoxylon. The name Mesoxylon
Felicis might be provisionally adopted for this form of
Cordaitean leaf.
5. The Fructifications—We now come to the most
interesting point in our present subject—the reproductive
morphology of the Cordaiteae. The general arrange-
ment and external appearance of the inflorescences have
already been described. Our knowledge of these organs
has been built up by the labours of successive observers,
notably Carruthers, Grand’Eury, Renault, and, more
recently, C. E. Bertrand. It is- to Renault) thargome
acquaintance with the intimate structure of the flowers
is chiefly due, for he was so fortunate as to find silicified
specimens, allowing of minute structural investigation,
which were clearly of the same nature as the catkins
found on the branches of the Cordaiteae. As, however,
the petrified fructifications could not be referred with
certainty to the particular members of the family to
1 See M. Benson, “‘ Cordaites Felicis,’’ Ann. of Bot. vol. xxvi. 1912,
p. 201. The measurements in this paper require to be multiplied
by ten. Compare Felix, “‘ Untersuch. tber den inneren Bau west-
falisher Carbonpflanzen,” Abh. d. K. Geolog. Landesanstalt, Berlin,
Bd. vii. 1886, p. 61.
CORDAIANTHUS 293
which they belonged, the generic name Cordaianthus was
applied to them, and is still used, as a matter of con-
venience.
A. The Male Fructification
The specimen shown in longitudinal section in Fig.
107, and known as Cordaianthus Penjoni, Renault, is a
single male catkin,! corresponding to one of those which
are represented in their external aspect in Fig. 99, borne
laterally on the peduncles. The catkin (about a centi-
metre in length) consists of a rather thick axis, bearing
spirally arranged bracts, between which the stamens
(using the word provisionally) are inserted (Fig. 107, A).
The stamens are either isolated, each in the axil of a
bract, or are grouped, two or three together, around the
apex of the catkin. Each stamen consists of a filament,
surmounted by three, four, or more ? long, vertical pollen-
sacs. The filament is traversed by a vascular bundle,
which sends a branch to the base of each pollen-sac
(Fig. 107, B, g). Some of the sacs in Renault’s specimens
had already undergone dehiscence, by a longitudinal
opening (Fig. 107, B, e); others are preserved intact,
and are still filled with the pollen-grains (e’). The wall
of each pollen-sac consists of a single layer of cells (Fig.
107, B). In other species (e.g. C. Saportanus) the stamens
are limited to the apical region of the catkin, and are
fewer in number, with shorter filaments.
The morphology of these male catkins of Cordaites
is open to various interpretations. Renault regarded the
male “‘ flower ’”’ as consisting of a group of two or three
stamens at the apex of the catkin, but as reduced to a
single stamen where the position is axillary. Solms-
1 The word catkin is used, rather than cone, to avoid any assump-
tion cf homology with the male cone of the Coniferae.
2 Renault gave the number as three or four, but, as pointed out
by Solms-Laubach, the transverse section shows five or six sacs to
each stamen.
294 STUDIES IN FOSSIL BOTANY
bf
Laubach preferred to regard each of Renault’s “‘ stamens °
as itself constituting a male “ flower,’ the stalk on which
the pollen-sacs are borne thus representing a pedicel,
and not a filament, while the pollen-sacs are themselves
the stamens. On this view there would be a certain
resemblance to the male flowers of Gnetaceae. In
Gnetum, for example, the male flower consists of a stalk
A B
Fic. 107.—Cordaianthus Penjon:. A. Longitudinal section of male catkin. a, axis; b,
sterile bracts; c, filament, bearing the pollen-sacs (e) at the top; d, junction of fila-
ment with pollen-sacs; f, detached pollen-sac; v, apex of axis, with stamens around
it. »* 6}. B. Stamens, more highly magnified. g, vascular bundle of filament,
sending branches to the pollen-sacs; e, pollen-sac after dehiscence; e’, sac still full of
pollen; p, apex of axis. Other letters asin A. ™X 23. Both after Renault.
bearing two pollen-sacs, each of which is considered to
represent a sessile stamen. In Ephedra the arrangement
is similar, but the sessile stamens vary in number, accord-
ing to the species, from two to eight, and each consists
of two pollen-sacs. The Gnetaceae, however, are a
highly modified group, as to the geological history of
which we have no certain information. We must be
CORDAIANTHUS 295
cautious in using their morphology (which in itself is
none too clear) to explain that of an ancient family like
the Cordaiteae, which flourished in the Carboniferous
period. If, as has been suggested, the flowers of the
Gnetaceae are reductions from a much more complex type
like that of the Bennettitales (see Chap. V.) it is clear
that the family can have only the most remote affinity
with the Cordaiteae.!
Renault’s summary of the morphological conditions
in the male Cordaianthus certainly has the merit of
simplicity. He said: “In the midst of sterile bracts
arose one or more fertile bracts, the filament of which,
scarcely modified, bore at its summit three or four sacs
containing the pollen.”’? On this view, the stamens
would in no case be axillary structures, but would repre-
sent so many sporophylls, interspersed among sterile
bracts. We might compare each stamen to that of
Ginkgo; in the latter the pollen-sacs are usually only
two in number, though stamens with three or four sacs
sometimes occur, and are pendulous instead of erect ;
these differences, however, are of trifling importance.
The male catkin of Cordaianthus would thus chiefly differ
from that of Ginkgo, in the presence of sterile bracts
among the sporophylls, a difference comparable to the
relation which we find, in a remote family, between the
strobilus of a Calamostachys and that of a recent Equisetum.
The data, however, are insufficient to justify any definite
conclusion as to the exact morphology of the male Cor-
daianthus. It is quite clear, at any rate, that its structure
is totally distinct from that of the male cone of a Cycad,
and very different from that of a Conifer, or from the
male inflorescence of Gnetaceae. On the whole, Ginkgo
affords perhaps the best parallel. The stamens of the
1 See Arber and Parkin, ‘‘ Studies on the Evolution of the Angio-
sperms: the Relationship of the Angiosperms to the Gnetales,”’ Ann.
of Bot. vol. xxii. July 1908, and the papers there cited.
2 Renault, Tiges de la flove carbonifére, p. 308.
296 STUDIES IN FOSSIL BOTANY
Araucarieae with their numerous pendulous pollen-sacs
also offer some analogy.
The pollen-grains of Cordaianthus were rather large,
measuring, in some examples studied by Renault,
‘0g x05 mm., their form thus being ellipsoidal. The
outer membrane had a rather rough surface; in the
interior of the pollen-grain, a small group of cells (pro-
thallus or antheridium) can often be detected (Fig. 109, C),
an important observation, to which we shall return when
speaking of the phenomena of pollination.
B. The Female Fructification }
Renault found that the young female catkins of
Cordaites were scarcely to be distinguished from the
male by external characters, though somewhat more
globular in form. In the early stages, the ovules were
completely hidden by the overlapping bracts. Here
also, sections of the silicified specimens have revealed
the internal organisation. In a fructification, to which
the discoverer gave the name of Cordaianthus William-
soni (Fig. 108, A), the axis bore numerous, spinal
disposed bracts, most of which were sterile, while in
the axils of some of them the ovules (c) were borne.
Each ovule was situated at the end of a very short lateral
stalk (d), which according to Renault bore some bracteoles;
a transverse section of a similar fructification showed
four ovules. The supposed bracteoles are of extremely
doubtful nature, and Bertrand with good reason considered
that they had been wrongly interpreted.
The ovule has a single, thick integument, as was
shown by Bertrand. .At a later stage the inner layer
of the integument became hard and resistant, the outer
remaining fleshy. In the middle was the nucellus (Fig.
108, B, g, m) (somewhat shrivelled in the specimen figured),
1 See C. E. Bertrand, Le Bourgeon femelle des Cordaites, d’atres
les préparations de Bernard Renault, Nancy, 191t.
CORDAIANTHUS 297
| the upper part of which contained the pollen-chamber.
A vascular bundle entered the chalaza, and sent out two
Fic. 108.—Cordaianthus Williamsoni. A. Somewhat tangential section of a female catkin,
showing two ovules. a, axis; b, sterile bracts, and bundles running to them; c, ovules ;
d, axillary pedicel, bearing an ovule; m, nucellus. »* about ro. B. Ovule, more
highly magnified. d, short pedicel, terminated by the ovule; b, supposed bracteole ;
c-f, outer, e, inner layer of integument ; ch, chalaza; m, shrivelled nucellus; g, apex
of nucellus. x about 35. After Renault.
branches into the integument, and no doubt others into
the nucellus.
298 STUDIES IN FOSSIL BOTANY
Further details were worked out in a fructification,
specifically distinct, named Cordaianthus Grand’ Euryi by
Renault. Here the axis, apparently terminated by the
ovule (shown detached in Fig. 109, A), bore several
bracts. The integument is broken and displaced, leaving
the nucellus nearly isolated in the middle of the ovule.
Fic. 109.—Cordaianthus Grand’Euryi. A. Longitudinal section of female catkin, showing
one ovule, just pollinated. d, axis; b, bracts; c, integument; 7, nucellus; cp, pollen-
chamber; g, canal of pollen-chamber; , pollen-grains in chamber, and p’, in canal.
~ 24. B. Canal of pollen-chamber enlarged. g, dilated cells, enclosing the canal,
0; p, p’, two pollen-grains in the canal; ev, outer membrane of pollen-grain ; im, group
of prothallial or antheridial cells within the grain. 150. C. Grains of pollen, showing
internal cells ; the smaller grain from an anther, the larger from the canal of an ovule.
x about 100. All after Renault.
In the upper part of the nucellus, we see the pollen-
chamber (cp), surmounted by a very curious neck, shown,
on a large scale, in Fig. 109, B. Both in the pollen-
chamber itself and in the canal leading to it, pollen-
grains (p) are contained, so that this ovule, as Renault
said, was “‘ surprised at the very moment of pollination.”
The wall of the canal has a characteristic structure, for the
CORDAIANTHUS 299
cells in its lower part are transversely elongated, so as to
partially close the passage (Fig. 109, B, g). Possibly this
may have been an arrangement for shutting the entrance
to the pollen-chamber after pollination had been effected.
The pollen-chamber is, as we have already seen
(Chap. I. p. 68, and Chap. III. p. 206), a general feature
in Palaeozoic seeds. The pollen-chamber of 7v7igono-
Fic. 110.—Cycas, sp. Longitudinal section of Fic. rrr. — Pollen-chamber enlarged,
ovule, showing the thick double-layered in- showing pollen-grains in the canal.
tegument enclosing the nucellus. The round Two pollen-grains, further en-
body in the lower half of the nucellus is the larged, on the left. From Griffith,
embryo-sac ; the flask-shaped cavity in the 1852.
upper part is the pollen-chamber containing
pollen-grains. From Griffith, 1852.
carpus, for example, among the Pteridosperms bears
a rather close resemblance to that of a Cordaitean seed
(see Fig. 79, p. 205). The Cycadaceae and Ginkgo are
the only recent plants in which this organ is known ;
the pollen-chamber of Cycas was originally discovered
before the middle of the last century by our
countryman Griffith, who gave excellent figures of
it, which are here reproduced! (Figs. 110, 111). Many
1 Griffith, Icones Plant. Asiat. Partiv. Pl. 377 and 378, 1852. Notulae
ad Plant. Asiat. pp. 6-8, 1854. Both these works were posthumous ;
Griffith died in 1845.
300 STUDIES IN SEOSSi-E BOTAN i
years later it was rediscovered independently by De
Bary and Brongniart, both of whom were unaware of
Griffith’s observations.
The pollen-grains in the canal and pollen-chamber
of the ovule of Cordaites are larger than those still con-
tained in the anther, and their internal group of cells
is more developed (Fig. 109, C); grains, which were
found lying free in the matrix, were in an intermediate
condition ; Renault drew the conclusion that the pollen-
grains continued to grow after their discharge from the
anther, and more especially after their entrance into the
pollen-chamber.
The cells within the pollen-grain of Cordaites are more
numerous than in most recent Gymnosperms; in the
pollen-tube of Muicrocycas, however, described by Cald-
well,t sixteen spermatozoids are produced, while in that
of Avaucaria the number of nuclei present ranges from
about twenty to forty-four.2 In the pollen-grains of
Cordaites, as Renault pointed out, the cells appear to
have been all of one kind. That this structure, whether
it be regarded as a prothallus or as an antheridium,
should have been more developed in primaeval seed-
plants than is usual in those of our day, is quite what
we should expect, from our knowledge of the analogous
conditions in the heterosporous Cryptogams.%
Pollen-grains have now been observed, in a number
of instances, within the pollen-chambers of Pterido-
spermous and Gymnospermous seeds of the Carboniferous
period. There appears to be little or no evidence at
present for the formation of pollen-tubes, though the
preservation is sometimes good enough for even so
delicate a structure to have been detected. It is prob-
able that such pollen-grains as those of Cordaites or
1 “* Microcycas calocoma,’’ Bot. Gazette, vol. xliv. 1907, p. 118.
2 Lopriore, ‘‘ Uber die Vielkernigkeit der Pollenkérner von Avaucaria
Bidwillu,’’ Ber. d. Deutsch. Bot. Gesellschaft, vol. xxiii. 1905, p. 335.
% See the account of Slephanospermum above, p. 209.
CORDAIANTHUS 301
Stephanospermum may have been rather more like the
Cryptogamic microspore than those of Cycas or Ginkgo,
that no pollen-tube was developed, but that the relatively
| large antheridium at once produced a number of sper-
matozoids, for we are probably justified in regarding
the cellular body within the pollen-grain of Cordaites as
an antheridium, rather than as a vegetative prothallus.
In the absence of a _ pollen-tube, the spermatozoids
would have needed to be more numerous, for, having
a longer distance to cover by their own movements,
they would presumably have reached their goal with
less certainty. The pollen-tube may probably be re-
garded as a later adaptation, which served the purpose
of economising spermatozoids, and ultimately rendered
their motility unnecessary. Even in the Cycads and
Ginkgo, where the pollen-tube serves mainly as an anchor-
ing and food-absorbing organ, its growth ultimately
brings the spermatozoids with much precision to their
goal—the necks of the archegonia.}
Returning to the ovules, it may be mentioned that
they are somewhat flattened in the plane tangential to
the catkin; the two integumental bundles are placed
laterally, one near each edge of the ovule. The integu-
ment terminated above in a bi-lobed body, interpreted
by Bertrand as an apparatus for collecting the pollen.
A certain number of the ovules in a catkin seem to have
been abortive.
The flattened ovule of Cordaianthus was evidently
destined to develop into a platyspermic seed. Bertrand
found that the structure agrees most closely with seeds
of Brongniart’s genus Dzflotesta, which is nearly allied
to Mitrospermum, a seed described below.
The organisation of the catkin bearing the ovules
was worked out in detail by Bertrand. The axis, which
is completely clothed by the bases of the bracts, contains
1 See, for example, Webber, Sftermatogenesis and Fecundation of
Zamia, U.S, Dept. of Agriculture, 1901, p. 63.
302 STUDIES IN SFOSSI-* BOTANY
a vascular ring of about ten isolated strands. Each
bract receives a single bundle, described as identical
with one of the nerves of the vegetative leaf of Cordaites.
The free bract is strengthened by hypodermal bands of
fibrous tissue. It will be remembered that the catkins
are borne on a naked stalk, forming the main axis of the
inflorescence (see Fig. 99).
Mesoxylon.—Until recently nothing was known as
to the structure of the fructification in the Cordaiteae
of the British Coal-measures, though various impressions
referred to’ Cordaianthus had been described. There is
now, however, good evidence that the axillary shoots
of Mesoxylon multivame, already mentioned, were the
inflorescence of that plant. These shoots, as they appear
in the axils of the leaves, are naked, somewhat fleshy
organs. Free specimens show the general structure of
the whole shoot. It is bilaterally symmetrical, consist-
ing of a leafless main axis, containing a flattened stele
and bearing distichously arranged bud-like branches,
lying in the plane of the major axis of the main shoot.
Each branch or bud bears numerous spirally arranged
bracts of strong, mechanical construction (see Fig. 112,
which shows the main axis and one of the buds). As
regards the anatomy of the bud, it possesses a ring of
vascular strands, from which each bract receives a single
leaf-trace, of mesarch structure.
The morphology of these shoots is identical with that
of various species of Cordaianthus, described by Grand’-
Eury in 1878. The main ‘axis of the inflorescencesie
described by him as fleshy and as a “ naked peduncle.”’
He laid stress on the distichous arrangement of the buds
on the axis, saying that “‘ the distichous arrangement of
the buds is the sign of a new destination,”’ 7.e. of their
reproductive function. The buds and their bracts agree
closely in organisation and structure with the catkins
of Cordaianthus, minutely described by Bertrand. It
thus appears to be proved that the peculiar axillary
CORDAIANTHUS 393
shoots of Mesoxylon multirame constitute the Cordaranthus
of that species.
sth.
Fic. 112.—Mesoxylon multirame. Somewhat oblique transverse section of a fertile shoot,
showing a bud or catkin attached to the main axis of the inflorescence. st, stele of axis ;
st.b., stele of bud; br, a bract of the bud. x about 15. S. Coll. 3040. (G. T. G.)
The sex of the Mesoxylon inflorescence could not be
determined for certain, as neither stamens nor ovules
are preserved im situ. Renault speaks of the bracts of
304 STUDIES IN FOSSIL BOTANY
the female catkin as thicker and more coriaceous than
those of the male. This points to the Mesoxylon catkins
having been female, as the bracts are strongly built,
and agree exactly with those of the female buds described
by Bertrand. Seeds of Mitrospbermum compressum are
associated, but not connected, with the fertile shoots.
It thus appears that the reproductive apparatus of
Mesoxylon, like the vegetative organs, was constructed
on the same plan as that of Cordaites.
Morphology.—Former speculations on the morphology
of the female Cordaianthus have to a great extent lost
their basis, in consequence of Bertrand’s more accurate
observations. The comparison with Gnetaceae no longer
has any point, now that the Cordaitean ovule is proved
to have possessed only a single integument, and, as the
supposed presence of bracteoles on the pedicel of the
ovule is now discredited, we can no longer assume that
the pedicel represents an axillary shoot ; it may merely
be the funiculus of the ovule itself.
Taking the facts as they stand, the female catkin
may be described as a very simple form of cone, with
each megasporangium apparently axillary to a subtending
bract, an arrangement for which an analogy can of course
be found in the quite unrelated genus Selaginella. The
fact that most of the bracts are sterile is, however, remark-
able, and another peculiar feature is the great elongation
of the mature pedicel in various fructifications referred
to Cordaianthus. Such cases may suggest a vague
analogy with Ginkgo, but the pedicel of Cordaianthus
never bears more than one seed, and if it is an axillary
shoot there is nothing to represent the carpel. The data
are, in fact, insufficient for the interpretation of the
female catkin in terms of any recent Gymnospermous
fructifications. We can only say that the indications
of affinity point towards Coniferae or Ginkgoales rather
than towards Cycads, with which the Cordaiteae seem
to have little in common, so far as the fructifications,
CORDAIANTHUS 305
apart from the seed itself, are concerned. We must,
however, remember that our living Cycadaceae only
represent one or two special surviving groups of a class
once vastly more extensive and varied. The possibility
of a comparison between the reproductive morphology
of the Cordaiteae and that of the Mesozoic Bennettitales
(Chapter V.) has been maintained by some botanists,
though on inadequate grounds.
The highly specialised inflorescences of the Cordaiteae,
whether male or female, are clearly as remote as possible
from the simple fructifications of the Pteridosperms, in
which, so far as we know, both pollen-sacs and seeds were
borne on portions of the frond differing but little from
the vegetative foliage. There is a wide gap here, though
in other respects, especially in the structure of the seeds
themselves, a certain affinity between the two groups is
plainly manifested.
6. The Seeds.—In some cases seeds, in a more or less
ripe state, have been found attached to the inflorescence,
and in connection with the leafy twigs of Cordaiteae.
These seeds sometimes appear to have been solitary, a
single seed representing the female catkin as above
described. This may indicate a real morphological
difference, like that between Taxus or even Ginkgoaceae
and the Coniferae with true cones, but it may be equally
well explained if we suppose that only one ovule in each
catkin developed into a ripe seed. In some specimens,
as in Cordaianthus anomalus, Carruthers, each seed was
seated on a long slender stalk or peduncle ;1 this may
have been developed during the ripening of the seed.
Our knowledge of the comparative morphology of the
Cordaiteae has unfortunately made little progress in
recent years, owing to the want of adequate material.
In certain cases, the seeds found in connection with
1 Carruthers, “‘ Notes on some Fossil Plants,” Geol. Mag. vol. ix.
1872.
20
306 SE£UDIES IN. FOSSIL. BOTANY
the inflorescences of Cordaites have a_ characteristic
cordate form. This has rendered it possible to identify,
with great probability, a certain number of the isolated
seeds as belonging to this family. Such direct evidence
is very necessary, for, as we have already seen (Chaps. I.
and III.), a large number of the Palaeozoic seeds belonged
to Pteridospermeae, and, where they were of the platy-
spermic type, may be extremely difficult to distinguish
from those of Cordaiteae.. It 1s also probable that the
seeds of primitive Coniferae and Cycadophyta (both of
which groups already existed, at least in the later Palaeo-
zoic times) may be represented among the detached seeds.
We will first describe a type of seed which is known, from
the evidence of attached specimens, to have been pro-
duced by the Cordaiteae, and was therefore named
Cordaicarpus by Renault,! though the old name Cardio-
carpus is now reinstated.
These seeds are heart-shaped at the base, and some-
what flattened, being of the platyspermic type. The
testa is double, the outer envelope, or sarcotesta, having
been soft and fleshy during life, while the inner layer,
or sclerotesta, was hard and lignified. Renault regarded
the two layers of the testa as having been derived from
two integuments, a view for which there is no sufficient
evidence. So in the case of recent Cycadaceous seeds,
some botanists have regarded the double testa as repre-
senting two integuments, while others, with better reason,
consider that a single integument has undergone differ-
entiation into distinct layers.
The vascular bundle which enters the chalaza gives
off branches, both into the testa and into the nucellus ;
1 These seeds were originally named Cardiocarpon and subsequently
Cardiocarpus by Brongniart, a name used by Carruthers and William-
son in the form Cardiocarpon. As pointed out in Vol. I. Chapter VI.
(p. 175), certain ‘“‘seeds”’ referred by Williamson to Cardiocarpon
really belonged to Lycopods and are now named Lepidocarpon. A
valuable account of seeds referred to Cordaiteae will be found in Seward’s
Fossil Plants, vol. iii. chap. xxxv., iii. Cardiocarpales.
CARDIOCARPUS 307
the former traverse the inner part of the sarcotesta,
a double bundle running up on each side of the seed,
just outside the lateral edges of the sclerotesta (cf. khabdo-
carpus, Fig. 92), while the latter enter the nucellus and
traverse its tissue. At its micropylar end, the nucellus,
which was probably free from the integument, contains
a pollen-chamber, provided with a neck, which projects
into the micropyle. Apart from its bilateral symmetry,
the seed agrees very nearly in structure with the Tvigono-
fae
NW
Qr
ar er
ESI \/- =
Dm ae te A
4 {
eae | eg) eer 5"! \
(nic ons vigil wy Vat:
Fic. 113.—Cycadinocarpus augustodunensis. Upper part of seed, in longitudinal section. |
int, integument ; mi, micropyle; nu, remains of nucellus; #.c., pollen-chamber, con-
taining pollen-grains; the chamber has a long neck or canal, extending up into the
micropyle ; pr, endosperm ; ar, archegonia. Magnified. After Renault.
carpus type, described on p. 204. In certain species of
Cardiocarpus the archegonia have been found. They
occur in the usual position, at the upper end of the
endosperm, and two of them are shown in a longitudinal
section of the seed.
Our illustration, Fig. 113, is from a seed which Renault
and Bertrand separate generically from Cardiocarpus, on
account of the distribution of the vascular bundles.
In Cycadinocarpus, as the genus is named, the inner
vascular system follows the endotesta, and does not enter
308 STUDIES IN FOSSIL BOTANY
the nucellus, a course which resembles that in the seeds
of recent Cycads, with the exception of Bowenia. The
outer bundles are given off from the chalazal strand after
it has entered the sclerotesta, and not below it, as in
Cardiocarpus. In other respects the seed agrees with
Cardiocarpus. Two archegonia (ar), spherical in form,
are clearly shown; between them, the endosperm has
an upward prolongation, which is interesting, as it
exactly corresponds to the structure found in Ginkgo
at the present day, and compared by Hirase to a tent-
pole, supporting the nucellar membrane, which repre-
sents the tent. The pollen-chamber (f.c.), with its long
neck rising up into the micropyle (m7; cf. Figs. 110 and
III), contains pollen-grains. Only the sclerotesta (it)
of the seed-coat is shown in the figure.
A seed, frequent in the coal-balls of the British Lower
Coal-measures, was named Cardiocarpon compressum by
Williamson, but has been placed in a distinct genus,
Mitrospermum, by Dr. Agnes Arber, who investigated
its structure.1 This seed is closely associated with the
fertile shoots of Mesoxylon multirame and may have
probably belonged to that plant, though the evidence is
not decisive.
The diagrams in Fig. 114 and the transverse sections
in Fig. 115 will give a sufficient idea of the structure of
the seed. It is markedly platyspermic, as the specific
name implies, and measures, when complete, nearly a
centimetre in the principal plane by about 3 mm. in the
other direction. In surface view, the seed is somewhat
heart-shaped. The sarcotesta forms two extensive wings
at the sides and extends above the sclerotesta at the
micropylar end. Inside the sclerotesta or shell there are
some remains of an “inner flesh’’ as in the seeds of
Cycads. There are indications that the shell may have
split into valves when mature.
1 A. Arber, ‘‘ On the Structure of the Palaeozoic Seed Mitrospermum
compressum (Will.),’’ Ann. of Bot. vol. xxiv. IgIo.
MITROSPERMUM 309
The distinction from Cardiocarpus lies in the course
of the bundles supplying the seed.
In Cardiocarpus, as
already mentioned, the lateral integumental strands are
given off from the main supply in the sarcotesta, before
the shell is reached.
In Mitrospermum the main bundle
passes through a foramen in the sclerotesta before branch-
ing, so that the lateral strands have to traverse the base
Sa
p.c.
\\\
AY
\\
CA
Zr
A
A
B
A
A
Br
Z
BA:
a\
Fic. 114.—Mitrospermum compressum. Diagrammatic sections of seed.
plane ; showing the wings.
A, in principal
megaspore and nucellus; 1.f., inner flesh ; sc, sclerotesta; v.b.’, one of the lateral bundles
of the integument; sa, sarcotesta, forming the wings; mi, micropyle; p.c., pollen-
chamber.
B. In plane at right angles to the former.
h, hilum at base of seed; v.b., main supply-bundle; m, n,
Dr. Agnes Arber, modified to show the micropyle.
For lettering see A. After
of the shell before entering the sarcotesta (Fig. 114, A)
They then turn upwards, following the lateral ee
of the shell (see the transverse sections in Fig. 115).
Each
bundle is much flattened, forming a tracheal plate.
, There
are also tracheides at the base of the nucellus, but whether
they extend up into the free nucellus could not be deter-
mined.
The nucellus is not well preserved, and the form of
310 STUDIES IN FOSSIL SUTanyY
the pollen-chamber is not clear. As the micropyle is
approached, however, the nucellus contracts to a small
size (Fig. 115, A), and it is probable that the contracted
region may be taken as representing the pollen-chamber,
for pollen-grains have been found in it. The pollen-
grains are elliptical, measuring about 120p x 80p, a size
comparable to that of the pollen found in the Cordaianthus
ovules. In favourable cases, the prothallus filling the
megaspore is more or less completely preserved.
Fic. 115.—Mitrospermum compressum. ‘Two seeds lying side by side in transverse section.
The upper figure is in section through the body of the seed, the lower about at the base
of the micropyle. In both figures the wings are conspicuous. v.b.1, v.b.?, the lateral
bundies in the body of the seed; v.0.5, v.b.4, the same in the micropylar region; mg,
megaspore membrane; #, nucellus; p.c. (in lower figure) the pollen-chamber. The
sarcotesta and sclerotesta are evident in both figures. % about 14. S. Coll. 3025.
(G. T. G.)
It is evident that Mitrosbermum is a seed belonging
to one of the Cordaiteae, and in all probability to a
Mesoxylon. It is possible, as Dr. Agnes Arber points
out, that more than one species may be embraced under
the name Mitrospbermum compressum.
Diplotesta, the seed that Bertrand regarded as repre-
senting the ripened ovule of Renault’s Cordaianthus, only
differs from Mitrosbermum in small details of structure.
1 See Scott, 1919, above cited, Pl; ii. Figs. r5 andur6,;
AFFINITIES OF CORDAITEAE 311
Although so many Pteridospermous and Gymno-
spermous seeds have been discovered in the Carbon-
iferous formation, and often in a wonderful state of
preservation, no embryo has, as yet, been found in any
of them: The possible explanation of this fact has
been discussed in connection with the seed of Lyginopteris
(see Chapter I. p. 71).
The investigation of the Palaeozoic seeds, which was
allowed to rest for some time after the classical researches
of Brongniart, Renault, and Williamson, has since been
actively pursued, having been greatly stimulated by the
discovery of the seeds of the Pteridosperms.!
7. Affinities—We have now completed our sketch
of the principal characters of the Cordaiteae, and may
briefly sum up the conclusions to which we are led.
In their vegetative characters, the Cordaiteae hold
the balance very evenly between Cycads and Conifers,
while at the same time showing much that is peculiar
to themselves. The structure of stem and root is, on
the whole, very near that of the Coniferae ; the secondary
wood especially would by itself rouse no suspicions that
we had anything but an Araucarian Conifer before us.
The large size of the pith in the stem, however, is unlike
anything known in Coniferae, and rather suggestive of
a Cycad, though in its peculiar discoid structure the pith
of some Cordaiteae is quite different from that of Cycads.
The double leaf-trace is a striking point of agreement
with Ginkgo on the one hand, and with certain of the
Pteridosperms on the other ; Poroxyleae form a connect-
ing link with the latter in this respect.
The wood of the stem was wholly centrifugal in
1 An interesting interpretation of the seeds of Tavrus and its allies,
in the light of the seed-structure of Cordaiteae, will be found in B.
Sahni, ‘““ On Certain Archaic Features in the Seed of Taxus baccata,
with Remarks on the antiquity of the Taxineae,”’ Ann. of Bot. vol.
XXXiV. 1920, p. II7.
312 STUDIES IN. FOSSIE-BOrAN®
development, in many of the specimens investigated
belonging to undoubted Cordaiteae; but this distinc-
tion is not constant, for, as we have seen, there are stems,
of true Cordaiteae (Mesoxylon), in which centripetal
wood is present, as it is in the Poroxyleae and Pityeae.
If the seeds of Poroxylon are represented, as Grand’Eury
believed, by Rhabdocarpus, the very close affinity of this
family to true Cordaiteae is further confirmed.
The leaves, in their general form and venation, recall
those of such Coniferae as Agathis, though often greatly
exceeding those of any known Conifer in size.t In
internal structure the leaves agree almost exactly with
the single pinnae of the leaf in Cycads.
In general habit, the lofty stem, with well-marked
internodes, departs altogether from the ordinary Cycadean
type, and much more resembles that of a Conifer, but,
in many species, at any rate, the crown, with its abund-
ance of huge simple leaves, must have presented an ap-
pearance totally unlike anything in either of the recent
families.
It is to the reproductive organs—the male and female
fructifications and the seeds—that we naturally attach ”
the chief importance in considering the affinities of the
Order. It is just in these organs, however, that we
find the most remarkable combination of characters, both
such as are common to various other families and such
as are altogether peculiar to the fossil group. ~The
staminiferous flowers (however we may interpret them)
are very different from anything known to us, either in
the Cycadaceae or the true Coniferae. A comparison,
though in either case a remote one, is possible with the
Gnetaceae (Gnetum or Ephedra), on the one hand, or with
Ginkgo, on the other. On the former alternative, we
1 In Agathis macrophylla, from the Queen Charlotte Islands, the
leaves attain a length of 17 cm. and a breadth of 5 cm. Seward
and Ford, ‘‘ The Araucarieae,’’ Phil. Trans. Royal Soc. B, vol. 198,
1906, p. 315.
AFFINITIES OF CORDAITEAE 313
should have to regard the stalked tuft of pollen-sacs
as representing an axis, bearing sessile anthers ; on the
latter, we should interpret it as a single sporophyll, with
terminal microsporangia. The latter view is the simpler,
and the analogy with Ginkgo, in many respects a primitive
type, is more valuable than that with the highly special-
ised Gnetaceae. On any view, however, the organisation
of the male flower of Cordaiteae is quite peculiar and
unlike that in other Gymnosperms, and even if it stood
alone would serve to mark them as a distinct Order.
The female strobilus, like the male, is as remote as
possible from that of the Cycads, but may be better
compared with the cone of the Coniferae.
Prof. B. Sahni considers that the Taxales (Taxus,
Cephalotaxus, Torreya), as well as Ginkgo, are most closely
connected with the Cordaiteae. This is, of course, a
perfectly tenable view, but the uncertainty as to the
morphology of the Cordaianthus catkin leaves everything
in doubt.
Prof. Sahni further discusses the relation of Cordaiteae
to the Pteridosperms, dwelling especially on the important
’ differences between the two groups, both in the fructifica-
tion and the foliage. He distinguishes between Phyllo-
sperms, with leaf-borne seeds (including Pteridosperms
and Cycads) and Stachyosperms, with stem-borne seeds
(including Cordaiteae, Ginkgoales, and all Conifers). It is,
however, by no means certain that this distinction holds
good. In Cordaiteae, as we have seen, the evidence for
the axile nature of the ovular pedicel has been shaken.
In Coniferae, if we adopt the placentar interpretation of
the ovuliferous scale, the seeds are leaf-borne, not stem-
borne.
The comparison of the female inflorescence with that
of the Gnetaceae seems to rest on a very weak basis.
There is no longer any ground for believing that the
1 See Sahni, ‘‘ On the Structure and Affinities of Acmopyle Pancheri,’’
Phil. Trans. R.S. Ser. B. vol. 210, 1920, p. 296.
314 STUDIES IN FOSSIL BOTANY
ovule of Cordaiteae had two integuments, still less is
there any indication that the two were of a different
morphological nature, as appears to be the case in
Gnetaceae. It is possible that the affinities of the
Gnetaceae may he in quite a different direction, namely,
in that of the Mesozoic Bennettitales (see Chapter V.).
The structure of the seeds which are known to have
belonged to Cordaiteae is altogether Cycadean, and, as
we have seen, even minute details, such as the form of
the pollen-chamber, can be exactly paralleled among
recent Cycads. These facts, together with the foliar
structure, appear to prove conclusively a real affinity
between the two families, though in other respects they
diverged widely from one another. But just in the
points where there is a strong agreement with Cycadaceae
(with Bennettitales the relation, as regards the seed-
structure, is much less close) the Pteridosperms are like-
wise approached. The anatomical characters, together
with the seed-characters and those of the multicellular
pollen-grain, show such manifest correspondence, that
there can scarcely be a doubt that Cordaiteae sprang
from the same stock with Pteridosperms, though at a
very remote period. The characters which they share
with the Cycadophyta are no doubt due to a common
origin rather than to any direct connection in later
periods.
Returning for a moment to the anatomical characters,
it may be pointed out that the general structure of
the leaf in Cordaiteae agrees so closely in essential points
with that of Poroxylon, that we can scarcely doubt that
the two groups were nearly allied. Poroxylon retained
centripetal wood in the stem, a primitive character
which some of the Cordaiteae had lost. The Poroxyleae
appear thus to combine the characters of Lyginopterideae
or Calamopityeae with those of Cordaiteae, though their
horizon is too late for us to regard this family as an
actual link with the Pteridosperms. The Pityeae belong
7
AFFINITIES OF CORDAITEAE 315
to the earliest Carboniferous times, and recent work has
shown that they formed a distinct group.
The affinities of the Cordaiteae and of the Cordaitales
generally are, as we have seen, extraordinarily complex,
and cannot be cleared up until our data are much more
extensive than at present. The great step which has
been made in the last few years is the full confirmation
of the affinity between Cordaitales and the Pteridosperms,
which the discovery of the seeds of the latter class has
afforded. The relations to Cycadophyta, Ginkgoaceae,
and Coniferae have long been recognised, and thus a
strong presumption is established that the whole of the
Gymnosperms sprang originally from the same ancient
stock (see Chapter VI.).
CHAPTER. WV.
THE MESOZOIC GYMNOSPERMS
I. CYCADOPHYTA
Our studies have so far been almost entirely limited
to plants of Palaeozoic age; in order to carry out our
plan of directing attention to discoveries ‘of fundamental
botanical importance, we have now to give an account
of the Mesozoic Cycadophyta, a group among which
some of the greatest triumphs of Palaeobotany have
been won.
From the Trias onwards to the Lower Cretaceous,
the Mesozoic vegetation maintained, on the whole, a
very uniform character, widely different from that of
the preceding Palaeozoic period. Throughout the earlier
Mesozoic ages true Ferns were abundant, more so, no
doubt, than in the preceding period; Conifers, often
much resembling recent types, had become a dominant
group, and the family now represented solely by the
Maidenhair tree (Ginkgo) was of considerable importance.
The most striking feature of the vegetation, however,
in all parts of the world, was the abundance of plants
belonging to the same great class with the recent Cy-
cadaceae, now so limited a group. The Cycadophyta,
in fact, were as characteristic of Mesozoic vegetation as
are the Dicotyledons of our present Flora. Among the
commonest remains are leaves, which in many cases
closely simulate those of existing Cycadaceous genera,
and have hence received the names Zamites, Dioonites,
316
yo
CYCADOPHYTA 317
and Cycadites. These generic resemblances, however,
are usually deceptive ; the Zamites ag@ Dioonites leaves
are now known to have belonged to plants which had
only a somewhat distant affinity with the Order
Cycadaceae, while in certain leaves once referred to
Cycadites, or even to Cycas itself, the similarity to those
of the recent genus has proved to be illusory (see below,
p. 368). In other leaf-genera, again, such as Otozamites
and Anomozamites, the foliage, while of a Cycadean
type, differs evidently from that of any of the existing
genera.! :
In addition to the leaves, fossil trunks, which present
the external characters of Cycadean stems, are of common
occurrence in the older Secondary rocks, as, for instance,
in the Wealden of Sussex and in the well-known “ dirt-
bed ”’ of the Lower Purbeck strata in the Isle of Portland,
and at other places along the Dorsetshire coast. The
stems are usually short, though they may appear shorter
than they actually were, owing to pressure of the super-
incumbent strata. The surface is usually covered by
the closely-set bases of the leaves ; the upper end of the
stem is commonly hollowed out, owing to the decay of
the growing apex. “‘ Fossil crows’ nests”’ is the name
by which such specimens are known to the Portland
quarrymen. In certain trunks from the Sussex Wealden,
named Bucklandia by Mr. Carruthers, an alternation of
the scars of foliage and scale leaves has been traced,
-such as is found in Cycas at the present day. These
stems, however, are now believed to have belonged to
Williamsomia, a group quite remote from the recent
Cycadaceae (see p. 353). In some cases the stems at-
tained a moderate height, as in bucklandia and the
Cycadeoidea gigantea of Seward, a fine specimen of which,
1 Numerous figures of the leaves of Mesozoic Cycadophyta will
be found in Seward’s Catalogue of the Mesozoic Plants in the Department
of Geology, British Museum, Parts ii.-iv. 1895-1904. See also his
Fossil Plants, vol. iii. chap, xXxxix. 1917.
318 STUDIES IN FOSSIC BOTANY
almost 4 feet high, with a girth of 34 feet, was found
some years ago in the Isle of Portland, and is now set
up in the Geological Department of the British Museum.
In favourable cases the Cycad-like stems are completely
silicified, and their structure preserved with wonderful
perfection. A number of important specimens of this
nature, referred to many species, have been found in
our own country, France, Italy, and other parts of
Europe, but the United States of America are far richer
than any other country in such material. No less than
sixty species of silicified trunks of Cycadophyta have
already been described from the Mesozoic of North
America, ranging in age from the Upper Triassic to the
Lower Cretaceous. In the Eastern States the Potomac
beds of Maryland (approximately of Wealden age) have
yielded nine species, but the richest localities are in the
West, on the Rim of the Black Hills of Dakota and the
Freezeout Hills of Wyoming ; from the Upper Jurassic
and Lower Cretaceous beds of these districts fifty or
more species have been obtained. The specimens are very
numerous; thus twenty-nine species from the Black
Hills of South Dakota were represented by nearly 1000
more or less complete trunks.?- The Cycadophyta of the
American Mesozoic rival in palaeontological value the
gigantic Saurian animals, with the remains of which
they are often associated. Fig. 116 represents the trunk
of Cycadeoidea marylandica, the first American fossil
Cycad to be discovered ; it was found about the year
1860, between Baltimore and Washington, by the geo-
logist Philip Tyson. A species from Colorado was the
first to be described; this was in 1876. Many years
1 Seward, “‘ On Cycadeoidea gigantea, a New Cycadean Stem from
the Purbeck Beds of Portland,’’ Quarterly Journal of the Geol. Soc.,
vol. liiil. 1897.
2 See Wieland, American Fossil Cycads, Carnegie Institution,
Washington, vol. i. 1906, and vol. ii. 1916, and the systematic
works by Lester Ward, there cited.
CYCADOPHYTA 319
elapsed before any further discoveries were made ; it
was not till 1893 that additional specimens came to light
in Maryland and that the rich deposits of the Black
Hills of Dakota began to be explored. In recent years
Fic. 116.—Cycadeoidza marylandica. ‘The earliest discovered American fossil Cycad. From
an original daguerreotype. Nearly thirty young fruits are marked in the present view
by the groups of bract-scars interpolated between the old leaf-bases. About } natural
size. From Wieland.
Mexico has proved to be extraordinarily rich in fossil
Cycads.
The vast majority of the Mesozoic Cycadophyta at
present investigated differ essentially from the existing
order Cycadaceae, and have been grouped under the
320 SLUDIES“IN FOSSiL. BOTANY
class Bennettitales or Cycadeoideae, which may be pro-
visionally divided into the families Bennettiteae and
Williamsonieae.
I. BENNETTITALES.—In a great number of cases,
fructifications have been found in actual connection, or
in close association, with the stems of Cycadophyta, and
it is only in the rarest instances that these fructifica-
tions have proved to be of the Cycadean type, as known
to us from its recent representatives. In an overwhelming
majority of the fructifications belonging to the Mesozoic
Cycadophyta (using that form of name, as suggested by
Prof. Nathorst, to indicate a group enormously wider
than our recent Cycadaceae), the structure of the organs
of reproduction is found to have been totally different
from anything known in the recent Order, and of a far
more highly differentiated type. The main purpose of
the present chapter is to give some account of these
plants, which formed the dominant group of Cycadophyta
in the Mesozoic period.
A. Bennettiteae
The first family to be considered is that of the Bennetti-
teae, so named from the type-genus LGennettites, founded
by Carruthers in 1868, for several species, ranging .
from the Middle Oolite to the Lower Greensand. The
characters of the genus were thus given by the author
in his classic memoir: ‘‘ Tvunk ovoid, in transverse
section elliptical, covered with the somewhat long per-
manent bases of the petioles. Medulla entirely cellular,
with numerous gum-canals. Wood consisting of a thin
interrupted cylinder of striated tissue, everywhere pene-
trated by medullary rays. Frwts borne on secondary
axes, not protruding beyond the bases of the petioles.” 4
1 Carruthers, ‘‘ On Fossil Cycadean Stems from the Secondary
Rocks of Britain,’’ Tvans. Linnean Soc. vol. xxvi. 1870.
BENNETTITES 321
The elliptical transverse section of the stem is not
generally accepted as a generic or even a specific character,
but on the whole the short description just quoted still
holds good. The American palaeobotanists use Buck-
land’s generic name Cycadeoidea in preference to Bennett-
ites, and this usage has been adopted by Prof. Seward
in his Fossil Plants.
The following account is based in the first instance
on the observations of Carruthers (who laid the founda-
tion of our knowledge of the group), Solms-Laubach,
Lignier, and others, confirmed, as regards the fructifica-
tion of Bennettites Gibsonianus, by a study of the original
preparations. The still more important results obtained
from the investigation of the American material by Dr.
Wieland have profoundly modified our conception of the
group, and will be considered in due course.
In external aspect the stems of the Bennettiteae
presented the same general appearance as those of the
recent Cycads in which the stem remains clothed in an
armour of persistent leaf-bases (see Fig. 117, B). The
"dimensions were also of the same order. The stem of
B. Gibsonianus, shown in Fig. 117, from Carruthers’
paper, attained a maximum diameter of Ir inches; a
considerable part of this diameter was made up of the
persistent leaf-bases, as shown in the figure. The
American species Cycadeoidea marylandica, represented
in Fig. 116, was of larger dimensions, and may serve as
a typical example of the external characters of the
family. The great feature in which these stems differ,
even in outward aspect, from those of any recent Cycads
is the presence of numerous short lateral branches, resem-
bling large buds, which are wedged in here and there
between the bases of the leaves (Figs. 116, 117, /)._ These
lateral appendages are the fructifications, one of which
is shown in Fig, 117, A, in longitudinal section, inserted
‘by a short stalk on the stem, and lying horizontally
between the bases of the leaves. It is probable that the
21
322 STUDIES IN FOSSIL BOTANY
position of the fructifications was axillary ; in any case
they were lateral branches, and cannot have been terminal
on the main axis, thus differing in position from the cones
Pic. 117.—Bennettites Gibsonianus. A. Stem in transverse section, showing the ring of
wood, x, surrounding the large pith, the leaf-bases, 1.b., completely covering the surtace,
and a fructification, f, seen in longitudinal section, between the leaf-bases. B. Stem
in tangential section, through the armour of leaf-bases, the vascular bundles in which
are shown. Several fructifications, f, are seen, in transverse section. Both reduced.
From the Linnean Soc. Trans. After Carruthers.
of most living Cycads. Hence, the fertile stem of Bennett-
ites appears to have had a monopodial, and not, as is
usual in the recent Order, a sympodial construction.
The main features in the anatomy of the stem were
BENNETTITES 323
worked out by Carruthers, whose conclusions have
been confirmed by the work of later investigators. The
structure is shown with special clearness in Lenmnettites
Saxbyanus, a species from the Wealden beds of Brook
Point, in the Isle of Wight (see Fig. 118). The large
pith is surrounded by a ring of wood and bast, of no
great thickness, built up, as in normal Gymnospermous
Fic. 118.—Bennettites Saxbyanus. Transverse section of stem. , pith; x, wood, ph.,
phloem, together constituting a, ring of collateral bundles; J.t., leaf-trace bundles,
passing out through the cortex, and subdividing repeatedly ; /.b., bases of leaves, which
clothe the stem. Reduced. From the Linnean Soc. Trams. After Carruthers.
stems, of anastomosing vascular bundles with collateral
structure. The histological details of both wood and
bast (which were minutely studied by Count Solms-
Laubach in an Italian species, and more recently by
Dr. Wieland in the American material) agree with the
corresponding structures in some recent Cycads. The —
tracheides are usually scalariform, as in Stangeria.
It is only when we come to the course of the bundles
324 STUDIES IN FOSSIL BOTANY
passing out to the leaves that important differences
show themselves. In recent Cycads, as is well known
to the botanical student, the course of the leaf-traces is
peculiar and characteristic. To supply each leaf, two
bundles leave the stele; they start near together, and,
curving in opposite directions, pass nearly half way round
the stem, thus entering the leaf-base on the opposite side
from their starting-points. They then subdivide, to form
the numerous bundles of the petiole. In their course
through the cortex the outgoing bundles are connected
by cross-branches with one another, as well as with other
leaf-traces, and with the bundles of the primary ring.
In Bennettites the arrangement is a far simpler one.
A single bundle leaves the ring, starting from the lower
angle of one of the meshes, which (as shown in tangential
section) are occupied by the primary medullary rays.
As the leaf-trace passes out through the cortex, it assumes
a horse-shoe form, with the concave side inwards. It
then breaks up by successive subdivisions into a number
of smaller bundles, which enter the base of the leaf (see
Fig. 118, /.t.).
In the petiole the vascular bundles arrange them-
selves in an almost closed curve, slightly open and in-
voluted towards the upper surface, as is well shown in
tangential sections passing through the armour of leaf-
bases (see Fig. 117, B).
In some Bennettiteae, as, for example, in the species
B. Peachianus, from the Middle Oolite of Sutherland,
the pith contains several isolated rings of differentiated
tissue, which at first sight suggest medullary. vascular
strands, and were at one time erroneously compared
with the central steles or “‘ star-rings’”’ of the Permian
Medulloseae.2. More recent observations leave no doubt
>)
1 See De Bary, Comparative Anatomy of Phanerogams and Ferns,
English edition, p. 608.
2 See above, Chapter III. p. 190. The statement, to this effect, in
Solms-Laubach’s Fossil Botany, p. 98, was corrected by him in his
BENNETTITES 325
that the medullary rings occurring in Lenneltites have
nothing to do with the vascular system, and consist
merely of bands of internal periderm, an abnormal
condition which is often met with in the stems of recent
Cycads.
We see, then, that the structure of the Bennettiteae,
so far as it is at present known, was a simple monostelic
one, resembling in its main features that of the less
complex Cycads now living, but differing from any exist-
ing Cycads in the simpler course of the bundles supplying
the leaves. In this latter point, the Bennettitean stem
was compared by Solms-Laubach with the peduncle of
recent Cycads, an organ which in other points also ap-
pears to show a more primitive anatomy than that of
the vegetative stem.!
In Cycadeoidea Yatesii, and another pei species,
there is evidence for the presence of two or more suc-
cessive zones of wood and bast, as in the recent Cycas
and Macrozamia.
In Bb. Gibsonianus the vascular bundles of the leaf-
bases are beautifully preserved, and show essentially
the same structure as the foliar bundles of the recent
Cycadaceae. They are of the collateral mesarch type,
whereas those of the stem are endarch; the centripetal
wood forms a mass of large elements, with a band of the
radially arranged tracheae of the centrifugal wood on
the outside. The same structure is found in various
American species, but in Cycadeoidea muicromyela, a
French species probably of Liassic age, centripetal wood
appears to be entirely absent.2, The detailed structure
of the xylem in the bundles of Bennettiteae still needs
further investigation. Beyond the wood is the phloem,
joint work with Capellini, on the trunks of Italian Bennettiteae, Mem.
hk. Accad. Sci. Bologna, vol. 1. 1891.
1 See Chapter I. p. go.
2 Lignier, “‘ Végétaux foss. de Normandie, III. Cycadeoidea micro-
myela,”’ Mém. Soc. Linn. de Normandie, t. xx. 1901.
326 STUDIES IN FOSSIL BOTANY
often well preserved, and the outer edge of the bundle
is occupied by a group of bast-fibres.
The parenchymatous tissue, both of the stem and
leaf-bases, abounds in large gum-canals, the contents
of which have often become fossilised. ‘hese. organs
closely resemble the similar secretory passages in recent
Cycads.
Between the leaf-bases, and around the fructifications
and their bracts, the spaces are densely packed with
multicellular hairs, very different from anything known
in Cycadaceae, but closely resembling the ramenta of
Ferns. The hairs are scale-like structures, one cell
thick near the margin, but reaching a thickness of from
two to five cells in their middle part (see Fig. 120,08);
The cells of which they are composed attain a great
length in the longitudinal direction of the ramentum.
The ramenta are borne both on the leaf-bases and on
the bracts, which, as we shall see, envelop the fructi-
fication. The Fern-like character presented by the
ramenta is a surprising homoplastic feature in a genus
so far advanced in Phanerogamic organisation as
Bennettites.
A stem, Colymbetes Edwardsi, Stopes, probably of
Wealden age, shows an extraordinary structure. The
large pith and the groups of primary wood are like
those of other Cycadophytes; the peculiar feature is in
the secondary wood, which consists of ten or more
successive zones, all, as it appears, the product of a
single cambium. The zones alternate, the elements
of each zone running in a direction approximately at
right angles to those of its neighbours, vertically in
the one, horizontally and tangentially in the next,
and so on. This has the curious effect that the trans-
verse and radial sections appear just alike, every alter-
nate zone being cut radially in transverse section
and transversely in radial section and wice versa. All
the zones, however, are quite continuous one with
BENNETTITES 327
another. This remarkable structure appears to be without
analogy.!
Dr. Marie C. Stopes has also described, under the
name Bennettites Scottii, the smallest known Bennettitean
stem ; the specimen (of unrecorded locality and horizon)
measures 8-5 cm. in total height and 7 = 5 cm. in diameter.
Well-preserved young fronds are attached to the axis,
the whole having a bud-like character. All the anatomical
features of the genus are shown. In the vascular bundles
of the leaves the whole of the xylem is centripetal, perhaps
on account of their youth. The ramenta (unlike those
of B. Gibsonianus) are only one cell thick. A dense
covering of hairs, distinct from the ramenta, clothes
the under-side of the pinnae. There are indications of
an abscission-layer at the base of the specimen, suggesting
that it may have been a lateral bud, detached from a
larger stem.”
The same author has further described, for the first
time, roots or rootlets attributable to a Bennettites,
probably B. Saxbyanus. The roots, about I mm. in
diameter, are traversed by a strand of scalariform
tracheides, and are clothed with long and numerous
root-hairs.®
We now come to the consideration of the fructifica-
tions themselves, and in approaching this subject we
must divest our minds of all preconceptions drawn from
a knowledge of existing Cycadean cones. The repro-
ductive organs of the Bennettitales are wholly different
in organisation, both from the cones which characterise
1 See M. C. Stopes, Catalogue of the Cretaceous Flora, Part i. p.
314, British Museum, 1915. For Cycadeoidea Yatesii, referred to
above, see p. 295 of the same volume.
2M. C. Stopes, ‘‘ Bennettites Scottii, sp. nov., a European Petri-
faction with Foliage,’ Journal of Linnean Society, Botany, vol. xliv.
1920, p. 483.
3M. C. Stopes, “‘ Roots in Bennettites,’’ Ann. of Bot., vol. xxxi.
1917, P- 257- .
328 STUDIES IN FOSSIL BOTANY
the majority of recent Cycadaceae, and from the rosette
of leaf-like carpels which forms the female system in the
genus Cycas.
The following description of the fructification is
based, in the first instance, on the species Bennettites
Gibsomanus+ of Carruthers. In this species only the
female organs are known, but, as we shall see later, the
investigation of the American material has proved that
in most cases, and possibly in all, the fructification was
hermaphrodite. We have already learnt that each
fructification is a lateral appendage, seated by a short
stalk on the main stem. The whole fruit is somewhat
pear-shaped, and about 5 cm. in extreme length.
Although fully ripe in the specimens investigated, as
shown by the condition of the seeds, the fruit is com-
pletely enclosed in imbricated bracts, which spring from
the stalk, and close in over the apex (see diagram, Fig.
120, A, and Fig. 119).
The stalk is expanded into a hemispherical receptacle,
on which all the organs of the fruit are inserted. From
the convex surface of the receptacle spring a great number
of slender pedicels, which pass vertically upwards, or
diverge slightly towards the curved surface of the fruit.
Each of these pedicels bears at its end a single erect
seed, with the micropyle directed outwards (see Fig. 119,
and diagram, Fig. 120, A). The seeds are so placed that
their micropyles meet the surface of the fruit approxi-
mately at a right angle.
The spaces between the pedicels are packed with
sterile appendages, which may be called the interseminal
scales. Towards the periphery of the fruit, in its lower
portion, the sterile organs are more numerous than else-
1 The original specimen of this magnificent fossil was found by
Mr. T. F. Gibson in 1856 or 1857 in the Lower Greensand at Luccomb
Chine, in the Isle of Wight. Part of the specimen is now at Kew, and
part at the British Museum (Natural History). A second specimen
was afterwards discovered by Dr. Leeson, of Bonchurch, Isle of Wight.
BENNETTITES
329
where, and around the base of the receptacle the former
are present alone (lig. 120, A).
All the organs of the fruit are closely packed together,
and at its periphery (?.e. immediately within the envelop-
ing bracts) the tissue
appears to be actually
continuous, forming,
as it were, a closed
pericarp, perforated
only by the micro-
pyles of the seeds (see
Fig. 120, A and D, #).
The pericarp is formed
by the cohesion of the
interseminal scales.
These organs are
dilated at their distal
ends, between the
seeds, so as to form
a continuous en®
velope, only inter-
rupted by narrow
pits, into which the
seeds exactly fit (see
Figs. 119 and 120, A,
and cf. Fig. 123). In
the lower part of the
fruit, below the region
of the seeds, the peri-
carp is formed by the
union of the outer
and shorter scales.
In order to make the
Fic.
Longitudinal
section of a fructification. 1, receptacle; br,
bracts, enclosing the fruit; s, seeds, each borne
at the summit of a long pedicel, ped.; i.s.,
interseminal scales. % about 2. From Linnean
Soc. Trans. After Carruthers.
119. — Bennettites Gibsonianus.
somewhat complicated arrangement more intelligible, we
may further quote Count Solms-Laubach’s summary :
“We have in the fructification (spadix) two kinds of
organs of different character and closely crowded to-
330 STUDIES IN. FOSSIL BOTANY
gether: the seed-stalks (cords) [our pedicels] diverging
P
KTM
2
Z
Z
A
g
Z
Z
Z
Z
g
Z
Z
Z
Z
Z
g
Z
Z
Z
Z
Z
Z|
Z
Z)
Z
Z
Z
Z
Af
All
Z
Z
g
g
Z
Z
z
Fic. 120.—Bennettites Gibsonianus. A. Diagram of the fruit, in radial section. rc, receptacle ;
br, bracts, which overlap at the top of the fruit ; s, seeds, each borne on a long pedicel,
springing from the receptacle; in each-seed the dicotyledonous embryo is indicated ;
p, dilated ends of the interseminal scales, which, in nature, are more numerous and
become confluent, forming the pericarp.
Modified, after Solms-Laubach and Potonié.
B. Ramenta, in transverse section.
,
x about 15. C. Transverse section of a seed.
1, the double-layered testa; , membrane representing the nucellus; ct, the two coty-
> y ’ ’ 5S ’ ’
ledons of the embryo: in each cotyledon the procambial vascular bundles are visible.
* about 12. S. Coll. 350. D. Somewhat oblique longitudinal section through the
micropyle of a seed.
em, radicular end of embryo; 7, apex of radicle; e, remains of
endosperm (?); m, micropyle, obliquely cut by the plane of section; 1, outer layer
of testa; p, part of pericarp: c, c, crevices in pericarp, corresponding to the limits
of its constituent interseminal scales. 20. S. Coll. 357. The original figures B,
C, and D, as well as Figs. 121 and 122, are from sections cut for Count Solms from the
type-specimen, and now in the Scott collection. (G. T. G.)
above, cluster-wise, and each terminating in a seed ;
and the interstitial organs [our interseminal scales],
BENNETTITES 331
increasing constantly in length from the periphery of
the cluster towards the inside, appearing by themselves
in the periphery, but mixed with the seed-stalks further
in, overtopping the seeds with their apices, and forming
by the union of their apices the homogeneous tissue-
laver of the surface of the fructification. In consequence
of this arrangement, every seed is sunk in a pit, the
orifice of which then narrows over the seed, owing to the
lateral outgrowth of its walls.”’ 3
This description should be compared with the diagram,
Fig. 120, A, and with the more detailed Figs. 119, 120,
ID, and 121. We will now take the various constituent
organs of the fruit, and consider their structure a little
more in detail.
The receptacle forms, as we have seen, the enlarged
termination of the axis of the fruit. The peduncle has
a structure like that of the stem, on a small scale, and
the bundles given off to the bracts divide up like those
of the vegetative leaves, though only to a small extent.
A remarkable feature in the anatomy of the peduncle
is the great development of the phloem, which much
exceeds the wood in thickness. This peculiarity, which
recurs in some of the American species, may be explained
by the great demands on the organic food-supply made
by the crowded reproductive organs, and especially by
the seeds. In the vegetative stem, however, the phloem
is also largely developed. The receptacle itself is poorly
preserved, but shows here and there sections of collateral
vascular bundles, on their way out to the appendages.
The bracts have, on the whole, the structure of reduced
foliage-leaves. Their outer surface is clothed by ramenta,
and stomata have been detected in their epidermis.*
Towards the inner surface of the bract, the mesophyll
has a fibrous structure, but the bulk of the parenchyma
1 “On the Fructification of Bennettites Gibsonianus,’’ Annals of
Botany, vol. v. 1891, p. 446.
2 C. A. Barber, in MS.
332 STUDIES IN FOSSIE SOTANY
is formed of short cells with a curious scalariform thicken-
ing on their walls. Several large gum-canals traverse
the bract, which in this species usually contains three
vascular bundles. These bundles are reduced in structure,
but near the base, where they are best developed, they
seem to be of the mesarch type usual in the foliar bundles
of Cycads.
The seed-pedicels, which are seen in great numbers
in the transverse section of the fruit (see Fig. 121), have
Fic. 121.—Bennettites Gibsonianus. Transverse section of fruit, not quite complete. b,
bracts; s, seeds, ranged in a ring around the fructification; , pedicels, belonging
to other seeds, borne at a higher level; between the pedicels the interseminal scales
can be recognised. The pericarp is the dark zone in which the seeds are embedded.
% about 3. From a photograph by Dr. Bousfield. S. Coll. 350.
an approximately cylindrical form, with their sides some-
what flattened by pressure. Through the middle of
each pedicel runs a vascular bundle, which, so far as the
preservation allows of an opinion, appears to have had
a concentric structure. Outside the vascular strand is a
well-marked bundle-sheath, succeeded by a wide cortex
1 It has been suggested, however, that the ‘‘ bundle-sheath ”’ is
really the boundary of the cortex, and that the wide surrounding zone
is wholly made up of a many-layered epidermis. Cf. p. 338.
BENNETTITES 333
and an epidermis of tubular cells, ‘The whole is surrounded
by the epidermis belonging to the adjacent interseminal
scales.
Each pedicel terminates directly in an orthotropous
seed. The xylem of the bundle ends at the chalaza in
a small disc or cup of tracheides, while the adjacent
tissues of the pedicel pass over into the testa. The seeds
have a length of over 3 mm., not counting the micropylar
tube, and‘a diameter of nearly 2 mm. The seeds which
have been investigated were fully ripe, for each, when
well preserved, contains a large embryo, nearly filling
the cavity (see Figs. 121, s, 120, C, and 122). The testa
is made up of three layers, an inner and outer layer of
small comparatively thin-walled cells, and a middle
layer of large square or palisade-like cells, which appear
almost solid, an appearance which may be due to extreme
thickening of their cell-walls (Fig. 120, C and D).
Towards the micropyle, the middle layer of the testa
is greatly dilated, and is here several cells in thickness ;
it is surrounded by the external zone, which in this part
is very distinct (Fig. 120, D). The inner layer of the
testa forms the internal tube of the actual micropyle, —
which, however, in these ripe seeds is closed, as is usually
the case (see Fig. 120, D, which represents a somewhat
oblique longitudinal section through the micropylar end
of a seed). The distal end of the micropyle (not shown
in our figure) narrows out considerably, owing to reduc-
tion of the middle layer of cells, but appears to be some-
what dilated again at the extremity. The testa is every-
where closely adherent to the surrounding tissue of the
pericarp. In the body of the seed, the nucellus is only
to be traced as a structureless membrane (see Fig. 120,
C, ), but it is better preserved at the apex (Fig. 120, D, m).
The embryo so nearly fills the cavity of the seed
that the latter may be spoken of as exalbuminous,
though it is quite possible that here, as in most so-called
exalbuminous seeds, some slight remains of the endo-
334 SLUDIES IN FOSSIE- BOTANY
sperm persisted. The small mass of tissue marked e in
Fig. 120, D, in which the nuclei appear to be preserved,
may probably be a portion of the remaining endosperm,!
though it might also be interpreted as belonging to the
root-cap of the embryonic radicle.
The embryo is very well preserved, indeed the Bennet-
titeae afford the only cases in which it has been possible
to study the embryos of fossil plants in detail. The
embryo is a typical dicotyledonous one, with the pointed
radicle directed towards
the micropyle. The hypo-
cotyl is short ; more than
half the whole length of
the embryo is occupied by
the two thick cotyledons,
the surfaces of which are
in contact (see Figs. 120,
C, 122). Between them
the growing point of the
plumule has been recog-
nised in favourable pre-
parations (Fig: 12aZ 90a)
Fic. 122. — Bennettites Gibsonianus. Longi- The tissue of the embryo
tudinal section of seed, showing dicotyle- iS to some extent pre-
donous embryo. ¢, c, the two cotyledons ; ang
a, apex of plumule; 6, radicle. x 12, Served, and the position
er tacos by Dr. Bousfield. G£ the young vascular
bundles in the cotyledons
can be determined (see I’ig. 120, C, which represents a seed
in transverse section, passing through the two cotyledons
(ct). The vascular cylinder of the hypocotyl has also
been recognised, and its connection with the cotyledonary
bundles traced.2, The number of seeds in which the
embryo is well preserved, both in this fossil and in other
species, is so considerable as to leave no doubt regarding
1 On the possible presence of endosperm see also Wieland, American
Fossil Cycads, vol. ii. 1916, p. 141 (Cycadeoidea Wielandt).
2 Solms-Laubach, /.c. p. 440.
BENNETTITES 335
the correct interpretation of the main facts. The general
structure of the dicotyledonous embryo is in no way
surprising in a plant of Cycadean affinities, but the
practically exalbuminous character of the seed is without
example among recent Gymnosperms. Of course, in
speaking of Bennettiteae as Gymnosperms, we are
referring rather to their presumed affinities than to the
actual structure of the fruit, which comes very near to
being angiospermous.
The interseminal scales, which combine to form the
pericarp, have proved difficult to investigate, owing to
their state of preservation. In their lower part, where
they pass between the pedicels of the seeds, they are
crushed out of shape, and much disorganised, so as to
be reduced in many cases to a vascular bundle with
an irregular epidermis loosely surrounding it, the inter-
mediate tissue having disappeared. The interseminal
scales are somewhat similar in structure to the pedicels
of the seeds, but the homologies of their respective
tissues are not yet clearly understood.
The expanded outer ends of the interseminal scales
unite to form the “ pericarp,’ a dense, apparently con-
tinuous zone, starting at the base of the fruit, from the
sides of the receptacle, and extending, with increased
thickness, over the top. In its upper portion, as already
explained, it encloses the seeds, and is perforated by their
micropyles. Its external surface is furrowed, the furrows
forming a network. The pericarp, from its dense struc-
ture, has at first sight the appearance of a distinct organ
of the fruit, but, as above stated, there is no doubt that
it is in reality built up of the distal parts of the inter-
seminal scales (Fig. 120, A). The furrows thus corre-
spond to the lines of junction of the constituent scales.
The outer surface is coated by a distinct epidermis,
which extends into and lines the furrows (see Fig. 120,
D,c; cf. Fig. 123). The inner tissue of the pericarp-zone
(p) is formed of parenchymatous cells, with moderately
ce
336 | STUDIES IN FOSSIL BORANY
thick walls and abundant dark contents, perhaps in-
dicating the presence of some reserve food-substance
during life. Tangential sections of the upper part of
the fruit show the micropyles of the seeds, lying at the
angles where the limits of the constituent interseminal
organs meet. In Fig. 120, D (from a radial section),
Fic, 123.—Bennettites albianus. ‘Transverse section through micropyle of a seed and parts
of surrounding interseminal scales. mn, nucellar mass plugging micropyle: met, inner
limiting layer of micropyle tube; mf, fibrous layer; mo, outer layer of micropyle ;
pl, epidermal layer of scales, adhering to micropylar tube; /pl, similar layers of scales,
fused ; s, stone-cells of scales; cy, a crystal-cell. x about 80 (?). After M. C. Stopes.
two of the furrows marking these limits (c) are shown
close together, having been cut at a short distance from
the micropyle towards which they converged. Vascular
bundles run out into the pericarp between the seeds,
and are the continuation of those seen in the lower portion
of the interseminal scales.
BENNETTITES 337
So far as the bracts and gynaecium are concerned,
the classic Bennettites Gibsonianus may still serve as a
type of the complex Bennettitean fructification. Other
similar European examples have been described, among
which one from Normandy, called Bennettites Morieret,
and probably derived from the Gault, was fully investi-
gated by Prof. Lignier of Caen.1 The specimen is a
detached fruit, not known in connection with the stem
on which it grew. It has hence been supposed that
it may have had a longer stalk than that of B. Gibsoni-
anus, and so may have been more easily detached. The
fruit is somewhat larger than in our English species,
with which, however, it agrees in all essential points of
structure. The exceptionally beautiful preservation en-
abled Prof. Lignier to work out the details of structure
with remarkable precision.
A remarkable Bennettitean fruit from the Gault of
Folkestone has recently been described by Dr. Marie
C. Stopes under the name bennettites albianus.2, Though
only a fragment, 55x30 mm. in area, the specimen is
exceptionally well preserved. ‘The fruit, when complete,
must have been much the largest known in the family ;
it could not have been less than 70 mm. in diameter, and
the curvature of the surface in the portion preserved.
suggests a diameter of asmuchas1z0mm. The diameter
of the fruit of 6. Morierei, one of the largest previously
known, is little more than 30 mm. The number of seeds
was likewise enormous; a single transverse section of
the fragment contained 250, and it is estimated that the
total number in the complete fruit may have run into
thousands. It is probable that the form of the whole was
flatter and more cushion-like than in other Bennettiteae.
1 QO. Lignier, Végétaux fossiles de Normandie, ‘‘ Structure et affinités
du Bennettites Morierei,’”’ Caen, 1894. ‘‘ Le Bennettites Morierei, ne
serait-il pas d’origine infracrétacée ?’’ Bull. de la Soc. Linn. de Nor-
mandie, sér. 6, vol. ii. 1909.
2M. C. Stopes, “New Bennettitean Cones from the British
Cretaceous,” Phil. Trans. Royal Soc., Series B. vol. 208, 1918, p. 389.
22
338 STUDIES IN FOSSIL BOTANY
The general construction of the fruit is on the same
lines as in other species, but the terminal expansions
of the interseminal scales are more completely fused and
are composed of highly sclerotic tissue, forming a strong
and hard pericarp. In the completely fused region the
epidermis is lost, but it reappears higher up in the form
of the very distinct “ plastid-layer,’’ which is united to
the micropylar tubes of the seeds as well as to the adjacent
scales (Figs. 123 and 124, B).
The vascular strands, both of the interseminal scales
and of the seed-pedicels, are little developed. In the
latter the wide apparent “‘ cortex”’ is regarded by the
author as representing a many-layered and lacunar
epidermis of tubular cells, possibly forming a spongy
water-holding tissue, compensating for the scanty vascular
supply. The base of the seed is embedded in an aril-
like cup, formed by the tubular cells; they are reduced
to a single layer above, where they constitute a kind of
cupule round the seed (Fig.°124, A).
The seeds are small and slender, not more than 1:2 mm.
in diameter ; the apex usually has five ribs. Inside the
cupule there is a “ deliquescent layer’ of a transitory
nature, while the integument proper consists of three
layers, the outer stony and square-celled, the middle
stony and fibrous, and the inner thin-walled. The same
layers can be recognised, in a modified form, in the micro-
pylar region (Fig. 123). The vascular supply is provided
by a single, very small strand, which dies out in the
base -of the nucellus (Fig. 124, B). The micropyle is
plugged by an outgrowth from the nucellus; a cavity
in the plug probably represents the pollen-chamber
(Fig. 124, B). The seeds appear to be without endo-
sperm; the usual dicotyledonous embryo is present, but
the hypocotyl and radicle are relatively more massive
than in other species.
As Dr. Stopes points out, there is no evidence for the
presence of two integuments in the Bennettitean seed,
BENNETTITES 339
Neither does the plugging of the micropyles in the ripe
fruit afford any presumption of parthenogenesis, as
I'1c. 124.—Bennettites albianus. A. Restoration of seed, enclosed in its ‘‘ cupule ’’ of tubular
cells (not all shown) extending from the seed-stalk. R.Ap., ribbed apex; st, stalk.
B. Restoration of seed and adjacent scales in median longitudinal section. int, integu-
ment of seed: d, ‘‘ deliquescent layer”: ft, tubular cells of ‘ cupule’’; m, nucellus ;
mn, nucellar plug in micropyle; e, embryo; st, seed-stalk; v, its vascular bundle,
dying out in base of nucellus; F, region of fusion of interseminal scales with micropyle
of seed; sc, interseminal scale; iv, vascular strand of scale; ep, lateral epidermis
of scale ; pl, upper epidermis, running also round micropyle-neck. After M. C. Stopes.
Lignier supposed. The micropyle may well have been
open at the pollination stage.
340 STUDIES INS FOSSIL BOTANY
The hard and massive fruit of B. albianus represents
the culminating point of differentiation in this respect,
among the known Bennettiteae. The Gault is a late
horizon for the family, which may then have reached its
extreme development, as it approached extinction.
It is, however, to the investigation of the magnificent
American material that the remarkable progress during
the present century in our knowledge of Mesozoic Cycado-
phyta is principally due, and some account of the chief
results attained must now be attempted.
As regards habit, the American, like the contemporary
European Bennettiteae, seem to have been plants of no
great stature ; there is no evidence at present for trunks
of a height of more than Io or 12 feet, while the great
majority of the stems were quite short, like that shown
in Fig. 116. In some cases the stems were nearly spheri-
cal; often several are connected together as branches
of the same stock. In seeking analogies among recent
Cycads we must therefore go to the shorter-stemmed
genera, such as Bowenia or Stangeria, or certain Macro-
zamias, rather than to tall plants like Microcycas and
various species of Cycas and Dioon.
So far as the foliage and the external features of
the trunk are concerned, the remarks made at the begin-
ning of the chapter apply to the American as well as to
the European forms. The latter are now included by
their investigators in Buckland’s genus Cycadeoidea
(synonymous with Bennettites of Carruthers); a new
genus, Cycadella, founded by Lester Ward for a number
1 The name Cycadeoidea has been employed by some European
writers for trunks of the Bennettitean type without fructifications,
as in the case of Prof. Seward’s Cycadeoidea ingens. In discussing
the American species I follow the usage of the palaeobotanists of that
continent, employing the name Cycadeoidea throughout. Prof. Seward
has recently adopted the name Cycadeoidea in preference to Bennettites
for the whole group. See his Fossil Plants, vol. iii. p. 370. This is
the consistent course, but, in agreement with Dr. Wieland’s practice,
the familiar name Bennettites is here kept up for the European species.
CYCADEOIDEA 341
of dwarf stems, from the Jurassic of Wyoming, dis-
tinguished by their abundant ramental covering, has
since been merged in Cycadeoidea by Dr. Wieland.
Anatomically, the American stems so far investigated
agree wonderfully closely, often down to the most minute
detail, with the European species of Bennedttites. It is,
however, quite probable that when the investigation of
the vast material has proceeded further, more variety
may be found. As regards the form and structure of
the leaves of the Bennettiteae, our first information came
from Dr. Wieland, who in various specimens succeeded
in finding the young leaves still folded in the bud and
preserved in great perfection. His observations were
originally made on Cycadeoidea ingens, a species in which
he estimates the length of the mature leaf at about
10 feet, and on C. (Cycadella) ramentosa, a much smaller
plant, so that both the later and the earlier types are
represented. It is sufficient, without going into details,
to say that Dr. Wieland’s investigations show that in
form, prefoliation, venation, and anatomical structure
these leaves show a close agreement with those of recent
Cycads of the suborder Zamieae ; the vascular bundles
were collateral and mesarch, without radial arrangement
of the centrifugal wood or phloem. Speaking especially
of Cycadeoidea ingens, Dr. Wieland says: ‘“‘ Were one to
adjudge the taxonomic position of the fossil species on
the basis of its foliage only, one might, bearing in mind
the general absence of scale-leaves, place it near Macro-
zamia or Encephalartos.’’1 The leaves of C. vamentosa
only differ in details; the structure of the-pinnules is
found to be almost identical with that in the recent
Bowenia.* This close correspondence in foliar characters
with the recent Cycadaceae is the more remarkable when
we consider how totally the two groups differed in their
reproductive organs, the organisation of which was first
fully revealed by Dr. Wieland’s researches.
1 American Fossil Cycads, vol. i. p. 94. A Le. pi TOL,
342 STUDIES IN FOSSIL BOTANY
The European specimens had yielded scarcely any
information as to the nature of the microsporangiate
organs of the Bennettiteae. In an Italian species,
Cycadeoidea etrusca,: bodies interpreted as pollen-grains
were discovered by Count Solms-Laubach in the interior
of a fructification, lying in the space between the apex
of the ovuliferous receptacle and the surrounding bracts.
Though, owing to bad preservation, the stamens were
not detected, the inference was drawn that they were
probably borne in the same fructification with the ovules.
This suggestion has been completely confirmed by the
investigation of the perfectly preserved specimens which
have since come to light in America.
The male sporophylls of the Bennettiteae were first
discovered in 1899, in the Dakota species Cycadeoidea
ingens, already referred to;* their relation toygiie
gynaecium was established two years later, in the same
species, when the organisation of the hermaphrodite or
bisexual flower was described for the first time.? Numer-
ous trunks with bisexual fructifications, belonging to
various American species, have now been investigated.
The fructifications were borne laterally on the stem,
precisely in the same way as those of bennettites Gibsoni-
anus and other European forms, which were probably
also bisexual (see p. 321). The plant bore a consider-
able number of fructifications at the same time (see Fig.
116); on a single specimen of Cycadeoidea dacotensis
sixty-one fruits, all more or less at the same stage of
1 The specimen was found on an Etruscan tomb at Marzabotto near
Bologna ; Capellini and Solms-Laubach, “ I tronchi di Bennettitee dei
Musei Italiani,’ Mem. d. R. Accad. delle Sc. dell’ Ist. di Bologna, series v.
vol. ii. 1892. Dr. Wieland, who reinvestigated the fructifications and
found some further remains of structure, compares them with those
of the Cycadella species. See his “ Historic Fossil Cycads,"” Amer.
Journal of Science, vol. xxv. February 1908, p. 93.
2 Wieland, ‘‘ A Study of some American Fossil Cycads, Parti. The
Male Flower of Cycadeoidea,”’ Amer. Journ. Science, vii. 1899.
83 L.c. Part iv. ‘‘On the Microsporangiate Fructification of
Cycadeoidea,”’ Amer. Journ. Science, ‘xi. IQOI.
CYCADEOIDEA 343
development, were counted, and Dr. Wieland is inclined
to think that the plants were
‘monocarpic,’ fruiting
once for all and then perishing, as is the case with many
Palms and Bamboos at
the present day. This
opinion has been much
strengthened by his
later work, to which we
shall refer.
The structure of the
bisexual fructification
or “ flower,’ as it may
be appropriately called,
will first be described in
the case of Cycadeoidea
dacotensis, one of the
species most fully in-
‘vestigated. It may,
however, be said at
once that few important
differences in the floral
morphology of the dif-
ferent species have been
detected. Some recent
observations will be
mentioned below.
The whole fructifi-
cation has a length of
about 12 cm., protrud-
ing somewhat beyond
the leaf-bases of the
imme, (See the tre-
stored section shown
in Fig. 125.) About
Fic. 125.—Cycadeoidea dacotensis. Median longi-
tudinal section of a bisexual flower. The
peduncle, with the surrounding leaf-bases and
bracts, is drawn from one section ; the ovulate
cone and microsporophylls are drawn from
several other sections of similar strobili. s,
the incurved microsporophyils; 0, the ovu-
liferous cone; a, eroded outer border of the
armour and bracts, forming the trunk-surface ;
vy, Tamenta between outermost bracts and
adjacent leaf-base ; /, leaf-base; c, cortex of
trunk ; ¢, bundles supplying peduncle. About
2 natural size. From Wieland.
half this length consists of the stout peduncle, which
bears 100 or more spirally arranged bracts on its upper
part. The centre of the flower is occupied by the ovu-
344 . STUDIES IN FOSSIL BOTANY
liferous receptacle, about 4 cm. in height, terminating
the peduncle, as in Bennettites Gibsonianus (cf. Fig. 120,
A). InC. dacotensis, however, the form of the receptacle
is much more acutely conical, and the stage of develop-
ment, in the present case, is a far earlier one, minute
Fic. 126.—Cycadeoidea dacotensis. Longitudinal section through the summit of an un-
expanded bisexual flower. In the middle is the upper part of the ovuliferous cone,
showing the zone of ovules and interseminal scales and the terminal tuft. To the right
and left the compound stamens are seen, with their tips unfolded parallel to the sides
of the central cone. The upper curved portion of each stamen is missing (cf. Fig 125, s).
The pinnae, each bearing a series of synangia, are cut longitudinally. On the outside
of all are the bracts. X 2. Froma photograph. After Wieland.
immature ovules taking the place of the ripe seeds of
the specimens previously described.
The stalked ovules and and interseminal scales here
form a layer only 1°5 mm. in height (see Fig. 126, where
this zone is better shown), whereas in the mature, seed-
bearing condition these organs have grown to at least
ten times the length. We have, in fact, at the stage
new under consideration, to do with a flower, while the
CYCADEOIDEA 345
fructification, described above, in Benneltites Gibsonianus
and other species, was already a /rwit. The receptacle
bears ovules in its middle region; the base and apex
are sterile, and clothed only with the barren interseminal
scales, which at the apex are prolonged into a tuft
(Fig. 126). The details of structure of the ovules at this
stage have not yet been made clear.
Surrounding the ovuliferous cone, and enclosed by
the bracts, is the whorl of compound microsporophylls
which forms the most striking feature of the flower.
The microsporophylls, or stamens, are numerous, number-
ing from eighteen to twenty in C. dacotensis, and are
ranged ina single verticil ; they are inserted hypogynously,
below the base of the gynaecium (see Fig. 125), and their
stalks are united to form a continuous sheath (the “ disk ”’
of Wieland), like the monadelphous stamens of a Mallow
(see diagrams, Figs. 127 and 128). The connate sheath
extends up to about the height of the top of the gynaecium ;
at this level the stamens become free from each other :
they are large and complex structures about 10 cm.
in length, if straightened out; they are always found,
however, to be infolded in a circinate manner, the sporo-
phylls curving over towards the gynaecium, so that their
deflexed tips reach down almost to its base (see Figs.
125 and 126). Each stamen is a pinnately compound
leaf with about twenty pairs of alternate pinnae, directed
inwards from the concave side of the whole organ (Figs.
125 and 120; cf. the diagrams, Figs. 127 and 128). The
apical and basal pinnae are sterile; all the rest bear
synangia, arranged in two rows, the synangia numbering
about ten in each row in the case of the longest pinnae.
If, with Dr. Wieland, we regard each synangium as
representing a reduced pinnule, the whole sporophyll
must be called bipinnate. The stamen was thus a highly
complex organ, recalling the fertile frond of a Fern rather
than the comparatively simple type of microsporophyll
which we meet with in the stamens of the higher plants.
346 STUDIES IN FOSSIL BOTANY
The elaborate organisation of the whole flower is well
shown in the diagrammatic figures 127 and 128, drawn
by Dr. Wieland to represent the flower in an expanded
condition. These diagrams are based on the species
Cycadeoidea ingens, in which the number of stamens 1s
less than in C. dacotensis. It will be noticed that the
arrangement of the parts is just the same as in a typical
Fic. 127.—Cycadeoidea ingens. Restoration of an expanded bisexual flower in longitudinal
section, showing the central ovuliferous cone, the hypogynous whorl of pinnately com-
pound stamens, bearing numerous synangia, and the surrounding bracts, hairy with
ramenta. About half natural size. From Wieland.
Angiospermous flower, with a central superior gynaecium,
a whorl of hypogynous stamens, and an enveloping
perianth, here represented by the bracts.
The anatomical structure of the microsporophylls
has not yet been fully investigated, but it is known
that two ranks of vascular bundles are present in the
connate disk, and that a considerable number enter each
rachis as it becomes free. The general arrangement of
———
CYCADEOIDEA 347
the bundles is compared with that in the rachis of a
Cycad leaf.
The synangia, as already mentioned, are inserted in
two rows on each pinna ; their insertion is described by
Dr. Wieland as “ sub-lateral.’” Such a position is common
Fic. 128.—Cycadeoidea ingens. Plan of the bisexual flower, showing the central ovuliferous
cone, the whorl of thirteen compound stamens, united at the base, and bearing synangia
on their pinnae, and a series of the hairy bracts. The diagram is about on the same
scale as Fig. 127, and shows the flower as it would appear, seen from above, if all its
parts were fully expanded. From Wieland.
on the modified fertile fronds of Ferns, where the insertion
of the sporangia on the lower surface, usual in the case
of unreduced sporophylls, is often departed from. The
shortly-stalked synangia are much broader than long,
contain two rows of loculi (Figs. 129 and 130), and closely
348 STUDIES EN FOSSIL BOTARY
resemble those of certain Marattiaceae, simulating in a
remarkable degree the stalked synangia of Marattia
Kaulfussit.1 The analogy of this species, though not
of any taxonomic significance, shows that there is no
absolute necessity to regard the pedicellate synangia of
the Bennettiteae as representing distinct leaflets.
The form of the synangia in Cycadeoidea is somewhat
ae Yh)
ioe | - \
‘f
WD
é > *. =
(ee. =e
O7) QERVZ Be
=
<0) 10/4) 9) @ eM J
CEL OCR;
ar i ,
SS wi Li
ee “Sas
Cp,
SD A
PPAR ae
Gating ny
Ins
VB
Fic. 129.—Cycadeoidea dacotensis. Transverse section through rachis of a sporophyll and
adjacent synangia. The middle and lower synangia are cut transversely, the upper
very obliquely. The palisade-layer, walls of the loculi, and spores are all shown.
x about 25. From Wieland.
affected by their crowded arrangement in the limited
space afforded by the infolded sporophyll (Fig. 129).
The synangia shown in Fig. 129 are for the most part
cut transversely, showing the full number (20-30) of the
loculi, while Fig. 130 represents a single synangium cut
longitudinally through the short stalk, in a plane at
right angles to the rows of loculi, so that two loculi only
are shown. The exterior of the synangium is formed by
a well-developed palisade-layer, thickened near the base
1 See Christ, Farnkrduter der Erde, p. 359, Fig. 1129, 1897.
CYCADEOIDEA 349
(Fig. 130) ; this is lined by a layer of small, thin-walled
cells, which also form the inner walls of the loculi (Fig.
129). In dehiscence the two rows of loculi appear to
have split apart, the synangium thus opening by two
valves, while the individual
loculi dehisced by longitudinal
slits (Figs. 129 and 130). If
this was the case, the resem- Ye
blance to Marattia extended to GI
the mode of dehiscence. Yi Wry =
The microspores or pollen- —DWi7i
grains have been carefully ex- COTES
Q
Ss.
a
Ws
amined by Dr. Wieland, but Ske
without finding any decisive = il iy? WS
proof of the presence of an- Si! Y : HS
theridial cells. In size the ayy? dt R LS
microspores are intermediate Sy 8 Kt 1S
between those of Cordaiteae A 5 =
and recent Cycads. Sh, ey
Although, as already men- I) =
tioned, the structure of the 5 =
flower in both American and S =
European Bennettiteae appears ZB =,
to have been comparatively Yr oe
uniform, some new points of . .
2 ; Fic. 130.—Longitudinal section of a
interest have been raised by
synangium, showing short stalk
. ’ attaching it to rachis. The
Dr. Wieland’s later observa- Behe ob ae aah net
tions.! of the wall is shown; also two
loculi, in longitudinal section,
In a flower-bud referred to containing some pollen - grains.
; ; Dehi s to have be-
Cycadeoidea colossalis, Ward, api Stak ter ag
gun. xX 40. From Wieland.
Dr. Wieland finds that each
of the ten stamens bears at the back two prominent
flat wings or crests which appear to have extended to
the apex of the flower, forming collectively a kind of
1 See his American Fossil Cycads, vol. ii., ““ Taxonomy,’’ Carnegie
Institution, Washington, 1916.
350 5 PUDIEAIIN POSSIE, BOTAN
domed summit. This curious complication of the struc-
ture may also have occurred, in a certain degree, in
other species. The sterile region of the staminal rachis
was immensely developed in the case of C. colossalis,
leaving a rather limited space for the fertile part, bearing
the synangia.!
The question has arisen, whether all Bennettitean
flowers were functionally bisexual or whether monoecism,
by abortion of one or other organ, may not have occurred
in certain cases. The best evidence for the latter condi-
tion was found by Dr. Wieland in Cycadeoidea Jenneyana,
Ward. Here, in a very immature flower-bud, there were
thirteen stamens, bearing large synangia already nearly
mature. The central receptacle was much elongated,
ending in a point, and bore only a very thin ovulate zone,
the female organs being so small as to suggest abortion.
In a relatively mature ovulate cone on the same stem,
with a hemispherical receptacle, the seeds were large
enough to have contained embryos, while the pedicels
and interseminal scales were well developed. The line
of insertion of the hypogynous staminal disc appeared
as if completely grown over, and Dr. Wieland infers that
it could never have been much developed. He regards
this as ‘‘a clear case of Cycadeoidean monoecism.” ?
The evidence, however, hardly seems to be decisive, for
the differences between the two fructifications may after
all be due merely to age. Other cases are less clear,
but there is no doubt a possibility that monoecism may
have occurred.
Some of the American species of Cycadeoidea belong
to the same group as the British bennettites Gibsonianus,
as shown by the shortened, cushion-like receptacle and
other characters. In some of these the bisexual char-
acter of the flower has been demonstrated, so that there
is a strong presumption that the same was the case in
B. Gibsonianus, the absence of stamens in the specimens
1 See Wieland, /.c. p. 70. 2 Wieland, /,c. p. 41.
- ee
CYCADEOIDEA 351
observed being simply due to the maturity of the fruit
at the time of fossilisation. In many of the American
fructifications, both young and old, where the stamens
were not preserved, Dr. Wieland was able to detect the
remains of the staminate disk seated on the rim of the
receptacle. Prof. Seward points out that in b. Gibsoni-
anus there is no indication of any similar remnant of
a whorl of microsporophylls, and finds it difficult to
believe that any such fertile leaves ever existed.1 The
negative evidence, however, seems to carry little weight.
One cannot expect always to be able to detect the
remains of stamens in a ripe fruit, especially in a fossil
one.
So far as the Bennettiteae are concerned, the evidence
appears to be overwhelming that the flowers generally
were morphologically bisexual, and that monoecism, if
it ever occurred, was due to the arrested development
of organs already present in the bud.
Direct proof of the occurrence of bisexual flowers in
European species is not wanting. In a magnificent fossil
Cycad, now named Cycadeoidea Reichenbachiana, prob-
ably of Lower Cretaceous age, preserved in the Zwinger
Museum at Dresden, and found as long ago as 1753 near
Cracow, Dr. Wieland has demonstrated in some of the
flowers the presence of a staminal disk, which in this
case consists of sixteen stamens. They appear to be
well preserved, though sections have not been cut. The
ovulate cones are also present, but Dr. Wieland leaves
open the question whether the flowers were functionally
bisexual throughout or partly monoecious.” The floral
structure appears to agree in all essential respects with
that of the American species, C. dacotensis.
In a British species, Bennettites maximus, Carr, from
the Lower Greensand of the Isle of Wight, Dr. Marie C.
Stopes has found extremely young fructifications, in
1 Fossil Plants, vol. ui. p. 395.
2 See Wieland, /.c. p. 123.
352 STUDIES“IN- FOSSIL’ BOTANY
which she was able to demonstrate the presence of a
whorl of fourteen organs, no doubt the male sporophylls,
surrounding the central receptacle; the latter is of a
flattened form and bears the immature ovules. These
flower-buds appear to be the youngest which have yet
been investigated in the family, and so far afford the
only example in a British species of the preservation of
the bisexual stage.
From the comparison of younger and older stages
of the flower (as, for example, in Cycadeotdea dacotensis)
it is evident that as the fruit matured, the expanding
gynaecium encroached on, and ultimately filled, the space
originally occupied by the whorl of stamens. It has
sometimes been maintained that the flowers of the
Bennettiteae were proterandrous, the pollen being ripe
before the ovules were ready for fertilisation; as we
know practically nothing of the structure of the ovules
at the fertilisation stage, there have never been any
good grounds for this supposition. A recent observation
of Dr. Wieland’s seems, in fact, to point in the opposite
direction.
In describing a young flower-bud of Cycadeoidea
Painei, he says: ‘“‘ Although the ovulate outlines appear
early, the initial synangial growth is late.”’* Thus, in
this case, the ovules seem to have preceded the pollen-
sacs in their development.
The probable “‘monocarpy ” of some of the Bennett-
iteae has already been noticed (p. 343). The term is
applied to ‘“‘Seed-plants which fruit once only in the
normal life-time and then die down.’’? T[‘ive species of
Cycadeoidea are regarded by Dr. Wieland as more or less
)
1M. C. Stopes, ‘‘ New Bennettitean Cones from the Lower Cre-
taceous,” Phil. Tvans. Royal Soc. Series B, vol. 208, 1918.
2 G. R. Wieland, ‘‘ A Study of some American Fossil Cycads: VIII.
Notes on Young Floral Structures,’ American Journal of Science,
vol. xlvi. 1918, p. 645.
3G. R. Wieland, ‘“‘ Monocarpy and Pseudo-monocarpy in the
Cycadeoids,” American Journal of Botany, vol. vill. 1921.
ee 0- . eee i Bee
CYCADEOIDEA 353
completely monocarpic. The best example is the great
Hermosa Cycadeoid (C. Dartont), in which the specimen
consists of the upper half of a trunk, originally about
a metre in height. The remaining portion is wonder-
fully preserved, and the armour is packed with mature
fruits, of which there are not less than five hundred,
practically all with ripe embryos. A few may have been
abortive, but the specimen strongly suggests that the
plant was fruiting all over, and once for all, especially
as the leaves at the apex are small and rudimentary,
as if the plant were moribund. This wonderful specimen,
perhaps the most striking fossil plant known, was found
at an isolated locality in S. Dakota.?
The family Bennettiteae is characterised by relatively
short, thick stems, densely clothed with leaf-bases,
Cycad-like foliage, and lateral flower-buds, the flowers
bisexual, or perhaps sometimes monoecious by abortion,
enclosed in bracts; the androecium consisting of a con-
nate whorl of compound stamens, the gynaecium of
numerous erect, stalked ovules intermixed with inter-
seminal scales; the seeds exalbuminous or nearly so.
Fertilisation was no doubt of the Gymnospermous type,
for the micropyles are exposed ; whether it was effected
by motile spermatozoids or otherwise must remain an
open question.
B. Williamsonieae
Many years before the existence of such a family
as that of the Bennettiteae was even suspected, certain
remarkable fossils were described from the Lower Oolite
of the Yorkshire coast, under the name of Zama gigas.”
The fullest account of these fossils is that presented by
1G. R. Wieland, American Fossil Cycads, vol. ii. chap. vii.
2 Lindley and Hutton, Fossil Flora of Great Britain, 1830. Originally
figured by Young and Bird, Geological Survey of the Yorkshire Coast,
1822.
23
354 SPURIES: IN FOSSIE BOTANY
Williamson to the Linnean Society in 1868. Our Fig. 131
(from Williamson’s memoir) represents the plant in a
restoration which has been proved by more recent in-
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Fic. 131.—Wdulliamsonia gigas. Williamson’s original restoration of the plant, showing
the upright stem, with rhomboidal leaf-scars, the crown of Zamia-like leaves, and the
scaly, spherical fructifications. From the Linnean Soc. Trans.
vestigations to be essentially correct. Mr. Carruthers,
in his paper on Cycadean stems above referred to, estab-
lished the genus Williamsonia for the reception of Zamia
SS ee ee
WILLIAMSONIA 355
gigas and allied forms, and this name is the one now
used.
The various organs of the plant are, as usual among
fossils, almost always found separately. They consist
of the large Zamia-like leaves (from which the old generic
name was taken), portions of the stem, covered with the
rhomboidal leaf-scars, and lastly the fructifications, with
the long scaly stalks on which they were borne. William-
son pieced these various parts together, as shown in his
restoration, and Brongniart confirmed his conclusions,
but other authorities entirely rejected them, regarding
the fructifications as those of Monocotyledons, and as
having nothing to do with the Cycadean foliage or stem.
Williamson’s view proved to be the correct one, and his
plant has turned out to represent an important family.
The fructification of Williamsonia gigas is in size and
appearance something like a common artichoke, and
was borne at the end of a Jong stalk, 20 or 30 cm. in
length, covered with spirally arranged scale-leaves. The
exterior of the globular fructification was formed by
the overlapping, involucral bracts. No petrified speci-
mens of this. species are known. Consequently, the
organisation is difficult to explain, and has given rise
to some interpretations, more ingenious than probable,
which cannot be discussed here. The established facts
appear to be that the ovulate cone had essentially the
same structure as in Bennettiteae, but probably had a
sterile apex or corona, comparable to that of William-
somella described below (p. 361). The gynaecium was
surrounded by bracts, the whole flower-bud attaining a
great size (4? inches in diameter, for example).
A male flower or disk, probably referable to this
species, has been described by Mr. H. Hamshaw Thomas.
It is still uncertain whether the ovulate cone and the
1 Williamson, “‘ Contributions towards the History of Zamia gigas,”’
Linnean Society’s Transactions, vol. xxvi. (published 1870) ; Carruthers,
l.c., in same volume.
356 STUDEES' IN POSSI bora
staminate disk formed parts of the same flower, or the
sexes were separate, but the balance of evidence seems
to incline to the conclusion that the flowers were uni-
sexual.! |
Prof. Seward and others, from the study of a York-
shire specimen in the Yates collection now at Paris,
have proved conclusively that the Williamsonia flowers
and the Zamuites leaves were borne on the same stem.
The leaves and floral peduncles are shown in connection
with the axis.”
The investigations of Nathorst, Halle, and Thomas
have brought to light various other species of Wrlliam-
sonia from the Oolite of Yorkshire. Male and female
organs are found separate, among the foliage, and have
been referred to different species. A staminate flower
of W. spectabilis, Nathorst, as restored by Mr. Thomas,
is shown in Fig. 132, and probably gives a faithful repre-
sentation of this type of androecium. It is, in this case,
of the same general type as the staminate disk of the
Bennettiteae. The microsporophylls are fused below into
a cup-shaped tube; above, they become free and bend
inwards. The free limbs are pinnate, and the slender
pinnae bear the synangia. The pinnae are said to have
sprung from the midrib and not from the margins of the
sporophyll. No bracts are present, unless, indeed, they
were completely adherent to the whorl of stamens. In
another Yorkshire flower, W. whitbiensis, described by
Nathorst, the microsporophylls appear to have been
simple, each bearing two parallel rows of synangia.
The female cones are in all cases of the Bennettitean
type; some are sufficiently well preserved (in a car-
bonised state) to show clearly the micropyles of the
1H. H. Thomas, “‘ On some new and rare Jurassic plants from
Yorkshire: the male flower of Williamsonia gigas,’’ Proc. Cambridge
Phil. Soc. vol. xviii. p. 105, 1915.
2 Figures of the critical specimen will be found in Wieland, American
Fossil Cycads, vol. ii. Fig. 64, A, and Seward, Fossil Plants, vol. iii.
Fig. 541.
WILLIAMSONIA 357
seeds among the interseminal scales—as in W. Leckenbyi,
Nathorst.
Williamsonias have been described from most parts
of the world. In the island of Sardinia British species
have been recognised. India and Mexico are countries
peculiarly rich in such fossils. From the province of
Oaxaca, in the south of Mexico, Dr. Wieland has made
magnificent collections, including many Williamsonian
fructifications, closely associated with the Cycad-like
y VL
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Wipes
ae Ni
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Fic. 132.—Williamsonia spectabilis. Restoration of an almost mature male flower, showing
the connate sporophylls, with pinnae bearing synangia. Slightly reduced. After
H. H. Thomas.
foliage, and sometimes with the stems.! The flora is
of Liassic age. The female flowers and fruits, enclosed
in bracts and sometimes borne on a slender stalk, are
frequent. The structure is sufficiently preserved to
prove that the gynaecium was essentially like that of
Bennettiteae, often with a considerable sterile region
of scales only at the base, and sometimes with a sterile
apex. Dr. Wieland says that in none of the forms can
1 See his fine memoir (in Spanish), La Flora liasica de la Mixteca
Alta, Instituto Geologico de Mexico, 1916, with Atlas of 50 plates.
The chief results are incorporated in American Fossil Cycads, vol. il.
358 STUDIES IN FOSSIL BOTANY
it be definitely determined whether an hypogynous
staminate disk was present or not.
The most important specimen for the androecium is
found in Williamsonia mexicana, the famous ‘“ El Con-
suelo Cycad.’’ Here the staminate disk is bell-shaped
and about 5 cm. in total length. The greater part is
completely connate, the free limbs of the sporophylls
being only about a centimetre in length. They are
perfectly simple, and each bears two rows of synangia,
one on each side of the rachis. Dr. Wieland describes
the stamens as “‘ simply pinnate ”’ ; this is on the assump-
tion that each synangium represents a pinna, which may
or may not be the case. On any view the microsporo-
phylls of this species are remarkably simple compared
with those of most Cycadeoideas or of Williamsonia
spectabilis, while they are comparable in this respect to
those of W. whitbiensis of the Yorkshire coast. It is
noticeable that this simple type of male apparatus occurs
in a relatively early representative of the group.
Throughout the genus Williamsoma we find little
evidence of bisexual flowers; male and female organs
generally occur separately, and there is thus a certain
presumption that the flowers were unisexual, especially
as it is difficult to fit the parts together on the opposite
hypothesis. One specimen, however, from the York-
shire coast, now in the Yates collection at Paris, “is
evidently from the apical synangial zone of a bisporan-
giate strobilus of the Cycadeoid type.’ ? Thus it is
possible that both conditions may have occurred within
the genus.?
1 For Figures see Wieland, American Fossil Cycads, vol. ii. Fig. 81,
A; Flora liasica, lam. xxii. and lam. xxix. Figs. 1 and 2.
2 Wieland, American Fossil Cycads, vol. il. p. 204, Fig. 80, D.
% Much of our knowledge of Williamsonia fructifications, especially
those of the Yorkshire coast, is due to Prof. Nathorst. See his
‘ Beitrage zur Kenntnis einiger mesozoischen Cycadophyten,”’ Kongl.
Svenska Vet.-Akad. Handl. vol. xxxvi. 1902, Stockholm; ‘‘ Uber
Williamsonia,”’ etc., bid. vol. xlv. 1909; “‘ Neue Beitrage zur Kenntnis
der Williamsonia-Bliten,” ibid. vol. xlvi. 191t.
WILLIAMSONIA 350
Petrified specimens referable to Williamsonia are rare ;
considerable interest therefore attaches to a cone, named
Williamsonia scotica by Prof. Seward, of which the
structure is preserved in a silicified condition. The
specimen, found at Eathie, Cromarty, was originally
described and accurately figured in its external aspect
by Hugh Miller, from whose description the following
lines are quoted: “In one of these [cones] the ligneous
bracts or scales, narrow and long, and gradually tapering
till they assume nearly the awl-shaped form, cluster out
thick from the base and middle portions of the cone,
and, like the involucral appendages of the hazel-nut or
the sepals of the yet unfolded rose-bud, sweep gracefully
upwards to the top, where they present at their margins
minute denticulations.”’ 4
The specimen has been fully investigated, by means of
sections, by Prof. Seward. Its age, regarded by Hugh
Miller as Liassic, is now believed to be much later (Upper
Jurassic), though this is somewhat doubtful. The cone
is about 11 cm. long by 6 cm. in maximum diameter.
The ‘‘ minute, denticulations’’ on some of the bracts,
mentioned by the discoverer, are interpreted by Prof.
Seward as rudimentary pinnae. A remarkable feature
of the cone is the presence of a branch, near the base.
The hairy covering consists, not of ramenta, but of simple
or branched hairs, like those of some recent Cycads.
The upper part of the axis forms the receptacle, and is
densely covered with ovules and interseminal scales ;
thus the gynaecium was of the same type as in Bennett-
iteae. The cone was at a young stage; the ovular
zone is only about 2 mm. thick. Ovules and _ inter-
seminal scales are much alike; the former, however,
are somewhat narrower and more cylindrical. Each
ovule, which is shortly stalked, is surrounded by five or
six of the polygonal scales. In the ovule the nucellus can
1 Hugh Miller, ZLestimony of the Rocks, Edinburgh, 1857, p.
480.
360 STUDTES: IN FOSSIL BOTANY
be distinguished, surmounted by the long micropylar
region, with a narrow canal.
There seems to have been no room beneath the
gynaecium for any stamens, which, if they existed, ought
to have been evident at so young a stage. There is thus
a strong presumption that the flower was unisexual.
This character favours the reference to Williamsonia
rather than to Bennettites. Neither is it likely, from the
habit of the cone, that it was ever enclosed among
crowded leaf-bases, as in the latter genus. The specimen
may be provisionally accepted as the petrified female
flower of a Williamsonia.}
We may now refer to some other genera, provisionally
included in the Williamsonian tribe. Mr. H. H. Thomas
has described an interesting new genus, Williamsoniella,?
of which the best-known species is W. coronata, Thomas,
from the Middle Jurassic (Middle Estuarine Series) of
Gristhorpe Bay, Yorkshire. The species is represented
by flower-buds, mature flowers, detached microsporo-
phylls, and female organs. Leaves and stems, belonging
in all probability to the same plant, have also been
recognised.
The flower was borne on a long stalk, and when fully
open was a little more than an inch in diameter (see
Fig. 133). It was not enclosed in bracts (though detached
bracts or bud-scales have been found), and consisted of
a whorl of twelve to sixteen free microsporophylls or
stamens, surrounding the female receptacle. Each
stamen was simple, with a marked longitudinal ridge
on the upper surface, bearing the synangia; there were
usually six of the latter, three on either side of the
median ridge. Each synangium appears to have been
1 Seward, “ A petrified Williamsonia from Scotland,” Phil. Trans.
Royal Soc. Series B, vol. 203, 1912. See also his Fossil Plants, vol. iii.
Pp. 449.
* H. H. Thomas, “ On Williamsoniella, a new type of Bennettitalean
Flower,”’ Phil. Trans. Royal Soc. Series B, vol. 207, 1915.
— eS eee
WILLIAMSONIELLA 361
partitioned into numerous loculi, containing the pollen-
grains.
The gynaecium was, broadly speaking, of the type
usual throughout the Bennettitales ; it consisted of an
elongated receptacle, bearing numerous ovules and inter-
seminal scales, closely crowded together (Fig. 133). The
most remarkable feature is that the receptacle was pro-
longed above into a
sterile summit, the
corona, with fluted
sides and sometimes
with a terminal ap-
pendage. Examina-
tion of unopened
flower-buds showed
that the fluting of
the corona was due
to the pressure of
the tips, of the
stamens before they
opened out.
The ovules pos- if |
sessed no distinct
stalks, and have
been described as
sessile; the inter-
. l l Fic. 133.—Williamsoniella coronata. Mature flower,
semina scales are showing peduncle, ovulate strobilus, surmounted
club-shaped : in the by the corona, and microsporophylls attached. x 2.
After H. H. Thomas.
mature flower the
long micropyles of the ovules project between the sur-
rounding scales.
Thus the flower of Williamsoniella was bisexual, with
remarkably simple stamens, not united to a disk, and
with a gynaecium characterised by its sterile, crown-
like summit. The question arose, to what sort of'plant
did this fructification belong? In close and constant
association with the flowers, Mr. Thomas found numerous
362 STUDIES IN FOSSIL BOTANY
leaves of the form known as Taentopteris vittata, Brongt.
—narrow, simple leaves, with a midrib and forked lateral
veins (Fig. 134). The stomata of these leaves agree
exactly in structure with those found on the stamens
of the Williamsoniella flower. Thus there is the strongest
probability that the leaves and flowers belonged to the
SN
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Fic. 134.—Wulliamsomiella coronata.
Restoration of part of the plant, showing the forked
stem, the supposed Taeniopteris foliage (upper leaves removed), and the flowers. The
central flower has shed its stamens. About half natural size. After H. H. Thomas.
same plant. Further, in association with both, portions
of forked stems were found, of a comparatively slender
form. Leaf-scars are met with on the stem, and agree
with the scar at the base of a detached leaf.
Thus Mr. Thomas has been able, with much prob-
ability though not with certainty, to effect a reconstruc-
tion of the plant in all its essential features. Fig. 134
shows the result. It will be seen at once that the habit, -
as inferred from the available data, was totally unlike
WIELANDIELLA 363
that of a Cycad or a Lennettites. The long, slender
stems, falsely dichotomous, bore scattered, simple leaves ;
the stalked flowers were probably produced in the forks.
Yet the structure of the epidermis of the Taeniopteris
leaves agrees essentially with that in the pinnate foliage
of evident Cycadophytes. Thus, Williamsoniella strongly
confirms the opinion that some of the earlier “ fossil
Cycads ”’ differed widely in habit both from the recent
Cycadaceae and from the Bennettiteae of later Meso-
ZOIC age.
Mr. Thomas’s genus has much in common with a
plant from the Rhaetic of Sweden previously discovered
by Nathorst, and named Wirelandiella angustifolia! In
this case fructifications have been found, im situ, at the
forks of the comparatively slender, branched stem. ‘The
associated leaves, probably borne in rosettes below the
points of forking, are of the Anomozamites type, 1.e. the
small frond may be entire or divided into a small number
of very unequal segments. There is thus an approach
to the simple, Taeniopteris form of leaf referred to
Williamsoniella.
As regards the fructifications, where the gynaecium
is preserved it is that of a small Williamsonia or Lennett-
ites; the micropyles of the seeds, among the inter-
seminal scales, can be clearly recognised, and bracts are
also present. In other specimens the club-shaped
receptacle is stripped of bracts, seeds, and scales, but
around the base there is a palisade-like ring, apparently
of very small sporophylls, from which pollen-grains have
been obtained. The staminal disk is thus either very
rudimentary or very imperfectly preserved. The infer-
ence is that the flowers were bisexual, morphologically
if not functionally.
The genera Wailliamsoniella and Wielandiella, so
1 See Nathorst’s memoir of 1909, above cited, and earlier papers
there mentioned. Prof. Seward has re-examined the specimens ;
see his Fossil Plants, vol. ili. p. 463.
364 STUDIES IN FOSSIL BOTANY
different in habit from the typical Cycads, have recently
been placed by Wieland in a special family, the Micro-
florae.t. The relationship to Williamsonia is, in any case,
evident.
A fructification, described by Nathorst under the
name Cycadocephalus Sewardi, is regarded with good
reason as belonging to the Williamsonian group. The
fossil comes from the Lower Rhaetic of Sweden, and is
thus an early example of the family. It is a large flower,
ro cm. long by 7 cm. broad, and consists of a considerable
number (16-18) of sporophylls, which are free from one
another except at the base. The whole is seated on a
stout peduncle. Each sporophyll bears on its inner side
two rows of appendages, one row on either side of the
midrib. The appendages are slender and about an inch
in length. They were found to contain microspores
(pollen-grains) in groups. Nathorst regarded the ap-
pendages as synangia of enormous dimensions; it is
more probable, perhaps, that they represent pinnae
bearing synangia. No trace of female organs was found.
The specimen thus appears to be a staminate flower of
the Williamsonia type, but its exact interpretation is
doubtful.?
The fossils known as Weltrichia, from the Rhaetic of
South Germany, are even more obscure, but may probably
be of the same nature as Cycadocephalus.
Little is known of the vegetative anatomy of the
Williamsonian family ; some information has, however,
been obtained by Dr. Nellie Bancroft from the study of
Indian specimens referred to Williamsonia pecten. The
stem was 5-6 cm. in diameter, and clothed with an armour
of leaf-bases. The single compact woody zone with its
narrow medullary rays is described as a characteristic
1 Wieland, “ Classification of the Cycadophyta,’’ American Journal
of Science, vol. xlvii. 1919.
* See Nathorst, “Zur Kenntnis der Cycadocephalus-Blite,” K.
Svenska Vetenskaps-Akad. Handl. vol, xlviii. 1912; Seward, Fossil
Plants, vol. iii. p. 473.
THE WILLIAMSONIAN TRIBE 305
feature. ‘‘ The Indian wood, however, shows multi-
seriately pitted tracheides like those of recent Cycads,
instead of the scalariform type usually occurring in the
fossil stems.’’ The structure of the fronds and_ their
pinnae is in general agreement with that found in the
Bennettiteae.!
Dr. Wieland lays great stress on the distinctness of
the Williamsonian tribe from the Cycadeoideas (Bennett-
iteae) and on the importance of the former. The
Williamsonia type, he points out, was the most plastic
and generalised, while the Cycadeoideae were specialised ;
they are “ the stereotyped terminal forms of a side branch
from a great plastic and dominant precursor race.’’ ?
The Williamsonian stem had, as a rule, a fairly compact
wood zone (comparable to that of Cordaiteae or Conifers)
and was normally slender and branching. On the other
hand, the robust stems of Cycadeoidea, with their thin
wood, immense medulla and heavy armour, “are excep-
tional to the point of abnormality.”’? Dr. Wieland adds
that the Cycadeoidea stems were no more characteristic
in those days than Cactus stems are now, while the small-
flowered microphyllous and plastic types (e.g. Wve-
landiella) are of far greater importance.*
Thus the Williamsonian tribe, in the wide sense, is
regarded as representing most nearly the main line of
Cycadophyte evolution, while the specialised Bennettiteae
are relegated to a lateral position. This view recognises
the fact that, on the whole, the more ancient Mesozoic
Cycads are Williamsonian, the later Bennettitean. The
separation of the Microflorae (Williamsomiella and Wie-
landiella) as a distinct family *> does not materially affect
1 Nellie Bancroft, ““On some Indian Jurassic Gymnosperms,”’
Trans. Linn. Soc. London, 2nd Series, Botany, vol. vii. 1913.
2 American Fossil Cycads, vol. 1. p. 178.
Bn Dp. SOE: 2.0. Dp. 225.
5 See Wieland, “‘ Classification of the Cycadophyta,’’ Amer. Journal
of Science, vol. xlvii. 1919. The scheme developed in this paper is too
elaborate to be reproduced here.
366 STUDIES TN. FOSSIL: BOTANY
the position, for these genera are clearly of the William-
sonian cycle, and indeed may be said to represent that
type in its most extreme and least Cycad-like form.
The geological history of the whole class is thus
summed up by Dr. Wieland. “ The Cycadeoids [1.e. the
Bennettitales as a whole] first become dominant Seed-
plants in the Lunz of Austria (Keuper) [Triassic] and so
continue to the close of the Wealden. They thus typify
the Jurassic, about equally overlapping the beginning
and close of that period. In the Rhaetic the Cycadeoids
first reach notable proportions; they culminate in
numbers in the lowermost Lias of Oaxaca and begin
to decline in the Wealden, few being left in the Upper
Cretaceous.’’ 1
2. CYCADALES.—Side by side with the Bennettitales,
true Cycadaceae, or closely allied plants, probably
existed in Mesozoic times, but the evidence for their
presence is scanty in the extreme.
Male cones, of a Cycadean type, have been recorded
under the name of Androstrobus, as, for example, A.
Nathorsti, a species from the Wealden of Sussex, described
by Prof. Seward.2 The thick axis of this cone bears
spirally arranged, more or less triangular scales or sporo-
phylls, 1 to 1-5 cm. in length. “ Towards one end of
the specimen the basal part of a scale is seen in surface
view, and on it are clearly preserved what are taken to
be the outlines of pollen-sacs. . . . The striking regularity
with which these impressions are arranged is much more
marked than in the pollen-sacs of recent Cycads. On
the lower surface of a staminal leaf of Dioon or En-
cephalartos we find, on the removal of the pollen-sacs,
a fairly distinct reticulate marking, but of much less
regularity than in the fossil.’ From the evidence of
this specimen and one or two similar fossils, it has been
1 American Fossil Cycads, vol. ii. p. 214.
* Fossil Plants of the Wealden, Part ii. p. 110.
3 Seward, /.c. p. III.
so
CYCADALES 307
inferred that male cones, not essentially different from
those of living Cycads, occurred in Mesozoic floras. The
evidence, however, is not wholly convincing, and was
considerably shaken by Nathorst’s discovery that a cone
originally described by him as Androstrobus Scotti, and
referred to Cycadaceae, was in reality a Lycopodineous
fructification with megaspores, for which he created the
new genus Lycostrobus.4
As regards female cones of the Cycadaceae, such as
are characteristic of the recent sub-order Zamieae, the
fossil evidence is unsatisfactory. Various species of
Zamiostrobus have been described ; it is quite probable
that cones of this affinity really occur in various Mesozoic
deposits, but, generally speaking, the state of preserva-
tion of such specimens is so poor that it is impossible to
distinguish them with any certainty from Coniferous
strobili of similar habit.?
We have already seen (Chapter III., p. 238) that
fructifications, possibly referable to Cycadophyta, occur
even in the Permian beds, though their true affinity is
an open question.
The recent genus Cycas differs entirely from other
members of the Order in the structure of the female
fructification. The carpels are among the most char-
acteristic of vegetable organs, and fossils resembling
1 A, G. Nathorst, ‘‘ Palaobotanische Mitteilungen. 3. Lycostrobus
Scotti,” Kongl. Svenska Vetenskaps-Akad. Handl. vol. xliu. No. 3, 1908.
2 Cf. Seward, Fossil Plants of Wealden, Part ii. p. 113. One of the
most perfect specimens attributed to the Zamieae is the Beania gracilis
of Carruthers (‘‘ On Beania, a New Genus of Cycadean Fruits from the
Yorkshire Oolites,’”’ Geol. Mag. vol. vi. 1869), which consists of an
elongated axis, bearing a number of peltate sporophylls, on each of
which two seeds are inserted. The sporophylls themselves agree
closely with those of a recent Zamia, but they are much more remote
from each other than in that genus. Prof. Seward was once in-
clined to regard Beania as more probably belonging to Ginkgoaceae
than to the Cycads, but has since modified his opinion. See Seward
and Gowan, “ The Maidenhair Tree,’”’ Annals of Botany, vol. xiv. 1900.
Also Seward, Jurassic Flora, Part i. 1900, p. 272; Fossil Plants,
vol. ill. p. 502.
368 STUBIES IN FOSSIL “BOTANY
them have been recorded from various Mesozoic strata ;
e.g. from the Lias of Mexico. In another case (Cycado-
spadix Hennoquet, Saporta, from the Lower Lias of
Metz) the carpel, fimbriated like that of Cycas pectinata,
bears the scars of the seeds. The evidence for the existence
of near allies of Cycas in Mesozoic times so far seems
strong, but, on the other hand, much doubt has recently
been cast on the nature of the leaves referred to Cycas
or Cycadites, with which the carpels are sometimes
associated. Nathorst? showed that in several species
from the Cretaceous of Greenland, formerly placed in
the genus Cycas, the vascular bundle of the pinna was
not single, as in the recent genus, but double, and that
the distribution of the stomata was also quite unlike
that in Cycas. He therefore placed these forms in a
new genus, Pseudocycas, and no longer regarded them
as belonging to the same sub-order as Cycas. It 1s prob-
able that the species now placed in Cycadites may prove
to have similar peculiarities.®
The genus Cycadocarpidium, Nathorst, is of interest
in connection with fossil Cycadales. It consists of cones,
compared to those of Zama, but differing greatly in the
fact that each sporophyll has a long, foliaceous, ovate
or lanceolate lamina; at the base of the leaf-blade
two seeds are inserted, accompanied, in one species, by
appendages, which may be interpreted either as cupules
or as pinnae. These fructifications probably belonged
to the vegetative organs known as Podozamites, Braun.
The nature of the latter genus has been much disputed,
but it is now believed to represent leafy stems, the slender
1 See Saporta et Marion, L’ Evolution du vegne végétal ;: Les Phanéro-
games, t.i. p. 111, fig. 59, A, 1885. e,
VI Eee
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Fico:
Hornea Lignieri
_ Fic. 136.—Restoration of Rhynie plants. 3. Hornea Lignieri, showing tuberous rhizome
with rhizoids, forked aerial stems and terminal sporogonia. 4. Asteroxylon Mackiet,
showing hairless rhizome, transitional region, and leafy, branched aerial stems. On
the right, an associated fertile shoot, with small terminal sporangia, is shown. Both
about half natural size. After Kidston and Lang.
he identified with Riynia) “ while still Thallophytic in
390 > LUDIES: IN-FOSsSIL BOTANY
habit may occupy anatomically a place half-way be-
tween the Thallophyta and Pteridophyta.’’! This does
not materially differ from the opinion that these plants
are the most primitive of the Pteridophyta known
to us.
Kidston and Lang have repeatedly called attention
to the Thallophytic, and more especially Algal characters
of the Rhyniaceae. Their suggestion that these plants
may find their place “near the beginning of a current
of change from an Alga-like type of plant to the type
of the simpler Vascular Cryptogams”’ has already been
quoted. In a later memoir they recognise the possi-
bility that some of the Early Devonian plants may show
‘such combinations of characters as would break down
any sharp distinction between the Algae and the simplest
Pteridophytes.” ? Although they do not think that this
holds good for the Rhyniaceae, they point out that “ the
members of this class are the Pteridophyta which are
most readily comparable with the Algae.”
A certain affinity with the Bryophyta has also been
recognised, and it has even been held that the Rhyniaceae
should be assigned to this sub-kingdom. The Sphagnum-
like structure of the columellate sporangium or sporo-
gonium of Hornea and Sporogonites may be regarded as
supporting the Bryophytic attribution, which may then
readily be extended to RAynia. Prof. Bower has said :
“Comparison of the Bryophytes will leave little doubt
that the sporangium of Psilophytales and the sporo-
gonium are kindred structures.’”’ He adds: ‘‘ The new
facts are thus seen to link the Bryophytes and the Pterido-
phytes more closely together than before.’ * Kidston
and Lang themselves point out that all three groups,
1 E. A. N. Arber, Devonian Floras: A Study of the Origin of Cormo-
phyta, Cambridge University Press, 1921, p. 49.
* Kidston and Lang, /.c. Part iv. 1921, p. 843.
3 Ff. O. Bower, The Earliest Known Land Flora, Royal Institution
of Great Britain, April 30, 1920, p. 9.
GENERAL RESULTS—PSILOPHYTALES’* 391
Pteridophyta, Bryophyta, and Algae, are brought nearer
together by the Rhynie fossils.
If we were to take the view that the Khyniaceae were
Bryophytes, or on the way to becoming Bryophytes, we
should probably be led to regard them as in course of
reduction, for their long, branched stems, though nearly
or quite leafless, were far more developed than the seta
of any Moss or Liverwort. The opposite theory, that
they were on the up-grade, from more typical Bryophytes
towards Vascular Cryptogams, scarcely seems tenable,
for it would leave the admitted Alga-like features un-
explained. It is wisest, however, not to carry specula-
tion too far, and to be content with recognising that these
Early Devonian plants, while themselves of the nature
of very simple Pteridophytes, yet have certain points
in common with the Bryophytic line. The presence of
these common characters is a significant fact, whether
due to affinity or to parallel development.
Dr. Church’s opinion (not based on any fossil evidence)
that the Land Flora sprang from highly organised Algae
and that the chief features of morphological differentia-
tion had already been acquired during marine life, has
previously been cited.t. Kidston and Lang, however, have
pointed out that the absence of leaves and roots in the
Rhyniaceae gives us, within the Vascular Cryptogams,
a simpler starting point than this theory postulates.’
As already mentioned, the existing Algae which the
Rhyniaceae most nearly simulate are by no means the
highest of their race. It is, however, not impossible
that the modest peat-plants of the Rhynie Flora might
have already undergone some reduction, a_ possibility
hinted at above, in connection with their Bryophytic
characters. However that may be, the facts clearly
point to a general analogy, if not affinity, between the
Rhyniaceae and fairly advanced Seaweeds. We cannot
Pip eek
2 Kidston and Lang, Part iv. p. 844.
392 STUDIES IN’ FOSSIL’ BOTANY
go further than this, for on Dr. Church’s hypothesis the
transmigrant Algae belonged to some extinct group, of
which we have no direct knowledge.
The uniform simplicity of the Rhyniaceae is em-
phasised by Kidston and Lang’s conclusion that they
were in all probability leafless throughout. There was
at first a possibility that in Rhynia Gwynne-Vaughani
the hemispherical emergences might represent rudi-
mentary leaves. Recent observations have rendered
this interpretation very improbable, for Kidston and
Lang now find that the emergences were developed late,
by the growth and division of cells of the epidermis and
subjacent layers, immediately below a stoma. Thus,
as they say, “it is clear that the hemispherical projec-
tions cannot be regarded as part of the primary construc-
tion of the plant as at first developed.’’! Hence “ the
only possible conclusion at present appears to be that
the Khyniaceae afford no clear indication as to the first
origin of leaves.’’ 2
There is a considerable gap between the bare, thalloid
stems of the Rhyniaceae and the leafy, Clubmoss-like
shoots of Asteroxylon. This relatively advanced genus has
been so fully discussed in Chap. X. (V.i.) that little remains
to be said. Astevoxylon, at any rate, was an unquestion-
able Pteridophyte. In their later work Kidston and
Lang compare it with Thursophyton Milleri (formerly
Lycopodites Milleri), a Middle Devonian plant, known
from impressions, looking much like a Lycopodium. The
authors find that the similarity of Astervoxylon is “ so
great that they may be only different conditions of
preservation of one species.’’? There seem to be some —
difficulties in the way of this identification, for in species
referred to Thursophyton, axillary sporangia, totally
different from the fructification attributed to Aster-
oxylon, have been described.* In any case, however,
1 Kidston and Lang, Part iv. p. 833. 2 L.cup, Cam
2.06. 2, G52, 4 See Arber, Devonian floras, p. 29.
GENERAL RESULTS—PSILOPHYTALES 393
the similarity in the vegetative habit of the two genera
is striking.
Asteroxylon, if it were not for the peculiar fertile
shoots associated with it, might be regarded as an early
representative, or at least precursor, of the Lycopod
series, resembling the Psilotales in the absence of differ-
entiated roots. If we accept the fertile shoots as belong-
ing to the plant (which seems very probable from the
close association) we get the extraordinary combination
of characters already discussed in Vol. I. Until certainty
is attained on this point, it is useless to carry the dis-
cussion further.
The most fundamental question concerning the affini-
ties of the Vascular Plants is whether their several phyla
diverged from a common stock, already vascular, or ran
back in distinct parallel lines to different ancestral races
among the Algae. Unfortunately the question is in-
soluble, and both views are maintained by competent
authorities. Attention has already been called to the
extreme polyphyletic theory of Dr. Church, and to the
monophyletic origin suggested by Dr. Halle The
former holds that “all the main lines of what is now
Land Flora must have been differentiated in the Benthic
Epoch of the sea (7.e. as algal lines).’”’? Dr. Halle, after
pointing out the possible relation of the Ps:lophyton type
to both Lycopods and Ferns, remarks that “ from this
point of view the whole pteridophytic stock would be
monophyletic, the Lycopsida and Pteropsida being derived
from a common form already vascular.”’
Kidston and Lang accept Halle’s conclusion as “a
fair statement of the present bearing of the imperfectly
known facts.’’ While they hold that the type of the
Khyniaceae “ suggests the convergence of Pteridophyta
and Bryophyta backwards to an Algal stock,” they
1 V.i. pp. 416 and 421.
2 A. H. Church, “ Thalassiophyta and the Sub-aerial Transmigra-
tion,’’ Botanical Memoirs, No. 3, Oxford, 1919, p. 41.
394 STUDIES IN FOSSIL BOTANY
add: “The knowledge of Astevoxylon confirms and
enriches our conception of a more complex but archaic
type of the Vascular Cryptogams which supports the
idea of the divergence of the great classes of Pterido-
phyta from a common type and links this on to the
Rhyniaceae.”’1 In a later memoir they express the
further opinion that “it is perhaps better to regard the
point of divergence as represented by plants somewhat
simpler than the Asteroxylaceae in that they did not
possess definite small leaves.” 2 .
On the other hand, Dr. Arber, like. Dr.-Church, but
from a quite different point of view, maintained a poly-
phyletic evolution of the higher plants. He recognised
three distinct main lines of descent, the Sphenopsida,
Pteropsida, and Lycopsida, descended severally from
Thallophytic Algae of different types. He regarded it,
however, “as probable that the Psilophyton habit was
primitive for all three lines of Cormophytic descent.” 3
He derived the Sphenopsida ‘“‘ from Thallophytic Algae
bearing whorled branches,”’ of limited growth and “ typi-
cally small, converted into leaves which were originally
and always microphyllous.’”’ The Pteropsida were “ de-
scended from Thallophytic Algae in which the branches
were large, numerous, scattered and not whorled.”’ The
compound branches were ‘‘ eventually metamorphosed
to megaphyllous leaves.’ On the other hand, Arber
derived the Lycopsida from Algae ‘‘in which the aerial
axes were rarely branched and then usually in a dicho-
tomous manner. The branches bore emergences, which
were metamorphosed to microphyllous leaves.’ 4
Arber separated the Psilotales altogether from the
Palaeozoic lines, making them ‘‘a quite independent
1 Kidston and Lang, Part ili. p. 675.
* Kidston and Lang, Part iv. p. 843.
3 E. A. N. Arber, Devonian Floras, p. 72.
* Arber thus adopted Lignier’s distinction between true leaves,
modified from thalloid branches, and _ phylloids, derived from
emergences.
GENERAL RESULTS—PSILOPHYTALES 395
race, also of Algal origin, which appeared on the scene
long after the other races—possibly in Mesozoic times,
or even later.’’ !
On the whole the recent trend of botanical speculation
has perhaps been in a polyphyletic direction. At the
same time it must be admitted that the discovery of the
existence, in Early Devonian times, of an excessively
simple race of Vascular Plants may turn the scale in
favour of a common origin from a vascular stock. The
important characters common to all existing Pterido-
phyta, however diverse, have always supported the idea
of a single origin. Among such characters the chief are :
the alternation of generations with the sporophyte pre-
dominant ; the development both of the asexual and
the sexual reproductive organs, and the histology, as
shown especially in the vascular tissues and the stomata.
So far as the evidence shows, these common characters
probably extended to the fossil groups also. Such
arguments, however, are far from conclusive, for the
community in reproductive phenomena may be explained,
with Dr. Church, on the principle that such phases are
inevitably passed through, and must therefore be the
same in all phyla. In like manner some of the common
somatic features may be the necessary consequence of
the sub-aerial transmigration.
In framing a provisional classification of the great
groups of Vascular Plants we must therefore realise that
the relations between them are still wholly hypothetical.
With this reservation we may adopt the following scheme,
modified from that given in the second edition of this
book, but as far as possible following the same general
lines.
P { Rhyniaceae
SILOPHYTALES -
| Asteroxylaceae
LYCOPSIDA eee al (?)
Lycopodiales
© Ather, £6. p37:
396 STUDIES IN° FOSSIL BOTA
Equisetales |
SPHENOPSIDA . ~ Pseudoborniales
Sphenophyllales
-Arvticulatae.
Filicales
} Pteridospermeae
Gymnospermeae -Spermophyta.
Angiospermeae |
PTEROPSIDA
The position provisionally assigned to the Psilotales
in this scheme requires a word of explanation. I now
regard their affinities as entirely uncertain. We are
not directly concerned with them in these ‘“ Studies,”’ for
no fossil representatives are known. In previous editions,
however, great stress was laid on the apparent affinity
of this recent family with the Palaeozoic Sphenophyl-
lales. In the second edition the evidence was given in
some detail, and the Psilotales were definitely included
under the Sphenopsida. Since that time our knowledge
of this recent group has been greatly enriched owing to
the discovery and investigation of the prothallus and
embryo by Darnell-Smith, Lawson, and Holloway.
Prof. ,Lawson expresses himself favourably towards the
affinity with Sphenophyllales, while pointing out that
the gametophyte generation can offer no positive evidence.
Dr. Holloway in his later paper says: ‘“‘ The extreme
simplicity of the Tmesipteris embryo, wholly devoid as
this is of appendicular organs, is full of significance, and
the demonstration of a rootless and leafless condition in
the earliest known land-plants strengthens the belief that
the Psilotaceae have preserved in the first stages of their
development primitive features.’’? Thus he supports,
in a general way, the views of Kidston and Lang.
i -. Apilawseon. “* Phe Prothallus of Tmesipteris tannensis,’’ Trans.
Royal Soc. Edinburgh, vol. li. 1917 ; G. P. Darnell-Smith, “‘ The Gameto-
phyte of Psilotum,” ibid. vol. lil. 1917; A. A. Lawson, ‘‘ The Gameto-
phyte Generation of the Psilotaceae,’’ zbid. vol. lii. 1917; J. E. Hollo-
way, ‘“‘ The Prothallus and Young Plant of Tmesipteris,’’ Trans. New
Zealand Institute, vol. 1. 1918; ‘‘ Further Studies on the Prothallus,
Embryo and Young Sporophyte of Tmesipteris,”’ ibid. vol. lili. 1921.
2 Holloway, /.c. 1921, p. 421.
GENERAL RESULTS—PSILOPHYTALES 397
Hence there are four theories in the field as to the
position of this problematic group :
rt. That of Kidston and Lang, now supported by
Holloway and Bower,! that the Psilotales are
nearest to the Devonian Psilophytales.
2. Arber’s suggestion that they are of late and in-
dependent origin from Algae.
3. The hypothesis maintained by A. P. W. Thomas,
and formerly by Bower and myself, of an affinity
with the Sphenophyllales.
4. The old-fashioned view that the Psilotales are
essentially Lycopods.
On present evidence it seems probable that the Psilo-
tales may have retained some primitive characters,
notably the negative one of the absence of roots; as no
root appears in the embryo of Jmesipteris, we may
suppose that this is an original deficiency. On the other
hand, any near affinity to the Psilophytales seems to the
present writer improbable—Psilotum has obviously under-
gone reduction, and Zmesipteris appears to bear no
resemblance in external morphology to any of the Early
Devonian plants. The synangia are evidently advanced
and specialised organs; the anatomy, however, shows
a considerable likeness to that of Astevoxylon on the one
hand, and certain Lycopods on the other. It is perhaps
safest at present to return to the old idea of a certain
relationship to the latter class, while such primitive
features as are present in the Psilotales may be recog-
nised by putting them near the Psilophytales, though
within the Lycopsida. It seems more probable that
they are aberrant Lycopsida than that they were directly
derived from the remote Devonian group.
The theory once held that the Psilotales are nearest
to the Sphenophylls must, it seems, be dropped. There
are no doubt some remarkable analogies, especially in
the morphology of the synangia, but these may well
1“ The Earliest Known Land Flora,’’ R.I. 1920, p. 6.
398 SLUDIES IN POSSE. BOTANY
be only homoplastic. The whorled phyllotaxis is so
constant throughout the recognised Sphenopsida that it
should probably be accepted as an essential character
of the Division. The remarkable variations in the
sporophylls of Tmesipteris, observed by A. P. W. Thomas,
retain their interest, but have perhaps been over-estimated
as indications of affinity.2 The analogy of some of
his peculiar forms, with Sphenophyllum majus, on which
stress was formerly laid by the present writer, proves to
be less close than it then appeared (see VY. 1. p. 101).
Thus the affinities of the Psilotales remain quite an
open question; the position now assigned to them in
our scheme is merely intended to indicate a tenable
suggestion.
With reference to the scheme given on p. 395, it must
be pointed out that, while our old Division Pteropsida is
retained, the Spermophyta are now regarded as an inde-
pendent phylum, not descended from the Filicales, though
very probably derived ultimately from a common source
with them.
LYCOPSIDA
The points of agreement, both external and structural,
between the ancient genus Asteroxylon and some of the
Lycopods have already been pointed out in Chap. X.(V.1i.).
Several of the Early Devonian plants had a more or less
Clubmoss-like habit, and it seems not improbable that a
real affinity may exist between the Lycopodiales and
some of the Psilophytales. Thus there is now a possible
clue to the early history of the Lycopod phylum.
The dubious position of the Psilotales, which we have
placed provisionally under the Lycopsida, has been
sufficiently discussed above.
1 A. P. W. Thomas, “ The Affinity of Tmesipteris with the Spheno-
phyllales,’’ Proc. Royal Society of London, vol. lxtx. 1902, p. 343.
2 Cf. Holloway, /.c. 1921, p. 417.
GENERAL RESULTS—LYCOPSIDA 399
In the first edition of these ‘“ Studies ’’ I laid stress
on the relation of the Lycopods to the Sphenophyllales,
and, through them, to the Equisetales. Prof. Jeffrey,
on independent grounds, united all these classes in his
Lycopsida,! as a main division of Vascular Plants, while
his Pteropsida included all the remaining groups. It
now appears probable that the Articulatae were derived
from relatively megaphyllous plants, whereas we have
at present no evidence that the Lycopods were ever
anything but microphyllous, like their predecessors
among the Psilophytales. Further, the Articulatae are
‘“ sporangiophoric,”’ bearing their sporangia on special
appendages, whereas throughout the Lycopods we find
a single sporangium seated directly on the sporophyll,
or in its axil. This simple arrangement may also be
due to reduction ; the ventral outgrowth of the sporo-
phyll which bears the sporangium in Sfencerites has
been compared to the sporangiophore of Sphenophyllales,
and Dr. Benson has interpreted the sterile tissue of the
sporangium in Mazocarpon as representing a sporangio-
phore. These suggestions are very interesting, but at
present too hypothetical for any conclusion as to affinity
to be based on them ? (see below, p. 407).
In the anatomy there is no doubt a considerable
analogy between the Lycopods, especially the Palaeozoic
types, and the Sphenophyllales. The stelar structure
of Cheirostrobus, for example, is much like that of a
Lepidodendron such as L. selaginoides, allowing for the
fact that the leaf-arrangement is verticillate in the one
and spiral in the other. This type of stele, however,
1 E. C. Jeffrey, “ Structure and Development of the Stem in the
Pteridophyta and Gymnosperms,”’ Phil. Trans. Royal Soc. B, vol. 195,
1902, p. 144; also his earlier papers there cited. - See also his later
work, The Anatomy of Woody Plants, Chicago, 1917, chap. xviii.
2 See also Miss M. G. Sykes (Mrs. Thoday), ‘‘ Notes on the
Morphology of the Sporangium-bearing Organs of the Lycopodiaceae,”’
New Phytologist, vol. vii. 1908, p. 41. The views of Kidston and
Lang are given in their fourth memoir on Oli Red Sandstone Plants,
etc., p. 849, 1921. 3 J.e. an exarch protostele.
400 STUDIES IN- FOSSIL BOTAN:
may also occur in Ferns (though not characteristic of
that class) ; its wide distribution is one of the facts in
favour of an ultimate common origin for all the vascular
phyla (see above, p. 393).
The Lycopods manifestly attained their highest
development in later Palaeozoic times as regards abund-
ance, stature, and organisation, both vegetative and
reproductive. In spite of their immense development at
that time compared with their very subordinate position
at the present day, the Lycopods, as a whole, constitute
a very homogeneous class of plants, characterised through-
out by a microphyllous habit, an anatomy based on an
exarch type of protostele (sometimes slightly mesarch) ,
and a simple relation between sporangium and _ sporo-
phyll. There is no departure from the first-named char-
acter; for though the leaves were often long, they were
never large in proportion to the plant, and were always
of the simplest form. The double bundle of Sigillariopsis,
a form of leaf belonging to certain species of the some-
what advanced genus Szgillaria, is the only departure
from the prevailing simple type of foliar structure (V. 1.
pe207):
Attention has already (V. i. 112) been called to the
simplicity of the primary anatomical structure of the
stem in Palaeozoic Lycopods, the one character in which
these plants have proved to be more “ primitive ” than
most of their recent allies. A gradual transition may
be traced from the protostelic type, through the medul-
lated forms of Lepidodendyon and the ribbed Sigillarias,
to the smooth-barked Sigillarias, in which the ring of
wood separates, more or less completely, into distinct
bundles (V. i. 198). It is these last forms which depart
most widely from the common Lycopod type, but the
change is not a great one, and does not appear to indicate
a transition to any form of Gymnospermous stem.
As regards the secondary growth, characteristic of the
arborescent Lepidodendreae, there are some peculiarities ;
GENERAL RESULTS—LYCOPSIDA 401
the agreement with the normal secondary thickening of
Gymnosperms and Dicotyledons is somewhat less exact
in this class than in the Sphenopsida or the Pteridosperms.
In some forms (Lefidophloios /uliginosus, for example,
V. i. 137) the zone of thickening is extremely irregular, and
although in other Lepidodendreae it approaches the
normal type more nearly, it is doubtful whether in any
case the same cambium remained continuously active
throughout. The secondary growth of Jsoétes presents
some interesting analogies with that of the Lepido-
dendreae.
The enormous development of the secondary cortical
tissue, chiefly phelloderm, is a striking feature of the
tree Lycopods, and with this again the growth of the
cortex in /soétes alone presents any analogy, though, at
best, only a remote one.
The difficult question of the morphology of Stigmaria,
the subterranean part of the Lepidodendroid plant,
already discussed (V.1i. 236), suggests that the differentia-
tion between “root and shoot”? may have been less
sharp in this group than in other Vasculares. Similar
indications are to be found in the rhizophores of Sela-
ginella and the stem-like roots of some Lycopodiums at
the present day. The absence of true roots in the Psilo-
phytales is significant in this connection. A suggestion
has been made by Prof. F. E. Weiss that an analogy
for the Stigmarian axes may be found in the protocorm,
the rudimentary, somewhat thalloid, stem which is the
first product of germination in some species of Lyco-
podium, and appears to be persistent in the tuber of
Phylloglossum. In Hornea, among the Psilophytales of
the Devonian, the rhizome was of the nature of a proto-
corm (see V. 1. 388). 3
It is a curious fact that among the very numerous
fructifications that have been investigated, no certain
instance of a homosporous Palaeozoic Lycopod has yet
been discovered. Wherever the material has allowed of
26
402 STUDIES IN FOSS BOTANY
a definite conclusion, two forms of spore, as sharply
differentiated as in any recent ‘members of the class,
have been found. Sfencerites is sometimes cited as an
exception, but the evidence is inconclusive, and the
spores are singularly unlike those of any known homo-
sporous Lycopod (V.1i. 170). The oldest known genus of
Lycopods, Bothrodendron, was markedly heterosporous,
as shown both in the Upper Devonian and the Coal-
measure species. Among the herbaceous as well as the
arborescent Lycopods, only heterosporous forms have
so far been detected ; in some of the former (Selaginellites
primaevus) there is an exact agreement with the recent
Selaginella (V.1. 241).
It must, however, be remembered that heterospory
is always easier to demonstrate than homospory. It is
impossible to doubt that homosporous Lycopods existed
in Palaeozoic times, but the prevalence of higher methods
of reproduction shows how far the class had already
advanced at the period when the fossil record of in-
dubitable Lycopodiales begins.
Certain Carboniferous Lycopods, as we have seen
(V. i. 173), went beyond mere heterospory, and developed
organs closely analogous to true seeds. Of the two
genera in which seed-like organs are known, the one,
Lepidocarpon, clearly belonged to the Lepidodendreae,
while the other, Miadesmia, appears to have been a small
herbaceous plant, perhaps, as Dr. Benson has suggested,
epiphytic on the larger Lycopods with which it is associ-
ated. The affinities of Miadesmia, which in some respects
resembles a Selaginella, are not yet determined, but in
any case it seems clear that this genus acquired the seed
habit on its own lines, and independently of Lepidocarpon.
The single-spored units formed on the fragmentation
of the megasporangium of Mazocarpon offer a certain
analogy with seeds.
The seed-like organs of Miadesmia and Lepidocarpon,
though they may probably have been functionally seeds
GENERAL RESULTS—LYCOPSIDA 403
in the same sense as those of the Pteridosperms, are
greatly inferior to the latter in morphological differentia-
tion, and stand much nearer the Cryptogamic type of
megasporangium. They are, in fact, the only really
‘primitive ’’ seeds known to us, and as such are of special
interest, though they probably only represent a side-
line of evolution.
As regards the relation of the Palaeozoic to the recent
Lycopods, only the heterosporous forms of the latter
come under consideration, for as yet we know nothing
certain of the history of the homosporous Lycopodiaceae,
apart from the possible relation to the Psilophytales.
It now seems clear that the genus Selaginella, or types
scarcely distinguishable from it, already existed in the
later Palaeozoic Flora, and that it had no near relation
to the arborescent Lepidodendreae. On the other hand,
there may well be some connection between the Lepido-
dendreae and the greatly reduced heterosporous genus
Isoétes, which, in the structure and insertion of its spor-
angia, as well as in anatomical characters, has much
in common with the Palaeozoic tree Lycopods. In the
occurrence of sterile trabeculae in the sporangia of some
Lepidostrobi, Prof. Bower has recognised an interesting
point of agreement with Jsoétes.1
The question of a possible relationship between the
Palaeozoic Lycopods and certain Seed-plants will be
discussed when we come to the Gymnosperms.
1 The curious Triassic genus Pleuromeia has been regarded as a link
between the two groups, but if, as is stated, the sporangia of Pleuromeia
were borne on the underside of the sporophyll, there is great difficulty
in accepting this view. On Pleuromeia see Solms-Laubach, ‘‘ Uber
das Genus Pleuromeia,’’ Bot. Zeitung, Bd. lvii. 1899, p. 227; H. Fitting,
“Sporen im Buntsandstein—die Makrosporen von Pleuromeia?’’
Ber. d. Deutschen Bot. Gesellschaft, Bd. xxv. 1907, p. 434. For a
possible solution of the difficulty see Dr. M. Benson, ‘‘ Mazocarpon,
or the structure of Sigillariostrobus,’’ Ann. of Bot. vol. xxxii. 1918,
p. 586.
404 STUDIES IN FOSSIL BOTANY
SPHENOPSIDA
The general morphological agreement between the
two classes Sphenophyllales and Equisetales is manifest,
and extends to Nathorst’s class Pseudoborniales. The
articulated stem, and the constant verticillate arrange-
ment of the appendages, are characters obviously common
to the whole series. Avchaeocalamites, the oldest of the
known Equisetales, distinctly approaches the Spheno-
phyllales in the superposition of the verticils and in the
dichotomously divided leaves, while in many Calamari-
aceae the individual leaves resemble the leaves or leaf-
segments of the plurifoliate Spheniphyllums so closely
as to be almost indistinguishable. Lignier endeavoured
to carry the comparison further and to place it on an
anatomical basis. In the species of Sphenophyllum,
regarded as typical, there are six leaves in a whorl, but
the vascular strands supplying each two leaves start
from the same angle of the triarch stele, suggesting that
three was the original number of leaves in a verticil, a
supposition for which there is no palaeontological evidence.
In some species (e.g. Sphenophyllum Dawsoni, V. 1. 90)
the stele itself is hexarch, each of its angles being double.
When the leaves are further segmented, a further forking
of the bundles takes place within the cortex, and it might
be supposed that the numerous leaves of such a species
as S. myrniophyllum represent the segments of a few
deeply divided original appendages. As a matter of
fact, however, the oldest known species of Sphenophyllum
(c.g. S. subtenerrimum from the Upper Devonian) have
numerous leaves, narrow and forked, in a whorl. In
the Calamariaceae, on Lignier’s view, the supposed process
had gone further, the increased dimensions of the stem
involving a corresponding multiplication of the leaves
and of the bundles in the stem. In cases like the axis
of Calamostachys, we may find an analogy with Spheno-
phyllum in the fact that each two bracts receive their
GENERAL RESULTS—SPHENOPSIDA 405
vascular supply from the same axial bundle, while in
Palaeostachya vera the axial bundles are themselves dup-
licated, forming evident pairs (V. i. 57). While Lignier’s
theory is not supported in detail by the fossil evidence,
a clear analogy between the Sphenophylls and the Cala-
mariaceae can be traced. That the leaves of the Sphen-
opsida were originally compound or much cut is suggested
by the presence of such divided leaves in the early fossils
Archaeocalamutes, and more especially Pseudobornia, the
leaves of which, when found isolated, were actually
taken for the fronds of a Fern.
In anatomy, the Sphenophyllales, with their solid
protostele, appear to be clearly more primitive than the
Equisetales, which in all cases have a pith and distinct
vascular bundles. The anatomical gap between the
two classes appeared a very wide one, until it was partly
bridged by the discovery of centripetal wood in the
stem of the Lower Carboniferous Protocalamites (V. i. 32).
The evidence from the fructifications strongly supports
the affinity between Sphenophyllales and Equisetales,
though the detailed comparison presents some difficulties.
The minute structure of the sporangia is. Strikingly
similar in the two classes, and the BS Oe Ts iat
to the sporangiophores. Those of Cheirostrobus in particu-
lar, which have four sporangia, are almost identical with
those of Calamostachys (V.1i. 48, 103). Where the number
of sporangia is smaller the resemblance to the Equisetal
type becomes less evident.
The question of the nature of the sporangiophore has
been profoundly affected as we shall see by recent work
on the Early Devonian plants. We may first recapitulate
the facts.
Throughout the Sphenophyllales the sporangiophores
occupy the position of ventral lobes of the sporophyll ;
in one species, S. fertile (V. i. 100), the dorsal lobes are
also enlisted for the same service. This latter case is
of special interest, because the dorsal and ventral lobes
406 STUDIES IN FOSSIL BOTANY
are on an equal footing, both being organised in the same
way; the segments of each lobe constitute typical
bisporangiate sporangiophores. I incline to regard this
form as a secondary modification rather than a primitive
type, partly because the case is at present altogether
exceptional and of no special antiquity, and partly
because the dorsiventral arrangement seems best ex-
plained on the supposition that the dorsal lobes were
originally sterile and protective in function. It may be
added that the very leaf-like character of the bracts in
most Sphenophylls, and especially in Spi. magus (V.1. 101),
makes it difficult to explain them as sterilised sporangio-
phores. But whether we regard S. fertile as a modified
or a primitive form,! it may be interpreted as showing
that the sporangiophores and bracts have equal claims
to be regarded as lobes of the sporophyll. Or we may,
with Dr. Margaret Benson, call the sporophyll here “a
leaf wholly composed of sporangiophores.’’ The ventral
position holds good also for Chetrostrobus ; it is only
in Sphenophyllum emarginatum that the sporangiophores
and bracts appear to have been independent, as they
have left separate scars on the axis of the cone.’
In Calamostachys, among the Equisetales, the two
organs are externally quite separate, but the course of
the bundles supplying the sporangiophores suggests that
the latter may represent displaced ventral appendages
of the bracts (V. i. 53). Palaeostachya, from the position
of the sporangiophores immediately above the bracts
(V.i. 58), seemed at first to form a link with the Spheno-
phyllales, but Dr. Hickling’s observations on the vascular
supply rather suggest a modification of the Calamostachys
arrangement. The Equisetum type of strobilus appears
to have been already represented in Palaeozoic times,
1 The latter view was maintained by Lady Isabel Browne in her
interesting résumé of the ‘‘ Phylogeny and Inter-relationships of the
Pteridophyta,” New Phytologist, vol. vil. 1908, p. 94.
2 As shown by unpublished observations of Mr. W. Hemingway’s. ~
GENERAL RESULTS—SPHENOPSIDA 407
and in Archaeocalamites the bract-whorls were, at most,
few and scattered. It has been proposed to derive the
bractless arrangement from that found in Sphenophyllum
fertile, the assumption being that the lobes of a wholly
fertile sporophyll underwent a displacement like that
which appears to have taken place between the sterile
and fertile lobes in Calamostachys.1. The evidence, how-
ever, is as yet insufficient to establish any such interpreta-
tion, and it may well be that the Sphenophyllum analogy
has been pushed too far. There is no need to reduce
every sporangiophore to a leaf-lobe, for it is possible
to hold that in the Sphenopsida, as in the Pteropsida,
the spore-bearing organ may be sometimes a lobe of a
leaf, sometimes an entire leaf, or not of foliar nature
at all.
Prof. Bower regarded the sporangiophore as “a part
sui generis as much as the sporangium is, and not the
result of modification of any other part.’ We now have
good reason, from the evidence furnished by the Rhyni-
aceae, for believing that the sporangium itself is not an
organ sui generis, but the modified end of a branch.?
Hence it seems natural to suppose that the sporangium-
bearing organ, the sporangiophore, represents a fertile
branch of the early Pteridophytic thallus. Dr. Margaret
Benson, in 1908, anticipated this suggestion, saying,
‘““ With the new hypothesis [Prof. Lignier’s] in view, such
organs may be explained as units of the Pteridophytic
thallus which still exist as relics of the condition in which
the limits of axis and leaf were not fixed.’’4 Kidston
and Lang, writing in the light of their Rhynie discoveries,
say: “‘ The sporangiophores would appear to represent
the last persisting remains of the original leafless branch-
‘
1 Scott, ““ Present Position of Palaeozoic Botany,’’ Progressus Rei
Botanicae, Bd. i. p. 162, 1906.
2 Origin of a Land Flora, p. 426.
* Dee Ved. 404;
4 M. Benson, “‘ The Sporangiophore, a Unit of Construction in the
Pteridophyta,’”’ New Phytologist, vol. vii. 1908, p. 148.
408 SEUDIES-IN -POSSLE BOLANY
systems of the Rhyniaceae.’’! They apply this com-
parison to the sporangiophores of the Equisetales and
Sphenophyllales, with which we are here concerned, as
well as to those of Helminthostachys, the fertile appendages
of the Psilotaceae, and “with greater difficulty and
obscurity to the position of the sporangia of the Lyco-
podiales.”’
Thus the cauline theory of the sporangiophore is con-
firmed, but with a difference ; we need not regard this
organ as belonging to the category “‘axis’”’ as distin-
guished from “leaf’’; it represents the “branch of a
thallus and belongs to a phase before leaf and axis were
differentiated.2, It seems quite probable that this inter-
pretation may hold good for many cases ; it must, how-
ever, be remembered that the leaf is also, on the view
now held, a modified branch of a thallus. It is possible
that sometimes the leaf may have preceded the specialised
sporangiophore in its differentiation. Thus, if, as we
have suggested, the fertility of both dorsal and ventral
segments in Sphenophyllum fertile is a secondary and
not a primitive character, it is probable that the dorsal
part was a leaf before it became converted into sporangio-
phores.
However this may be, there is no doubt that our
present knowledge of the simple morphology of the
Rhyniaceae greatly illuminates the question of the
sporangiophore, and brings into harmony various diver-
gent views previously maintained. The independent
sporangiophores of the Archaeocalamites type ® may quite
1 Kidston and Lang, Part iv. p. 850.
* Cf. M. G. Sykes (Mrs. Thoday), ‘‘ Anatomy and Morphology of
Tmesipteris,”’ Ann. of Bot. vol. xxii. 1908, especially p. 82.
% On the sporangiophores of the Equisetum type, see Lady Isabel
Browne, “‘ Anatomy of the Cone and Fertile Stem of Equisetum,’’ Ann.
of Bot. vol. Xxvi, 1912, vol. xxix. 1915, vol. xxxiv. 1920, VOluse
1921. Also Kate Barratt, ‘ A Contribution to our Knowledge of the
Vascular System of the Genus Equisetum,” Ann. of Bot. vol. xxxiv.
1920,
GENERAL RESULTS—SPHENOPSIDA 409
well be interpreted as derived directly from fertile thallus-
branches ; in other cases the association between spor-
angiophore and leaf has become so close that it is im-
possible to say which was the first to be differentiated.
The genus Sphenophyllum, as we have seen, goes back
to the Upper Devonian. Very little is known of the
earlier history of the Articulatae, but Nathorst has
described a plant (Hyenia sphenophylloides) from West
Norway, probably of Middle Devonian age, which seems
to have been a precursor of Sphenophyllum. The fossil
only differs from that genus in the absence of definite
nodal lines, and perhaps in the number of leaves in a
whorl, which was more probably four than six. Nothing
is known of the fructification.' This seems to be the
earliest authentic geological record for the Sphenopsida.
On the whole of the evidence there can be no doubt
that a real affinity exists between the Sphenophyllales
and the Equisetales, the former being clearly the more
primitive class of the two, or rather the representatives
of a more primitive stock, for the known Sphenophylls
are evidently specialised in various directions. The argu-
ments for the aquatic habit of Sphenophyllum do not
hold good, as already pointed out (V.i. 77); the great
development of the wood relatively to the size of the
stem is the reverse of what one would expect in a water-
plant; on the other hand, Prof. Seward’s suggestion
that Sphenophyllum may have been “a slender plant
which flung itself on the branches and stems of stronger
forest trees for support,’’? agrees well with the habit
and structure. The occurrence of extensive secondary
growth in this genus is interesting, as showing that this
character was not necessarily correlated, even in Palaeo-
zoic times, with an arborescent habit.
1 A. G. Nathorst, “ Zur Devonflora des westlichen Norwegens,”’
Bergens Museums Aarbok, 1914-15, No. 9. See also Arber, Devonian
Floras, p. 53.
2 Fossil Plants, vol. i. 1898, p. 392.
410 SLUDLES IN-FOSSiE- BOTANY
The enormous development of the Equisetales in early
geological periods, compared with their reduced condition
at the present day, is a striking fact. It is of interest
to consider in what respects the gigantic Palaeozoic
Horsetails differed fron their humbler successors.
One great and obvious difference was the formation
of secondary wood and bast and of periderm. Starting
with a structure in stem and root essentially like that
of a recent Equisetum, the Calamariaceae, by the activity
of a normal cambium, produced new wood and phloem,
to an indefinite extent, precisely as in a Gymnospermous
tree, and replaced their primary cortex by a broad zone
of secondary periderm. It was one of Williamson’s ©
greatest services to science that he always, in the face
of much opposition, insisted on the true “ exogenous
growth’ of the Calamites, while maintaining with equal
decision their Cryptogamic nature. He thus established
one of the most striking instances of homoplastic modi-
fication, for the close agreement in these anatomical
characters between certain Cryptogams and Phanero-
gams is not, in itself, any proof of affinity.
As has already been pointed out, it is probable that
the microphyllous character is not a primitive one in
Equisetales, and that the leaves are reduced from a
larger and more complex type, as seen in Archaeocalamites
and Pseudobornia. Although Arber spoke of the Spheno-
psida as “‘ microphyllous ”’ he recognised a sharp distinc-
tion between their leaves and those of the Lycopsida.
The old opinion of the French school, that some Cala-
mariaceae were seed-bearing plants, has not been sub-
stantiated by later work. Heterospory, however, appears
in a perfectly well-marked form in some of the fructifica-
tions, though the differentiation of the two kinds of
spore was not so extreme as in heterosporous Lycopods
or the recent Water-ferns. In other Calamarian strobili
the evidence is all in favour of homospory ; ‘the abortion
of certain spores in sporangia of this type may have
GENERAL RESULTS—SPHENOPSIDA 411
prepared the way for the heterospory of the more advanced
members of the group (V. i. 49). In this respect the Equiset-
ales seem to have reached a higher level than the Spheno-
phyllales, among which only doubtful indications of
incipient heterospory have so far been detected. The
Pseudoborniales, however, are described as heterosporous.
Considering the high development of the Palaeozoic
Equisetales, it is an interesting question whether our
living Equiseta are their degenerate descendants, or the
offspring of a simpler stock which may have co-existed
with the arborescent forms in ancient times. The earlier
Mesozoic Equisetales appear to have been intermediate
in certain respects between the Calamariaceae and the
recent genus, as shown especially by Prof. Halle’s results
(V.i. 72). By Wealden times, forms almost identical with
modern Horsetails had appeared. These facts favour
the hypothesis of reduction, though, as in all such ques-
tions, we cannot hope to trace direct descent. The
Equisetales, as a class, have conspicuously failed to hold
their own in the secular struggle for existence, though
the survivors are extraordinarily well adapted to parti-
cular conditions, and maintain their ground, when once
established, with singular obstinacy.
PTEROPSIDA
Filicales.—The result of the palaeobotanical research
of the last twenty years has been to exalt the import-
ance of the Fern phylum, on account of its remarkable
parallelism with the Pteridosperms, probably the source
from which a large part, if not the whole, of the Seed-
plants was derived. At the same time the recent dis-
coveries have greatly reduced our estimate of the actual
number of the true Ferns in Palaeozoic times (most of the
so-called Ferns having been Seed-plants at that period),
and difficulties have arisen in discriminating between the
Ferns proper and the Pteridosperms. Among indubitable
412 STUDIES IN-FOSSIL BOTANY
Palaeozoic Filices we have, in the first place, the Order
Botryopteridaceae and a few other forms probably allied
to them. We may follow the late Dr. Arber?! in using
the name Primofilices for the whole group. As regards
the Marattiaceae, long considered as the dominant Ferns
of the Carboniferous period and really an important
group, the question is in some respects more difficult,
as has been shown in Chapter VIII. (V.1.).
There is no reasonable doubt that the Botryopterid-
aceae were true Ferns; all their characters, both
vegetative and reproductive, point in this direction, and
the evidence has been materially strengthened by the
observation of spores in process of germination, agree-
ing closely with corresponding early stages in the develop-
ment of recent Fern prothalli (V. 1. 333). |
Anatomically, the Botryopteridaceae show two types
of structure, the one (Botryopterideae, V. 1. 337) exceed-
ingly simple as regards the stem-structure, while the
other (Zygopterideae, V. i. 288) shows a considerable degree
of differentiation. The solid strand of tracheides, sur-
rounded by phloem, which constitutes the central cylinder
in the Botryopteris group, is perhaps the simplest form
of stele known in any Fern, but it would be rash to infer
from this fact that these plants were necessarily of a
specially primitive nature. Their roots are diarch, like
those of most recent Ferns, their petioles attain some
degree of complexity in vascular structure, while the
differentiation of special fertile fronds, for which there
is here some evidence, may indicate a rather high grade
of organisation.
The affinities of the Botryopteridaceae with other Ferns
have been fully discussed in Chapter IX. (V.i.), and the
conclusion arrived at, that while they show some analogy
with various Filicinean families of later origin, they can-
not be considered as on the direct line of their descent.
1 FE. A. N. Arber, ‘“‘ On the Past History of the Ferns,” Amn. of
Bot. vol. xx. 1906, p. 221.
GENERAL RESULTS—FILICALES 413
This line will have to be sought among other Primofilices,
of which, as yet, we have only a scanty knowledge,
though the occurrence of annulate sporangia on ordinary
Fern pinnules, as in Pteridotheca Williamson, is a
promising indication (V. 1. 205).
Some relation between the Botryopteridaceae and
the Ophioglossaceae was recognised by Renault when
he first discovered the fossil family, the resemblances he
detected lying in the fructification and in the occurrence
of reticulated tracheides. He regarded the Botryo-
pteridaceae as intermediate in stem and _ fructification
between the Hymenophyllaceae, representing the Ferns
properly so-called, and the distinct group Ophioglossaceae.!
These relations have been discussed in Chapter [X. (V. 1.).
The sporangia of Staurvopteris (a genus not known to
Renault) present an almost exact agreement with those of
Botrychium, as regards their structure and the mode of
attachment by vascular pedicels.2, It may be recalled
that the structure of the stem in the Zygopteridean genus
Botrychioxylon (V. i. 319) if it lost the internal wood
(a change likely to occur, from the analogy of parallel
cases elsewhere *) would be almost exactly that of
Botrychium, in which medullary tracheides sometimes
occur. The fact that the frond (at least the fertile frond)
of many Zygopterids branched in more than one plane
has been compared with the dorsiventral branching of
the frond characteristic of Ophioglossaceae.*
On the whole, a real if somewhat remote affinity
_ between the fossil and the recent family seems probable
—in fact, of known plants, it is the Botryopteridaceae
which appear to have most in common with the Ophio-
glossaceae.
1 B. Renault, Végétaux silicifiés d’ Autun, etc., Autun, 1878, p. 114.
2 In Botrychium they are short, in this respect resembling those of
Botryopteris.
3 See below, p. 421.
4 Lady Isabel Browne, ‘“‘ Phylogeny and Inter-relationships of
Pteridophyta, vi. Filicales,’”’ New Phytologist, vol. vii. 1909, p. 27.
414 SLUDIES IN FOSSID BOTAN
A relation between the Botryopteridaceae and the
Osmundaceae has been clearly established, especially by
the anatomical investigations of Kidston and Gwynne-
Vaughan (see V. 1. 362).
Prof. Kubart’s discovery of the fructification of Ana-
choropteris (V. 1. 354) shows that plants included under
Botryopteridaceae had developed complex synangia,
comparable to those of advanced Marattiaceae. The
agreement in this respect is so close, as to suggest an
affinity between the two groups. But this is no more
than a suggestion. There can be no reasonable doubt
that the Marattiaceae or allied Ferns formed a consider-
able element in the Upper Carboniferous Flora (Chapter
VIII., V. 1.), but we know nothing of their history in
earlier periods.
True Ferns (e.g. Avchaeopteris) appear to have been
well developed in the Upper Devonian times; at least
there is no sufficient reason for assuming that the fern-
like plants of that age were all Pteridosperms. When
we go back to the Early Devonian, the case is quite
altered, for, as we have already seen, the evidence seems
to indicate that the so-called Ferns of those days did
not possess a lamina, but bore fronds of the nature of
a naked, branched rachis (V. 1. 415). Such “fronds” are
scarcely to be distinguished from the ramifications of a
thalloid stem. Thus the available facts suggest that in }
the older Devonian Flora, Ferns, as such, may not yet
have existed, though of course their precursors (such
as Lignier called Primofilicinées) were present. Possibly
we may have, in plants such as Stauropteris, a Carbon-
iferous race which had retained the naked rachis while
in other respects attaining the grade of Ferns (see V. 1.
335) 423):
Spermophyta.—While we have no proof of the existence
of true Ferns in the Early Devonian period, there is good
evidence for the presence of highly organised Pterido-
spermous or Gymnospermous stems (e.g. Palaeopitys
GENERAL RESULTS—SPERMOPHYTA = 415
Millert) in the Middle Devonian, This subject is now
under further investigation, but the existing data, such as
they are, support the opinion that the Seed-plants cannot
have been derived from Ferns, properly so called, for the
line of the Spermophyta seems to go back as far as, or
even farther than, that of the Ferns themselves.
The resemblances which have been traced between the
Marattiaceae and the Pteridosperms, especially between
the sporangia of the former and the pollen-sacs of the
latter, are not likely to be due to descent of the Spermo-
phytic from the Cryptogamic group, for, so far as we
know, the Pteridosperms are considerably older than
the Marattiaceae. Dr. Kidston’s opinion that the two
races had a common origin is perfectly tenable, but the
common source probably lay very far back. The present
evidence indicates that the Spermophytes have been an
independent phylum from very early times, and were
not derived from Ferns or any of the higher Vascular
Cryptogams, but more probably from some long-extinct
stock, perhaps comparable to the Psilophytales.
The Pteridosperms, paradoxical as it may sound, are,
in fact, too much like Ferns to be descended from them.
So close a resemblance in habit (sufficient to deceive
almost all botanists from Sir Joseph Hooker downwards)
if it indicated affinity at all, must imply a near affinity,
which is at once negatived by the vast differences in
essential characters, e.g. seed-reproduction as opposed to
homospory. The most probable interpretation of the
facts seems to be, not that the Seed-plants are descended
from Ferns, but that the Spermophytes once passed
through a fern-like phase, running parallel with the
true Cryptogamic Ferns; they may have sprung, with
them, from some quite early race of land-plants. We
have no reason to believe that the Seed-plant phylum
was ever any more fern-like than the Pteridosperms
themselves.
The idea that the Seed-plants were derived from the
416 Se Din: TN. -POSSEL BOTAN
Ferns having been abandoned, it may be asked why
the former are still included in our scheme under Ptero-
psida? The justification may be found in the parallel-
ism which undoubtedly exists between the Pteridosperms
and the Ferns. Wherever any analogy can be traced
between the Pteridosperms and the Cryptogams, whether
in anatomy or external morphology, it is with the Ferns
alone that comparison is possible. This fact retains its
importance, though all belief in any actual filiation of
the two classes may be given up.
The more detailed relationships of the families re-
ferred to Pteridosperms have already been considered in
Chapter III. We have hitherto tacitly assumed that the
Pteridosperms represent the earliest type of Seed-plants.
It must be pointed out, however, first, that the concep-
tion of Pteridosperms is a very vague one; the group
no doubt included very heterogeneous members. And
secondly, we cannot be sure that all Seed-plants passed
through the Pteridosperm phase ; there may have been
other parallel lines.
Some recent work no doubt tends to link up the two
great Palaeozoic groups, Cordaitales and Pteridosperms.
Mesoxylon, for example, is essentially a Cordaites with
centripetal wood in the stem, a character suggesting a
possible affinity with the type of Lyginopteris or Calamo-
pitys. In fact, among the Calamopityeae, Zalessky’s
genus or sub-genus Evistophyton seems to approach the
Cordaitales.
The most important point of agreement between the
two groups is, however, in the seeds, for no constant
distinction has been observed between the seeds of
Pteridosperms and those of Cordaitales. This community
of seed-structure would seem to indicate a close affinity.
The Cordaitales themselves may prove to be a some-
what heterogeneous assemblage. As regards the family
Cordaiteae, we have no evidence that they existed in
Devonian times, nor do we know much about them in
GENERAL RESULTS—SPERMOPHYTA 417
the Lower Carboniferous—they are essentially an Upper
Carboniferous and Permian group. The Poroxyleae, so
far as is known, are only of Permo-carboniferous age.
On the other hand, the Pityeae are as old as any known
Pteridosperms ; Zalessky’s genus Callixylon, an evident
ally of Pitys, is an Upper Devonian fossil. |
It is evident from Dr. Gordon’s work, though not yet
published in full, that the Pityeae formed a very distinct
family as shown by the characteristic foliage and various
anatomical peculiarities (see p. 256). They are very
different from the other Cordaitales, and show no distinct
approach to the Pteridosperms either. It is possible that
they may represent a separate line, of relatively early
origin. But as we know nothing of their fructification
we cannot come to any definite conclusion. We have
found it simpler to treat the early Seed-plants provision-
ally as a single main phylum, though realising that here
also diverse parallel lines may be represented ! (see also
below, p. 420).
Prof. F. W. Oliver’s interesting discovery of a spor-
angium (Tvacheotheca), similar to that of certain Botryo-
pterideae, containing tracheides in the inner layers of
its wall,? suggests a certain analogy with seed-structure,
and may prove to be a valuable indication. At present,
however, the case is too isolated for any phylogenetic
significance to be attached to it.
In later Palaeozoic times, the Cycadoxyleae appear
(p. 229). Their stems have taken an aberrant line of
development, through the suppression of primary wood
and the elaboration of anomalous secondary growth, and
thus present some analogies with the more modified of
1 For the latter view see Chamberlain, ‘“‘ The Living Cycads and the
Phylogeny of Seed Plants,’’ American Journal of Botany, vol. vii. 1920;
Sahni, “‘ On the Structure and Affinities of Acmopyle Pancheri,”’ Phil.
Trans. Royal Soc. Series B, vol. 210, 1920; Benson, “‘ The Grouping
of Vascular Plants,’’ New Phytologist, vol. xx. 1921.
2 F. W. Oliver, ‘On a Vascular Sporangium from the Stephanian
of Grand Croix,’”’ New Phytologist, vol. i. 1902, p. 60.
27
418 STUDIES IN. FOSSIL) BOTANY
the recent Cycadaceous stems. They may well have
been Cycadophyta, though probably not closely allied
to the known Mesozoic or recent types.
The relation of the Pteridosperms to the Cycadophyta
is clear, and indeed, as we have seen, it is sometimes
difficult to draw the line between the two classes. For
the present, it is convenient to keep the Pteridosperms
distinct, on account of their relatively primitive character,
but there is every reason to hope that further discoveries
will effectually link them on to the typically Gymno-
spermous Cycadophyta. The anatomical resemblances,
whichled to the recognition of the ““Cycadofilices,” prepared
us for the discovery of the seeds, which are sufficient in
themselves to demonstrate a near affinity between certain
of the Pteridosperms and the Cycads. Curiously enough,
the relation is closest with the seeds of the recent Cyca-
daceae, a group of which the geological history is still
obscure. Those of the Mesozoic Bennettitales are not
so readily comparable, and evidently represent a more
advanced stage of evolution, their seeds having been
modified and in some respects simplified in correlation
with the development of the complex fruit.
As regards the microsporangiate organs of the Pterido-
sperms, our present somewhat scanty information in-
dicates that they were of the nature of synangia (p. 77) ;
they thus find a remarkable analogy in the compound
pollen-sacs of the Mesozoic Bennettitales (p. 345). The
sporophylls, so little differentiated from the vegetative
foliage, may be compared with the stamens of Bennet-
titeae on the one hand, or with the foliaceous carpels of
Cycas on the other.
The question whether the Lyginopterideae or the Medul-
loseae were the nearer to the main line of Cycadophytic
evolution may be a sterile one, for there were many other
races of Pteridosperms, among which the true ancestry
may lie concealed. A few points of comparison. may,
however, be noted. So far as the anatomy of the stem
GENERAL RESULTS—SPERMOPHYTA —=§ 419
is concerned, Lyginopteris shows analogies with the
Cycads, for the general organisation is of a similar char-
acter, and the mesarch structure of the bundles is still
retained in the peduncles of the cones of some recent
Cycads as well as in the leaves (p. 27). The habit
and anatomy of the Lyginopteris foliage is, however,
unlike anything known either in Mesozoic or recent
Cycadophyta.! It has been suggested that Lagenostoma,
the seed of Lyginopteris, may have given rise to the
seed of Cycadaceae by the cupule becoming adherent
to the integument, and thus constituting the supposed
outer integument of the Cycadean ovule.? This view,
however, assumes that the integument of the seed in
recent Cycads is double, an interpretation which is open
to much doubt.
Seeds of the Tvigonocarpus type (p. 204), referable
to Medulloseae, appear to have much in common with
those. of the Cycadaceae, as shown by the drupe-like
differentiation of the testa, the double vascular system,
and the form of the pollen-chamber. The chief difference
lies in the free nucellus of the Trigonocarpeae, which
contains the inner vascular system, whereas in the Cyca-
daceae the nucellus is adherent to the integument, and
the inner vascular system appears usually to belong to
the latter, though in Bowenza it is described as nucellar.
In spite of these differences, I am inclined to regard
the Tvigonocarpus type as the nearest approach among
Pteridosperms, so far as we know at present, to the seed
of the Cycadaceae.
1 It is conceivable that a phyllodineous reduction of a leaf of the
Sphenopteris type might lead to a structure not unlike that of the leaf
in the genus Cycas, with uninervate pinnae. The very curious Annam
species, C. Micholitzii, Dyer, with quadrifid pinnae, is of interest from
this point of view. See Gardener’s Chronicle, August 19, 1905.
2 M. C. Stopes, “‘ Beitrage z. Kenntnis der Fortpflanzungsorgane der
Cycadeen,’’ Flora, Bd. xciit. 1904; ‘“‘On the Double Nature of the
Cycadean Integument,” Ann. of Bot. vol. xix. 1905. Cf. Salisbury,
“On the Structure and Relationships of Trigonocarpus shorensis,’’
Ann. of Bot. vol. xxvili. 1914, p. 72.
420 STUDIES IN FOSSIL BOTANY
Anatomically, the Medullosean stem differs from that
of recent or Mesozoic Cycadophyta in being polystelic
(except in the peculiar protostelic Swécliffia). Certain
local peculiarities in the vascular system of various
Cycads, due to anomalous distribution of the cambium,
have been interpreted as relics of a polystelic structure,
but these exceptional irregularities do not appear to bear
more than a superficial resemblance to the primary
polystely of the Medulloseae.t | The theory of a possible
derivation of the Cycadales from a monostelic line of
Medulloseae represented by Sutcliffia has already been
discussed (p. 219). |
It is a significant fact that the structure of the petiole
and the organisation of the leaves generally are very similar
in Medulloseae and Cycadaceae, and the resemblance
extends to the Bennettiteae of the Mesozoic. On the
whole of the evidence available it appears likely that
some at least of the Cycadophyta may have been derived
from plants resembling the .Medulloseae (Neuropterideae)
in certain characters, though probably with monostelic
rather than polystelic structure of the stem.
Leaving the Cycadophyta for the moment, we may
now further consider the relation of the Pteridosperms
to the Cordaitales, the characteristic Gymnosperms of
the Palaeozoic. In some respects two groups of plants
could scarcely appear more different than the Fern-like
Spermophyta and the family Cordaiteae. In habit there
is no resemblance, the Cordaitean trees having externally
much more in common with Araucarian Conifers than
with any of the known Pteridosperms (pp. 267, 269).
The specialised cones or catkins of the Cordaiteae, grouped
1 Some of the most striking cases of so-called “ polystely ’’ among
recent Cycads occur in the voot, an organ which in the Medulloseae was
monostelic. For the polystelic interpretation of Cycadean structure
see Worsdell, ‘‘ Structure and Origin of the Cycadaceae,”’ Ann. of Bot,
vol. xx. 1906, p. 129; Matte, Récherches sur l'appareil libévo-ligneux des
Cycadacées, 1903.
abet: ws <
GENERAL RESULTS—SPERMOPHYTA = 4ar
in inflorescences, are wholly remote from the compound,
scarcely differentiated sporophylls, springing from the
main stem, which bore the seeds and pollen-sacs in the
Pteridosperms. The Cordaiteae are altogether on a far
higher level of organisation, and deserve the place among
true Gymnosperms which has always been assigned to them.
There are, however, marked indications of affinity
between Pteridosperms and Cordaitales, great as the
differences between them appear. The strongest mark of
affinity, as already pointed out, is in the seeds, which are
essentially of the same type in the two groups. Of seeds
already known in detail, the closest agreement is between
the Zvigonocarpus group and the Cordaiteae (p. 204) ;
they have in common the double vascular system, the
drupe-like testa, the form of the pollen-chamber, and
probably the free nucellus. On the other hand, they
differ in the fact that the Trigonocarpeae are radiospermic,
the Cordaiteae platyspermic, but this distinction has no
general validity, for we have good evidence that bilateral
as well as radial seeds occurred among the Pteridosperms
(pp: 2202222).
Rhabdocarpus, attributed to Poroxylon by Grand’-
Eury, only differs in small details from the seeds of the
family Cordaiteae (p. 252). We know nothing as yet
of the seeds of the somewhat isolated group Pityeae,
the third family making up our class Cordaitales.
As regards the anatomy, there is a very complete
series leading from the stem of the Lyginopterideae to
that of the typical Cordaiteae, as described by Renault.
In Calamopitys (Eristophyton) we find the first signs of
the dying out of the centripetal wood in the lower part
of the leaf-trace bundle (pp. 124, 127). In Poroxylon the
same condition recurs, with a general structure much like
that of Cordaites itself (p. 248). Inthe Lower Coal-measures
the stems of Mesoxylon, otherwise indistinguishable from
those of Cordaites, have well-marked centripetal wood in
the stem (p. 275). The Pityeae have, however, a quite
422 STUDIES IN. FOSSIL BOTANY
peculiar arrangement of the primary xylem, suggest-
ing a distinct line of descent, supported, as we have
seen, by the characteristic foliage, discovered by Dr.
Gordon. It is at least an interesting point that the
older Cordaitalean stems generally show some trace of
the centripetal wood, while it seems to have disappeared
in the late Carboniferous or Permian species of Cordaites
which Renault investigated. Concurrently with the
gradual extinction of the old Cryptogamic wood, we find
on the whole a tendency to greater density of the second-
ary wood, with a diminution in the width of the medullary
rays. The double leaf-trace is a common, though not a
constant, character at all stages, the division of the trace
extending, on the whole, lower down into the stem in
the later forms. Other details, such as the structure of
the outer cortex, are also common to many members
of the series, from the Lower Carboniferous Calamo-
pityeae to the Permian Cordartteae. Without for a
moment supposing that we have here the actual course
of evolution before us, the series seems to afford some
support to the theory that the Cordaitales (apart from
the Pityeae) sprang from a Pteridospermous stock, while
the leaf-structure supports this conclusion, the mesarch
or exarch foliar bundles of Poroxyleae and Cordaiteae
being a distinctly Pteridospermous character. On the
evidence of the seed-structure and the anatomy together,
the affinity of certain Cordaitales with the Pteridosperms
seems to be well supported, though in point of time the
connection must lie very far back. The question of the
Pityeae must be left open.
The various Cycad-like characters which have long
been remarked in both vegetative and reproductive
organs of the Cordaiteae are doubtless not to be explained
by any direct relation to the Cycads, but may suggest a
common descent from an early Pteridospermous stock.
The possible Pteridospermous affinities of the Cor-
GENERAL RESULTS—SPERMOPHYTA = 423
daitales have an important bearing on the question of
the systematic position of the Coniferae. It has gener-
ally been recognised that the family Cordaiteae is related
to the Coniferae, and if this be so, it follows that the
latter may also have been ultimately of Pteridospermous
descent, and thus find a place in the great phylum of the
Pteropsida.
Some authors, however, have endeavoured to derive
the Conifers from the Lycopodiales,t while others have °
limited this theory to a portion only of the Coniferae,”
implying that the order is an artificial assemblage, made
up of at least two unrelated groups.
Prof. Seward regarded the Araucarieae as probably
of Lycopodineous origin, while he left the question open
for the rest of the Coniferae.* Recently he has expressed
the opinion that the Conifers are probably monophyletic.
Some brief discussion seems necessary here, as the issue
involved is that of the single or multiple origin of the
existing Spermophyta. The position of the Araucarieae
will be primarily considered, since it is this group espe-
cially which has been in dispute.
The Araucarieae present a close agreement with the
Cordaiteae in the structure of the stem, and especially
in that of the wood, which, as universally admitted, is
often indistinguishable in the two families. The essential
feature is that the mass of the wood, apart from the
medullary rays, is composed of tracheides with multi-
seriate bordered pits on their radial walls. This is the
1 E.g. D. H. Campbell, Lectures on the Evolution of Plants, New
York, 1899, pp. 166-167.
2 E.g. H. Potonié, Lehrbuch der Pfianzenpaldontologie, Berlin, 1899,
p. 320. Also the new edition by Gothan, 1921, p. 485.
$ A. C. Seward and S. O. Ford, ‘‘ The Araucarieae, Recent and
Extinct,”’ Phil. Trans. Royal Soc. B, vol. 198, 1906, pp. 305-411. For
Seward’s later views see his Fossil Plants, vol. iv. 1919, p. 166. See
also R. Boyd Thomson, “‘ On the Comparative Anatomy and Affinities
ot the Araucarineae,”’ Phil. Trans. Royal Soc. B, vol. 204, 1913, and
L. Burlingame, “ The Origin and Relationships of the Araucarians,”’
Bot. Gazette, vol. 1x. 1915.
424 STUDIES INV FOSSIL BOTANY
characteristic type of wood throughout the Cordaitales
and Pteridosperms, while it is practically unknown
among Lycopods,! in which the tracheides are very con-
stantly scalariform. The absence of centripetal wood
in the Araucarian stem presents no difficulty on the
hypothesis of Cordaitean affinity, for its gradual dis-
appearance in certain Pteridosperms and in the older
Cordaitales can be traced, until it is lost in the stems
of the typical Cordaiteae. No such links with the stem-
structure of Lycopods are known.
The roots in Araucarieae (and Conifers generally)
are essentially of the same type as in Cordaitales, and
show none of the peculiarities of Lycopod roots.
The leaves of Araucarieae, with their numerous
parallel bundles, agree generally, though not in detail,
with those of Cordaiteae. That the multinervate
character is primitive is indicated by the fact that the
cotyledons likewise contain several ‘bundles. Lycopods
as a rule have only one foliar bundle, which, in the case
of Sigillariopsis, divides into two. If the Araucarieae
are relatively primitive Conifers, a point on which I am
disposed to agree with Prof. Seward, it appears that
the more complex type of leaf-structure is the original
one for the Order. While the general anatomy of the
leaf is thus entirely favourable to Cordaitean affinities,
the histology lends no decided support to either view of
the affinities. The vascular bundles have no typical
centripetal wood, but are accompanied by transfusion-
tissue, which we may either regard, with Mr. Worsdell
and M. Bernard, as representing the centripetal xylem
of Cordaiteae,? or may compare with the well-developed
transfusion-tissue occurring in fossil Lycopods. On any
1 The only case I know of is in Renault’s Sigillariopsis Decaisnet,
where some of the tracheides are pitted, though they do not appear
to agree at all closely with those of the Araucarieae. .
* It will be remembered that, according to Dr. Stopes’s observa-
tions, transfusion-tissue, as well as centripetal xylem, occurs in the
Cordaitean leaf (p. 290).
GENERAL RESULTS—SPERMOPHYTA = 425
view, the centripetal part of the xylem is a tissue which
becomes modified or lost in the higher plants.1
Passing on to the organs of reproduction, the male
cones of Araucarieae show some points in common with
those of Cordaiteae. As we have seen, the stamens of
the latter group have been well compared with those of
Ginkgo. The stamens of Araucarieae, with their distally
attached pollen-sacs, are of the same type as in Ginkgo,
but the large number of the sacs brings them nearer to
the Cordaitean stamen; on the other hand, they differ
absolutely from the sporophylls of the Lycopods, in
which the constant relation of one sporangium to one
sporophyll is a character diagnostic of the class.2 The
numerous nuclei in the pollen-tube of the Araucarieae
present a manifest analogy, as Prof. Seward recognises,
with the multicellular pollen- grains of Cordaiteae and
Pteridosperms. At present we know nothing of the
fertilisation of the ‘‘ seed-bearing ’’ Lycopods, so on this
side the material for an equally close comparison is
wanting.
The female cones of the Araucarieae alone appear
to afford any support to the Lycopod theory. The
single ovule on the upper surface of the cone-scale offers
an evident analogy with the sporangium and sporophyll
of a Lycopod, though if the Cretaceous Protodammara,
with three ovules on each scale, is rightly referred to
Araucarieae (p. 380), the value of the analogy becomes
very doubtful. In any case the vascular system of the
Araucarian cone-scale is totally different from anything
in the sporophylls of Lycopods. The comparison between
1 The structure of Araucarian seedlings obviously cannot be used
in the comparison with a fossil group. Recent work, however, shows
that the anatomy of the seedling in Araucarieae conforms to the same
type as that of the Cycadaceae and Ginkgo, while other Coniferae show
a modification of the type in the direction of reduction.
* The comparison of the Araucarian stamen with the sporangiophore
of Cheirostrobus, suggested by Prof. Seward, is interesting, but by no
means supports a relation to the Lycopods, with which Chetrostrobus
can only have the most remote affinity.
426 STUDIES IN FOSSIL BOTANY
Araucaria, in particular, and Lefidocarpon, on which
Prof. Seward lays stress, appears to amount to no more
than a distant analogy, for the part which envelops
the ovule in Avaucaria is not, as in Lepidocarpon, the
integument itself, but an extra covering enclosing an
already integumented megasporangium.!
Until the nature of the so-called ligule, and, generally,
the relation of the female cones of Araucarieae to those
of other Coniferae, are cleared up (which is far from
being the case at present), it is useless to compare these
strobili with fossil fructifications. It appears probable,
however, that the comparison of the cone-scales with
Lycopod sporophyls, though seductive, may be fallacious,
the great complexity of the Araucarian cone-scale
suggesting that the resemblance is limited to external
characters. In particular, there seems to be little like-
ness, except in name, between the ligule of the higher
Lycopods and the structure called the “ligule ”’ in the
Araucarians.
The absence of a pollen-chamber in the Coniferous
ovule is no doubt correlated with the abandonment of
fertilisation by spermatozoids.
Without extending the discussion further, it may, I
think, be concluded that the Araucarieae have many
points in common with the Cordaitales, of sufficient
weight to establish a real affinity, while the resemblances
to the Lycopodineae are of a more doubtful and superficial
nature, and appear to be completely outweighed by the
great differences which separate these two groups.
Since the Araucarieae have been chosen as the family
most favourable to the Lycopod theory of Coniferous
descent, it does not seem necessary to discuss the question
for the other families. The idea that the Coniferae
include two wholly diverse groups, belonging to distinct
phyla, appears to me quite untenable—either all are
Lycopsida or all Pteropsida. The separatist view, which
1 See Figs. 25 and 26, p. 362 of Seward and Ford’s Araucarieae,
GENERAL RESULTS—SPERMOPHYTA = 427
is probably no longer maintained, arose from paying
attention too exclusively to particular organs rather
than to the whole sum of characters.
Taking all the characters into account, there thus
appears to be a decisive balance of evidence in favour
of deriving the whole of the Coniferae from the Cor-
daitales, in a wide sense, without tracing them through
the particular family Cordaiteae (of which, after all, our
knowledge is still very narrow). The Conifers thus fall
within the great division Pteropsida, though in their
case the analogies with Ferns have disappeared. This
view involves the conclusion that the microphyllous
habit, which characterises so many of the Coniferae,
is the result of reduction in the leaf, correlated with the
increasing ramification of the stem, and also expressing
a more perfect adaptation to the conditions of life on
dry land.!
The relations of the Ginkgoales to the Cycads and
Cordaiteae are universally admitted, and need not be
further discussed here (pp. 311, 384).
The characteristic Mesozoic Cycadophyta, the Ben-
nettitales, were fully considered in the last chapter.
Although the fossil Angiosperms do not fall within the
scope of these “ Studies,’”’ a few words may be added
on the relation of the great modern sub-kingdom to the
scarcely less dominant Cycadophyta of the Secondary
Period.
The general arrangement of the organs in the Bennet-
titalean fructification, as shown by Dr. Wieland’s classical
1 I] have purposely refrained from discussing the views of Prof.
E. C. Jeffrey and his school, according to whom the Abietineae are the
most primitive Conifers and the Araucarieae are derived from them.
Such a discussion would demand a much fuller consideration of the
Coniferae than is possible here. For a summary of Prof. Jeffrey’s
theory, see his Anatomy of Woody Plants, 1917, chap. xxiv. For
criticisms, see the papers on Araucarieae above cited; also Gothan,
Potonié’s Lehrbuch, 1921, p. 342; and Seward, Fossil Plants, vol. iv.
1919.
428 SlUDIES IN2FOSSiL -BOoian®y
investigations, is essentially the same as in a typical
Angiospermous flower, with a central pistil, a surround-
ing whorl of stamens, and an enveloping perianth (see
PP. 343, 375). The whole organisation, as Dr. Wieland
at once recognised, is best compared with that of the
flower in Magnoliaceae, such as the Tulip-tree (Livio-
dendron), while the resemblance extends to other orders
of polypetalous Dicotyledons, e.g. Ranunculaceae and
Nymphaeaceae. The occurrence, in some cases, of unl-
sexual flowers does not affect the comparison. These
groups, especially the Magnoliaceae, have been widely
accepted as relatively primitive, and there is evidence
for their occurrence in Cretaceous rocks. |
As we have seen, the gynaecium of Bennettitales
shows some approach to the condition of a closed Angio-
spermous ovary, while the seed of Bennettites was
practically exalbuminous, the large Dicotyledonous
embryo filling the embryo-sac—a feature otherwise met
with only among the Angiosperms.
Taking the whole of the characters into consideration,
the evidence for some affinity between the Mesozoic
Cycadophyta and the Angiosperms appears strong. It
cannot, of course, be supposed that the Bennettitales
were on the direct line of Angiospermous descent, for
there are manifest points of difference, notably (apart
from the anatomy) in the complexity of the stamens
(though this was by no means constant) and in the
organisation of the ovary-wall or pericarp, which was
not formed by the carpels themselves, but by the
associated sterile scales. The connection was probably
nearer with the older Williamsonian tribe than with the
specialised Bennettiteae themselves. Dr. Wieland points
out that in Wrelandiella and Williamsoniella the branch-
ing was but little simpler than in some Magnolias.}
There is much difference of opinion as to the nearness
of the relation between Bennettitales and the higher
1 Fossil Cycads, vol. li. pp. 54 and 219.
GENERAL RESULTS—SPERMOPHYTA = 429
Flowering Plants; some would reduce it to a mere
analogy ; but the points of agreement are so striking
that we may fairly conjecture that a real relation may
exist, and that the ancestry of the Angiosperms, hitherto
the most obscure subject in the phylogeny of plants, may
perhaps be sought somewhere among the great plexus of
-Cycadophytes, which overspread the world during the
Mesozoic Period.!
This conclusion opens up the question of the rela-
tion of Monocotyledons to Dicotyledons. If the Angio-
sperms are related to Cycadophyta, it would appear
to follow that the Dicotyledons were first evolved, for
their structure has clearly much more in common with
the Cycad type than that of the. Monocotyledons. The
latter would thus be regarded as a branch line of descent,
diverging, no doubt at a very early stage, from the main
Dicotyledonous stock. This view has been maintained,
on other grounds, by various modern botanists. So far,
however, as the palaeontological record shows, the two
classes are of almost equal antiquity, both being recorded
for the first time in Lower Cretaceous rocks.” By the
Upper Cretaceous age the Angiosperms had already
seized the dominant position which they now hold; the
Monocotyledons were always subordinate in numbers to
the other class, but the occurrence of typical Palm-wood
in Cretaceous rocks is a striking proof of the early evolu-
tion of one of the most characteristic Monocotyledonous
families.
The relation of the Bennettitales to the Pteridosperms
1 See Arber and Parkin, “‘ The Origin of pases ee Journal
Linn. Soc. (Bot.), vol. xxxvili. 1907.
2 The discovery of several distinct types of highly ae Dico-
tyledonous stems in the Lower Greensand, shows that the history of
this class must run enormously further back than it has yet been traced.
See Dr. Marie C. Stopes, Catalogue of the Cretaceous Flora, vol. ii. 1915,
pp. 258-294.
3 The very remarkable Middle Jurassic fruits (Caytonia and Gris-
thorpia) discovered by Mr. Hamshaw Thomas, but not yet fully described,
may throw a new light on the question of Angiospermous evolution.
430 SPUDIES INCPOSSIL- BOTANY
has been sufficiently emphasised in preceding pages. We
are thus led to the conclusion that the whole of the
Angiospermeae, the dominant sub-kingdom of Flowering
Plants, if akin, as is suggested, to the Cycadophyta,
belonged ultimately to a phylum which, from its analogy
with the Ferns, is included in Pteropsida. We may add
that the Gymnosperms, as a whole, may probably be
referred to the same stock, for evidence has been adduced
that the small group of the Gnetales (the only outstand-
ing Gymnospermous family) may have been derived, by
reduction of the floral organs, from forms allied to the
Bennettitales.1 |
It thus appears, if the views here taken are justified,
that the whole of the Spermophyta, whether Angio-
spermous or Gymnospermous, may have been ultimately
derived through primitive Seed-plants of the nature of
Pteridosperms, from one ancient stock, which may like-
wise have been the ultimate source of the Ferns. With
this far-reaching hypothesis we may conclude our con-
sideration of the phylogenetic results of our studies.
In bringing these “Studies” to a close; 11 1S saee
to recall the necessary limitations of all attempts to
unravel the past history of organisms. Our ideas of
the course of descent must of necessity be diagram-
matic ; the process, as it actually went on, during ages
of inconceivable duration, was doubtless infinitely too
complex for the mind to grasp, even were the whole
evidence lying open before us. We see an illustration,
on a small scale, of the complexity of the problem, in the
case of domesticated forms, evolved under the influence
of man. Though we know that our cultivated plants, for
instance, have been developed from wild species within
the human period, and often within quite recent years,
yet nothing is more difficult than to trace, in any given
1 Arber and Parkin, ‘“‘ Relationship of the Angiosperms to the
Gnetales,’’ Annals of Botany. vo). xxii. 1908.
CONCLUSION 431
instance, the true history of a field-crop or a garden plant,
or even, in many cases, to fix its origin with certainty.
In the history of natural groups, where the geological
record takes the place of the cultivator’s notes, the
problem increases so immeasurably in difficulty that a
full solution becomes impossible.
But although, in endeavouring to form an idea of
the course of evolution of any part of the Vegetable
Kingdom, we can only hope, at the best, to construct a
scheme, representing in a much simplified form the real
succession of events, we must take care not to be misled
by our own constructions. We must remember that, at
all periods, competition among living things was as keen
as now, and that in every age all the available places
must soon have been filled. Hence, even in the earliest.
times of which the palaeontologist takes cognisance, there
must always have been specialised forms, and even what
we call “synthetic ’’ types were themselves specialised
to suit some particular set of conditions. Thus, at
every step in the investigation of the fossil evidence,
the same caution in distinguishing between the newer
and the older characters 1s demanded as when we are
dealing with recent organisms.
The present difficult position of the Theory of Descent, |
now that the Darwinian period, with its confident out-
look, has passed by, imposes greater caution than ever
on our speculations. In our complete ignorance, now
realised, of the methods of Evolution, we cannot hope
for very definite success in tracing its course. A more
tentative and diffident tone seems to be demanded in
discussing phylogenetic problems, and may be found,
it is hoped, in the present issue of this book.
Yet, in spite of all these difficulties, and others, more
obvious, which will at once occur to the mind, there
can be no question that the study of the actual records
of the past is of inestimable value in attacking a problem
which is in its essence an historical one.
432 STUDIES: IN FOSSIL SOAR Y
In these “ Studies ’’ the fossil record has been con-
sidered almost wholly from a morphological and evolu-
tionary point of view. There is room, even with the
material already available, for important work on other
lines. The subject of the biology and ecology of fossil
plants, as illustrated especially by their physiological
anatomy when suitably preserved, offers a wide and
promising field of research. Such biological studies
would be of the greatest intrinsic interest, and may
also throw a new and welcome light on the problems of
Evolution.
a — a
INDEX
An asterisk indicates a figure on the page cited.
Abietineae, 380, 381
Acanthophyllum, 41
Actinopteris, 384
A diantites, 220
Adiantum, 220
Aeschynomene, 285
Aetheotesta, 210
elliptica, 226
Agathis, 288, 290, 312, 369, 380
macrophylla, 312
Albian, 380
Alethopteris, 170, 171, 182, 184, 189,
190, 196, 204, 207, 212
Grandint, 170, 212
lonchitica, *172, 183, 208
Pfeilstickert, 170
Algae, 387, 391, 392, 393, 394, 397
thallophytic, 394
Allen, J., 56
Alternation of generations, 395
Amyelon, 287
~ vadicans, *286
Anachoropteris, 414
Anatomy, 419
Androecium, 353, 356, 358, 372, 377
Androstrobus Nathorstt, 366
Scottit, 367
Aneimiteae, 220-221
Aneimites, 220, 221, 222, 240
fertilis, 220
tenutfolius, 221
Angtopterts, 172
Angiosperms, 275, 335, 346, 373, 375;
377, 386, 396, 427, 428, 429
affinities, 427-429
Anodic, 32
Anomozamites, 317, 363
Antarcticoxylon, 284
Priestleyt, 284
Anther, 300, 313, 369
Antheridium, 296, 300, 301
Antherozoids, 211
Antholithus, 266, 271
Anthostrobilus, 373
Aphlebiae, 161, 162, 168, 172
Araucaria, 228, 265, 270, 273, 288,
300, 378, 379, 420, 425, 426
excelsa, 259, 260, 378
affinities, 260 *
Araucarieae, 273, 296, 379, 380
affinities, 423-426
Araucarioxylon, 269, 270, 273, 274,
378
Brandlingtt, *274
Rhodeanum, 378
Avraucarites Beinertianus, 126. See
Calamopitys Betnertiana
Tchthatcheffi, 283. See Mesopitys
Arber, Agnes, 308, 310
Brper, EAS NN. 72,73 178s av 7s
183, 373, 385, 388, 394, 395, 397,
410, 412
Arber and Parkin, 429, 430
Archaeocalamites, 404, 405, 407, 408,
410
Archaeopitys, 256, 260, 261, 262, 263,
264
Eastmanit, 258, 261
Archaeopteris, 414
Archegonium, 88, 209, 301, 307,
308
Arctopodium radiatum, 159, 161, *162,
*163, 164
Argonne, 380
Articulatae, 396, 399, 409
Artisia, 270. See Sternbergia
Asterophylliteae, 386
Asteroxyleae, 394, 395
Asteroxylon, 387, 392, 393, 394, 397;
398
Mackiet, *389
Autun; 17,192, 194, 216, 223, 238;
244, 284
Ayrshire, 133
433 28
434
Batera, 384, 385
Raymond, 384
virginiana, 384
Balaton See, 126
Bamboo, 343
Bancroft, 364
Barner, C. A.,-383
Barnsley, 88
Beanta gracilis, 367
Beck, R., 170
Bennettitales, 295, 305, 314, 320-366,
369, 418, 427, 428, 430
affinities, 370-377
Bennettiteae,. 219, 236, 320-353, 357;
359, 363, 3605, 370, 371, 375, 420,
428
characters, 353
embryo, 333-335, *334, 338, *339
flowers, 342-352, *343, *344, *346,
*347
fruit, 328-340, *329, *330, *332,
*336
leaves, 324, 341
ramenta, 326, 327
root, 327
seed; 328-330; *330, *334, +336,
*339
Stem, 320-327, 340, 341,:°310;, *322,
*323
Bennettites. See also Cycadeoidea,
71, 320-341, 360, 363, 428
diagnosis, 320
albianus, *336, 337, *339, 340
Gibsonianus, 221, 321, *322, 325,
327, 3287329, *330, *332; *334,
337, 342, 344, 345, 350, 351
MAXIMUS, 351
Morteret, 337, 374
Peachianus, 324
Saxbyanus, *323
Scottit, 327
Benson, M., 11, 78, 81, 83, 291, 292,
399, 402, 407
Benthic, 393
Bernard, 424
Bertrand, C. E., 244, 248, 251, 252,
253, 296, 301, 304
Bertrand, Paul, 156, 157, 158, 161,
162, 164, 166, 168, 169, 213, 215,
220; 227, 226
Berwickshire, 160
Bilignea, 107
veSINOSA, 134.
solida, 134, 135
Binney, 21, 204
Black flints, 287
Black pebbles, 209
Bohemia, 3
Bothrodendron, 402
STUDIES. IN FOSSIL BOTANY
Botrychioxylon, 413
Botrychium, 413
Botryopteridaceae, 412, 413, 414
Botryopterideae, 412, 414, 417
Botryopteris, 412
Bowenta, 250, 308, 340, 341, 419
Bower, F. O., 390, 397, 403, 407
Brachyphyllum, 380
Braun, 384
Brenchley, 42
Brongniart, A., 194, 209, 252," 300:
311, 355, 386
Brook Point, 323
Browne, Lady I., 406
Bryophyta, 390, 393, 394
Bucklandia, 317
Bud, 225, 281, 290, 302,)327.000am
350, 352, 360, 361, 371, 372, 379
Burntisland. See Pettycur
Cactus, 365
Caenoxylon, 283, 284
Scotti, 283
Calamariaceae, 404, 405, 410, 411
Calamites, 410
Calamopityeae, 94, 107-132, 144,145,
240, 241, 243, 256, 273, B14, 4am
new, 132-135
Calamopitys, 108-132, 145, I51, 154,
246, 249, 282, 406, 416, 421
affinities, 129-135
americana, 108, 109-116, *111,
*112, *17r3, *I15, L250, Leos
128; 129, 131, 132, mee
annularis, 108, I09, I12, 116-118,
*I17, II9Q, 124, 129, 130;5ta
134, 156
Betinertiana, 108, 109, 126-128, 129,
T31, 198, 276, eae
fascicularis, 107, 108,
*723'-329, Lar
vadiata, 133, 145
Saturnt, 108,. 109, 118-122). "110,
724, 126, 129, 130, 13%, 13a,080
synopsis, 128-129
zonata, 133
Calamopteris, 121
Htippocrepis, 121
Calamostachys, 29, 295, 404, 405, 407
Calciferous sandstone series, 57, 95,
122, 133, 134, 147, 160
I22-126,
Caldwell, O., 300
California, 380
Callipteris, 190, 224
Callitris, 381
Reichii, 381%
Callixylon, 262, 264, 265, 417
Newberryt, 204
Owent, 264
INDEX
Callixylon (contd,)—
Trifilievi, 262, *263, 280
Calymmatotheca Stangert, 57, 71
Campbell, D. H., 423
Canopy, 67, 83, 86
Carboniferous, 132,
402, 412, 422
Limestone Series, 59, 72, 122, 126,
133
Lower, 3, 79, 80, 84, 107, 108, 122,
126, 133, 134, 145, 153, 157, 160,
165, 220, 227, 229, 254, 256, 257,
261, 405, 417, 421, 422
Permo-, 223, 225, 244, 284, 417
Upper, 79, 100, 282, 378, 414,417,429
Cardtocarpon, 306
compressum, 308
Cardtocarpus, 306
Carpentier, A., 73, 170, 215
Carruthers, W., 292, 317, 321, 323, 324
Casparyan strip, 54
Casts, 204
Catkin, 271, 292, 293, 295, 296, 301,
304, 305, 313, 420
Caulopteris, 223
Cephalotaxus, 313, 382
Chalaza, Bennettites, 333
Cardtocarpus, 306
Lagenostoma, 67
Physostoma, 85
Sphaerostoma, 82
Trigonocarpus, 206, 207
Cheirostrobus, 391, 392, 393, 394, 395,
399, 405, 406
Chodat, R., 76, 77, 91, 92
Church, A. H., 393, 395
Cladoxyleae, 156-169, 176, 227, 228,
229, 231, 235, 237, 238, 239, 241
affinities, 166-169
Cladoxylon, 57, 158-164
dubium, 165, 227
Kidstoni, 158, 160, *167
mirabile, 158, 159, 161
Solmst, 158, 159, 160, 164
taentatum, *157, 158, 159, 164
Classification of Vasculares, Scheme,
395, 396
Clepsydropsis antiqua, 156
Clubmoss, 392, 393
Coal-balls, 87, 281, 291
Coal measures, 270, 281, 292, 304,
369, 384
Lower, 72, 173, 185, 186, 208, 276,
287, 291
Middle, 3, 21, 88, 202, 220
Upper, 17, 21, 186, 209, 212, 216,
221, 228), 287
Westphalian, 203
Colne, 185
265, 300,
294,
435
Colorado, 318
Colpoxylon, 194-196
aeduense, 194, *195
Colymbetes Edwardst, 326
Commentry, 216
Compositae, 375
Conclusion, 430-432
Conifer, 130, 146, 160, 228, 231, 265,
266, 271, 273, 285, 290, 295, 365,
369, 420, 423, 424, 427
Coniferae, 268, 270, 271, 281, 292,
304, 305, 306, 311, 312, 315, 310,
377-383
affinities, 422-427
Conostoma, 86
anglo-germanicum, 87
intermedium, 81
oblongum, 87
ovale, 80
Corda? A: Jj., 2
Cordatanthus, 310, 313
anomalus, 305
female, 296-304
Grand’ Euryt, *298
male, 293-296
morphology, 304-305
Penjont, 293, *294
pollination, 300
Saportanus, 293
Williamsoni, *297
Cordaicarpus, 306
Cordaitales, 132, 241, 243-315, 385
affinities, 416, 417, 420-427
Cordaiteae, 130, 206, 265-315, 373,
385, 420-427
affinities, 311-315
Cordaites, 260, 265, *272, 273, 281,
284, 315, 378
angulosostriatus, 288, *289
Brandlingit, *274, 285
cvassus, 290
external characters, 266-271
Felicis, 291
fructification, 292-305
leaves, 287-292
lingulatus, *289, 290
principalis, 290
rhombinervis, *28 )
root, 286-287
seeds, 305-311
shorensis, 287
stem, 271-275
Wedekindt, 292
Cork, 200, 251
Cormophytic, 394
Corylus Colurna, 66
Coseley, 215
Cotta, B., 190
Cotyledon, *330, *334, *339
436
Cracow, 351
Craigleith, 254
Cretaceous, 368, 380, 381,
425, 428
Lower, 316, 318, 351, 429
Upper, 366, 381
Crossotheca, 74-80, 89, 93, 216, 217,
223, 224, 369
Hontnghaust, *75, 76,
Hughesiana, 78
Crows’ nests, fossil, 317
‘““ Cryptogamic ”’ wood, 236, 422
Cryptogams, vascular, 240, 386, 390,
394, 410, 415, 416
Cryptomerta, 380
Cupressineae, 381
Cupressinoxylon vectense, 383
Cupule, 57, 93, 419
Calymmatotheca Stangeri, 72, frontis-
piece
Gnetopsis, 87, 88
Lagenostoma Lomaxt,
765, "07, *68
E.. Sinclair, 72; *73
Neuropteris, *216
Sphaerostoma, 81, *82
Sphenopteris Dubutssonis, 73
Cuticle, 384
Cycadaceae. See Cycadales, 89, 179,
218, 219, 299, 305, 312, 317, 363,
367, 370, 371, 418-420
382, 383,
477, 7OOo
63-66, *64,
Cycadales, 219, 366-369, 370, 371,
376, 420
Cycadella. See Cycadeotdea, 340, 341
Cycadeoitdea. See also Bennettites,
340-353
colossalis, 349, 350
dacotensts, 342, 343, 344, 345, *346,
*347, 351; 352
Darton, 353
etvusca, 342
gigantea, 317
ingens, 342, *346, *347
J enneyana, 350
marylandica, 318, *319, 321
micromyela, 325
Patinet, 352
vamentosa, 341
Reichenbachiana, 351
Yatesu, 325
flower, 342-352
fruit, 352, 353
gynoecium, 343-345
monoecism, 350
stamens, 345-349
Cycadeoideae. See
358, 365, 376
Cycadinocarpus augustodunensis, *307
Cycadites, 317, 368
Bennettiteae,
SLUDIES/“IN FOSS BOTAN
Cycadocarpidium, 368, 369
Cycadocephalus, 364
Cycadofilices, 2, 69, 94, 106, 131, 153,
166, 239, 241, 418
Cycadophyta, 3, 89, 219, 235, 237, 238,
240, 243, 306, 314, 315, 316-377
affinities, 369-377, 418-420, 427-430
results of American research, 340-
353, 357-358
Cycadospadix Hennoquet, 368
milleryensts, *238
Cycadoxyleae, 229-239, 417
Cycadoxylon, 229-233
Fremyt, 232, 233, 236
robusium, 229, ‘230, 231, 232eaas
235, 236
Cycas, 317, 325, 367, 369, 374, 376,
418
ovule, *299
Micholitzit, 419
pectinata, 368
Cyclopteris, 172
Dacrydium, 382
Dadoxylon, 229, 264, 269
oldhamium, 21. See Lyginopteris
Spencert, 282. See Parapitys J
Dakota, 318, 319, 342, 353
Dalry, 134
Darnell Smith, 396
Darwinian, 431
Davallia aculeata, 55
Dearnley, 199, 200
De Bary, 32, 300
De Fraine, 185, 199, 200, 201, 219
Dehiscence, 293, 349
Descent, theory of, 431
Devonian, 220, 397, 416
Early, 386, 387, 390, 391, 395, 397;
398, 405
Middle, 392, 409, 415
Upper, 108, 100, 157, 262,209
305, 402, 404, 414, 417
Dialystelic, 188
Diarch, 412
Dichasium, 371
Dicksonia, 186, 221
Dicksontites, 221
Dicotyledons, 237, 285, 316, 334, 335»
338, 386, 428, 429
Dictyopteris, 170, 273,
pterts
Dictyostelic, 188
Dictyoxylon, 3, 26
cortex, 28, 34, 166
oldhamium, 21
Dioon, 238, 340, 371
Dioonttles, 316, 317
Diplolabis, 106
See Litno-
INDEX 437
Diplotesta, 301, 310
Diplotmema, 11
Dirt-bed, 317
Discoid pith, 271, 281, 311
Disk, 345, 351, 355, 356, 358, 363
Dolerophyllum, 225, 226, 242
Berthiert, 225
Goeppertt, 225
Donetz basin, 262, 281
Dorycordaites, 221, *267, 268
Dracaena, 263
Dudley, 76, 77, 78, 202
Duisburg, 87
Dulesgate, 17
Dumbartonshire, 133, 134
Eastman, C., 109
Eathie, 359
Ecology, 432
Embryo, absence of, in palaeozoic
seeds, 7I, 311
Benneitites, 333, *334, 428
Cycadeotdea, 353
Psilotales, 396
Embryo-sac, 206. See Megaspore
Encephalartos, 188, 237, 310
Endarch, 148, 283, 284
Endosperm, 307, 308, 331, 333, 334;
335, 338
Endotesta, 307
Ephedra, 294
Epidermis, 208, 363, 372
Equisetales, 396, 399
affinities, 404-411
Equisetum, 295, 410, 411
Eremopteris artemtsiaefolia, 221
Eristophyton. See Calamopitys, 151,
154, 416, 421
Eu-Calamopitys. See Calamopitys
Eu-Cordaites. See Cordaites, 267
Eu-Heterangium. See Heterangitum,
12, 18, 20, 98
Euphorbiaceae, 270
Eustele, 61
Evolution, 431-432
Exalbuminaous, 333, 353, 376, 428
Exarch, 240
Falkenberg, 108, 126, 145, 165
Ferns, 9, 168, 170; 176, 186, 188, 202,
203, 213, 218, 316, 326, 345, 347,
377, 384, 386, 393, 430
affinities, 89-90, 240, 411-414, 415,
416
tree, T52, 175
Fertile shoot of Mesoxylon, *303
Fertilisation, 426
Filicales, affinities, 398, 411-414
Filices, 412
Filicineae, 155
Fliche, 380
Flora, 386. See Devonian
land, 391, 393
Flowers, 293, 295, 384, 385
angiospermous, 428
Bennettiteae, 342-352
Williamsonieae, 355-364
Treezeout Hills, 318
Fumaria officinalis, 10
Funicle, 304, 373
Gametophyte, 396
Gault, 337
General results, 386-432
Genessee shales, 10g
Gibson, T. F., 328
Ginkgo, 275, 282, 295, 299, 301, 304,
308, 311, 312, 313, 316, 384, 385,
425
Ginkgoaceae. See Ginkgoales
Ginkgoales, 304, 313, 383-385, 427
Ginkgottes, 384
Gland, Lyginopteris oldhamia, *48,
*65
Gletchenta, 8, 61
Gleicheniaceae, 61
Gnetaceae, 87, 294, 205, 304, 312,
313, 314
Gnetales, 430
Gnetopsis anglica, 88
elliptica, 87, 88
Gnetum, 312
Goeppert, H. R., 145, 165, 188, 226,
254, 283
Goniatite, 196
Gordon, W. T., 95, 100, 106, 256, 261,
202; 2055, 417,422
Gothan, W., 76, 77, 170, 225, 383
Gourlie, 21
Grand Croix, 225
Grud Bury, ©, 73, 22, 213, 214,
2i7, 220, 224, 244, °250,-252, 206,
268, 271, 292, 298, 302, 312, 421
Greenland, 368
Greensand, Lower, 320, 351, 382
Griffith, W., 299, 300
Gristhorpe Bay, 360
Gullane, 257
Gum Canals, Bennettites, 326, 332
Medullosa, 182
Poroxylon, 246, 247
Gwynne-Vaughan, D. T., 136, 138,
141, 144, 414
Gymnospermeae, 396
Gymnosperms, 2, 107, 124, 130, 156,
221, 239, 243, 251
affinities, 414-427
mesozoic, 316-385
438 STUDIES IN [FOSSIL BOTAN”
Gynaecium, Bennettiteae, 357, 359,
360, 361, 363, 372, 373, 374,
428
Hairs in Lyginopteris, 66
Williamsonia, 359
Haitingeria, 369
Halifax, 282
Halle, DT. G., 356, 393; 411
Haltwhistle, 122
Hapaloxylon, 285-286
Rochet, 286
Helminthostachys, 408
Hemingway, W., 406
Herminiera, 285
Hermosa cycad, 353
Heterangium, 2-19, 24, 91, 95-98,
HOO, 1OL, DLL, (£392) 270;--194,
201, 225, 241
affinities, 18-21, 60-63
alatum, 12
Andret, 18
hibractense, 17
Duchartret, 17
geriense, 186. See Medullosa gert-
ensts
Grievit, 3-11, *4, 3; o; “95 9)
*I0
leaf-trace and leaves, 8-11
root, II
seed, 80-84
stem, 3-8
intermedium, 19
Lomaxt, 17
minimum, 13
paradoxum, 3
polystichum, 12
punctatum, 17
Renaultit, 17
shorense, *16
Schustert, *13
Sturt, 12
tiliaeoides, 14, *15, 177, 183, 248
Heterospory in Calamariaceae, 410
Lycopods, 401, 402, 403
Hexapterospermum, 213, 214
Hexarch, 404
Hickling, G., 406
Hierogramma mysticum, 163, *164
Hirase, S., 210, 308
Hollick, H., and Jeffrey, E. C., 380
Holloway, J. E., 396, 397
Homoplastic, 398
Homospory in Calamariaceae, 410
Lycopods, 401
Hooker, Sir J., 204, 415
Hornea, 390, 401
Horsetails, 410, 411
Hough Hill, 173
Hyenta sphenophyllotdes, 409
Hymenophyllaceae, 413
Hypocotyl, 334, 338
Hypogynous, 346, 358
Iberts, 32
Ikeno, 210
India, 357
Integument, 206, 296, 297, 338, 419,
426
Interseminal scales, 335, 336, 338,
344, 350, 359, 361, 363, 371, 372,
373, 374, 376
Isle of Wight, 382
Isoétes, 401, 403
Jasmineae, 270 ?
Jeffrey, -E. C.s 26%, 381,363) 200
Jongmans, W. J., 203
Jurassic, 341, 366, 369, 370, 381, 384,
385
Lower, 228
Middle, 360
Upper, 318, 359
Kaloxylon Hookeri, 49. See Root of
Lyginopterts
Kalymma, 114, *115, 116; 125, aaes
128; 129
Karroo, 228
Kathodies 31; 33
Kauri Pine, 268
Kentucky, I09, 117, 118, Faigpemeos
256, 261
Keuper, 366
Kidston, R., 10, 57; 72, 90, Is2,emeas
138, I41, 144, 153, 158, 160, 202,
213, 214, 217, 223, 390, 392, 396,
407, 414
Kidston and Gwynne-Vaughan, 414
Kilpatrick Hills, 122
Krasser, 369
Kraus, 145, 273
Kubart, 12, 18, 58, 60, 414
Lagenospermum, 73
Lagenostoma, 81, 84, 86, 419. ee
Lyginopteris oldhamia, seed
Lomaxt, 63-71, *64, *65, *66, *67,
*68 "70; 72 735,00
Canopy, 67
Chalaza, 67
Cupule, 63, 65, 66, 71
Gland, *65
Micropyle, 68, 69
Nucellus, 68
pollen-chamber, 68, 71
pollen-grains, 68, 69, 71
pollination, 68
a
INDEX
Lagenostoma Lomaxi (contd,)—
prothallus, 69, 70
ovotdes, 74
physoides. See Physostoma elegans
Sinclairi, *72, *73
Lagenostomales, 86, 89
Lagenostome, 68, 83, 86, 88, 93
Lang, W. H., 390, 392, 393, 407
Langendreer, 87
Langton Burn, 141
Lawson, A. A., 396
Leaf, origin of, 408
Leaves, A gathis, 312
Alethopteris, 172
Aneimites, 220
Anomoszamites, 317, 363
Bennettites, 327
Cordaites, 266, 269
Cycadeoidea, 341
Cycadites, 317, 369
Cycas, 369
Dioonites, 316
Dolerophyllum, 225, 226
Heterangium Grievit, 8, 10, 11
Hyenta, 409
Medullosa anglica, 182
Mesoxylon, 280, 281
Neuropteris, 171
Otozamites, 317
Pecopteris Pluckenett, 222
Pitys, 259, 260, 261, 262, 265
Poroxylon, 244, 250, 251
Pseudocycas, 369
Pterophyllum, 238
Sphenopsida, 405
Sphenozamites , 238
Taentopteris, 362
Titanophyllum, 196
Wielandiella, 363
Williamsonia, 355
Williamsoniella, 362, 363
. Zamites, 316
Leeson, Dr., 328
Le Goc, 92
Leguminosae, 285
Lepidocarpon, 402, 425, 426
Lepidodendreae, 400, 401, 402, 403
Lepidodendron, 400, 401
selaginotdes, 106, 399
Lepidophlotos fuliginosus, 401
Lepidostrobus, 403
Liane, 188, 229
Lias, 357, 366, 385
Lower, 368
Upper, 380
Lignier, O., 321, 337, 339, 372, 404,
407, 414
Lignites, 383
Ligule, 426
439
Limburg, 203
Linopteris, 213, 214
Brongniartt, 217
Germari, 216
obliqua, 214, 217
Lirtodendron, 428
Liverwort, 391
Loire, 270
Lomax, J., 173, 196
Loxsoma, 186
Luccomb Chine, 328
Lunz, 369
Lunzia, 369
Lycopodiaceae, 4.03
Lycopodiales, 395, 398, 410, 423
heterosporous, 402
homosporous, 401
Lycopodineae, 426
Lycopodites Mulleri=Thursophyton,
392
Lycopodium, 392, 393, 401
Lycopods, 253, 367, 397-403,
424-426
Lycopsida, 393, 394, 395, 397
affinities, 398-403
Lycostrobus Scotti, 367
Lyginangium, 14, 18, 20
Lyginodendreae, 2
Lyginodendron. See Lygenopteris, 21
vobustum, 229
Lyginopterideae, 1-93, 94, 95, 96, 99,
£00, 107, 146, .532, 201, 218,232,
240, 241, 243, 256, 314, 418, 421
affinities, 88-93
anatomical characters, 60-63
fructification, 63-88
Lyginopteris, 18, 19-57, 78, 81, 91,
PLO; LIT-T13,, E52, °154-156;, 176,
201, 204, 224, 231, 235, 236, 237,
246, 247, 249, 251, 252, 253, 275;
282, 311, 416, 419
reproduction, 63-80, and frontis-
piece
heterangtotdes, 19, 20, III
lacunosa, 60
oldhamia, 18, 21-57, *23, *25, *26,
2 a ae ae Pade 7 ota |
PAA, TAS, 7 40,) 798, 750, SE,
ra3i 63-71, TG: 72; 76, 119,
125, 220, 230, 234, 236, 240
anomalies, 40-42
branching, 26-40
glandular spines, 47-49
habit, 55-57
leaf, 42-47
microsporangia, 74-80
reproduction, 63-80
roots, 49-55
seed, 63-71
410,
440 SPUDIES INsFOSSEL "BOTANY
Lyginopterts oldhamia (contd.)—
stem, 22-36
tristicha, 60
Lyginorachts, 57-60
Papilio, 57-59
Taitiana, 59
Macconochie, 135
Macrozamia, 188, 2373 325
Madagascar, 146, 380
Magnoliaceae, 428
Maidenhair tree.
Mallow, 345
Mangrove, 46
Marattia, 349
Kaulfusstt, 348
See Ginkgo, 68, 385
Mara ttiaceae, 76, -90,°223, 24600377,
412, 414
Martopteris, 224
muricata, 224, 225
Marsh, A. S., 91
Marsilia, 186
Maryland, 318, 319
Masien, A. ]., 276; 278, a8r
Matheson, A., 135
Matte, H., 420
Mazocarpon, 399, 402
M‘Lean, R. C., 60
Medullosa, 160, 173-194, 196, 198,
201, 207, 218, 219, 241, 250, 289
angitca, 173-185, *174, *175, *177,;
7479, *18X,. *IO1, 193; 194,
108, 200, (207,, 208, 212,), 210,
248, 251
leaf, 179-183
root, 183-184
stem, 173-179, 187
summary, 184
centrofilis, 185-186, 192, 194
elegans, 190. See Myeloxylon
gertensis, 186
gigas, 190, 192, 232
Leuckarti, 189, *191, 193, 194
Ludwigtt, 226. See Steloxylon
porosa, 190, *191, 192
pusilla, 185, 186
Solmsi, 189, *I91, 192, 193, 200
stellata, 186, 187, 189, I90, *I9gI,
192, 193, 200
var. corlicata, *191
var. gigantea, 187, *191
var. lignosa, 192
Medulloseae, 95, 98, 100, 159, 167,
170-220, 228, 240
affinities, 201, 217-220,-418, 420
anatomy, 173-201
fructification, 201-217
habit, 170-173
Megaloxyleae, 94, 101-107, 125, 240
Megaloxylon, 100, I0I-107, 125
Scottt;-I0L, Toe; *1035 *z05
Megaphyllous, 394
Megaphyton, 151, 154
Megasporangium, 89, 402, 403, 426
Megaspore in Lagenostoma, 69
_Mitrospermum, 310
Physostoma, 86
Sphaerostoma, 83
Trigonocarpus, 206
Meristele, 198, 199, 200
Mesarch, 5, 24, 240, 256, 284, 288,
302, 325, 400, 419
Mesopitys, 133, 283-284
Tchthatcheffi, 283
Mesoxylon, 154, 252, 272, 275-281,
284, 291, 310, #12, 416; 4m
anatomy, 275-282
fertile shoots, 302-304
Demetrianum, 281
Felicis, 292
Lomaxt, 278, 280, 281
multirame, *277, 278, 279, 280,
302, *303, 308
platypodium, 278, 279, 280, 281
poroxyloides, 277, 278, *279, 281
Sutcliffit, *276, 278, 279, 280
Mesoxylopsis, 281-282
Arberae, 281
Mesozoic, 152, 284, 315-385, 395, 411,
419, 420, 429
Metacordaites, 284-285
Metaxylem, 106
Metz, 368
Mexico, 319, 357, 358
Miadesmia, 402
Microcyvcas, 300, 340
Microflorae, 364, 371
Microphyllous, 399, 400, 410
Micropyle, Aneimites, 220
Bennettites, 328, 329, 335, 336, 338,
339 :
Cardiocarpus, 307
Cycadinocarpus, 308
Gnetopsis, 88
Lagenostoma, 67
Mitrospermum, 310
Neuropteris, 203
Physostoma, 84
Sphaerostoma, 81, 83
Stephanospermum, 209
Trigonocarpus, 207, 208
Wielandiella, 363
Williamsonia, 356, 360
Williamsontella, 361%
Microsporangia and microspores, Cros-
sotheca, 90, 223, 224
Cycadeoideae, 342, 349
Cycadocephalus, 364
Si ——
INDEX
Microsporangia, etc. (contd,)—
Lyginopteris (Crossotheca), 74-80
Neuropterideae, 214-217
Microsporophylls, 377
Cycadeotdea, 345, 340, 351
Lunszia, 369
Pramelreuthia, 369
Willtamsonia, 356, 358
Williamsoniella, 360
Miller, Hugh, 359
Millstone Grit, 220
Mitrospermum, 301, 308
compressum, 304, *309, *310
Monadelphous, 345, 377
Monocarpic, 343
Monocotyledons, 266, 355, 415, 429
Monoecism, in Bemnettiteae, 350, 351
Monophyletic, 393
_ Monospermic, 374, 375
Monostelic, 194, 420
Mont- Pelé, 225
Moravia, 381
Mosses, 391
Myeloxylon = petioles of Medullosa,
180, 181, 182, 190, 193, 194,
196
elegans, 190
Landriotu, 181, 182, 184, 189
vadiaium, 190
Nathorst, A. G., 356, 363, 367, 369,
382, 404, 409
Neuropterideae. See Medulloseae, 420
Neuropteris, 1, 170, I71, 202, 203,
240
male organs, 214, 215
seed, *202, 203
Carpentiert, 215, 217
flexuosa, 213
gigantea, 213, 215, 217
heterophylla, *171, *202, 203, 212,
Sis. 204, “216, 257.
obliqua, 203
Schlehant, 213
Neuropterocarpus, 203
Neurospermum, 203
New York, 380
Nield, 229, 230, 231
Nodules, Calcareous, roof, 174, 196
199, 281
seam, 196
Norfolk Island, 378
Norham Bridge, 58, 135, 136
Norway, West, 409
Nucellus. See ovule and seed, 81, 82,
85, 206, 207, 208, 209, 219, 297,
298, 306, 307, 308, 309, 310, 333,
359, 419, 421
Nymphaeaceae, 428
?
441
Oaxaca, 357, 366
" Odontopteris, 170, 190, 213
Oldham, 229
Oliver, F. W., 79, 83, 86, 209, 417
Oolite, 320, 356
Inferior, 353, 385
Middle, 324
Upper, 381
Ophioglossaceae, 413
affinities, 413
Orthotropous, 67
Osmunda, 33, 61, 91, 172
Osmundaceae, 62, 106, 414
Ostrau, 12, 18, 60
Otozamites, 317
Ovary, 428
Ovule, Araucarieae, 425
Bennettiteae, 352, 376
Cordaiteae, 271, 296-305,
*298, *299-310
Cycadeotdea dacotensis, 343-345
Cycas, *299, 419
Williamsonia scotica, 359
Wiulliamsoniella, 361 -
"257;
Pachytesta gigantea, 212
Palaeophyllales, 385
Palaeostachya vera, 405
Palaeozoic, 378, 383, 384, 385, 401,
409
Palissya, 382
Palm, 343
wood, 429
Parapitys, 282-283, 284
Spenceri, 264, 282
Parkin, J., 373
Parthenogenesis, 339
Peat plants, 387, 391
Pecopterideae, 221-225
Pecopteris, 90, 221-224, 225
exigua, 90, 223
Pluckeneti, 221, *222, 240
Sterzelt, 221, 222, 223
Pedicel, 304, 350, 371, 372, 373, 374;
375, 413
Peduncle, 21, 293, 302, 303, 325, 328,
330, 331, 333, 334, 335, 343, 344,
356, 364, 371, 419
Perianth, 428
Pericarp, 335, 336, 338, 428
Pericycle, 24, 97, 112, 184, 280
Periderm, Bennettiteae, 325
Calamariaceae, 410
Calamopitys, 133
Cordattes, root, 287
Hapaloxylon, 285
Lyginopteris, 26
Medullosa, 178, 179, 183
Mesoxylon, 285
442
Periderm (contd. )—
Poroxylon, 249
Ptychoxylon, 235
Rhexoxylon, 228
Stenomyelon, 138
Sutcliffia, 200
Permian, 106, 185, 186, 188, I90, 192,
194, 224, 225, 226, 238, 283, 378,
379, 384, 417, 422
Upper, 380
Petrifactions, 204, 265, 382
Pettycur, 3; 81, 84, 95, 392
Phanerogams, 168, 410
Phelloderm, 184
Phellogen, 179
Phylloglossum, 401
Phyllosperms, 313
Phyllotaxis in Calamopitys, 125, 127
Cladoxvlon, 164
Heterangium, 10, 13
Lyginopteris oldhamia, 24
Medullosa, 174, 175
Megaloxylon, 103
Metacordaites, 284
Poroxylon, 246
Protobitys, 154
Ptychoxylon, 233
Sphenopsida, 398
Phylogenetic results, 432
Physostoma elegans, 84-86, *85
Pinus, 270, 381
Pits bordered, 151, 152, 155, 159
significance of, 166, 168, 273, 423
Pityeae, 253-265, 272, 312, 314, 417,
421, 422
affinities, 265, 417
Pitys, 254, 261, 262; 264
leaves, 258, 260
stem, 254-260
antiqua, 254, *255, 280
Dayt, 254, *257, *258, *259, 261
primaeva, 254
Witham, 254
Plate-rings, 193
Platyspermic, 220, 221, 252, 301, 306,
308, 421
Pleurometa, 403
Plumule, 334
Poacordaites, 268
Podocarpeae, 382
Podocarpus, 268, 382
Podozamites, 368, 369
Pollen-chamber, 84, 314
Aetheotesta, 226
Bennettites, 338
Cardiocarpus, 307
Cordatanthus, 297, 298
Cycadinocarpus, 308
Cycas, 299
STUDIES IN FOSSIL BOTANY
Pollen-chamber (contd.)—
Lagenostoma, 68
Mitrospermum, 309, 310
Physostoma, 85, 86
Sphaerostoma, 83
Stephanospermum, 209-211
Trigonocarpus, 205, 206
Pollen-grains, 425
Cordatanthus, 293-298, 300, 301
Cycadeoideae, 342, 349
Dolerophyllum, 225, 226
Lyginopteris, 69
Physostoma, 86
Stephanospermum, 209-212
Pollen-sac, Araucarieae, 425
Batera, 385
Cordaianthus, 293-296
Cycadeotdea, 352
Pramelreuthia, 369
Pollen-tube, 211, 300, 301, 425
Pollination, 84, 86, 295, 298,
339
Polyangium, 14, 18, 20, 98
Polydesmic, 17, 241
Polyphyletic, 395
Polystely, 167, 176, 178; UGas ee
188, 194, 218, 250, 22peeeur
DAT
Poroxyleae, 243-253, 265, 277, 278,
281, 311; 312, 314, Ais
Poroxylon, 92, 154, 243-253, 273, 275;
278, 312, 314, 421
branches, 251
leaf, 249-250
LOO, 251
seed, 252
stem, 244-249
Boysetti, *245, *249, 251
Edwardsu, *245, *247, 248, 251
Sutchiffit, 252
Portlandian, 381
Potomac, 318, 382
Potonié, H., 22, 42, 94
Potoniea adiantiformis, 215, *216
Pottsville beds, 220
Pramelreuthia, 369
Prankerd, <2 2b,
Prepinus, 381
Priestley glacier, 284
Primofilices, 62, 412, 413
Primofilicinées, 414
Pro-anthostrobilus, 373
Proterandrous, 352
Prothallus, Lagenostoma, 69
Mitrospermum, 310
Physostoma, 86
Psilotales, 396
Sltephanospermum, 209
Protocalamites, 4.05
299;
INDEX
.Protocorm, 401
Protodammara, 380, 425
Protopityeae, 145-156, 241
affinities, 153-156
Protopitys, 145-156, 160, 161, 166,
241
Buchiana, 138, 145-153, *146, *147,
*r49, “150, 155
rvadicans, 153
Protostele, 4, 20, 61, 62, 95, 102,
106, III, 144, 400, 405, 420
Protoxylem, 6, 11, 24, 9I, 97, 104,
106, IO, II5, 124, 133, 137, 139,
T4060, TAS, £50, 156; TOT, 166, 176,
178, 183, 198, 232, 247, 256, 277,
278, 286, 290
Psarontus, 62, 218, 223
Pseudoaraucaria, fructification, 380
Pseudobornia, 405, 410
Pseudoborniales, 404, 411
Pseudocvcas, 368
Pseudosteles, 41
Psilophytales, 20, 168, 240, 390, 395,
397, 398, 401, 403
affinities, 387-398
Psilophyton, 359, 393, 394
Psilotaceae, 408
Psilotales, 394-395
affinities, 396-398
Psilotum, 397
Psygmophyllum, 385
Pteridophyta, 108, 218, 416
affinities, 387-414
Pteridospermeae, 1-242, 306
affinities, 414-423
and Cordaitales, relations of, 416-
422
ferns, relation of, 414-416
summary, 239-242
Pteridotheca Williamsonii, 76, 413
Pterispermostrobus bifurcatus, 74
Pterophyllum, 238
Pteropsida, 407, 426, 427
affinities, 411-430
Ptychoxylon, 233, 234, 235, 239, 275
Levyt, 233, *234, 235, 236
Purbeck, 382
Lower, 317
Rachiopteris aspera, 49
Williamsoni, 196, 198
Radicle, 338
Radiospermic, 73
Radstock, 287
Ramenta, 326, 327, 331, 359, 370
Ranunculaceae, 428
Receptacle in Bennettites, 328, 331,
344, 350, 352, 361
Williamsonieae, 359, 361, 363
443
192,
244,
292,
413,
Renault, B., 17, 87, 182, 189,
194, 209, 225, 232, 235, 238,
252, 206, 272, 275, 284, 288,
295, 300, 300, 311, 379, 495,
422
Renier, A., 213
Reparatory strands, 7, 32, I12, 144,
149, 150, I51
Resin canals, 284
Rhabdocarpus, 202, 252, 307, 312,
421. Cf. tunicatus, 213
subtunicatus, *253
369,
Rhaetic, 228, 239, 284, 363, 366,
380, 381, 382, 384 :
Lower, 364
Rhetinangieae, 95-101, 107
Rhetinangium, 60, 95-101, 106, 107
Arberi, 95, *96, *97, *99
Rhexoxylon, 161, 228, 229, 240, 241,
284
africanum, 228
Rhymia, 389, 390
Gwynne-Vaughant, *388, 392
major, *388
Rhyniaceae, 387, 390, 391, 392, 393,
394, 395, 407, 408
Rhynie, 387, 388, 391, 407
restorations, *388, *389
Root-apex, 54
Root, 236, 401, 412
Araucarieae, 424
Bennettttes, 327
Calamopitys, 128
Cordaiteae, 286-287
Hapaloxylon, 285
Heterangium Grievtt, 11
Lyginopteris, 49-55
Medullosa, 183, 184
Poroxylon, 251, 252
Protopitys, 153
Rootless plants, 387, 391, 397
Rootlets, orientation of, 53
Saalfeld, 156, 158, 159
Sahni, 313
St. Croix; 267
St. Etienne, 186, 221, 287
Salisbury, E. J., 86, 87, 88, 208
Samaropsis, 221
acuta, 221
Sapindacae, 188, 201
Sarcotesta, 204, 206, 207, 208, 209,
219, 306, 308, 309
Sardinia, 357
Saurian, 357
Saxony, 190
sCalsriform, 6,24, 91, Ti5,. 151, X52;
159, 165, 176, 247, 273, 323, 332
Scale-leaves, 341
444 STUDIES IN-FOSSIL BOTANY
Schimper, 4, 6
Schizaa, 384
Schizodendron, 378
Schizolepis, 381
Sclerotesta, 204, 206, 207, 208, 209,
214, 219, 307, 308, 309
Sclerotic nests, 126, 138, 228
Scott, Capt., 284
Secondary growth,
400, 410
Secretory canals, 178, 180
gland, 291
Sacs, 135, 235, 274
Seed, 2, 89, 218, 219, 416, 419, 421
Aneimites, 220-221
Bennettiteae, 328-339
Cardtocarpus, 306
Conostoma, 86
Cordaiteae, 305
Cycadinocarpus, 307
Cycadocarpidum, 368
Cycadospadix, 238
Evremopteris, 221
Gnetopsts, 87
Heterangium, 80-84.
stoma
Hexapterospermum, 213
Lagenostoma, 63-74
Lyginopterideae, 84-88
Lyginopterts, 63-74.
stoma
Medulloseae, 201-214
Mitrospermum, 308
Neuropteris, 202, 203
Palissya, 382
Pecopteris, 221-222
Physostoma, 84
Protodammara, 380
Rhabdocarpus, 252, 253
Stachyotaxus, 382
Stephanospermum, 209-212
Trigonocarpus, 204-208
Walchia, 379
Wielandiella, 363
Williamsoma, 356
Selaginella, 304, 402, 403
Selaginellites primaevus, 402
Semipalatinsk, 226
Sequoia gigantea, 380
Seta, 391
Seward, A. C., 102, 108, 152, 161,
196, 229, 232, 236, 263, 283, 317,
321, 340, 351, 356, 359, 379, 384,
409, 423
Shore, 173, 196, 199, 208
Siberia, 283, 385
Sigillaria, 253, 400
Sigillarieae, 386
Sigillariopsis, 253, 400, 424
discussion on,
See Sphaero-
See Lageno-
Silesia, 108
Smedley, H. E., 64
Snake-rings, 193, 194
Soap-stone, 185
Solenostele, 186
Solms-Laubach, Graf H. zu, 108, 117,
120, 126, 131, 145, 149, 155, 158;
161, 165, 169, 226, 241, 203,)3205
323, 325, 329, 342
South, F. W., and Compton, King
371
Sparganum cortex,.26, 110, 152.0emen
120, 137, 136,048
Spencerites, 399, 401
Spermatozoids, 210, 211, > 300, 59005
426
Spermophyta, 80,/168, 241, 242, 386,
396, 398
affinities, 414-430
Mesozoic, 316-385
Palaeozoic, I-315
Sphaerostoma, 80-84.
ovale, 80, 81, *82
Sphagnum, 390
Sphenophyllales, 396, 397, 399, 404,
405, 406, 408, 409, 411
Sphenophyllum, 404, 409
Dawsont, 409
emarginatum, 406
fertile, 405, 406, 407, 408
majus, 398, 406
myriophyllum, 404.
subtenerrimum, 404
Sphenopsida, 394, 396, 398, 400
affinities, 404-411
Sphenopteris, 76, 90
Dubutssonis, 73
elegans, *3, *4, *5, 10
Honinghaust, 22, 42, *43, 56, 57, 72;
73, 74, 76
obtustloba, 73
vefracta, 165
Stangert, 72
Sphenozamites, 238
Sporangiophore, morphology, 399,
405, 406, 407, 408, 409
Sporangium and spores, 390, 392,
399, 400, 402, 405, 412, 413, 425
nature of, 407
Crossotheca, 76-78, 223, 224
Dolerophyvllum, 226
Neuropteris, 214, 215
Telangium, 78-80
Tracheotheca, 417
Sporogonites, 390
Sporogonium, 390
Sporophyll, 203, 242, 372, 399, 405,
418, 425
Cordaianthus, 295, 313
or
INDEX
Sporophyll (contd,)—
Cycadeotdea, 342
Cycadocephalus, 364
» Cycadospadix, 238
Wrelandiella, 363
Williamsonia, 363
Sporophyte, 395
Stachyotaxus, 382
Stamen, 374, 376, 377, 428
Araucarieae, 425
Batera, 385
Cordatanthus, 293-295
Cycadeoidea, 342, 345-352, 372
Williamsonia, 356-358
Williamsoniella, 360-362
Staminate disk, 226
Stangeria, 91, 323, 340
paradoxa, *27
Star-rings, 139, 190, 192, 193
Stauropteris, 413, 414
oldhamia, 248
Steloxylon, 157, 166, 226, 227, 228,
241
Stenomyeleae, 135-145
Stenomyelon, 135-145
affinities, 143-145
diagnosis, 143
tripartitum, 135, 141-143, 144
tuedianum, 135-141, *136,
*140, 143, 152
Stenzel, K. G., 188
Stephanospermum, 209-212, 301
akentioides, *210, *211
Sternbergia, 270, 378
Sterzel, J. T., 188; 190, 192, 218, 222
Stigmaria, 116
morphology, 401
Stolon of Neuropterideae, 217
Stomata, 8, 290, 331, 362, 392, 395
Stopes, M. C., 54, 73, 290, 292, 327,
337, 351
Strobilites, 238
Strobilus, 313, 406
Sik, D.,. 3,57; 71; E70
Sutcliffia, 100, 196-201, 218, 420
imsignis, 196, *197
Williamsont, 199
Swarth Fell, 153
Sweden, 364
Synangia, 78, 79, 90, 345, 347, 348,
350, 356, 358, 360, 364, 376, 377,
397, 418
Synthetic types, 431
*1309,
Taentopteris, 190, 363
vittata, 362
Taxaceae, 382
Taxales, 313
Taxodieae, 380
445
Taxus, 305, 313
Tecoma, 41
Telangium, *79, 80, 93
affine, 79
bifidum, 79
nutans, 79
Scottit, 78, 79, 90
Tertiary, 380
Testa, 204, 208, 306, 333, 419, 421
Thallophyta, 388, 390
Thallus, 407, 408, 409
Thamnopterts, 106
Thomas, A. P. W., 397, 398
Ethel N., 275
H. Hamshaw, 355, 360, 361, 374
Thomson, Boyd, 250, 285
Thuringia, 108, 118, 121
Thursophyion Milleri, 390
Titanophyllum, 196
Tmestpteris, 396, 397, 398
Todea, 55
Torreya, 313
Trabeculae, 403
Tracheotheca, 417
Transfusion tissue,
292, 424
Travellers’ Tree, 146
Tree-fern, 222, 223
Triassic, 228, 316, 366, 369, 375, 380,
384, 385
Upper, 318
Trigonocarpus, 203, 204-208, 209, 218,
226, 307, 419, 421
Parkinsoni, 204, *205, *206, *207,
208; 212, 273
shorensis, 208
Tulip tree, 428
Tylodendron, 318
Tyson, Philip, 318
288, 2090,
Unger, 116, 118, 156
Ural, 225, 283
Van Tieghem, 53, 252
Vascular plants, 387
classification, 395-396
Vasculares, 107, 387, 401
Vegetable kingdom, 431
Verticillate, 399
Volkelia, 157, 161, 165-166
vefracta, *167
Volkmann, Io
Voltzia, 380
Walchia, 378, 379
filiciformis, 379
frondosa, 379
Walnut, 270
Walton, John, 228
446
Ward, Lester, 340
Wardia fertilis, 220, 221
Water-ferns, 410
Watson, D. M.S., 54
Waverley shale, 109, 261
Wealden, 317, 318, 326, 366, 381,
382, 411
Weber, O., 182, 190, 192, 218
Weiss, F. E., 53, 54; 55, 401
Weltrichia, 364
Westphalian, 76, 87, 215, 292
Whalley, P., 185
White, David, 220
Wieland, G.R:,-318," 321; 341;,°343,
345, 349, 352, 357, 304, 370, 373,
376, 427
Wtelandtella, 239, 363, 365, 371, 428
angustifolia, 363, 371
Wild, G., 173
Williamson, W. C., 3, 21, 49, 68, 80,
204, 229, 270, 275, 282, 811, 354,
410
Williamsonia, 317, 359, 300, 428
gigas, *354, 355
Leckenbyt, 357
mexicana, 358
pecten, 364
scotica, 359
spectabilis, 356, *357, 358
TALE.
SL UDIES INS POSSIL: BOTANs
William onia (contd.)—
whitbiensts, 356, 358
Williamsonian tribe, 428
Williamsonieae, 320, 353-366,
3 luo 7 57 S77
affinities, 365, 366
Williamsoniella, 360, 363, 365, 371,
374, 375, 428
coronata, 355, 360, *361, *362
Witham of Lartington, 254 .
Worsdell, W. C., 424
370,
Xenoxylon phyllocladotdes, 152
Xerophytic, 290
Yoredale Rocks, 145, 152
Young, 133 ui
Yucca, 266, 268
Zalessky, 108, 130, 33%; 23s, soe"
260A 231 Ad O.eAsae
Zalesskya, 106
Zamia, 238, 288, 354, 368
gigas, 353
Zamieae, 239, 341, 367, 369, 370
Zamitostrobus, 367
Zamites, 3165, 317, 356
Zeiller, 56, 76, 90, 215, 221, 223, 380
Zygopterideae, 106, 168, 412, 413
END
BY THE SAME AUTHOR :
AN INTRODUCTION TO
STRUCTURAL BOTANY
Part I. FLOWERING PLANTS (Tenth Edition).
Illustrated with 118 Figures.
Crown 8vo. Price 5s. net. Cloth.
. SOME PRESS OPINIONS.
‘‘In noticing elementary books in these pages, we have lamented nothing more than the
want of a book which should do for structural botany what Prof. Oliver's ‘ Lessons’ has
long done for the study of the principal natural orders. It seems hard to realize that this
grievance is no more, and that we possess such a book in our own language, and a book that
no honest critic will fail to assess at a higher value than any known book in any language that
has the same scope and aim. Nothing could well be more plain and simple, or more severely
accurate or better judged from beginning to end.”—/owrnal of Botany.
“ As an introduction to botany, which is all that this work pretends to be, this is so excellent
that we commend it most heartily to all who desire to be well grounded in the first principles
of each department of botany, not of one only.” —Gardener's Chronicle.
“ An introduction to the study of structural botany has long been a desideratum in this
country. . . . Dr. Scott’s little book supplies this need in a most admirable manner, and he
has thoroughly earned the gratitude both of teacher and student alike for the freshness and
clearness with which he has presented his subject.”—-Wature.
Part Il, FLOWERLESS PLANTS (Eighth Edition).
Illustrated with 120 Figures.
Crown 8vo. Price 5s. net. Cloth.
SOME PRESS OPINIONS.
“‘ The second part of Dr. Scott’s admirable manual of Structural Botany is now before us-
It consists of a most carefully worked out history of the structure of flowerless plants, which
constitute more than half of the vegetable world. . . . 1t is one which cannot fail to hold its
place among the most thoughtful of students of botany.” — Science Gossip.
“We have nothing but praise for this neat little volume. With its companion (Part I.
Flowering Plants) it forms as good an introduction as one can imagine, in our present knowledge,
to the study of the plant-world of to-day. . . . We can only fear lest, amid such a wealth of
illustration, the student may deem an examination of the actual specimens to be unnecessary.”
—Guardian.
“Students of botany will welcome the second part of Dr. D. H. Scott's ‘Introduction to
Structural Botany’ which has just appeared. . . . The language is clear and not unnecessarily
technical, which is a great advantage to a beginner. We believe many are deterred from the
fascinating study of botany by the extremely numerous technical terms with which so many
manuals abound. . . . We do not remember reading a clearer description of the growth of
ferns than that in the chapter on vascular cryptogams.”— Westminster Review. .
PUBLISHED BY A. & C. BLACK, LTD., 4, 5 & 6 SOHO SQUARE, LONDON, W.I.
OTHER BOOKS ON BOTANY
OUTLINES GF THE
HISTORY OF, BOTA
By Ro J. GHARVEY-GIBSON
C.B. Ex, "Dua... Mae Sey dR.
EMERITUS-PROFESSOR OF BOTANY IN. THE UNIVERSITY OF LIVERPOOL
Large Crown 8vo. Price 12s. 6d. net. Bound in Cloth.
**Tn this sketch of the history of botany Professor Harvey-Gibson has undertaken a useful
bit of work, and he has carried it out well.”—-7he Times.
“From a book so good throughout it is not easy to select parts for special commendation.
The main lines of the search in the physiology, morphology,and evolution of plants are all clearly
traced, and the significance of every great advance explained.” —7The Journal of Education.
BRITISH PLANT NAMES
AND THEIR DERIVATIONS
By Re J7 HARVEY-GIBSON
CBr aan MA. DD: Se, FE Rise
EMERITUS-PROFESSOR OF BOTANY IN THE UNIVERSITY OF LIVERPOOL
Crown 8vo. Price 2s. 6d. net. Limp Cloth.
“* Professor Harvey-Gibson has now written a real, satisfying text-book for students and
botanists ; its cheapness is likely to add greatly to its sphere of usefulness. ””—L7verpool Courier.
PLANT Cire
By CHARLES A. HALE, FoR Mie
With 74 Full-page Illustrations, 24 being from Photographs by the
Author, and 50 in Colour from Drawings by C. F. NEWALL.
Square Demy 8vo. Cloth.
Published at 20s. net. Now offered at 10s. net.
** A botanist might take both pleasure and profit from a perusal of the volume, though the
book is not addressed to scientific students, but to amateurs who like instruction less
specialised and less technical than the heavier text-books make it. ... Not the least
interesting chapter of the work deals with the new field botany which studies the relation of
plants to their environment. . . . But everywhere in the book the matter is made interesting
by the author’s well-practised skill in the exposition and simplification of the scientific |
teaching. The work derives an unusual value from the extent and variety of its illustrations,
which, while always strictly documentary in their fidelity, have artistic merits that make them
invariably pleasing to look over.” —The Scotsman.
A PLANT BOOK FOR SCHOO.
Being an Easy Introduction to the Study of Plant Life
BY. O.°V.. DARBISHIRE, B.A: Pai
PROFESSOR OF BOTANY IN THE UNIVERSITY OF BRISTOL
Demy 8vo. Cloth. Containing 115 Illustrations,
mostly from Photographs. Price 3s. 6d.
**. . . We can cordially recommend this ‘ Plant Book’ as a really helpful and stimulating
introduction to the study of plant life.”—JZanchester Guardian.
**. . . This is one of the best introductory books in botany we have met with for a very
long time. . . .”-—Pyvactical Teacher.
PUBLISHED BY A. & C. BLACK, LTD., 4, 5 & 6 SOHO SQUARE, LONDON, W.I.
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