CHAPTER XXXVI.. Cycadophyta.

CYCADOPHYTA.

The term Cycadophyta, suggested by Nathorst, 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 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, 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 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.

BENNETTITALES.

=Cycadeoidea.= Buckland.

In 1827 Buckland 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 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 withdrew Mantellia as it had been previously used by Parkinson for a sponge and substituted Cycadites. Some years later Carruthers 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, 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. The subsequent researches of Carruthers 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, 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 but has not been generally used. A further complication in the nomenclature of Cycadean stems was introduced by Saporta’s institution of Bulbopodium and Cylindropodium: in the former genus he included the small ovoid stem figured by Lindley and Hutton as Cycadeoidea pygmaea 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 has pointed out, both Saporta’s genera may be merged in Cycadeoidea. Fliche and Zeiller 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, the type-species being Cycadeoidea micromyela Mor., from the Lias of Calvados, which has recently been investigated by Lignier who wisely adopts Morière’s designation. Another unnecessary generic name is Schizopodium given by Morière to a stem, S. Renaulti, 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 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, but my usage of the two generic names has not been consistent, the name Cycadeoidea being afterwards employed in a more comprehensive sense. The investigation of the reproductive shoots of American Lower Cretaceous and Upper Jurassic Cycadean stems 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 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. Without access to the actual specimen it is impossible to say whether or not the two ‘laminated circles’ described and figured by Buckland 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. 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 (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, 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, C. nana, 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 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 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. 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. 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 may be present; no medullary bundles have been discovered.

The correlation of the numerous fronds 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; but only unexpanded leaves have been found in actual connexion with Cycadeoidea stems. Wieland 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, 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. 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 (fig. 513). A remarkable feature is the enormous number of flowers on a single stem; in Cycadeoidea Dartoni, 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 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 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). 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.

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The splendid petrified stem, Cycadeoidea etrusca Cap., 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.’ The specimen named by Goeppert Raumeria Reichenbachiana 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, but as Ward pointed out the species is clearly a Cycadeoidea (fig. 507). In 1894 Lester Ward 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, 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, 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.’ 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, 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 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 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 contributed additional data derived from a careful study of a well preserved strobilus from the Gault of Normandy. Wieland’s researches 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 of a specimen from the Inferior Oolite of Charmouth, Dorset (fig. 560), which he referred to the genus Podocarya (= Williamsonia Bucklandi): 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, 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, 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 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 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) 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. It is not improbable that some of the flowering branches of Cycadeoidea were branched. Solms-Laubach 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. A fertile shoot agrees in structure with the main axis and Scott 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. 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.

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 of Vaches-Noires, Normandy. It was first described by Morière, then by Saporta and Marion, who named it Williamsonia Morierei, and it has since been thoroughly investigated by Lignier. 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 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.

A. Transverse section of the micropylar tube containing the apex of the nucellus; Ei, inner epidermis; Tf, ground-tissue; e, outer epidermis with the thickening of the walls shown in a few of the cells. B. Transverse section of the upper part of the micropylar tube; lettering as in fig. A. C. Transverse section at the level of the wings formed by the fibrous layer and corresponding to the angles of the seed, approximately at the level cp in fig. 525; cn, nucellar cavity; Ei, inner epidermis of seed-coat; cf, fibrous layer of wings, f, which extend across the fleshy layer, tch, to the radial layer ar (cf. fig. 525); at, tubular layer; Ee, epidermis of adjacent scale detached from the other tissues, ase, along the line of fracture d; EE, epidermis of two adjacent scales. D. Transverse section of peduncle; tr, tracheids; ac, coloured subepidermal layer; Et, tubular epidermis, double in places; EE, epidermis formed from neighbouring scales. (From Prof. Lignier’s drawings; A, B, D, × 118; C, × 90.)]

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. 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.

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.

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. 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 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, 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 says, consisting of a conical axis bearing numerous fertile and sterile carpels enclosed by a perianth of bracts. Worsdell, 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.’

The letters a, b, c, in this figure correspond to cp, cf, and ar in figs. 525, 526.]

Cycadeoidea dacotensis (McBride).

McBride first described this Lower Cretaceous species from the Black Hills of South Dakota as Bennettites dacotensis, the generic name Cycadeoidea being adopted by Ward 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. 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 affords an admirable example of a method of branching exhibited by some stems: as shown in Wieland’s photographs 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. Similar clusters of short and thick trunks occur in Cycadeoidea superba and other American species.

In the small bisporangiate flowers of this species 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 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.

Cycadeoidea Reichenbachiana (Goeppert).

Goeppert referred this species to his genus Raumeria, a generic name retained by Carruthers though, as Solms-Laubach 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, 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. 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 as Cycadeoidea Niedźwiedzkii.

Cycadeoidea gigantea Seward.

This species is founded on a large stem from the Upper Purbeck series of the Isle of Portland 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. 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. 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 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; originally referred to the Conifers, it was afterwards described by Morière as Cycadeoidea micromyela. As regards external features the stem is of the usual Cycadeoidea type: Saporta 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, 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 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. Fig. 539 represents an ovulate strobilus referred to this species by Wieland.

Cycadeoidea pumila Fliche and Zeiller.

This French Portlandian species 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 from Corallian beds in France as Bulbopodium micromerum, and Cycadeoidea nana Ward 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; 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 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 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 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 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 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 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 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.

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+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.