CYCADOPHYTA.
+I. Cycadean Stems other than Cycadeoidea.+
Most of the stems now under consideration are represented by casts
or impressions and afford no information with regard to anatomical
characters. They are in many cases more slender and less tuberous than
typical Cycadeoideas, and a few are characterised by an irregular
form of branching, as is shown in some specimens of pith-casts from
Wealden strata in Tilgate Forest figured by Mantell[1318] and now in
the British Museum. The genus _Wielandiella_[1319] (fig. 566) is an
altogether distinct type represented by flowers as well as vegetative
organs. Several generic names have been proposed for Cycadean stems
agreeing with those of many recent Cycads in the possession of an
armour of persistent leaf-bases, but distinguished from _Cycadeoidea_
in the absence of any fertile lateral shoots intercalated among the
petiole-bases. It is, however, impossible in most cases to give any
satisfactory definition by which these genera can be distinguished
from one another; the characters employed by Carruthers[1320],
Saporta[1321], and other authors are of comparatively little
importance as trustworthy criteria and to a large extent are merely
the expression of different states of preservation or of differences
in age. Attention has elsewhere been called to the absence of any
clear dividing line between stems referred to _Bucklandia_, _Yatesia_,
_Fittonia_ and _Cylindropodium_. The species _Cycadeoidea gigantea_
described on a previous page affords an instructive example of the
difficulty of drawing a generic distinction between certain types of
Cycadean stems: in habit, in the form and structure of the leaf-bases,
and in the ramenta this species is identical with other species of
_Cycadeoidea_, but it differs in the absence of lateral fertile shoots,
a feature that may have no morphological significance. It has already
been pointed out that the absence of flowers intercalated among the
leaf-bases may simply mean that the plant had not reached the stage of
flower-production, or their absence may be due to some unfavourable
conditions. Similarly the stems for which Saporta proposed the generic
name _Clathropodium_ agree in every respect with _Cycadeoidea_ except
in the absence, apparent or real, of lateral flowering branches.
Such types as _Clathropodium foratum_ Sap. and _C. sarlatense_
Sap.[1322], the latter probably from Upper Jurassic beds and the
former from an unknown locality, should be included in the genus
_Cycadeoidea_. The stem referred by Saporta to his genus _Platylepis_
as _P. micromyela_[1323] was originally assigned to _Cycadeoidea_ and
more recently Lignier has wisely adopted the original generic name.
The generic term _Bolpopodium_, also instituted by Saporta[1324], is
applied to small tuberous stems which appear to be identical with the
_Cycadeoidea_ type.
Having regard to the meagre data supplied by casts of stems preserved
in various stages of defoliation, and in view of the impossibility
of drawing other than purely arbitrary generic distinctions, it is
preferable to employ one generic name in a liberal sense for stems
that there is good reason to regard as plants that cannot reasonably
be referred to _Cycadeoidea_. The name _Bucklandia_ is thus employed,
and a few examples are described in illustration of the external
features of stems that are undoubtedly Cycadean but in most cases
readily distinguished from _Cycadeoidea_. There are substantial grounds
for stating that plants which bore flowers of the _Williamsonia_
type possessed stems having the characters of _Bucklandia_. It
should, however, be remembered that we cannot always draw a clearly
defined distinction between flowers included in _Williamsonia_ and
_Bennettites_, or _Cycadeoidea_, particularly when they are represented
only by detached ovulate strobili as in _Cycadeoidea_ (_Bennettites_)
_Morierei_ and _Williamsonia scotica_.
=BUCKLANDIA.= Presl.
_Bucklandia_ was proposed by Presl[1325] for a plant described by
Mantell[1326] from the Wealden of Tilgate Forest and compared by him
to the Euphorbiaceae and arborescent Ferns; the same generic name was
given by Robert Brown in 1832 to a recent member of the Hamamelidaceae.
Stokes and Webb[1327] referred the same fossil to _Clathraria_, a name
applied by Brongniart[1328] to certain types of Sigillarian stems and
afterwards adopted by him for the Tilgate Forest species, _C. Lyelli_.
Presl ‘with remarkable discrimination’ recognised the Cycadean nature
of the specimen. Carruthers[1329] in his definition of _Bucklandia_
includes a statement as to the nature of the carpellary leaves and
suggests that a cone associated with the stems may be a staminate
strobilus: the cone is undoubtedly a megastrobilus of an Araucarian
plant and there is no evidence with regard to the nature of either the
male or female reproductive organs in the material that he describes
though, as already pointed out, there are reasons for believing
that _Williamsonia_ flowers were borne on branches of _Bucklandia_
stems. The flowering shoots were not short and intercalated among
the petiole-bases as in _Cycadeoidea_ with the strobili barely
projecting beyond the surface of the leaf-base armour, but they formed
comparatively long branches, sometimes forked, at the apex of the main
stem (_cf._ figs. 541–543).
_Bucklandia_ is usually represented by casts, from Rhaetic to Lower
Cretaceous strata, differing from _Cycadeoidea_ in the absence of
numerous axillary short fertile shoots, in the more slender form and
greater length of the stems, and in the less uniform size of the
persistent leaf-bases which assume various forms. Some of the specimens
reach a length of 4 feet and afford evidence of occasional branching:
the surface is covered with leaf-bases preserved as imbricate, broad,
and obtuse or truncate scales (fig. 575), or as slightly convex
polygonal areas in some cases showing a tendency towards an irregular
zonal arrangement of larger and smaller leaf-bases (fig. 576). Within
the armour of leaf-bases there may be a cast of the large pith the
surface-features of which are practically identical with the cast of
a recent pith reproduced in fig. 398. Casts of the pith preserved as
separate fossils are included in the genus _Cycadeomyelon_.
There is evidence of the occurrence of more than one zone of vascular
tissue in a stem from Lower Greensand beds of Bedfordshire described by
Carruthers as _Yatesia Morrisii_[1330] (= _Bucklandia Yatesii_), and
Dr Stopes[1331] has recently described a species, _B. buzzardensis_
(fig. 578), with several zones of conducting tissue. This feature has
not so far been satisfactorily demonstrated in _Cycadeoidea_. An Indian
species, _Bucklandia indica_, shows that the secondary xylem is more
compact than in typical _Cycadeoidea_ stems, and the tracheids have
multiseriate pitting.
Two long and narrow stems figured by Nathorst from the Rhaetic of
Scania as _Bucklandia Saportana_[1332] differ from other species in
the irregular arrangement of the leaf-bases which in certain regions
are crowded as in the typical example of the genus shown in fig. 576,
but in the intervening portions of the stem they are few in number
and widely separated by the finely striated bark. This type, though
similar to some specimens of English, Mexican, and Indian Bucklandias
in the zonal differences in the leaf-bases, represents an extreme case
of the alternation of smaller and crowded and larger and scattered
leaf-scars. It is by no means unlikely that _Bucklandia Saportana_
forms a transition between _Bucklandia_ and the stem of _Wielandiella_
described by Nathorst from the same region: in _Wielandiella_ the
leaf-scars are concentrated at the region of forking but a few occur
elsewhere: in _B. Saportana_ there is no evidence of branching and in
this respect it differs from _Wielandiella_.
_Bucklandia anomala_ (Stokes and Webb).
This species, from Wealden beds in Sussex, was first described by
Stokes and Webb[1333] as _Clathraria anomala_, and the same type was
figured by Mantell and other authors as _Clathraria Lyelli_. The
specimens referred by Carruthers to _Bucklandia anomala_ and _B.
Mantelli_[1334] do not exhibit any well defined specific differences,
and there would seem to be no reason for retaining both specific
names. The petiole-bases are usually sub-rhomboidal in form and convex
or flat, but in some stems more of each petiole is preserved and the
surface is covered with broad imbricate scales (fig. 575) similar
to some of the detached scales described under the generic name
_Cycadolepis_. Pith-casts occur both in connexion with the _Bucklandia_
stems and as detached specimens. The leaf-bases often show an irregular
zonation of smaller and larger rhomboidal areas. The pith-cast in the
lower part of the specimen from the Wealden of Cuckfield in Sussex
shown in fig. 575 is 5 × 3·5 cm. in diameter.
[Illustration: Fig. 575. _Bucklandia anomala._ (British Museum, No.
V. 3690; rather less than natural size.)]
_Bucklandia Ruffordi_ Seward.
This species, from the Wealden beds on the Sussex coast[1335], was
originally described as _Fittonia Ruffordi_, but in the absence of
any well defined distinctive features that can be regarded as of
morphological significance it is better to include it in _Bucklandia_.
The species affords a good example of a long and narrow type of stem,
one specimen reaching a length of nearly 80 cm. with a breadth of
about 10 cm.; the surface is covered with persistent leaf-bases 1·7
cm. in depth with a scar agreeing in size and shape with the base of
a frond of _Otozamites Goeppertianus_ (Dunk.)[1336] found in the same
beds. There is no indication of any alternation of large and small
leaf-bases, and the species is characterised by the uniform size and
relatively greater depth in a vertical direction of the leaf-base
areas. In all probability the stem bore fertile branches similar to
those of _Williamsonia gigas_ with flowers of the _Williamsonia_ type:
the fronds may have been those known as _Otozamites Goeppertianus_, but
this has not been demonstrated. A stem described by Carruthers from the
Lias of Lyme Regis as _Yatesia gracilis_[1337] and afterwards included
by me in _Cycadeoidea_[1338] is very similar to _B. Ruffordi_ in its
long and narrow form and in the shape of the leaf-bases; it should be
transferred to _Bucklandia_ as _B. gracilis_ (Carr.).
_Bucklandia Milleriana_ Carruthers.
This species was founded on a cast from Lower Oolite beds at Brora
in Sutherlandshire[1339] characterised by leaf-bases very similar to
those of _B. anomala_ but smaller. Casts from the same locality were
named by Carruthers _Yatesia crassa_ and _Y. Joassiana_[1340], but an
examination of specimens in the Dunrobin Museum leads me to regard
these forms as indistinguishable from _B. Milleriana_. The specimen
reproduced in fig. 576 from the Great Oolite of Brora illustrates the
external characters of a typical stem and shows the variation in the
size of the leaf-bases. A portion of the pith-cast is exposed in the
lower part of the stem.
[Illustration: Fig. 576. _Bucklandia Milleriana._ Brora, Scotland.
(Manchester Museum, L. 7229. _ca._ ½ nat. size.)]
_Bucklandia Yatesii_ (Carruthers).
This type from the Lower Greensand of Bedfordshire (fig. 577) was
described by Carruthers as _Cycadeoidea Yatesii_ and subsequently
named _Yatesia Morrisii_[1341]. Ward expressed the opinion that the
name should be _Yatesia Yatesii_, but as _Bucklandia_ is now used
to include _Yatesia_ this combination is fortunately avoided. The
stem is cylindrical, 20–30 cm. long and 12 cm. in diameter, covered
with rhomboidal leaf-bases separated from one another by a ramental
reticulum. There are two concentric vascular cylinders as stated by
Carruthers. In a recent account of this species Dr Stopes[1342] adds
further details: the xylem-cylinders are 5–8 mm. wide and the tracheids
occur in single rows or there may be bands 4–5 elements broad; the
circular bordered pits are uniseriate or in two alternate series.
The medullary rays are broad but the cells are not preserved. The
pith-cast is of the usual Cycadean type.
[Illustration: Fig. 577. _Bucklandia Yatesii._ Type-specimen in the
British Museum.]
The type-specimen was presented by the Cirencester College to the
British Museum.
_Bucklandia buzzardensis_ (Stopes).
[Illustration: Fig. 578. _Bucklandia buzzardensis._ Rough sketch of a
block of wood showing parts of at least eight concentrically arranged
rings of secondary wood. (After Stopes; × ⅔.)]
This species, from Lower Greensand beds at Leighton Buzzard and
believed to be derived from Wealden strata, is described by Dr
Stopes[1343] as _Cycadeoidea buzzardensis_. Though agreeing generally
with _B. Yatesii_, the stem is specifically separated on the ground
that the petiole-bases are more expanded laterally and because of the
occurrence of several vascular cylinders (fig. 578), sometimes as many
as eight, each with a maximum diameter of 1 cm. Dr Stopes thinks it
possible that _B. buzzardensis_ is an older form of _B. Yatesii_.
_Bucklandia squamosa_ (Brongniart).
Sternberg first described this species as _Conites Bucklandi_[1344] and
regarded it as a cone bearing large imbricate cone-scales; it was named
by Brongniart _Bucklandia squamosa_[1345] and Carruthers[1346] retained
this designation. The type-specimen, in the Oxford Museum, from the
Stonesfield Slate is 18 cm. long, showing in the lower part a cast
of the pith. The surface of the stem is covered with thick imbricate
petiole-bases very like those on the stem of a recent _Encephalartos_.
_Bucklandia_ (_Fittonia_) _squamata_ (Carruthers).
Carruthers[1347] founded the genus _Fittonia_ on a single specimen from
the Wealden beds of the Isle of Wight, separating it from _Bucklandia_
on the ground of the occurrence on a portion of the stem of large
imbricate leaf-bases which are at first reflexed and then ascending;
the stem is also broader and more tuberous than most species of
_Bucklandia_. The type-specimen, in the Museum of the Geological Survey
(Jermyn street), bears a close resemblance to a trunk of a recent
_Encephalartos_, but the part of the stem from which the imbricate
stumps have fallen is practically identical with a _Bucklandia_.
As in certain recent Cycads the surface-features probably changed
with the age of the plant; when the foliage-leaves were first shed
a portion of the ascending petiole remained on the stem, and at a
later stage this was cut off leaving a clean-cut rhomboidal scar like
those on the _Bucklandia_ shown in fig. 576. The difference between
_Fittonia_ and _Bucklandia_ may, therefore, be a question of age. While
substituting _Bucklandia_ for _Fittonia_ as the generic name the latter
designation is added in parentheses to denote the possession of certain
features which, though possibly of generic value, are not regarded as
sufficiently important morphologically to warrant generic recognition.
The type-specimen of Saporta’s species _Fittonia insignis_[1348],
in the Paris Museum, from the Oxfordian of Poitiers, appears hardly
distinguishable from _F. squamata_ Carr. Another type with broader
imbricate petiole stumps is described by Saporta from the Portlandian
near Boulogne as _Fittonia Rigauxi_[1349].
[Illustration: Fig. 579. _Bucklandia indica._ A, side-view showing
the leaf-bases and attached petioles of _Ptilophyllum_, also (to the
left) a fragment of a detached _Ptilophyllum_ leaf. B, transverse
section showing the pith, xylem cylinder, cortex, and sections of
petioles. (British Museum; nat. size.)]
_Bucklandia indica_ sp. nov.
Oldham and Morris[1350] and subsequently Feistmantel[1351] described
some specimens of Cycadean stems from the Rajmahal Hills of India
of Lower Jurassic age: the latter author regarded them as stems of
_Williamsonia_ because of their association with flowers of that
type, a conclusion fully justified by the evidence. Feistmantel also
called attention to the resemblance of the Indian stems to specimens
described from British strata as _Bucklandia_ and _Yatesia_. Although
the Indian examples are very similar to stems from Mexico discovered
by Wieland[1352] and to some of the English types, it seems desirable
to refer to them under a specific name and I therefore suggest the
institution of the specific name _indica_, the type-specimen being that
represented in fig. 579. This specimen is particularly interesting
because it affords some information as to anatomical features and
is one of the few fossil stems preserved in organic connexion
with leaves (fig. 579, B). A short account of it was published in
1900[1353] and more recently Miss Bancroft[1354] has made a fuller
investigation of this and other Indian specimens. The stem shown in
fig. 579 from the Rajmahal Hills, and now in the British Museum, bears
fronds of _Ptilophyllum cutchense_ Morr., a type that appears to be
indistinguishable from _P. pecten_; and with similar stems from the
same beds are associated flowers of _Williamsonia_. Miss Bancroft
describes a bract-covered shoot which agrees very closely with those of
English stems reproduced in figs. 541, 542. In addition to the evidence
based on close association, there is the more important argument
furnished by the discovery of ramental hairs like those on the bracts
of _Williamsonia scotica_ and of anatomical characters in the bracts
similar to those in the Scotch strobilus. The persistent leaf-bases
are far from uniform in size; in this respect and in their form they
agree closely with those on _Bucklandia_ stems from English and Mexican
localities. The secondary wood is more compact than in recent Cycads or
in _Cycadeoidea_, though it resembles that of _Cycadeoidea micromyela_;
the medullary rays are uniseriate and the tracheids have multiseriate
bordered pits on their radial walls instead of the scalariform pitting
in the majority of _Cycadeoidea_ stems. Secretory canals are abundant
in the parenchymatous ground-tissue; the cambium and phloem are not
preserved[1355].
The transparent nature of the silicified material rendered very
difficult the examination of the tissues, but enough was discovered
to show that these Indian stems are characterised by certain
features, the more compact nature of the secondary xylem and the
presence of multiseriate pitting, which distinguish them from the
_Cycadeoidea_ type. Further knowledge of the anatomical features of the
_Williamsonia_ (_Bucklandia_) stems from other localities might enable
us to recognise these or other peculiarities as constant distinguishing
characters of _Bucklandia_ in contrast to the Cycadeoidea stems which
bore the _Bennettites_ type of flower.
=Cycadeomyelon.= Saporta.
Casts of the pith-cavity of Cycadean stems, like that shown in fig. 575
projecting beyond the armour of leaf-bases, are occasionally found as
separate fossils and cannot always be referred to a particular species
of stem. For such detached casts Saporta[1356] instituted the name
_Cycadeomyelon_: they are characterised by their comparatively large
diameter and by the possession of surface-features similar to those
on the corresponding cast from a recent Cycadean stem shown in fig.
398, namely spirally disposed, more or less prominent, lozenge-shaped
areas formed by the sand or mud filling the cavities left on the decay
of the parenchyma of the broad medullary rays of a manoxylic stem.
Occasionally a slit at the lower end of a medullary ray area marks the
position of the leaf-trace bending outwards from the lower angle of the
mesh in the xylem-lattice[1357]. Lignier figures part of a pith-cast of
_Cycadeomyelon Apperti_[1358] in which each medullary-ray area has a
circular depression and not a slit extending from the lower angle: this
may indicate that the surface shown on the cast is slightly external to
the inner edge of the stele and in a plane where the leaf-traces were
embedded in the parenchyma of the rays and free from the xylem-cylinder.
Large and branched examples of _Cycadeomyelon_ were figured by some
of the earlier authors from English Wealden beds as species of
_Clathraria_[1359] and in many cases these are undoubtedly pith-casts
of _Bucklandia_ stems: a similar cast is figured under this name by
Schenk from the Wealden of North Germany. From Liassic beds in Normandy
Lignier figures two species of _Cycadeomyelon_, _C. Apperti_ and _C.
densecristatum_. The surface-features of _Cycadeomyelon_ resemble
those of the Palaeozoic genus _Tylodendron_ (see Vol. +iv.+), but in
the latter genus the nodal swellings are a characteristic peculiarity.
Though medullary casts of this type are of no great botanical
importance and their specific distinctions are of little value, it is
safe to assume that broad medullary casts with comparatively large
lozenge-shaped areas belong to Cycadean stems, while narrower specimens
with smaller lozenges are more likely to be pith-casts of Coniferous
stems.
Lester Ward[1360] instituted the genus _Feistmantelia_ for some Lower
Cretaceous casts from the Black Hills which he compared with an
Indian fossil from Cutch described by Feistmantel as ‘the stem of a
Coniferous plant[1361],’ and with pith-casts figured by Stokes and Webb
as _Clathraria anomala_. It is impossible to determine the systematic
position of such imperfect specimens as that on which Ward founded his
species _F. oblonga_: they may, as Hollick and Jeffrey[1362] suggest,
be casts of the bark of some Conifer; there is certainly no good reason
for connecting them with Cycads.
=COLYMBETES.= Stopes.
_Colymbetes Edwardsi_ Stopes. This genus[1363] is founded on the
inner portion of a petrified trunk which was probably cylindrical
and more than 12 cm. in diameter, consisting of a pith, 7·5 cm. in
diameter, and part of a vascular cylinder of remarkable structure.
The type-specimen is of Aptian age and may have come from Leighton
Buzzard (Bedfordshire). The pith (fig. 580, _p_) consists of large
parenchymatous cells and numerous secretory canals: the perimedullary
zone, _pm_, is characterised by the occurrence of loosely disposed
tracheids in groups and radial rows pursuing a sinuous longitudinal
course in the accompanying parenchyma. The tracheids in this region
are small in diameter and have oval, scalariform, or circular pits.
Abutting on the perimedullary zone is the secondary xylem the inner
edge of which forms bays, and this is composed of alternating zones of
vertical and horizontal tracheids (fig. 580, _y₁_–_x₅_; fig. 581) with
bordered, scalariform, pits on their walls traversed by medullary rays
generally biseriate and from 4 to 30 cells deep. The disposition of
the tracheids is such as to render transverse and radial longitudinal
sections practically identical in appearance; the first zone of
secondary xylem with its bayed inner edge consists of vertically
running elements; this is succeeded by a zone in which the tracheids
pursue a horizontal course, and beyond this second zone is another
band of vertical elements (fig. 581). ‘Where the one zone passes
into the next, a curving of the elements is frequently evident, and
in a few cases it is quite possible to trace a single radial series
of tracheids through an angle of 90° running in the same section,
first as a transverse and then as a vertical series. One and the same
medullary ray also can sometimes be followed, first in transverse and
then in radial longitudinal section, which later again turns to true
transverse. The inference is therefore drawn that there was but a
single cambium, which had periodic changes of direction.’ Leaf-traces
(fig. 580, _lt_) are large and numerous; they are spirally disposed
and pass nearly straight through successive xylem-zones: each trace
consists of a small-celled ground-tissue including stone-cells and
patches of tracheids in more or less regular radial rows. Tangential
sections of the wood show that the tracheids follow a sinuous course
forming loops enclosing numerous medullary rays.
[Illustration: Fig. 580. _Colymbetes Edwardsi_. Transverse section
showing ten alternating zones of wood outside the perimedullary zone,
_pm_; _y₁_, _y₂_, etc., vertically running xylem series; _x₁_, _x₂_,
etc., horizontally running xylem series; _p_, pith; _lt_, leaf-traces.
(After Stopes; × 2.)]
[Illustration: Fig. 581. _Colymbetes Edwardsi._ Diagram of stem in
transverse (A) and radial longitudinal (B) section. _p_, pith; _pm_,
perimedullary xylem; _b_, bays of first, vertically running, secondary
xylem; _x₁_, _x₂_, etc., zones of horizontally running secondary
xylem cut transversely in the radial and radially in the transverse
section of the stem; _y₁_, _y₂_, etc., longitudinally running xylem
cut transversely in the transverse and longitudinally in the radial
section. (After Stopes.)]
As the pith and xylem are the only tissues preserved it is on their
structure that any speculation as to affinity must be based. The close
arrangement of the leaf-traces (about 1 cm. apart), as Dr Stopes says,
indicates small leaf-bases, assuming that each leaf received a single
trace. In some respects the xylem and medullary rays resemble those of
Cycads, and the author of the genus includes it in the Cycadophyta; but
as she points out there are many peculiar features, and it is clearly
impossible to assign the new type to a more precisely defined position.
The possibility of any purely mechanical explanation of the course of
the tracheids in the alternating zones is ruled out by the straight
course of the outgoing leaf-traces, and it would seem that the cambium
must have turned over at right-angles at regular intervals during the
growth of the stem.
=Cycadolepis.= Saporta.
This name was used by Saporta[1364] for linear-lanceolate scales from
Upper Jurassic rocks in France which he compared with bud-scales of
recent Cycads. The imperfect scale described as _Cycadolepis villosa_
bears a striking resemblance to the hairy bracts of _Williamsonia_
and may well belong to that genus. Saporta’s term may be usefully
employed in a more extended sense, including not only lanceolate
scales but larger and much broader scales resembling the flattened
petiole-bases on stems of _Macrozamia_, _Encephalartos_, and some
other recent genera, as well as detached carpellary scales, other
than _Cycadospadix_, and microsporophylls which cannot be assigned
to a particular stem. Two qualifying subgeneric terms have been
proposed[1365]:
i. _Cycadolepis_ (_Dory-Cycadolepis_). Scales more or less
linear-lanceolate like those described by Saporta and a specimen
from Jurassic rocks of India named by Feistmantel[1366] _Cycadolepis
pilosa_. This type of _Cycadolepis_ may be identical with the bracts of
_Williamsonia_ flowers, though in the absence of any definite evidence
of such affinity the provisional generic name is more appropriate.
ii. _Cycadolepis_ (_Eury-Cycadolepis_). Broadly oval or orbicular thick
scales (figs. 582, 583), the broadest part being frequently nearer the
distal than the proximal end. These larger scales though usually found
as detached fossils have in one instance been obtained attached to an
imperfectly preserved stem.
[Illustration: Fig. 582. _Cycadolepis_ (_Eury-Cycadolepis_) sp. From
the Wealden beds of Sussex. (Brit. Mus. No. V. 2799.)]
[Illustration: Fig. 583. _Cycadolepis_ (_Eury-Cycadolepis_) sp. Scale
from the Wealden beds of Sussex. (British Museum, No. V. 2131_a_; nat.
size.)]
_Eury-Cycadolepis_ sp.
This type of scale, represented by specimens from the Wealden of
Sussex[1367] (figs. 582, 583), reaches a length of 13 cm. and a breadth
of 7 cm. and is sometimes almost orbicular. The lamina is convex
but shows no definite venation and bears a close resemblance to the
scale-like petiole-stumps on an old stem of _Macrozamia_. On some of
the smaller specimens (fig. 583) several forked veins extend vertically
from the broad base. Since these specimens were first described
additional examples have been discovered in the Wealden beds of Sussex,
some of which are attached to a piece of stem[1368] in such a manner
as to give support to the view that they are leaf-bases very similar
to those on such fossil stems as _Bucklandia_ (_Fittonia_) _Rigauxi_
(Sap.)[1369] and _B._ (_Fittonia_) _squamata_ (Carr.)[1370]. One
partially carbonised scale yielded pieces of cuticle showing numerous
stomata similar to those of recent Cycads and the outlines of very
thick-walled epidermal cells[1371].
_Eury-Cycadolepis Jenkinsiana_ (Tate).
The large and approximately orbicular or broadly ovate scales
so named are believed to be identical with Tate’s _Cyclopteris
Jenkinsiana_[1372] from the Uitenhage series of Cape Colony (Wealden).
The scales reach a length of 12 cm. and were attached by a broad base;
the lamina, which may be strongly bent as though folded over some
immature organ as a protective bract, shows numerous repeatedly forked
veins of the _Cyclopteris_ type and several anastomosing and irregular
lines between the veins suggesting that the scales were tomentose.
+II. Reproductive Organs of Cycadean Plants other
than those of the Bennettitales.+
The fact that practically all known Cycadean stems bore flowers
either of the _Bennettites_ or _Williamsonia_ type prepares us for
the scarcity of reproductive organs like those of recent Cycads. No
specimens have been discovered in a petrified state affording any
evidence of their close affinity to the cones, sporophylls, or seeds
of the Cycadales. Such genera as _Cycadospadix_, _Androstrobus_,
and _Zamiostrobus_, as the following descriptions show, are founded
on material that is too imperfect to throw much light on their true
morphological nature. The probability is that some at least of the
specimens included in these genera are the reproductive organs of
Cycadean plants more closely allied to the existing Cycads than to
the Bennettitales. Among the numerous fossil seeds referred to such
genera as _Cycadeospermum_ and _Cycadinocarpus_ there are but few
that can confidently be assigned to the Cycadales rather than to the
Ginkgoales or Coniferales. While the seeds of the Bennettitales are
clearly distinguished by their much smaller size from those of modern
Cycads, many of the latter agree in size and form with those of some
other Gymnosperms and in the absence of anatomical details could
not easily be identified as fossils. Some of the examples included
in the miscellaneous collection described by authors as species of
_Carpolithus_ or _Carpolithes_ agree closely in external features with
the seeds of modern Cycads, but it is seldom possible to accept them as
undoubted records of Cycadalean plants.
The general conclusion is that such meagre evidence as we possess
affords strong confirmation of the conclusion based on stems and
foliage from Jurassic and Cretaceous strata, namely that the present
representatives of the Cycadophyta are a relatively late product of
evolution, though retaining in their anatomical features many survivals
from a remote antiquity. The occurrence of Cycadean characteristics in
the vegetative organs of the Medulloseae and the recurrence of what may
be called the Cycadean seed-plan, with certain more or less striking
peculiarities reminiscent of earlier stages of evolution, in several
types of Palaeozoic seeds such as _Cycadinocarpus_, _Stephanospermum_,
_Lagenostoma_ and others bear testimony to the antiquity of the
Cycadean stock.
=CARPOLITHUS[1373].= Linnaeus.
This generic name, as Nathorst[1374] has recently pointed out, was
used by Linnaeus in 1768 for ‘Phytolithus fructus’ and has therefore
priority over Sternberg’s genus _Carpolites_ employed in 1825. Lester
Ward[1375] attributes _Carpolithus_ to Stokes and Webb (1824) and
states that in the plural form the name was used by Walch in 1771.
_Carpolithus_ is a convenient term to apply to fossil seeds that cannot
be assigned to a particular group of plants and which do not exhibit
any peculiarities of form sufficiently striking to deserve generic
recognition. Pomel[1376] proposed the genus _Ulospermum_ but it never
came into general use. Schimper’s genus _Cycadinocarpus_ and Saporta’s
_Cycadeospermum_ (preferable in its morphological implication),
though useful in the case of detached seeds of undoubted Cycadean
affinity, can seldom be employed without an admission that they may
imply a relationship that cannot be absolutely established. In the
great majority of cases the better plan is to be content with the more
non-committal term _Carpolithus_ with the addition of a family-name
when there are reasonably good grounds for a more definite reference.
No useful purpose would be served by attempting a complete survey of
the numerous casts and impressions of supposed Cycadean seeds recorded
in palaeobotanical literature, but a few types are briefly described as
examples of specimens with fairly well defined characters, which are in
all probability Cycadean.
_Carpolithus conicus_ (Cycadales?) Lindley and Hutton.
[Illustration: Fig. 584. _Carpolithus conicus._ The type-specimens in
the Manchester Museum; nat. size. (_a_, No. 361; _b_, _c_, No. 360.)]
[Illustration: Fig. 585. _Carpolithus conicus._ From a specimen in
the Malton Museum; nat. size.]
The original specimen figured by Lindley and Hutton[1377] from the
Coralline Oolite of Malton, Yorkshire, as _Carpolithes conica_
and now in the Manchester Museum, is represented in fig. 584. A
second ‘species,’ _Carpolithus Bucklandi_ Lind. and Hutt. ex Will.
+MS.+[1378], from the same locality is no doubt specifically identical
with _C. conicus_. The seeds are conical, broadly truncate at one
end, presumably the base, and tapered to a blunt apex; the broad end
is characterised by the presence of three ridges or in some specimens
by a single median ridge illustrating an oscillation between the
radiospermic and platyspermic form similar to that in _Ginkgo biloba_.
As usually obtained the seeds are probably nucules or casts showing the
surface-features of the inner wall of the sclerotesta, the sarcotesta
having been destroyed before fossilisation: the irregular marginal
teeth at the truncate end suggest casts of vascular bundles in the
integument. The scattered tubercles on the sides of some of the seeds
(fig. 584, _a_) are probably casts of holes in the shell bored by
insects and comparable with those occasionally preserved on the casts
of _Trigonocarpus_. A specimen in the Malton Museum shown in fig. 585
which may be an example of this species illustrates the occurrence
of an internal cast enclosed by the remains of a thick testa. These
Jurassic casts resemble the seeds of _Macrozamia Fraseri_, but it is
impossible to determine their systematic position with confidence.
_Carpolithus_ sp. (Cycadales?) Seward.
An unusually well preserved specimen from the Wealden beds of the
Sussex coast described under this name in 1895[1379] consists of a
kernel and mould, 1·8 × 1·1 cm. The mould from which the kernel is
readily removed is lined with a thin structure representing part of the
testa and between this and the surrounding rock is a layer of coal.
On the surface of the kernel, probably the cast of the seed-cavity,
a reticulum of narrow grooves indicates the course of the vascular
bundles over the surface of the nucellus.
_Carpolithus_ (Cycadales?) _Pomelii_ (Saporta).
The specimen from the Upper Corallian of Châteauroux (Indre) on
which this species was founded by Saporta[1380] under the name
_Cycadeospermum Pomelii_ is a large ovate cast, 5·5 cm. long and 3·5
cm. broad, closely resembling some of the larger recent Cycadean seeds:
it cannot be accepted as a true record of the group without reservation.
Saporta describes other species of _Cycadeospermum_ but none of them
are of any real importance from a botanical point of view: the same
remark applies to the seeds referred by Fontaine[1381] from Potomac
beds to the same genus, also to many other recorded examples of seeds
that afford no decisive evidence of affinity.
Some specimens described by Compter[1382] from the Lettenkohle of
Apolda (Thuringia) as Cycadean fruits—too imperfect to be determined
with accuracy—furnish an additional illustration of the slender
foundation on which many of the records of supposed Cycadean
reproductive organs are based.
=CYCADOSPADIX.= Schimper.
This name was proposed by Schimper[1383] for some French Jurassic
fossils, described by Pomel[1384] as _Crossozamia Hennocquei_ and
_C. Moraeana_, on the ground that they bear a close resemblance to
the megasporophylls of _Cycas_. Their occasional association with
_Otozamites_ fronds suggested a reference to the same parent-plant, but
such data as we have point to _Otozamites_ fronds having been borne
by plants with the _Williamsonia_ type of flower. Schenk[1385], who
figured a specimen of _Cycadospadix_ from France as the inflorescence
of a Cycad, expresses the more probable opinion that it belonged
to a plant with _Cycadites_ fronds. A Permian species described by
Renault as _Cycadospadix Milleryensis_ is now transferred to the genus
_Strobilites_[1386].
_Cycadospadix Pasinianus_ Zigno.
This species, first described from Jurassic strata in Northern
Italy[1387], is recorded also from the Kimmeridgian of France[1388] and
Scotland[1389]. Zigno’s figures give a fairly accurate representation
of the type-specimens in the Padua Museum. The megasporophylls, almost
identical in shape with those of some recent species of _Cycas_ (figs.
381; 392, A–C), consist of a broadly lanceolate or triangular limb
with deeply laciniate sides terminating a pedicel, or the distal
expansion may be preserved without the stalk from which it was no
doubt easily detached as in certain recent Cycads (_cf._ fig. 392, A).
In the specimen from Scotland there are no clear indications of veins
in the lamina, which may have been woolly as in _Cycas_. In some of
the specimens figured by Saporta[1390] and now in the École des Mines,
Paris, the stalk is absent, but in pedicellate examples scars occur
on the sides of the narrow axis and casts of seeds are found in the
same beds. A good example of _Cycadospadix Hennocquei_ is figured by
Saporta from a drawing supplied by Schimper showing two seed-scars
near the base of the lamina: the same specimen, as figured by Saporta
and Marion[1391], bears a seed, but this is presumably a partial
restoration. The occurrence of _Cycadites rectangularis_ Brauns at
Hettange in association with _Cycadospadix_ strengthens the conclusion,
based on the form of the megasporophylls, that some of the Jurassic
Cycads bore megasporophylls very similar to those of existing species
of _Cycas_.
_Cycadospadix integer_ Nathorst.
This Rhaetic species from the south of Sweden[1392] was instituted
for an imperfect broadly lanceolate lamina recalling the distal end
of the megasporophyll of a _Cycas_: the discovery of a more complete
example[1393] justifies Nathorst’s use of the name _Cycadospadix_,
though without further evidence one hesitates to regard the species as
a thoroughly trustworthy record of a Cycadean fertile leaf. The species
is characterised by the entire margin of the broad and relatively short
and thick terminal limb borne on a broad stalk with alternate lateral
projections presumably marking the position of the seeds.
These species of _Cycadospadix_ are particularly interesting as
evidence—though not amounting to demonstration—of the production
by some Jurassic and Rhaetic plants of fertile leaves agreeing
closely with those of _Cycas_. It would seem from the abundance of
Bennettitalean flowers and the very scanty remains of fertile leaves
or cones like those of modern Cycads that the existing type was
exceptional in Mesozoic floras.
=BEANIA.= Carruthers.
_Beania gracilis_ Carruthers.
[Illustration: Fig. 586. _Beania gracilis._ (After Carruthers; ½ nat.
size.)]
The generic name _Beania_[1394] was given to a branched fertile shoot
(fig. 586) from the Middle Jurassic beds at Gristhorpe, Yorkshire,
characterised by loosely disposed sporophylls bearing two sessile
seeds: each sporophyll is given off at a wide angle from a fairly stout
axis and the seeds are borne on the adaxial side of a peltate distal
expansion. Carruthers compared the type-species with a cone of _Zamia_
with which it agrees in the general plan of construction but differs
in the more open habit and in the longer and more slender seed-bearing
pedicels. The same type of shoot was figured by Lindley and
Hutton[1395] as _Sphaereda paradoxa_. _Beania_ is generally regarded as
a Cycadean reproductive shoot, but there is no doubt that the majority
of Jurassic Cycadophyta possessed flowers of the _Bennettites_ types,
and it is clear that _Beania_ differs considerably from _Bennettites_
and _Williamsonia_. Another suggestion is that _Beania_ may belong to
some member of the Ginkgoales[1396]: though very different from the
normal ovuliferous shoot of a _Ginkgo_, it resembles some abnormal
forms (_e.g._ fig. 631, D) in which the ovules occur on elongated
pedicels, but they are borne singly and the micropyle is directed
outwards, while in _Beania_ the ovules are attached in pairs to the
inner face of a distal expansion. There is no conclusive evidence in
support of either interpretation, though the general agreement between
the Jurassic type and the cones of recent Cycads would seem to favour
the inclusion of _Beania_ among the Cycadophyta.
A specimen described by Nathorst[1397] from Upper Jurassic rocks in
the North of Scotland as _Beania Carruthersi_ closely resembles the
type-species, differing chiefly in its smaller size and in the rather
closer arrangement of the sporophylls. The seed-like bodies borne
in pairs on the adaxial side of the terminally expanded pedicels
are covered with small granulations which Nathorst thinks may be
clusters of microspores, the apparent seeds being ‘antherangia.’ The
granulations are, however, very similar to those on the larger detached
seed-like bodies originally described by Nathorst from Rhaetic beds
in Sweden as _Antherangiopsis rediviva_[1398]: subsequent examination
of that species demonstrated that the granulations are due to the
presence of resinous bodies in the tissues of true seeds[1399], and
it is not improbable that a similar interpretation may hold for the
surface-features in the supposed male organs of _Beania Carruthersi_.
Pending further evidence it may be suggested that _Beania Carruthersi_
is like _B. gracilis_ a seed-bearing shoot. The Rhaetic specimens
described by Nathorst as _Stenorrachis scanicus_[1400] are similar in
habit to _Beania_ but differ in the forking of the sporophylls (fig.
656) and in the absence of any terminal swelling on which the seeds are
borne: Nathorst considers that _Stenorrachis_ may be the female organ
of a _Nilssonia_ and it is not improbable that that genus and _Beania_
are closely allied types. We have no definite information with regard
to the reproductive organs of the Nilssoniales: the closer resemblance
which their fronds bear in the structure of the epidermal cells to
those of recent Cycads is consistent with the view that their fertile
shoots were also more like those of existing types. It is, however,
still an unsettled point whether _Beania_ is more closely allied to
the Cycadophyta or to the Ginkgoales, but the balance of opinion is in
favour of the former alliance.
=Zamiostrobus.= Endlicher.
=Cycadeostrobus.= Carruthers.
Though instituted by Endlicher[1401] for a cone figured by Lindley
and Hutton as _Zamia macrocephala_[1402] which is almost certainly
Abietineous and has no claim to be included in the Cycadales, the genus
_Zamiostrobus_ has been adopted by many authors for Cycadean ovulate
cones, not only such as are believed to be closely allied to those of
_Zamia_ but for Cycadean cones generally. Carruthers[1403] suggested
_Cycadeostrobus_ as a more suitable name on the ground that it is less
limited in its implication of affinity; but, as Fliche points out,
Endlicher’s generic name has been widely adopted in a comprehensive
sense as standing for Cycadean megastrobili, excluding the supposed
_Cycas_-like megasporophylls, included under _Cycadospadix_.
Many of the specimens described as species of _Zamiostrobus_ are of
little or no value as records of Cycadean plants, _e.g._ _Zamiostrobus
orientalis_ Heer[1404] from the Jurassic beds of Amurland. A
Lower Cretaceous (Albian) species described by Fliche[1405] as
_Zamiostrobus Loppineti_, though not entirely satisfactory, is more
likely to belong to the Cycadales. The type-specimen is an elliptical
strobilus, 5·5 cm. × 3·2 cm., consisting of an axis bearing at
right-angles numerous small, contiguous, peltate megasporophylls
each with two small seeds on the lower surface. The figures given
by Fliche are, however, not convincing. An examination of specimens
in the British Museum, from Wealden and Jurassic rocks, described
by Carruthers as species of _Cycadeostrobus_, convinced me that
several are undoubtedly Araucarian cones[1406]. Solms-Laubach[1407]
called attention to the Araucarian appearance of _Cycadeostrobus
Brunonis_, a cone from an unknown locality, and this with other
species, _e.g._ _C. elegans_, _C. sphaericus_, _C. truncatus_, etc.,
may safely be referred to _Araucarites_. The specimen figured by
Lindley and Hutton[1408] as _Zamia crassa_ from the Inferior Oolite
of Towcester (Northamptonshire) affords no satisfactory evidence of
Cycadean affinity. The Lower Cretaceous Bohemian specimens described
by Corda[1409] and Velenovský[1410] as _Microzamia gibba_ should not
be included in a genus implying Cycadean affinity: though Velenovský
states that the megasporophylls bear a pair of seeds his illustrations
do not afford any satisfactory evidence of this Cycadean character.
Similarly the fossil regarded by Carruthers[1411] as probably a male
flower of _Bucklandia_ is almost certainly an Araucarian cone. A small
cone from the Lower Miocene of Armissan (Aude) named by Schimper
_Zamiostrobus Saportana_ and figured by Saporta and Marion[1412] may,
as Solms-Laubach says, be Cycadean, but we have no information with
regard to the internal structure or as to the presence or position of
the seeds.
=Androstrobus.= Schimper.
Schimper[1413] instituted this genus for ‘amenta, cycadeacea
antherifera, cylindrica, e squamis imbricatis, latere postico antheras
sessiles ferentibus efformata.’ It may conveniently be applied to
fossils which resemble the male cones of recent Cycads sufficiently
to justify the use of a name implying relationship. As so defined,
_Androstrobus_ is used in a more restricted sense than the word
suggests, just as _Masculostrobus_[1414] has been employed for fossils
that are believed to be the corresponding organs of Conifers. Among
the few species assigned to Schimper’s genus reference may be made to
_A. Balduini_ Sap., originally named by Schimper _A. zamioides_, from
the Upper Bathonian of Etrochy, and _A. Guerangeri_ (Brongn.), another
French type[1415]. Heer’s species _A. sibirica_[1416] of Jurassic age
is represented by a slender axis bearing numerous appendages which in
surface-view have the form of polygonal discs: there are no indications
of microsporangia and the evidence of Cycadean affinity is far from
convincing. Nathorst’s Rhaetic species _A. borealis_[1417] is no more
satisfactory as a record of a Cycadean strobilus. A fossil from the
Lower Cretaceous of Bohemia described as _Zamites familiaris_ and
regarded by Corda[1418] and Carruthers[1419] as a male flower of a
Cycad though not above suspicion may be included in _Androstrobus_.
Under the name _Fričia nobilis_ Velenovský[1420] described some cones
from the Lower Cretaceous plant-beds of Bohemia which he regards
as male strobili of some Cycadean plant: the cone, as shown in
Velenovský’s restoration, is 10 cm. long and 5 cm. in diameter; it
bears a close superficial resemblance to a large cone of _Zamia_ and
consists of a stout axis bearing contiguous peltate, hexagonal, scales
gradually contracted towards the proximal end, similar to those of
_Androstrobus_. The evidence on which this species is identified as a
male cone rests on the occurrence of numerous pits on the surface of
the scales; but no spores or sporangia were found and the pits as shown
in the published figures do not present the appearance of scars of
sporangia.
The Rhaetic specimen originally named by Nathorst _Androstrobus Scotti_
and afterwards transferred to the genus _Lycostrobus_ was described in
Volume +ii.+[1421]
_Androstrobus Nathorsti_ Seward.
The type-specimens were obtained from the Wealden beds of Sussex: they
were referred to the genus _Androstrobus_ on evidence which cannot
be regarded as decisive[1422]. A fairly stout axis, 6·5 cm. long,
bearing spirally disposed sub-triangular scales hexagonal in section
and attached to the axis by a broad base; the scales, or sporophylls,
are 1–1·5 cm. long and gradually tapered towards a pointed or slightly
rounded apex. Near the proximal end of some of the sporophylls there
are regularly arranged polygonal depressions which may be impressions
of microsporangia. The regular disposition of the depressions is a
striking feature and in contrast to the less regular reticulum exposed
after the removal of the sporangia from the microsporophyll of a recent
Cycad. An examination of the cuticular membrane of the microsporophylls
shows that the epidermal cells have thick and straight walls[1423],
characters consistent with the supposed Cycadean affinity of the
strobilus.