Araucarian pitting to the genus _Dadoxylon_, while wood of the same
general type from more recent strata is by many authors referred to
_Araucarioxylon_[650]. This arbitrary distinction based on a difference
in age is open to serious objection. Fossil wood of the Araucarian type
is widely scattered in strata ranging from Carboniferous to Jurassic
periods; it also occurs in later formations. The fact that on the one
hand Araucarian plants, as recognised by cones and foliage-shoots, are
especially characteristic of Jurassic floras and occur more rarely in
Rhaetic and Triassic floras, and on the other hand that _Cordaites_ and
its allies reached their greatest development in Permo-Carboniferous
times, renders it probable that in the majority of cases a distinctive
name based on geological age would be in accordance with botanical
differences. But we have no satisfactory data as to the upper limits
of the Cordaiteae or the lower limits of the Araucarineae: in all
probability the two families overlapped and co-existed for more than
one geological period. It is, moreover, the plants from formations
where overlapping occurred that are the most critical from a botanical
standpoint. The age-distinction is therefore at best an artificial
one and may be seriously misleading. Potonié[651] and Gothan[652]
have emphasised the desirability of adopting the name _Dadoxylon_ for
all wood of the Araucarian type irrespective of age. If a particular
specimen can be correlated definitely with _Cordaites_ or some other
genus it should be so designated, but the fragmentary nature of the
records usually precludes this simple course. The most logical plan is
to use the name _Dadoxylon_ for all woods with Araucarian characters if
there is no sufficient reason for employing a less provisional term.
If the evidence clearly points to the Araucarineae the generic name
_Araucarioxylon_ should be added in parentheses after _Dadoxylon_,
but whether or not this is done, a statement as to the geological
age of the fossil will in itself be some assistance in enabling the
student to form an opinion on the balance of probability in favour
of a Cordaitean or an Araucarian affinity. The course suggested
by Gothan[653], namely to add _Cordaites_ after _Dadoxylon_ if an
_Artisia_ pith is present, is rendered inoperative now that we know
that a discoid pith occurs in more than one genus. In this chapter we
are concerned primarily with _Cordaites_ and with such stems as may
fairly be regarded as Cordaitean: examples of fossil wood from later
formations are dealt with in another place. A distinction between
_Araucarioxylon_ and _Cordaioxylon_ stems has been based by Felix on
the nature of the pith-casts; those of the _Artisia_ type he refers to
_Cordaioxylon_, while Palaeozoic stems with _Tylodendron_ pith-casts
are assigned to _Araucarioxylon_[654]. This distinction can, however,
only be made in the comparatively few cases in which the pith-cast is
preserved. Its validity is, moreover, open to question. A _Tylodendron_
(= _Schizodendron_) cast shows on its surface the characters of the
inner face of the secondary xylem, projecting spindle-shaped areas
representing the inner ends of medullary rays and a reticulum of
grooves formed by the more resistant and prominent inner edges of
the rows of tracheids (fig. 746). A pith-cast of a stem in which the
destruction by decay of the medullary parenchyma had not extended to
the edge of the xylem-cylinder might show transverse diaphragms. The
occurrence of _Tylodendron_ casts means that decay had extended to the
surface of the wood. But in view of the occurrence of _Tylodendron_
casts in stems that are not those of _Cordaites_ a short account of the
genus is given on another page[655].
The main features of the stem of _Cordaites_ have already been
enumerated. The stele agrees with that of _Araucaria_ and _Agathis_
and especially with _Agathis_ in the double nature of the leaf-trace.
Williamson[656] in 1877 described pieces of wood from the English
Coal Measures and the Lower Carboniferous of Scotland which he
referred to _Dadoxylon_ but without any specific name. These include
the Coalbrookdale stem in which he had previously demonstrated the
connexion between _Artisia_ and _Dadoxylon_. The structure of the
xylem is like that in _D. Brandlingii_ and the specimens may belong
to that species. The most interesting fact recorded by Williamson
is the occurrence of double leaf-traces, a feature which led him to
suspect a remote generic affinity to _Ginkgo_. This double trace may
be an important diagnostic feature but unfortunately the majority of
descriptions of species of _Dadoxylon_ throw no light on the character
of the foliar bundles.
Thomson and Allin[657] have recently pointed out that a double
leaf-trace occurs in a stem from the Permian of Kansas described by
Penhallow[658] as _Pityoxylon chasense_ and referred to that genus
because of the supposed occurrence of resin-canals in some of the
medullary rays: the canals are apparently leaf-traces traversing broad
rays in the secondary wood.
The primary xylem of _Cordaites_ is in direct continuity with
the secondary tracheids and does not form mesarch strands as in
_Mesoxylon_. The pith is usually discoid. The pitting on the tracheids
is a character of special importance: while it is true to say
that as a rule the number of pits on the radial walls of a single
tracheid is larger than in the Araucarineae, this is not always the
case. In _Araucaria_ there are occasionally as many as five rows
of alternate polygonal pits (fig. 691, A) and in some Palaeozoic
Dadoxylons there are only one[659] or two rows. The very broad zone
of transitional elements at the inner edge of the xylem-cylinder
is a characteristic feature shared by the Araucarineae[660]; the
spiral protoxylem-tracheids are succeeded by scalariform elements and
these, by the gradual anastomosing of the transverse bars, pass into
tracheids with multiseriate pitting. In this broad zone we probably
have a primitive feature, an epitome in a single stem of the course
of development of multiseriate from scalariform pitting. In some
Palaeozoic species with wood of the pycnoxylic type and agreeing
generally with typical _Cordaites_ the bordered pits are sometimes
separate and circular, and opposite pits occasionally replace the
usual alternate arrangement. Another feature on which stress has been
laid is that in _Cordaites_ the pits occupy the whole breadth of the
tracheal wall; but this, though frequently the case, is by no means a
constant feature. In _Dadoxylon Newberryi_[661] the pits tend to form
groups, leaving unpitted areas, as in the genus _Coenoxylon_[662].
In the stem of _Dadoxylon materiarum_ Daws. represented in fig. 475
the pits do not always cover the whole of the tracheid-walls: this
stem is also instructive as an example of the different appearance
presented by pitted tracheids according to the state of preservation.
In some places an oblique pore is well shown while in others only the
outer border of the pit is seen. Gothan[663] has described a specimen
in which some of the pits are circular and occupy only the central
area of the xylem elements: separate circular pits occur also in _D.
Pedroi_ Zeill.[664] (fig. 476). Similar departures from the normal
are illustrated by recent species of Araucarineae. The absence of a
torus is another feature shared by _Dadoxylon_ and true Araucarian
wood. Annual rings other than incomplete and spasmodically formed rows
of narrower tracheids are not as a rule present, and in this respect
also _Araucaria_ affords a close analogy. Thomson[665] has figured
a transverse section of a root from English Coal Measures in which
rings of growth are well defined; and other instances are recorded.
In an Australian species named by Arber _D. australe_[666], there are
well-marked rings of growth, and this is equally the case in some
Indian wood[667] of Permo-Carboniferous age, more nearly allied to
_Mesoxylon_ than to _Cordaites_, and in a _Dadoxylon_ of similar age
from South Africa. On the other hand the statement that annual rings
occur in Palaeozoic wood is often incorrect, partial rings having been
confused with regular concentric cylinders of summer elements. Dawson
and Matthew[668] described rings in _D. ouangondianum_, and Goeppert
and Stenzel[669], who examined the Canadian material, refer to circles
like annual rings; but Penhallow[670] states that there is no evidence
of true growth-rings.
The medullary rays are uniseriate and consist of thin parenchymatous
cells with unpitted walls; they vary considerably in depth, usually
comparatively shallow but in some cases 40 or 50 cells deep. In recent
Araucarineae the rays are generally shallower. The absence of special
receptacles, other than occasional resiniferous tracheids, for products
of secretion is a feature common to _Dadoxylon_ and the Araucarineae.
The phloem presents no features of special interest, but our knowledge
of this tissue is comparatively meagre.
Among other examples of large _Dadoxylon_ stems some of which no
doubt bore Cordaitean foliage—though as a rule we have insufficient
information as regards anatomical characters to enable a decision
to be made between _Cordaites_ and _Mesoxylon_—reference should be
made to the imposing array of silicified trunks in the grounds of the
Chemnitz Museum[671]. These were obtained from Lower Permian strata
at Hilbersdorf near Chemnitz from beds overlain by porphyry tuff and
resting on quartz porphyry, the volcanic material which furnished
the siliceous solutions. Several large pieces of wood were found in
association with stems of _Medullosa_ and _Psaronius_, leaves of
_Cordaites_, _Artisia_ pith-casts, and _Cardiocarpus_ seeds with
specimens of _Walchia_, _Gomphostrobus_ and other plants. Sterzel
describes a stem 16·5 met. long and 1·5 met. in diameter; on the main
trunk the branch-scars are scattered but on some branches there is
a tendency to a whorled arrangement. This and many other stems are
referred to _Araucarioxylon_ (or _Dadoxylon_) _saxonicum_, a species
first described by Reichenbach as _Megadendron saxonicum_. In one
specimen Sterzel states that the bordered pits are generally in 1–2
rows, though rarely in 3–4 rows, on the radial walls of the tracheids
which they do not completely cover: the medullary rays reach a depth of
between 20 and 30 cells. It is noteworthy that the stem 16·5 met. long
has a pith-cast of the _Tylodendron_ type.
_Dadoxylon_ (_Cordaites_) _Brandlingii_ (Lindley and Hutton).
1831. _Pinites Brandlingii_ Lindley and Hutton, Foss. Flor. Vol. +i.+
Pl. +i.+
1850. _Araucarites Brandlingii_ Goeppert, Foss. Conif. p. 232, Pls.
+xxxix.–xli.+
1890. _Cordaioxylon Brandlingii_ Schenk, in Schimper and Schenk, p.
853, fig. 408.
This species was founded on ‘a fossil giant of the vegetable kingdom’
discovered at Wideopen near Newcastle in Carboniferous strata on the
estate of Mr Brandling. The stem, 72 ft long and far from complete,
showed an irregular and not a whorled distribution of branch-scars. It
is noteworthy that in _D. medullaris_ (Goepp.)[672], a Permian species
from Saxony, the branch-scars, while for the most part irregularly
scattered, in one case showed an approach to a whorled disposition
as in recent Araucarias. Witham[673] gave a fuller account of the
structure of the stem than is included in the original description,
and the species has been described by many later authors from both
Permian and Carboniferous localities. The pith is discoid and the broad
transitional region at the inner edge of the wood is a characteristic
feature[674]. Thomson[675] points out that there is a tendency to a
retention of the scalariform type of pitting in the region of the
medullary rays. There are 1–5 rows of pits on the radial walls of the
tracheids. The rays may reach a depth of 40 cells; they are usually one
cell broad. It has recently been shown that as many as six vascular
strands[676] may form one leaf-trace instead of the customary pair,
a feature suggesting comparison with _Metacordaites Rigolloti_ Ren.
with its five foliar bundles. Other species agree very closely with
_D. Brandlingii_ and it is impossible to determine with accuracy the
precise specific limits of stems agreeing generally with this type; but
for the sake of emphasising the variation in anatomical structure it
is worth while to draw attention to a few more or less divergent forms
from different geographical areas.
_Dadoxylon protopityoides_ Felix.
An interesting feature in this Westphalian type from Germany is the
occurrence of transversely elongated pits on the tracheids[677]
associated with those of normal form closely simulating the pits in the
xylem elements of _Protopitys_.
_Dadoxylon nummularium_ White.
In this Brazilian wood[678] from Permo-Carboniferous beds the medullary
rays are very numerous, mostly uniseriate and 1–30 cells in depth.
The pits on the tracheids are in 1–2 rows and are often contiguous.
In another type, _D. meridionale_, described by the same author[679],
the pits are strictly uniseriate and generally contiguous. As White
says, the absence of the pith and cortex and of any evidence as to
the structure of the primary xylem renders impossible any definite
expression of opinion as to the affinity of these and many other
species.
_Dadoxylon Nicoli_ Seward.
Dr Arber[680] in naming this species, from the Newcastle
(Permo-Carboniferous) Series of New South Wales, _Dadoxylon australe_,
does not mention Crié’s earlier account of some wood from New Caledonia
under the name _Araucarioxylon australe_[681]. The latter generic name
according to the usage adopted in this volume should be superseded by
_Dadoxylon_, and this necessitates a fresh specific name for Arber’s
specimens. The name _Nicoli_ is suggested in place of _australe_, as
the sections on which Arber founded his species form part of the Nicol
collection in the British Museum.
The xylem shows distinct rings of growth, a feature also seen in
Indian stems of approximately the same geological age and recorded
by Shirley[682] in wood from Queensland which needs more careful
examination. The bordered pits, usually multiseriate and contiguous,
are not infrequently in 1–2 rows and separate. The uniseriate
medullary rays are very numerous as in White’s Brazilian species _D.
nummularium_, and as a rule 6–12 cells deep. Some well-preserved
specimens from Permo-Carboniferous strata in Natal and Zululand have
been described by Warren[683] as _Dadoxylon australe_ Arb., showing
interesting anatomical features, but the material almost certainly
includes more than one specific type and would repay more detailed
investigation.
_Dadoxylon materiarum_ Dawson.
This species was described by Dawson[684] from Carboniferous strata
in Nova Scotia and afterwards referred by Penhallow[685] to the genus
_Cordaites_. In the transverse section reproduced in fig. 474, A, the
tracheid-walls have been reduced in thickness by partial decay, but
some of the bordered pits are clearly shown on the radial walls; the
pits usually form 2–4 contiguous rows (fig. 475) in some cases with an
oblique pore while others are represented either by the outer border of
the pit or by the pore only. The narrow medullary rays are as a rule
uniseriate and may be 60 cells deep (fig. 474, B). Dawson states that
some specimens have large _Artisia_ pith-casts, a fact that formerly
would have been regarded as proof of the _Cordaites_ nature of the
wood, but in the absence of evidence with regard to the nature of the
primary xylem it is impossible to say whether the stem is _Cordaites_
or _Mesoxylon_.
_Dadoxylon_ sp.
Some wood received from Mr Leslie, collected at Vereeniging, South
Africa, in Permo-Carboniferous rocks, shows well-defined rings of
growth. The pits form either a single row, a double, alternate and
contiguous row, or rarely three series on the tracheid walls. The
medullary rays are usually uniseriate and 1–30 cells deep.
_Dadoxylon Kayi_ Arber.
This species is represented by some large trunks, in some cases with
a diameter of 40 cm., discovered by Mr Kay in the Coal Measures of
Worcestershire[686]. The pith is very small and shows no indication of
a discoid structure, but owing to its poor preservation no sections
could be obtained of this region. The secondary wood is characterised
by the large number of uniseriate medullary rays 1–27 cells in depth;
the tracheids have usually two or sometimes three rows of alternate and
contiguous bordered pits on the radial walls. Arber regards the absence
of a discoid pith as a fatal objection to a reference of the stems to
_Cordaites_ and speaks of them as affording further evidence of the
occurrence of Coniferae in the higher Coal Measures of the Midlands. It
is, however, impossible to determine the position of the species in the
absence of any data with regard to the structure of the perimedullary
region, and without such information we are hardly justified in
regarding _Dadoxylon Kayi_ as a member of the Coniferales.
[Illustration: Fig. 474. _Dadoxylon materiarum._ Transverse (A) and
tangential (B) sections of the secondary xylem. (Kidston Coll. 222,
224.)]
[Illustration: Fig. 475. _Dadoxylon materiarum._ A–C radial
longitudinal sections of the secondary xylem. (Kidston Coll. 225.)]
_Dadoxylon Pedroi_ Zeiller.
This species from Upper Carboniferous or possibly Lower Permian strata
in Brazil[687] has a pith 3·8 cm. in diameter composed of parenchyma
with scattered secretory sacs and characterised by the occurrence of
three equidistant bays projecting into the cylinder of wood (fig. 476,
A) which extend through the length of the specimen (6 cm.): these, as
Zeiller suggests, may be connected with the departure of leaf-traces
or branches. The xylem is entirely composed of centrifugal elements
and shows a broad transitional zone (fig. 476, B) including spiral,
scalariform, and reticulate tracheids, but the bordered pits are less
numerous and less crowded than in many species of _Dadoxylon_. The rays
are 1–2 cells broad and reach a depth of 50 cells. The most striking
features are the solid and not discoid pith with its three rounded
bays and secretory canals, also the smaller number and frequently
circular form of the pits on the tracheids. Zeiller considers that
the stem is that of some Cordaitean plant though probably not a true
_Cordaites_. White[688] questions the advisability of adopting the
generic name _Dadoxylon_ and suggests the possibility, though without
any satisfactory evidence, that it is the stem of a _Gangamopteris_.
Failing further information, there would seem to be no sufficient
reason for the institution of a distinctive generic name.
[Illustration: Fig. 476. _Dadoxylon Pedroi._ A, transverse section
showing the pith and part of the secondary wood. B, longitudinal
section of part of the secondary wood. (After Zeiller.)]
_Dadoxylon permiense_ (Renault).
This Permian species from Autun[689] differs from typical examples of
the genus in the differentiation of the pith into a central thin-walled
region contracted into transverse diaphragms surrounded by a cylinder
of stouter tissue and in the greater breadth of the medullary rays. The
tracheids have 3–4 rows of pits of the usual type. Spirally disposed,
decurrent, leaf-bases occur on the surface of the stem, and the cortex
includes secretory canals and strands of hypodermal stereome. A small
number of veins pass up the median part of the lamina which in this
respect and in its greater thickness differs from that of _Cordaites_
leaves. Renault speaks of the rays as a cycadean feature, but they are
only two cells in width and shorter than in recent Cycads.
_Dadoxylon spetsbergense_ Gothan.
In this species[690] from Spitzbergen, of doubtful age though probably
Palaeozoic, there is no xylem-parenchyma and the medullary rays are
from 2 to 5 cells deep; the bordered pits occur in 1–2 or rarely 3
rows on the radial walls of the tracheids; they are alternate but not
flattened and characterised by their small size (7μ high); they do not
cover the whole face of the tracheids. It is pointed out that in many
Palaeozoic and Mesozoic Dadoxylons the pits are larger than in recent
species (16–17·5μ as compared with 9–12μ) while in _D. spetsbergense_
they are still smaller. The large size of the medullary-ray cells
is another noteworthy feature, also the absence of annual rings, a
character possibly connected with conditions of growth in northern
regions. It is, however, pointed out by Nathorst[691] that the fossil
was not found _in situ_ and, as he says, it may have been carried by
currents from a more southern locality.
=Metacordaites.= Renault.
_Metacordaites Rigolloti_ Renault.
Renault founded this species[692] and genus on a stem from Autun which,
like _D. Pedroi_, differs in certain respects from stems usually
attributed to _Cordaites_. The pith is solid and contains secretory
ducts and cells; the tracheids have often a single row of pits, and
multiseriate pitting is much less common than in _Dadoxylon_. The
medullary rays are generally 1–6 cells deep. A striking feature is
the occurrence of groups of five vascular bundles penetrating the
secondary wood in V-shaped groups, each group being regarded as a
multiple leaf-trace, a type recently recognised by Thomson in _D.
Brandlingii_. In one of Renault’s figures a larger scar, presumably a
branch-scar, is shown immediately above a group of foliar bundles. The
genus _Metacordaites_ is considered by its author to be intermediate
between Conifers and the Cordaitales, but nearer to the former. This
conclusion is, however, based on insufficient evidence, as nothing is
known of the reproductive organs.
+Roots.+
In 1871 Williamson[693] gave an account of a petrified plant from
the Lancashire Coal Measures which he named _Dictyoxylon radicans_,
but he afterwards came to the conclusion that the specimens so named
were portions of the subterranean axis of some other plant, possibly
_Asterophyllites_, and proposed a new generic term _Amyelon_[694].
In 1874 he brought forward fresh evidence in support of connecting
_Amyelon radicans_ with _Asterophyllites_ or _Sphenophyllum_, genera
which Williamson believed to be very closely related. It has since
been recognised that _Amyelon_ is the root of _Cordaites_ or of some
closely allied member of the Cordaitales. Our knowledge of Cordaitean
roots is based chiefly on the work of Williamson and Renault[695],
and more recently Osborne[696] has added new facts of considerable
interest. In the larger roots the primary xylem may be diarch or
there may be as many as four or five protoxylem groups (fig. 477).
The primary tracheids are spiral or scalariform and the space, _s_,
separating them from the surrounding secondary xylem seen in fig. 477,
B, was no doubt originally occupied by conjunctive parenchyma. The
secondary wood is composed of tracheids, with contiguous bordered pits
identical with those in the xylem of the stem, and narrow medullary
rays. The section, 4 mm. in diameter, represented in fig. 477, A, shows
a tetrarch primary xylem strand enclosed by secondary wood composed of
rather thin-walled elements succeeded by a zone of phloem including
some secretory sacs, and beyond this is a cylinder of periderm, _p_.
In a section of a root figured by Renault from Autun the periderm is
separated from the stele by a broad band of parenchyma which appears
to be cortical, but in the British specimens the deep-seated origin
of the periderm is clearly shown: Osborne states that it arises in
a layer immediately outside the endodermis. In one of the specimens
figured by Williamson[697] the secondary wood shows clearly marked
irregular concentric lines simulating rings of growth, but there is
no evidence of any regularly recurring variation in the diameter of
the xylem-elements. From the descriptions of Williamson and Osborne it
is evident that the roots of _Cordaites_ were profusely branched and,
as the latter author has shown, the method of branching points to the
formation of coralline roots like those of recent Cycads, some Conifers
and Dicotyledons. Osborne found that the cortex of small rootlets
is composed of two zones, an outer parenchyma without cell-contents
and an inner parenchymatous tissue characterised by the occurrence in
some of the cells of tangled masses of fungal hyphae almost always
unseptate. In some cases the hyphae bear terminal vesicles similar to
those observed on fungal hyphae in the cortex of _Podocarpus_ roots.
Osborne makes out a good case for regarding the fungus as symbiotically
related to the tissues of the lateral roots, a relationship identical
with that in many existing trees, particularly _Myrica_ and _Alnus_.
It is suggested that the formation of the coralline root-tubercles is
a feature consistent with the view that _Cordaites_ lived in saline
marshes, a physiologically dry habitat favourable to the occurrence of
mycorhiza.
[Illustration: Fig. 477. A, root of _Cordaites_. B, centre of the
root enlarged; _p_, periderm; _s_, space. (Kidston Coll. 1906.)]
[Illustration: Fig. 478. Root (_Cordaites_?) exposed in the bed of
the Vaal river. (After Mellor and Leslie.)]
Reference has already been made to the habit of Cordaitean roots in the
general account of the genus (figs. 468, A, 478). The specimen shown in
fig. 478 may be a root of _Cordaites_ (_Noeggerathiopsis_) _Hislopi_,
but nothing is known as to its structure[698].
+Reproductive Organs.+
=Cordaianthus.= Grand’Eury.
We have as yet no definite knowledge of the nature of the reproductive
organs of _Mesoxylon_ and _Poroxylon_, but having regard to their
close resemblance in other respects to _Cordaites_, particularly in
the case of _Mesoxylon_, the presumption is that some of the seeds and
fertile shoots attributed to _Cordaites_ may belong to other members
of the Cordaitales. Despite the abundance of _Cordaites_, or at least
of material assigned to that genus, and the comparative frequency of
fertile shoots in actual connexion with foliage-shoots, the practical
identity of _Mesoxylon_ and _Cordaites_ leaves precludes any confident
use of the latter name in a strict sense.
In 1822 Brongniart[699] described a small bud-like fossil of Tertiary
age as _Antholithes liliacea_, and this generic name in the form
_Antholithus_ became widely used for fertile shoots or flowers from
different geological horizons. As knowledge became more precise other
names replaced _Antholithus_, though Renault[700] retained it for some
inflorescences from Commentry which could not definitely be included
in _Cordaites_. Lindley and Hutton[701] employed the genus for a
specimen, now recognised as a Cordaitean fertile shoot, from the Coal
Measures which they called _Antholithus Pitcairniae_, the specific
name being chosen to indicate a possible affinity to the Bromeliaceous
genus _Pitcairnia_. A few years later Morris[702] described a similar
inflorescence as _A. anomalus_. In 1872 Carruthers[703] substituted
Brongniart’s term _Cardiocarpon_ for _Antholithus_ and called _A.
Pitcairniae Cardiocarpon Lindleyi_ and Morris’s species _C. anomalum_.
The specific name _Lindleyi_ has been widely adopted, but there would
seem to be no adequate reason for disregarding the priority-rule.
It is, however, customary to use Grand’Eury’s term _Cordaianthus_
for all Cordaitean inflorescences. Goeppert[704] suggested the name
_Botryoconus_ for an inflorescence similar to _C. Pitcairniae_ and for
this C. E. Weiss[705] substituted _Noeggerathianthus_ on the ground
that he considered Goeppert’s specimen to be the male inflorescence of
_Noeggerathia_. Grand’Eury resuscitated _Botryoconus_[706] for some
spikes from the Gard coalfield connected by him with _Dory-Cordaites_.
The nature of the seeds borne by the inflorescences has largely
influenced authors in the choice of a generic name: Carruthers used
_Cardiocarpon_ while Zeiller[707] speaks of _Samaropsis Pitcairniae_.
The genus _Cardiocarpon_ was founded by Brongniart for compressed
cordiform seeds, but it was not until later that their gymnospermous
nature was recognised. Further reference to the nomenclature of
seeds of the _Cardiocarpon_ type will be found in Chapter +xxxv.+
The correlation by Grand’Eury and other authors of different species
of inflorescences and species of _Cordaites_ is frequently based on
association, and in the absence of more satisfactory evidence the safer
course is to deal with Cordaitean fertile shoots in a general sense.
[Illustration: Fig. 479. _Cordaianthus._ From the Middle Coal
Measures of Lancashire. (Manchester Museum; ⅓ nat. size.)]
(_a_) _Ovulate shoots._ These are represented by a considerable number
of forms in both European and American localities. In rare cases the
compound shoot reaches a length of 30 cm. (fig. 479), but it is usually
much shorter; the lateral compact buds may be more or less widely
separated: the seeds have long pedicels (fig. 480, A) or appear to
be sessile (fig. 480, B) and there may be one or several seeds on a
single lateral shoot. The seeds are platyspermic and, as seen in fig.
480, A, in some inflorescences they show very clearly the _Samaropsis_
features. It would, however, be unsafe to assume that all _Samaropsis_
seeds were borne on Cordaitean plants. Among other types of seed
referred by authors to _Cordaites_ are _Cardiocarpus_, _Cordaicarpus_,
_Sarcotaxus_, _Taxospermum_, _Diplotesta_, and _Leptocaryon_. But in
most cases there is no evidence of actual connexion between seeds and
vegetative organs, and while it is possible to state with confidence
that many of the seeds represented by impressions described as species
of _Samaropsis_ and _Cordaicarpus_ are undoubtedly Cordaitean, it is
certain that not all seeds referable to these genera were borne by
Cordaitalean plants. Cordaitean seeds are characterised by certain
morphological features recalling those found in recent Cycads and in
the seeds of _Ginkgo_ as illustrated by species of _Cardiocarpus_ and
some allied types. As most of the Palaeozoic seeds known in a petrified
state cannot be assigned to their parent-plants they are dealt with in
a separate chapter[708].
_Cordaianthus Pitcairniae_ (Lindley and Hutton).
This type of inflorescence[709] is considered by Kidston to belong to
the tree which bore leaves known as _Cordaites principalis_, but if
this is the case it is probable that the stem possessed the anatomical
characters of _Mesoxylon_.
[Illustration: Fig. 480. A, _Cordaianthus Pitcairniae_ with
_Samaropsis_ seeds. B, _Cordaianthus Volkmanni_. B′, portion of B
enlarged. (A, B, nat. size; Kidston Coll. 2374, 1174.)]
The portion of an inflorescence shown in fig. 480, A, from the Middle
Coal Measures of Yorkshire, illustrates the occurrence of the bud-like
fertile shoots and the stalked _Samaropsis_ seeds. A species described
by Renault[710] from Commentry as _Cordaianthus acicularis_ may be
identical with the British species.
_Cordaianthus Volkmanni_ Ettingshausen.
The example of this species[711] seen in fig. 480, B, shows the
relatively small size of the lateral buds, presumably unexpanded,
compared with the large subtending bracts.
=Petrified specimens of Cordaianthus.=
Our knowledge of the structure of _Cordaianthus_ is based on
the researches of Renault[712], supplemented by those of Prof.
Bertrand[713] to whose kindness I owe the photographs reproduced in
fig. 481. The inflorescences described by Renault are referred by
him to different species, but in the following brief account these
are treated from a generic standpoint. The tangential section of
_Cordaianthus Williamsoni_ Ren. shown in fig. 481, D, was originally
figured by Renault and more recently by Bertrand; it shows the spirally
disposed leaf-traces in the lower part of a stout axis, and at the
sides some vascular bundles are seen passing up into the bracts. A very
small proportion of the bracts subtend ovules; two are seen at _a_ and
_b_, and at _c_ is the tangentially cut micropylar canal of a third
borne near the apex and covered by the terminal cluster of bracts. The
ovule _a_, separated by a narrow space from its short stalk, consists
of a thick single integument—not two as stated by Renault—extended
at the apex as a micropylar canal: the apical extension is more
completely shown in the tangentially cut ovule _b_. The central body is
much contracted and the two spaces, _s_, at the base are regarded by
Bertrand as cavities in the integument separated from one another by a
central strand of conducting tissue which gives off two bundles to the
integument, one at each end of the long axis of the seed (fig. 481, A,
_v_). The dark patch, _n_ (fig. D), is the upper and broader end of
the shrunken nucellus the apex of which extends upwards as a slender
beak, and this originally no doubt fitted into the micropyle. Fig. 481,
C, shows a female inflorescence in transverse section; the stele
consists of a ring of bundles separated by broad medullary rays and
enclosing a comparatively large pith: the leaf-traces are seen in the
cortex and one is cut through as it bends out into a bract which is not
yet free from the axis. Two ovules, seen in section at _a_ and _b_, are
represented by the bilaterally symmetrical and compressed integument
enclosing small pieces of nucellar tissue. Fig. 481, E, is a transverse
section of an inflorescence at a higher level and above the apex of the
axis: there are four large ovules and one aborted ovule, _a_. Bertrand
describes two vascular bundles in the integument of the ovule _a_, one
at each end of the long axis.
[Illustration: Fig. 481. A, B, _Cordaianthus Grand’Euryi_,
ovule showing apex of nucellus, B, with microspores, _p_; _pc_,
pollen-chamber; _b_, beak of nucellus; _v_, vascular bundle.
C, transverse section of flower-bud with ovules, _a_, _b_. D,
_Cordaianthus Williamsoni_, longitudinal section; _a_–_c_ ovules;
_s_, spaces; _n_, nucellus. E, _Cordaianthus Zeilleri_, transverse
section showing four large ovules and one aborted ovule (_a_);
_v_, vascular bundle. F, transverse section of male flower; _m_,
microsporangia. (From photographs supplied by Prof. Bertrand.)]
Fig. 481, A, B, _Cordaianthus Grand’Euryi_ Ren., shows a longitudinal
section of the nucellus, 1·5 × ·7 mm., and part of the integument of
an ovule at the time of pollination, which was probably aided by the
secretion of a drop of mucilage as in the ovules of recent Conifers.
The integument, separated by a broad space from the nucellus, is cut
in the plane of the two vascular strands, _v_. From the centre of its
broad upper surface the nucellus projects upwards as a beak, _b_,
and this originally engaged with the micropylar canal formed by the
integument: the lighter patch below the beak is the pollen-chamber
(fig. 481, B, _pc_) containing two microspores, and two more, _p_, are
seen above the nucellar beak. In another species described by Renault,
_C. Lacattii_, the nucellus fills the space bounded by the integument.
* * * * *
(_b_) _Staminate inflorescences._ The male inflorescence, though
smaller, is similar in habit to the ovulate shoot: the secondary branch
consists of a short axis bearing crowded, spirally disposed, bracts,
and the actual flowers are represented by single stamens or groups of
2–3 highly specialised microsporophylls. Each microsporophyll consists
of a long filament with a central vascular strand bearing at its apex
3–4 long microsporangia (fig. 481, F, _m_) which open longitudinally
as seen in fig. 482, A. The microsporangia are 2·5–3 mm. long covered
by dark palisade cells and thin-walled parenchyma, shown as indistinct
patches in the photograph. Some of the elliptical and comparatively
large microspores are seen in fig. 482, B; the exine is finely punctate
and inside are the remains of a few thin cells in which presumably
spermatozoids were developed. The microspores shown in fig. 482,
B, have a maximum length of 0·1 mm.: Renault describes some as 0·9
mm. long while others are much smaller. Fig. 481, F, is a transverse
section of a staminate inflorescence showing near the centre five
groups of microsporangia, each sporangium having the form of a curved
incomplete dark band indicating that dehiscence has occurred.
[Illustration: Fig. 482. _Cordaianthus._ Microsporangia, A, and
Microspores, B. (University College Collection, London.)]
=Mesoxylon.= Scott and Maslen.
This generic name was instituted for stems obtained by Messrs Lomax
from the Lower Coal Measures of Lancashire[714] previously referred by
Scott[715] to _Cordaites_ and _Poroxylon_. Further investigation showed
that while agreeing closely with those genera they possessed certain
distinctive features demanding recognition. The name chosen suggests
the intermediate nature of the stems. The more striking features may
be summarised as follows: In the largest specimens so far described
the stem, including leaf-bases, reaches a diameter of 5 or 6 cm.; the
large pith consists in the central region of diaphragms of parenchyma
separated by horizontal spaces produced by splitting and shrinkage
consequent on the failure of the tissue to keep pace with the general
growth of the stem. The secondary xylem is of the Araucarian type and
has narrow medullary rays varying in depth from 1 to 25 cells. The
leaf-traces are represented by twin-bundles which fuse in the downward
direction, the level at which fusion occurs being regarded as a
specific character. The presence of centripetal xylem is an essential
feature of the traces: the occurrence of single or double traces
consisting of centripetal elements and, externally, a large amount
of centrifugal xylem is an important feature in which _Mesoxylon_
differs from _Cordaites_. The double leaf-traces divide after
emerging from the secondary wood and each strap-like leaf receives
several collateral bundles (fig. 483, C). An axillary bud may occur
at the base of each leaf (fig. 483, A, _b_). The phloem, including
sieve-tubes and secretory sacs, is succeeded by a broad pericycle,
and the comparatively narrow cortex is traversed by successive bands
of periderm. In the outer region of the cortex the presence of radial
bands of fibres is a characteristic feature. The reproductive organs
are unknown. The anatomical features are well illustrated by _M.
Sutcliffii_ first described by Scott, who provisionally placed it in
_Poroxylon_, and afterwards more fully investigated by Maslen[716].
_Mesoxylon Sutcliffii_ Scott.
The average diameter of the stem is 3 cm.: the section reproduced in
fig. 483, A, has a maximum breadth of 3·5 cm.; the leaf-bases cut at
different levels give an irregular contour to the surface like that of
a _Lepidodendron_. An axillary bud, either reproductive or vegetative,
is seen at _b_ consisting of a short axis bearing crowded bud-scales.
The leaves are crowded and according to Maslen have a phyllotaxis of
⁸⁄₂₁: the lamina is linear like that of _Cordaites_ with 16 collateral
bundles in the petiole. The presence of a meristematic band at the
base of the lamina affords evidence of a deciduous habit. The large
size of the pith is a striking feature with its central tissues in
the form of transverse diaphragms and a narrower peripheral zone
of solid parenchyma (fig. 483, A, _a_). The secondary wood of the
stele is composed of tracheids with 2–3 contiguous alternate rows of
bordered pits on the radial walls, but none on the tangential walls.
In the stem shown in fig. 483, A, the secondary wood is preserved
only in patches. Numerous blunt teeth varying in prominence project
into the pith; these consist chiefly of serially disposed centrifugal
tracheids distinguished by their spiral and scalariform structure and
by the medullary rays which are broader than those in the more external
xylem. Further reference is made to these perimedullary strands in the
description of the leaf-traces. The medullary rays are uniseriate and
usually 1–6 cells in depth: beyond the secondary wood is a cambium
and a cylinder of secondary phloem (fig. 483, D, _ph_²) consisting of
tubular elements, presumably sieve-tubes, and elongated secretory sacs.
The pericycle is composed of several rows of rather large and short
cells and has an ill-defined outer boundary. A succession of arcs of
periderm-like tissue and phellogen, which may invade the pericycle
and phloem, forms a prominent feature in the cortex; radially placed
bands of fibres similar to those in _Lyginopteris_ and other genera
occur in the outer cortex. At the edge of the pith the more prominent
projections of xylem are arranged in pairs (fig. 483, B) and as each
pair travels downwards the component strands gradually fuse[717]. Each
bundle of a double trace consists internally of an arc of centripetal
xylem, the elements of which are arranged in rows (fig. 483, B, _cp_),
with a single protoxylem group in the middle of the inner face, _px_.
It is not clear whether any primary centrifugal tracheids are present,
but there are indications that such are occasionally represented.
In most cases the primary xylem of the leaf-traces is exarch, but
the existence of mesarch bundles is not improbable. The bulk of each
foliar bundle is formed of a fan-shaped mass of secondary centrifugal
xylem (fig. 483, B, _cf_) and an island of parenchyma occurs next
the protoxylem. There is no clearly defined boundary between the
outer or centrifugal xylem of the leaf-traces and the tracheids of
the stem-wood; the latter may consist exclusively of tracheids with
bordered pits or the inner rows of the xylem-cylinder may be of the
scalariform or spiral type. Differences shown in transverse sections
of the inner portion of the xylem are due to the circumstance that in
certain parts of the inner face of the secondary wood leaf-traces are
unrepresented, while in other places the dwindled remains of the outer,
centrifugal, portions of a trace are still recognisable. As each double
leaf-trace passes down the pith the bundles fuse and the single strand
retains for a time some centripetal xylem; this gradually disappears
and at a lower level the centripetal xylem also dies out. The space
enclosing the obtuse apices of the bundles shown in fig. 483, B, was
originally occupied by thin-walled tissue which accompanied the trace
in its outward course. In _Mesoxylon Sutcliffii_ the leaf-strands pass
almost horizontally through the secondary wood, bend outwards in the
phloem and follow a steeply ascending course to the leaves. In fig.
483, B, a double leaf-trace is seen at the inner edge of the secondary
wood with the centrifugal xylem, _cf_, continuous with that of the
stele: fig. 483, D, _lt_, shows a leaf-trace in the pericycle where one
of the bundles has divided and the other is tangentially extended and
partially divided. The branching is carried further in the cortex, as
seen in fig. 483, C, where the trace is represented by a curved row of
six bundles, _lt_, and at a higher level further subdivision may occur.
The leaf-bundles are collateral and in the leaf retain both centripetal
and centrifugal tracheids. In the section shown in fig. 483, C, the
oval stele of an axillary shoot is seen at _s_ subtended by the row of
collateral bundles: the stele has a fairly large pith surrounded by a
zone of secondary xylem with broad medullary rays.
[Illustration: Fig. 483. _Mesoxylon Sutcliffii_. Transverse sections
of stem. A. _a_, outer pith; _b_, axillary bud; _x_² secondary xylem.
B. _cp_, _cf_, centripetal and centrifugal xylem; _px_, protoxylem. C.
_lt_, leaf-traces in the cortex; _s_, stele of axillary branch; _ph_²,
secondary phloem. D. Leaf-trace bundles, _lt_, external to the phloem,
_ph_². (A, C, D, sections in the Manchester Collection, 717 _b_; B,
Cambridge Botany School, 530.)]
* * * * *
Among other species of _Mesoxylon_ mention may be made of _M. Lomaxi_
and _M. poroxyloides_. _M. Lomaxi_ Scott and Maslen[718] generally
resembles _M. Sutcliffii_ but shows the following distinctive features:
the leaves are more scattered and less crowded; the twin-bundles of the
leaf-traces fuse immediately on entering the pith, thus appearing for
the most part as single and not double strands in the perimedullary
zone; the centripetal xylem is well developed, the medullary rays are
deeper and the outer cortex has shorter bands of mechanical tissue.
In _Mesoxylon poroxyloides_ Scott and Maslen[719], the twin-bundles
of the traces unite soon after reaching the pith as in _M. Lomaxi_,
the secondary tracheids have only two rows, or sometimes a single row,
of bordered pits and the tracheids are rather smaller than in _M.
Lomaxi_ (20–40μ as compared with 30–60μ) and the medullary rays are
shallower. There is a particularly broad zone of spiral and reticulate
transitional tracheids at the inner edge of the wood as in _Cordaites_
and in _Dadoxylon Pedroi_ (fig. 476). The leaves of this species are
believed to be represented by the type described by Dr Benson as
_Cordaites Felicis_ (fig. 465)[720], but, as already suggested, it is
very probable that many or possibly nearly all the leaves from British
Coal Measures described as _Cordaites_ may belong to _Mesoxylon_.
The chief interest of the genus _Mesoxylon_ is its close resemblance
in certain characters to _Cordaites_ and _Poroxylon_: the presence
of strands of centripetal xylem in the perimedullary region is an
important feature in which _Mesoxylon_ differs from stems assigned
(under the generic name _Dadoxylon_) to _Cordaites_. _Mesoxylon_
differs from _Poroxylon_ in having a discoid pith like that of
_Cordaites_, but a more important difference is the absence in the
leaf-trace xylem of _Mesoxylon_ of bordered pits of the Araucarian
type, whereas in _Poroxylon_ Araucarian pits occur in both the
centripetal and centrifugal tracheids. In _Poroxylon_ the secondary
xylem is manoxylic; in _Mesoxylon_, as in _Cordaites_, it is pycnoxylic.
=The range of Cordaites and a consideration of other imperfectly known
genera.=
An increased precision in knowledge derived from anatomical
investigation often tends to demonstrate the untrustworthiness
of criteria based on external features previously employed with
confidence. This inevitable though, from the point of view of the
systematist, inconvenient result of intensive study is well illustrated
by the recent discovery of the stems named by Scott and Maslen
_Mesoxylon_[721]. A separation of _Cordaites_ from _Mesoxylon_, which
no doubt extended far beyond the British area, is possible only
if well-preserved petrified material is available. The leaves of
_Mesoxylon_, so far as our imperfect knowledge of them enables us to
express an opinion, are constructed on a plan almost identical with
those of _Cordaites_ and, as already stated, it is almost certain
that many of the impressions referred to _Cordaites_ were borne on
_Mesoxylon_ stems. An additional source of confusion is supplied by
the _Cordaites_-like leaves of _Poroxylon_. It is evident, therefore,
that even within the limits of the Carboniferous and Permian formations
the recognition of true _Cordaites_ leaves must often be attended with
considerable risk of error. Apart from the possible confusion between
the foliage of _Cordaites_ and _Mesoxylon_ there are other difficulties
as regards detached leaves which depart more or less widely from
the typical Cordaitean form. Leaves such as _C. circularis_ (fig.
468, B) and _C. grandifolius_ emphasise the lack of any thoroughly
satisfactory dividing line separating single pinnules of _Cardiopteris_
or _Cyclopteris_ on the one hand and leaves of _Psygmophyllum_
on the other from _Cordaites_. The petrified buds described as
_Dolerophyllum_[722] have been quoted by several authors as examples of
unexpanded shoots of _Cordaites_ though anatomical evidence warrants a
generic separation. In the case of species founded on leaves described
in this chapter as _Cordaites_ it should be remembered that further
research may necessitate an alteration in nomenclature.
Among the species included in _Cordaites_ is _Noeggerathiopsis
Hislopi_[723] (figs. 470–472), a type widely spread in India and in
other parts of Gondwana-Land: if the change of generic name is accepted
it involves the extension of the geographical range of _Cordaites_ from
Northern Europe and North America to the southern botanical province.
We have as yet no proof of the existence of _Cordaites_ in the Arctic
regions. The range in time of _Cordaites_ or of the Cordaitales has
generally been stated to be from the Upper Devonian to the Permian.
It is, however, by no means certain that the genus flourished before
the Carboniferous period, though it is clear that closely allied
types must have lived in pre-Carboniferous floras. The strata in New
Brunswick from which Dawson recorded his supposed Devonian _Cordaites_
have been shown to be Upper Carboniferous in age[724]. As regards the
length of time during which the Cordaitales existed we have no decisive
evidence. In recent years the tendency has been to extend their range
into the Mesozoic era, and there are several pieces of evidence in
favour of this. There is no doubt that considerations of age based on
the arbitrary divisions of the geological scale sometimes insinuate
themselves too thoroughly into questions connected with the duration
of plant-types whether represented by families or genera. We have been
accustomed to regard _Cordaites_ as a genus confined to the Palaeozoic
period, a type which with many others carried on the tradition of
Upper Carboniferous forests to the Permian floras and then made way
for the precursors of Mesozoic types. There is, however, no valid
reason for supposing that _Cordaites_ and other Palaeozoic genera did
not survive as less prominent members in succeeding floras. It must be
admitted that evidence in support of Mesozoic Cordaitales is not above
suspicion, though the probability is that _Cordaites_ or some allied
genera still flourished in the earlier stages of the Mesozoic era.
The data on which this opinion is based cannot be fully discussed in
a general treatise, but a few of the facts may be briefly considered.
Zeiller[725] and other authors have expressed the view that the
Cordaitales were not exclusively Palaeozoic. In addition to _Cordaites_
(_Noeggerathiopsis_) _Hislopi_ recorded from Rhaetic floras, other
possible representatives of the group are illustrated by specimens
included in such genera as _Yuccites_, _Bambusium_ and _Krammera_.
=Pelourdea= gen. nov.
The name _Yuccites_[726] was given to some detached, broad, linear
leaves from the Bunter sandstone of the Vosges which were compared with
the foliage of _Yucca_ and classed among Monocotyledons. The authors
of the genus also described a cylindrical cast as a _Yuccites_ stem,
including both stem and leaves in _Yuccites vogesiacus_. The supposed
stem, as Fliche[727] has shown, is a pith-cast and is appropriately
named by him _Endolepis vogesiacus_. The Vosges leaves are assigned
by this author to the genus _Cordaites_, a change of name which may
eventually be justified though as yet based on insufficient evidence.
There are objections to the institution of a new name in place of
_Yuccites_, but it is undesirable to retain a designation suggesting
false ideas with regard to affinity. A new name _Pelourdea_ (after
M. Pelourde of Paris, whose recent death deprives Palaeobotany of an
able and promising investigator) is therefore proposed for leaves of
the _Yuccites_ type which in form, venation, and spiral phyllotaxis
agree with those of _Cordaites_ but cannot confidently be assigned to
that genus or even to the Cordaitales. For linear leaves, especially
from Jurassic strata, resembling those of _Phoenicopsis_ the name
_Desmiophyllum_[728] is employed: these are very similar to those of
_Pelourdea_; they are characterised by their fairly uniform breadth and
afford no indication of their arrangement on the supporting axis.
_Pelourdea vogesiaca_ (Schimper and Mougeot).
The linear-lanceolate leaves described by Schimper and Mougeot as
_Yuccites vogesiacus_ and transferred by Fliche to _Cordaites_ are
probably specifically identical with specimens described by Mr
Wills[729] from Lower Keuper rocks in Worcestershire. The English
leaves were described by Arber[730] as _Zamites grandis_,—the name
_Zamites vogesiacus_ having been previously used by Schimper and
Mougeot,—on the ground that the supposed leaves were probably pinnae
of a cycadean frond, a view in agreement with an opinion previously
expressed with regard to similar leaves from Stonesfield[731]. A later
discovery by Wills of specimens, on which the drawing reproduced in
fig. 484 is based, of the same type of leaf showing the foliar nature
of the fossils necessitated the abandonment of the pinna-hypothesis,
and the original name _Yuccites vogesiacus_ was resuscitated[732]. The
leaves reach a length of 50 cm. and a maximum breadth of 6·5 cm.; the
lamina is entire, lanceolate or linear-lanceolate, the apex acuminate,
and the lower part rather abruptly contracted and attached by a broad
crescentic base; veins numerous, parallel, and occasionally forked.
Fliche records the occurrence of a small _Artisia_-like pith-cast and
pieces of stem with leaf-scars (4 × 3 mm.) in association with leaves
of _Pelourdea vogesiaca_ in Triassic strata in Lorraine. An imperfectly
preserved specimen described by Fliche as _Cordaianthus Minieri_[733]
resembles an inflorescence of _Cordaites_. It consists of an axis 15
cm. long, the lower part forming a peduncle, and on the upper portion
are linear bracts subtending oblong bodies which may be lateral fertile
shoots.
[Illustration: Fig. 484. _Pelourdea vogesiaca_. Reconstruction of a
foliage-shoot. (After Wills.)]
_Pelourdea hadroclada_ (Halle).
Dr Halle[734] recently published an account of some imperfect
leaves and stem-fragments from the Rhaetic of Scania which he named
_Phyllotenia_ (_?_) _hadroclada_, the generic name provisionally
adopted having been proposed by Salfeld[735] for some rather obscure
remains from the Corallian of Germany. It appears to have escaped
the notice of both authors that Saporta[736] in 1894 had adopted the
designation _Phyllotenia_ for some examples of broad parallel-veined
leaves from Lower Cretaceous rocks in Portugal very similar to
Velenovský’s _Krammera mirabilis_[737]. Some other generic name must
therefore be used. For the Rhaetic species the name _Pelourdea_ would
seem appropriate. The type-specimen consists of an axis 10–12 mm. in
diameter with spirally disposed transversely elongated leaf-scars
bearing sessile linear leaves similar to _Poa-Cordaites_; none of
them are complete, the largest is 6 cm. long and 5–7 mm. broad with
8–12 parallel veins. An examination of the original specimens in the
Stockholm Museum satisfied me that Dr Halle is justified in the opinion
that they may be fragments of some Cordaitalean plant and that he
was well advised to avoid the use of the name _Cordaites_. Salfeld’s
species, _Phyllotenia longifolia_, may be an imperfectly preserved
example of _Phoenicopsis_[738], but the material is too incomplete to
be identified with any degree of confidence.
_Pelourdea Imhofi_ (Heer).
The Triassic leaves from Switzerland described by Heer[739], and more
recently by Leuthardt[740], as _Bambusium Imhofi_, were referred by
Fliche[741] to the genus _Cordaites_. The lamina is ensiform, 25 cm.
long with a maximum breadth of 2·4 cm. Leuthardt’s photograph of
aerial stems and rhizomes of this supposed Monocotyledon are far from
convincing.
_Pelourdea keuperiana_ (Compter).
The leaves from the Lower Keuper of Thuringia assigned by Compter[742]
to _Cordaites_ without adequate evidence resemble those of _P.
vogesiaca_, but there is no evidence as to their manner of attachment;
they are 30–40 cm. long and from 1·5 to 2 cm. broad.
_Pelourdea megaphylla_ (Phillips).
This species was first described by Phillips[743] from the Middle
Jurassic Stonesfield Slate and afterwards referred to _Zamites_[744]:
the leaves bear a striking resemblance to foliage of the type
_Cordaites borassifolius_; the lamina is 30 cm. long and attains a
breadth of 3 cm., the apex is acuminate and slightly contracted towards
the broad concave base. My former comparison of these Stonesfield
leaves with the long pinnae of _Ceratozamia mexicana_ seemed to be
supported by Phillips’s type-specimen of _Palaeozamia longifolia_.
It may be that the supposed pinnae in Phillips’s type are spirally
disposed leaves: if this is the case the specimen may be a fragment
of a _Podozamites_; its specific identity with the larger detached
specimens, though probable, cannot be demonstrated. Some leaves figured
by Zigno[745] from Jurassic rocks of Italy as _Yuccites Schimperianus_
may be identical with _P. megaphylla_.
_Pelourdea mirabilis_ (Velenovský ex Corda +MS.+).
The generic name _Krammera_, suggested by Corda, was employed by
Velenovský[746] for large _Cordaites_-like leaves from the Lower
Cretaceous of Bohemia, for casts of cones regarded by him as stems, and
for fruit-like bodies. The leaves, previously described as _Flabellaria
chamaeropifolia_ Goepp., _Dammara albens_ Presl, etc., bear a close
resemblance to the large broadly linear leaves of _Cordaites_; the
lamina reaches a length of 40 cm. and between the veins occur 1–4 finer
striations. The fossils identified by Velenovský as stems bearing
crowded imbricate scales, which he regarded as the persistent bases
of _Krammera_ leaves, are probably cones; they agree very closely in
size and shape, also in the form of the scales, with cones of _Agathis_
and some other recent Conifers. As the designation _Krammera_ was
instituted primarily for cones and not leaves the name _Pelourdea_ is
substituted for it.
=Niponophyllum.= Stopes and Fujii.
_Niponophyllum cordaitiforme_ Stopes and Fujii.
The generic name _Niponophyllum_[747] was proposed for some petrified
specimens of leaves or possibly leaflets from Upper Cretaceous beds
in Japan which, though not definitely assigned to a group or family,
are considered by the authors of the genus ‘to lie [anatomically]
somewhere between _Cordaites_ and _Cycadeoidea_’ ‘with a closer
similarity to the former than to the latter if we compare the whole
_Cordaites_ leaf with our blade.’ The data on which this conclusion
is based are, however, insufficient to justify a reference of
_Niponophyllum_ to the Cordaitales or indeed to lend any substantial
support to the opinion that the Japanese specimens are anatomically
more akin to _Cordaites_ than to other plants. The type-species is
represented by two specimens of leaf-fragments about 0·4 mm. thick and
from 6 to 9 mm. broad containing from 21 to 33 vascular bundles; the
upper part of the mesophyll is composed of palisade tissue and the
stomata appear to be confined to the lower epidermis. Each bundle is
accompanied by an =I=-shaped girder, and small patches of sclerenchyma
occur next the upper epidermis between the girders; there are no
resin-canals: the vascular bundles are collateral, the xylem is said
to be almost entirely centripetal and exarch, but in the absence of
evidence afforded by longitudinal sections the details of structure
cannot be definitely determined. A comparison is made with Cycadean
leaves and with leaves of Araucarineae and Podocarpeae, also with
_Cordaites_; another type with which _Niponophyllum_ may be compared is
_Desmiophyllum Solmsi_[748].
The genus is interesting as an example of a petrified gymnospermous
type of leaf characterised by the absence of resin-ducts and
transfusion-tracheids, the possession of collateral, apparently
exarch, bundles enclosed in a double sheath; but the data supplied
are insufficient to enable us to allocate the specimens to a position
within the class.
A specimen described by Schenk[749] as _Eolirion primigenium_ from
Lower Cretaceous beds in the Carpathian mountains closely resembles in
habit a foliage-shoot of _Poa-Cordaites_; the leaves are narrow and
linear with obtuse apices and attached, apparently, in a close spiral.
Schenk assigns the plant to the Monocotyledons, but its systematic
position must be left unsettled.
* * * * *
The list of Mesozoic specimens resembling _Cordaites_ leaves might
be extended. Apart from some Triassic and Rhaetic examples which may
well be Cordaitalean, there are many others which, though similar in
form and venation to _Cordaites_, are in all probability more closely
related to _Agathis_ and other genera; the species _Dammarites Bayeri_
recently described by Zeiller[750] from the Upper Cretaceous of
Bulgaria is a case in point. The Araucarian character of the wood of
_Cordaites_ precludes any satisfactory discrimination between Mesozoic
Araucarian stems and those of Cordaitalean species, at least in the
case of such material as is usually available.
=Titanophyllum.= Renault.
_Titanophyllum Grand’Euryi_ Renault. The remarkable leaves on which
this genus and species are founded[751] were discovered in the
Commentry coalfield; they occur as detached specimens and cannot be
correlated with any known stem. Renault suggests that the Autun stems
referred to _Colpoxylon_ may have borne the _Titanophyllum_ leaves,
but this correlation rests only on the dimensions of the stems and
the occurrence of transversely elongated scars on the surface. The
lamina is thick and coriaceous, 70–75 cm. long and 20–25 cm. in
breadth; the veins are parallel but not branched; numerous longitudinal
striations on the upper surface indicate the presence of hypodermal
stereome-strands; stomata are abundant on the lower surface and the
more or less rectangular cells in the neighbourhood of the stomata
appear to be papillose (fig. 485, A, B). The distal region of the
lamina is often torn into strips (fig. 485, A); the approximately
rectangular leaf has a broad elliptical base 9–10 × 3–4 cm.
[Illustration: Fig. 485. _Titanophyllum Grand’Euryi._ A, leaves
¹⁄₃₀ nat. size; B, stomata on the lower surface of the lamina. (After
Renault and Zeiller.)]
Dr White[752] describes a specimen from the Lower Coal Measures of
Missouri as ? _Titanophyllum Brittsii_ which he speaks of as the thick
base of a leaf similar to that described by Renault but, as White says,
no formal diagnosis is possible without more satisfactory material.
Such evidence as is available suggests that _Titanophyllum_ is a type
of Cordaitalean leaf probably closely allied to _Cordaites_.