Chapter XXX: II. Medulloseae (2)

The generic name _Trigonocarpum_ was instituted by Brongniart in 1828[329] for ovoid longitudinally ribbed ‘fruits’ from Upper Carboniferous strata, the type-species being named _T. Parkinsoni_. The generic name is often altered to _Trigonocarpon_: Williamson[330], who adopted this form, states that Brongniart substituted _Trigonocarpon_ for _Trigonocarpum_ in his _Tableau_[331], but in that work the original termination is used, the form _Trigonocarpon_, probably the result of a slip, appearing only in the index. In his later work on seeds Brongniart adopted the name _Trigonocarpus_, and in recent years this has been widely employed. Among other species named by Brongniart are two previously referred by Sternberg to _Palmacites_. Several examples of Brongniart’s genus were described by Lindley and Hutton, and in their description of _T. Noeggerathii_ the statement is made that a fractured specimen demonstrated that ‘the fossil in its ordinary state is an interior part divested of fleshy covering’[332]; this suspicion of the true nature of the nut-like fossils was afterwards proved correct by the investigations of Hooker and Binney[333] and by the later work of Williamson. The specimens on which the genus was founded are casts of seed-cavities and it is in this state that the seeds are usually preserved, often in large numbers, in the sandstones of the Coal Measures, as in the block shown in fig. 423 from the famous quarry at Peel near Bolton, Lancashire. Another type of preservation is represented by the seeds figured by Lindley and Hutton as _Carpolithes alata_[334], but the generic identity of the two states was not recognised until the discovery of petrified material afforded the clue. Figs. 424, 1, 425 illustrate the appearance of _Trigonocarpus_ when preserved as a carbonised impression showing a thick fleshy envelope enclosing an oval kernel with a hard wall prolonged upwards as a longer or shorter micropyle. Casts of the seed-cavity are represented in figs. 423; 424, 2, 3. The surface of these casts occasionally shows one or more short cylindrical projections which are probably extensions of the sand or mud into holes formed in the testa by boring insects. The view that _Trigonocarpus_ seeds are ‘obviously Palm fruits’ was not accepted by Hooker and Binney who inclined to regard them as the seeds of Conifers and compared them especially with the similar nuts of _Ginkgo_ seeds (_cf._ fig. 631, C). It was Mr Wild[335] who was first struck by the association of _Trigonocarpus_ and the petioles of _Medullosa_ (_Myeloxylon_) and by some resemblances in structure between the testa and the hypoderm of the petioles; though, as Scott and Maslen[336] point out, the agreement is not so close as Wild believed, his view of a possible connexion between the reproductive and vegetative organs has been confirmed. Williamson extended our knowledge of the genus by his account of _Trigonocarpus olivaeformis_ Lind. and Hutt., a form that is specifically identical with _T. Parkinsoni_ Brongn. This author also drew attention to the close resemblance between Brongniart’s three genera _Trigonocarpus_, _Hexapterospermum_, _Tripterospermum_ and expressed doubts as to the possibility of founding specific differences on casts of the _Trigonocarpus_ type without the evidence of anatomy. Our knowledge of the structure of _Trigonocarpus_ has in recent years been considerably extended by the researches of Oliver, Scott and Maslen, and Salisbury.

(Manchester Museum. ½ nat. size.)]

_Trigonocarpus Parkinsoni_[337] Brongniart.

The seeds of this species like all examples of the genus are radiospermic, that is radially symmetrical in contrast to the flattened or platyspermic seeds. The complete seed is elongate oval in form when preserved as an impression (fig. 425, A) and reaches a length of 4–5 cm.: the casts of the seed-cavity are ovoid and provided with three prominent ridges (fig. 424, 2, 3). The testa forms a thick covering differentiated into three regions, an outer flesh or sarcotesta, a sclerous shell or sclerotesta, and an inner flesh. Transverse sections show that the sclerotesta has three sharp longitudinal keels with corresponding furrows on the inner face, and between each pair of main ribs are 2–3 less prominent ridges, usually 12 in all (fig. 426). The sarcotesta consists of thin-walled parenchyma passing externally into a more lacunar tissue with a palisade-like hypoderm: the sclerotesta consists of thick cells which interlace and form an efficient protective shell. Both the sarcotesta and sclerotesta are continued into the apical region as the wall of the long micropyle, the sarcotesta being prolonged beyond the sclerotesta at the apex of the integument[338]. The micropyle is triangular in section and may exceed in length the whole seed (figs. 425; 426, A). Its form as seen in transverse section (fig. 426, B) suggests the presence of wings: this appearance may be deceptive and due to pressure or, more probably, it represents an original feature. The seed-body, that is the portion enclosed by the integument, consists of the nucellus, represented by a few crushed layers of cells, bounded by a well-defined epidermis; the nucellus is separated from the integument from the base of the seed upwards, an important feature in which this and some other Palaeozoic seeds differ from _Lagenostoma_ and the seeds of recent Cycads which are characterised by an integument adnate to the nucellus up to the level of the shoulder; the seeds of the Conifer _Phyllocladus_ afford an example of separation of integument and nucellus as in _Trigonocarpus_. The innermost layer of the nucellus consists mainly of tracheal tissue investing the large megaspore (fig. 426, A, C, _m_) which is preserved as a contracted membrane detached from the nucellus after the death of the seed. At the summit of the nucellus is a relatively small pollen-chamber (fig. 426, A, _Pc_) like a broad and low cupola bearing a terminal beak which extended some distance into the micropylar tube. No microspores have been found in this species, but Oliver[339] records the occurrence of multicellular microspores in _Trigonocarpus pusillus_. The pedicel of the seed had a central strand of sclerous tissue penetrated by a concentric vascular bundle which gives off six strands to supply the sarcotesta (fig. 426, C, _v_) and then passes into the nucellus where it forms a tracheal sheath (fig. 426, A, _nt_) surrounding the lower part of the megaspore and at a higher level breaks up into anastomosing strands of tracheids which reach up to the plane of insertion of the pollen-chamber.

B. Specimen with long micropyle. (A, nat. size; from the Lower Coal
Measures of Kilmarnock; B, nat. size; Middle C. M. of Yorkshire.
Kidston Coll., 1579 and 1062.)]

A second species described by Scott and Maslen as _Trigonocarpus Oliveri_ has been further investigated by Salisbury who finds that it is an 8-angled seed which cannot be retained in the genus _Trigonocarpus_: its systematic position ‘must for the present remain uncertain[340].’ Dr Arber has recently described a new species of _Trigonocarpus_, _T. Moyseyi_[341], from the Nottingham Coal-field (Middle Coal Measures), similar to _T. Parkinsoni_ but much broader in proportion to its length: this species is founded on an impression without structure.

The species _Trigonocarpus Dawesi_ Lind. and Hutt.[342], from the Middle Coal Measures of Lancashire, was founded on casts differing in their large dimensions from those of _T. Parkinsoni_: specimens referred to this species were described by Fiedler[343] from Saxony in 1857 and Lesquereux[344] figures similar casts from the Upper Carboniferous and Permian rocks of North America.

_Trigonocarpus shorensis_ Salisbury.

This species, founded on specimens from the Lower Coal Measures of Shore, Lancashire[345], may exceed 4 cm. in length and has a breadth of 2·5 cm. In general plan it agrees with _T. Parkinsoni_ but there are certain well-marked differences: the micropyle is much shorter; the thick sarcotesta, attaining a breadth of 6 mm. at the base of the micropyle, is characterised by the presence of six peripherally placed vascular bundles (fig. 426, D, _v_) in contrast to the deeply embedded bundles of _T. Parkinsoni_. Below the epidermis of the sarcotesta is a hypoderm formed of radially disposed plates of sclerous tissue similar to that of _Myeloxylon_ and different from the palisade-like hypoderm of the type-species. Within the sarcotesta is a hard shell, the sclerotesta, characterised by three prominent ribs extending from base to apex and three shorter ribs which reach from the chalaza to about a third of the length of the seed. The fact that the sarcotesta and sclerotesta pass gradually into one another is a point in favour of the view that the integument is a single structure. There appears to be good evidence of the restriction of an inner flesh to the micropylar region, whereas this tissue in _T. Parkinsoni_ was probably continuous over the whole inner face of the sclerotesta. The sarcotesta is lacunar in its outer part as in some other types of Palaeozoic seeds, a feature probably connected with floating efficiency. _Trigonocarpus shorensis_ occurs in association with _Myeloxylon_ petioles, and there is a resemblance between the seed and the vegetative organs in the structure of the hypoderm as also in the structure of the secretory sacs which are particularly numerous in this species. Salisbury draws attention to the close resemblance between the form of _T. shorensis_ and the seeds found in organic connexion with pinnae of _Neuropteris obliqua_[346].

The species _T. corrugatus_ described by Renault[347] bears a close resemblance to _T. shorensis_.

+Other Genera founded in part on Reproductive Organs which may belong
to the Medulloseae.+

=Codonotheca=, =Schützia=, =Whittleseya=, =Dolerophyllum=, =Ottokaria=,
=Strobilites=.

=CODONOTHECA.= Sellards.

_Codonotheca caduca_ Sellards. This genus was founded on some spore-bearing bodies from the Coal Measures of Illinois[348]: nothing is known as to the plant which bore them, but Sellards is inclined to associate them with _Neuropteris decipiens_ Lesq.[349], a species abundant in the same coal-field. Whatever may have been the parent-plant it is probable, as the author of the genus believes, that _Codonotheca_ is the microspore-bearing organ of a Pteridosperm. As shown in fig. 427, 5, the form is that of a stalked cup consisting in the basal portion of a stout axis, the peripheral tissue of which is believed to have been fleshy, containing an axial rod of conducting tissue running up to the floor of the cup, _c_, and then dividing into six vascular strands, each of which forks into two branches. The upper part is composed of six linear segments united basally to form the sloping surface of the cup. On the inner face of each segment is a more or less well-defined depression covered with large elliptical spores ·29–·31 mm. long by ·18–·19 mm. broad (fig. 427, 6, 8). The presence of a median ridge (fig. 427, 8) indicates a bilateral origin. ‘There is no grouping of the spores or other indication of the location of the sporangia, which were doubtless more or less completely immersed in the tissue, the dividing wall disappearing at maturity.’ The spores are seen in fig. 427, 2, 3, on the inner face of the lobes. Some of the specimens have a fairly long pedicel: in the example shown in fig. 427, 1, the fleshy part of the basal portion is not preserved, only the more resistant vascular core. In a later account of these organs Sellards speaks of several lying by the side of a central stalk to which he thinks they were originally attached by slender pedicels. In view of Dr Benson’s interpretation of the morphology of _Telangium_ it is permissible to suggest that if a central sporangium in such a synangium as that of _Codonotheca_ developed a megaspore and the peripheral sporogenous lobes were sterilised, the result would be an arrangement not unlike the apical region of the seed _Physostoma_, the tentacles of which have been homologised with the canopy of _Lagenostoma_. There are obvious difficulties in the way of this, perhaps strained, comparison: the larger size of the spore-bearing linear segments of _Codonotheca_ led Sellards to regard each as a synangium rather than a single sporangium. But precise information as to the structure of the American fossils is not as yet available. If the association of _Codonotheca_ with _Neuropteris_ fronds has any significance it would favour a reference of these organs to the Medulloseae. In the absence of anatomical data it is impossible in some cases to distinguish microspore-bearing organs of the _Codonotheca_ type from small seeds enclosed in a lobed cupule or even seeds with a lobed integument: a case in point is the New Brunswick species _Pterispermostrobus bifurcatus_ Stopes[350].

A Spitzbergen, Culm, fossil recently described by Nathorst[351] as _Codonotheca (?) pusilla_ is briefly referred to under the genus _Pterispermostrobus_.

=SCHÜTZIA.= Geinitz.

This generic name was instituted by Geinitz[352] for some Permian fossils obtained by Bergmeister Schütz and regarded by the author of the genus as probably fertile branches of some Conifer. A more complete account was published by Goeppert[353] in his ‘Permian Flora,’ where the name _Anthodiopsis Beinertiana_ occurs on the Plates, printed before the publication of Geinitz’s description, but in the text the specimens are referred to _Schützia anomala_.

_Schützia anomala_ Geinitz.

The type-species, recorded from Bohemia and Silesia, is represented by fertile shoots consisting of a thick main axis bearing apparently two-ranked though probably spirally disposed short lateral branches, each of which terminates in a receptacle with numerous crowded linear-lanceolate bracts superficially resembling a partially expanded inflorescence of a Composite. Goeppert believed that the branches bore seeds and he refers to this species a number of detached, longitudinally striated and bluntly terminated, seeds. The same author describes other specimens from the same localities associated with _Schützia anomala_, which he names _Dictyothalamus Schrollianus_[354]: in habit these agree closely with _Schützia_ but the receptacles, the reticulate appearance of which suggested the generic name _Dictyothalamus_, bear a large number of small bodies regarded as seeds. The preservation of the fossils is not such as to enable us to determine their true nature but it is probable that _Schützia_ and _Dictyothalamus_ are not generically distinct. In his description of _Dictyothalamus_ Goeppert suggests that the two associated types may be the male and female shoots of one plant, but he speaks of seeds in both cases. Schimper[355], who unites _Dictyothalamus_ with _Schützia_, regards the latter as female and the former as male.

_Schützia Bennieana_ Kidston.

This species, described by Kidston[356] from the Calciferous series of Scotland, differs from _S. anomala_ in its much more slender axis and in the relatively narrower and less globular clusters of bract-like appendages. The principal axis bears three lateral branches with terminal clusters of acute and narrow linear scale-leaves. No seeds were found in association with the specimens.

_Schützia permiensis_ (Renault).

Renault founded this Permian species as _Antholithus permiensis_[357] on a specimen from Lodève; it consists of an incomplete inflorescence 6·4 cm. long bearing four lateral branches with stalks 1·5 to 2 cm. long terminated by clusters of small oval bracts 5 mm. long. Renault compares the fossil with the recent Conifers _Glyptostrobus_ and _Tsuga_, but it exhibits a much closer resemblance to _Schützia anomala_.

The genus _Schützia_, originally described from Permian strata, is recorded also from Westphalian strata in North Africa[358] as well as from Lower Carboniferous rocks in Scotland. The data at present available are insufficient to determine the morphological nature of the fertile branches: the evidence adduced by Goeppert in support of the occurrence of seeds is not convincing and the interpretation of the bract-like appendages is still an open question; they may have formed a cupular investment to seeds, but in the Scotch species the general appearance rather suggests that they may be microspore-bearing organs comparable with those of _Codonotheca_[359]. There are no adequate grounds for supposing _Schützia_ to belong to the Coniferales, a view advanced by some authors; it is much more likely to represent the fertile shoots of a Pteridosperm.

=WHITTLESEYA=. Newberry.

The genus _Whittleseya_, referred by many authors to the _Ginkgoales_, has no substantial claim to be regarded as allied to that group: its position is still uncertain, but the recent discovery of fertile specimens suggests the probability of a relationship to _Potoniea_ and an identification of Whittleseya as another form of microsporophyll of a Pteridosperm.

A, C. _Whittleseya elegans_. A, single leaflet, from Pennsylvania.
(After Lesquereux; ⅚ nat. size.) C, diagrammatic sketch of part
of a leaflet showing the teeth, the striated texture of the
carbonised layer, and the vein-like markings on a lower
surface. (After Thomas; enlarged.)
B. _Whittleseya brevifolia_. (After White; the smaller figure ⅚ nat.
size.)]

The generic name was given by Newberry[360] to some leaves, or possibly leaflets, originally described by C. Whittlesey from the Coal Measures of Ohio. Whittleseya is represented by species from several North American localities[361] in Ohio, Pennsylvania, Arkansas, Nova Scotia, and New Brunswick[362]; it occurs in Silesia and has recently been found in the English Coal Measures[363]. The genus is confined to Upper Carboniferous strata.

The leaves are fairly thick; the lamina is oblong, cuneate, broadly triangular or linear, usually rounded and truncate (fig. 428, A, C), generally dentate at the distal end, the proximal portion being gradually or abruptly contracted and occasionally prolonged into a short pedicel. The veins or ribs are parallel to the sides of the lamina and except near the base unbranched.

_Whittleseya elegans_ Newberry.

The type-species, from North America and Europe, is characterised by its shovel-like lamina from 3 to 6 cm. long closely resembling in shape some lepidopterous scales; the surface is ribbed, each rib corresponding to a tooth on the distal margin; on each of the parallel ridges are 4–5 longitudinal lines indicating either veins or stereome strands (fig. 428, A, C). The examination of preparations made by Dr Kidston from a leaflet of this species enables me to add a few facts with regard to the microspores. The spores, which cover almost the whole surface of the lamina, show a tendency to a more or less definite arrangement in longitudinal rows. Two types of cuticularised membrane are represented among the associated fragments: in some pieces of cuticle the cells are short and have straight walls while in others the preservation is inferior and the cells appear to be longer and narrower. One or both of these membranes probably belong to the sporangia. The oval slit, which is a striking feature on several of the spores (fig. 429), points to their bilateral nature and dehiscence along the major axis. A comparison of these spores with those obtained by Kidston from the English species _Whittleseya fertilis_ reveals a very close agreement both in size and shape and confirms the identification of the Staffordshire specimens as leaflets of _Whittleseya_. The large size of the microspores and the gaping oval aperture in some of them are features in which they agree closely with the spores of _Dolerophyllum fertile_ described by Renault[364]. In both cases the spores tend to be arranged in long groups and they are practically identical in form and in the nature of the exine; those of _Dolerophyllum_ are 280μ long while those of _W. fertilis_ reach a length of 220μ. In some of the _Whittleseya_ spores the exine has split as in the specimen shown in fig. 429, but in others there are two curved lines along which dehiscence has begun, a character in which the spores appear to be identical with those of _Dolerophyllum_ described by Renault who speaks of dehiscence by means of an operculum. There is, I venture to think, little doubt as to the very close affinity of the two types. The systematic position of _Dolerophyllum_ is not certainly established; if the generic identity of the leaves described as _D. Berthieri_ Ren. and the petrified specimens named _D. fertile_ is assumed, it is a legitimate inference that the genus is founded on fertile pinnules of a Pteridosperm with foliage of the _Neuropteris_ or _Cyclopteris_ form. It would seem probable that both _Whittleseya_ and _Dolerophyllum_ _fertile_ are microspore-bearing leaflets of Pteridosperms, possibly of some Medullosan plants. The leaflets of _Whittleseya_ agree in form fairly closely with those of _Potoniea adiantiformis_ Zeill. described on a previous page[365] as the male organs of a Pteridosperm.

The specimens described by Lesquereux from Pennsylvania as _W. integrifolia_ and _W. undulata_ are less satisfactory than _W. elegans_. The Arkansas species _W. microphylla_[366], characterised by the obcuneate form of the lamina, is said to occur not only as detached leaflets but in loose bunches at the ends of slender axes, a circumstance favourable to the suggestion, based on the recently described English specimens, that the _Whittleseya_ leaves may be fertile pinnules of a Pteridosperm frond. Among other species attributed to Newberry’s genus is _W. brevifolia_ Wh. from Nova Scotia[367] with much smaller broadly triangular leaves 7 mm. long exclusive of the petiole and 8 mm. broad at the distal end (fig. 428, B). Dr Matthew[368] has also described a Canadian species _W. concinna_ from New Brunswick in beds assigned by Dr Stopes[369] to the Westphalian series.

_Whittleseya fertilis_ Kidston.

Since the discovery of _Whittleseya elegans_ in the Coal Measures of Staffordshire recorded by Mr Thomas, Dr Kidston has published an account of some specimens from the same district under the name _Whittleseya (?) fertilis_[370]: these consist of smaller cuneate scale-leaves or leaflets 1·4–2·4 cm. long and 8–9 mm. broad; the lamina has a dentate upper margin and is longitudinally ribbed. The scales occur in superposed pairs, closely fitting but not organically connected, at least in the state in which they are preserved; each pair forms a sporangium-like case enclosing numerous spores but the actual sporangia or synangia have not been preserved. Kidston describes the spores as 210–222μ in length, elliptical, and characterised in many cases by an oval slit; they are practically identical with the microspores of _W. elegans_.

=DOLEROPHYLLUM=. Saporta.

This name was proposed[371] primarily for a large ovoid petrified bud composed of rolled Cyclopteroid leaves from Permian rocks in the Ural Mountains, which had been previously described by more than one writer under different names and regarded as a young shoot of a Palm or other Monocotyledon. Eichwald[372], who published good drawings, called the fossil _Noeggerathia Goepperti_. Saporta connected with this species some leaf-impressions from the Permian of Bohemia described by Goeppert[373] as _Noeggerathia cyclopteroides_: in his family Dolerophylleae[374] the French author included other leaves which are probably not closely related to the type-species, _Dolerophyllum Goepperti_. The Dolerophylleae are spoken of by Saporta and Marion[375] as Progymnosperms. Before the publication of Saporta’s note Grand’Eury had instituted the genus _Doleropteris_[376] and the family Doleropteroideae; in the former he included several forms of leaves agreeing generally with Goeppert’s _Noeggerathia cyclopteroides_. Zeiller[377] adopts Grand’Eury’s designation for the Russian fossil in preference to _Dolerophyllum_, a choice justified by considerations of priority; but the latter name is retained in this account as it was assigned by Saporta to the specimen of greatest botanical interest, namely _Dolerophyllum Goepperti_, and because it does not suggest affinity to Ferns.

_Dolerophyllum Goepperti_ (Eichwald).

The type-species is from the Zechstein of Orenburg in the Urals and no specimens having precisely the same structure have been found elsewhere. Eichwald assigned it, with leaf-impressions of various kinds, to the Noeggerathieae and named it _Noeggerathia Goepperti_: it had previously been described by Kutorga[378] as _Aroides crassispatha_ and Unger[379] included it among the Palms as _Palaeospathe aroidea_. The species has been described also by Saporta and Marion and by Renault[380]. The following account is based on sections cut from a specimen in the British Museum[381] which, though assigned on the label (within a query) to France and named _Dolerophyllum Berthieri_, is undoubtedly Eichwald’s species from East Russia.

The specimen (fig. 430) is 9 cm. long and 4·2 cm. broad: at the slightly contracted and broken base is a piece of immature axis (fig. 430, B, _a_) 12 mm. in diameter overtopped by a mass of closely packed leaves encircling one another like the bulb-scales of an Onion (fig. 430 A, C)[382]. Most of the leaves included in the bud were attached to the axis below the broken base. The curved, dichotomously branched, veins are seen on some of the pieces of lamina on the surface of the bud (fig. 430, A). The considerable breadth of the leaves is demonstrated by the longitudinal and transverse sections. In fig. C most of the laminae can be traced through the whole height of each of the steep-sided arches: a few overlapping margins are seen in fig. D. The veins are for the most part imperfectly preserved and appear as clear spaces at regular intervals in the brown mesophyll. The axis of the shoot consists of homogeneous parenchyma except near the sloping sides where narrow dark bands (fig. 430, B, _a_) mark the position of desmogen-strands of thin-walled elongated elements representing an early stage in the development of vascular bundles some of which have already produced spiral tracheids. Short secretory cells accompany the immature conducting elements. The lamina slightly exceeds 2 mm. in thickness in the broadest part: the mesophyll is composed of large parenchymatous cells of elliptical or spherical form often loosely attached owing to the well-developed system of intercellular spaces. The lower epidermis, assuming that the outer face of the rolled leaves is the morphologically lower surface, forms a uniform layer of palisade cells characterised by their free conical ends (fig. 431, A, B, _e_) which in some oblique sections appear as sharply pointed papillae with almost filiform apices; but while the cells were doubtless papillose like those of the epidermis of a velvety petal, the pointed form is due in part to the greater distinctness of the dark contents as compared with the lighter cell-walls. The upper epidermis is much less distinct; it consists of smaller flattened cells with occasional stomata. Renault[383] figures a specimen with stomata in a better state of preservation. The vascular bundles are rendered conspicuous by large secretory cells on the lower side, in the larger veins in the form of an arc or irregular group (fig. 432, A), but in the finer veins as single cells (fig. 431, A, B). These sacs resemble the tannin cells accompanying the veins in a leaf of _Ginkgo_ (_cf._ fig. 631, G). The xylem-elements are of two kinds, (i) elongated spiral and scalariform conducting elements, forming a vertical plate of a few rows in the larger veins (figs. 431, 432) or a small compact group in the more slender veins (fig. 413, A, B); (ii) much larger isodiametric cells with reticulate or spiral thickening resembling the transfusion-tracheids of Conifers or, perhaps more closely, similar elements in the leaves of _Lepidodendron_. These short tracheids are especially abundant on the flanks of the conducting tracheids (figs. 431, _t_; 432, A, _t_), but they sometimes form a complete investment. In the obliquely cut vein reproduced in fig. 431, D, the transfusion-tracheids are abundant: a few are enlarged in fig. 431, E. In the smaller veins (fig. 431, A, B) they are represented by the larger elements, _t_, on the sides of the conducting strands. The protoxylem lies close to the upper edge in the middle line (_px_, figs. 431, A; 432, A); it is difficult to determine its precise position, but it would seem to be slightly internal, the bundle being not quite endarch. No phloem was recognised in the British Museum specimen, but it presumably occurred, if present, where the black patch is shown in fig. 432, A. Renault describes some phloem in sections which he examined.

The mesophyll next the upper surface is in most cases represented by spaces between the veins which give a crenulated outline to the parenchyma (fig. 430, C, D); in some places the spaces contain remains of very loose and crowded cells suggesting the original presence of very lacunar tissue or possibly of thin-walled storage-cells. The confinement of stomata to what is assumed to be the upper surface may, as Renault and others have suggested, indicate leaves which floated on water, an inference opposed to the view that the gaps in the mesophyll mark the position of water-tissue.

No specimens have been described which enable us to correlate with certainty mature leaves or foliage-shoots with the petrified bud. It is, however, not improbable that the impression from Mount Pelé near Epinac named by Renault _Dolerophyllum Berthieri_[384] may be correctly referred to the same genus. The type-specimen consists of an axis, whether a rachis of a compound leaf or a shoot with simple leaves cannot be determined, bearing partially overlapping more or less orbicular leaves 18–20 cm. in diameter, with a _Cyclopteris_ venation. Among other leaves of unknown affinity referred to the same genus attention is drawn to _Dolerophyllum pseudopeltatum_ (Grand’Eury)[385] with an orbicular lamina reaching in some specimens 22 × 19 cm. Specimens of _Dolerophyllum pseudopeltatum_ are figured by Renault from the Commentry coal-field[386], some of which reach a diameter of 12 cm. The only British specimen of a leaflet of this type which I have seen is one in Dr Kidston’s collection from the Stephanian series, Glamorganshire. It is probable that some at least of the impressions assigned to _Dolerophyllum_ or _Doleropteris_ would be more appropriately included in _Cyclopteris_ or _Cardiopteris_ and may have been borne on the axis of large Pteridosperm fronds. Grand’Eury[387] has also called attention to the difficulty of distinguishing the larger _Cyclopteris_ leaflets from _Dolerophyllum_. Some of the Cyclopteroid leaflets figured by Roehl[388] on _Neuropteris_ fronds differ but slightly from those of _D. pseudopeltatum_. The shoot showing large leaf-scars figured by Saporta and Marion[389] as probably the axis of a _Dolerophyllum_ may well be a piece of _Cordaites_.

_Microsporophylls assigned to_ Dolerophyllum.

Certain problematical fossils found in association with the sterile leaves of _Dolerophyllum Berthieri_ have been described by Renault as the male organs of that species. These are elliptical discs, 6 × 5 cm., with an excentrically placed stalk: embedded in a carbonised lamina are numerous rows of elliptical bodies, 410μ × 280μ, characterised by two curved longitudinal grooves on the surface and regarded by Renault as pollen-grains. The chains of these microspores radiate outwards from the neighbourhood of the stalk and cover most of the surface of the disc (fig. 432, B). Some silicified pieces of similar spore-bearing discs from Grand’ Croix named _Dolerophyllum fertile_[390] afford additional information as to these remarkable reproductive organs. The earlier account of this species by Renault is confirmed by Solms-Laubach[391] who examined the original sections. The peltate fleshy discs preserved as incomplete specimens consist of lacunar parenchyma 15–18 mm. thick traversed at right angles to the surface by numerous loculi (fig. 432, C), circular or oval in transverse section, containing large numbers of microspores, _s_, similar in size and form to those on the carbonised discs of the Mt Pelé specimen. Vascular strands occur between and parallel to the spore-chambers. The spores contain 8–10 cells (fig. 432, D) and Renault believes that dehiscence of the exine occurred along the two deep grooves which mark the limits of an operculum. He emphasises the peculiar structure of the microspores by speaking of them as prepollinia: in size and in the presence of internal cells (? male prothallus) they resemble the spores found in the pollen-chamber of a seed described by Renault as _Aetheotesta elliptica_[392] which he thinks may belong to a member of the Dolerophylleae. It has also been suggested that _Codonospermum_ may be a seed of _Dolerophyllum_[393]. An unconvincing specimen described by Saporta and Marion[394] as a seed-bearing bract is regarded by them as referable to _Dolerophyllum_, but the evidence for any connexion is far from satisfactory.

There is nothing definite to be said with regard to the affinity of _Dolerophyllum Goepperti_ or the microsporophylls represented by _D. fertile_ and the specimens associated with _D. Berthieri_. Renault considers that both sterile and fertile specimens belong to the same genus, which he assigns to a position between Pteridophytes and Cycads. As Solms-Laubach says, the evidence supplied by the structure of the veins of _D. Goepperti_ in favour of a cycadean alliance is not convincing. The type of vernation is unlike that of any known Cycad or indeed of any Gymnosperm: the large size of the leaves is another though weaker objection to this comparison, as the pinnae of _Bowenia_ (fig. 391) and especially those of some species of _Zamia_ (fig. 388), are of equal or larger dimensions. If, as seems probable, the xylem-strands are mesarch that is a point of contact with recent Cycads, but the bundle as a whole bears but a remote resemblance to that of a cycadean leaf and is much more like the veins of _Ginkgo_. The bud shown in fig. 430, A, is probably a young shoot and not merely a large compound leaf. If it were an unexpanded frond of _Neuropteris_ bearing _Cyclopteris_ pinnules we should expect to find indications of scattered desmogen-strands such as would occur in the _Myeloxylon_ type of rachis. The resemblance to most forms of _Cordaites_ is by no means close though a few leaves referred to that genus (_e.g._ _C. circularis_, fig. 468, B) are similar to those of _Dolerophyllum_[395].

The male organs are unlike those of any other plant: they may be described as sporophylls with microsporangia or perhaps synangia embedded in the mesophyll and containing microspores similar to those of some Pteridosperms or true Gymnosperms. Attention has been called to the close resemblance of the spores shown in fig. 432, C, D to those recently discovered by Kidston and referred to the genus _Whittleseya_ (fig. 429), and it is very probable that the striking similarity is an index of affinity.

=Ottokaria.= Zeiller.

_Ottokaria bengalensis_ Zeiller. A specimen of doubtful affinity from the Lower Gondwana (Karharbari beds) of Passerabhia, India, was originally described by Zeiller[396] as _Feistmantelia bengalensis_, but in a postscript he substituted the name _Ottokaria_ on the ground that _Feistmantelia_ had previously been employed by Lester Ward. Fig. 433 is drawn from the original specimen: it consists of a stalk attached in a slightly excentric position to an almost orbicular lamina, 2·5 cm. in diameter, with subacute marginal teeth and traversed by numerous radially disposed striations. Zeiller compares the fossil with _Whittleseya elegans_ and _Rhipidopsis ginkgoides_ and assigns it with some hesitation to the Salisburieae. An examination of the type-specimen led me to form the opinion that it may be a cupular organ of a Pteridosperm that enclosed a seed. The lamina is slightly concave and has the form of a shallow cup; moreover the surface-features resemble those of a bract rather than the regularly veined lamina of a foliage-leaf. The specimen bears a very close resemblance to one figured by Bertrand[397] as the cupule of _Hexapterospermum modestae_ which he connects with fronds of _Neuropteris gigantea_.

_Ottokaria_ occurs in association with fronds of _Glossopteris indica_ and with the large seeds described by Zeiller[398] as _Cardiocarpus indicus_. I have lately obtained some evidence in favour of assigning Feistmantel’s seeds _Carpolithes Milleri_[399] to the genus _Glossopteris_: among several specimens from the Lower Gondwana rocks of India I found an example showing a seed partially covered by a scale-leaf in its natural position which appears to be identical with scale-leaves of _Glossopteris_. It may be that the specimen represented in fig. 433 belongs to _Cardiocarpus indicus_, though this is a mere guess: my belief is that _Ottokaria_ is a cupular organ that enclosed the base of a seed borne on a Pteridosperm. There is little doubt that as additional data are obtained it will be found that Pteridosperms played no inconsiderable part in the vegetation of Gondwana Land.

=Strobilites.= Schimper and Mougeot.

_Strobilites Milleryensis_ (Renault).

This species, from the Permian of France, was placed by Renault in _Cycadospadix_[400], but having regard to the fact that it differs essentially in habit from Mesozoic examples of that genus the provisional name _Strobilites_[401] is suggested. The type-specimens are long and narrow spikes or loose strobili, 8–16 cm. long and 2–2·6 cm. broad; a stout axis bears spirally disposed bracts 8–10 mm. long attached by a slender decurrent pedicel expanded distally into a fan-shaped laciniate lamina with a convex upper face, and there are said to be two seeds attached to the sides of each pedicel (fig. 434). The oval seeds appear to be platyspermic and resemble _Samaropsis fluitans_ Daws. Two of the strobili figured by Renault are attached at right angles to a second axis, a habit suggesting comparison with that of a large compound frond. Renault is inclined to regard these fertile shoots as cycadean and suggests a possible connexion with the Permian stems _Ptychoxylon_ or _Poroxylon_, both of which are known to have produced fairly numerous branches. In habit the spikes are similar to some of the longer examples of _Cordaianthus_, but their preservation is not sufficiently good to afford accurate information as to the relation of seed to sporophyll. _Strobilites Milleryensis_ is, perhaps, more likely to be the fertile branch of a compound frond of a Pteridosperm, and it is significant that the seeds have been found in association with _Callipteris_ leaves.

=COLPOXYLON=. Brongniart.

_Colpoxylon aeduense_ Brongniart. The genus was founded by Brongniart[402] on a piece of stem 15 cm. in diameter from the Permian of the Autun district and regarded by him as a distinct type, with certain resemblances to recent Cycads. A thick section in the British Museum, 13 cm. in diameter (fig. 435, A), illustrates the main anatomical features described by Renault[403], to whom our knowledge of the genus is chiefly due. There are two large steles of irregular outline closely resembling those of _Medullosa Leuckarti_ (_cf._ fig. 416, H); each consists of a band of secondary xylem with broad medullary rays and a narrow zone of phloem enclosing a central region composed of parenchyma, in which strands of primary tracheids, both reticulate and spiral, pursue a more or less horizontal course, associated with a few small groups of vertical xylem-strands at the inner edge of the secondary wood. The manoxylic nature of the wood is clearly shown in fig. 436; the continuous ink-line marks the position of the cambium and the dots show the internal protoxylem. Homogeneous parenchyma surrounds the steles and beyond this is crushed tissue containing large secretory canals and nests of stereome fibres either as separate groups or in contact with the canals (fig. 435, C). In the same peripheral tissue occur scattered collateral vascular bundles (fig. 435, D) identical with those of _Myeloxylon_. The outer cortex of the stem is marked off from the more homogeneous inner region by a fairly distinct line where there is some indication of periderm. The anatomical features are clearly shown in fig. 436, a photograph from a section in Dr Kidston’s collection. At _a_ is an imperfectly preserved vascular bundle with a crescentic group of secondary xylem which is probably a leaf-trace that has just emerged from the secondary cylinder. Renault speaks of these more or less circular strands as possibly connected with reproductive shoots, but it is more probable that they are homologous with the strands in the pericycle and inner cortex of _Medullosa_ and represent leaf-traces before division into smaller collateral strands. Renault describes the stem as possessing seven vascular cylinders in the apical region and suggests branching of the main axis as the cause of the increase in number: there is, however, no evidence to support such correlation. The two steles seen in fig. 435, A, become merged at a lower level into a single stele of sinuous form (fig. 435, B).

Beyond the facts furnished by the leaf-trace bundles in the outer cortex and the occurrence of two large scars about 5 cm. in breadth on a stem figured by Renault, we have no positive information as to the form of the leaves or the structure of the reproductive organs. There is little doubt that the fronds were large and compound like those of most species of _Medullosa_. There is, however, some slight evidence that _Alethopteris Grandini_ Brongn. and seeds of the _Pachytesta_ type (fig. 497) were borne on _Colpoxylon_ stems; this rests solely on the association in the Loire coal-basin[404] of _Alethopteris_ fronds with stems presenting structural resemblances to _Colpoxylon aeduense_.

The striking resemblance between _Colpoxylon_ and _Medullosa Leuckarti_ has led certain authors[405] to propose the substitution of _Medullosa_ for _Colpoxylon_. The resemblances though close are hardly sufficient to warrant this course. In _Colpoxylon_ the stelar system is simpler; there is no central region with star- or plate-rings as in _Medullosa Leuckarti_ but, as in _Medullosa anglica_, the vascular tissue consists only of large steles without a medullary system. _Colpoxylon_ differs from _M. anglica_ in the reduction in some parts of the stem of the vascular system to a single stele and, moreover, the primary portion of the steles is much more parenchymatous in structure and contains more irregularly anastomosing tracheal strands than is the case in _M. anglica_.

The alteration in the pattern formed by the vascular system at different levels in some Medullosan stems, especially in _Colpoxylon_, may be compared with the varying disposition of the vascular strands in the thick dorsiventral rhizomes of _Polypodium heracleum_ Kunz. and _P. quercifolium_ L. In the rhizome of _P. heracleum_ there are two vascular systems, an outer, cortical, system in the form of a hollow cylinder composed of a lattice-work with polygonal meshes from which branches are given off to the roots, and a more complex medullary system that is concerned with the emission of leaf-traces. As shown by a series of drawings reproduced in an account by Klein[406] of the anatomy of these species of _Polypodium_, the inner system of steles consists of two cylinders connected towards the upper surface of the stem by a rounded arch of vascular strands; nearer the leaf-base the two cylinders meet and eventually a larger cylinder is produced partly from the upper halves of the two cylinders of the previous section and in part from the connecting arch: the remains of the two smaller cylinders become connected with the outer vascular system. These and other changes suggest comparison with _Colpoxylon_ as also with the stelar changes in the stem of _Ptychoxylon_. The comparison cannot be carried beyond the grosser features and is chiefly interesting as affording a further illustration of a similarity in plan between some recent Ferns and extinct Pteridosperms and other Palaeozoic genera.

=RHEXOXYLON=. Bancroft.

_Rhexoxylon africanum_ Bancroft. The genus _Rhexoxylon_ was instituted for a new type of stem represented by a single incomplete specimen from the Karroo series of South Africa: its precise geological horizon is not known but it may be referred provisionally to the lower or Palaeozoic portion of the series. Though our knowledge of the morphological features of the type-species is far from complete owing in part to the method of preservation of the specimen and in part to the destruction of the outer portion of the vascular tissue and the whole of the cortex, Miss Bancroft’s careful description[407] demonstrates the existence of characters which justify the employment of a new generic name. _Rhexoxylon_ is more nearly related to the Medulloseae than to any other group and is particularly interesting as the first recorded example of this group from the Southern Hemisphere.

Fig. 437 shows a transverse section (7 × 5 cm.) of the stem. The ground-tissue consists of fairly large-celled parenchyma with sclerous nests and a few bands of periderm. At the periphery of the stem are radially disposed groups of vascular tissue varying in size and to some extent in shape. Unfortunately the stem is incomplete and it is impossible to say how much vascular or other tissue originally existed beyond the present corroded edge. The vascular groups, or steles as they may legitimately be called, follow a vertical course through the length of the block (6·5 cm.) and afford only slight evidence of branching or anastomosing. A close examination of the steles shows that they consist of portions of two series, an inner and outer set; there is also a curved vascular band in the central ground-tissue (fig. 437, _c_) and some isolated and scattered patches of vascular elements. Each stele of the inner series is made up of two parts, an outer smaller and normally orientated group of secondary xylem and a larger inversely orientated inner group of identical structure. A single stele of the inner series is shown in fig. 438, B, C; the larger inner portion consists of slightly divergent rows of tracheids and uniseriate medullary rays and is separated from the smaller portion by a narrow space, _a_, occupied by crushed tissue which may correspond to the ‘partial pith’ or primary xylem of a Medullosan stele. The two groups of xylem are no doubt the products of two cambium arcs, the protoxylem of each group being situated on the flat inner face. The cambium and phloem are represented only by crushed brown cells on the curved outer edge of the xylem. The separate individuality of the two portions of each stele is indicated not only by the presence of the ‘partial pith’ but by the discontinuity of the tissue at the ends of the narrow space. The tracheids seen at _b_, fig. C, are in oblique longitudinal section and are probably being detached to form a leaf-trace. This type of stele may be compared with the steles of _Medullosa Solmsi_ (fig. 416, L) but those of _Rhexoxylon_ differ in the lack of continuity of the secondary xylem round the narrow band of crushed primary xylem. The other steles of the inner ring exhibit the same dual nature though with local modifications. In the stele seen in fig. 438, B, there is a close approach to a continuous cylinder of secondary xylem especially on the right-hand side. External to the inner series are several portions of normally orientated secondary xylem-groups (fig. 437): these probably represent a second series of steles separated from the inner series by a narrow crushed arc of tissue on which the protoxylem strands of the outer groups abut. The xylem of the outer steles agrees in its normal orientation with the outer and smaller part of the inner steles and, as there is no accompanying group of inversely orientated xylem corresponding to the larger mass of secondary xylem of the inner series, the outer strands are designated partial steles. The central stele consists of two curved irregular bands composed of vertically and obliquely running tracheids: the central part of this stele consists of crushed tissue that probably represents primary xylem like that between the two parts of each of the peripheral steles.

_Rhexoxylon_ differs from the usual Medullosan type in the structure of the secondary xylem which is composed of tracheids with an Araucarian form of pitting: there are usually two alternate rows of contiguous pits (fig. 438, A) and occasionally one or three rows. The medullary rays are uniseriate and 3 to 15 cells in depth, a feature characteristic of coniferous wood and not of the wood of the Medulloseae.

In the absence of more complete information as to the anatomical structure of this stem and of all information as to the leaves or reproductive organs it is impossible to fix with precision the systematic position of the genus. It is, however, clear that _Rhexoxylon_ is closely connected with _Medullosa_ in certain features though in the structure of the wood it exhibits important peculiarities. The imperfectly known stem _Cladoxylon Kidstoni_[408] shows a fairly close agreement with the African plant in the form of the steles (fig. 460) but the pitting is scalariform.

=SUTCLIFFIA.= Scott.

_Sutcliffia insignis_ Scott.

The generic name _Sutcliffia_ was given by Dr Scott[409] to a peculiar type of stem from the Lower Coal Measures of Shore, Lancashire, in recognition of the valuable services rendered to Palaeobotany by the late Mr W. H. Sutcliffe, the owner of the colliery from which several new types of plants have been obtained. Two stems are recorded, the type-specimen and a more recently discovered stem, also from Shore, described by Miss de Fraine[410], which differs in several particulars from Dr Scott’s species. In view of the well-marked peculiarities of the second stem it is convenient to speak of it as _forma β_ instead of including it without a distinctive epithet in _Sutcliffia insignis_. We know nothing of the reproductive organs of the genus.

1. _Sutcliffia insignis, forma α._

This consists of a piece of stem approximately 12 × 7 cm. in diameter characterised by a broad cortex of parenchyma with secretory sacs and ducts and strands of mechanical tissue (fig. 439, A). Decurrent and massive leaf-bases form a prominent feature as in the stem of _Medullosa anglica_. The stele, though compressed before petrifaction, was probably not quite cylindrical but more or less polygonal or broadly triangular in section; it consists of groups of large primary tracheids (350μ in diameter) with numerous bordered pits (fig. 439, B, and fig. 440) embedded in an anastomosing system of parenchyma containing scattered secretory sacs, a type of protostele like that of _Heterangium_ and _Medullosa_ _anglica_ except in the possession of exarch protoxylem strands. The metaxylem tracheids contiguous to the external protoxylem elements have a dense spiral or scalariform type of pitting. In the lower part of the stem the primary xylem is enclosed by a cambium which has added a few secondary tracheids (120μ in diameter), but in the upper part of the specimen the cambium is only partially developed and the addition of secondary xylem has hardly begun (fig. 440). A narrow band of secondary phloem was recognised in places consisting of small-celled parenchyma with some sieve-tubes and medullary rays continuous internally with the parenchyma of the primary stele. In close association and occasionally in organic connexion with the surface of the stele are several tangentially elongated and large groups of vascular tissue associated with smaller oval strands varying considerably in size. These groups, designated meristeles (Fig. 439, A), are identical in structure with the main stele and are occasionally invested by a feebly developed zone of secondary xylem and phloem. The meristeles are detached at intervals from the parent stele around which they form by anastomoses an irregular network: the larger meristeles give off smaller strands and from these the actual leaf-traces are produced by subdivision. It appears, however, that in this type the meristeles are not completely used up in the production of the leaf-traces, portions of them behaving as cauline vascular strands. A protoxylem of a meristele still attached to the central protostele occupies an internal position, and at a higher level, as separation of the meristele is effected, the spiral tracheids occur on the inner face. New meristeles are given off at intervals from the main stele ‘to compensate for those parts of the reticulum which were used up in the formation of leaf-trace strands[411].’ The meristeles form the starting-point for the leaf-traces, an intermediate system between the main stele and the actual leaf-traces; they differ, therefore, from the parent leaf-traces of _Medullosa anglica_, which are completely used up by repeated subdivision. Moreover in _Sutcliffia_ the leaf-bundles are concentric and not collateral.

A. Transverse section of stem; _a_, _b_, double rows of leaf-trace
bundles. The larger black masses are the meristeles; the smaller
patches represent bundles derived from the meristeles.
B. Longitudinal section of a radially symmetrical bundle from a
leaf-base.
C. The junction between the primary and secondary xylem.
D. Vascular system in transverse section: _m_, _m′_, meristeles; _s_,
main stele; _e_, extrafascicular strands; _lt_, leaf-traces; _c_,
secondary cortex.
E. Vascular bundle from petiole showing a ring of large sieve-tubes
surrounding the xylem, and portions of stereome strands.]

A conspicuous feature of the stem of _forma α_ is the occurrence of two double rows of vascular strands stretching across the cortex (fig. 439, A, _a_, _b_). These are interpreted by Scott as downward continuations in the stem of the inner surface of leaf-bases. The outer cortex of the stem and leaf-bases has hypodermal strands of stereome which remain separate or rarely anastomose, and form a superficial zone exactly like that of some species of _Medullosa_. The leaf-trace bundles may be radially symmetrical or unilateral in the arrangement of the xylem which is in all cases completely surrounded by phloem. Fig. 439, B, shows part of a longitudinal section of a large leaf-trace bundle: spiral protoxylem elements (_px_) abut on the phloem (_ph_) and are succeeded to the left by narrow scalariform and large reticulately pitted tracheids. In the larger and radially constructed traces there are several protoxylem-strands distributed over the surface of the xylem, while in the smaller unilateral traces there may be one or two protoxylem strands. A characteristic feature of the xylem of the leaf-traces is the admixture of parenchyma with the tracheids (fig. 439, B, E) and another noteworthy character is the occurrence of large thin-walled tubes in the phloem described by Scott as sieve-tubes and compared with the large sieve-tubes in Marattiaceous leaf-bundles. Immediately internal to the hypoderm is a row of leaf-bundles (fig. 439, A) each of which is accompanied by stereome strands.

The petioles, which reach a diameter of 12 cm., contain numerous, occasionally anastomosing, concentric bundles. Nothing is known of the fronds as a whole beyond the fact that they are spirally disposed and had decurrent bases of large dimensions in proportion to the stem.

_Sutcliffia insignis, forma β._