and agreeing in their plan of organisation, even more closely than
the seeds of the Trigonocarpales, with those of recent Cycads. The
nucellus is free laterally from the integument and there is a series of
vascular bundles in the nucellus. The testa consists of an outer flesh,
the sarcotesta, which may reach a considerable thickness, a shell
or sclerotesta, and in some genera an endotesta. In seeds preserved
as impressions the sarcotesta often gives them a winged appearance
(_Samaropsis_). The pollen-chamber is relatively small, resembling in
this respect the chamber in recent Cycads. A central prolongation of
the prothallus-tissue in the form of a blunt column or ‘tent-pole’
is a characteristic feature; the same feature occurs in seeds of the
Lagenostomales, but in the Cordaitales it resembles more nearly the
‘tent-pole,’ as it was called by Hirase, in recent Cycadean seeds and
in _Ginkgo_. The presence of two vascular strands in the sarcotesta
in the principal plane of the seeds is a character shared with the
seeds of _Cycas_: the position and course of these bundles are useful
characters for distinguishing different types within the group. The
microspores are multicellular.
Genera. _Cardiocarpus_; _Cyclospermum_; _Cycadinocarpus_;
_Rhabdospermum_; _Mitrospermum_; _Diplotesta_; _Leptocaryon_;
_Taxospermum_; _Compsotesta_. These generic names are all used in the
following pages for seeds known to possess certain anatomical features;
there are also included in the Cardiocarpales the genera _Samaropsis_,
_Cordaicarpus_, and _Rhabdocarpus_, but it is proposed to limit their
use to specimens which furnish no anatomical data and cannot therefore
be assigned with equal confidence to a section of seeds based on
definite morphological characters. It is certain that some at least of
the seeds described under these names would, if preserved as petrified
specimens, be included in one or other of the genera named above.
There is ample proof that some of these seeds were borne on Cordaitean
plants and that the group as a whole represents the seeds of the
Cordaitales[908]. It is, however, certain that some Platyspermic
seeds were produced by Pteridosperms. No little confusion has been
caused by the employment of the same generic names for petrified
seeds and for casts and impressions affording no evidence as to
similarity in anatomical characters. With a view to avoid the risks
necessarily entailed by following this practice it is suggested that
a clearer distinction should be drawn between genera based primarily
on structural features and form-genera. The following notes on the
genera _Cardiocarpus_, _Cordaicarpus_, _Cyclocarpon_, _Cycadinocarpus_,
_Jordania_, and _Samaropsis_, may serve to illustrate some of the
difficulties connected with the terminology of Palaeozoic seeds.
_Cardiocarpus_. Brongniart[909] proposed the name _Cardiocarpon_ in
1828 for Upper Carboniferous seeds described as compressed lenticular,
cordiform or reniform ‘fruits’ with an acute apex: in his later
work[910] he recognised their true morphological nature and gave an
account of some exceptionally well-preserved examples from Grand’
Croix. Brongniart in common with other authors believed _Cardiocarpus_
seeds to belong to Cordaitean plants, a view that in several cases is
based on conclusive evidence. The specimen represented in fig. 501,
D, illustrates the characteristic form of a cast of a _Cardiocarpus_
seed, and the sections shown in fig. 501, A and B, are from an
identical or a very closely allied species. The generic characters
are: (i) the presence of a narrow flattened border or wing surrounding
a platyspermic nucule, (ii) the cordiform base and more or less
pointed apex, (iii) the differentiation of the testa into a sarcotesta
and sclerotesta free from the nucellus except at the base, (iv) the
‘tent-pole’ prolongation of the prothallus (fig. 510, A, _b_) and the
presence of a fairly large pollen-chamber, _pc_, (v) the occurrence of
two sets of vascular bundles, an inner nucellar series and two double
vascular strands (fig. 500, A, _v_, B) which are given off from the
main supply before it reaches the sclerotesta. The term _Cardiocarpus_
as used by Brongniart signifies a type of seed possessing both certain
anatomical and external characters. The proposal is to restrict the
generic appellation to seeds exhibiting definite structural features
agreeing in essentials with _Cardiocarpus sclerotesta_ and _C.
drupaceus_.
_Cordaicarpus_. This name was first employed by Geinitz[911] in the
form _Cordaicarpon_, the type-species being _C. Cordai_ (fig. 502, C)
from the Coal Measures of Germany, a seed referred by the author of
the genus to _Cordaites principalis_ but, as Kidston has pointed out,
there is evidence that this correlation may be incorrect: there is,
however, no doubt as to its Cordaitean parentage. Specimens included
in this genus agree closely with species of _Cardiocarpus_, but they
are usually described as being distinguished by the absence of a flat
border and by a more rounded and less cordate base. In the example
of _Cordaicarpus Cordai_ shown in fig. 502, C, and in other species
assigned by authors to this genus there is a narrow border and the
form of the base is an inconstant character. As Kidston[912] and other
authors point out, there are no definite and constant characters by
which to distinguish _Cardiocarpus_ from _Cordaicarpus_ as regards the
form of the seeds preserved as casts or impressions. A further account
of _Cordaicarpus_ is given on a later page.
_Cordaispermum_. This designation was formerly adopted by Renault[913]
for seeds having the form and anatomical features of _Cardiocarpus_
which there is good reason for attributing to _Cordaites_ or to some
allied genus. In view of the fact that the majority of the seeds under
consideration are undoubtedly Cordaitean there is no need to employ
this additional generic name.
_Cyclocarpon_. Fiedler[914] instituted this term for seeds previously
described by Berger as _Cardiocarpon emarginatum_ (fig. 502, B,
now included in _Samaropsis_) and added a new species _Cyclocarpon
nummularium_. Brongniart[915] subsequently described the structure
of two species, _C. tenue_ and _C. nummulare_, which he referred to
Fiedler’s genus, and Bertrand[916] has shown that these differ from
the genus _Cardiocarpus_ in the recurrent course of the bundles given
off from the chalazal strand as in the genus _Rhabdospermum_ (cf.
fig. 501, E). There are no good grounds for retaining the designation
_Cyclocarpon_ for casts and impressions, as the specimens so named are
indistinguishable from impressions referred to _Cordaicarpus_. The
generic name _Cyclocarpus_, retained by Bertrand only for _C. tenuis_
and _C. nummularis_ simply for anatomical reasons, is now altered to
_Cyclospermum_ on the ground that the designation _Cyclocarpon_ has
been used for impressions affording no information with regard to
anatomical features.
_Cycadinocarpus_. Renault[917] transferred to this genus Brongniart’s
species _Cardiocarpus augustodunensis_ on the ground that the vascular
system exhibits in a greater degree than the other types included
by Brongniart in _Cardiocarpus_ a resemblance to that in recent
cycadean seeds. Bertrand[918] confirms Renault’s account and retains
_Cycadinocarpus augustodunensis_ as a species worthy of generic
distinction. A short account of this seed is given on a later page.
_Jordania_. This name was given by Fiedler[919] to compressed
ovate-cordate seeds characterised by a broad membranous border bearing
a superficial resemblance to the seeds of _Bignonia_. The type-species,
_J. bignoniodes_ (fig. 502, I), from the Coal Measures of Saarbrücken
has the form usually associated with the designation _Samaropsis_,
and as the latter term is generally adopted there are no adequate
reasons for the retention of _Jordania_. The name _Jordania_ has also
been applied, by Schenk[920], to fossil Dicotyledonous wood and was
previously used by Boissier[921].
[Illustration: Fig. 499. _Samaropsis emarginata_, from the
Westphalian series, Yorkshire. (Kidston Coll., 4227; × 2.)]
_Samaropsis_. Goeppert[922] defined _Samaropsis_ as ‘Fructus
samaroideus membranaceus, compressus, margine alatus, monospermus.’ The
type-species, _S. ulmiformis_, from the Permian of Brenau, is a small
seed with a broad wing or border, but a better example of _Samaropsis_
is figured by Goeppert as the wing of an insect[923]. Examples of
the genus are shown in figs. 502, A–H; 503; 504. Seeds included in
_Samaropsis_ differ from those referred to _Cordaicarpus_ in the
presence of a broader and more clearly defined border which in some
cases, as in the genus _Mitrospermum_ (fig. 494, K, L), undoubtedly
represents a lateral wing-like extension of the sarcotesta. In some
instances the wing may be a tangentially expanded integument comparable
with the perianth of _Welwitschia_, and in some Jurassic seeds referred
by Heer[924] to _Samaropsis_ the lateral appendages are probably true
wings. It is advisable to restrict the designation _Samaropsis_
to Palaeozoic seeds. Nucules deprived of the broad border would be
referred to _Cordaicarpus_ as usually employed for impressions. The
generic name _Samaropsis_ serves a useful purpose as a distinctive term
for platyspermic seeds preserved as casts or impressions characterised
by the possession of a wide border or wing broader than in typical
examples of _Cordaicarpus_. The specimen represented in fig. 499
affords a good illustration of the difference between _Samaropsis_ and
_Cordaicarpus_. In this specimen the border clearly consists of two
portions, an inner narrower border (black in the drawing) and an outer
more delicate portion; the former is the impression of the sclerotesta
and the outer represents the fleshy sarcotesta which in the living seed
may have formed a wing. If, as often happens, the seed were preserved
with the narrow border only it would be assigned to _Cordaicarpus_,
many species of which are undoubtedly incomplete _Samaropsis_ seeds.
The seeds described by Lindley and Hutton as _Cardiocarpon acutum_
(fig. 444, p. 171) have been made by Arber[925] the type of a new genus
_Cornucarpus_, the distinguishing feature being the triangular form
and the apical horns of the wing. The seeds figured by Arber[926] from
the Kent coalfield as _Cornucarpus acutus_ are, however, not identical
with the type of Lindley and Hutton, which has the characters of
_Samaropsis_. _Samaropsis_ is widely distributed in Permo-Carboniferous
rocks in Europe and North America and is recorded also from India[927]
(fig. 504), China[928], South Africa[929] (fig. 503), South
America[930] (fig. 502, F, G) and Australia[931]. Some seeds of this
form were certainly borne on Cordaitean plants (cf. fig. 480, A), but
seeds of similar type have been found in organic connexion with the
foliage of Pteridosperms (figs. 442, 445, pp. 167, 172). The Permian
‘cone-scales’ bearing seeds described by Geinitz as _Cardiocarpon
triangulare_[932], represented by well preserved impressions in the
Dresden Museum, appear to be of the _Samaropsis_ type: the same
author referred some _Samaropsis_ seeds to the Conifer _Walchia_, but
Weiss[933] dissents from this correlation as the seeds often occur
in beds in which _Walchia_ is not represented. Renault states that
the seeds of the fertile shoot described by him as _Cycadospadix
Milleryensis_[934] from Autun [= _Strobilites Milleryensis_ (Ren.)]
closely resemble _Samaropsis fluitans_ Daws. as figured by Weiss. The
suggestion by White[935] that _Samaropsis_ seeds were borne on fertile
leaves of _Gangamopteris_ adds a further difficulty to the use of the
generic characters of _Samaropsis_ as criteria of systematic position.
The Permian seeds figured by Goeppert[936] as _Oreodoxites Martianus_
are possibly specimens of _Samaropsis_.
The designation _Samaropsis_, though usually restricted to Palaeozoic
species, is applied by some authors to ‘winged’ seeds from Mesozoic
strata; but as some of the Jurassic seeds[937] so named appear to have
true wings like those of some recent Conifers it is advisable to adhere
to the more limited use of the name.
It is safe to assert that many _Samaropsis_ seeds agreed generally
in structure with Cordaitean seeds such as the petrified examples
described by Brongniart as _Cardiocarpus_. The species _Mitrospermum
compressum_[938] is an example of a petrified seed having the external
features of _Samaropsis_.
=Cardiocarpus.=
This generic title I propose to restrict to petrified seeds exhibiting
the characters described by Brongniart[939] and more recently by
Bertrand[940] in _C. sclerotesta_ and _C. drupaceus_. In general
organisation seeds of this generic type agree with those of recent
Cycads and with the seed of _Ginkgo biloba_, but there are certain
distinguishing features. An important character is afforded by the
course and place of origin of the lower vascular strands from the main
supply at the base of the seed. The outer vascular system consists
of two bundles given off from the main strand, before it reaches
the sclerotesta, which pass up the sarcotesta (fig. 500, B). In
_Rhabdospermum_, on the other hand, the corresponding bundles arise
at a higher level and form recurrent strands which penetrate the
sclerotesta before passing up the fleshy part of the integument (cf.
fig. 501, E).
[Illustration: Fig. 500. _Cardiocarpus drupaceus_ var. _expansus_.
A, transverse section of the testa approximately in the middle of the
seed; _v_, vascular bundles. B, diagrammatic sketch, adapted from
Brongniart’s drawing of the base of the seed showing the sarcotesta,
_sa_, the sclerotesta, _sc_, and the pad of vascular tissue, _d_, at
the base of the nucellus. (After Brongniart.)]
_Cardiocarpus sclerotesta_ Brongniart. The testa is differentiated into
an inner shell and an outer sarcotesta (fig. 501, A; the sclerotesta
is shown in black); there is a well developed pollen-chamber (_pc_)
and below this the prothallus-tissue is prolonged as a blunt and short
tent-pole, _b_, as in _Gingko_ and in several fossil seeds. On each
side of the apical tent-pole the slightly shrunken prothallus shows two
small archegonia, _a_, which in the relatively small size and spherical
form of the egg-cells resemble those of _Ginkgo_. In transverse section
(fig. 501, B) the seed is bi-convex and at each end of the major axis
the sclerotesta forms a small keel. There are two sets of vascular
bundles concerned in the supply of material to the ovule; a lower pair
of bundles given off from the central strand in the sarcotesta (fig.
500, B) which pass to the apical region in the inner tissues of the
sarcotesta in the principal plane (fig. 500, A, _v_), and an inner set
of bundles that pass up the peripheral tissue of the nucellus.
The species described by Brongniart as _Cardiocarpus (Cyclocarpus)
tenuis_ and _C. nummularis_ have been removed by Bertrand[941] from
_Cardiocarpus_ on the ground that the integumental bundles pursue a
course like that in _Rhabdospermum_; it is now referred to the new
genus _Cyclospermum_[942].
[Illustration: Fig. 501. A, _Cardiocarpus sclerotesta_ in longitudinal
section; _pc_, pollen-chamber, _b_, tent-pole, _a_, archegonia. B,
transverse section; _a_, archegonia. D, cast of the same or a similar
type of seed. C, E, _Rhabdospermum cyclocaryon_, longitudinal section
and a diagrammatic sketch of the seed-base; _m_, micropyle; _b_,
tent-pole; _a_, archegonium. (A, B, C, after Brongniart; D, after
Renault and Zeiller; E, adapted from Brongniart.)]
=Cyclospermum.= Gen. nov. (= _Cyclocarpus_ Bertrand).
As stated on a previous page Bertrand[943] re-establishes the
generic name _Cyclocarpus_, founded on impressions without reference
to anatomical characters, for two petrified seeds from St Étienne
described by Brongniart as _Cardiocarpus tenuis_ and _Cyclocarpus
nummularis_[944]. These types differ from _Rhabdospermum_ in the
absence of an apical snout but agree with that genus in the steeply
descending course of the vascular strands in the basal region of the
seed. As stated on a previous page, the name _Cyclospermum_ is proposed
as a substitute for _Cyclocarpus_ because of the employment of the
latter term for impressions.
=Cycadinocarpus.= Schimper[945].
_Cycadinocarpus augustudunensis_ (Brongniart[946]). In the possession
of two sets of vascular bundles this type agrees with _Cardiocarpus_,
but the more internal strands pass up on the inner face of the
sclerotesta without penetrating into the nucellus, a feature in which
_Cycadinocarpus_ agrees with the majority of recent cycadean seeds: the
outer bundles are given off from the main supply after it has entered
the sclerotesta and not before as in _Cardiocarpus_; they follow an
oblique course in the sclerotesta and emerge into the sarcotesta at
the shoulders of the basal curve of the seed. As in _Cardiocarpus_ and
_Rhabdospermum_ the two outer bundles lie in the principal plane of
the seed. There is a pollen-chamber at the apex of the nucellus and
the latter tissue is prolonged as a tent-pole which engages with the
micropyle. In the absence of data as to the course of the vascular
bundles in the chalazal region it would not be possible to distinguish
between this genus and _Cardiocarpus_.
=Rhabdocarpus= Berger and =Rhabdospermum= gen. nov.
It is proposed to restrict the name _Rhabdocarpus_[947] to impressions
and casts of seeds of the type represented by _R. tunicatus_ as figured
by Berger[948] and reproduced in fig. 506, K, the term _Rhabdospermum_
being applied to seeds of similar form in which are shown certain
distinguishing anatomical features. _Rhabdocarpus tunicatus_ Berger
is a species founded on a specimen from the Coal Measures of Silesia
characterised by an outer carbonised testa prolonged apically as a
blunt snout and, as seen in fig. 506, K, covering an apparently ribbed
nucule, but the ‘ribs’ are due to the presence of fibrous strands and
are not ribs in the ordinary sense. The outer tissue shows numerous
longitudinal striations due presumably to the presence of fibrous
elements in the sarcotesta like those shown in the petrified seed
represented in fig. 501, C. The genus is defined by Berger as follows:
‘Semina ovata vel elliptico-oblonga secundum longitudinem parallele
nervosa vel tenuissime striata, putamine (interdum deficiente)
instructa.’ As used by Berger and many other authors _Rhabdocarpus_
includes a miscellaneous collection of seeds often differing widely
from the type-species. Many of the examples correctly referred to
Berger’s genus are platyspermic though a bilateral symmetry is by no
means always clear. Renault and Zeiller[949] in their definition of
_Rhabdocarpus_ include bilateral symmetry as a characteristic feature
and speak of the seeds as oblong or oval with a pointed or truncate
apex and a rounded base. Impressions of _Rhabdocarpus_ differ from
those of _Cardiocarpus_ or _Cordaicarpus_ in their more elongate
form, always longer than broad, and in the absence of a basal sinus.
The seeds found attached to _Neuropteris_ pinnae and, in external
features, agreeing with many specimens included in Berger’s genus, have
been transferred by P. Bertrand[950] and Arber[951] to a new genus
_Neurospermum_[952]. Arber[953] in his recent revision of British seeds
proposes to restrict the name _Rhabdocarpus_ to platyspermic seeds
having a ‘large unsymmetrical nucule enclosed in a large unsymmetrical
wing or sarcotesta,’ that is to forms symmetrical in one plane. In
this category he includes _Rhabdocarpus tunicatus_ Berg. (fig. 506,
K) and _R. subtunicatus_[954] Grand’Eury, but it is not clear on what
grounds Berger’s species is spoken of as symmetrical in only one
plane: in the species _R. Lilleanus_ Arb.[955] the symmetry is hardly
sufficiently well defined to rank as a generic character. In the case
of the _Neuropteris_ seeds the apical snout is slightly curved, thus
giving them an unsymmetrical appearance (cf. fig. 422, p. 114). The
Carboniferous and Permian seeds usually referred to _Rhabdocarpus_
are transferred by Arber to his genus _Platyspermum_[956], a
designation for which it is proposed to substitute Nathorst’s genus
_Holcospermum_[957]. In seeds preserved as more or less flattened
impressions it is practically impossible in many cases accurately to
determine the symmetry: as fig. 506, A, shows, casts indistinguishable
from some examples of _Platyspermum_ are radially symmetrical.
Brongniart[958] extended the original definition of _Rhabdocarpus_ to
include certain anatomical characters, and these have been more fully
defined by Bertrand[959]. It is for seeds showing these anatomical
features that the name _Rhabdospermum_ is now proposed. This course is
followed on the ground that it is advisable to avoid confusion between
petrified specimens and impressions which in spite of superficial
resemblance may not be closely related. In some cases it is practically
certain that an impression of the _Rhabdocarpus_ type is generically
identical with a seed of similar form showing the anatomical structure
of _Rhabdospermum_, but unless identity is established a distinct
terminology is preferable. The use of the generic name _Rhabdospermum_
carries with it an implication of platyspermy, but under _Rhabdocarpus_
may be included seeds which are radiospermic and platyspermic. Some
seeds agreeing with _Rhabdospermum_ are referred by Grand’Eury[960]
to _Poroxylon_, and it is probable that _Rhabdospermum_ like
_Cardiocarpus_ is a Cordaitean seed. On the other hand _Rhabdocarpus_
may well include species, apart from those transferred to
_Neurospermum_, that belong to Pteridosperms. A species, _Rhabdocarpus
Oliveri_, recently described by Kidston[961] from the Staffordshire
coalfield is an example of a radiospermic seed which may be assigned
to a Pteridosperm. The type-specimen is an ovate seed 4 cm. long and 2
cm. broad agreeing in form and surface-features with _Rhabdocarpus_ as
already defined, but the evidence it affords of internal structure is
insufficient to determine its position with regard to genera founded on
anatomical characters. Other examples of _Rhabdocarpus_ are described
by Lesquereux[962] and White[963] from American Coal Measures, by
Grand’Eury[964] from the Loire, by Renault[965] from Autun, and by many
other authors.
=Rhabdospermum.= Gen. nov.
The platyspermic seeds included in this genus agree in size and form
with impressions assigned to _Rhabdocarpus_ and as regards the main
features conform anatomically to _Cardiocarpus_; they were probably
borne on Cordaitean plants. Fig. 501, C, represents a longitudinal
section of the species _Rhabdospermum cyclocaryon_ described
by Brongniart as _Rhabdocarpus cyclocaryon_: the sarcotesta is
particularly well developed in the apical region; at the apex a portion
of the micropyle is seen at _m_ and near the nucellus are pieces of
the sclerotesta shown in black. The presence of anastomosing fibres
near the surface is a characteristic feature: these, as Bertrand points
out, do not form a hypodermal tissue in the strict sense as they may
be separated by some of the thin-walled parenchyma of the sarcotesta
from the epidermis. The sclerotesta is only partially preserved but the
inner portion forms a dark line enclosing the nucellus, the superficial
tissue of which is separated from the shrunken prothallus represented
by the almost spherical dotted region: the remains of an archegonium
are seen at _a_ (fig. 501, C) and the characteristic tent-pole apex
of the prothallus is shown at _b_. While in shape and in the general
plan of organisation _Rhabdospermum_ agrees with _Cardiocarpus_, the
vascular system in the chalazal region constitutes a distinguishing
feature. In _Rhabdospermum_ the main vascular strand passes through
the sclerotesta, _e_, _e′_, fig. 501, E, before giving off two bundles
which bend back (‘faisceaux récurrents’), traverse the shell, and then
pass up the sarcotesta in correspondence with the feebly developed
lateral keels as far as the micropyle, while in _Cardiocarpus_ (fig.
500, B) the bundles are given off before the main strand reaches the
sclerotesta. Similar recurrent bundles occur also in _Mitrospermum_
(fig. 494, K)[967].
=Mitrospermum.= A. Arber.
_Mitrospermum compressum_ (Williamson). Mrs Arber[968] proposed the
name _Mitrospermum_[969], suggested by the peculiar form of the
seed-base, as a substitute for _Cardiocarpon_ for Williamson’s species
_C. compressum_[970] from the Lower Coal Measures of Lancashire. The
seed is platyspermic and there is some evidence that it split into two
valves along the principal plane (the longer axis of the section, fig.
494, L). The diagrammatic and partially restored longitudinal section
reproduced in fig. 494, K, shows the main features: a sarcotesta, _sa_,
covers the surface of the testa as a thin layer except at the edges
of the flattened sides where it forms a wing-like border; preserved
as an impression the seed would be assigned to _Samaropsis_. The
sclerotesta, _sc_, has a pointed apex which surrounds the lower third
of the micropyle and a broad base perforated by the chalazal vascular
strand. There was probably a narrow inner flesh as in _Trigonocarpus_
and recent Cycadean seeds (fig. 494, K, _cf_). The nucellus was free
from the integument except at the base, as in _Trigonocarpus_ and
_Stephanospermum_ (fig. 494, K, _n_): internal to the shrivelled
remains of the inner flesh there was a nucellar tapetum surrounding the
megaspore. Details as to the pollen-chamber are lacking though there
are indications that it resembled that of some species of Cordaitean
seeds. The main vascular supply passes through the sclerotesta and then
forms a low cushion of short reticulate elements below the base of the
nucellus from which two bundles are given off (fig. 494, K, _v_) in the
principal plane. The course of the bundles which pierce the sclerotesta
led Mrs Arber to remove this seed from _Cardiocarpus_, as recently
defined by Bertrand[971], since in that genus the integumental bundles
have their origin below the sclerotesta. In the course of the vascular
bundles _Mitrospermum_ is intermediate between _Rhabdospermum_ and
_Taxospermum_.
This genus is founded on a detached seed, but its resemblance to
undoubted Cordaitean species favours its attribution to that group
though, as Mrs Arber points out, some markedly platyspermic seeds are
known to have been borne on fern-like fronds and _Mitrospermum_ may
belong to some genus of Pteridosperms.
=Diplotesta.= Brongniart.
_Diplotesta Grand’Euryana_ Brongniart. The generic name _Diplotesta_,
suggested by Grand’Eury, was given by Brongniart[972] to a Grand’ Croix
seed which he compared with that of the Conifer _Cephalotaxus_. The
type-specimen is elliptical and platyspermic (fig. 495, H, p. 322),
and differs from _Taxospermum_ in the cordate form of the seed-cavity,
also in the more restricted union of nucellus and testa. The testa
is differentiated into a sarcotesta (_sa_) and sclerotesta, and the
latter forms two feebly developed keels in the principal plane: a
characteristic feature shared with _Mitrospermum_ is the splitting
of the shell into two equal valves (fig. 495, F). Fig. 495, H, shows
the contracted cylindrical nucellus and the pollen-chamber: the
sarcotesta (_sa_) is only partially preserved. _Diplotesta_ differs
from _Cardiocarpus_ in the course of the integumental vascular bundles
which are of the type illustrated by _Rhabdospermum_, _Taxospermum_,
and _Cyclocarpus_, but from these genera it is distinguished by the
dehiscence of the shell, also by its form and certain anatomical
features as described by Brongniart and Bertrand[973].
In this genus Bertrand includes Brongniart’s species _Sarcotaxus
avellana_ (fig. 495, F), a correlation suggested by the latter author.
=Leptocaryon.= Brongniart.
Brongniart[974] founded this genus for a single species, _Leptocaryon
avellana_, represented by a Grand’ Croix specimen 12 × 10 mm., which
he believed to be related to _Taxus_. _Leptocaryon_ differs from
_Taxospermum_ in the structure of the testa, but resembles it in
external features. Bertrand[975] in his revision and extension of
Brongniart’s account says that the sections throw no light on the
nature of the vascular supply, and it is therefore impossible to form a
satisfactory opinion as to the relationships of the genus. Renault[976]
referred this genus to the Cordaitales, but we have no evidence as to
the parent-plant.
=Taxospermum.= Brongniart.
Brongniart[977] gave this name to a small elliptical seed, 15×9 mm.,
recalling in external features the seed of _Taxus_, a genus to which
he believed the Grand’ Croix species to be related. The type-species
_Taxospermum Grüneri_ (fig. 495, G) has a comparatively thin testa
characterised by the absence of a sub-chalazal pad formed by the
swelling of the sclerotesta. The nucellus is attached by a broad
base to the testa and the two regions appear to be connected for
a short distance on the flanks[978]; in this feature the seed is
comparable with that of the Conifer _Torreya_ and differs from the
other platysperms, _Diplotesta_, _Rhabdospermum_, etc. Bertrand[979]
states that the main vascular strand extends from the hilum to the
chalaza before giving off the two opposite bundles which ‘follow the
floor of the shell-cavity, and on reaching the flanks traverse the
shell obliquely from below upwards[980].’ In the course and position
of the integumental bundles _Taxospermum_ differs from _Cardiocarpus_,
_Cycadinocarpus_, and _Rhabdospermum_. In this genus Bertrand includes
_Sarcotaxus angulosus_ Brongn. and _S. olivaeformis_ Brongn.[981]
=Compsotesta.= Bertrand ex Brongniart +MS.+
_Compsotesta Brongniarti_ Bertrand. The generic name
_Compsotesta_[982], though adopted by Brongniart for some incomplete
specimens from Grand’ Croix, was not published either by him or
Renault: it has recently been revived by Bertrand[983] in his account
of the anatomical details of Brongniart’s sections. This seed appears
to be closely allied to the polypterous forms _Ptychotesta_ and
_Hexapterospermum_: the testa consists of a sarcotesta differentiated
into two zones the outer of which contains vascular bundles in
correspondence with the ribs, and an inner shell. There is a nucellar
vascular supply and the nucellus is free on the flanks as in
_Stephanospermum_ and _Trigonocarpus_.
=Samaropsis.= Goeppert.
The characters of this Permian and Carboniferous genus have already
been described: the name has reference only to superficial features
especially the samara-like ‘wing,’ and connotes no special anatomical
features.
_Samaropsis fluitans_ (Dawson). The species described by Dawson[984]
as _Cardiocarpum fluitans_ from Carboniferous strata in Nova Scotia,
is represented by oval seeds with a fairly broad border usually
showing an apical notch. Fig. 502, A, is a copy of Dawson’s figure:
the apparent absence of an apical sinus in the ‘wing’ is probably
due either to an error in interpretation or to some imperfection in
the specimen. As fig. 502, A, shows, the type-specimens are far from
satisfactory, and it may be that they are not specifically identical
with the more complete specimens from European strata referred to
Dawson’s species. Zeiller[985] points out that seeds of this species
vary considerably in size, but there is always in well-preserved
examples a bifid beak at the apex. Seeds of similar form though not
specifically identical are described from the Coal Measures of Missouri
as _Cardiocarpon (Samaropsis) Branneri_ Fairch. and White[986]. Good
examples of _S. fluitans_ are figured by Weiss[987] from the Coal
Measures of Saarbrücken and the species is widely distributed in Upper
Carboniferous beds generally.
_Samaropsis bicaudata_ Kidston. This species (fig. 502, E) originally
described[988] from Lower Carboniferous rocks in Scotland as
_Cardiocarpus bicaudata_ and subsequently assigned to _Samaropsis_, is
characterised by a greater development of the flat wing-like border
which is divided into two long tapering basal lobes. Seeds of similar
form are figured by Lesquereux[989] from Pennsylvania as _Cardiocarpus_
(_Ptilocarpus_) _bicornutus_.
_Samaropsis_ (_Samarospermum_) _moravica_ (Helmhacher). This type[990]
(fig. 502, H) is characterised by the great length of the wing-like
border and on that account it was transferred by Arber to a new genus.
It was originally described by Helmhacher from the Permian of Moravia
as _Jordania moravica_ and the type-specimen has been refigured by
Zeiller[991] who records the species from Upper Carboniferous and
Permian rocks in France: it is recorded also from several localities
in Germany[992]. Seeds figured by Potonié[993] from the Permian of
Thuringia as _Samaropsis Crampii_ (Hartt) are undoubtedly examples of
_S. moravica_: the true _S. Crampii_ has recently been well illustrated
by Dr Stopes[994] from the Westphalian of New Brunswick. The species is
recorded by Arber[995] from the Kent coalfield.
_Samaropsis emarginata_ (Goeppert and Barger).
The seed represented in fig. 502, B, from the Lower Coal Measures
of Kilmarnock, Scotland[996], affords a good example of the genus:
the species was originally described by Berger as _Cardiocarpon
emarginatum_ and it was on this type that Fiedler founded the
genus _Cyclocarpon_[997]. It has been referred by many authors to
_Cardiocarpon_ and might be regarded as a type intermediate between
_Cordaicarpus_, as used in this chapter, and _Samaropsis_, though the
breadth of the border is more in keeping with the latter designation.
The figured specimen is 1·6 cm. long and 1·4 cm. broad; the nucule has
a slightly cordate base and shows several faint converging ribs which
are too inconspicuous to be represented in a natural-size drawing.
A narrow median groove in the apical region shows the position of a
vascular strand. The species is recorded from several countries:
similar though specifically distinct seeds, described by Dawson
as _Cardiocarpon cornutum_, have recently been re-described by Dr
Stopes[998] from the Westphalian of New Brunswick where they occur in
association with the leaves of _Cordaites Robbii_ Daws.
[Illustration: Fig. 502. A, _Samaropsis fluitans_. B, _Samaropsis
emarginata_. C, D, _Cordaicarpus Cordai_. E, _Samaropsis bicaudata_.
F, _Samaropsis Seixasi_. G, _Samaropsis barcellosa_. H, _Samaropsis
moravica_. I, _Samaropsis bignonioides_. K, _Samaropsis Newberryi_. (A,
after Dawson; B, R. K. 1576; C, R. K. 1899; D, R. K. 4647; E, after
Kidston; F, G, after White; H, after Zeiller; I, after Fiedler; K, R.
K. 2313. All nat. size.)]
_Samaropsis Newberryi_ Andrews.
This species was originally described by Andrews[999] from the Coal
Measures of Ohio: the specimen shown in fig. 502, K, was sent to Dr
Kidston by Mr Claypole. The whole seed is 5 cm. wide and 3·5 cm. in
depth; it is characterised by a short and relatively broad nucule
surrounded by a very broad and flat border showing faintly marked
radially disposed lines and in places some irregularly distributed
pits. The apex is emarginate and there is a broad and deep sinus in
the sarcotesta in the chalazal region. The seed resembles _Samaropsis
alata_ Kidst.[1000] and _S. Baileyi_ (Daws.)[1001] but it differs from
these in the greater breadth of the ‘wing’ and in the form of the
nucule.
The seed described by Fiedler[1002] as _Jordania bignonioides_
(fig. 502, I) agrees closely with _S. alata_ Kidst. but is probably
specifically distinct.
_Samaropsis barcellosa_ (White).
White[1003] described this species (fig. 502, G) from
Permo-Carboniferous rocks in Brazil (Rio Grande do Sul) as
_Cardiocarpon barcellosum_. The nucule is said to be cordate but, as
seen in the figure, there is no clear indication of a basal sinus: the
presence of a relatively broad ‘wing,’ as White says, entitles the seed
‘to a place in the _Samaropsis_ section of the genus.’ The author of
the species compares it with seeds described from Westphalian rocks in
Ohio[1004] and Pennsylvania[1005]. It is interesting to find a type
which is common in both Europe and North America in the western portion
of Gondwana Land. Seeds of similar form are recorded also from India,
South Africa, and Australia[1006].
_Samaropsis Seixasi_ (White).
This Brazilian species from the same beds is described by White as
_Gangamopteris_ (_Samaropsis_) _Seixasi_[1007]: it is characterised by
a small ovate nucule 8–10 mm. long and 5 mm. broad, in some specimens
surrounded by a complete ‘wing’ extending above the apex and below the
base, giving the seed an appearance similar to that of _Samaropsis_
(_Samarospermum_) _moravica_ while sometimes, as in the example shown
in fig. 502, F, the broad border is preserved only at the sides.
These seeds are abundant in the Santa Catharina beds, where they were
discovered by Dr Esdras do Prado Seixas, in association with leaves of
_Gangamopteris_, and White thinks that they were borne on the fertile
leaves of that genus which he has named _Arberia_[1008]. Although
there is as yet no proof of a connexion between _Gangamopteris_ and
seeds of this or any other type it is almost certain that it was a
seed-producing plant.
_Samaropsis Leslii_ sp. nov.
[Illustration: Fig. 503. _Samaropsis Leslii_. From Vereeniging, S.
Africa. (Mr Leslie’s Collection; nat. size.)]
The seed on which this species is founded was discovered by Mr T. N.
Leslie in the Ecca beds (Permo-Carboniferous) of Vereeniging, South
Africa, a locality from which the same geologist has obtained leaves of
_Cordaites_, _Psygmophyllum_, _Glossopteris_ and other genera[1009].
In the slightly cordate base and tapered apex (fig. 503) the nucule
agrees closely with those of European examples, but the Vereeniging
type is distinguished by its larger dimensions and by the wider border
indicating a thick sarcotesta continued basally into a stout stalk. The
apex is emarginate and a median rib marks the position of a vascular
strand. There is no evidence as to the nature of the parent-plant.
_Samaropsis indica_ (Zeiller).
Prof. Zeiller[1010] described this species as _Cardiocarpus indicus_
from the Karharbari (Lower Gondwana) beds of India. An examination of
the type-specimens enables me to confirm the accuracy of the original
account. The platyspermic seed is 5·5 cm. long and 4·5 cm. broad;
a cordate nucule is enclosed by a flat border similar to that of
_Samaropsis Leslii_ but narrower especially on the sides of the nucule.
At the apex there is a deep sinus extending to the nucule, and at the
base a fairly broad band of carbonaceous matter shows the position of
the chalazal vascular strand. The seed is characterised by its large
size and by its almost orbicular form: it occurs as a detached specimen
in beds containing _Cordaites_ (_Noeggerathiopsis_) and _Glossopteris_.
A species from Arkansas described by Lesquereux[1011] as _Cardiocarpus
ingens_ [= _Cordaicarpus ingens_ (Lesq.)] affords another example of a
large seed similar to _C. indicus_ and, except in its more orbicular
form, to _Samaropsis Leslii_.
_Samaropsis Milleri_ (Feistmantel).
[Illustration: Fig. 504. _Samaropsis Milleri._ (Indian Geological
Survey, Calcutta; nat. size.)]
An examination of the type-specimen from the Calcutta Museum enables
me to amplify the original description in an important particular. The
species was found in Lower Gondwana (Katharbari) beds in India and
referred by Feistmantel[1012] to the genus _Carpolithes_. Arber[1013],
who tentatively employed the generic name _Cardiocarpus_ in place
of _Carpolithes_, suggests that the seeds may be radiospermic, as
Feistmantel’s drawings show only a very narrow border to the nucule.
The specimen reproduced in fig. 504 was figured by Feistmantel without
any indication of a definite sarcotesta or wing, but as seen in the
drawing the ovate cordate sclerotesta is surrounded on one side and at
the base by an outer envelope: this is clearly seen at the apex where
it shows a rounded termination sloping downwards towards the micropyle
precisely as in _Samaropsis indica_ (Zeill.). The border is narrow at
the sides and broader at the base as in _S. Leslii_. The seed is 4·5
cm. long and 2·3 cm. broad, differing from _S. indica_ in its rather
smaller size and in the slightly narrower nucule. Though there is no
decisive evidence as to the parent-plant the occurrence of a specimen
of this species partially covered by a scale-leaf of a type[1014]
very similar to that which is generally recognised as belonging to
_Glossopteris_ suggests the possibility that the seeds may belong to
that genus. Scale-leaves of _Glossopteris_ are described in Volume
+ii.+, but it may be added here that leaves similar in form to those
from India, Australia, and elsewhere are figured by Geinitz[1015]
from the Altai Mountains as _Trigonocarpus_? _actaeonelloides_: the
specimens are represented with the basal scar at the apex.
=Cordaicarpus.= Geinitz.
In view of the fact that the generic names _Cardiocarpus_,
_Cordaicarpus_, and other designations have been applied to casts
and impressions which cannot be distinguished by any constant or
important feature it is proposed to adopt the name _Cordaicarpus_
for platyspermic seeds, preserved as casts or impressions, having
a comparatively narrow border enclosing an ovate or cordate-ovate
nucule; the base is either rounded or cordate. The choice between
_Cordaicarpus_ and _Samaropsis_ depends on the breadth of the border.
_Cordaicarpus_, though more suggestive of a Cordaitean alliance, may in
some cases be a Pteridosperm seed.
_Cordaicarpus Cordai_ (Geinitz). Lenticular seeds more or less
orbicular or broadly ovate (fig. 502, C, D), often slightly cordate at
the base of the nucule and with a broadly acute apex: the border is
narrow or sometimes hardly represented as in the seeds described by
Berger as _Rhabdocarpus ovoides_, a species similar to but more oval
than _Cordaicarpus Cordai_. The latter species[1016] occurs in several
coalfields in Britain, France, Germany, and elsewhere. Fig. 502, C,
shows a good example from the Middle Coal Measures of Yorkshire, 9 mm.
long by 8 mm. broad; on the very slightly cordate nucule are several
faint ribs converging towards the base and apex and between them
fine striations, characters too indistinct to be reproduced in the
natural-size drawing. The flat border represents the sclerotesta. The
seed shown in fig. 502, D, from the Westphalian series of Warwickshire
belongs to the same species or is a closely allied type: the faint
suggestion of reticulation on its surface might be regarded as a reason
for referring it to _C. areolatus_ Boul.[1017], a form characterised
by a reticulation on the testa, described by Zeiller[1018] and other
authors. This reticulation is, however, in some cases at least, formed
by crumpling and splitting of the superficial carbonised film into more
or less regular meshes: the figured specimen occurs with several other
seeds of the same type, most of which have a smooth surface. Dr Kidston
tells me that a recent critical examination of seeds in his collection
leads him to regard some specimens (_e.g._ fig. 502, D) previously
referred by him to _C. Cordai_ as identical with _Carpolithes
membranaceus_ Goepp.[1019]
[Illustration: Fig. 505. _Cordaicarpus Cordai._ Cuticle of the testa.
(Kidston Collection.)]
The photograph reproduced in fig. 505 shows the result of chemically
treating the carbonised cuticle of a seed of _Cordaicarpus Cordai_, a
method little used as yet in the case of Palaeozoic plants but which
may be useful in distinguishing seeds which cannot be satisfactorily
separated by microscopic features. The superficial cells have very
thick walls and present an appearance similar to that of the sclerous
cells in the testas of some petrified specimens.
The larger seed shown in fig. 501, D, from Commentry, described by
Renault and Zeiller[1020] as _Cardiocarpus sclerotesta_, is another
example of _Cordaicarpus_ as now defined.
IV. +Miscellaneous Seeds.+
In this section are included genera based on characters of
comparatively little morphological importance; their claim to treatment
under a common heading is that we know little or nothing of their
anatomical features or of the parent-plants.
i. _Ribbed seeds._
The seeds represented by the following genera possess ribs or
flanges usually in multiples of three; the transverse section may be
triangular, hexagonal, or polygonal. The symmetry is generally radial,
but it is difficult to determine whether a slight departure from the
radiospermic form is an original feature or the result of pressure.
Some of the ribbed seeds with which we are now concerned are no doubt
closely allied to _Trigonocarpus_ and should be included in the
Trigonocarpales, but others may well be distinct forms.
Genera: _Hexagonocarpus_, _Decagonocarpus_, _Polypterocarpus_,
_Rhynchogonium_, _Boroviczia_, _Diplopterotesta_, _Musocarpus_,
_Holcospermum_.
=Hexagonocarpus.= Renault.
This generic name is adopted by Renault[1021] for casts from Commentry
which, while probably identical with Brongniart’s _Hexapterospermum_,
afford no confirmatory anatomical evidence. The species _Hexagonocarpus
crassus_[1022] is represented by casts or nucules characterised
by six well-defined ribs and grooves with a length of nearly 3
cm. In this genus may be included the cast from the Coal Measures
of Lancashire described by Williamson[1023] as _Hexapterospermum
Noeggerathi_ (fig. 506, H), and another British example is afforded
by _Hexagonocarpus Hookeri_ Kidst.[1024], a rare fossil in the South
Staffordshire coalfield. It is impossible confidently to assign these
ribbed casts to genera founded on petrified specimens as they almost
certainly belong to different types, but the employment of the name
_Hexagonocarpus_ may conveniently be used for casts or impressions of
seeds with six longitudinal ribs differing in their relatively broader
and less prominent form from the wing-like flanges of _Polypterocarpus_
(cf. fig. 496, B). The seeds described by Dr P. Bertrand[1025] as
_Hexapterospermum modestae_, and believed by him to belong to a plant
with _Neuropteris_ fronds, should be included in _Hexagonocarpus_ as we
have no definite knowledge of their anatomical features.
=Decagonocarpus.= Renault.
This name, proposed by Renault[1026], is applied to seeds without
petrified tissues characterised by ten ribs; an example is afforded
by _Decagonocarpus olivaeformis_ from the Commentry coalfield, an
elliptical seed which bears a close resemblance to _Holcospermum
sulcatum_ (fig. 506, A) except in the smaller number of ribs.
=Polypterocarpus.= Grand’Eury.
Grand’Eury[1027] adopted this generic name for seeds from St Étienne
characterised by the presence of three, six, or more deep wings
or flanges. The term _Pterospermum_ has recently been proposed by
Arber[1028] for a seed from the Coal Measures of Staffordshire, which
he names _P. anglicum_: the type-species of the genus has three deep
wings, one from each angle. For the same seed Kidston[1029] proposed
the name _Tripterospermum ellipticum_, but as Arber’s account was
published first his specific name has priority. _Pterospermum_ had,
however, been previously used for a genus of Sterculiaceae, and partly
on this account but mainly because Grand’Eury’s genus _Polypterocarpus_
is available the latter designation is adopted. In _Polypterocarpus
anglicus_ (fig. 496, B) the flanges project slightly beyond the apex
of the seed and there is a small notch at the base; the nucule is 5
cm. long and 1 cm. broad. While it is not improbable that this seed
is generically identical with Brongniart’s _Tripterospermum_[1030],
it is safer, in the absence of structural details, to employ the less
committal term. There is no information with regard to the nature of
the parent-plants of species of _Polypterocarpus_. The English seed
from the Middle Coal Measures of Derbyshire and the Staffordshire
coalfield described by Arber[1031] as _Radiospermum ornatum_ and by
Kidston[1032] as _Polypterospermum ornatum_ affords another example of
_Polypterocarpus_ as the generic name is here employed.
=Rhynchogonium.= Heer.
Heer[1033] proposed this generic name for some globose, ovate, or
oblong ‘fruits’ from Lower Carboniferous strata in Spitzbergen,
including also fragments of ‘leaves’ which without satisfactory
evidence he believed to belong to the same plant. The supposed
fruits are clearly seeds, and Nathorst regards the ‘leaves’ as
portions of a Fern rachis. Heer described four species, but these
have since been reduced to two, and indeed it is probable that only
one type, _Rhynchogonium costatum_, is represented. Nathorst[1034]
compares Heer’s seeds with a Lower Carboniferous species described
by Young[1035] as _Trigonocarpum gloagianum_, the resemblance of
which to the Spitzbergen seeds was pointed out by Kidston. A seed of
_Rhynchogonium costatum_ is about the size of a hazel-nut and may
reach a length of 21 mm.; it is ovate, with a broad rounded base,
and in the upper third is tapered and conical, the sides of the
characteristic snout being distinguished from the smooth surface of
the rest of the seed by the presence of eight ribs converging towards
the apex (506, G). Zalessky[1036] recorded closely allied seeds from
Lower Carboniferous beds in Northern Russia, assigning them to a new
genus _Boroviczia_, the type-species being _B. Karpinskii_; he adduced
arguments in favour of Heer’s interpretation of the fossils as fruits
but, according to Nathorst, this view has been abandoned. In his recent
memoir on the Culm flora of Spitzbergen Nathorst[1037] discusses the
morphological nature of _Rhynchogonium_ seeds and describes additional
specimens. Without the aid of petrified examples it is hardly possible
to determine the true nature of the fossils.
[Illustration: Fig. 506. A, _Holcospermum sulcatum_. B, C,
_Codonospermum anomalum_. D, _Diplopterotesta spitzbergensis_ (×
3). E, _Gnetopsis elliptica_ (cupule). F, _Thysanotesta sagittula_.
G, _Rhynchogonium costatum_. H, _Hexagonocarpus Noeggerathi_. I,
_Boroviczia Karpinskii_. K, _Rhabdospermum tunicatum_. (A, Kidston
Collection; B, after Grand’Eury; C, after Renault and Zeiller; D, F,
G, after Nathorst; E, after Renault; H, after Williamson; I, after
Zalessky; K, after Berger.)]
Some specimens of _Rhynchogonium sulcatum_ in Dr Kidston’s collection
show the original surface-features: the carbonised integument is
divided in the upper region into linear lobes separated from one
another at their origin by fairly wide sinuses, a type of integument
suggesting comparison with _Physostoma_. This species was originally
described by Lindley and Hutton as _Carpolithes sulcata[1038]_ from
Lower Carboniferous rocks at Newhaven in Scotland and has recently been
figured by Zalessky[1039] from specimens in the Kidston collection
from the Lower Calciferous sandstone of Midlothian. Nothing definite
can be said as to the parent-plant, but it is significant that in
Midlothian _Rhynchogonium sulcatum_ occurs in a bed full of isolated
pinnules of a _Cardiopteris_ almost to the exclusion of any other
fossils[1040].
The seed figured by Nathorst[1041] from the Culm of Spitzbergen as
_Lagenospermum? glandiforme_ agrees closely with _Rhynchogonium_
and _Boroviczia_, and it is impossible to decide whether the lobed
appearance is due to the presence of a cupule or to the divisions of an
integument.
=Boroviczia.= Zalessky.
The specimens from Lower Carboniferous beds in Russia[1042] on which
this genus was founded are perhaps unnecessarily separated from
_Rhynchogonium_; they are ovate and beaked, 10 mm. long with a maximum
breadth of 6 mm. The type-species, _Boroviczia Karpinskii_ (fig. 506,
I), is represented both by specimens in which the cast is complete
and by others in which the apical snout of the integument is split
into separate lobes identical in form and apparently in number with
those of _Rhynchogonium_. Nathorst[1043], who retains the generic name
and describes two additional species from Spitzbergen, points out
that in Boroviczia the tapered apex is more sharply differentiated
from the broader basal portion, a difference hardly worthy of generic
recognition. If _Boroviczia_ is retained as a genus distinct from
_Rhynchogonium_ it should include the seeds described by Young as
_Trigonocarpum gloagianum_.
=Diplopterotesta.= Nathorst.
_Diplopterotesta spitzbergensis_ (Heer). Heer[1044] included in
_Samaropsis_ some seeds, described as _Samaropsis spitzbergensis_, from
Lower Carboniferous strata in Spitzbergen which differ considerably
from typical examples of the genus. These have recently been made the
type of a new genus _Diplopterotesta_[1045]: they are platyspermic
seeds nearly twice as long as broad, 6–9 × 3·5–5 mm., characterised
by a thin sclerotesta expanded throughout the length of the seed into
two prominent transversely striated wing-like ribs or flanges (fig.
506, D). At the apex, which is broad in contrast to the pointed basal
end of the seed, the sclerotesta forms a crown of eight lobes about
the flat summit of the seed-body. As Nathorst points out, this species
closely resembles the Carboniferous seeds figured by Grand’Eury[1046]
as _Polypterocarpus_, but in the latter type there are more than two
wings. Nathorst’s figures, one of which is reproduced in fig. 506, D,
suggest a difficulty in determining the number of the flanges, which
would seem to be more than two, but this appearance is regarded by
Nathorst as misleading and he believes that except at the apex there
are only two wings.
=Musocarpus.= Brongniart.
Brongniart[1047] proposed this name for two species, _M. prismaticus_
and _M. difformis_, from French Coal Measures, but gave no description
of the specimens. The type-species, described from the Loire by
Grand’Eury as _Musocarpus prismaticus_[1048], is an ovate seed nearly
3 cm. long with six longitudinal ribs, three being more prominent
than the others, and characterised by a ribbed prolongation of
the base of uniform diameter spoken of as a carpophore, which was
apparently articulated to the lower part of the seed-proper from which
it was easily detached by a natural absciss-layer. Nothing is known
of the structure or of the affinity of the genus. Some specimens
in Dr Kidston’s collection from Westphalian beds in Lanarkshire
are closely allied to or perhaps identical with _M. prismaticus_.
In the presence of a distinct basal region _Musocarpus_ resembles
_Codonospermum_[1049], though without any knowledge of the anatomy of
the former type it is impossible to say whether or not this resemblance
has any morphological importance.
=Holcospermum.= Nathorst.
_Holcospermum sulcatum_ (Sternberg). The cast reproduced in fig. 506,
A, affords a good example of a form of seed recorded under several
generic names and not uncommon in Upper Palaeozoic rocks in Europe
and North America, which in most cases cannot be assigned to a genus
implying the possession of certain anatomical characters. This type
was figured by Sternberg[1050] from the Coal Measures of Radnitz as
_Carpolites sulcatus_. Some ‘fruits’ collected on the beach near
Newhaven, Midlothian, from the Calciferous Sandstone series, are
figured by Lindley and Hutton[1051] as _Carpolithes sulcata_, but
as already stated these have been transferred[1052] to the genus
_Rhynchogonium_. Several authors have referred specimens of the type
now included in _Holcospermum_ to _Rhabdocarpus_, but that genus, as
stated on a previous page, is restricted to seeds agreeing in form
with _R. tunicatus_. Renault[1053] instituted the genus _Colpospermum_
for a partially petrified seed from Commentry agreeing externally with
_Carpolites sulcatus_ Sternb. and regarded by him as specifically
identical, characterised by longitudinal ribs which represent folds
of the testa, the intervening grooves being occupied by an irregular
reticulum formed by occasionally anastomosing smaller ribs. The generic
name _Colpospermum_ should therefore be reserved for ribbed seeds
showing the anatomical features described by Renault and Zeiller:
its application to Sternberg’s species is inadvisable on the ground
that we have no information with regard to the morphological nature
of the ribbing. More recently Arber[1054] has proposed the name
_Platyspermum_, a name previously applied to a Cruciferous plant,
for Stephanian and Permian seeds formerly assigned to Berger’s genus
_Rhabdocarpus_, which are symmetrical in two planes. In this genus
he includes _Platyspermum sulcatum_ and among other species _P.
Kidstoni_ founded on a seed originally identified by Kidston[1055] as
_Rhabdocarpus multistriatus_ Sternb. which, though probably a distinct
species, is of the same general type as _C. sulcatus_ Sternb.
The cast represented in fig. 506, A, from the Middle Coal Measures of
Yorkshire is 3·5 cm. long and has 18 regular longitudinal ribs: it is
radially symmetrical and does not conform in this respect to Arber’s
definition of _Platyspermum_. In many cases, _e.g._ the flattened seed
figured by Kidston as _Rhabdocarpus multistriatus_, it is impossible to
determine the symmetry of the seed. The old generic name _Carpolites_,
_Carpolithes_ or _Carpolithus_ has been used in a very wide sense and
does not connote any well-defined features; it should be reserved,
in the form _Carpolithus_ as used by Linnaeus, for seeds that cannot
be assigned to a systematic position or which do not exhibit any
distinctive characters worthy of emphasis by the institution of a
special name. The generic term _Holcospermum_, recently proposed
by Nathorst[1056], is a suitable name for this type of seed; as
defined by the author, it includes seeds that may be radiospermic or
platyspermic. Specimens of the type-species, _H. dubium_[1057],from
the Lower Carboniferous beds of Spitzbergen, agree closely in size
and shape with some examples of _Rhynchogonium_ and _Boroviczia_, but
they are distinguished by prominent ribs extending the whole length
of the cast. In some seeds similar to _H. sulcatum_ the ribs form
sharp ridges, but the difference between rounded and sharp ridges is
often determined by the method of preservation: a specimen deprived of
its outer flesh would form a cast more sharply ribbed than a seed in
which the sarcotesta had been moulded on to the ribbed sclerotesta.
On the other hand some ribs are formed by blunt sclerotestal folds as
in _Colpospermum_: both types of ribbing are included in the genus
_Holcospermum_.
ii. _Other Genera._
=Malacotesta.= Williamson.
This generic name was instituted by Williamson[1058] for a petrified
seed from the Coal Measures of Lancashire which he named _Malacotesta
oblonga_: the type-specimen is a small seed 6–7 mm. long characterised
by a thick fleshy integument. The structure is however insufficiently
known to admit of a satisfactory comparison of the imperfectly
preserved specimen figured by Williamson with other types.
=Thysanotesta.= Nathorst.
Nathorst[1059] founded this genus on a single seed from the Lower
Carboniferous plant-beds of Spitzbergen which exhibits features
sufficiently distinctive to justify its recognition as the type of a
separate genus.
_Thysanotesta sagittula_ Nathorst. The type-specimen is a long and
narrow seed, 20 mm. long, ovate below and prolonged apically into a
slender beak, 8 mm. in length, which probably represents a micropylar
tube; the beak bears numerous stiff hairs (fig. 506, F). The seed
closely resembles a carpel of _Erodium_ without the horizontal part
of the awn. There is no evidence as to the nature of the parent-plant
but the species affords an interesting example of a Palaeozoic seed
apparently adapted for wind-dispersal, or possibly the bristles may
have served the same purpose as in the fruits of _Erodium_. Attention
is called elsewhere[1060] to the frequent resemblance of Palaeozoic
seeds such as _Thysanotesta_ to fruits of recent flowering plants.
=Carpolithus.= Linnaeus.
Nathorst[1061] has pointed out that this generic name was employed by
Linnaeus for fossil fruits: in the form _Carpolites_ (Sternberg) or
_Carpolithes_[1062] it has been widely used and differently defined
by authors, usually in a comprehensive sense including fossil seeds
from both Palaeozoic and Mesozoic strata which cannot be assigned to
a definite position in the plant-kingdom. It is desirable to adopt
some designation for seeds from strata of different ages which do not
exhibit any features sufficiently distinctive to justify the creation
of a special genus. By employing such a name as _Carpolithus_, without
attempting to define its characters within prescribed limits, for casts
or impressions of seeds which are not distinguished by any striking
characters and cannot be allocated to any particular section of
seed-bearing plants the unnecessary multiplication of generic titles
is avoided: when any additional data are obtained differentiating
particular types from other forms of _Carpolithus_ the provisional
term should be superseded by some distinctive generic name. Among
seeds from the Coal Measures there are several examples of both large
and small types without any regular ribs or lacking such features
as serve to distinguish the genera already described, which are
appropriately included in _Carpolithus_. The two species _Carpolithus
Wildii_ Kidst.[1063] and _C. bivalvis_ Goepp.[1064] are two examples
of seeds from Upper Carboniferous rocks which it is desirable to refer
to this comprehensive genus pending further discoveries as to their
morphological features. The Jurassic species _C. conicus_ Lind. and
Hutt.[1065] is another type which it has been customary to include in
_Carpolithus_.
(_Microspermum._ Arber.)
The generic name _Microspermum_ has recently been proposed by
Arber[1066] for some Westphalian seeds described by Carpentier[1067]
from the North of France as _Carpolithes? samaroides_ and for similar
fossils from the Middle Coal Measures of Nottingham. The supposed seeds
are small, ovate or pyriform bodies, 5–12 mm. long and 2·5–6 mm. broad,
with one extremity broadly rounded and the other acute: one side is
keeled, the other grooved, and a large foramen occurs near the broader
end and on the grooved surface. Arber emphasises the fact that the
specimens are symmetrical in one plane only. As the author of the genus
points out the morphological nature of the fossils is not thoroughly
established, nor is the parent-plant known. In view of the ill-defined
characters of the specimens so far discovered it is hardly desirable
to institute a new generic name implying their seed-nature; moreover
_Microspermum_ has previously been employed for a genus of Compositae.
An examination of specimens leads me to doubt their seed-nature and it
would seem more likely that they are foliar organs, possibly bracts
which originally bore seeds or sporangia.
* * * * *
An examination of some of the specimens of supposed Permian seeds for
which Geinitz[1068] proposed the generic name _Guilelmites_ convinced
me that they are inorganic structures, probably nodules in shale
smoothed and rounded by slickensiding.