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.
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.
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.
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 [Symbol: 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.
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.
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].
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.
(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].
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.
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.
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.
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.
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.
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].
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, ph2) 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.
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.
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.
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.
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.