XXXV. PALAEOZOIC GYMNOSPERMOUS SEEDS…

XXXV. PALAEOZOIC GYMNOSPERMOUS SEEDS

Seeds are abundantly represented as fossils from Carboniferous to Post-Tertiary deposits. The importance of fossil and sub-fossil species in the later geological series has been demonstrated by the investigations of Mr and Mrs Clement Reid and a few other workers in this neglected field. In cases where it is possible to assign seeds to their parent-plants the descriptions of casts, impressions, or petrifactions are added to the account of vegetative organs; but it frequently happens that seeds are preserved only as detached specimens many of which have little or no value as botanical records, while others that afford striking examples of the possibilities of petrifaction as a means of preserving the most delicate structures, are of great importance. In Volume +ii.+ an account was given of such Palaeozoic seed-bearing organs as Lepidocarpon and Miadesmia, and the genera Lagenostoma, Sphaerostoma, and Trigonocarpus are dealt with in this volume under Lyginopteris, Heterangium, and Medullosa. Certain seeds afford some evidence as to the systematic position of the parent-plants though insufficient to warrant more than a surmise as to the nature of the vegetative organs: in several cases it is only from the resemblance of detached seeds to types that on the strength of more or less convincing evidence are referred to definite parent-plants that any conclusions can be drawn with regard to precise systematic position. In view of the occurrence of several different types of seeds that retain their morphological features, but cannot be assigned with any degree of certainty to genera founded on vegetative organs, a special chapter is devoted to a comparative study of selected examples with the object of directing attention to data bearing on evolutionary problems. The chief interest of Palaeozoic seeds to the botanist lies in the facts they contribute towards the elucidation of questions connected with the promotion of the megasporangium and megaspore of the Pteridophyta to the higher stage represented by the integumented megasporangium (nucellus) and single megaspore that in the main fulfil the definition of a seed[790]. ‘With the evolution of the seed,’ as Oliver says, ‘the plant rose at a bound to a higher plane, and this structure in its perfected form has become the very centre of the plant’s existence[791].’ We can as yet form a very partial conception of the successive stages in the adoption of the seed-habit, but since 1855, the year in which Hooker and Binney[792] published their paper on the structure of Trigonocarpus, ample proof has been furnished of the importance of Palaeozoic seeds from the standpoint of affinity between recent Gymnosperms and extinct seed-bearing plants, and of the modus operandi of evolutionary tendencies. A cursory examination of Palaeozoic seeds suffices to demonstrate their resemblance to those of recent Cycads and the seed of Ginkgo biloba; but while it is clearly with these Gymnosperms that the majority of the seeds described in the following pages are most closely allied, the extinct types possess many distinguishing features that throw light on some at least of the factors concerned in the production of the modern type. In many of the Palaeozoic seeds the nucellus stands free within the integument, to which it is attached only in the chalazal region, in contrast to the lateral union between integument and nucellus in the ovules of recent Cycads. It has been suggested by Oliver[793] that the seed of the Conifer Torreya affords a clue to the interpretation of this difference and that the lower part of the seed in Cycads and Torreya represents a later intercalation in the basal portion of the ovule, the ancient type having a free nucellus in contrast to the nucellus of modern seeds which is free only at the apex. It has been objected[794] that there are no adequate grounds for assuming the addition of an intercalated zone or of the elongation of the ovule that this implies, the more probable view being that the lateral union of nucellus and integument represents congenital fusion in the ancestral type, a fusion comparable with that of the coherent petals of a gamopetalous corolla. In the presence of a pollen-chamber most of the Palaeozoic seeds agree with those of recent Cycads, but in the extinct forms it is usually a more highly developed structure. The name pollen-chamber was given by Brongniart[795] to the pollen-containing cavity in the free region of the nucellus in the petrified seeds from St Étienne in ignorance of the use of the same term by Griffith[796] in a posthumous work published in 1852 for the nucellar chamber in Cycas[797]. The genus Stephanospermum (fig. 494, A) illustrates the means by which the pollen-chamber was liberally supplied with water and thus adapted to the requirements of fertilisation by motile gametes. The pollen-chamber and its vascular supply paved the way for siphonogamy, that is the development of a pollen-tube for the more direct transmission of the male sperms. The highly developed mantle of tracheal tissue at the periphery of the nucellus in Stephanospermum, represented on a reduced scale by the separate vascular strands of other seeds, may be compared with the tracheal investment to the nucellus in the recent Dicotyledonous genus Cassytha[798]. The presence of a nucellar vascular system in several Palaeozoic seeds is a feature in which they differ from those of recent Cycads with the exception of Bowenia. The retreat of the vascular supply from the immediate neighbourhood of the pollen-chamber in recent Cycads may, as Oliver points out, be correlated with the evolution of the pollen-tube—the substitution of siphonogamy for zoidiogamy. The diagram reproduced in fig. 492 represents a synthetic type based on such seeds as Stephanospermum and Cardiocarpus which illustrate an arrangement of conducting tissue frequently found in Palaeozoic seeds: the main strand gives off a pair of bundles in the sarcotesta in the principal plane, as in Cardiocarpus[799]; from the tracheal mass in the chalazal region numerous bundles pass up the nucellus as far as the floor of the pollen-chamber. The nature of the vascular supply in this generalised type and in individual genera should be compared with that in the seeds of recent Cycads[800] described in Chapter +xxviii.+

Recent research has revealed the not unexpected fact that in such Upper Carboniferous petrified seeds as have been investigated—a small proportion of the large number produced in the Palaeozoic forests—there was a remarkable range in the mechanism connected with pollination and the maturation of the microspores. A comparison of the genera Physostoma, Lagenostoma, Conostoma, Trigonocarpus, Stephanospermum and others reveals the occurrence of very different though not unrelated structural features especially in the apical region of the seed. These seeds, including Physostoma, probably the most archaic type, represent a stage in evolution already far removed from the starting-point: the diversity of plan recalls the variety in the form of the chloroplasts in the Green Algae, and in both cases we are in touch with an experimental phase representing a tentative advance towards greater efficiency.

In its differentiation into an outer fleshy region, the sarcotesta, a stony layer, the sclerotesta, and in many cases an inner flesh, the Palaeozoic seeds resemble recent Cycads: in both extinct and modern seeds the balance of evidence would seem to be in favour of attributing a single rather than a double origin to the integument.

Among the numerous types of Palaeozoic seeds are several which invite comparison with the fruits or carpels, apart from the seeds, of Angiosperms. Impressions of Samaropsis seeds (figs. 502, B–K; 503; 504) bear a close resemblance to the laterally expanded fruits of the common Crucifer Thlaspi arvense; the ribbed testa of Hexagonocarpus (fig. 506, H) and other genera recalls the fruit-wall of Alstroemeria; the recently described Lower Carboniferous seed Thysanotesta sagittula Nath. (fig. 506, F) simulates a carpel of Erodium. These and similar instances of a close parallelism in external features between organs that are not homologous, though in themselves of no morphological significance, are at least interesting as illustrating the plasticity displayed by reproductive structures, which in the Palaeozoic period marked a morphological achievement comparable in its importance with the still greater achievement represented by the highly specialised fruits of the modern Flowering plants. The range in form and surface-features of Angiospermous fruits was foreshadowed by Palaeozoic seeds. Structural types and in some cases, superadded to these, features which may reasonably be supposed to have facilitated dispersal had been acquired by the seeds of Palaeozoic plants in forms that in a much later period were adopted by fruits even to a greater degree than by seeds. Characters useful in seed-dispersal, that are now shared by fruits and seeds, are illustrated by the fleshy and possibly edible seeds of extinct Gymnosperms, the plumes and hairy beak of Gnetopsis (fig. 494, E) and Thysanotesta (fig. 506, F) suggestive of feathery stigmas and other appendages. The lacunar sarcotesta of Aetheotesta, the thick endotesta of Pachytesta (fig. 497), and the air-chamber of Codonospermum (fig. 498), are strictly comparable with aids to buoyancy in fruits of existing Flowering plants. The mucilage-hairs and superficial cells in Physostoma (fig. 494, I) and Stephanospermum may be compared with the thick mucilaginous investment of the megaspores of recent water-ferns and with similar tissues of some Angiospermous seeds.

The bionomics of Palaeozoic plants is a subject worthy of more serious attention than it has so far received. The search for morphological characters that may have facilitated the wanderings of widely distributed genera and species and a closer investigation of physiological-anatomical problems presented by the vegetative organs of petrified plants would not only extend our knowledge of the morphology of ancient types but would stimulate comparative study and, incidentally, relieve the dullness of pure description. It may be argued that we should first establish a more solid foundation by further observations on living plants; but even at the risk of allowing speculation too free a hand the attempt is worth making, and it may be urged that, as in phylogenetic enquiries so in other branches of botany, facts obtained from plants of other ages may serve to supply deficiencies in knowledge based only on existing forms. One of the difficulties inseparable from the study of fossil plants, namely the identification of impressions and casts with specimens exhibiting anatomical characters, is particularly well illustrated by seeds. The description of a genus based on mere external form may sometimes be extended without great risk of error to include species founded on anatomical characters, but on the other hand, there are many instances in which—despite a general resemblance in form and size between petrifactions and impressions—lack of evidence of generic identity requires the employment of distinctive names. The determination of impressions is, as Lesquereux recognised, ‘subject to a great deal of uncertainty,’ and many of the genera founded on external features are purely artificial and include species that have no essential features in common. Moreover in the case of petrified specimens the apparent absence of an external fleshy layer is often due to destruction before preservation: as Solms-Laubach[801] points out, it is obviously impossible to be certain as to the number of integumental layers in seeds that are not well preserved in all their parts. Goeppert founded a new genus, Acanthocarpus, on a Permian seed described as A. xanthioides[802], because of the occurrence of spinous processes attached to an obcordate kernel: these apparent spines are in all probability the remains of a very imperfectly preserved sarcotesta. The preservation of the central portion of a seed, that is the seed-cavity with the enclosing shell, conveniently called the nucule, has often led to an unnecessary multiplication of generic terms. Other examples of confusion resulting from different states of preservation are quoted in the accounts of some of the selected types.

Williamson in 1877 pointed out that we learn from the large number of different kinds of Palaeozoic seeds that ‘there were in the Carboniferous forests many gymnospermous stems clothed with foliage of which we have not yet discovered any traces, probably because these Gymnosperms did not flourish upon the low swampy grounds which were the homes of the great mass of the coal-producing plants[803].’ Prof. Zeiller[804] has also drawn attention to the numerical excess of seeds over vegetative organs. This discrepancy has to a large extent been explained by the discovery that many of the supposed Ferns were seed-bearing plants, and a further explanation is suggested by the superiority of seeds over stems and leaves in their adaptation to dispersal by water.

In 1874 Brongniart[805] described several petrified seeds from material discovered by Grand’Eury in the St Étienne coal-field, and seven years later his descriptions were republished[806], with the addition of several beautifully executed drawings, as a posthumous volume edited by his distinguished pupil Renault. Williamson’s researches supplied much additional information, and in recent years the more detailed study of French and English seeds by Bertrand and particularly by Oliver and his pupils has further emphasised the interest and importance of this field of work. Brongniart proposed a two-fold classification of French seeds: (i) bilaterally symmetrical seeds, more or less flattened in section, which he believed to be Cordaitean; (ii) radially symmetrical seeds, circular in transverse section: the latter group he considered to be less closely allied to recent types. The employment of the terms Platyspermeae and Radiospermeae, proposed by Oliver[807] for Brongniart’s divisions, serves a useful purpose if due regard is paid to the adequacy of the evidence as to symmetry and if it is recognised that this classification cannot be rigidly employed in all cases. It was pointed out by Brongniart that the occasional occurrence of tricarinate seeds of Ginkgo (fig. 631) and Taxus is an exception to the general rule of bilateral symmetry: seeds of Cycas are normally bilateral, but radially symmetrical forms also occur[808]. The genus Conostoma (fig. 494, B) represents an intermediate type which, though almost radially symmetrical, exhibits a slight tendency towards platyspermy. Evidence recently brought forward by Nathorst[809] renders probable a connexion of a presumably radiospermic seed Lagenospermum Arberi[810] with the Lower Carboniferous fronds Adiantites bellidulus Heer, and this furnishes an interesting illustration of the association of both platyspermic and radiospermic seeds with the same generic type of foliage. While retaining Radiosperm and Platysperm as convenient descriptive terms, I have not adopted them as group-designations on the ground that they do not in themselves serve as trustworthy criteria of relationship. Attention is called by Salisbury[811] to the occurrence of bilaterally and radially symmetrical fruits among British Carices and to a similar mixture in the family Polygonaceae.

The acquisition of more detailed and accurate knowledge of Palaeozoic seeds led to an extension of the two-fold division of Brongniart and Oliver which is based on such characters as the position of the vascular tissue in relation to the integument and nucellus, the form of the pollen-chamber, and other features. The division Lagenostomales has been instituted for Lagenostoma and some other Radiosperms connected by certain important characters: these seeds may be referred to the Pteridospermeae though it is only in the case of Lagenostoma, and to a less extent Sphaerostoma, that a correlation between vegetative organs and seeds has been rendered sufficiently probable to justify an assumption of generic identity. The name Trigonocarpeae[812] has recently been used for a section of Radiosperms represented by Trigonocarpus, Stephanospermum, and other genera. Although the genus Stephanospermum, as Oliver[813] says, may be regarded as the type-genus of a group of seeds, it is more fitting, as the same author[814] insists, to adopt a divisional term based on the generic name of the much more widely spread and more familiar Trigonocarpus. For the sake of uniformity in nomenclature it is proposed to adopt the name Trigonocarpales instead of Trigonocarpeae to rank with Lagenostomales.

The Platyspermeae comprise such seeds as Cardiocarpus, Mitrospermum, and Rhabdospermum, genera characterised by well-marked anatomical features and probably Cordaitean; it has, however, been shown that typical Platysperms were also borne on leaves of Pteridosperms and, as Mrs Arber[815] says, the notion that every member of the Platyspermeae was necessarily a Cordaitean seed has been discredited by the discovery of the seeds of Aneimites (Wardia) and Pecopteris Pluckeneti[816]. For general purposes it is hardly necessary to adopt the subdivisions of the Lagenostomales used by Oliver and Salisbury[817], though as facts accumulate we shall no doubt be able to make further advances towards a natural system of classification. The following three divisions of Permo-Carboniferous seeds include genera founded on petrified specimens and thus afford valuable morphological data. The groups Lagenostomales and Trigonocarpales include types belonging to closely related plants, a relationship clearly expressed in the seed-characters.

I. +Lagenostomales.+

The seeds included in this group are for the most part Radiosperms, but in its slightly developed bilateral symmetry Conostoma oblongum is a type transitional between Radiosperms and Platysperms. The testa may be ribbed and the ribs vary in number. The nucellus (megasporangium) is united to the integument not only at the base but laterally as far as the shoulder of the seed up to a level corresponding to the base of the pollen-chamber (lagenostome) as in all recent Cycads and in the majority of Conifers. The seeds proper apart from the cupule are supplied with a single set of vascular bundles; there is no vascular tissue in the nucellus, a feature no doubt correlated with the fusion of nucellus and integument[818]. The free portion of the integument is more or less deeply lobed or, in Lagenostoma, it forms a pyramidal canopy of fused lobes enclosing the lagenostome. The presence of a tapetal zone surrounding the megaspore is believed to be a feature characteristic of the group[819]. The testa, wholly or partially ribbed, is relatively thinner than in the Trigonocarpales and Cardiocarpales, and in its differentiation agrees less closely with the testa of recent Cycadean seeds. In Lagenostoma and possibly in other genera a loose sheath or cupule surrounded the ovule, while in Gnetopsis a similar envelope enclosed two to four seeds.

The microspores are multicellular and smaller than those of Trigonocarpales, the average dimensions (Conostoma, Physostoma, Lagenostoma) being 67μ × 52μ.

Genera. Physostoma; Conostoma; Sphaerostoma; Lagenostoma; Gnetopsis.

Lagenostoma may safely be referred to Lyginopteris, and Sphaerostoma with but little risk of error to Heterangium: the parent-plants of the other genera are unknown, but all may be regarded as the seeds of Pteridosperms and probably of genera more nearly allied to the Lyginopterideae than to the Medulloseae. The genus Lagenospermum, recently instituted by Nathorst[820], is dealt with in Chapter +xxxi.+

=Physostoma.= Williamson.

Physostoma elegans Williamson.

The generic name Physostoma[821] was applied by Williamson[822] to a seed from the Lower Coal Measures of Lancashire which he named P. elegans; he afterwards described it as Lagenostoma physoides, but the original name has been revived by Oliver[823] to whom our knowledge of this type is chiefly due. The specimens figured by Williamson[824] as Sporocarpon ornatum also belong to Physostoma elegans. The seeds are circular in section, approximately 6 mm. long with a maximum diameter of 2 mm. The testa has about 10 longitudinal ribs passing in the apical region into a ring of free lobes or tentacles surrounding and considerably overtopping the nucellar apex: these tentacles take the place of a micropylar tube (fig. 494, I; fig. 493, D) and are a feature ‘in which this seed differs from all other known seeds, fossil or recent[825].’ A single vascular strand passes through the chalazal region and divides into 10 bundles, one to each rib and tentacle. The single integument consists of a few layers of cells, those of the epidermis being prolonged into clavate mucilaginous hairs, fig. 494, I, h, that may reach a length of ·5 mm. and in the living seed almost covered the whole surface of the testa, being especially long on the ribs and tentacles. There is no special development of sclerous tissue, the vascular bundles, v, being embedded in parenchyma in the inner portion of the integument. The nucellus is represented by a zone rich in secretory cells, and internal to this is a tapetum. Integument and nucellus are coalescent up to the apical region where the former splits into 10 tentacles. The nucellar apex has the form of a tall dome surrounded by a bell-shaped pollen-chamber (fig. 494, I, pc; fig. 493, C, D, c) into which it projects like the base of a wine-bottle. The circular opening of the pollen-chamber overtops the roof of the dome formed of the secretory tissue of the nucellus and the carbonised remains of the tapetum: this dark band surrounds the large megaspore-cavity (fig. 494, I). Physostoma is the only member of the Lagenostomales in which the megaspore projects into the free nucellar apex: in other genera intercalary growth has produced a more or less prominent plinth, the name given to the free portion of the nucellus between the megaspore and the pollen-chamber. Williamson[826] described the mammillated apex of the nucellus as pushed up into the base of the lagenostome which ‘looks like a bladder half full of fluid resting upon and overhanging the end of a soda-water bottle’: it was this appearance that suggested the name Physostoma. The section reproduced in fig. 493, D, shows in the centre the limiting tissue of the nucellus surrounded by the pollen-chamber, c, and external to this are the tentacles with their groups of long hairs: the vascular bundles are represented by spaces in the more internal small-celled tissue (see also fig. 494, I). A characteristic feature is the presence of a tapetum or megaspore-jacket[827] in the nucellus: immediately internal to the vascular bundles stretching from the chalaza to the apex of the megaspore-cavity is a layer of delicate cells with secretory sacs, and this is succeeded by a broad black layer of rather larger cells, a tissue which was probably in full activity in a younger stage of development.

A comparable tapetal layer is described by Lang[828] in the ovule of Stangeria: the majority of the sporogenous cells surrounding the megaspore become disintegrated and are absorbed, but the outermost zone forms a more definite tapetal layer: as already suggested, this tissue in Physostoma may be a group-character. No archegonia have been found, but in a few cases some of the delicate prothallus-tissue occurs in the interior of the seed. Microspores are often abundant in the pollen-chamber (fig. 493, C, c); in one seed 80 are recorded. The occurrence of so many microspores suggested to Oliver that insect-agency may have been responsible for the precision in pollination that is greater than one would expect in anemophilous plants. The spores are smaller than those of Lagenostoma (55μ × 45μ) and in several of them the remains of a cellular tissue are preserved (fig. 494, N), also some sub-reniform bodies (fig. 494, M) similar to those described as spermatozoids by Dr Benson in Lagenostoma (fig. 408, D).

The most interesting features of Physostoma are: the absence of a continuous micropylar tube and its replacement by a circle of integumental lobes; the apical prolongation of the nucellar apex into the pollen-chamber, and the presence of long mucilaginous hairs on the integument. The large pollen-chamber is a character which distinguishes Physostoma from Conostoma and its form is very different from that in Lagenostoma.

The tentacles of the integument and the form of the nucellar apex are features consistent with Oliver’s view that Physostoma is the most primitive of Palaeozoic seeds though, as Burlingame[829] says, the elaborate form of the encasing envelope marks a considerable advance beyond the earliest type of megasporangium integument.

A new type of Physostoma has been briefly described by Gordon[830], without a specific designation, from the Lower Carboniferous beds of Pettycur (Fife): it was found in association with Heterangium and Sphaerostoma ovale.

We have no knowledge of the plant to which Physostoma belonged, but the general plan of organisation of the seed points to a near relationship to Lagenostoma and presumably, as regards the parent-plant, to a genus related to Lyginopteris.

=Conostoma.= Williamson.

This name[831], suggested by the funnel-like pollen-chamber or lagenostome, was applied by Williamson[832] to some seeds from the Lower Coal Measures of Lancashire and Yorkshire and from the Lower Carboniferous beds of Burntisland. The Burntisland seeds, referred by Williamson to two species, have recently been united and described by Miss Benson as Sphaerostoma ovale[833]. The English species has been thoroughly investigated by Oliver and Salisbury[834] who have also described a second species, C. anglo-germanicum, from the Coal Measures of Lancashire and Germany.

Conostoma oblongum Williamson.

This rare type is represented by approximately cylindrical seeds with an average length of 5 mm. and a maximum breadth of 2·3 mm. borne on a relatively stout stalk and tapering to a blunt apex characterised by a canopy of six short lobes (fig. 494, B, C) in marked contrast to the long tentacles of Physostoma. In the basal region the integument has six prominent ribs which soon die out when traced upwards: a transverse section through the body of the seed is hexagonal (fig. 494, D), the angles corresponding to the basal ribs, and there is a slight tendency to platyspermy. The testa has an epidermal mucilaginous layer which becomes exfoliated through the lifting-up of the cuticle by the underlying mucilage: below this, at the apex of the seed, is a cap of fleshy tissue (fig. 494, B, sa) which, it is suggested, may have had a secretory function in connexion with a drop-mechanism in pollination like that in recent Conifers. No microspores have been found in the pollen-chamber. The epidermis, called by Oliver and Salisbury the blow-off layer (fig. 494, B, m), together with the cap of soft tissue constitute a feebly developed sarcotesta. A sclerotesta consisting of a palisade-layer and a fibrous hypoderm extends over the main body of the seed below the epidermis; it forms the basal ribs and increases considerably in breadth at the apical region to form a sclerous cone penetrated by six strands of parenchyma enclosing vascular bundles (fig. 494, D) which pass up from the conducting tissue immediately external to the nucellus. The nucellus is coalescent with the integument, as in Physostoma, as far as the level of the domical free apex of the nucellus where the tapetal tissue that lines the seed-cavity passes across the almost flat top of the central region originally occupied by the megaspore. In some sections prothallus-tissue was found with an apical ‘tent-pole’ protuberance. A striking feature of Conostoma is the mechanism for the reception of the microspores. The free part of the nucellus consists of the plinth, a broad tapering region originally filled with parenchyma but in most cases represented only by its epidermis: the plinth, p, is seen in fig. 494, B, to be two-storeyed, the upper and narrower storey being a space formerly filled by a pad of tissue suspended from the floor of the superposed lagenostome (pollen-chamber)[835]. The greater development of the domical plinth is a feature in which Conostoma differs from Physostoma. At the apex of the plinth and resting on a slight depression is a small lagenostome, bowl-shaped in section, and like the pollen-chamber of Lagenostoma, formed as the result of enzyme-action on the apical papilla of the nucellus (fig. 494, B, B′, l′). The mouth of the lagenostome engages with the micropylar tube by a projecting flange (fig. 494, B′, f) of tissue lining the micropylar canal and by a second flange (f′) at the base of the lagenostome where the roof of the plinth (fig. 494, B′, p) bends downwards and inwards. The walls of the lagenostome are formed by strong cells with thickening bands giving them the appearance of tracheids (l′), but the floor of the lagenostome is made of thinner cells which become disorganised, allowing the microspores to fall into the large plinth-cavity below (p, fig. 494, B), an arrangement comparable with the two-storeyed pollen-chamber of Bowenia[836] and, to a less extent, with the micropyle of the Conifer Tsuga. The microspores are multicellular and ellipsoidal measuring 75μ × 65μ.

The species Conostoma anglo-germanicum agrees closely with C. oblongum in general form and organisation, but it has eight ribs, four more prominent than the others, and differs also in other minor characters from the rather shorter seeds of the type-species. Conostoma differs from Lagenostoma in the absence of the tubular prolongation of the lagenostome, the micropyle being like that in recent Gymnosperms. In Conostoma the tracheid-like elements of the lateral wall of the lagenostome are a characteristic feature, and no evidence has been found of the existence of a central core of tissue such as occupies the centre of the seed-apex in Lagenostoma. The long hairs of Physostoma are represented in Conostoma by the much smaller mucilaginous cells of the epidermis and in Lagenostoma by the less closely united mucilage-cells of the superficial layer of the testa.

=Sphaerostoma.= Benson.

As already pointed out in Chapter +xxix.+ where this genus is described as probably the seed of Heterangium, there is a fairly close general resemblance between Sphaerostoma and Lagenostoma. In the presence of free apical lobes the former genus resembles Conostoma, and while agreeing with Lagenostoma in its annular pollen-chamber it is peculiar in the retention of an epidermis over the roof of the pollen-chamber: as in Lagenostoma the seed is enclosed by an outer integument or cupule.

=Lagenostoma.= Williamson.

An account of this type of seed is included in the description of Lyginopteris[837]. The more striking peculiarities are exhibited by the pollen-chamber and the free region of the integument: the annular pollen-chamber (fig. 493, D, c; fig. 409) surrounds a central nucellar cone and is prolonged upwards as a tube engaging with the micropyle in contrast to the form of the pollen-chamber and the absence of a tubular prolongation in Conostoma. The tentacles of Physostoma and the short apical lobes of Conostoma are replaced by an apical cone formed by the coalescence of the integument containing nine cavities originally filled with parenchyma (figs. 409; 493, B). The presence of a cupule is a characteristic feature of young seeds, but from negative evidence in the case of most other seeds it is unsafe to assume that the cupule of Lagenostoma is an exceptional feature. The nucellus and testa are united as far as the shoulders of the seed as in the seeds of recent Cycads and in contrast to their lateral independence in Trigonocarpus, Stephanospermum, and other genera.

=Gnetopsis.= Renault.

This generic name was given by Renault[838] to some small petrified seeds from the Stephanian of Grand’ Croix and to impressions from the Commentry coal-field which he believed to belong to some Gnetaceous plant. Saporta and Marion[839] and other authors have accepted these seeds as evidence of the existence of Palaeozoic Gnetales: it has, however, been shown[840] that Gnetopsis has no claim to such relationship and is a type of seed closely allied to Conostoma. Renault described three species, afterwards adding three from another locality[841]; the genus is recorded also from Commentry[842] and Gard[843]. More recently Depape and Carpentier[844] have described examples from the Westphalian of Valenciennes which they place in the Pteridosperms in accordance with the conclusion of Oliver and Salisbury. Gnetopsis has also been discovered by Mr Hemingway in the Middle Coal Measures of England[845] (fig. 494, H).

Gnetopsis elliptica Renault.

The seeds of this species, slightly oval in section, occur in groups of 2–4 in a cupular investment (fig. 506, E, p. 359) described by Renault as an ovary but correlated by Oliver and Salisbury with the cupule which surrounds the single ovule of Lagenostoma. The cupule is lined with hairs similar to those on the wall of the cupule of Lagenostoma. A characteristic feature of the French seeds is the presence of three or four long plumes of hairs at the apex (fig. 494, E, F). As seen in fig. 494, E, a small lagenostome (pollen-chamber) rests on the roof of a broad plinth precisely as in Conostoma, and four vascular bundles, corresponding to the six bundles in Conostoma, pass into the apical cap of sclerous tissue enclosed by a sarcotesta, sa (fig. 494, E, G). A ‘tent-pole’ prolongation (fig. 494, E, t) occurs at the apex of the prothallus. Renault described a portion of the integument as consisting of lacunar tissue which Oliver and Salisbury homologise with the superficial mucilaginous layer of Conostoma: this is seen above the sclerotesta in the apical region of fig. 494, E, sa.

Gnetopsis anglica Kidston +MS.+

This species (fig. 494, H) is represented by seeds from the Middle Coal Measures near Barnsley, Yorkshire, 4 mm. long with apical appendages at least 2·2 cm. in length and probably four in number. The appendages do not show the hairs which form a prominent feature in the French specimens, but this is probably the result of imperfect preservation: there are indications of hairs on other specimens in Dr Kidston’s Collection. The type-specimen, in Dr Kidston’s Collection, was generously lent to me for examination.

Gnetopsis, while agreeing with Conostoma in the more important features, is distinguished by the apical plumes, the very slight development of a tent-pole prolongation of the nucellar apex (fig. 494, E, t), the smaller number of vascular bundles, and by the presence of an enclosing cupule (fig. 506, E). In its slight departure from radial symmetry Gnetopsis forms a transition between the Radiospermeae and the Platyspermeae. It is undoubtedly the seed of a Pteridosperm, but nothing is known as to the nature of the vegetative organs of the parent-plant.

II. +Trigonocarpales.+

In this group are included radially symmetrical seeds for the most part belonging to members of the Medulloseae. The peripheral zone of the nucellus is supplied with vascular tissue and the nucellus is free within the integument except at the base; it is superior and not semi-inferior[846] as in recent Cycads and in Lagenostomales. The ovule of Myrica Gale, in which the nucellus stands free within the single integument, affords an interesting parallel to seeds of this class in contrast to the usual Angiospermous type with a laterally coalescent nucellus. In Myrica Gale[847] the vascular supply is confined to the integument. There is a comparatively broad pollen-chamber and in some types the lateral tissue of the nucellus is prolonged as a tube within the micropyle. The usually ribbed testa is differentiated into an outer flesh (sarcotesta), a sclerotesta, and probably in most cases an endotesta or inner flesh. The ribs of the sclerotesta are in the majority of genera in multiples of three and in position correspond to the outer ring of vascular bundles. The presence of lacunar tissue in the sarcotesta of several genera may be correlated with dispersal by water. The apical region of the integument is not lobed but extends as a longer or shorter micropylar tube above the summit of the nucellus. In the differentiation of the testa, the form of the pollen-chamber, and in some other features, the seeds of this group present a general agreement with those of recent Cycads.

The microspores are multicellular and larger than those of the Lagenostomales: in Stephanospermum akenioides they measure 160μ × 100μ[848] while in Aetheotesta[849] they reach 360μ × 290μ.

Genera. Trigonocarpus; Tripterospermum; Ptychotesta; Hexapterospermum; Polypterospermum; Pachytesta; Stephanospermum; Polylophospermum; Codonospermum; Aetheotesta; Eriotesta; Gaudrya.

=Trigonocarpus.= Brongniart.

A description of the morphological features of Trigonocarpus Parkinsoni and T. shorensis is given in the chapter on Medullosa (p. 117), as there is good evidence that they are the seeds of that genus. There is considerable difference in size and to some extent in the form of casts included in Trigonocarpus and, in the absence of anatomical data, it is hardly possible to determine the actual systematic position of many of the specimens so named. Dr Arber[850] has recently proposed a new generic name Schizospermum for casts very like those of T. Parkinsoni, but distinguished by the splitting of the shell into three valves, a character which leads him to conclude that it is the external surface which is preserved and not a mere cast of the seed-cavity. It is, however, more probable that the specimens are casts of a split sclerotesta. In Trigonocarpus pusillus[851] the shell is divided into three valves, the dividing lines being marked by greatly reduced ribs, and in T. schizocarpoides Grand’Eury[852], a species that may not be a true Trigonocarpus, there is also evidence of splitting. Arber points out that the species Rhabdocarpus Boschianus Berg. is founded on a Trigonocarpus from which the outer flesh has disappeared leaving the shell as the external covering. Trigonocarpus seeds are widely distributed in Carboniferous and Permian rocks in Europe and North America: from the latter continent Newberry[853] has described several different forms that afford good examples of the abundance and variety of the genus. Some of the specimens included by Newberry[854] in Trigonocarpus are probably distinct generic types: his species T. multicarinatus may be identical with the ribbed cast shown in fig. 506, A. The casts described by Lindley and Hutton and by other authors as T. Dawesi[855] are nearly 5 cm. long, and if these are correctly included in the genus they point to the occurrence of seeds much larger than the type-species. The French species Trigonocarpus pusillus[856] Brongn., one of the smallest Palaeozoic seeds, from 6·5 to 15 mm. long, differs from Trigonocarpus Parkinsoni and T. shorensis in the absence of prominent ribs and in the much feebler development of the sarcotesta. Specimens of the German type T. sporites Weiss, believed by some authors to be megaspores, were described by Zeiller[857] from Valenciennes as seeds: these are from 2·5 to 3·5 mm. long and have three small ribs. Zeiller quotes the presence of cell-outlines on the surface as evidence of their seed-nature, but it may be that this feature represents a sculpturing of the exine of a spore. Typical Trigonocarpus seeds agree in several morphological characters with those of recent Cycads. They differ in the lack of a lateral union between nucellus and integument; the presence of nucellar tracheids, though a feature shared with Bowenia, distinguishes them from the majority of recent Cycadean seeds. In the comparatively long and fleshy micropylar tube a seed of Encephalartos Lehmanni presents a fairly close resemblance to a Trigonocarpus. Salisbury has pointed out that the three species T. Parkinsoni, T. shorensis, T. pusillus form a consecutive series illustrating the gradual disappearance of the secondary ribs that form a prominent feature in T. Parkinsoni; but for a comparison of these with other types of fossil and recent seeds the reader is referred to Salisbury’s summary[858].

=Tripterospermum.= Brongniart.

The seed on which this genus was founded by Brongniart[859] is clearly very closely related to Trigonocarpus and, as Oliver[860] says, the distinguishing character described by the author of the genus is unimportant. Brongniart describes the type species, T. rostratum, as characterised by the presence of three prominent wings composed of a testa differentiated into an inner hard tissue and an outer lacunar tissue. It is, however, hardly possible to say whether the outer soft tissue was originally flattened in the form of ‘wings’ or pressed down on to the harder shell. Renault[861] notes the association of seeds that he refers to this genus with the leaves of Dorycordaites, but apart from the improbability of any connexion between Tripterospermum and Cordaites, Renault’s seeds are too imperfect to demonstrate their identity with Brongniart’s genus. Kidston[862] has described an impression of a three-winged seed from the coal-field of Staffordshire as Tripterospermum ellipticum, a form described on page 357 as Polypterocarpus anglicus (fig. 496, B).

=Ptychotesta.= Brongniart.

The type-species of this genus[863], Ptychotesta tenuis[864], about 3 cm. long, is characterised by six very prominent flanges or wings formed by the fissured or folded sclerotesta (fig. 495, B). There is no information as to the vascular supply or other anatomical details. It is not at all improbable that there is no real distinction between this genus and Brongniart’s genus Hexapterospermum.

=Hexapterospermum.= Brongniart.

In this genus Brongniart[865] included two species, Hexapterospermum stenopterum and H. pachypterum: the shell is hexagonal in transverse section, each angle being prolonged as a narrow flange. In one of the sections figured by Brongniart (fig. 495, E) the ribs are not fissured: this is said to be a feature distinguishing Hexapterospermum from Ptychotesta, but the occurrence of a fissured rib in another section suggests that in the structure of the ribs there is no essential difference between the two genera. In Ptychotesta pachypterum the testa is prolonged at the chalazal end as in Polylophospermum, and it is possible that there is no generic difference. Williamson described a cast from the Coal Measures of Lancashire as Hexapterospermum [= Hexagonocarpus] Noegerrathi[866] (fig. 506, H), but in the absence of anatomical characters it is preferable to avoid the use of Brongniart’s term and to assign them to Renault’s genus Hexagonocarpus[867]. Similarly the seeds referred by Dr P. Bertrand[868] to Hexapterospermum may appropriately be included in the genus Hexagonocarpus.

=Polypterospermum.= Brongniart.

This generic name was proposed for an ovoid seed from St Étienne described as Polypterospermum Renaultii[869]; hexagonal in section with six deep and sharp flanges at the angles alternating with six secondary ridges distinguished by their blunter edges and slightly smaller depth (fig. 495, A). Without further anatomical details it is hardly possible to say whether or not the species represents a well-defined generic type, but it is not improbable that a fuller knowledge would confirm Brongniart’s institution of a new generic designation. The seeds described by Arber[870] and Kidston[871] respectively as Radiospermum ornatum and Polypterospermum ornatum are transferred to Polygonocarpus on the ground that they afford no evidence of anatomical characters of the Polypterospermum type.

=Pachytesta.= Brongniart.

Brongniart[872] established this genus for some unusually large seeds (fig. 496, A) from the Coal Measures of France reaching a length of 11–12 cm. and resembling in form and size a hen’s egg. Petrified examples have been described by Brongniart and Renault[873], and Oliver[874] has given a lucid statement of the more interesting features of this Permo-Carboniferous genus.

Pachytesta gigantea (Grand’Eury).

In the separation of nucellus and integument Pachytesta agrees with Stephanospermum and Trigonocarpus. There is a double series of vascular bundles in the outer part of the testa or exotesta (fig. 497, ex) consisting of a spongy tissue bounded externally and internally by sclerotic layers: the exotesta is succeeded by a broader endotesta of spongy consistency which Renault suggested may have served as a floating mechanism, and this is intimately associated with the nucellus by means of grooves engaging with short ridges (fig. 497, nr) on the surface of the nucellar tissue. The exotesta is divided into three valves by radial extensions of the sclerotic tissue (b, c, fig. 497; at a the exotesta is shown in an unsplit condition). In connexion with each radial plate are two curved plates of fibrous tissue which extend towards the grooves in the endotesta (fig. 497, t): as Oliver suggests, these plates may have served a mechanical purpose for the support of the bulky nucellus. The peripheral region of the nucellus is supplied by several vascular bundles (fig. 497, n) from the tracheal chalazal disc. The exotesta is regarded by Oliver as corresponding to the sarcotesta and sclerotesta of other seeds, and the grooves in the endotesta interlocking with the nucellar ridges are compared with the interlocking of nucellus and canopy in Lagenostoma, as also with the ruminated endosperm of Torreya.

We have no definite information as to the plants which bore Pachytesta, but it is probable that they were members of the Medulloseae. Grand’Eury[875] believes Pachytesta to be the seed of Alethopteris Grandini, though this view requires confirmation. This author figures several Pachytesta seeds attached in two oblique rows to a comparatively slender axis which may be the rachis of a large compound frond[876]. Renault and Zeiller[877] have figured specimens of P. gigantea and P. incrassata from Commentry which afford a good idea of the form of these large seeds; the genus is recorded also from Gard, Blanzy[878], and other localities. Kidston[879] described a large oval seed, blunt at each end, from the Middle Coal Measures of Lancashire as Carpolithus Wildii which he thinks may be allied to Pachytesta, but adds, ‘I do not think we are justified in placing mere impressions of plants in genera, whose distinctive characters are derived from their internal organisation, unless there is conclusive evidence to show their identity.’ On this specimen Arber[880] has founded a new genus Megalospermum, but as the type-specimen shows no distinctive features other than large dimensions it would seem preferable to retain the more general designation Carpolithus[881].

Another example of a seed that may be generically identical with Pachytesta is that described by Lesquereux from North American Coal Measures as Rhabdocarpus Mansfieldi and more recently recorded by White from Missouri as Rhabdocarpus (Pachytesta) Mansfieldi[882]. There is little doubt that this and other species of seeds preserved as impressions are examples of Pachytesta but, as Kidston says, it is preferable to reserve the name for specimens showing anatomical features.

=Stephanospermum.= Brongniart.

The genus Stephanospermum, founded by Brongniart[883] on petrified specimens from French Stephanian beds, affords a good example of a radiospermic seed without ribs differing in certain well-marked characters from such seeds as Lagenostoma, Physostoma, and Conostoma, notably in the complete separation of the nucellus from the integument and in the possession of a nucellar vascular system. The descriptions by Brongniart and Renault[884] have been extended by the thorough investigations of Oliver[885].

Stephanospermum akenioides Brongniart.

This species is represented by ellipsoidal seeds, 10 mm. long with a maximum breadth of 4–4·5 mm., circular in transverse section. The integument consists of a thick sclerotesta lined internally by a thinner soft layer, the endotesta (fig. 494, A, sc, e), and in all probability covered by an outer flesh or sarcotesta as in Trigonocarpus, though this tissue is not preserved and is omitted from the section shown in fig. 494, A. The sclerotesta is composed of a broad outer band of thick-walled palisade cells—the contracted contents of which are a striking feature in the silicified seeds (fig. 493, F); these are succeeded by an inner zone of longitudinal fibres. In the structure of the palisade-layer Stephanospermum bears a close resemblance to the sporocarp wall of Pilularia[886]. In the apical region the shell forms a circular ridge surrounding a peri-micropylar trough, a character expressed by the term ‘crown-seed[887]’ employed by Grand’Eury: the trough sometimes contains partially destroyed tissue that may be a remnant of a sarcotesta. A Stephanospermum seed, with its apical core and surrounding depression with remnants of some partially destroyed tissue, may be compared with a fruit of Attolia speciosa (Palmae) in which a tuft of fibrous tissue picked out by decay from the mesocarp surmounts the conically pointed apex of the harder interior of the fruit-wall. The base of the sclerotesta is perforated by a vascular strand which expands into a tracheal disc, td, fig. 494, A, at the base of the megaspore from which a continuous mantle 2–3 cells broad, of short spiral and scalariform tracheids (fig. 493, G), spreads over the whole of the nucellus immediately below the nucellar epidermis as far as the lower part of the sides of the pollen-chamber: this mantle forms the floor of the large domical pollen-chamber excavated out of the nucellar cone (fig. 494, A, pc). The fact that in sections of older seeds the tracheal floor shows signs of splitting and disorganisation led Oliver to conclude that in the living seed the tracheids underwent a gradual disintegration prior to fertilisation, thus allowing the passage of the antherozoids to the egg-cells (fig. 494, A, a). The presence of a continuous tracheal sheath instead of separate vascular bundles is a special feature in which Stephanospermum differs from Trigonocarpus and other Palaeozoic seeds as well as from those of recent Cycads; as Oliver suggests, ‘the apparent perfection of the vascular mantle in Stephanospermum may have proved an obstacle to further development[888]’ and was not retained by the more successful types. In its tracheal sheath Stephanospermum resembles the seeds of Ginkgo. The nucellar cone is prolonged as a beak into the micropyle formed by the tubular integument. The megaspore occupies the central portion of the seed and in the course of its development it compressed the megasporangium (nucellus) to such an extent that little more than the epidermis remains: there is a definite megaspore-membrane surrounding the prothallus-tissue in which there were probably two archegonia (fig. 494, A, a)[889]. The nucellus stands free within the integument from which it is separated by a space (s, fig. 494, A). Microspores are frequently met with in the pollen-chamber in which they matured after their introduction through the micropyle, probably with the aid of a drop of mucilage: they are large oval bodies with an average size of 160μ × 100μ, some reaching over 200μ, in length and, as Renault was the first to point out, within a finely granulate exospore there are several thin-walled cells: this statement was not accepted by some authors but Prof. Oliver’s researches have amply confirmed it, and an examination of the original preparations convinced me that Renault had correctly described the structural features. Oliver shows that there are about 20 cells within each microspore regularly arranged as rows of five wedge-shaped elements with their pointed ends directed towards the centre, and he thinks that these cells may have undergone further division to produce sperm-mother-cells, though there is not such good evidence of this as in the differently constituted microspores of Stephanospermum caryoides. No trace of pollen-tubes was found and it is probable that the antherozoids were liberated by the rupture of the delicate prothallus-tissue. The tracheal sheath afforded an adequate means of water-supply to the pollen-chamber and this enabled the motile antherozoids to reach the archegonia.

Stephanospermum caryoides Oliver[890].

This species, founded on a specimen from ., is a larger seed (15·5 × 12·5 mm.) and more globular than S. akenioides; there is a shorter micropylar beak and a less developed peri-micropylar trough. As in S. akenioides the nucellus is free from the base and the two species conform to the same general type of construction. The microspores are distinguished by the presence of only two internal cells which do not occupy the whole of the spore-cavity but are surrounded by a large peripheral cell comparable with the tube-cell in recent microspores, though there is no proof that a tube was formed: in the case of S. akenioides Oliver considers that fertilisation was not assisted by the production of a pollen-tube. The two cells by further division gave rise to a secondary cell-complex consisting of at least eight antherozoid-mother-cells. No antherozoids have been found in the microspores but it is possible that two small bodies, 17μ × 15μ, met with in a pollen-chamber may represent the nuclei of sperms. Their small size differentiates them from the much larger male gametes of Cycads and from the supposed sperms of Physostoma and Lagenostoma.

We have no proof as to the nature of the plant which bore seeds of the Stephanospermum type, but it is significant that the specimens occur in close association with fragments of Alethopteris and Myeloxylon, a circumstance that favours the view, based on the resemblance of these seeds to Trigonocarpus, that Stephanospermum is the seed of a member of the Medulloseae.

=Polylophospermum[891].= Brongniart.

The type-species Polylophospermum stephanense Brongn.[892], founded on partially preserved material from Grand’ Croix, is a narrow hexagonal seed 15 mm. long. Additional facts as to the structural features have been contributed by Oliver[893]. The testa is differentiated into an inner shell (sclerotesta) and an outer flesh (sa, fig. 495, C, D): the sclerotesta has six prominent, fissured, ribs, one at each angle, and between these are six solid and less prominent secondary ribs. Oliver states that there is an outer series of vascular bundles in the sarcotesta, one bundle immediately external to each secondary rib (fig. 495, C, v). In the presence of two kinds of ribs and in the relation of ribs to tracheal strands Polylophospermum agrees with Trigonocarpus Parkinsoni. Strands of short tracheids supply the peripheral region of the nucellus and, as in Stephanospermum, reticulate elements extend as far as the floor of the large pollen-chamber. There was probably no lateral union between nucellus and integument. A striking feature is the prolongation of the testa at each end of the seed to form an open chamber surrounding the micropylar beak and the seed-base (fig. 495, D, s, s): the apical chamber, though relatively more prominent, is comparable with that in Stephanospermum, while the basal chamber recalls that in the seed named by Scott and Maslen Trigonocarpus Oliveri[894] but subsequently removed by Salisbury[895] from that genus. There is no evidence as to the parent-plant of Polylophospermum, but it may be assumed to have been a Pteridosperm, probably one of the Medulloseae.

=Codonospermum[896].= Brongniart.

Our knowledge of this peculiar genus is derived from Brongniart’s description of the type-species Codonospermum anomalum[897] (fig. 506, B, C) from St Étienne and from Renault’s account of C. olivaeforme[898]. The seeds are globular or ellipsoidal and reach a length of 2 cm.: the testa is differentiated into an outer flesh and a sclerotesta and has usually eight ribs. The most striking feature is the division of the seed into two regions, an upper portion containing the nucellus and megaspore and a lower portion in the form of an empty chamber that probably served as a float (fig. 498, A, s). Externally the upper half or seed-proper forms a depressed cupola with eight slightly developed ribs, separated by a circular transverse constriction from the basal chamber (fig. 498, B). There is a fairly large pollen-chamber, pc, in which Renault found multicellular microspores in C. olivaeforme. In C. anomalum 16 vascular bundles (fig. 498, B, v) surround the central region of the seed probably in the peripheral tissue of the nucellus; these bundles unite in the chalazal region to form a strand that passes up the centre of the empty chamber. In C. anomalum the testa of the lower half has eight ribs and corresponding with each rib is a strand of fibrous tissue (fig. 498, B, f). In C. olivaeforme the testa is thicker than in C. anomalum and the lower region of the seed is smooth and circular in section.

Impressions of Codonospermum are described[899] from Commentry, from the Loire—the Gard district[900], and by Zeiller[901] from Blanzy. There is no decisive evidence as to the parent-plant, but some French authors[902] regard the frequent association of Codonospermum with leaves of Dolerophyllum as significant.

=Aetheotesta.= Brongniart.

Aetheotesta elliptica Renault.

Brongniart instituted the genus Aetheotesta[903] for an incomplete seed (A. subglobosa) from Grand’ Croix, and Renault[904] subsequently founded the species A. elliptica on much better material. The testa of the elliptical seed, 3 cm. long, consists of an outer region very thin on the flanks but highly developed at the apex and base which forms a sarcotesta characterised in the apical region by large radially disposed spaces, fig. 498, C, s; the sclerotesta, composed of harder tissue, is prolonged as an apical beak. There is a large pollen-chamber, pc, in which Renault found multicellular microspores (320μ–400μ). In the chalazal region the main vascular supply forms a cup-like investment, v, in the basal portion of the nucellus, and at a higher level this breaks up into several nucellar strands. Renault thinks that Aetheotesta is the seed of Dolerophyllum, but there is no proof of any connexion. The presence of large spaces in the sarcotesta may be interpreted, as Renault suggests, as evidence of adaptation to dispersal by water.

=Eriotesta.= Brongniart.

Brongniart[905] instituted this genus[906] on an incomplete transverse section of a seed from Grand’ Croix, 8 mm. in diameter, which he called Eriotesta velutina, characterised by a ribbed and probably octagonal testa bearing numerous elongated hairs over the whole surface. The material is, however, too meagre to throw any light on the important features of the seed.

=Gaudrya.= Grand’Eury.

Gaudrya trivalvis Grand’Eury.

The generic name Gaudrya[907] was proposed for two petrified seeds from the Gard coal-field briefly described as G. trivalvis, the type-species, and G. lagenaria. The testa of the former species shows signs of splitting along three equidistant lines; it consists of a sarcotesta enclosing an endotesta with six longitudinal ribs: Grand’Eury speaks of lacunae between the endotesta and nucellus which he regards as spaces in a tissue which made the seed buoyant and facilitated dispersal by water. It is not clear whether the nucellus and integument were originally connected or laterally free: the lacunae may be the remains of an inner flesh and not spaces in a spongy tissue. The genus is radiospermic and characterised by a long micropyle and a broad pollen-chamber. On the available evidence it is difficult to assign the specimens to their systematic position, but the genus is probably a member of the Trigonocarpales.

III. +Cardiocarpales.+

Platyspermic seeds for the most part belonging to Cordaitalean plants and agreeing in their plan of organisation, even more closely than the seeds of the Trigonocarpales, with those of recent Cycads. The nucellus is free laterally from the integument and there is a series of vascular bundles in the nucellus. The testa consists of an outer flesh, the sarcotesta, which may reach a considerable thickness, a shell or sclerotesta, and in some genera an endotesta. In seeds preserved as impressions the sarcotesta often gives them a winged appearance (Samaropsis). The pollen-chamber is relatively small, resembling in this respect the chamber in recent Cycads. A central prolongation of the prothallus-tissue in the form of a blunt column or ‘tent-pole’ is a characteristic feature; the same feature occurs in seeds of the Lagenostomales, but in the Cordaitales it resembles more nearly the ‘tent-pole,’ as it was called by Hirase, in recent Cycadean seeds and in Ginkgo. The presence of two vascular strands in the sarcotesta in the principal plane of the seeds is a character shared with the seeds of Cycas: the position and course of these bundles are useful characters for distinguishing different types within the group. The microspores are multicellular.

Genera. Cardiocarpus; Cyclospermum; Cycadinocarpus; Rhabdospermum; Mitrospermum; Diplotesta; Leptocaryon; Taxospermum; Compsotesta. These generic names are all used in the following pages for seeds known to possess certain anatomical features; there are also included in the Cardiocarpales the genera Samaropsis, Cordaicarpus, and Rhabdocarpus, but it is proposed to limit their use to specimens which furnish no anatomical data and cannot therefore be assigned with equal confidence to a section of seeds based on definite morphological characters. It is certain that some at least of the seeds described under these names would, if preserved as petrified specimens, be included in one or other of the genera named above.

There is ample proof that some of these seeds were borne on Cordaitean plants and that the group as a whole represents the seeds of the Cordaitales[908]. It is, however, certain that some Platyspermic seeds were produced by Pteridosperms. No little confusion has been caused by the employment of the same generic names for petrified seeds and for casts and impressions affording no evidence as to similarity in anatomical characters. With a view to avoid the risks necessarily entailed by following this practice it is suggested that a clearer distinction should be drawn between genera based primarily on structural features and form-genera. The following notes on the genera Cardiocarpus, Cordaicarpus, Cyclocarpon, Cycadinocarpus, Jordania, and Samaropsis, may serve to illustrate some of the difficulties connected with the terminology of Palaeozoic seeds.

Cardiocarpus. Brongniart[909] proposed the name Cardiocarpon in 1828 for Upper Carboniferous seeds described as compressed lenticular, cordiform or reniform ‘fruits’ with an acute apex: in his later work[910] he recognised their true morphological nature and gave an account of some exceptionally well-preserved examples from Grand’ Croix. Brongniart in common with other authors believed Cardiocarpus seeds to belong to Cordaitean plants, a view that in several cases is based on conclusive evidence. The specimen represented in fig. 501, D, illustrates the characteristic form of a cast of a Cardiocarpus seed, and the sections shown in fig. 501, A and B, are from an identical or a very closely allied species. The generic characters are: (i) the presence of a narrow flattened border or wing surrounding a platyspermic nucule, (ii) the cordiform base and more or less pointed apex, (iii) the differentiation of the testa into a sarcotesta and sclerotesta free from the nucellus except at the base, (iv) the ‘tent-pole’ prolongation of the prothallus (fig. 510, A, b) and the presence of a fairly large pollen-chamber, pc, (v) the occurrence of two sets of vascular bundles, an inner nucellar series and two double vascular strands (fig. 500, A, v, B) which are given off from the main supply before it reaches the sclerotesta. The term Cardiocarpus as used by Brongniart signifies a type of seed possessing both certain anatomical and external characters. The proposal is to restrict the generic appellation to seeds exhibiting definite structural features agreeing in essentials with Cardiocarpus sclerotesta and C. drupaceus.

Cordaicarpus. This name was first employed by Geinitz[911] in the form Cordaicarpon, the type-species being C. Cordai (fig. 502, C) from the Coal Measures of Germany, a seed referred by the author of the genus to Cordaites principalis but, as Kidston has pointed out, there is evidence that this correlation may be incorrect: there is, however, no doubt as to its Cordaitean parentage. Specimens included in this genus agree closely with species of Cardiocarpus, but they are usually described as being distinguished by the absence of a flat border and by a more rounded and less cordate base. In the example of Cordaicarpus Cordai shown in fig. 502, C, and in other species assigned by authors to this genus there is a narrow border and the form of the base is an inconstant character. As Kidston[912] and other authors point out, there are no definite and constant characters by which to distinguish Cardiocarpus from Cordaicarpus as regards the form of the seeds preserved as casts or impressions. A further account of Cordaicarpus is given on a later page.

Cordaispermum. This designation was formerly adopted by Renault[913] for seeds having the form and anatomical features of Cardiocarpus which there is good reason for attributing to Cordaites or to some allied genus. In view of the fact that the majority of the seeds under consideration are undoubtedly Cordaitean there is no need to employ this additional generic name.

Cyclocarpon. Fiedler[914] instituted this term for seeds previously described by Berger as Cardiocarpon emarginatum (fig. 502, B, now included in Samaropsis) and added a new species Cyclocarpon nummularium. Brongniart[915] subsequently described the structure of two species, C. tenue and C. nummulare, which he referred to Fiedler’s genus, and Bertrand[916] has shown that these differ from the genus Cardiocarpus in the recurrent course of the bundles given off from the chalazal strand as in the genus Rhabdospermum (cf. fig. 501, E). There are no good grounds for retaining the designation Cyclocarpon for casts and impressions, as the specimens so named are indistinguishable from impressions referred to Cordaicarpus. The generic name Cyclocarpus, retained by Bertrand only for C. tenuis and C. nummularis simply for anatomical reasons, is now altered to Cyclospermum on the ground that the designation Cyclocarpon has been used for impressions affording no information with regard to anatomical features.

Cycadinocarpus. Renault[917] transferred to this genus Brongniart’s species Cardiocarpus augustodunensis on the ground that the vascular system exhibits in a greater degree than the other types included by Brongniart in Cardiocarpus a resemblance to that in recent cycadean seeds. Bertrand[918] confirms Renault’s account and retains Cycadinocarpus augustodunensis as a species worthy of generic distinction. A short account of this seed is given on a later page.

Jordania. This name was given by Fiedler[919] to compressed ovate-cordate seeds characterised by a broad membranous border bearing a superficial resemblance to the seeds of Bignonia. The type-species, J. bignoniodes (fig. 502, I), from the Coal Measures of Saarbrücken has the form usually associated with the designation Samaropsis, and as the latter term is generally adopted there are no adequate reasons for the retention of Jordania. The name Jordania has also been applied, by Schenk[920], to fossil Dicotyledonous wood and was previously used by Boissier[921].

Samaropsis. Goeppert[922] defined Samaropsis as ‘Fructus samaroideus membranaceus, compressus, margine alatus, monospermus.’ The type-species, S. ulmiformis, from the Permian of Brenau, is a small seed with a broad wing or border, but a better example of Samaropsis is figured by Goeppert as the wing of an insect[923]. Examples of the genus are shown in figs. 502, A–H; 503; 504. Seeds included in Samaropsis differ from those referred to Cordaicarpus in the presence of a broader and more clearly defined border which in some cases, as in the genus Mitrospermum (fig. 494, K, L), undoubtedly represents a lateral wing-like extension of the sarcotesta. In some instances the wing may be a tangentially expanded integument comparable with the perianth of Welwitschia, and in some Jurassic seeds referred by Heer[924] to Samaropsis the lateral appendages are probably true wings. It is advisable to restrict the designation Samaropsis to Palaeozoic seeds. Nucules deprived of the broad border would be referred to Cordaicarpus as usually employed for impressions. The generic name Samaropsis serves a useful purpose as a distinctive term for platyspermic seeds preserved as casts or impressions characterised by the possession of a wide border or wing broader than in typical examples of Cordaicarpus. The specimen represented in fig. 499 affords a good illustration of the difference between Samaropsis and Cordaicarpus. In this specimen the border clearly consists of two portions, an inner narrower border (black in the drawing) and an outer more delicate portion; the former is the impression of the sclerotesta and the outer represents the fleshy sarcotesta which in the living seed may have formed a wing. If, as often happens, the seed were preserved with the narrow border only it would be assigned to Cordaicarpus, many species of which are undoubtedly incomplete Samaropsis seeds.

The seeds described by Lindley and Hutton as Cardiocarpon acutum (fig. 444, p. 171) have been made by Arber[925] the type of a new genus Cornucarpus, the distinguishing feature being the triangular form and the apical horns of the wing. The seeds figured by Arber[926] from the Kent coalfield as Cornucarpus acutus are, however, not identical with the type of Lindley and Hutton, which has the characters of Samaropsis. Samaropsis is widely distributed in Permo-Carboniferous rocks in Europe and North America and is recorded also from India[927] (fig. 504), China[928], South Africa[929] (fig. 503), South America[930] (fig. 502, F, G) and Australia[931]. Some seeds of this form were certainly borne on Cordaitean plants (cf. fig. 480, A), but seeds of similar type have been found in organic connexion with the foliage of Pteridosperms (figs. 442, 445, pp. 167, 172). The Permian ‘cone-scales’ bearing seeds described by Geinitz as Cardiocarpon triangulare[932], represented by well preserved impressions in the Dresden Museum, appear to be of the Samaropsis type: the same author referred some Samaropsis seeds to the Conifer Walchia, but Weiss[933] dissents from this correlation as the seeds often occur in beds in which Walchia is not represented. Renault states that the seeds of the fertile shoot described by him as Cycadospadix Milleryensis[934] from Autun [= Strobilites Milleryensis (Ren.)] closely resemble Samaropsis fluitans Daws. as figured by Weiss. The suggestion by White[935] that Samaropsis seeds were borne on fertile leaves of Gangamopteris adds a further difficulty to the use of the generic characters of Samaropsis as criteria of systematic position. The Permian seeds figured by Goeppert[936] as Oreodoxites Martianus are possibly specimens of Samaropsis.

The designation Samaropsis, though usually restricted to Palaeozoic species, is applied by some authors to ‘winged’ seeds from Mesozoic strata; but as some of the Jurassic seeds[937] so named appear to have true wings like those of some recent Conifers it is advisable to adhere to the more limited use of the name.

It is safe to assert that many Samaropsis seeds agreed generally in structure with Cordaitean seeds such as the petrified examples described by Brongniart as Cardiocarpus. The species Mitrospermum compressum[938] is an example of a petrified seed having the external features of Samaropsis.

=Cardiocarpus.=

This generic title I propose to restrict to petrified seeds exhibiting the characters described by Brongniart[939] and more recently by Bertrand[940] in C. sclerotesta and C. drupaceus. In general organisation seeds of this generic type agree with those of recent Cycads and with the seed of Ginkgo biloba, but there are certain distinguishing features. An important character is afforded by the course and place of origin of the lower vascular strands from the main supply at the base of the seed. The outer vascular system consists of two bundles given off from the main strand, before it reaches the sclerotesta, which pass up the sarcotesta (fig. 500, B). In Rhabdospermum, on the other hand, the corresponding bundles arise at a higher level and form recurrent strands which penetrate the sclerotesta before passing up the fleshy part of the integument (cf. fig. 501, E).

Cardiocarpus sclerotesta Brongniart. The testa is differentiated into an inner shell and an outer sarcotesta (fig. 501, A; the sclerotesta is shown in black); there is a well developed pollen-chamber (pc) and below this the prothallus-tissue is prolonged as a blunt and short tent-pole, b, as in Gingko and in several fossil seeds. On each side of the apical tent-pole the slightly shrunken prothallus shows two small archegonia, a, which in the relatively small size and spherical form of the egg-cells resemble those of Ginkgo. In transverse section (fig. 501, B) the seed is bi-convex and at each end of the major axis the sclerotesta forms a small keel. There are two sets of vascular bundles concerned in the supply of material to the ovule; a lower pair of bundles given off from the central strand in the sarcotesta (fig. 500, B) which pass to the apical region in the inner tissues of the sarcotesta in the principal plane (fig. 500, A, v), and an inner set of bundles that pass up the peripheral tissue of the nucellus.

The species described by Brongniart as Cardiocarpus (Cyclocarpus) tenuis and C. nummularis have been removed by Bertrand[941] from Cardiocarpus on the ground that the integumental bundles pursue a course like that in Rhabdospermum; it is now referred to the new genus Cyclospermum[942].

=Cyclospermum.= Gen. nov. (= Cyclocarpus Bertrand).

As stated on a previous page Bertrand[943] re-establishes the generic name Cyclocarpus, founded on impressions without reference to anatomical characters, for two petrified seeds from St Étienne described by Brongniart as Cardiocarpus tenuis and Cyclocarpus nummularis[944]. These types differ from Rhabdospermum in the absence of an apical snout but agree with that genus in the steeply descending course of the vascular strands in the basal region of the seed. As stated on a previous page, the name Cyclospermum is proposed as a substitute for Cyclocarpus because of the employment of the latter term for impressions.

=Cycadinocarpus.= Schimper[945].

Cycadinocarpus augustudunensis (Brongniart[946]). In the possession of two sets of vascular bundles this type agrees with Cardiocarpus, but the more internal strands pass up on the inner face of the sclerotesta without penetrating into the nucellus, a feature in which Cycadinocarpus agrees with the majority of recent cycadean seeds: the outer bundles are given off from the main supply after it has entered the sclerotesta and not before as in Cardiocarpus; they follow an oblique course in the sclerotesta and emerge into the sarcotesta at the shoulders of the basal curve of the seed. As in Cardiocarpus and Rhabdospermum the two outer bundles lie in the principal plane of the seed. There is a pollen-chamber at the apex of the nucellus and the latter tissue is prolonged as a tent-pole which engages with the micropyle. In the absence of data as to the course of the vascular bundles in the chalazal region it would not be possible to distinguish between this genus and Cardiocarpus.

=Rhabdocarpus= Berger and =Rhabdospermum= gen. nov.

It is proposed to restrict the name Rhabdocarpus[947] to impressions and casts of seeds of the type represented by R. tunicatus as figured by Berger[948] and reproduced in fig. 506, K, the term Rhabdospermum being applied to seeds of similar form in which are shown certain distinguishing anatomical features. Rhabdocarpus tunicatus Berger is a species founded on a specimen from the Coal Measures of Silesia characterised by an outer carbonised testa prolonged apically as a blunt snout and, as seen in fig. 506, K, covering an apparently ribbed nucule, but the ‘ribs’ are due to the presence of fibrous strands and are not ribs in the ordinary sense. The outer tissue shows numerous longitudinal striations due presumably to the presence of fibrous elements in the sarcotesta like those shown in the petrified seed represented in fig. 501, C. The genus is defined by Berger as follows: ‘Semina ovata vel elliptico-oblonga secundum longitudinem parallele nervosa vel tenuissime striata, putamine (interdum deficiente) instructa.’ As used by Berger and many other authors Rhabdocarpus includes a miscellaneous collection of seeds often differing widely from the type-species. Many of the examples correctly referred to Berger’s genus are platyspermic though a bilateral symmetry is by no means always clear. Renault and Zeiller[949] in their definition of Rhabdocarpus include bilateral symmetry as a characteristic feature and speak of the seeds as oblong or oval with a pointed or truncate apex and a rounded base. Impressions of Rhabdocarpus differ from those of Cardiocarpus or Cordaicarpus in their more elongate form, always longer than broad, and in the absence of a basal sinus. The seeds found attached to Neuropteris pinnae and, in external features, agreeing with many specimens included in Berger’s genus, have been transferred by P. Bertrand[950] and Arber[951] to a new genus Neurospermum[952]. Arber[953] in his recent revision of British seeds proposes to restrict the name Rhabdocarpus to platyspermic seeds having a ‘large unsymmetrical nucule enclosed in a large unsymmetrical wing or sarcotesta,’ that is to forms symmetrical in one plane. In this category he includes Rhabdocarpus tunicatus Berg. (fig. 506, K) and R. subtunicatus[954] Grand’Eury, but it is not clear on what grounds Berger’s species is spoken of as symmetrical in only one plane: in the species R. Lilleanus Arb.[955] the symmetry is hardly sufficiently well defined to rank as a generic character. In the case of the Neuropteris seeds the apical snout is slightly curved, thus giving them an unsymmetrical appearance (cf. fig. 422, p. 114). The Carboniferous and Permian seeds usually referred to Rhabdocarpus are transferred by Arber to his genus Platyspermum[956], a designation for which it is proposed to substitute Nathorst’s genus Holcospermum[957]. In seeds preserved as more or less flattened impressions it is practically impossible in many cases accurately to determine the symmetry: as fig. 506, A, shows, casts indistinguishable from some examples of Platyspermum are radially symmetrical. Brongniart[958] extended the original definition of Rhabdocarpus to include certain anatomical characters, and these have been more fully defined by Bertrand[959]. It is for seeds showing these anatomical features that the name Rhabdospermum is now proposed. This course is followed on the ground that it is advisable to avoid confusion between petrified specimens and impressions which in spite of superficial resemblance may not be closely related. In some cases it is practically certain that an impression of the Rhabdocarpus type is generically identical with a seed of similar form showing the anatomical structure of Rhabdospermum, but unless identity is established a distinct terminology is preferable. The use of the generic name Rhabdospermum carries with it an implication of platyspermy, but under Rhabdocarpus may be included seeds which are radiospermic and platyspermic. Some seeds agreeing with Rhabdospermum are referred by Grand’Eury[960] to Poroxylon, and it is probable that Rhabdospermum like Cardiocarpus is a Cordaitean seed. On the other hand Rhabdocarpus may well include species, apart from those transferred to Neurospermum, that belong to Pteridosperms. A species, Rhabdocarpus Oliveri, recently described by Kidston[961] from the Staffordshire coalfield is an example of a radiospermic seed which may be assigned to a Pteridosperm. The type-specimen is an ovate seed 4 cm. long and 2 cm. broad agreeing in form and surface-features with Rhabdocarpus as already defined, but the evidence it affords of internal structure is insufficient to determine its position with regard to genera founded on anatomical characters. Other examples of Rhabdocarpus are described by Lesquereux[962] and White[963] from American Coal Measures, by Grand’Eury[964] from the Loire, by Renault[965] from Autun, and by many other authors.

=Rhabdospermum.= Gen. nov.

The platyspermic seeds included in this genus agree in size and form with impressions assigned to Rhabdocarpus and as regards the main features conform anatomically to Cardiocarpus; they were probably borne on Cordaitean plants. Fig. 501, C, represents a longitudinal section of the species Rhabdospermum cyclocaryon described by Brongniart as Rhabdocarpus cyclocaryon: the sarcotesta is particularly well developed in the apical region; at the apex a portion of the micropyle is seen at m and near the nucellus are pieces of the sclerotesta shown in black. The presence of anastomosing fibres near the surface is a characteristic feature: these, as Bertrand points out, do not form a hypodermal tissue in the strict sense as they may be separated by some of the thin-walled parenchyma of the sarcotesta from the epidermis. The sclerotesta is only partially preserved but the inner portion forms a dark line enclosing the nucellus, the superficial tissue of which is separated from the shrunken prothallus represented by the almost spherical dotted region: the remains of an archegonium are seen at a (fig. 501, C) and the characteristic tent-pole apex of the prothallus is shown at b. While in shape and in the general plan of organisation Rhabdospermum agrees with Cardiocarpus, the vascular system in the chalazal region constitutes a distinguishing feature. In Rhabdospermum the main vascular strand passes through the sclerotesta, e, e′, fig. 501, E, before giving off two bundles which bend back (‘faisceaux récurrents’), traverse the shell, and then pass up the sarcotesta in correspondence with the feebly developed lateral keels as far as the micropyle, while in Cardiocarpus (fig. 500, B) the bundles are given off before the main strand reaches the sclerotesta. Similar recurrent bundles occur also in Mitrospermum (fig. 494, K)[967].

=Mitrospermum.= A. Arber.

Mitrospermum compressum (Williamson). Mrs Arber[968] proposed the name Mitrospermum[969], suggested by the peculiar form of the seed-base, as a substitute for Cardiocarpon for Williamson’s species C. compressum[970] from the Lower Coal Measures of Lancashire. The seed is platyspermic and there is some evidence that it split into two valves along the principal plane (the longer axis of the section, fig. 494, L). The diagrammatic and partially restored longitudinal section reproduced in fig. 494, K, shows the main features: a sarcotesta, sa, covers the surface of the testa as a thin layer except at the edges of the flattened sides where it forms a wing-like border; preserved as an impression the seed would be assigned to Samaropsis. The sclerotesta, sc, has a pointed apex which surrounds the lower third of the micropyle and a broad base perforated by the chalazal vascular strand. There was probably a narrow inner flesh as in Trigonocarpus and recent Cycadean seeds (fig. 494, K, cf). The nucellus was free from the integument except at the base, as in Trigonocarpus and Stephanospermum (fig. 494, K, n): internal to the shrivelled remains of the inner flesh there was a nucellar tapetum surrounding the megaspore. Details as to the pollen-chamber are lacking though there are indications that it resembled that of some species of Cordaitean seeds. The main vascular supply passes through the sclerotesta and then forms a low cushion of short reticulate elements below the base of the nucellus from which two bundles are given off (fig. 494, K, v) in the principal plane. The course of the bundles which pierce the sclerotesta led Mrs Arber to remove this seed from Cardiocarpus, as recently defined by Bertrand[971], since in that genus the integumental bundles have their origin below the sclerotesta. In the course of the vascular bundles Mitrospermum is intermediate between Rhabdospermum and Taxospermum.

This genus is founded on a detached seed, but its resemblance to undoubted Cordaitean species favours its attribution to that group though, as Mrs Arber points out, some markedly platyspermic seeds are known to have been borne on fern-like fronds and Mitrospermum may belong to some genus of Pteridosperms.

=Diplotesta.= Brongniart.

Diplotesta Grand’Euryana Brongniart. The generic name Diplotesta, suggested by Grand’Eury, was given by Brongniart[972] to a Grand’ Croix seed which he compared with that of the Conifer Cephalotaxus. The type-specimen is elliptical and platyspermic (fig. 495, H, p. 322), and differs from Taxospermum in the cordate form of the seed-cavity, also in the more restricted union of nucellus and testa. The testa is differentiated into a sarcotesta (sa) and sclerotesta, and the latter forms two feebly developed keels in the principal plane: a characteristic feature shared with Mitrospermum is the splitting of the shell into two equal valves (fig. 495, F). Fig. 495, H, shows the contracted cylindrical nucellus and the pollen-chamber: the sarcotesta (sa) is only partially preserved. Diplotesta differs from Cardiocarpus in the course of the integumental vascular bundles which are of the type illustrated by Rhabdospermum, Taxospermum, and Cyclocarpus, but from these genera it is distinguished by the dehiscence of the shell, also by its form and certain anatomical features as described by Brongniart and Bertrand[973].

In this genus Bertrand includes Brongniart’s species Sarcotaxus avellana (fig. 495, F), a correlation suggested by the latter author.

=Leptocaryon.= Brongniart.

Brongniart[974] founded this genus for a single species, Leptocaryon avellana, represented by a Grand’ Croix specimen 12 × 10 mm., which he believed to be related to Taxus. Leptocaryon differs from Taxospermum in the structure of the testa, but resembles it in external features. Bertrand[975] in his revision and extension of Brongniart’s account says that the sections throw no light on the nature of the vascular supply, and it is therefore impossible to form a satisfactory opinion as to the relationships of the genus. Renault[976] referred this genus to the Cordaitales, but we have no evidence as to the parent-plant.

=Taxospermum.= Brongniart.

Brongniart[977] gave this name to a small elliptical seed, 15×9 mm., recalling in external features the seed of Taxus, a genus to which he believed the Grand’ Croix species to be related. The type-species Taxospermum Grüneri (fig. 495, G) has a comparatively thin testa characterised by the absence of a sub-chalazal pad formed by the swelling of the sclerotesta. The nucellus is attached by a broad base to the testa and the two regions appear to be connected for a short distance on the flanks[978]; in this feature the seed is comparable with that of the Conifer Torreya and differs from the other platysperms, Diplotesta, Rhabdospermum, etc. Bertrand[979] states that the main vascular strand extends from the hilum to the chalaza before giving off the two opposite bundles which ‘follow the floor of the shell-cavity, and on reaching the flanks traverse the shell obliquely from below upwards[980].’ In the course and position of the integumental bundles Taxospermum differs from Cardiocarpus, Cycadinocarpus, and Rhabdospermum. In this genus Bertrand includes Sarcotaxus angulosus Brongn. and S. olivaeformis Brongn.[981]

=Compsotesta.= Bertrand ex Brongniart +MS.+

Compsotesta Brongniarti Bertrand. The generic name Compsotesta[982], though adopted by Brongniart for some incomplete specimens from Grand’ Croix, was not published either by him or Renault: it has recently been revived by Bertrand[983] in his account of the anatomical details of Brongniart’s sections. This seed appears to be closely allied to the polypterous forms Ptychotesta and Hexapterospermum: the testa consists of a sarcotesta differentiated into two zones the outer of which contains vascular bundles in correspondence with the ribs, and an inner shell. There is a nucellar vascular supply and the nucellus is free on the flanks as in Stephanospermum and Trigonocarpus.

=Samaropsis.= Goeppert.

The characters of this Permian and Carboniferous genus have already been described: the name has reference only to superficial features especially the samara-like ‘wing,’ and connotes no special anatomical features.

Samaropsis fluitans (Dawson). The species described by Dawson[984] as Cardiocarpum fluitans from Carboniferous strata in Nova Scotia, is represented by oval seeds with a fairly broad border usually showing an apical notch. Fig. 502, A, is a copy of Dawson’s figure: the apparent absence of an apical sinus in the ‘wing’ is probably due either to an error in interpretation or to some imperfection in the specimen. As fig. 502, A, shows, the type-specimens are far from satisfactory, and it may be that they are not specifically identical with the more complete specimens from European strata referred to Dawson’s species. Zeiller[985] points out that seeds of this species vary considerably in size, but there is always in well-preserved examples a bifid beak at the apex. Seeds of similar form though not specifically identical are described from the Coal Measures of Missouri as Cardiocarpon (Samaropsis) Branneri Fairch. and White[986]. Good examples of S. fluitans are figured by Weiss[987] from the Coal Measures of Saarbrücken and the species is widely distributed in Upper Carboniferous beds generally.

Samaropsis bicaudata Kidston. This species (fig. 502, E) originally described[988] from Lower Carboniferous rocks in Scotland as Cardiocarpus bicaudata and subsequently assigned to Samaropsis, is characterised by a greater development of the flat wing-like border which is divided into two long tapering basal lobes. Seeds of similar form are figured by Lesquereux[989] from Pennsylvania as Cardiocarpus (Ptilocarpus) bicornutus.

Samaropsis (Samarospermum) moravica (Helmhacher). This type[990] (fig. 502, H) is characterised by the great length of the wing-like border and on that account it was transferred by Arber to a new genus. It was originally described by Helmhacher from the Permian of Moravia as Jordania moravica and the type-specimen has been refigured by Zeiller[991] who records the species from Upper Carboniferous and Permian rocks in France: it is recorded also from several localities in Germany[992]. Seeds figured by Potonié[993] from the Permian of Thuringia as Samaropsis Crampii (Hartt) are undoubtedly examples of S. moravica: the true S. Crampii has recently been well illustrated by Dr Stopes[994] from the Westphalian of New Brunswick. The species is recorded by Arber[995] from the Kent coalfield.

Samaropsis emarginata (Goeppert and Barger).

The seed represented in fig. 502, B, from the Lower Coal Measures of Kilmarnock, Scotland[996], affords a good example of the genus: the species was originally described by Berger as Cardiocarpon emarginatum and it was on this type that Fiedler founded the genus Cyclocarpon[997]. It has been referred by many authors to Cardiocarpon and might be regarded as a type intermediate between Cordaicarpus, as used in this chapter, and Samaropsis, though the breadth of the border is more in keeping with the latter designation. The figured specimen is 1·6 cm. long and 1·4 cm. broad; the nucule has a slightly cordate base and shows several faint converging ribs which are too inconspicuous to be represented in a natural-size drawing. A narrow median groove in the apical region shows the position of a vascular strand. The species is recorded from several countries: similar though specifically distinct seeds, described by Dawson as Cardiocarpon cornutum, have recently been re-described by Dr Stopes[998] from the Westphalian of New Brunswick where they occur in association with the leaves of Cordaites Robbii Daws.

Samaropsis Newberryi Andrews.

This species was originally described by Andrews[999] from the Coal Measures of Ohio: the specimen shown in fig. 502, K, was sent to Dr Kidston by Mr Claypole. The whole seed is 5 cm. wide and 3·5 cm. in depth; it is characterised by a short and relatively broad nucule surrounded by a very broad and flat border showing faintly marked radially disposed lines and in places some irregularly distributed pits. The apex is emarginate and there is a broad and deep sinus in the sarcotesta in the chalazal region. The seed resembles Samaropsis alata Kidst.[1000] and S. Baileyi (Daws.)[1001] but it differs from these in the greater breadth of the ‘wing’ and in the form of the nucule.

The seed described by Fiedler[1002] as Jordania bignonioides (fig. 502, I) agrees closely with S. alata Kidst. but is probably specifically distinct.

Samaropsis barcellosa (White).

White[1003] described this species (fig. 502, G) from Permo-Carboniferous rocks in Brazil (Rio Grande do Sul) as Cardiocarpon barcellosum. The nucule is said to be cordate but, as seen in the figure, there is no clear indication of a basal sinus: the presence of a relatively broad ‘wing,’ as White says, entitles the seed ‘to a place in the Samaropsis section of the genus.’ The author of the species compares it with seeds described from Westphalian rocks in Ohio[1004] and Pennsylvania[1005]. It is interesting to find a type which is common in both Europe and North America in the western portion of Gondwana Land. Seeds of similar form are recorded also from India, South Africa, and Australia[1006].

Samaropsis Seixasi (White).

This Brazilian species from the same beds is described by White as Gangamopteris (Samaropsis) Seixasi[1007]: it is characterised by a small ovate nucule 8–10 mm. long and 5 mm. broad, in some specimens surrounded by a complete ‘wing’ extending above the apex and below the base, giving the seed an appearance similar to that of Samaropsis (Samarospermum) moravica while sometimes, as in the example shown in fig. 502, F, the broad border is preserved only at the sides. These seeds are abundant in the Santa Catharina beds, where they were discovered by Dr Esdras do Prado Seixas, in association with leaves of Gangamopteris, and White thinks that they were borne on the fertile leaves of that genus which he has named Arberia[1008]. Although there is as yet no proof of a connexion between Gangamopteris and seeds of this or any other type it is almost certain that it was a seed-producing plant.

Samaropsis Leslii sp. nov.

The seed on which this species is founded was discovered by Mr T. N. Leslie in the Ecca beds (Permo-Carboniferous) of Vereeniging, South Africa, a locality from which the same geologist has obtained leaves of Cordaites, Psygmophyllum, Glossopteris and other genera[1009]. In the slightly cordate base and tapered apex (fig. 503) the nucule agrees closely with those of European examples, but the Vereeniging type is distinguished by its larger dimensions and by the wider border indicating a thick sarcotesta continued basally into a stout stalk. The apex is emarginate and a median rib marks the position of a vascular strand. There is no evidence as to the nature of the parent-plant.

Samaropsis indica (Zeiller).

Prof. Zeiller[1010] described this species as Cardiocarpus indicus from the Karharbari (Lower Gondwana) beds of India. An examination of the type-specimens enables me to confirm the accuracy of the original account. The platyspermic seed is 5·5 cm. long and 4·5 cm. broad; a cordate nucule is enclosed by a flat border similar to that of Samaropsis Leslii but narrower especially on the sides of the nucule. At the apex there is a deep sinus extending to the nucule, and at the base a fairly broad band of carbonaceous matter shows the position of the chalazal vascular strand. The seed is characterised by its large size and by its almost orbicular form: it occurs as a detached specimen in beds containing Cordaites (Noeggerathiopsis) and Glossopteris.

A species from Arkansas described by Lesquereux[1011] as Cardiocarpus ingens [= Cordaicarpus ingens (Lesq.)] affords another example of a large seed similar to C. indicus and, except in its more orbicular form, to Samaropsis Leslii.

Samaropsis Milleri (Feistmantel).

An examination of the type-specimen from the Calcutta Museum enables me to amplify the original description in an important particular. The species was found in Lower Gondwana (Katharbari) beds in India and referred by Feistmantel[1012] to the genus Carpolithes. Arber[1013], who tentatively employed the generic name Cardiocarpus in place of Carpolithes, suggests that the seeds may be radiospermic, as Feistmantel’s drawings show only a very narrow border to the nucule. The specimen reproduced in fig. 504 was figured by Feistmantel without any indication of a definite sarcotesta or wing, but as seen in the drawing the ovate cordate sclerotesta is surrounded on one side and at the base by an outer envelope: this is clearly seen at the apex where it shows a rounded termination sloping downwards towards the micropyle precisely as in Samaropsis indica (Zeill.). The border is narrow at the sides and broader at the base as in S. Leslii. The seed is 4·5 cm. long and 2·3 cm. broad, differing from S. indica in its rather smaller size and in the slightly narrower nucule. Though there is no decisive evidence as to the parent-plant the occurrence of a specimen of this species partially covered by a scale-leaf of a type[1014] very similar to that which is generally recognised as belonging to Glossopteris suggests the possibility that the seeds may belong to that genus. Scale-leaves of Glossopteris are described in Volume +ii.+, but it may be added here that leaves similar in form to those from India, Australia, and elsewhere are figured by Geinitz[1015] from the Altai Mountains as Trigonocarpus? actaeonelloides: the specimens are represented with the basal scar at the apex.

=Cordaicarpus.= Geinitz.

In view of the fact that the generic names Cardiocarpus, Cordaicarpus, and other designations have been applied to casts and impressions which cannot be distinguished by any constant or important feature it is proposed to adopt the name Cordaicarpus for platyspermic seeds, preserved as casts or impressions, having a comparatively narrow border enclosing an ovate or cordate-ovate nucule; the base is either rounded or cordate. The choice between Cordaicarpus and Samaropsis depends on the breadth of the border. Cordaicarpus, though more suggestive of a Cordaitean alliance, may in some cases be a Pteridosperm seed.

Cordaicarpus Cordai (Geinitz). Lenticular seeds more or less orbicular or broadly ovate (fig. 502, C, D), often slightly cordate at the base of the nucule and with a broadly acute apex: the border is narrow or sometimes hardly represented as in the seeds described by Berger as Rhabdocarpus ovoides, a species similar to but more oval than Cordaicarpus Cordai. The latter species[1016] occurs in several coalfields in Britain, France, Germany, and elsewhere. Fig. 502, C, shows a good example from the Middle Coal Measures of Yorkshire, 9 mm. long by 8 mm. broad; on the very slightly cordate nucule are several faint ribs converging towards the base and apex and between them fine striations, characters too indistinct to be reproduced in the natural-size drawing. The flat border represents the sclerotesta. The seed shown in fig. 502, D, from the Westphalian series of Warwickshire belongs to the same species or is a closely allied type: the faint suggestion of reticulation on its surface might be regarded as a reason for referring it to C. areolatus Boul.[1017], a form characterised by a reticulation on the testa, described by Zeiller[1018] and other authors. This reticulation is, however, in some cases at least, formed by crumpling and splitting of the superficial carbonised film into more or less regular meshes: the figured specimen occurs with several other seeds of the same type, most of which have a smooth surface. Dr Kidston tells me that a recent critical examination of seeds in his collection leads him to regard some specimens (e.g. fig. 502, D) previously referred by him to C. Cordai as identical with Carpolithes membranaceus Goepp.[1019]

The photograph reproduced in fig. 505 shows the result of chemically treating the carbonised cuticle of a seed of Cordaicarpus Cordai, a method little used as yet in the case of Palaeozoic plants but which may be useful in distinguishing seeds which cannot be satisfactorily separated by microscopic features. The superficial cells have very thick walls and present an appearance similar to that of the sclerous cells in the testas of some petrified specimens.

The larger seed shown in fig. 501, D, from Commentry, described by Renault and Zeiller[1020] as Cardiocarpus sclerotesta, is another example of Cordaicarpus as now defined.

IV. +Miscellaneous Seeds.+

In this section are included genera based on characters of comparatively little morphological importance; their claim to treatment under a common heading is that we know little or nothing of their anatomical features or of the parent-plants.

i. Ribbed seeds.

The seeds represented by the following genera possess ribs or flanges usually in multiples of three; the transverse section may be triangular, hexagonal, or polygonal. The symmetry is generally radial, but it is difficult to determine whether a slight departure from the radiospermic form is an original feature or the result of pressure. Some of the ribbed seeds with which we are now concerned are no doubt closely allied to Trigonocarpus and should be included in the Trigonocarpales, but others may well be distinct forms.

Genera: Hexagonocarpus, Decagonocarpus, Polypterocarpus, Rhynchogonium, Boroviczia, Diplopterotesta, Musocarpus, Holcospermum.

=Hexagonocarpus.= Renault.

This generic name is adopted by Renault[1021] for casts from Commentry which, while probably identical with Brongniart’s Hexapterospermum, afford no confirmatory anatomical evidence. The species Hexagonocarpus crassus[1022] is represented by casts or nucules characterised by six well-defined ribs and grooves with a length of nearly 3 cm. In this genus may be included the cast from the Coal Measures of Lancashire described by Williamson[1023] as Hexapterospermum Noeggerathi (fig. 506, H), and another British example is afforded by Hexagonocarpus Hookeri Kidst.[1024], a rare fossil in the South Staffordshire coalfield. It is impossible confidently to assign these ribbed casts to genera founded on petrified specimens as they almost certainly belong to different types, but the employment of the name Hexagonocarpus may conveniently be used for casts or impressions of seeds with six longitudinal ribs differing in their relatively broader and less prominent form from the wing-like flanges of Polypterocarpus (cf. fig. 496, B). The seeds described by Dr P. Bertrand[1025] as Hexapterospermum modestae, and believed by him to belong to a plant with Neuropteris fronds, should be included in Hexagonocarpus as we have no definite knowledge of their anatomical features.

=Decagonocarpus.= Renault.

This name, proposed by Renault[1026], is applied to seeds without petrified tissues characterised by ten ribs; an example is afforded by Decagonocarpus olivaeformis from the Commentry coalfield, an elliptical seed which bears a close resemblance to Holcospermum sulcatum (fig. 506, A) except in the smaller number of ribs.

=Polypterocarpus.= Grand’Eury.

Grand’Eury[1027] adopted this generic name for seeds from St Étienne characterised by the presence of three, six, or more deep wings or flanges. The term Pterospermum has recently been proposed by Arber[1028] for a seed from the Coal Measures of Staffordshire, which he names P. anglicum: the type-species of the genus has three deep wings, one from each angle. For the same seed Kidston[1029] proposed the name Tripterospermum ellipticum, but as Arber’s account was published first his specific name has priority. Pterospermum had, however, been previously used for a genus of Sterculiaceae, and partly on this account but mainly because Grand’Eury’s genus Polypterocarpus is available the latter designation is adopted. In Polypterocarpus anglicus (fig. 496, B) the flanges project slightly beyond the apex of the seed and there is a small notch at the base; the nucule is 5 cm. long and 1 cm. broad. While it is not improbable that this seed is generically identical with Brongniart’s Tripterospermum[1030], it is safer, in the absence of structural details, to employ the less committal term. There is no information with regard to the nature of the parent-plants of species of Polypterocarpus. The English seed from the Middle Coal Measures of Derbyshire and the Staffordshire coalfield described by Arber[1031] as Radiospermum ornatum and by Kidston[1032] as Polypterospermum ornatum affords another example of Polypterocarpus as the generic name is here employed.

=Rhynchogonium.= Heer.

Heer[1033] proposed this generic name for some globose, ovate, or oblong ‘fruits’ from Lower Carboniferous strata in Spitzbergen, including also fragments of ‘leaves’ which without satisfactory evidence he believed to belong to the same plant. The supposed fruits are clearly seeds, and Nathorst regards the ‘leaves’ as portions of a Fern rachis. Heer described four species, but these have since been reduced to two, and indeed it is probable that only one type, Rhynchogonium costatum, is represented. Nathorst[1034] compares Heer’s seeds with a Lower Carboniferous species described by Young[1035] as Trigonocarpum gloagianum, the resemblance of which to the Spitzbergen seeds was pointed out by Kidston. A seed of Rhynchogonium costatum is about the size of a hazel-nut and may reach a length of 21 mm.; it is ovate, with a broad rounded base, and in the upper third is tapered and conical, the sides of the characteristic snout being distinguished from the smooth surface of the rest of the seed by the presence of eight ribs converging towards the apex (506, G). Zalessky[1036] recorded closely allied seeds from Lower Carboniferous beds in Northern Russia, assigning them to a new genus Boroviczia, the type-species being B. Karpinskii; he adduced arguments in favour of Heer’s interpretation of the fossils as fruits but, according to Nathorst, this view has been abandoned. In his recent memoir on the Culm flora of Spitzbergen Nathorst[1037] discusses the morphological nature of Rhynchogonium seeds and describes additional specimens. Without the aid of petrified examples it is hardly possible to determine the true nature of the fossils.

Some specimens of Rhynchogonium sulcatum in Dr Kidston’s collection show the original surface-features: the carbonised integument is divided in the upper region into linear lobes separated from one another at their origin by fairly wide sinuses, a type of integument suggesting comparison with Physostoma. This species was originally described by Lindley and Hutton as Carpolithes sulcata[1038] from Lower Carboniferous rocks at Newhaven in Scotland and has recently been figured by Zalessky[1039] from specimens in the Kidston collection from the Lower Calciferous sandstone of Midlothian. Nothing definite can be said as to the parent-plant, but it is significant that in Midlothian Rhynchogonium sulcatum occurs in a bed full of isolated pinnules of a Cardiopteris almost to the exclusion of any other fossils[1040].

The seed figured by Nathorst[1041] from the Culm of Spitzbergen as Lagenospermum? glandiforme agrees closely with Rhynchogonium and Boroviczia, and it is impossible to decide whether the lobed appearance is due to the presence of a cupule or to the divisions of an integument.

=Boroviczia.= Zalessky.

The specimens from Lower Carboniferous beds in Russia[1042] on which this genus was founded are perhaps unnecessarily separated from Rhynchogonium; they are ovate and beaked, 10 mm. long with a maximum breadth of 6 mm. The type-species, Boroviczia Karpinskii (fig. 506, I), is represented both by specimens in which the cast is complete and by others in which the apical snout of the integument is split into separate lobes identical in form and apparently in number with those of Rhynchogonium. Nathorst[1043], who retains the generic name and describes two additional species from Spitzbergen, points out that in Boroviczia the tapered apex is more sharply differentiated from the broader basal portion, a difference hardly worthy of generic recognition. If Boroviczia is retained as a genus distinct from Rhynchogonium it should include the seeds described by Young as Trigonocarpum gloagianum.

=Diplopterotesta.= Nathorst.

Diplopterotesta spitzbergensis (Heer). Heer[1044] included in Samaropsis some seeds, described as Samaropsis spitzbergensis, from Lower Carboniferous strata in Spitzbergen which differ considerably from typical examples of the genus. These have recently been made the type of a new genus Diplopterotesta[1045]: they are platyspermic seeds nearly twice as long as broad, 6–9 × 3·5–5 mm., characterised by a thin sclerotesta expanded throughout the length of the seed into two prominent transversely striated wing-like ribs or flanges (fig. 506, D). At the apex, which is broad in contrast to the pointed basal end of the seed, the sclerotesta forms a crown of eight lobes about the flat summit of the seed-body. As Nathorst points out, this species closely resembles the Carboniferous seeds figured by Grand’Eury[1046] as Polypterocarpus, but in the latter type there are more than two wings. Nathorst’s figures, one of which is reproduced in fig. 506, D, suggest a difficulty in determining the number of the flanges, which would seem to be more than two, but this appearance is regarded by Nathorst as misleading and he believes that except at the apex there are only two wings.

=Musocarpus.= Brongniart.

Brongniart[1047] proposed this name for two species, M. prismaticus and M. difformis, from French Coal Measures, but gave no description of the specimens. The type-species, described from the Loire by Grand’Eury as Musocarpus prismaticus[1048], is an ovate seed nearly 3 cm. long with six longitudinal ribs, three being more prominent than the others, and characterised by a ribbed prolongation of the base of uniform diameter spoken of as a carpophore, which was apparently articulated to the lower part of the seed-proper from which it was easily detached by a natural absciss-layer. Nothing is known of the structure or of the affinity of the genus. Some specimens in Dr Kidston’s collection from Westphalian beds in Lanarkshire are closely allied to or perhaps identical with M. prismaticus. In the presence of a distinct basal region Musocarpus resembles Codonospermum[1049], though without any knowledge of the anatomy of the former type it is impossible to say whether or not this resemblance has any morphological importance.

=Holcospermum.= Nathorst.

Holcospermum sulcatum (Sternberg). The cast reproduced in fig. 506, A, affords a good example of a form of seed recorded under several generic names and not uncommon in Upper Palaeozoic rocks in Europe and North America, which in most cases cannot be assigned to a genus implying the possession of certain anatomical characters. This type was figured by Sternberg[1050] from the Coal Measures of Radnitz as Carpolites sulcatus. Some ‘fruits’ collected on the beach near Newhaven, Midlothian, from the Calciferous Sandstone series, are figured by Lindley and Hutton[1051] as Carpolithes sulcata, but as already stated these have been transferred[1052] to the genus Rhynchogonium. Several authors have referred specimens of the type now included in Holcospermum to Rhabdocarpus, but that genus, as stated on a previous page, is restricted to seeds agreeing in form with R. tunicatus. Renault[1053] instituted the genus Colpospermum for a partially petrified seed from Commentry agreeing externally with Carpolites sulcatus Sternb. and regarded by him as specifically identical, characterised by longitudinal ribs which represent folds of the testa, the intervening grooves being occupied by an irregular reticulum formed by occasionally anastomosing smaller ribs. The generic name Colpospermum should therefore be reserved for ribbed seeds showing the anatomical features described by Renault and Zeiller: its application to Sternberg’s species is inadvisable on the ground that we have no information with regard to the morphological nature of the ribbing. More recently Arber[1054] has proposed the name Platyspermum, a name previously applied to a Cruciferous plant, for Stephanian and Permian seeds formerly assigned to Berger’s genus Rhabdocarpus, which are symmetrical in two planes. In this genus he includes Platyspermum sulcatum and among other species P. Kidstoni founded on a seed originally identified by Kidston[1055] as Rhabdocarpus multistriatus Sternb. which, though probably a distinct species, is of the same general type as C. sulcatus Sternb.

The cast represented in fig. 506, A, from the Middle Coal Measures of Yorkshire is 3·5 cm. long and has 18 regular longitudinal ribs: it is radially symmetrical and does not conform in this respect to Arber’s definition of Platyspermum. In many cases, e.g. the flattened seed figured by Kidston as Rhabdocarpus multistriatus, it is impossible to determine the symmetry of the seed. The old generic name Carpolites, Carpolithes or Carpolithus has been used in a very wide sense and does not connote any well-defined features; it should be reserved, in the form Carpolithus as used by Linnaeus, for seeds that cannot be assigned to a systematic position or which do not exhibit any distinctive characters worthy of emphasis by the institution of a special name. The generic term Holcospermum, recently proposed by Nathorst[1056], is a suitable name for this type of seed; as defined by the author, it includes seeds that may be radiospermic or platyspermic. Specimens of the type-species, H. dubium[1057],from the Lower Carboniferous beds of Spitzbergen, agree closely in size and shape with some examples of Rhynchogonium and Boroviczia, but they are distinguished by prominent ribs extending the whole length of the cast. In some seeds similar to H. sulcatum the ribs form sharp ridges, but the difference between rounded and sharp ridges is often determined by the method of preservation: a specimen deprived of its outer flesh would form a cast more sharply ribbed than a seed in which the sarcotesta had been moulded on to the ribbed sclerotesta. On the other hand some ribs are formed by blunt sclerotestal folds as in Colpospermum: both types of ribbing are included in the genus Holcospermum.

ii. Other Genera.

=Malacotesta.= Williamson.

This generic name was instituted by Williamson[1058] for a petrified seed from the Coal Measures of Lancashire which he named Malacotesta oblonga: the type-specimen is a small seed 6–7 mm. long characterised by a thick fleshy integument. The structure is however insufficiently known to admit of a satisfactory comparison of the imperfectly preserved specimen figured by Williamson with other types.

=Thysanotesta.= Nathorst.

Nathorst[1059] founded this genus on a single seed from the Lower Carboniferous plant-beds of Spitzbergen which exhibits features sufficiently distinctive to justify its recognition as the type of a separate genus.

Thysanotesta sagittula Nathorst. The type-specimen is a long and narrow seed, 20 mm. long, ovate below and prolonged apically into a slender beak, 8 mm. in length, which probably represents a micropylar tube; the beak bears numerous stiff hairs (fig. 506, F). The seed closely resembles a carpel of Erodium without the horizontal part of the awn. There is no evidence as to the nature of the parent-plant but the species affords an interesting example of a Palaeozoic seed apparently adapted for wind-dispersal, or possibly the bristles may have served the same purpose as in the fruits of Erodium. Attention is called elsewhere[1060] to the frequent resemblance of Palaeozoic seeds such as Thysanotesta to fruits of recent flowering plants.

=Carpolithus.= Linnaeus.

Nathorst[1061] has pointed out that this generic name was employed by Linnaeus for fossil fruits: in the form Carpolites (Sternberg) or Carpolithes[1062] it has been widely used and differently defined by authors, usually in a comprehensive sense including fossil seeds from both Palaeozoic and Mesozoic strata which cannot be assigned to a definite position in the plant-kingdom. It is desirable to adopt some designation for seeds from strata of different ages which do not exhibit any features sufficiently distinctive to justify the creation of a special genus. By employing such a name as Carpolithus, without attempting to define its characters within prescribed limits, for casts or impressions of seeds which are not distinguished by any striking characters and cannot be allocated to any particular section of seed-bearing plants the unnecessary multiplication of generic titles is avoided: when any additional data are obtained differentiating particular types from other forms of Carpolithus the provisional term should be superseded by some distinctive generic name. Among seeds from the Coal Measures there are several examples of both large and small types without any regular ribs or lacking such features as serve to distinguish the genera already described, which are appropriately included in Carpolithus. The two species Carpolithus Wildii Kidst.[1063] and C. bivalvis Goepp.[1064] are two examples of seeds from Upper Carboniferous rocks which it is desirable to refer to this comprehensive genus pending further discoveries as to their morphological features. The Jurassic species C. conicus Lind. and Hutt.[1065] is another type which it has been customary to include in Carpolithus.

(Microspermum. Arber.)

The generic name Microspermum has recently been proposed by Arber[1066] for some Westphalian seeds described by Carpentier[1067] from the North of France as Carpolithes? samaroides and for similar fossils from the Middle Coal Measures of Nottingham. The supposed seeds are small, ovate or pyriform bodies, 5–12 mm. long and 2·5–6 mm. broad, with one extremity broadly rounded and the other acute: one side is keeled, the other grooved, and a large foramen occurs near the broader end and on the grooved surface. Arber emphasises the fact that the specimens are symmetrical in one plane only. As the author of the genus points out the morphological nature of the fossils is not thoroughly established, nor is the parent-plant known. In view of the ill-defined characters of the specimens so far discovered it is hardly desirable to institute a new generic name implying their seed-nature; moreover Microspermum has previously been employed for a genus of Compositae. An examination of specimens leads me to doubt their seed-nature and it would seem more likely that they are foliar organs, possibly bracts which originally bore seeds or sporangia.

* * * * *

An examination of some of the specimens of supposed Permian seeds for which Geinitz[1068] proposed the generic name Guilelmites convinced me that they are inorganic structures, probably nodules in shale smoothed and rounded by slickensiding.

Spotted a typo or a problem in this chapter? Tell us

XXXVI. CYCADOPHYTA

The term Cycadophyta, suggested by Nathorst[1069], is used in a comprehensive sense to include both recent Cycads and the much larger number of extinct types which it is customary to speak of as Cycadean plants or fossil Cycads. The designation ‘Cycads’ in the case of the majority of the fossil forms is, however, open to criticism on the ground that they differ too widely from existing genera to be associated with them in one class. It would be pedantic and inconvenient to give up the almost universal practice of extending the term Cycad beyond the limits defined by the characters of recent species. The important point is to adopt some classification which gives expression to our views as to the degree of affinity between recent and extinct types. In a considerable number of cases, especially impressions of presumably Cycadean fronds and stems that occur without any fertile shoots, it is impossible to determine the degree of relationship to modern types. It was with a view to a rational group-designation for such fossils that Nathorst proposed the term Cycadophyta, including in it the two classes Cycadales and Bennettitales. The Cycadales comprise the recent genera and such extinct types as may legitimately be included in the same class, but as we shall see later there are hardly any fossil species that can be assigned to this section on thoroughly satisfactory grounds. The term Bennettitales is used by Engler, Nathorst, and several other authors as a class-designation for a large number of Mesozoic Cycads agreeing in their more important morphological characters with the Lower Cretaceous stems on which Carruthers[1070] founded the genus Bennettites, placing it in a new tribe, the Bennettiteae. Some authors have followed Carruthers in the use of the family-name Bennettiteae for a subdivision of the Cycadales equal in rank to the Cycadaceae, while others, wishing to give greater emphasis to the difference between the extinct and recent plants, prefer to adopt the class-name Bennettitales. Carruthers regarded Bennettites as occupying the same position in relation to other Cycads as Taxus holds with regard to the cone-bearing members of the Coniferae. The adoption of Bennettitales is intended to convey the impression that the class is more distantly related to the recent Cycads than is implied by the analogy of Taxus. Nathorst[1071], as the result of his discovery of certain reproductive organs associated with some Rhaetic fronds described as Dioonites spectabilis, proposed a third subdivision, the Dioonitales, but he subsequently[1072] restored the fronds to their original designation Nilssonia pterophylloides, and on further examination found that the supposed microspore-bearing organs were seeds. Nilssonia pterophylloides would therefore find a more natural place in the class Nilssoniales instituted by Thomas[1073].

BENNETTITALES.

=Cycadeoidea.= Buckland.

In 1827 Buckland[1074] proposed the generic name Cycadeoidea for some petrified stems from the Purbeck beds in the Isle of Portland and published a description of two species, Cycadeoidea megalophylla and C. microphylla. Brongniart[1075] considered Buckland’s term Cycadeoidea inappropriate and proposed in its place Mantellia, the type-species being Mantellia nidiformis Brongn., the Portland stem which Buckland a month or two later called independently Cycadeoidea megalophylla. Subsequently Brongniart[1076] withdrew Mantellia as it had been previously used by Parkinson for a sponge and substituted Cycadites. Some years later Carruthers[1077] revived Mantellia for a type of Cycadean stem from Portland though one species, apparently indistinguishable from those referred to Mantellia, he named Bennettites portlandicus. There is no adequate reason for the retention of the generic name Mantellia. The close resemblance of the short and thick stems (12–30 cm. in height) described by Buckland to those of some recent Cycads was recognised by Robert Brown and Loddiges and the former suggested to Buckland the inclusion of the fossils in a new family Cycadeoideae. It was this suggestion that led Buckland to adopt Cycadeoidea as a generic name. In a later account of the Portland stems Buckland[1078], in deference to Brongniart’s opinion, substituted Brongniart’s name Cycadites for Cycadeoidea. It is noteworthy that no reference is made in the original description to the occurrence of lateral shoots among the persistent petiole-bases that encase the Portland stems, but in a later account such shoots are represented in one of the figured stems and are compared with the buds occasionally produced on stems of Cycas[1079]. The subsequent researches of Carruthers[1080] demonstrated the reproductive nature of precisely similar lateral shoots in the stem on which he founded the genus Bennettites. The generic name Echinostipes given by Pomel[1081], who had a passion for instituting new nomenclature, to Buckland’s Portland stems has not been adopted: his genus Crossozamia proposed for certain stems and fronds was revived by Carruthers[1082] but has not been generally used. A further complication in the nomenclature of Cycadean stems was introduced by Saporta’s institution[1083] of Bulbopodium and Cylindropodium: in the former genus he included the small ovoid stem figured by Lindley and Hutton as Cycadeoidea pygmaea[1084] and two French Jurassic species which might reasonably be assigned to Cycadeoidea. To Cylindropodium were referred some large French stems from Jurassic strata: an examination of the type-specimens in Paris convinced me that they are typical forms of Cycadeoidea. As Ward[1085] has pointed out, both Saporta’s genera may be merged in Cycadeoidea. Fliche and Zeiller[1086] also include the small globular stems named by Saporta Bulbopodium in the older genus Cycadeoidea: one such type from the Portlandian of Boulogne is described by these authors as Cycadeoidea pumila. Saporta also proposed the name Platylepis[1087], the type-species being Cycadeoidea micromyela Mor., from the Lias of Calvados, which has recently been investigated by Lignier[1088] who wisely adopts Morière’s designation. Another unnecessary generic name is Schizopodium given by Morière to a stem, S. Renaulti[1089], regarded by Lignier as indistinguishable specifically from C. micromyela.

The two names Cycadeoidea and Bennettites have been used by authors for stems which are unquestionably generically identical and as is often the case much confusion has been caused through the failure of palaeobotanists to arrive at an agreement. Lester Ward, a staunch advocate of the rule of priority, repeatedly pointed out that Buckland’s name Cycadeoidea should take precedence of Bennettites on the ground that stems for which these genera were instituted are clearly of the same type, and he added that the older genus, though abandoned by its author, cannot be given up without violating the inexorable rules of priority. On the other hand it has been urged that the genus Bennettites as defined by Carruthers is characterised by the possession of (i) fertile shoots bearing strobili and (ii) vegetative organs exhibiting certain anatomical characters. Buckland’s species of Cycadeoidea, though bearing lateral shoots, are not well enough preserved to afford definite information as to the morphological features of the strobili, nor have we satisfactory data with regard to the degree of resemblance between the vegetative features of Bennettites and the Portland stems. Carruthers laid stress on the elliptical section of the stele in Bennettites in contrast to the cylindrical cylinder of Buckland’s Cycadeoidea trunks. Subsequent research has shown that this difference is not in itself a valid criterion either of generic or specific rank but, as Wieland says, it is an open question to what extent the stem structure of Cycadeoidea and Bennettites agrees. The probability is that were our knowledge of the Portland stems less incomplete, they would be found to possess no anatomical features inconsistent with this generic union. Granting the correctness of this view, the adoption of the later generic term would be a reasonable course to follow on the ground that it stands for stems showing well preserved structure, while Cycadeoidea was in the first instance applied to stems showing only partially preserved stumps of strobili, and the name was not retained by its author. Graf Solms-Laubach[1090] and some other authors have used Bennettites for Cycadean stems possessing strobili of known structure such as those of Bennettites Gibsonianus, reserving Cycadeoidea for similar stems but without strobili sufficiently well preserved to afford evidence of morphological characters. This practice I followed in 1895[1091], but my usage of the two generic names has not been consistent, the name Cycadeoidea being afterwards employed[1092] in a more comprehensive sense. The investigation of the reproductive shoots of American Lower Cretaceous and Upper Jurassic Cycadean stems[1093] has demonstrated the practical identity of their ovulate strobili with those of the English Bennettites. It is clear that the American stems as well as numerous specimens from Italy and other European localities are generically inseparable from Bennettites. The adoption of Cycadeoidea by Wieland, following Ward, has naturally strengthened the claim of Buckland’s genus at least so far as wide usage is concerned, and with some reluctance I propose to fall in with this terminology and for the sake of convenience to give up the use of Bennettites. Among Mesozoic Cycadean stems agreeing with those of recent genera in habit and in the presence of an armour of persistent leaf-bases are several which afford no evidence either of the occurrence of fertile shoots or of lateral shoots with terminal flowers. To such stems the name Cycadeoidea has been applied, the designation Bennettites being restricted to stems with lateral fertile shoots: this practice of treating the absence of reproductive shoots as a characteristic feature of Cycadeoidea is regarded by Wieland as illogical and artificial; and if, as seems probable, he is correct in believing that the majority of the Mesozoic Cycadean plants culminated their vegetative period by prolific development of flowers, the absence of flowering branches would be contingent on a certain stage of development and not a generic character. Dr Stopes[1094] has recently published facts with regard to the anatomical features of Cycadean stems which have a bearing on the vexed question of nomenclature, but are more important from a morphological point of view as they indicate a closer agreement between certain types of Lower Cretaceous stems and those of Cycas and other recent genera, in which successive rings of vascular tissue are developed, than has previously been recognised. In her diagnosis of Cycadeoidea she includes the following statement: ‘In its internal anatomy the trunk shows two or more (up to eight are recorded) zones of secondary wood, the zones composed of distinct series of tracheids each more or less regularly arranged in radial sequence.’ It is claimed that the addition of this character constitutes for the first time a clear distinction between Cycadeoidea and Bennettites. Dr Stopes states that the two stems on which Buckland founded the genus Cycadeoidea are lost and adds that Buckland’s type has certain anatomical features which are not found in Bennettites. Buckland in his description of C. microphylla states that there are ‘two laminated circles’ in the stem instead of the usual single cylinder, a character suggestive of Cycas. In the original figure of this species there are no indications of any lateral fertile shoots though, as Dr Stopes says, many of the Portland stems undoubtedly possessed such flowers. This author makes no reference to Buckland’s later description of C. microphylla: in this it is stated that the stem bears numerous buds rising from the axillae of petioles, and these are shown in the illustration[1095]. Without access to the actual specimen it is impossible to say whether or not the two ‘laminated circles’ described and figured by Buckland[1096] are two distinct cylinders or parts of one cylinder separated by the infiltration of some inorganic substance. In his description of Cycadeoidea Yatesii Carruthers spoke of the occurrence of two cylinders of wood, and this was confirmed in a subsequent account of the type-specimen[1097]. Dr Stopes gives a fuller account of Carruthers’ type and re-confirm a the existence of two vascular cylinders; she also describes a new species, C. buzzardensis[1098] (fig. 578), in which there are 3–8 or more cylinders. Neither of these stems affords any evidence of the possession of fertile shoots; they agree closely with stems of the Bucklandia type in their comparatively slender habit and differ in this respect from Buckland’s Portland species. The occurrence of more than one vascular cylinder in the stems Cycadeoidea (= Bucklandia) Yatesii and C. (= Bucklandia) buzzardensis suggests the possibility that this feature was characteristic of other species included in Bucklandia.

It is clear that some at least of the stems referred to the genus Bucklandia bore flowers of the Williamsonia type[1099], and it is not improbable that the stems described by Dr Stopes as Cycadeoidea Yatesii and C. buzzardensis (fig. 578) possessed fertile shoots comparable with those of the Middle Jurassic species W. gigas. Dr Stopes’s contribution, while establishing a close agreement in anatomical features between some Lower Cretaceous stems and those of Cycas, does not warrant the further conclusion that these stems were in other morphological characters closely allied to modern Cycads. The main features of Cycadeoidea may be summarised as follows: The principal trunk is generally unbranched (fig. 507) and identical in habit with some species of Macrozamia, Dioon, and Encephalartos (cf. figs. 379, 382); in some species, e.g. Cycadeoidea Marshiana, C. superba[1100], C. nana[1101], the plant is represented by several approximately equal, thick, tuberous stems, in some cases easily separated from one another: a similar clustered habit is exhibited by certain forms of Encephalartos. The size of a Cycadeoidea trunk varies from a few centimetres in length with a diameter of similar dimensions, as in C. pumila, to over a metre long as in C. gigantea (fig. 535), or as much as 3–4 metres in C. Jenneyana with a diameter of about half a metre. The surface is covered with persistent leaf-bases, exactly as in many recent Cycads, embedded in a thick mass of ramental scales which often stand out as a prominent reticulum, the petioles having partially decayed before the penetration of the mineralising solution through their harder tissues (fig. 507). On the conical terminal bud preserved in some stems (fig. 536) the foliage-leaves are replaced by linear scales. The leaf-bases often show the vascular bundles which form a simpler system than in the majority of recent species, their arrangement being, as Wieland says, more Fern-like; they form a series of collateral strands following the outline of the petiole-base[1102] with a U-shaped invagination in the middle of the upper face (fig. 517, A). Beyond the structure of the bundles at the base of the fronds and in the cortex of the stem our knowledge of the anatomy of the vascular supply of the rachises is very meagre. At the petiole-base each bundle consists either entirely of radial rows of centrifugal scalariform tracheids and medullary rays usually one-cell broad (fig. 519, B) or of centrifugal and centripetal xylem in varying proportions. The ground-tissue is well supplied with large secretory canals and in the larger leaf-bases there is a considerable development of periderm at the surface (fig. 517, B) as in recent Cycads. The ramenta formed from the epidermal cells consist in most species of fairly broad scales one-cell thick at the edges and broader in the middle; in Cycadeoidea nigra[1103] they are generally one-cell thick throughout and similar ramenta are common in C. Gibsoniana (fig. 517, B). In C. micromyela unicellular hairs replace the scaly ramenta, but transitional forms occur between hairs and scales. In Williamsonia scotica (fig. 562) and in an Indian species of that genus the ramenta are exclusively long hairs as in recent Cycads, the scale-form of the ramenta in Cycadeoidea being a Fern-character. The degree of development of the ramental tissue varies in different species; in C. Stilwelli and C. excelsa it is feebly developed while in Cycadeoidea micromyela the ramenta almost cover the exposed leaf-base armour. The exceptional abundance of the ramental scales is a striking characteristic of some American stems referred to a separate genus, Cycadella[1104]. In the abundance of the ramental tissue, in the compact structure of the well protected cones, and in the thickly cuticularised epidermis of the bracts and leaves Cycadeoidea exhibits xerophilous characters in a very high degree.

With very few exceptions the stems of Cycadeoidea so far described afford no satisfactory evidence of the presence of more than one vascular cylinder in the main stem: in this respect Cycadeoidea agrees with such recent Cycads as Dioon, Ceratozamia, and Stangeria. In the stem of C. Jenneyana the secondary vascular tissue reaches a considerable thickness and shows signs of ‘rings’ in the xylem, but these are probably the result of some periodic interference with the uniform growth and not an indication of more than one xylem-cylinder. The secondary xylem (figs. 508, 509) consists only of centrifugal tracheids with some spiral elements on the inner edge; though manoxylic, Cycadeoidea has more compact wood than that of recent Cycads; the medullary rays are 1–2 cells broad except near the perimedullary region where they are broader and the individual cells are tangentially stretched (fig. 508, B). The tracheids are scalariform, but in C. micromyela, an exceptional type, some of the xylem-elements have 1–2 rows of separate bordered pits (fig. 538). The phloem (fig. 518, B) is characterised by an alternation of thick-walled elements and thinner cells[1105]. From the main stele branches are given off to supply the flowering shoots in the form of a cylindrical stele like that of the primary axis, and each leaf-trace arises as a single bundle which, in the form of a U-shaped strand (fig. 519, A), pursues a straight course to the leaf-base (fig. 510) where it breaks up into several branches (fig. 538, B). Both leaf-trace and peduncle stele are given off from the lower edge of a medullary ray. In the parenchymatous cortex large secretory canals (fig. 518, B) are a conspicuous feature, and accessory cortical steles similar to those in Cycas occasionally occur (fig. 511). The large pith consists of parenchyma and secretory canals, and internal periderm[1106] may be present; no medullary bundles have been discovered.

The correlation of the numerous fronds[1107] preserved in Mesozoic strata with their parent-stems is seldom possible. It is known that leaves of the Zamites type were borne on stems (Bucklandia) agreeing with Cycadeoidea in certain features but differing in the habit of the fertile shoots (fig. 542), and there is evidence that similar stems bore Ptilophyllum and Dictyozamites fronds[1108]; but only unexpanded leaves have been found in actual connexion with Cycadeoidea stems. Wieland[1109] discovered young pinnate fronds, agreeing in the form of the pinnae with Zamites and with some forms of Encephalartos, embedded in a thick mass of ramental scales in the terminal bud of a stem: the rachises were erect and the two-ranked pinnae imbricate and folded inwards (fig. 512), the vernation being like that of Dioon and not circinate as in Cycas and Ferns. The mesophyll of the leathery pinnae is differentiated into palisade and lacunar parenchyma, and the bundles are said to be ‘mesarch’ though on this point more information is desirable. Each bundle is surrounded by a sheath of thick-walled cells and the same tissue forms =I=-shaped girders as in similar recent leaves. In one species, Cycadella ramentosa[1110], the rachis of a young frond found among the leaf-bases had a broad U-shaped vascular strand.

In most Cycadeoidea stems a characteristic feature is the occurrence of reduced leaves, or bracts, arranged spirally about a cone which sometimes projects slightly beyond the general level of the persistent leaf-bases, or the cones may be fully developed yet still more or less hidden within the armour of petiole-bases (fig. 517, C). These cones, or flowers, are borne at the apex of lateral axillary shoots, and it is characteristic of the genus that they never project more than a very short distance beyond the truncate stumps of the old leaf-bases. The axis of a flowering branch bears numerous linear, hairy, bracts (figs. 513; 514, b) which with their thick felt of ramenta constitute an efficient protective investment. The summit of a fertile shoot forms a rounded hemispherical cushion (fig. 514), or the receptacle may be more elongate and conical (fig. 513) and in some species pyriform[1111]. The flowers are generally bisporangiate, but the fact that in flowers with mature microsporophylls the ovules are small and apparently immature (fig. 513) makes it difficult to determine whether the megasporophylls are merely immature or functionless as in the male flower of Welwitschia (cf. fig. 818). It would seem, however, that in most cases the flowers were bisexual[1112] (fig. 513). A remarkable feature is the enormous number of flowers on a single stem; in Cycadeoidea Dartoni[1113], 54 cm. long and 35 cm. broad, 500–600 flowers were counted on one side. On the other hand the large stem of C. gigantea (fig. 536) shows no flowers. All the flowers on a single trunk are approximately in the same stage of development: it would seem, as Wieland points out, that after a vegetative period of some considerable duration the plant produced a large crop of flowers, and it is conceivable that as in Corypha and some other recent Flowering plants this supreme effort set a limit to the plant’s existence. In the development of flowers from the old stem Cycadeoidea affords a striking example of cauliflory.

The structure of the flowers is one of the most obvious differences between Cycadeoidea and recent Cycads (cf. figs. 393, 394). The bisexual flowers of the fossil stems are comparatively small, not exceeding a few centimetres in length, like a hen’s egg or a medium-sized pear and in marked contrast to the male and female cones of modern Cycads (cf. figs. 393, 394). A verticil of pinnate microsporophylls is attached by a circular collar formed of the concrescent bases of the sporophylls to the lower portion of the receptacle; each pinnule bears several shortly-stalked synangia divided into loculi containing microspores usually with smooth walls and similar, except in their larger size, to those of modern Cycads (fig. 532). Sections of some microspores figured by Wieland[1114] show what appear to be cells in the spore-cavity, but they are larger than ordinary prothallial cells and their true nature is doubtful. We lack information both as regards the nature of the male gametes and the tissue formed on the germination of the spores. The free portions of the microsporophyll-whorl may consist of as many as 20 pinnate sporophylls, but the number is generally smaller; these are much longer than the ovulate part of the flower and in an immature state the ends of the sporophylls are bent inwards and downwards (fig. 513) between the bracts and the receptacle. After expanding and shedding the spores the whole male disc is thrown off leaving a narrow rim below the hemispherical or conical receptacle (fig. 514, d). The sterile distal end of a microsporophyll is generally slightly expanded and spathulate; in C. colossalis[1115] it bears a pair of wing-like appendages (fig. 533).

The upper part of the receptacle is covered with two kinds of organs which together form a layer of uniform depth; these are believed to be homologous, foliar structures; the majority are sterile and have the form of slender long and narrow appendages (fig. 514) each normally with a single axial vascular strand. These so-called interseminal scales increase in breadth in the apical region and form polygonal summits less than a millimetre in breadth or exceeding 2 mm. The low pyramidal apices of the interseminal scales give a mosaic-like appearance to the surface of the ovulate receptacle (fig. 515). In the lower part of the receptacle these sterile sporophylls are the only appendages, but over the greater part of the receptacle they are intermixed with a smaller number of similar appendages which bear a single terminal orthotropous ovule (fig. 514, s). Each ovule-bearing organ or megasporophyll (seed-stalk) is surrounded by 5—6 interseminal scales, and the narrow cylindrical micropylar tubes are readily distinguished from the sterile sporophylls in surface-view (figs. 516, 564). The seeds appear to be exalbuminous and the embryo is dicotyledonous (figs. 516, 521, 523)[1116]. The seeds are very small in comparison with those of living Cycads. The structure of the megasporophylls, both sterile and fertile, is described in more detail in the account of Cycadeoidea Morierei and other forms. Fig. 516 represents a longitudinal section of one of the smallest seeds of Cycadeoidea, between 3 and 4 mm. long; an embryo occupies the greater part of the seed-cavity: the micropylar tube is formed of three layers, a strong inner palisade-layer, a thin middle layer, and an outer palisade-tissue, the interior of the tube being filled with parenchyma; at the shoulder of the seed above the root-end of the embryo the surface of the testa is characterised by 5–6 wings formed by the radial extension of palisade-cells. After the shedding of the spores and the abscission of the microsporophylls the flowering shoot probably increased slightly in length, thus pushing the ripening seeds beyond the ends of the surrounding leaf-bases. The ripe flowers were eventually cut off by an absciss-layer immediately below the receptacle (figs. 521, C, a; 522, a), large cup-like depressions being left on the surface of the stem (fig. 534). The ovulate cone on which the species Cycadeoidea Morierei is founded probably represents the condition of a naturally detached flower of a Cycadeoidea. It is possible that the detached flowers freed from their encircling bracts may have been edible, the small seeds being dispersed by animal agency.

* * * * *

The splendid petrified stem, Cycadeoidea etrusca Cap.[1117], one of the treasures of the Bologna Museum, was found on a tomb 20 miles west of that city where it was doubtless placed by the Etruscans who obtained it from the Upper Jurassic scaly clays in the Apennine Hills. It was in an imperfectly preserved flower of this fossil that Graf Solms-Laubach discovered some microspores, but it was not until Wieland’s examination of the more complete American stems that information was obtained as to the spore-bearing organs. Another Italian stem, Cycadeoidea montiana Cap., was described in 1753 as a ‘congeries of barnacles[1118].’ The specimen named by Goeppert Raumeria Reichenbachiana[1119] was described in the middle of the eighteenth century as a mass of Hippurites or coral cups: this was found in a swamp in Galicia and is now one of the most striking objects in the Dresden Museum; a brief account of it is given on page 409. In 1859 Tyson discovered two large trunks in the Potomac beds of Maryland for which Fontaine subsequently proposed the name Tysonia marylandica[1120], but as Ward pointed out the species is clearly a Cycadeoidea (fig. 507). In 1894 Lester Ward[1121] recorded several additional stems from Tyson’s locality. It is, however, from the Black Hills of Dakota, an isolated spur of the Rocky Mountains, formed of older rocks encircled by Lower Cretaceous strata[1122], that the greatest number of Cycadean trunks have been obtained: the magnificent collection now in the Yale Museum is largely due to the energy and munificence of the late Prof. Marsh. From the Upper Jurassic beds in Carbon Co., Wyoming[1123], several stems have been collected, and a preliminary study of their external features led Ward to institute 20 species of a new genus Cycadella. Stems have also been discovered in the Freezout Hills of Wyoming and additional specimens have been found in the Potomac formation of Maryland. The discovery of over 1000 specimens of Cycadean stems in the Lower Cretaceous and Upper Jurassic beds of a few localities in the United States bears striking testimony to the abundance of these extinct Gymnosperms during the latter part of the Mesozoic era. It is perhaps true that, as Lester Ward wrote, ‘Cycads are to the vegetable kingdom what Dinosaurs are to the animal, each representing the culmination in Mesozoic times of the ruling Dynasties in the life of their age[1124].’ Although the number of stems obtained from European countries is relatively small, the abundance of specimens in the Upper Jurassic strata of the Isle of Portland and Northern Italy and their occurrence in Belgium[1125], France, Germany, Austria, Poland, India and elsewhere, together with an abundance of Cycadean fronds in practically all Jurassic and Lower Cretaceous plant-bearing beds, demonstrate the dominant position of the Bennettitales. The occurrence of the genus Williamsonia in many European localities as well as in India, Afghanistan, and other countries, and the not infrequent occurrence of stems assigned to Bucklandia, Yatesia, Cylindropodium, and other genera furnish evidence of the rich development of the Bennettitales in later Jurassic and Lower Cretaceous floras. Wieland’s recent discovery[1126] of numerous Cycadean fronds, Williamsonia flowers, and stems in Liassic rocks in Mexico shows that the group had already assumed an important position in the early part of the Jurassic period.

The memoir by Carruthers[1127] on British Cycadean stems contains the first account of the morphological features of Bennettitalean flowers based on petrified material. In 1891 Solms-Laubach contributed an important paper on the Bennettitean flower and several years later Lignier[1128] contributed additional data derived from a careful study of a well preserved strobilus[1129] from the Gault of Normandy. Wieland’s researches[1130] added very greatly to our knowledge, particularly with regard to the morphology of the microsporophylls. Among the earlier descriptions of the reproductive organs of the Bennettitales is Buckland’s account[1131] of a specimen from the Inferior Oolite of Charmouth, Dorset (fig. 560), which he referred to the genus Podocarya (= Williamsonia Bucklandi[1132]): a thorough examination of the type-specimen, which unfortunately cannot be found, would probably furnish many important facts.

{ Cycadeoidea (Bennettites) Gibsoniana (Carruthers). { Cycadeoidea (Bennettites) Saxbyana (Brown).

These two species serve to illustrate the type of stem for which Carruthers instituted the tribe Bennettiteae and the genus Bennettites. Bennettites Gibsonianus is the most important of the five species described by Carruthers[1133], as it was from its fertile shoots that information was first obtained as to the nature of the ovulate strobili of the Bennettitales. B. Saxbyanus[1134], originally described as Cycadites Saxbyanus from a specimen found by Mr Saxby at Bonchurch in the Isle of Wight and represented by Wealden examples from Brook Point, is chiefly interesting for the clear preservation of the anatomical features of the stem. Three other species were also described by Carruthers; they are: Bennettites maximus Carr., a large stem similar to B. Saxbyanus, in the Museum of the Geological Survey; B. portlandicus from the Lower Purbeck of the Isle of Portland, in the collection of the Geological Society; and B. Peachianus, a piece of a compressed stem, in the British Museum, from the Upper Jurassic of Helmsdale in N.E. Scotland.

Cycadeoidea (Bennettites) Gibsoniana.

This species was founded on a petrified portion of a large stem of Lower Greensand age discovered by Mr Gibson in Luccomb Chine in the Isle of Wight: the type-specimen is represented by pieces of the original block in the British Museum and in one of the Museums at the Royal Gardens, Kew. The following description is based partly on the published accounts and in part on an examination of sections in the British Museum, the Manchester University Museum, and in Dr Scott’s collection.

The elliptical form of the stem and vascular cylinder as seen in transverse section, regarded by Carruthers[1135] as a feature characteristic of the genus, has no morphological significance and is in part at least due to compression. In the large pith, the armour of persistent petiole-bases separated by dense ramental scales (fig. 517, A, B), and in habit, Cycadeoidea Gibsoniana agrees generally with the stems of many recent Cycads, but the resemblance of the vegetative organs is in marked contrast to the differences exhibited by the reproductive shoots. The pith consists of parenchyma with scattered secretory ducts but no medullary vascular bundles. In the pith of Cycadeoidea Peachiana there are patches of tissue superficially resembling vascular strands, but these are probably bands of internal phloem like those described by Solms-Laubach[1136] in some Italian stems. In none of the English stems are there any clear indications of the occurrence of more than one cambium in the stele. The secondary xylem is entirely centrifugal with some smaller crushed elements, presumably protoxylem, at the inner edge where the medullary rays are especially broad. The xylem is of the manoxylic type (fig. 518, A) as in recent Cycads; though the medullary rays, 1–2 cells broad, are rather smaller than in recent species. The tracheids are scalariform as in Stangeria (fig. 397). As in recent Cycads there is a broad cylinder of secondary phloem (fig. 518, B)[1137] composed of alternate layers of thick-walled and thinner elements—sieve-tubes and parenchyma: traces of lateral sieve-plates occur on some of the elongated elements. Each leaf-trace arises as a single strand from the lower edge of a mesh formed by the large inner end of a medullary ray: on emerging into the inner cortex the trace has the form of a U-shaped strand (fig. 519, A, lt) which passes direct to the petiole, following a steeply ascending course in Cycadeoidea Saxbyana and almost horizontal in C. Gibsoniana. Before entering the base of a leaf the trace breaks up into several collateral strands and these form a simple pattern as seen in a tangential section of the leaf-bases (fig. 517, A, C), the central bundles on the upper side forming a U-shaped involution. There is no indication of any girdling of the foliar bundles. The arrangement of the petiolar bundles is simpler and more Fern-like than in the majority of existing Cycads. Each vascular bundle consists in the petiole-base mainly of centrifugal secondary xylem and medullary-ray tissue (fig. 519, B); a group of centripetal tracheids is usually recognisable internal to the protoxylem: the structure is of the mesarch type with a variable amount of centripetal xylem, and agrees generally with that in recent Cycads.

The comparatively narrow cortex is composed of parenchyma with scattered secretory sacs (fig. 518, B, s), and occasionally an elliptical vascular strand (fig. 511) is present which is probably cauline as are the similar strands in Cycas. The persistent petiole-bases are covered with ramental scales which form a dense interfoliar packing: these frequently consist of a single layer of fairly thick-walled cells or, as seen in transverse section, of spindle-like scales one-cell thick at the edges and 2–3 cells broad in the middle (fig. 517, B).

The presence of fertile shoots, presumably axillary, is one of the most striking features of Bennettitean stems. The branching is monopodial and not sympodial as in most recent Cycads. The nearest approach to the method of branching in Cycadeoidea is afforded by some stems of Macrozamia recently described by Chamberlain[1138]. It is not improbable that some of the flowering branches of Cycadeoidea were branched. Solms-Laubach[1139] states that he observed certain characters in the secondary axes of Cycadeoidea Gibsoniana which led him to suspect that there may have been fascicled systems of fertile shoots emerging in a body or in close proximity to one another between the leaf-bases of the stem. An example of a branched flowering shoot is described in Williamsonia scotica[1140]. A fertile shoot agrees in structure with the main axis and Scott[1141] states that the phloem is particularly well developed, a feature by no means unusual in fertile branches. These lateral shoots (fig. 514) bear numerous linear bracts each with three collateral vascular bundles, and ground-tissue composed of thick-walled cells characterised by scalariform pitting (fig. 520): secretory sacs are abundant. The hypodermal stereome is especially developed on the inner face of the bracts. The apex of a lateral shoot has the form of a rounded cushion (figs. 514; 521, A, C) similar to the receptacle of many Composites, and on this are borne the sporophylls. It is characteristic of Cycadeoidea that the flowers project very slightly beyond the surface of the stem and the peduncles are not exposed except in tangential sections through the leaf-base armour (fig. 517, C, 1, 2). On the fall of the flower or ripe ‘fruit,’ which is effected by an absciss-layer (figs. 521, C, a; 522, a), a cup-like scar is left on the stem (cf. fig. 534). This method of flower-production suggests comparison, mutatis mutandis, with the phenomenon of cauliflory in certain recent Flowering plants; it is one of the distinguishing features between Cycadeoidea and stems bearing longer fertile shoots with flowers of the Williamsonia type.

Fig. 517, C, shows a tangentially cut surface of a portion of the stem of Cycadeoidea Gibsoniana with two axillary fertile shoots; one, 1, is cut across below the receptacle and shows the axis surrounded by bracts while the other, 2, is seen at a higher level, above the receptacle, where the section has exposed the numerous sporophylls. The rounded surface of the receptacle is covered with a dense cluster of long slender appendages, seed-stalks and interseminal scales, the latter being much more numerous than the former (fig. 521, A, B). These organs are believed to be homologous foliar structures, the seed-stalks being megasporophylls and the interseminal scales abortive or potential sporophylls (see also figs. 562, 563). Fig. 514 shows the form of a single flower from an American stem closely allied to Cycadeoidea Gibsoniana.

The megasporophylls are more or less polygonal in transverse section: there is a central concentric vascular strand surrounded by a thick cortex (fig. 527): at its upper end the sporophyll bears a single orthotropous seed containing a dicotyledonous embryo (figs. 521, D, E; 523). The vascular strand pierces the base of the testa and expands to form a shallow cup of tracheal tissue in the chalaza; there are no bundles in the single integument. The testa (fig. 521, D, t) consists of three regions, a median layer of rather large rectangular or palisade-cells with an inner and outer tissue composed of much smaller cells. The testa is prolonged distally as a slender cylindrical column or micropylar tube at the base of which it becomes broader owing to the increase in breadth of the middle or palisade layer. A nucellar beak projects as a cone into the base of the micropylar tube. No pollen-chamber has been found. It is noteworthy that the micropyle is closed in the ripe seeds. Internal to the testa there is a crushed membrane separated from the embryo by a space (fig. 521, D, sp): this is the remains of the nucellus and, as Solms-Laubach points out, there is no proof that any endosperm was present in the ripe seeds[1142]. The embryo consists of a short axis, the conical radicle and the very short apex of the epicotyl, also two equal cotyledons each with a few vascular bundles (fig. 521, D). The long interseminal scales, as seen in transverse section in the lower part of a flower between the sporophylls, appear as compressed polygonal organs (fig. 521, B, i) with an axial vascular strand surrounded by parenchyma and limited by a strong epidermis; they pass up between the seed-stalks, m, and in the distal end become considerably enlarged (figs. 514, 515), gradually expanding to form a truncate or slightly pyramidal apex (figs. 553, 563). The swollen peltate apices of adjacent scales form a continuous covering to the flower interrupted, except in the lower sterile part of the flower, by symmetrically disposed cylindrical micropylar tubes (fig. 515). The peripheral interseminal scales form a homogeneous parenchymatous tissue which springs from below the edge of the receptacle (fig. 521, A, B, pr) and the individuality of the scales composing this ‘pericarp’ is indicated by occasional invaginations of the epidermal layer which marks the boundary of the polygonal areas. The structure of the megasporophylls and scales is more fully described in the case of Cycadeoidea (Bennettites) Morierei[1143].

The flowers of Cycadeoidea Gibsoniana appear to be unisexual and ovulate: in view of the discovery by Wieland of numerous bisexual fertile shoots on American species of Cycadeoidea it would be reasonable to regard the apparently unisexual flowers of the English species as originally bisexual but preserved at a stage subsequent to the loss, by abscission, of the disc of microsporophylls. Fig. 514 shows a flower of an American Cycadeoidea practically identical with those of C. Gibsoniana, but the remains of the staminate disc are clearly seen at d below the swollen apex of the flowering axis. In the photograph of half of the same region in C. Gibsoniana reproduced in fig. 522 there is no indication of any similar trace of a whorl of microsporophylls. Admitting the fact that a shrivelled remnant of the persistent base of a whorl of microsporophylls might easily escape observation, it is difficult to believe that any fertile leaves ever existed in the flower represented in figs. 521, 522. It is equally difficult to regard the specimen represented in fig. 561 as other than a true unisexual (ovulate) flower.

Cycadeoidea (Bennettites) Morierei (Saporta and Marion).

The name Bennettites was adopted by Lignier for this species which was founded on a detached flower from the Gault[1144] of Vaches-Noires, Normandy. It was first described by Morière[1145], then by Saporta and Marion[1146], who named it Williamsonia Morierei, and it has since been thoroughly investigated by Lignier[1147]. There is no evidence as to the nature of the parent-stem though Morière suggested a possible connexion with Zamia Brongniarti Mor. (figured by Saporta[1148] as Fittonia Brongniarti) from the same locality. There can be no reasonable doubt that Bennettites Morierei was borne on a lateral branch of a stem of the Cycadeoidea type: it is constructed on essentially the same plan as the flowers of Cycadeoidea (Bennettites) Gibsoniana, and in both cases there is no indication of the presence of microsporophylls. The type-specimen is 5·5 cm. long and 3·5 cm. broad, ovoid, and characterised by a depressed cushion-like receptacle as in Cycadeoidea Gibsoniana. The enveloping bracts with their ramental scales agree generally in structure with those of the English species and, except as regards the ramenta, with Williamsonia scotica: numerous stomata occur on the lower surface; the ground-tissue consists of thick-walled parenchyma and the narrow pit-canals simulate the scalariform bands in Cycadeoidea Gibsoniana (cf. fig. 520). The pitted sclerous cells in the bracts of W. scotica are of the same type. There is an anastomosing system of secretory canals, also several vascular bundles like those in C. Gibsoniana but more numerous; the latter are composed of a group of phloem-elements abutting externally on fibres, a well-defined cambium, and radially disposed scalariform tracheids: internal to the protoxylem is a group of elements considered by Lignier to be centripetal xylem. From the branching and slightly divergent course of the bundles in the upper part of the bracts Lignier concluded that these organs represent the basal portions of leaves originally provided with a terminal limb. It may be that the small lateral appendages to some of the bracts of Williamsonia scotica (fig. 561, l) afford support to this view.

Megasporophylls (seed-stalks and seeds). These organs, 3–4·5 cm. long and approximately 1·5 mm. in diameter, are in most cases imperfectly preserved. In transverse section and at a level of 1 cm. above the receptacle a stalk bearing an atrophied seed shows the following features: an epidermis with very thick internal walls encloses a parenchymatous ground-tissue with an axial conducting strand. At a higher level the epidermal cells have walls of uniform thickness, and a hypodermal layer of cells with coloured contents is differentiated from the ground-tissue (fig. 524, D, ac). As the seed-base is approached the epidermal cells tend to separate from one another and divide longitudinally, the compact epidermal layer being replaced by an envelope of tubular, dissociated, cells (fig. 524, D, Et). Similar tubular elements occur in the seed-stalks of Cycadeoidea Gibsoniana. A fully developed seed-stalk bearing a complete seed cut across in the middle region shows the following features: a concentric vascular strand surrounded by thin-walled parenchyma and the coloured hypodermal layer (fig. 524, D, ac), the whole being enclosed in the tubular envelope of epidermal origin (Et) which is more strongly developed than in the stalks of imperfect seeds: there may be as many as 10–12 tubular cells on one radius. When traced downwards towards the receptacle the tubular envelope decreases in breadth, though the cells become more numerous and smaller, until in the immediate neighbourhood of the receptacle the tubular tissue is transformed into a compact parenchyma of large cells each of which corresponds to a group of tubes formed by the septation of the cells. Traced upwards this thin-walled parenchyma gradually passes into thick-walled tubes, and near the seed-base the tubular envelope is reduced to two layers, an inner consisting of relatively small cells with sinuous radial walls (the folded layer of Lignier) and an outer tubular layer. Lignier describes an interesting abnormality, a bifid seed-stalk enclosed in a common epidermis which he compares with the occasional branching of the seed-stalks of Ginkgo biloba.

Seeds. The seeds (figs. 525, 526), 6–7 × 2·5–3 mm., are tetragonal or pentagonal in the upper half (fig. 527, 1, 2), the angles being formed by thick but not very prominent wings of tissue (fig. 524, C, cf); they are orthotropous and have a single integument (figs. 525, 526). The tubular layer forming the outer portion of a seed-stalk near the seed-base is prolonged over the surface of the testa as a discontinuous covering in the form of isolated or small groups of tubes, giving a striated appearance to the seeds. This layer though apparently a part of the seed is derived from the neighbouring interseminal scales of which it is the epidermal layer; it consists of elongated cells and scattered stomata[1149]. The folded layer persists only in the lower part of the seed, being replaced by a layer of radially extended cells (radial layer; ar, figs. 524, C; 525, ar; 527, c) in the upper region of the seed. In the micropylar region both the tubular and folded layers undergo further change; the external, tubular, layer forms a kind of epidermis (at, figs. 524, 525), the subepidermal layer, consisting of the radially elongated cells (figs. 524, 525, ar; 527, c). The superficial layer assumes a different aspect in the micropylar region, its cells being thicker walled, as are also those of the subepidermal layer (fig. 524, A and B). The micropylar canal (figs. 524, 525, cm) is cylindrical in the lower part but at the apex is reduced to a long and narrow slit bounded by an internal epidermis of radially stretched cells which in the lower portion of the tube are thinner walled and isodiametric. The rest of the testa is differentiated into two regions; an outer fleshy region immediately internal to the folded (or radial) layer and an inner fibrous region next the nucellus, which is one-layer broad between the wings but opposite the wings it extends radially outwards across the fleshy tissue to the radial layer (figs. 524, C; 525; 527): in the winged portion of the seed this tissue forms the inner fibrous portion of the wings but in the lower part of the seed below the wings it forms a single layer of uniform breadth finally spreading out as a basal cup in the chalazal region where it is pierced by the vascular strand. The fleshy portion of the testa forms one layer in the proximal part of the seed and becomes several layers wide between the fibrous wings in the upper part. This fleshy tissue appears to be derived from the coloured, subepidermal, layer of the seed-stalk, while the internal parenchyma is regarded by Lignier as the equivalent of the fibrous layer of the testa. In the micropylar tube the fibrous layers are replaced by 2–3 layers of sclerous cells (fig. 524, A, B). The testa has no vascular supply: the concentric strand of the seed-stalk passes through the fibrous tissue at the base of the seed and reaches the base of the nucellus (fig. 525). The nucellar apex extends into the lower part of the micropyle (fig. 525, n), and in some cases Lignier noticed an axial canal formed by the breaking-down of the cells which abutted below on a cavity above the embryo, probably the remains of a pollen-chamber (figs. 525, 527). No microspores have been found. Two dark spots shown at co, fig. 525, may represent archegonia but this is doubtful, especially as the seed contains a well-developed embryo. The nucellus is free from the testa only in the apical region and a dicotyledonous embryo occupies the interior without any trace of endosperm. Lignier points out that in some seeds containing embryos the nucellar beak is not completely perforated: in this fact and in the absence of microspores in the micropylar canals he is inclined to see evidence of parthenogenesis[1150].

In several respects the seeds of Cycadeoidea agree with those of Gnetum: reference should be made to the account of the seed of Gnetum africanum in Chapter +lii.+ and to the papers referred to in the footnote[1151].

Interseminal scales. The young seed-stalks agree very closely with the interseminal scales: each seed-stalk is surrounded by 5–6 scales (fig. 527) as in other Bennettitean flowers (fig. 564). For the greater part of their length the interseminal scales are compressed, but above the seeds, where they are free from pressure (fig. 526), they become much thicker and form a covering (‘pericarp’) as in Cycadeoidea Gibsoniana. In its upper region an interseminal scale consists of an epidermis with strongly thickened inner walls, hypodermal thick-walled cells and parenchymatous ground-tissue with a single axial bundle. In the lower part the scale is more flattened and the thick-walled hypoderm is replaced by thin-walled parenchyma. Some of the scales at the periphery of the receptacle where there are no seed-stalks are broader and may have six vascular bundles; this, Lignier suggested, might be regarded as evidence of the reduction of the interseminal scales from leaves possessing a terminal limb; but a further examination of scales at the periphery of the flower led him to the conclusion that the distal swelling of the scales is solely due to the hypertrophy of conjunctive tissue and is not the result of the modification of a reduced limb[1152]. The morphological value of the interseminal scales and seed-stalks has not been definitely settled, though the probability is that they are homologous organs and foliar. Solms-Laubach[1153] suggested that both may be axial, the seed-stalks representing axes ending in a flower reduced to a single ovule; or, he adds, the seed-stalks may just as well be carpels, though in that case we should have the unusual phenomenon of terminal seeds. The interseminal scales may be aborted seed-stalks crushed between the latter; or if the seed-stalks are axes, the scales may be foliar. He is inclined to see in the scales the bracts and prophylls of seed-stalks to which must be added such bracteoles, preceding the seed or flower, as may happen to spring from the seed-stalks. Pearson[1154], on the assumption that the seed-stalks are axial structures, institutes a comparison between Welwitschia and Bennettites and regards each flower of Welwitschia as a much reduced Bennettitean strobilus. Lignier believes the interseminal scales to be leaves borne on the swollen apex (receptacle) of an axis of the second order, while the seed-stalks are fertile leaves of a unifoliar bud of the third order possibly axillary though not necessarily so to the interseminal scales. My own view, influenced by the examination of the immature flower of Williamsonia scotica, is that the seed-stalks (megasporophylls) and scales are homologous, the former being sporophylls and the latter sterile foliage leaves, the whole flower, as Wettstein[1155] says, consisting of a conical axis bearing numerous fertile and sterile carpels enclosed by a perianth of bracts. Worsdell[1156], who shares Čelakovsky’s opinion that sporophylls were originally radially symmetrical organs bearing a terminal sporangium, regards the flowers of Cycadeoidea Gibsoniana and other species as more primitive than those of recent Cycads: he does not see any justification for the view that the Bennettitalean flowers are in advance of those of existing Cycadean plants as regards a supposed tendency towards the Angiospermous type. He maintains that Bennettites ‘shows absolutely no indication of such an advanced structure in its essential organs, the sporophylls, which remain primitively radial in structure, bearing the ovules in a terminal position.’

Cycadeoidea dacotensis (McBride).

McBride[1157] first described this Lower Cretaceous species from the Black Hills of South Dakota as Bennettites dacotensis, the generic name Cycadeoidea being adopted by Ward[1158] who distinguished some of McBride’s specimens as Cycadeoidea McBridei. The stem is elliptical in section, 32 cm. long and 45 cm. in girth: owing to the partial decay of the petiole-bases the ramental reticulum forms a prominent feature. Numerous flowers, all of which are approximately at the same stage of development, project like conical buttons above the general level of the stem-surface[1159]. The bisporangiate flowers consist of a conical receptacle bearing interseminal scales and megasporophylls, the whole being surrounded by spirally disposed bracts (fig. 529). A whorl of 18 or 19 nearly mature microsporophylls is attached to the base of the receptacle (figs. 528, 530); each microsporophyll has a strong rachis extending beyond the apex of the flower-axis and bent inwards and downwards with the distal end tucked between the ascending rachis and the receptacle. The slender pinnules, in two alternate series, are bent downwards and bear synangia in rows. A transverse section just below the ovulate portion of the cone shows a continuous ring of tissue encircling the receptacle with vascular bundles parallel to the surface (fig. 530, A, m); at a higher level the bundles fall into groups preparatory to the breaking up of the disc into separate microsporophylls. Immediately above the apex of the central cone the coherent basal portion of the verticil of sporophylls is replaced by the separate rachises which in section have the form of isosceles triangles (fig. 530, B). Each microsporophyll is approximately 10 cm. long; the longest pinnule being 1·5 cm. in length and bearing two lateral series of synangia, 10 in each row. At maturity the microsporophylls probably spread out and the whole whorl was thrown off leaving an annular rim (fig. 514, d) such as is often seen at the base of older ovulate strobili. The immaturity of the ovules in this (fig. 528) and other specimens led to the suggestion that the strobili of Cycadeoidea were protandrous. The synangia (fig. 531) are several times broader than long and similar in size to those of the Fern Marattia. In each synangium are two rows of elongated loculi (fig. 532) containing oval microspores usually with a smooth exine and rather larger than those of recent Cycads. The synangium-wall is composed of a palisade-layer of thick-walled cells and a layer of smaller and thinner cells: the palisade-layer is narrowest at the apex where dehiscence occurs and broadest at the base where the hypodermal tissue is more abundant and forms a short thick pedicel. The two rows of loculi are bounded by flattened cells and there are 10–20 loculi in each of the two rows: dehiscence of the individual loculi occurs in the middle of the inner wall.

Cycadeoidea Marshiana Ward.

This Lower Cretaceous Black Hills species[1160] affords an admirable example of a method of branching exhibited by some stems: as shown in Wieland’s photographs[1161] there may be five or six large and massive trunks all in the same stage of fructification, differing but little in size and forming a cluster resembling independent plants growing in close proximity to one another. There is apparently no central or major axis and the habit is therefore very different from that of a branching Bucklandia. Cycadeoidea Marshiana bore large ovulate pyriform strobili projecting slightly beyond the leaf-bases; they are 5 cm. long with a maximum diameter of 3·5 cm. and have an elongated receptacle bearing short scales and sporophylls. The apical bud of one of the trunks shows particularly well in transverse section the dense ramental packing between the bud-scales[1162]. Similar clusters of short and thick trunks occur in Cycadeoidea superba and other American species.

In the small bisporangiate flowers of this species[1163] the microsporophylls, 11 or 12 in the verticil, are characterised by the presence of a ventral furrow which, as Wieland suggests, may be comparable on a much simpler scale with the winged sporophylls of Cycadeoidea colossalis (fig. 533). The disc splits up at a distance of 1 cm. above the apex of the receptacle into the microsporophylls, each of which is 5·5 cm. long and bears two rows of pinnules which in the middle region have a length of 1 cm.; a microsporophyll is elongate, elliptical, and acuminate. In this species as in some others there is a brush of sterile scales at the apex of the receptacle.

Cycadeoidea colossalis Ward.

Wieland[1164] has recently described some interesting features in the microsporophylls of a bisporangiate flower assigned to this Lower Cretaceous species from the Black Hills illustrating a departure from the usual type. The hairy bracts extend considerably above the apex of the flower-proper; in fig. 533, A, a transverse section above the receptacle, they are shown grouped about a circle of V-shaped structures, converging towards a central point, which are the sterile prolongations of the ten rachises of the free portions of the staminate disc. Each rachis is divided by a deep ventral furrow into a pair of wings (fig. 533, B, C), and it is these pairs of wings that form the V-shaped structures in fig. 533, A. The wings form a dome-like group above the flower-apex (fig. 533, D, E). The synangia are borne in two rows on the concrescent disc and on the free sporophylls, which in this type are much simpler than in other species and agree in the absence of pinnules with some forms of Williamsonia (cf. fig. 556). The receptacle is pyriform and bears very short scales and seed-stalks; from its apex several interseminal scales are prolonged as a terminal brush, a feature of interest in connexion with flowers of Williamsonia. Wieland compares the wings of the microsporophylls to the two horns on the distal surface of the corresponding organs of Ceratozamia and draws a comparison between them and the canopy of some Palaeozoic seeds, but it is doubtful whether homologies can be established between these elaborate sporophylls and the integuments of Pteridosperm seeds[1165].

Cycadeoidea Reichenbachiana (Goeppert).

Goeppert referred this species to his genus Raumeria[1166], a generic name retained by Carruthers though, as Solms-Laubach[1167] points out, the abundance of lateral fertile shoots among the leaf-bases shows it to be essentially similar to Cycadeoidea Gibsoniana. The type-specimen in the Dresden Museum is a splendid example of a fossil cycadean stem; it is probably of Lower Cretaceous age, but was found in Galicia as an isolated specimen. It consists of a portion of a cylindrical trunk similar in habit to C. gigantea, ·5 met. high and about the same in diameter. The pith, according to Schuster[1168], is 13 cm. in diameter and the xylem 8 cm. broad. There are many flowering shoots some of which are represented by cup-like depressions, the base of the cup consisting of the cylindrical axis and the sides bearing the impress of the encircling bracts (fig. 534). Goeppert compared these lateral shoots with the buds frequently produced on the stems of Cycas. It is interesting to find that some of the cups correspond very closely in size with Williamsonia flowers, another indication of the very close agreement between the Williamsonia and Bennettites types of strobili. Some flowers still in place show 16 bipinnate microsporophylls that were petrified before the synangium-bearing fronds unfolded[1169]. The ramental scales and other tissues figured by Schuster are of the usual type. A second specimen found as a boulder in Silesia and named by Goeppert Raumeria Schulziana may, as he suggests, be a younger example of C. Reichenbachiana. Another Galician stem, probably also Lower Cretaceous in age, is described by Raciborski[1170] as Cycadeoidea Niedźwiedzkii.

Cycadeoidea gigantea Seward.

This species is founded on a large stem from the Upper Purbeck series of the Isle of Portland[1171] where it was discovered in a shaly clay 17 ft above the great Dirt bed which yielded the trunks described by Buckland and other authors (fig. 535). The stem (fig. 554) is 1 met. 18 cm. high and has a maximum diameter of 1 met. 7 cm. It is the tallest fossil Cycadean stem so far found in a single piece though Cycadeoidea Jenneyana probably reached a greater height. The stem is elliptical in section (fig. 537), a form due in part at least to compression. The only tissues preserved are in the superficial region of the persistent leaf-bases. As the result of decay before mineralisation many of the petiole-bases are represented by cavities or meshes in a prominent reticulum of silicified ramental scales. Towards the apex the leaf-bases are smaller and a conical bud surrounded by linear scale-leaves occupies the summit: an irregular cap of ramental scales forms the apex of the terminal bud. In section the bud would no doubt present an appearance like that shown in Wieland’s photograph of the terminal cone of C. Marshiana[1172]. There is a striking resemblance both in the ramental cap and in the form of the protective scales between the fossil stem and such a Cycad as Encephalartos Altensteinii[1173]. A remarkable feature of C. gigantea is the absence of any fertile shoots among the leaf-bases. In one tangential section a small bud was found, but it affords no evidence of the presence of any reproductive organs. A similar bud is described by Lignier[1174] in the stem of C. micromyela. The absence of lateral flowers is, however, hardly a sufficient reason for separating this stem generically from other species of Cycadeoidea: negative evidence in this case is of doubtful value. While it is possible that the strobili were terminal as in most recent Cycads, it is more probable that they were lateral. The surface-features, though not perfect, are for the most part sufficiently well preserved to enable one to recognise the bract-encircled axes of strobili were any present. If as Wieland believes, and he is probably correct, the production of flowers was the culminating event in the life of these Cycadean plants, the absence of fertile shoots is merely an expression of immaturity. It is, however, difficult to understand how lateral branches could find their way to the surface among the crowded and cork-covered leaf-bases of the stem. The absence of flowers may be due to some unfavourable external conditions. The petioles consist of parenchymatous ground-tissue with many secretory sacs and in some cases twelve partially preserved vascular bundles: the xylem consists of radial rows of centrifugal tracheids and medullary rays, but it is not possible to say whether any centripetal xylem was present. A fairly thick band of phelloderm and periderm, apparently subepidermal in origin, forms the peripheral tissue, and in places epidermal cells with attached ramenta are clearly preserved. The ramenta are of the type characteristic of the majority of fossil Cycadean stems. Stomata were found showing a pair of guard-cells and apparently two subsidiary cells: the epidermal cells have straight walls.

Cycadeoidea micromyela Morière.

This Liassic species from Normandy has been fully investigated by Lignier[1175]; originally referred to the Conifers, it was afterwards described by Morière[1176] as Cycadeoidea micromyela. As regards external features the stem is of the usual Cycadeoidea type: Saporta[1177] assigned it to the genus Platylepis. The secondary xylem consists of tracheids with bordered pits on the radial walls arranged as single contiguous rows, resembling scalariform pitting, or as 1–2 rows of separate circular pits (fig. 538, A), a type different from that of the great majority of Mesozoic species. The uniseriate medullary rays are 7–20 cells deep, a character recalling the compact wood of Indian Williamsonia stems. Ramental scales are for the most part replaced by long unicellular hairs like those of Williamsonia scotica and some Indian stems. Lignier states that true ramenta occur on the young leaves and in older fronds become transformed by separation of the cells into long tubes. Each leaf-trace arises as a single bundle dividing into three as it leaves the stele and eventually splits up into several collateral bundles (fig. 538, B, C). The stele is elliptical. No fertile shoots are preserved: a single axillary bud is described which agrees very closely with that in Cycadeoidea gigantea.

Cycadeoidea Jenneyana Ward.

The stems of this species, from the Black Hills of Dakota[1178], resemble those of Cycadeoidea gigantea and C. Reichenbachiana in their thick columnar form but differ from the former in the presence of bisporangiate flowers associated with the leaf-bases. This species probably reached a length of 3–4 met. A striking feature[1179] is the unusual thickness of the xylem-cylinder, which shows clear indications of concentric rings, probably the expression of seasonal changes during the production of secondary conducting tissue by a single cambium. Similar concentric rings have been described in the stems of the recent Cycad Dioon spinulosum[1180]. Fig. 539 represents an ovulate strobilus referred to this species by Wieland.

Cycadeoidea pumila Fliche and Zeiller.

This French Portlandian species[1181] affords a good example of a very small bulbiform trunk, 3·5–4 by 2·5–3 cm., superficially resembling a Pine-cone: the leaf-bases are, however, less uniform in size and shape than Abietineous cone-scales; there are also indications of interpetiolar ramenta and a small lateral, presumably fertile, branch. A stem of similar form is described by Saporta[1182] from Corallian beds in France as Bulbopodium micromerum, and Cycadeoidea nana Ward[1183] from Dakota is another example of a small Zamia-like Mesozoic stem. A small tuberous stem, 8 × 7·5 cm., was described by Lindley and Button from Lyme Regis as Cycadeoidea pygmaea[1184]; no flowers are shown in the drawing, but occasional irregularities in the arrangement of the leaf-bases may be due to the presence of lateral fertile shoots.

=Cycadella.= Ward.

This generic name was instituted by Lester Ward[1185] for some petrified stems from Jurassic beds in Wyoming of relatively small size, bulbous or more or less spherical, and characterised by the presence of a thick layer (5–15 mm.) of dense ramental tissue. The unusually vigorous development of the ramental scales is an interesting feature, though it is perhaps questionable whether it is worthy of generic recognition. The flowers of Cycadella, though less than those of most Cycadeoidea stems, are of the same type. In a later account of the genus Ward[1186] describes a few additional species and in Cycadella ramentosa he notes the preservation of young fronds. The fronds are small and bear a few pinnae: the xylem is said by Wieland[1187] to be mesarch, but in the absence of more details the foliar bundles cannot be fully described. In some Cycadellas young flowers, less than 1 cm. in diameter, are preserved, those of Cycadella wyomingensis (7 mm. in diameter) being the smallest bisporangiate strobili so far recorded. The French species, Cycadeoidea micromyela Mor., resembles Cycadella in the profuse development of ramental tissue which may cover the surface of the stem.

=Amphibennettites.= Fliche.

This generic name was instituted[1188] for two species founded on very imperfectly preserved ‘fruits’ of Lower Cretaceous (Albian) age from the Argonne which, though in close agreement with Bennettites as represented by B. Gibsonianus and B. Morierei, are referred to a separate genus on the ground that the preservation is not such as to establish their generic identity with those species and because of certain distinctive features.

Amphibennettites Bleicheri Fliche. The ovulate strobili are sub-elliptical, 3·5 × 3 cm., with several elliptical pits close to the surface originally occupied by seeds borne on short stalks and larger than the seeds of other species of Cycadeoidea (Bennettites). Interseminal scales occur between the seeds. The second species, Amphibennettites Renaulti, is rather larger and more conical: the seeds reach a length of 11 mm. greater than that of any of the American seeds described by Wieland. In neither species is there any indication of an involucre of bracts. The preservation of the specimens leaves much to be desired, but it would seem that the Argonne fossils agree in their main characters with Bennettitean strobili and it is doubtful whether a distinctive generic name is necessary. The occurrence of seeds over the whole surface, a feature that suggested the name Amphibennettites, may be only apparent and the result of cutting the cone transversely. It is worthy of note that one of Fliche’s sections[1189] bears a close resemblance to an Araucarian cone, and in the absence of structure the two types of cone might easily be confused.

=Vectia.= Stopes. Genus incertae sedis.

Vectia luccombensis Stopes.

The generic name Vectia has been given by Dr Stopes[1190] to some petrified secondary phloem discovered by her at Luccomb Chine in the Isle of Wight: the fossil is from Aptian beds. The mass of phloem is 26 mm. in breadth and consists of regularly alternating bands of thin-walled sieve-tubes and very thick fibres associated with a little parenchyma (fig. 540). To the naked eye the specimen presents an appearance suggestive of rings of growth but this is due to the presence of bands of 2–3 narrow cells which are probably cork. The whole is penetrated by uniseriate medullary rays. A striking feature is the regular alternation of single rows of fibres with two bands of sieve-tubes; in places the two bands of sieve-tubes are separated by 2–4 rows of very flat, presumably, cork-cells, and similar bands may be adjacent to or pass obliquely across the fibres. The elongated elements described as sieve-tubes, though thin in comparison with the fibres, have thickened walls and on their radial faces are single rows of circular pits, often in pairs; these are almost certainly sieve-areas which have lost the finer pitting of the sieve-plates. The fibres are more or less square in transverse section and have excessively thick walls, the lumen being reduced to a small hole. Parenchymatous cells (fig. 540, a) occupy the angles between the sieve-tubes and occasionally stretch tangentially between a pair of tubes: these are compared by Dr Stopes to companion-cells, but their manner of occurrence hardly justifies the interesting suggestion that they may be precursors of the Angiosperm companion-cells. The medullary rays may be as wide as the elements which they traverse; they are characterised by their wavy walls, as seen in radial longitudinal sections; no pitting was noticed. A remarkable feature of the specimen is its considerable breadth: it is pointed out that in a giant stem of Sequoia with a girth of over 40 ft the secondary phloem does not exceed 3–4 mm. in breadth. The great thickness of the phloem in the fossil suggests comparison with the corresponding tissue in recent and fossil Cycadean stems, and the alternation of hard and soft phloem is a feature exhibited also by Cycadeoidea Gibsoniana (fig. 518, B). Dr Stopes concludes that the phloem is in the main similar to that in some Cupressineae, Taxineae, and Taxodineae. It is noteworthy that similar phloem with sieve-tubes and fibres associated with cork is described by Graf Solms-Laubach[1191] from Upper Jurassic beds in Franz Josef Land. The systematic position of Vectia cannot be definitely determined, but I believe that it is more closely allied to Cycadean than to Coniferous phloem.

* * * * *

+Note.+ It is unfortunate that Mr Wieland’s second volume dealing with American Cycads [Wieland (16)] did not come into my hands until nearly the whole of this volume was in type. Students will find in it many additions to our knowledge of Cycadeoidea and Williamsonia, much theoretical discussion that is suggestive and interesting, useful summaries of our knowledge of fossil Cycads, and many beautiful photographic plates illustrating the morphology of American species of Cycadeoidea.

Spotted a typo or a problem in this chapter? Tell us