Chapter XXXVII: BENNETTITALES (continued) (2)

This Upper Jurassic species from Portugal[1275] consists of a number of small bracts or leaves attached to a central axis and is of no value as evidence of the occurrence of _Williamsonia_.

_Williamsonia problematica_ (Newberry).

This species was first described from the Amboy clays as _Palaeanthus_ (_Williamsonia_) _problematica_[1276] and compared to a Composite inflorescence with long ray-florets. More recently Hollick[1277] has referred to this species specimens from the Cretaceous of Long Island and Martha’s Vineyard, but none of them afford conclusive evidence of Williamsonian affinity. Some of the examples, as suggested by Hollick, agree fairly closely with _Williamsonia cretacea_ Heer.

_Williamsonia Smockii_ Newberry.

The curious urn-like bodies from the Amboy clays[1278] on which this species is based are not unlike the capsules of a _Papaver_ but bear no real resemblance to a _Williamsonia_.

_Williamsonia Riesii_ Hollick.

A species from the Cretaceous rocks of Martha’s Vineyard[1279] referred to _Williamsonia_ on rather slender grounds and represented by imperfect material.

_Williamsonia_ (?) _phoenicopsoides_ Ward.

This fossil from the Cretaceous of the Black Hills, Dakota[1280], is much too imperfect to be accepted as a record of _Williamsonia_.

_Williamsonia elongata_ Lesquereux.

This species, founded on part of a conical receptacle with some appendages superficially resembling those of _Williamsonia_[1281], is too incomplete to be determined with any confidence. The type-specimen is from Cenomanian beds in Kansas.

_Williamsonia virginiensis_ Fontaine.

This is undoubtedly a true member of the genus; it is characterised by narrow ovate bracts bearing conspicuous hairs surrounding the base of a receptacle which shows a portion of an annular zone of interseminal scales[1282].

_Williamsonia_ (?) _gallinacea_ Ward.

This species from the Potomac beds[1283] is of no value as a record of _Williamsonia_.

_Williamsonia_ (?) _Bibbinsi_ Ward.

The imperfectly preserved specimen from the Potomac series so named by Ward[1284] is probably part of an Abietineous cone as stated by Berry[1285] who includes Ward’s type with other specimens referred to _Abietites macrocarpus_ Font.

_Williamsonia cretacea_ Heer.

Two specimens, figured by Heer[1286] from the Lower Cretaceous of Greenland, on which this species is founded, consist of an axis covered with small scale-leaves and at the broad apex bearing numerous narrow linear bracts forming a more or less spherical cluster 3·8 cm. in breadth. The species resembles _W. problematica_ (Newb.).

_Williamsonia recentior_ Dawson.

The specimens from the Middle Cretaceous of Canada figured by Dawson[1287] under this name are very imperfect and of no botanical value.

=WIELANDIELLA.= Nathorst.

The specimens on which this genus is founded were originally described by Nathorst from Höör in Scania as _Williamsonia angustifolia_[1288]: in a second paper[1289] a restoration of the plant was published (fig. 566). The examination of additional specimens from the Rhaetic of Bjuf and of cuticular preparations led to the establishment of a new genus _Wielandia_[1290] for which _Wielandiella_[1291] was afterwards substituted, _Wielandia_ having been previously employed for an existing plant. _Wielandiella_ agrees in the general morphology of its bisporangiate flowers with _Cycadeoidea_, but differs widely from nearly all other members of the Bennettitales in the repeatedly forked slender stem which is in marked contrast to the vegetative axis of any recent Cycad. Among recent Cycads with terminal strobili an indication of a primitive dichasium is afforded by the occurrence of an aborted bud in a stem of _Dioon edule_ described by South and Compton[1292]; but in the habit of the stem _Wielandiella_ is far removed from any recent Cycadean type. The microsporophylls are smaller and simpler than in _Williamsonia_ or _Cycadeoidea_ and the foliage-leaves are of the _Anomozamites_ type (_cf._ fig. 615).

_Wielandiella angustifolia_ Nathorst.

In an account of this species in 1902 Nathorst described two types of strobilus, male and female, but a re-investigation of the material led to a modification of the earlier conclusions. The stem is slender, rarely exceeding 1·5 cm. in breadth, repeatedly branched as a dichasial system with a fertile shoot in the forks formed by the equal and widely divergent branches. Nathorst’s restoration, as he points out, may exaggerate the regularity of the branching, but an examination of the original specimens in the Stockholm Museum convinced me that the habit represented in fig. 566 is substantially correct. The method of branching is similar to that in the inflorescences of Gnetalean plants and recalls some _Gleichenia_ fronds. The surface of the thicker pieces of stem shows fine longitudinal striae, while transverse striations like those on the axis of a _Heterangium_ frond characterise the more slender specimens. Closely set polygonal leaf-scars cover the stem for a short distance below each bifurcation and the surface of the short and relatively stout peduncles of the strobili (fig. 567). Though for the most part confined to the region of false dichotomy, leaf-scars occasionally occur on other parts of the stem. Small fronds, 7–8 cm. long, agreeing closely with _Anomozamites minor_ Brongn., occur in the same beds at Bjuf, and the striking resemblance between their long linear and winged petioles and the transversely striated bracts enclosing the strobili of _Wielandiella_ amply justifies Nathorst’s conclusion that _Wielandiella_ bore fronds of the _Anomozamites_ form[1293]. Small scars marking the position of bracts occur immediately below each strobilus and occasionally form narrow zones between the larger foliage leaf-scars. The strobili are met with in two forms representing two states of preservation and, probably, different ages. In one form the strobilus consists of a small pyriform axis separated from the peduncle by an annular swelling characterised by parallel striations (fig. 567), the so-called palisade-ring. From this ring Nathorst obtained many microspores scattered and in groups on the surface of short sporophylls, 2·5–3 mm. in length. It is these sporophylls which form the parallel striations; they occur as a circle of rather broad linear organs with irregularly toothed distal ends and an epidermis of papillose cells. The oval microspores, 32–42μ long, vary in size and, as Nathorst says, this may indicate immaturity. The precise mode of occurrence of the spores has not been ascertained, but they were probably produced in sporangia on the surface of the small microsporophylls. These strobili have in all probability lost the female organs which were borne on the pyriform axis, and the inference is that the strobili were protogynous. Thomas[1294] compares the ring at the base of the flower-axis from which spores were obtained by Nathorst to the whorl of microsporophylls of _Williamsoniella_, but in _Wielandiella_ the sporophylls are greatly reduced and possibly functionless. _Wielandiella_ may be intermediate between the bisexual _Williamsoniella_ and the unisexual _Williamsonia scotica_. In the second form of strobilus the pyriform axis is hidden and the specimens consist of a central ovate body, approximately 3 cm. long, surrounded by several linear bracts (fig. 568, A). The carbonised surface of the central region revealed on chemical treatment a fairly regular pattern formed by the contiguous polygonal ends of interseminal scales arranged round smaller cylindrical micropylar tubes which project beyond the level of the scales (fig. 568, B). This arrangement agrees closely with that of the corresponding organs in _Williamsonia_ and _Cycadeoidea_ (_cf._ figs. 515, 564). In _Wielandiella_ the micropylar tubes are of uniform diameter and the cells of the epidermis have smooth walls in contrast to the micropylar tubes of _Williamsonia_ (fig. 563). The strobilus in this state, before the scales and ovules have become detached from the axis, may be described as a small _Williamsonia_, but the habit of the stem is in itself a sufficient reason for the use of a distinctive generic name[1295].

A second species, _Wielandiella punctata_, described by Nathorst[1296] from Scania is founded on pieces of forked stems associated with fragments of a palisade-ring formed of contiguous segments (microsporophylls) with microspores 58μ in length. Fronds of _Anomozamites minor_ occur in the same beds.

Mr Hamshaw Thomas[1297] described some specimens from the Middle Jurassic beds of Marske in Yorkshire which he suggested might be pieces of a _Wielandiella_ stem. Additional material was subsequently found and this enabled Thomas to produce evidence in favour of connecting the branched vegetative axis with bisporangiate strobili and the fronds of _Taeniopteris vittata_. For the stems and flowers the new designation _Williamsoniella_ has been proposed. Further research will no doubt show that the _Wielandiella_ type of stem was not exceptional in Rhaetic and Jurassic floras.

Nathorst[1298] suggests the possibility that some specimens from the Solenhofen Slates described by Thiselton-Dyer[1299] as _Condylites squamatus_ may be allied to _Wielandiella_. The generic name _Condylites_ was suggested by the elbow-like branching of stems which bore imperfectly preserved and apparently terminal cones; the surface of the branches is covered with the scars of leaves. The resemblance to _Wielandiella_ is, however, slight and it would seem more probable that the Solenhofen fossils are Coniferous, though, as Nathorst says, the supposed scale-like ‘leaves’ may be scars of Cycadean fronds.

Wieland[1300] records the occurrence in Mexico of stems similar to those of _Wielandiella_ associated with some _Otozamites_ fronds.

=WILLIAMSONIELLA.= Thomas.

This genus was instituted for specimens discovered by Mr Hamshaw Thomas[1301] in the Middle Estuarine series of the Middle Jurassic plant-bed at Gristhorpe on the Yorkshire coast, and the genus is recorded also from the Cleveland district in the same county. _Williamsoniella_ occurs in those parts of the Gristhorpe bed where fronds of _Taeniopteris vittata_ are abundant.

_Williamsoniella coronata_ Thomas.

The type-species is represented by fertile shoots consisting of a central axis bearing both megasporophylls and microsporophylls (figs. 569, 571, A). Below its crown-like sterile apex the pyriform peduncle is covered with small interseminal scales and ovules similar to those of _Williamsonia_: this portion is 6 mm. in diameter and 1 cm. long. A whorl of separate cuneate microsporophylls forms a hypogynous ring below the basal interseminal scales: each sporophyll is attached by a narrow base (fig. 570) and bears 5–6 reniform synangia containing microspores. The flower is thus bisexual: it affords no conclusive evidence of the occurrence of any covering bracts like those of most Bennettitalean flowers. In young specimens the microsporophylls are closely packed round the axis (fig. 571, B). The flower-stalks reach a length of 3·5 cm. and are 3 mm. in diameter. Fig. 571, C, shows a receptacle from which the sporophylls have fallen: the microsporophylls having been no doubt attached to the collar-like swelling at the base. Towards the apex the axis becomes broader and at _s_ a few interseminal scales are left: above these is the apical disc (corona) characterised by longitudinal ribs. An apical disc is reproduced in fig. 572; it has the form of a royal crown 1–2 mm. high with 12–16 vertical ridges separating flat surfaces formed by the pressure of microsporophyll apices in the unexpanded flower. The corona is surmounted by a small conical elevation which represents the apex of the fertile axis. An apical view of an unexpanded flower is shown in fig. 571, B; the tips of 12 sporophylls are closely pressed against the corona which probably consists in part at least of fused interseminal scales. The microsporophylls were shed after the dehiscence of the synangia. Each sporophyll is flattened on the sides and thicker on the curved outer edge; the synangia, usually in two rows of three, are borne on the sloping sides (figs. 569, 570). The surface of a microsporophyll is covered with small rounded projections which produce a characteristic appearance. The form of a microsporophyll in section is shown in fig. 570: the synangia are similar in shape to those of _Cycadeoidea_ and _Williamsonia_ (_cf._ figs. 531, 549, etc.) but there are no external indications of septa like those seen in some other types. On macerating some specimens it was found that the spores occur in about 20 groups. The circular or elliptical spores are 0·02 mm. in diameter. The walls of the epidermal cells of the microsporophylls are straight: the stomata, which show the features characteristic of the Bennettitales, agree closely with those of _Taenopteris vittata_.

The interseminal scales associated with the ovules and covering the pyriform axis above the microsporophylls are more or less flattened and hexagonal and the micropylar tubes often project far beyond the scales. Each micropyle-tube is surrounded by 5–6 interseminal scales (_cf._ fig. 564). The ovules differ from those of _Cycadeoidea Gibsoniana_ in the absence of a distinct pedicel and agree with the corresponding organs of _Williamsonia scotica_[1302]. In the absence of epidermal papillae the micropylar tubes resemble those of _Wielandiella angustifolia_. As already stated, the flowers appear to be without protective bracts, but in the shale from which the specimens were obtained a few bract-like organs were discovered consisting of a lanceolate lamina 1·5 cm. long, and 2–3 mm. broad near the base, and some showed a small oval lamina at the apex with a midrib and dichotomously branched lateral veins. These bracts with the terminal lamina are regarded by Thomas as almost certainly reduced leaves of the _Taeniopteris vittata_ type: they are represented in the restoration (fig. 573) as occurring at the base of the flower-peduncle. Stomata were found on the bracts exactly like those on the microsporophylls, and this affords a strong argument in support of the view that _Williamsoniella_ belongs to the plant which bore _Taeniopteris_ fronds. There is a close parallelism between the bracts accompanying _Williamsoniella_ flowers and those described by Nathorst in connexion with _Wielandiella_[1303]. It seems reasonable to regard the bracts as serving the purpose of bud-scales.

An important point is the constant association with the flowers of _Taeniopteris vittata_ fronds, a species described in Vol. +ii.+ and by most palaeobotanists regarded as a Fern frond. _Taeniopteris_ leaves occasionally show a clean-cut base[1304] and in specimens described by Thomas there are two small humps on the surface of the proximal end of the petiole which represent vascular bundles. Humps of similar size occur on the leaf-scars of stems which are believed to have borne both _Taeniopteris_ leaves and _Williamsoniella_ flowers. Fragments of the stems were found in association with flowers: they are 7 mm.–2 cm. in diameter and frequently forked and there is evidence that the flowers were borne at the forks, the shoot forming a dichasial system. The habit of the plant is represented in fig. 573 reproduced from Mr Thomas’s paper.

_Williamsoniella Lignieri_ (Nathorst).

This species described by Nathorst as _Williamsonia_? _Lignieri_ from Whitby is regarded by Thomas as a _Williamsoniella_. The stomata on the microsporophylls agree with those of _Taeniopteris_ and the spores obtained from Nathorst’s flower-buds are like those of _Williamsoniella coronata_. Evidence is adduced by Thomas in favour of regarding _W. Lignieri_ as bisexual and not unisexual as Nathorst supposed.

In habit _Williamsoniella_ resembles _Wielandiella_: in the latter genus the foliage-leaves were confined to portions of the stem near the forks, while in _Williamsoniella_ they were more uniformly scattered: _Wielandiella_ bore leaves of the _Anomozamites_ form while _Williamsoniella_ flowers are always associated with _Taeniopteris_ fronds. The much greater spore-output of _Williamsonia_ may, it is suggested by Thomas, be correlated with the unisexual nature of the flowers of that species. The microsporophylls of _Williamsoniella_ differ in their more reduced form from the pinnate microsporophylls of _Williamsonia_, _e.g._ _W. spectabilis_, and agree more closely with those of _Wielandiella_. The microsporophylls of _Williamsoniella_ are free and not connate at the base as in _Cycadeoidea_ and _Williamsonia_. In its pyriform axis _Williamsoniella_ resembles _Williamsonia gigas_ and differs from _Williamsonia Leckenbyi_ in the possession of a sterile apical corona: _Williamsoniella_ has megasporophylls and microsporophylls both of which appear to be functional, while in _Cycadeoidea_ fully developed microsporophylls occur in association with megasporophylls which are immature and must have matured much later than the microsporophylls. The new genus agrees with _Williamsonia_ in its general features, but the flowers are smaller and are characterised by the considerable reduction and simplification of the male organs.

=CYCADOCEPHALUS.= Nathorst.

This genus was founded[1305] on a specimen from the Lower Rhaetic of Scania, at first regarded as a megastrobilus and on further examination[1306] found to be a collection of microsporophylls resembling those of _Williamsonia_ and _Cycadeoidea_. The type-species is _Cycadocephalus Sewardi_, and a second species, _C. minor_, was subsequently discovered by Dr Halle at a slightly higher horizon in the Rhaetic series. Prof. Nathorst’s most recent account of the genus affords a striking illustration of the possibilities of the method, which he has employed with conspicuous success, of investigating carbonised fossils by means of cuticular preparations.

_Cycadocephalus Sewardi_ Nathorst.

The type-specimen consists of an oval cluster of 16–18 linear microsporophylls, 9 cm. long, springing from a small circular disc formed of their concrescent and narrow bases. The whole flower (fig. 574) exclusive of the peduncle is 10 cm. long and 7 cm. broad. The portion of the comparatively slender peduncle that is preserved shows no trace of leaf-scars. In the middle of each linear microsporophyll is a keel-like midrib and on either side of this is a series of linear appendages (fig. 574) 2–3 cm. long lying in a radial direction towards the centre of the flower. These appendages were originally thought to be seeds (fig. 574, _a_), but it was suggested by Wieland that they might be synangia, the circle of leaves being the male portion of a bisexual flower of the _Cycadeoidea_ type. Nathorst’s more complete investigation of the specimen confirmed the first of these suggestions, but there is no evidence that there was an ovulate receptacle in the centre of the flower. The appendages are attached by a rather broad and slightly cordate base and are represented by a thin carbonised cuticle of rectangular cells showing in one case a row of imperfectly preserved stomata: on this are numerous groups of tetrahedral microspores, about 55μ in diameter, which show a more or less well marked arrangement in rows transverse to the long axis of the thin laminae. It is clear from Nathorst’s researches that the groups were enclosed in loculi bounded by thin-walled cells[1307], the loculi being in transverse rows on each side of a midrib. Nathorst speaks of the appendages as synangia characterised by the large number of the sporogenous compartments, and he compares them especially to the fertile leaflets of _Danaea elliptica_ as described by Bower[1308], each appendage being comparable with a revolute _Danaea_ pinnule in which the edges of the lamina are united. This is illustrated by the section of an appendage (fig. 574, D) reproduced from Nathorst’s restoration of a _Cycadocephalus_ microsporophyll. From a morphological point of view it would seem more appropriate to speak of the appendages as highly modified pinnules rather than synangia. The second species, _C. minor_, agrees closely except in its smaller size with the type-species. Nathorst regards _Cycadocephalus_ as a unisexual flower differing from those of _Williamsonia_ and from the microsporophyll-verticils of _Cycadeoidea_ in the structure of the synangia and in the tetrahedral form of the spores, though the latter feature he considers to be of secondary importance, as both bilateral and radial spores occur in recent Marattiaceae. He includes the genus in the Bennettitales but suggests that it should be referred to a separate family as an indication of the possession of characters which mark it off from _Williamsonia_, _Weltrichia_, _Wielandiella_, and _Cycadeoidea_.

=WELTRICHIA.= Braun.

The name _Weltrichia_ was given by Braun[1309] to some Rhaetic fossils discovered by Weltrich near Culmbach in Franconia which represent funnel-shaped structures, the lower part having the form of an incomplete cup made of the concrescent bases of about 20 broadly linear segments which in the upper part are separate lanceolate lobes each with a midrib and slightly curved inwards at the apex. The whole, nearly 10 cm. long and 9 cm. in diameter at the upper edge, is very similar to the specimen of _Williamsonia spectabilis_ reproduced in fig. 551. Braun described three species, but he realised the possibility that the different forms may be different stages in the development of a single type _Weltrichia mirabilis_. He assigned the genus to the Rhinantheae. Saporta[1310] drew attention to the resemblance of Braun’s species to some examples of _Williamsonia_ from Yorkshire which he considered to be portions of a sterile appendage borne at the apex of the flower. Some account is given of two types of funnel-like structures connected with _Williamsonia_ flowers on a previous page[1311]: one of these has been shown by Nathorst to be a whorl of microsporophylls, and it is with this that _Weltrichia_ agrees. An important feature of _Weltrichia_ is the occurrence of short linear segments, 5–8 mm. long, attached to the inner face of each of the free portions of the linear lobes: the lobes, or more correctly the free apical portions of the fertile leaves, and their slender appendages are compared by Nathorst[1312] to the microsporophylls and relatively long synangia-bearing appendages of _Cycadocephalus_. These, presumably fertile, segments of _Weltrichia_ project in the flattened impressions beyond the edges of the free lobes of the campanulate flower and look like marginal teeth, though they are actually attached on each side of the midrib and originally extended, as in _Cycadocephalus_, towards the centre of the funnel-shaped flower. The examination of one of the type-specimens acquired by Nathorst[1313] for the Stockholm Museum enabled him to confirm his earlier conclusion that _Weltrichia_ represents the male portion of a flower, whether unisexual or bisexual cannot be definitely determined, of a Bennettitalean plant. There is, as Nathorst states, a close agreement in plan between _Weltrichia_, _Cycadocephalus_, and _Williamsonia_, and indeed it is not clear in what respects _Weltrichia_ is sufficiently distinct from _Cycadocephalus_ to be retained as a separate genus. Our knowledge of _Weltrichia_ is, however, less complete than in the case of _Cycadocephalus_ and _Williamsonia_. It is noteworthy that Braun’s specimens and those on which _Cycadocephalus_ was founded were obtained from Rhaetic rocks. An account of _Weltrichia_ has also been published by Schuster[1314] who differs from Nathorst in his interpretation of the type-specimens: he considers that another fossil described by Braun and named by him _Palaeoxyris microrhombea_ is the central, female, portion of a _Weltrichia_ flower, a view that is not supported by any substantial evidence. The specimens referred by Braun to _Palaeoxyris_ and afterwards transferred by Schimper[1315] to the genus _Lepidanthium_ are too obscurely preserved to be determined with any degree of confidence, and their connexion with _Weltrichia_ is purely hypothetical. With _Weltrichia_ Schuster also connects the fronds known as _Otozamites brevifolius_ Braun and some impressions of stems, combining all in a restoration of a complete _Weltrichia_ plant which rests more on imagination than on fact. Attention has elsewhere[1316] been called to some wholly misleading and incorrect statements made by Schuster which vitiate the value of his descriptions.

Saporta[1317] described a species of _Weltrichia_, _W. Fabrei_. from French Rhaetic strata at Mende (Lozère) which bears at least a close superficial resemblance to _Williamsonia spectabilis_, and the same author founded another species, _Weltrichia oolithica_, on a drawing by Zigno of a specimen from Jurassic rocks in Italy; but this appears to be too imperfect for accurate identification.

All that can be said as to the nature of _Weltrichia_, as illustrated by the type-species, is that it represents a Rhaetic example of a verticil of microsporophylls very similar to those of _Williamsonia_ and _Cycadocephalus_, if not generically identical with the latter form.