A second species described by Scott and Maslen as Trigonocarpus Oliveri has been further investigated by Salisbury who finds that it is an 8-angled seed which cannot be retained in the genus Trigonocarpus: its systematic position ‘must for the present remain uncertain[340].’ Dr Arber has recently described a new species of Trigonocarpus, T. Moyseyi[341], from the Nottingham Coal-field (Middle Coal Measures), similar to T. Parkinsoni but much broader in proportion to its length: this species is founded on an impression without structure.
The species Trigonocarpus Dawesi Lind. and Hutt.[342], from the Middle Coal Measures of Lancashire, was founded on casts differing in their large dimensions from those of T. Parkinsoni: specimens referred to this species were described by Fiedler[343] from Saxony in 1857 and Lesquereux[344] figures similar casts from the Upper Carboniferous and Permian rocks of North America.
This species, founded on specimens from the Lower Coal Measures of Shore, Lancashire[345], may exceed 4 cm. in length and has a breadth of 2·5 cm. In general plan it agrees with T. Parkinsoni but there are certain well-marked differences: the micropyle is much shorter; the thick sarcotesta, attaining a breadth of 6 mm. at the base of the micropyle, is characterised by the presence of six peripherally placed vascular bundles (fig. 426, D, v) in contrast to the deeply embedded bundles of T. Parkinsoni. Below the epidermis of the sarcotesta is a hypoderm formed of radially disposed plates of sclerous tissue similar to that of Myeloxylon and different from the palisade-like hypoderm of the type-species. Within the sarcotesta is a hard shell, the sclerotesta, characterised by three prominent ribs extending from base to apex and three shorter ribs which reach from the chalaza to about a third of the length of the seed. The fact that the sarcotesta and sclerotesta pass gradually into one another is a point in favour of the view that the integument is a single structure. There appears to be good evidence of the restriction of an inner flesh to the micropylar region, whereas this tissue in T. Parkinsoni was probably continuous over the whole inner face of the sclerotesta. The sarcotesta is lacunar in its outer part as in some other types of Palaeozoic seeds, a feature probably connected with floating efficiency. Trigonocarpus shorensis occurs in association with Myeloxylon petioles, and there is a resemblance between the seed and the vegetative organs in the structure of the hypoderm as also in the structure of the secretory sacs which are particularly numerous in this species. Salisbury draws attention to the close resemblance between the form of T. shorensis and the seeds found in organic connexion with pinnae of Neuropteris obliqua[346].
The species T. corrugatus described by Renault[347] bears a close resemblance to T. shorensis.
Other Genera founded in part on Reproductive Organs which may belong to the Medulloseae.
Codonotheca, Schützia, Whittleseya, Dolerophyllum, Ottokaria, Strobilites.
Codonotheca caduca Sellards. This genus was founded on some spore-bearing bodies from the Coal Measures of Illinois[348]: nothing is known as to the plant which bore them, but Sellards is inclined to associate them with Neuropteris decipiens Lesq.[349], a species abundant in the same coal-field. Whatever may have been the parent-plant it is probable, as the author of the genus believes, that Codonotheca is the microspore-bearing organ of a Pteridosperm. As shown in fig. 427, 5, the form is that of a stalked cup consisting in the basal portion of a stout axis, the peripheral tissue of which is believed to have been fleshy, containing an axial rod of conducting tissue running up to the floor of the cup, c, and then dividing into six vascular strands, each of which forks into two branches. The upper part is composed of six linear segments united basally to form the sloping surface of the cup. On the inner face of each segment is a more or less well-defined depression covered with large elliptical spores ·29–·31 mm. long by ·18–·19 mm. broad (fig. 427, 6, 8). The presence of a median ridge (fig. 427, 8) indicates a bilateral origin. ‘There is no grouping of the spores or other indication of the location of the sporangia, which were doubtless more or less completely immersed in the tissue, the dividing wall disappearing at maturity.’ The spores are seen in fig. 427, 2, 3, on the inner face of the lobes. Some of the specimens have a fairly long pedicel: in the example shown in fig. 427, 1, the fleshy part of the basal portion is not preserved, only the more resistant vascular core. In a later account of these organs Sellards speaks of several lying by the side of a central stalk to which he thinks they were originally attached by slender pedicels. In view of Dr Benson’s interpretation of the morphology of Telangium it is permissible to suggest that if a central sporangium in such a synangium as that of Codonotheca developed a megaspore and the peripheral sporogenous lobes were sterilised, the result would be an arrangement not unlike the apical region of the seed Physostoma, the tentacles of which have been homologised with the canopy of Lagenostoma. There are obvious difficulties in the way of this, perhaps strained, comparison: the larger size of the spore-bearing linear segments of Codonotheca led Sellards to regard each as a synangium rather than a single sporangium. But precise information as to the structure of the American fossils is not as yet available. If the association of Codonotheca with Neuropteris fronds has any significance it would favour a reference of these organs to the Medulloseae. In the absence of anatomical data it is impossible in some cases to distinguish microspore-bearing organs of the Codonotheca type from small seeds enclosed in a lobed cupule or even seeds with a lobed integument: a case in point is the New Brunswick species Pterispermostrobus bifurcatus Stopes[350].
A Spitzbergen, Culm, fossil recently described by Nathorst[351] as Codonotheca (?) pusilla is briefly referred to under the genus Pterispermostrobus.
This generic name was instituted by Geinitz[352] for some Permian fossils obtained by Bergmeister Schütz and regarded by the author of the genus as probably fertile branches of some Conifer. A more complete account was published by Goeppert[353] in his ‘Permian Flora,’ where the name Anthodiopsis Beinertiana occurs on the Plates, printed before the publication of Geinitz’s description, but in the text the specimens are referred to Schützia anomala.
The type-species, recorded from Bohemia and Silesia, is represented by fertile shoots consisting of a thick main axis bearing apparently two-ranked though probably spirally disposed short lateral branches, each of which terminates in a receptacle with numerous crowded linear-lanceolate bracts superficially resembling a partially expanded inflorescence of a Composite. Goeppert believed that the branches bore seeds and he refers to this species a number of detached, longitudinally striated and bluntly terminated, seeds. The same author describes other specimens from the same localities associated with Schützia anomala, which he names Dictyothalamus Schrollianus[354]: in habit these agree closely with Schützia but the receptacles, the reticulate appearance of which suggested the generic name Dictyothalamus, bear a large number of small bodies regarded as seeds. The preservation of the fossils is not such as to enable us to determine their true nature but it is probable that Schützia and Dictyothalamus are not generically distinct. In his description of Dictyothalamus Goeppert suggests that the two associated types may be the male and female shoots of one plant, but he speaks of seeds in both cases. Schimper[355], who unites Dictyothalamus with Schützia, regards the latter as female and the former as male.
This species, described by Kidston[356] from the Calciferous series of Scotland, differs from S. anomala in its much more slender axis and in the relatively narrower and less globular clusters of bract-like appendages. The principal axis bears three lateral branches with terminal clusters of acute and narrow linear scale-leaves. No seeds were found in association with the specimens.
Renault founded this Permian species as Antholithus permiensis[357] on a specimen from Lodève; it consists of an incomplete inflorescence 6·4 cm. long bearing four lateral branches with stalks 1·5 to 2 cm. long terminated by clusters of small oval bracts 5 mm. long. Renault compares the fossil with the recent Conifers Glyptostrobus and Tsuga, but it exhibits a much closer resemblance to Schützia anomala.
The genus Schützia, originally described from Permian strata, is recorded also from Westphalian strata in North Africa[358] as well as from Lower Carboniferous rocks in Scotland. The data at present available are insufficient to determine the morphological nature of the fertile branches: the evidence adduced by Goeppert in support of the occurrence of seeds is not convincing and the interpretation of the bract-like appendages is still an open question; they may have formed a cupular investment to seeds, but in the Scotch species the general appearance rather suggests that they may be microspore-bearing organs comparable with those of Codonotheca[359]. There are no adequate grounds for supposing Schützia to belong to the Coniferales, a view advanced by some authors; it is much more likely to represent the fertile shoots of a Pteridosperm.
The genus Whittleseya, referred by many authors to the Ginkgoales, has no substantial claim to be regarded as allied to that group: its position is still uncertain, but the recent discovery of fertile specimens suggests the probability of a relationship to Potoniea and an identification of Whittleseya as another form of microsporophyll of a Pteridosperm.
The generic name was given by Newberry[360] to some leaves, or possibly leaflets, originally described by C. Whittlesey from the Coal Measures of Ohio. Whittleseya is represented by species from several North American localities[361] in Ohio, Pennsylvania, Arkansas, Nova Scotia, and New Brunswick[362]; it occurs in Silesia and has recently been found in the English Coal Measures[363]. The genus is confined to Upper Carboniferous strata.
The leaves are fairly thick; the lamina is oblong, cuneate, broadly triangular or linear, usually rounded and truncate (fig. 428, A, C), generally dentate at the distal end, the proximal portion being gradually or abruptly contracted and occasionally prolonged into a short pedicel. The veins or ribs are parallel to the sides of the lamina and except near the base unbranched.
The type-species, from North America and Europe, is characterised by its shovel-like lamina from 3 to 6 cm. long closely resembling in shape some lepidopterous scales; the surface is ribbed, each rib corresponding to a tooth on the distal margin; on each of the parallel ridges are 4–5 longitudinal lines indicating either veins or stereome strands (fig. 428, A, C). The examination of preparations made by Dr Kidston from a leaflet of this species enables me to add a few facts with regard to the microspores. The spores, which cover almost the whole surface of the lamina, show a tendency to a more or less definite arrangement in longitudinal rows. Two types of cuticularised membrane are represented among the associated fragments: in some pieces of cuticle the cells are short and have straight walls while in others the preservation is inferior and the cells appear to be longer and narrower. One or both of these membranes probably belong to the sporangia. The oval slit, which is a striking feature on several of the spores (fig. 429), points to their bilateral nature and dehiscence along the major axis. A comparison of these spores with those obtained by Kidston from the English species Whittleseya fertilis reveals a very close agreement both in size and shape and confirms the identification of the Staffordshire specimens as leaflets of Whittleseya. The large size of the microspores and the gaping oval aperture in some of them are features in which they agree closely with the spores of Dolerophyllum fertile described by Renault[364]. In both cases the spores tend to be arranged in long groups and they are practically identical in form and in the nature of the exine; those of Dolerophyllum are 280μ long while those of W. fertilis reach a length of 220μ. In some of the Whittleseya spores the exine has split as in the specimen shown in fig. 429, but in others there are two curved lines along which dehiscence has begun, a character in which the spores appear to be identical with those of Dolerophyllum described by Renault who speaks of dehiscence by means of an operculum. There is, I venture to think, little doubt as to the very close affinity of the two types. The systematic position of Dolerophyllum is not certainly established; if the generic identity of the leaves described as D. Berthieri Ren. and the petrified specimens named D. fertile is assumed, it is a legitimate inference that the genus is founded on fertile pinnules of a Pteridosperm with foliage of the Neuropteris or Cyclopteris form. It would seem probable that both Whittleseya and Dolerophyllum fertile are microspore-bearing leaflets of Pteridosperms, possibly of some Medullosan plants. The leaflets of Whittleseya agree in form fairly closely with those of Potoniea adiantiformis Zeill. described on a previous page[365] as the male organs of a Pteridosperm.
The specimens described by Lesquereux from Pennsylvania as W. integrifolia and W. undulata are less satisfactory than W. elegans. The Arkansas species W. microphylla[366], characterised by the obcuneate form of the lamina, is said to occur not only as detached leaflets but in loose bunches at the ends of slender axes, a circumstance favourable to the suggestion, based on the recently described English specimens, that the Whittleseya leaves may be fertile pinnules of a Pteridosperm frond. Among other species attributed to Newberry’s genus is W. brevifolia Wh. from Nova Scotia[367] with much smaller broadly triangular leaves 7 mm. long exclusive of the petiole and 8 mm. broad at the distal end (fig. 428, B). Dr Matthew[368] has also described a Canadian species W. concinna from New Brunswick in beds assigned by Dr Stopes[369] to the Westphalian series.
Since the discovery of Whittleseya elegans in the Coal Measures of Staffordshire recorded by Mr Thomas, Dr Kidston has published an account of some specimens from the same district under the name Whittleseya (?) fertilis[370]: these consist of smaller cuneate scale-leaves or leaflets 1·4–2·4 cm. long and 8–9 mm. broad; the lamina has a dentate upper margin and is longitudinally ribbed. The scales occur in superposed pairs, closely fitting but not organically connected, at least in the state in which they are preserved; each pair forms a sporangium-like case enclosing numerous spores but the actual sporangia or synangia have not been preserved. Kidston describes the spores as 210–222μ in length, elliptical, and characterised in many cases by an oval slit; they are practically identical with the microspores of W. elegans.
This name was proposed[371] primarily for a large ovoid petrified bud composed of rolled Cyclopteroid leaves from Permian rocks in the Ural Mountains, which had been previously described by more than one writer under different names and regarded as a young shoot of a Palm or other Monocotyledon. Eichwald[372], who published good drawings, called the fossil Noeggerathia Goepperti. Saporta connected with this species some leaf-impressions from the Permian of Bohemia described by Goeppert[373] as Noeggerathia cyclopteroides: in his family Dolerophylleae[374] the French author included other leaves which are probably not closely related to the type-species, Dolerophyllum Goepperti. The Dolerophylleae are spoken of by Saporta and Marion[375] as Progymnosperms. Before the publication of Saporta’s note Grand’Eury had instituted the genus Doleropteris[376] and the family Doleropteroideae; in the former he included several forms of leaves agreeing generally with Goeppert’s Noeggerathia cyclopteroides. Zeiller[377] adopts Grand’Eury’s designation for the Russian fossil in preference to Dolerophyllum, a choice justified by considerations of priority; but the latter name is retained in this account as it was assigned by Saporta to the specimen of greatest botanical interest, namely Dolerophyllum Goepperti, and because it does not suggest affinity to Ferns.
The type-species is from the Zechstein of Orenburg in the Urals and no specimens having precisely the same structure have been found elsewhere. Eichwald assigned it, with leaf-impressions of various kinds, to the Noeggerathieae and named it Noeggerathia Goepperti: it had previously been described by Kutorga[378] as Aroides crassispatha and Unger[379] included it among the Palms as Palaeospathe aroidea. The species has been described also by Saporta and Marion and by Renault[380]. The following account is based on sections cut from a specimen in the British Museum[381] which, though assigned on the label (within a query) to France and named Dolerophyllum Berthieri, is undoubtedly Eichwald’s species from East Russia.
The specimen (fig. 430) is 9 cm. long and 4·2 cm. broad: at the slightly contracted and broken base is a piece of immature axis (fig. 430, B, a) 12 mm. in diameter overtopped by a mass of closely packed leaves encircling one another like the bulb-scales of an Onion (fig. 430 A, C)[382]. Most of the leaves included in the bud were attached to the axis below the broken base. The curved, dichotomously branched, veins are seen on some of the pieces of lamina on the surface of the bud (fig. 430, A). The considerable breadth of the leaves is demonstrated by the longitudinal and transverse sections. In fig. C most of the laminae can be traced through the whole height of each of the steep-sided arches: a few overlapping margins are seen in fig. D. The veins are for the most part imperfectly preserved and appear as clear spaces at regular intervals in the brown mesophyll. The axis of the shoot consists of homogeneous parenchyma except near the sloping sides where narrow dark bands (fig. 430, B, a) mark the position of desmogen-strands of thin-walled elongated elements representing an early stage in the development of vascular bundles some of which have already produced spiral tracheids. Short secretory cells accompany the immature conducting elements. The lamina slightly exceeds 2 mm. in thickness in the broadest part: the mesophyll is composed of large parenchymatous cells of elliptical or spherical form often loosely attached owing to the well-developed system of intercellular spaces. The lower epidermis, assuming that the outer face of the rolled leaves is the morphologically lower surface, forms a uniform layer of palisade cells characterised by their free conical ends (fig. 431, A, B, e) which in some oblique sections appear as sharply pointed papillae with almost filiform apices; but while the cells were doubtless papillose like those of the epidermis of a velvety petal, the pointed form is due in part to the greater distinctness of the dark contents as compared with the lighter cell-walls. The upper epidermis is much less distinct; it consists of smaller flattened cells with occasional stomata. Renault[383] figures a specimen with stomata in a better state of preservation. The vascular bundles are rendered conspicuous by large secretory cells on the lower side, in the larger veins in the form of an arc or irregular group (fig. 432, A), but in the finer veins as single cells (fig. 431, A, B). These sacs resemble the tannin cells accompanying the veins in a leaf of Ginkgo (cf. fig. 631, G). The xylem-elements are of two kinds, (i) elongated spiral and scalariform conducting elements, forming a vertical plate of a few rows in the larger veins (figs. 431, 432) or a small compact group in the more slender veins (fig. 413, A, B); (ii) much larger isodiametric cells with reticulate or spiral thickening resembling the transfusion-tracheids of Conifers or, perhaps more closely, similar elements in the leaves of Lepidodendron. These short tracheids are especially abundant on the flanks of the conducting tracheids (figs. 431, t; 432, A, t), but they sometimes form a complete investment. In the obliquely cut vein reproduced in fig. 431, D, the transfusion-tracheids are abundant: a few are enlarged in fig. 431, E. In the smaller veins (fig. 431, A, B) they are represented by the larger elements, t, on the sides of the conducting strands. The protoxylem lies close to the upper edge in the middle line (px, figs. 431, A; 432, A); it is difficult to determine its precise position, but it would seem to be slightly internal, the bundle being not quite endarch. No phloem was recognised in the British Museum specimen, but it presumably occurred, if present, where the black patch is shown in fig. 432, A. Renault describes some phloem in sections which he examined.
The mesophyll next the upper surface is in most cases represented by spaces between the veins which give a crenulated outline to the parenchyma (fig. 430, C, D); in some places the spaces contain remains of very loose and crowded cells suggesting the original presence of very lacunar tissue or possibly of thin-walled storage-cells. The confinement of stomata to what is assumed to be the upper surface may, as Renault and others have suggested, indicate leaves which floated on water, an inference opposed to the view that the gaps in the mesophyll mark the position of water-tissue.
No specimens have been described which enable us to correlate with certainty mature leaves or foliage-shoots with the petrified bud. It is, however, not improbable that the impression from Mount Pelé near Epinac named by Renault Dolerophyllum Berthieri[384] may be correctly referred to the same genus. The type-specimen consists of an axis, whether a rachis of a compound leaf or a shoot with simple leaves cannot be determined, bearing partially overlapping more or less orbicular leaves 18–20 cm. in diameter, with a Cyclopteris venation. Among other leaves of unknown affinity referred to the same genus attention is drawn to Dolerophyllum pseudopeltatum (Grand’Eury)[385] with an orbicular lamina reaching in some specimens 22 × 19 cm. Specimens of Dolerophyllum pseudopeltatum are figured by Renault from the Commentry coal-field[386], some of which reach a diameter of 12 cm. The only British specimen of a leaflet of this type which I have seen is one in Dr Kidston’s collection from the Stephanian series, Glamorganshire. It is probable that some at least of the impressions assigned to Dolerophyllum or Doleropteris would be more appropriately included in Cyclopteris or Cardiopteris and may have been borne on the axis of large Pteridosperm fronds. Grand’Eury[387] has also called attention to the difficulty of distinguishing the larger Cyclopteris leaflets from Dolerophyllum. Some of the Cyclopteroid leaflets figured by Roehl[388] on Neuropteris fronds differ but slightly from those of D. pseudopeltatum. The shoot showing large leaf-scars figured by Saporta and Marion[389] as probably the axis of a Dolerophyllum may well be a piece of Cordaites.
Certain problematical fossils found in association with the sterile leaves of Dolerophyllum Berthieri have been described by Renault as the male organs of that species. These are elliptical discs, 6 × 5 cm., with an excentrically placed stalk: embedded in a carbonised lamina are numerous rows of elliptical bodies, 410μ × 280μ, characterised by two curved longitudinal grooves on the surface and regarded by Renault as pollen-grains. The chains of these microspores radiate outwards from the neighbourhood of the stalk and cover most of the surface of the disc (fig. 432, B). Some silicified pieces of similar spore-bearing discs from Grand’ Croix named Dolerophyllum fertile[390] afford additional information as to these remarkable reproductive organs. The earlier account of this species by Renault is confirmed by Solms-Laubach[391] who examined the original sections. The peltate fleshy discs preserved as incomplete specimens consist of lacunar parenchyma 15–18 mm. thick traversed at right angles to the surface by numerous loculi (fig. 432, C), circular or oval in transverse section, containing large numbers of microspores, s, similar in size and form to those on the carbonised discs of the Mt Pelé specimen. Vascular strands occur between and parallel to the spore-chambers. The spores contain 8–10 cells (fig. 432, D) and Renault believes that dehiscence of the exine occurred along the two deep grooves which mark the limits of an operculum. He emphasises the peculiar structure of the microspores by speaking of them as prepollinia: in size and in the presence of internal cells (? male prothallus) they resemble the spores found in the pollen-chamber of a seed described by Renault as Aetheotesta elliptica[392] which he thinks may belong to a member of the Dolerophylleae. It has also been suggested that Codonospermum may be a seed of Dolerophyllum[393]. An unconvincing specimen described by Saporta and Marion[394] as a seed-bearing bract is regarded by them as referable to Dolerophyllum, but the evidence for any connexion is far from satisfactory.
There is nothing definite to be said with regard to the affinity of Dolerophyllum Goepperti or the microsporophylls represented by D. fertile and the specimens associated with D. Berthieri. Renault considers that both sterile and fertile specimens belong to the same genus, which he assigns to a position between Pteridophytes and Cycads. As Solms-Laubach says, the evidence supplied by the structure of the veins of D. Goepperti in favour of a cycadean alliance is not convincing. The type of vernation is unlike that of any known Cycad or indeed of any Gymnosperm: the large size of the leaves is another though weaker objection to this comparison, as the pinnae of Bowenia (fig. 391) and especially those of some species of Zamia (fig. 388), are of equal or larger dimensions. If, as seems probable, the xylem-strands are mesarch that is a point of contact with recent Cycads, but the bundle as a whole bears but a remote resemblance to that of a cycadean leaf and is much more like the veins of Ginkgo. The bud shown in fig. 430, A, is probably a young shoot and not merely a large compound leaf. If it were an unexpanded frond of Neuropteris bearing Cyclopteris pinnules we should expect to find indications of scattered desmogen-strands such as would occur in the Myeloxylon type of rachis. The resemblance to most forms of Cordaites is by no means close though a few leaves referred to that genus (e.g. C. circularis, fig. 468, B) are similar to those of Dolerophyllum[395].
The male organs are unlike those of any other plant: they may be described as sporophylls with microsporangia or perhaps synangia embedded in the mesophyll and containing microspores similar to those of some Pteridosperms or true Gymnosperms. Attention has been called to the close resemblance of the spores shown in fig. 432, C, D to those recently discovered by Kidston and referred to the genus Whittleseya (fig. 429), and it is very probable that the striking similarity is an index of affinity.
Ottokaria bengalensis Zeiller. A specimen of doubtful affinity from the Lower Gondwana (Karharbari beds) of Passerabhia, India, was originally described by Zeiller[396] as Feistmantelia bengalensis, but in a postscript he substituted the name Ottokaria on the ground that Feistmantelia had previously been employed by Lester Ward. Fig. 433 is drawn from the original specimen: it consists of a stalk attached in a slightly excentric position to an almost orbicular lamina, 2·5 cm. in diameter, with subacute marginal teeth and traversed by numerous radially disposed striations. Zeiller compares the fossil with Whittleseya elegans and Rhipidopsis ginkgoides and assigns it with some hesitation to the Salisburieae. An examination of the type-specimen led me to form the opinion that it may be a cupular organ of a Pteridosperm that enclosed a seed. The lamina is slightly concave and has the form of a shallow cup; moreover the surface-features resemble those of a bract rather than the regularly veined lamina of a foliage-leaf. The specimen bears a very close resemblance to one figured by Bertrand[397] as the cupule of Hexapterospermum modestae which he connects with fronds of Neuropteris gigantea.