Volume 1 — CHAPTER XXVII.

GENERA OF PTERIDOSPERMS, FERNS, AND PLANTAE INCERTAE SEDIS.

The genera and species described in this Chapter are founded on sterile leaves or portions of leaves, and in the great majority of cases the reproductive organs are either imperfectly known or have still to be discovered. Some of the genera, the smaller number, are no doubt true ferns, while most of them may safely be regarded as plants which will ultimately be shown to belong to some other group, in most cases that of the Pteridosperms. It is possible that a few of the types may be members of the Cycadophyta rather than of the Pteridospermeae, but evidence as to systematic position is for the most part of a negative kind or too incomplete to lead to any definite expression of opinion as to the cycadean or pteridosperm nature of the imperfectly known Palaeozoic or Mesozoic species. Many of the genera are of little botanical interest, though even the most problematical are of importance as criteria of geological age. Genera which there is good reason for including in the Pteridosperms are dealt with in this section, in order that the Chapter in Volume III. devoted to this important group may be limited to more completely known types.

In most text-books it is customary to employ family names for sterile fern-like fronds which possess similar venation features or have in common certain vegetative characters, the value of which it is impossible to estimate. In the following account family or group names are not adopted, on the ground that such slight utility as they may have is more than counterbalanced by the risk attending a grouping under one name of plants which may agree only in unessential characters. The practice of classifying fossil plants has been carried to excess. Grouping together genera as a matter of convenience unavoidably creates a prejudice in favour of actual relationship, which may or may not exist.

Taeniopteris.

This generic name was instituted by Brongniart[1254] for simple linear or broadly linear leaves with a prominent midrib from which secondary veins, simple or dichotomously branched, are given off at right angles or obliquely. The frond of the type-species Taeniopteris vittata (fig. 332), characteristic of Jurassic floras, was compared by Brongniart with the pinnules of Danaea and Angiopteris. Among recent ferns the Taeniopteris form of frond and venation is represented by Oleandra neriiformis, Asplenium nidus, and many other species. Though usually applied to fronds which there is good reason for regarding as simple leaves, the generic designation Taeniopteris has been extended to include pinnate fronds, e.g. the Upper Palaeozoic species T. jejunata Grand’Eury, and T. Carnoti Ren. and Zeill. (fig. 330, A). The compound fronds from the Lower Coal-Measures of Missouri described by Dr White[1255] as T. missouriensis are characterised by decurrent and confluent Taeniopteroid pinnules. In a later reference[1256] to this plant White pertinently adds, “perhaps it belongs more properly in Alethopteris.”

Leaves of the Taeniopteris type are described by several authors as species of Oleandridium, Angiopteridium, Danaeites, Marattia, and other genera. In such species of Taeniopteroid leaves as have been dealt with in a former Chapter, the occurrence of sori justifies the substitution of a name denoting a close relationship to existing members of the Marattiaceae, but in the absence of fertile specimens the provisional designation Taeniopteris should be retained. It is often difficult to decide between Taeniopteris and Nilssonia as the more suitable name to apply to fragments of fossil leaves of Mesozoic age. Taeniopteris is, however, distinguished from the Cycadean genus by the greater prominence of the rachis, also by the dichotomous branching of the secondary veins, usually close to their origin and at varying distances between the axis of the frond and the edge of the lamina. The genus Taeniopteris, though most abundant in Rhaetic and Jurassic strata, occurs also in Upper Carboniferous and Lower Permian rocks. The generic name Macrotaeniopteris instituted by Schimper[1257] has been used for leaves differing only in size from the usual type of Taeniopteris, but there is no adequate reason for its retention.

The species included in Taeniopteris afford no satisfactory evidence as to their systematic position. It is obviously unwise to adopt such generic titles as Oleandridium, Marattiopsis, etc., merely because of resemblance in the venation of sterile fragments to Oleandra or Marattiaceous ferns.

Some specimens of Taeniopteris fronds described by Mr Sellards[1258] from Permian rocks of Kansas, which are referred to later, have furnished unconvincing evidence of reproductive organs.

Taeniopteris multinervis, Weiss. Fig. 329, A, B.

The late Dr Weiss[1259] instituted this species (which he designated Taeniopteris multinervia, though the specific name multinervis is constantly used) for a fragment of a leaf from the Lower Permian of Lebach characterised by numerous forked veins given off at right angles from a prominent rachis (fig. 329, B). This type of frond is recorded from the Permian of Trienbach (Alsace) by Zeiller[1260], by Renault[1261] and Zeiller[1262] from the Upper Carboniferous of Autun, and from other localities. The lamina of the simple leaf reaches a breadth of 6 cm. and a length of 40 cm. (fig. 329, A); the numerous secondary veins (25–36 per cm. of lamina) are either at right angles to the rachis or given off at an acute angle. The mesophyll consists of polygonal cells some of which are elongated at right angles to the surface of the lamina. A very similar form is described by Fontaine and White from the Permian of Virginia as T. Lescuriana[1263].

Fig.

329.

Taeniopteris multinervis, Weiss. (⅚ nat. size. After Zeiller.)

T. multinervis. (Enlarged. After Zeiller.)

Lesleya Delafondi. (× 2. After Zeiller.)

It is futile to expect to be able to separate the numerous Taeniopteris leaves into well-defined species: all we can do is to group the specimens under different names, using as artificial distinctions such characters as the shape of the leaf, the number of veins per centimetre, and the prominence of the rachis. Another Virginian species of Permian age described by Fontaine and White[1264], T. Newberriana, is said to bear sori, but no satisfactory information is given as to the nature of these organs. Specimens referred with some hesitation to this species and to a similar species, T. coriacea, have been described by Sellards[1265] from material obtained from Permian beds in Kansas. The lamina of the simple linear fronds is characterised by the occurrence of small oval bodies half immersed in the substance of the leaf between the secondary veins (figs. 330, D, E). One of these bodies is represented in an apparently dehisced condition in fig. 330, D. Sellards suggests the possibility that these bodies are sporangia, but, as he points out, they afford no indication of cellular structure nor are they in direct connexion with the veins.

Taeniopteris jejunata, Grand’Eury[1266].

This species differs from T. multinervis in its bipinnate fronds; the linear or oval-linear pinnae are attached by a short stalk to the primary rachis and reach a length of 25 cm.; the veins are less crowded, 12–15 per centimetre.

T. jejunata is recorded from the Coal-fields of the Loire and Commentry[1267] in France, from the Lower Permian of Thuringia[1268], and elsewhere.

Taeniopteris Carnoti, Ren. and Zeiller[1269]. Fig. 330, A.

This species, founded on portions of pinnate fronds from the Coal-field of Commentry, is characterised by rather broader (25–30 mm.) pinnules, with short pedicels and a cordate base, reaching a length of 25–30 cm. The secondary forked veins are more numerous than in T. jejunata. In T. multinervis the pinnules are still broader and have a stronger midrib.

•••••

Several species of Taeniopteris have been described from Triasso-Rhaetic rocks in Europe, India, Tonkin and elsewhere. In some cases it is practically impossible to recognise clear specific distinctions between Rhaetic and Jurassic types.

From the Damuda and Panchet series of India (Triasso-Rhaetic) Feistmantel has described large sterile fronds as Macrotaeniopteris Feddeni[1270] which reach a breadth of 20 cm.: these may be compared with the Indian species Taeniopteris lata Oldham[1271], and to T. gigantea from the Rhaetic of Franconia[1272] and Scania. A specimen of this species figured by Nathorst[1273] from Scania has a lamina 33 cm. broad. Other examples are afforded by M. Wianamattae Feist.[1274] from rocks of the same age in Australia and by Taeniopteris superba Sap.[1275] from Lower Rhaetic rocks near Autun.

From the Rhaetic of Tonkin, Zeiller records several species, among which may be mentioned T. Jourdyi Zeill.[1276] and T. spatulata MacClelland (fig. 330, B, C). Both have simple fronds. Those of T. Jourdyi reach a length of 10–40 cm. and a breadth of 10–70 mm.; the rachis is characterised by crowded and discontinuous transverse folds, and the secondary veins (35–50 per cm.) are usually at right angles to the rachis. This Tonkin species is compared by Zeiller with the European Rhaetic species T. tenuinervis Brauns.

The polymorphism of the fronds is a striking feature: in one case described by Zeiller the lamina appears to be divided into segments like those characteristic of the leaf of the Cycadean genus Anomozamites. It is obviously difficult in many instances to distinguish between detached Taeniopteroid pinnae of a compound frond and complete simple leaves. In some compound fern fronds, as in the recent Polypodiaceous genus Didymochlaena, the pinnules are deciduous, and the same feature undoubtedly characterised the fronds of many extinct species. A specimen figured by Zeiller which shows several petioles of T. Jourdyi attached to a thick stem[1277] demonstrates the simple nature of the leaves. In other cases, e.g. T. vittata, specimens occur in which the slightly enlarged petiole-base has a clean-cut surface indicating abscission from a rhizome (fig. 332).

The fronds described by Zeiller as T. spatulata[1278] (fig. 330, B, C) closely resemble Jurassic leaves from Victoria referred to Taeniopteris Daintreei McCoy[1279].

Fig.

330.

Taeniopteris Carnoti, Ren. and Zeill. (Nat. size. After Renault and Zeiller.)

T. spatulata, McClell. (Nat. size. After Zeiller.)

T. spatulata. (× 3. After Zeiller.)

Supposed sporangium of T. coriacea. (× 15. After Sellards.)

T. coriacea. (× 2. After Sellards.)

Whether specifically identical or not, these leaves represent a type distinguished from the other species of the genus by the small breadth of the linear-lanceolate or linear-spathulate lamina, which may be 6–15 cm. in length and 3–12 mm. broad. The lamina is often characterised by transverse folds (fig. 330, C).

Taeniopteris Carruthersi. Fig. 331.

1872. Taeniopteris Daintreei, Carruthers, Quart. Journ. Geol. Soc. Vol. XXVIII. Pl. XXVII. fig. 6.

1883. T. Carruthersi, Tenison-Woods, Proc. Linn. Soc. N. S. Wales, Vol. VIII. p. 117.

Fig. 331. Taeniopteris Carruthersi, Ten.-Woods. Nat. size.

The simple fronds included under this specific name are characterised by a strong midrib from which numerous simple or forked secondary veins are given off at a right angle or slightly inclined. The breadth of the lamina decreases gradually towards the petiole. The Australian species named by McCoy Taeniopteris Daintreei, to which Carruthers referred the Queensland fossils, has a much narrower and more linear form of frond, and for this reason Tenison-Woods instituted a new specific name. T. Carruthersi represents a form of leaf met with in Rhaetic, or possibly Upper Triassic, rocks in S. Africa[1280] and Australia. A very similar, perhaps an identical type, was described from Argentina by Geinitz[1281] as T. mareyiaca: among many other examples of this form of frond may be mentioned T. immersa[1282] Nath. from the Rhaetic rocks of Scania and T. virgulata from the Rhaetic of Tonkin[1283].

A comparison of Taeniopteris Carruthersi or various other “species” of Rhaetic fronds with the Jurassic species T. vittata illustrates the slight and unimportant differences on which specific separation is based. It is hopeless to attempt to draw a satisfactory distinction between the numerous Taeniopteris fronds from Upper Triassic and Jurassic rocks.

Taeniopteris vittata, Brongniart. Fig. 332.

The simple leaves to which Brongniart applied this name are characteristic of the Inferior Oolite flora of England, and examples of the same type are recorded from Jurassic rocks of India, Poland, the Arctic regions, Japan, China, Australia and other countries[1284].

Leaf linear-lanceolate, reaching a length of more than 20 cm. and a breadth of 3 cm. The lamina increases gradually in breadth from the base and tapers towards the apex. Numerous secondary veins are given off at right angles from a broad midrib: the lateral veins may be simple or forked close to their origin, near the margin, or in the intermediate portion, of the lamina.

It is exceedingly difficult to use Taeniopteris leaves of this form as evidence in regard to the Jurassic or Rhaetic age of plant-bearing strata. The species T. tenuinervis Brauns, as figured by Schenk[1285] from the Rhaetic rocks of Germany and Persia, and recorded from several other regions, presents a close agreement with T. vittata. Oleandridium lentriculiforme Etheridge[1286] from the Hawkesbury series of Australia is another similar leaf. The species T. vittata from the Yorkshire coast, represented in fig. 332, shows a well-preserved petiole with a clean-cut base like that of the petioles of Oleandra neriiformis and other recent ferns which are detached from the rhizome by the action of an absciss-layer.

Fig. 332. Taeniopteris vittata. (British Museum No. 39217. ⅔ nat. size.)

A broader form of frond with similar venation was described by Lindley and Hutton[1287] as Taeniopteris major. An examination of the type-specimen from the Inferior Oolite of Yorkshire, now in the Manchester Museum, led me to doubt the necessity of specific separation from T. vittata[1288].

A smaller frond of the same general type as T. vittata is recorded from Wealden strata of North Germany and England under the name T. Beyrichii[1289].

Weichselia.

This generic name was instituted by Stiehler[1290] for impressions of bipinnate sterile fronds, presumably ferns, from Lower Cretaceous rocks near Quedlinburg. The same type of leaf from English Wealden beds had previously been referred by Mantell and other authors to Pecopteris, and by Brongniart to his genus Lonchopteris[1291]. It is, however, advisable to follow Nathorst’s example[1292] and restrict the latter name to Palaeozoic species. As already suggested, it would obviate confusion to substitute a new generic designation for Lonchopteris in the case of Triassic species which are probably members of the Osmundaceae. The type-species of Stiehler, Weichselia Ludowicae[1293], does not differ in any important character from Weichselia Mantelli, the species originally described by Stokes and Webb from the Wealden of England as Pecopteris reticulata.

Weichselia Mantelli (Brongn.)[1294]. Fig. 333.

1824. Pecopteris reticulata, Stokes and Webb, Trans. Geol. Soc. [2]. Vol. I. p. 423, Pls. XLVI. XLVII.

1828. Lonchopteris Mantelli, Brongniart, Prod. p. 6; Hist. vég. foss. p. 369, Pl. CXXXI.

1894. Weichselia Mantelli, Seward, Wealden Flora, Vol. I. p. 114. Pl. X. fig. 3.

1899. Weichselia reticulata, Fontaine, in Ward, Ann. Rep. U. S. Geol. Surv. p. 651.

Frond bipinnate, rachis broad; pinnae very long, of uniform breadth and with prominent axes; pinnules crowded, entire, with obtuse apex, usually oblong but more or less triangular or rounded towards the distal ends of the pinnae. The pinnules, which may reach a length of 9 cm., are characterised by a fleshy lamina attached by the whole breadth of the base; the two rows of segments on each secondary rachis are usually inclined towards one another so that they form with the axis of the pinna a wide-open V instead of lying in one plane (fig. 333, C). From a median rib are given off numerous anastomosing branches (fig. 333, B).

Fig.

333.

Weichselia Mantelli.

Part of a frond from the Wealden of Sussex, England. (British Museum; v. 2630. ¾ nat. size.)

Pinnule from Bernissart, Belgium (× 3).

Weichselia erratica, Nath. Section of pinna. (After Nathorst.)

This characteristic Wealden species is recorded from England, Germany, France, Belgium, Austria, Russia, Bornholm, North America, and Japan. It is by no means certain that Weichselia Mantelli is a true fern: no satisfactory evidence of fructification has been adduced.

The broad and strong rachis is comparable with that of a Cycadean leaf and the thick lamina suggests a plant of xerophilous habit. I have retained the specific name Mantelli on the ground of long established usage instead of following Fontaine in his adherence to strict priority.

Glossopteris.

The name Glossopteris was proposed by Brongniart in 1822[1295] for an imperfect leaf-impression which he called Filicites (Glossopteris) dubius, but the specimen so named has since been identified as part of a sporophyll of a Lepidostrobus. The author of the genus afterwards published[1296] a diagnosis, based on well-preserved leaves from Permo-Carboniferous rocks in Australia and India, of the type-species Glossopteris Browniana, the Indian examples being distinguished as G. Browniana var. indica while the Australian form was named G. Browniana var. australasica. Schimper[1297] afterwards raised the Indian fossils to specific rank as G. indica though some authors[1298] have continued to consider the two forms as insufficiently distinct to be regarded as different species.

The genus Glossopteris may be defined as follows:

Leaves simple, varying considerably in size, shape, and venation characters, but almost without exception characterised by repeatedly anastomosing lateral veins. The leaves are of two kinds: (i) foliage leaves; apparently always sterile, usually spathulate, with an obtuse apex, a well-marked midrib which may persist to the apex or die out in the upper half of the lamina, characterised by its slight prominence and comparatively great breadth especially in the basal part of the frond. In most cases the lamina extends as a narrow margin to the leaf-base, but in a few forms there is a short petiole (fig. 334). Though usually spathulate, the frond may be linear-lanceolate, or ovate; the apex is sometimes acute. Leaves vary in length from 3 to 40 cm. and may in larger forms have a breadth of 10 cm. Numerous lateral veins curve upwards and outwards to the margin of the lamina or pursue a straight course almost at right-angles to the midrib. (ii) Scale-leaves[1299] which differ from the foliage-leaves in their much smaller size and in the absence of a midrib; they are deltoid, oval or cordate in shape and generally terminate in an acute apex; the edge of the lamina may be slightly incurved so that the leaf presents a convex upper surface supplied with anastomosing veins. The scale-leaves, which vary in length from about 1 to 6 cm., probably acted as sporophylls. The only evidence as to the nature of the fructification so far obtained is represented by empty sporangium-like organs (1·2–1·5 mm. long by 0·6–0·8 mm. broad) frequently associated with the scale-leaves[1300].

The leaves, in some cases at least, were borne near together on a cylindrical stem or rhizome which produced branched adventitious roots[1301]. The fossils long known as Vertebraria were recognised by Zeiller[1302] and by Oldham[1303] as the stems of Glossopteris.

The systematic position of Glossopteris must for the present be left an open question. Though usually spoken of as a fern, it is noteworthy that despite the enormous abundance of its foliage leaves in the Permo-Carboniferous strata of India, Australia, South Africa, and South America, no single example has been discovered which shows undoubted remains of sori or sporangia. Many authors have described fertile leaves of Glossopteris; but it was not until Arber’s discovery of sporangia in close association with the scale-leaves that any light was thrown on the nature of the reproductive organs.

The probability is that Glossopteris was not a true fern but a member of that large and ever-increasing class, the Pteridosperms. This opinion is based largely on negative evidence. Such sporangia as have been described may have contained microspores and the plant may have been heterosporous. The occurrence of seeds in association with Glossopteris fronds recorded by more than one writer[1304], though by no means decisive and possibly the result of chance association, is favourable to this view. Dr White[1305] has suggested that the small leaves described by Zeiller[1306] as Ottokaria bengalensis from Lower Gondwana (Permo-Carboniferous) rocks of India, and similar fossils recorded by himself from Brazil as O. ovalis, may represent “sporangiferous” organs of Glossopteris or Gangamopteris, “both of which are probably pteridospermic.” There is, however, no conclusive evidence in support of this suggestion.

The genus, whatever its position may be, has a special interest for the geologist and for the student of plant distribution; it is a characteristic member of a Permo-Carboniferous flora which flourished over an enormous area, including India, South Africa,—extending from Cape Colony to Rhodesia and German East Africa[1307],—Australia, and South America[1308]. This flora, known as the Glossopteris flora, differed considerably in its component genera from that which overspread Europe and North America and some more southern regions in the Upper Carboniferous and Permian periods.

The discovery by Amalitzky[1309] of Glossopteris, and other genera characteristic of the Glossopteris flora, in the Upper Permian rocks in Vologda (Russia) demonstrates the existence of a northern outpost of the southern botanical province, and Zeiller’s discovery of the genus in the Rhaetic flora of Tonkin[1310] shows that Glossopteris persisted beyond the limits of the Palaeozoic epoch. Dr David White[1311] has recently proposed to re-christen the Glossopteris flora the Gangamopteris flora on the ground that Gangamopteris is strictly Palaeozoic in its range, whereas Glossopteris persisted into the Mesozoic era; this is perhaps hardly a sufficient reason for giving up so well established a title as the Glossopteris flora. A fuller account of this southern flora must be reserved for another volume.

Glossopteris Browniana, Brongniart[1312]. Figs. 334–36.

The specific name Browniana is now applied to obtusely pointed leaves which sometimes reach a length of 15 cm., but are usually rather shorter. In form and venation they closely resemble the leaves of the recent genus Antrophyum and species of Acrostichum. The comparatively broad midrib may be replaced in its proximal portion by several parallel veins: from it are given off numerous lateral veins which form a reticulum characterised by meshes approximately equal in size and elongated in a direction parallel to the general course of the secondary veins (fig. 334).

Fig. 334. Glossopteris Browniana, Brongn. A. Nat. size: B × 3½.

The drawings, originally published by Zeiller[1313], reproduced in fig. 335 illustrate the venation and its range of variation; the meshes are usually hexagonal and arranged as shown in figs. A and B, but occasionally (fig. 335, C) they follow a more steeply inclined course.

Small leaves with a more or less distinct midrib, 2–3 cm. in length, supply transitional stages between foliage- and scale-leaves. In the true scale-leaves spreading and occasionally anastomosing veins take the place of the midrib and lateral veins of the ordinary frond. McCoy[1314] in describing some Australian specimens of Glossopteris in 1847 spoke of scale-like appendages of the rhizome which he compared with the large ramenta of Acrostichum and other ferns. It was, however, Zeiller[1315] who first recognised the leaf-nature of these scales and adequately described them; additional figures of scale-leaves have been published by Mr Arber[1316] and by myself[1317]. The importance of these small leaves has been considerably increased by Mr Arber’s discovery of associated sporangia which, as he suggests, were probably borne on their lower concave surface.

Fig. 335. Glossopteris Browniana, Brongn. (After Zeiller. × 2.)

The sporangia (fig. 336) are compared by Arber with the microsporangia of recent Cycads and with the Palaeozoic sporangia described by Zeiller as Discopteris Rallii (fig. 256, D); the latter are distinguished by the well-defined group of thicker walled cells representing the annulus of true fern sporangia. We know nothing as to the contents of the Glossopteris sporangia, whether they contained microspores or whether they are the spore-capsules of a homosporous plant.

Fig. 336. Glossopteris Browniana, Brongn. Sporangia. (× 30). After Arber.

The rhizome of Glossopteris Browniana has been described in detail by Zeiller, who first demonstrated that the fossils originally assigned by Royle[1318] to the genus Vertebraria represent the stem of this and, as we now know, of some other species of Glossopteris. Vertebraria occurs in abundance in Permo-Carboniferous strata in association with Glossopteris; the differences between Australian, Indian, and South forms, though expressed by specific names, are insignificant. The stems are usually preserved in the form of flattened, single or branched, axes sometimes bearing slender branched roots and characterised by one or two, or less frequently three, longitudinal grooves or ridges (fig. 337) from which lateral grooves or ridges are given off at right angles, dividing the surface into more or less rectangular areas 1 cm. or more in length. The surface of these areas is often slightly convex and in some specimens the outlines of cells may be detected. Mr Oldham has described some interesting examples of Vertebraria from India in which the longitudinal and transverse grooves are occupied by a dark brown ferruginous substance or by the carbonised remains of plant-tissues (fig. 338, C, D). In transverse section, a Vertebraria cast appears to be divided into a number of wedge-shaped segments radiating from a common centre. Prof. Zeiller[1319] has figured specimens of Vertebraria with portions of Glossopteris fronds still attached.

Fig. 337. Vertebraria indica, Royle. Nat. size. (After Feistmantel.)

The rhizome of Glossopteris, as represented by the Vertebraria casts, is aptly compared by Zeiller[1320] with that of the recent Polypodiaceous fern Onoclea struthiopteris. Sections of the recent stem (fig. 338, E, F) show that the form is irregularly stellate owing to the presence of prominent wings which anastomose laterally at intervals as shown by the examination of a series of sections. The leaf-traces are derived from the steles of adjacent wings. Fig. 338 (B and A) represents somewhat diagrammatically a longitudinal and transverse view of a Vertebraria; the radiating arms represented in the transverse section (fig. A) are the stem ribs or wings and the segments between them are intrusions of sedimentary material. The rectangular areas characteristic of the surface of a Vertebraria are the intruded segments of rock: these are separated at intervals by transverse grooves, which mark the course of vascular strands given off at each anastomosis of the longitudinal wings to supply the leaves.

Fig.

338.

A, B. Vertebraria indica. (After Zeiller.)

C, D. V. indica. (Nat. size. After Oldham.)

E, F. Onoclea struthiopteris. (× 2. After Zeiller.)

Mr Oldham, who discovered the connexion between Glossopteris and Vertebraria independently of Dr Zeiller, does not agree with the interpretation of the structural features of the rhizome which Zeiller bases on a comparison between Vertebraria and Onoclea struthiopteris. Oldham[1321] describes Vertebraria as consisting of a central axis “joined to an outer rind by a series of radial septa,” the spaces between the septa being divided into chambers by transverse partitions. His view is that the rhizome of Glossopteris was a cylindrical organ and not an irregularly winged axis like the stem of Onoclea. Zeiller[1322] has replied in detail to Oldham’s interpretation and adheres to his original view, that the rhizome consisted of a solid axis with radial wings or flanges which at intervals anastomosed transversely in pairs at the nodes. It may, however, be possible that the spaces between the longitudinal and transverse grooves on a Vertebraria axis, which have been filled with the surrounding rock, were originally occupied in part at least by secondary wood, and the transverse strips of carbonaceous material[1323] lying in the grooves may represent medullary-ray tissue and accompanying leaf-traces. The longitudinal striations seen in some specimens of Vertebraria on the areas between the grooves may be the impressions of woody tissue. It is impossible without the aid of more perfectly preserved material to arrive at a satisfactory conception of the structural features of a complete Glossopteris rhizome.

Fig. 339. Glossopteris fronds attached to rhizome. (From a specimen lent by Dr Mohlengraaff. Considerably reduced.)

In the specimen of Glossopteris Browniana shown in fig. 339 several leaves are attached to an axis which shows none of the surface-features of Vertebraria. I am indebted to the kindness of Dr Mohlengraaff of Delft for the loan of this specimen which was obtained from Permo-Carboniferous rocks in the Transvaal. An axis figured by Etheridge[1324] from an Australian locality bears a tuft of Glossopteris leaves, possibly G. Browniana; in place of the rectangular areas characteristic of Vertebraria it shows transversely elongated leaf-scars or, on the internal cast, imbricate rod-like projections which Etheridge suggests represent vascular bundles.

Glossopteris indica, Schimper. Figs. 340, A, 341.

It is a question of secondary importance whether or not the fronds which Brongniart spoke of as a variety of Glossopteris Browniana should be recognised as specifically distinct. The careful examination by Zeiller of the venation characters has, however, afforded justification for separating G. Browniana and G. indica. We must admit that the slight and not very constant differences in the size and form of the meshes produced by the anastomosing of the lateral veins are characters which cannot be recognised as having more than a secondary value, though, as a matter of convenience, we employ them as aids to determination. The arbitrary separation of sterile leaves, which differ by small degrees from one another in form and in the details of venation, by the application of specific names is a thankless task necessitated by custom and convenience; it is, however, idle to ignore the artificial basis of such separation. Mr Arber has recently published, in his valuable Glossopteris Flora, an analytical key which serves to facilitate the description and determination of different types of frond[1325].

Fig.

340.

Glossopteris indica, Schimper. (½ nat. size.)

Glossopteris angustifolia, Brongniart. (Nat. size.) From Arber, after Feistmantel.

The large leaves of Glossopteris indica, reaching a length in extreme cases of 40 cm. and a breadth of 10 cm., are characterised by a rather greater regularity in the arrangement of the meshes and by the greater parallelism of the upper and lower sides of each mesh (fig. 341) and by less difference in size between the venation meshes than in G. Browniana, the leaves of which are usually smaller. The relatively thick epidermis consists of rectangular cells with stomata in depressions[1326]. The scale-leaves[1327], rather larger than those of G. Browniana, are more or less rhomboidal with rounded angles and reach a length of 1·5–6 cm. and a breadth of 1·5–2·5 cm. The rhizome is practically identical with that of G. Browniana[1328].

Fig. 341. Glossopteris indica, Schimp. (× 1½.) From Arber, after Zeiller.

This species occurs in great abundance in the Permo-Carboniferous rocks of India, Australia, and in various parts of South Africa, and elsewhere. It has been recognised also by Amalitzky[1329] in Upper Permian beds in Russia and by Zeiller in the Rhaetic series of Tonkin[1330].

Fig. 342. Glossopteris angustifolia var. taeniopteroides. (× 3½.)

Glossopteris angustifolia, Brongniart. Figs. 340, B; 342.

It is convenient to retain this designation for linear fronds with an acute or obtuse apex and a venation-reticulum composed of long and narrow meshes (fig. 340, B). It is by no means unlikely, as Arber suggests, that the same plant may have produced leaves of the G. indica type and narrower fronds which conform to G. angustifolia. In his description of some Indian specimens of G. indica, Zeiller draws attention to the variation exhibited in regard to the extent of anastomosing between the secondary veins: some examples with very few cross-connexions agree more closely with Taeniopteris than with Glossopteris as usually defined[1331]. The venation shown in fig. 342 illustrates an extreme case of what is almost certainly a Glossopteris leaf of the G. angustifolia type. This specimen, which was discovered by Mr Leslie in the Permo-Carboniferous sandstone of Vereeniging (Transvaal), has been referred to a variety of Brongniart’s species as G. angustifolia var. taeniopteroides[1332] on account of the almost complete absence of any cross-connexions. The reference to Glossopteris, which my friend Dr Zeiller suggested, is amply justified by the form of the leaf as a whole, by the angle at which the lateral veins leave the midrib, a feature in contrast to the wider angle at which the lateral veins are usually given off in Taeniopteris (figs. 329, 332), and by the similarity to the Indian specimens already mentioned. Several authors have described leaves or leaflets under the generic name Megalopteris[1333] from Carboniferous and Permian rocks which bear a close resemblance to the South African variety, but in some cases at least Megalopteris is known to be a pinnate and not a simple leaf. The leaf figured by Jack and Etheridge as Taeniopteris sp.[1334] from Queensland may also be an example of Glossopteris. Comparison may be made also with the Palaeozoic leaves described in the first instance by Lesquereux and more recently by Renault and Zeiller as species of Lesleya[1335] (fig. 347).

Fig. 343. Blechnoxylon talbragarense, Eth.: s, scale-leaves; x, secondary xylem. (After Etheridge. A × 2; B × 3; C much enlarged.)

Blechnoxylon talbragarense, Etheridge. Fig. 343.

Under this name Etheridge[1336] described some specimens from the Permo-Carboniferous Coal-Measures of New South Wales, which he regards as a fern, comparable, in the possession of a cylinder of secondary xylem, with the recent genus Botrychium and with Lyginodendron and other members of the Cycadofilices. The slender axis (1–3 mm. in diameter) appears to consist of a zone of radially disposed tissue (fig. 343, C, x), which is probably of the nature of secondary xylem, enclosing a pith and surrounded externally by imperfectly preserved remnants of cortex. Unfortunately no anatomical details could be made out, but the general appearance, if not due to inorganic structure, certainly supports Etheridge’s determination. The stem bore at intervals clusters of linear-lanceolate leaves (reaching 12 mm. in length) in close spirals (fig. 343, A and B); the leaves are characterised by a strong midrib and forked secondary veins. Small “pyriform” bodies of the nature of scale-leaves occur in association with the fronds (fig. 343, B, s).

In his description of this interesting plant, Etheridge quotes an opinion which I expressed in regard to the comparison of the stem with those of Botrychium, Lyginodendron, and other genera. No satisfactory evidence has been found as to the nature of the fructification. Although the leaves of Blechnoxylon are much smaller than those of Glossopteris, I am now disposed to regard the genus as closely allied or even generically referable to Glossopteris. The crowded disposition of the leaves is like that in Glossopteris, shown in fig. 339 and in the figures published by Etheridge and by Oldham; the association of scale-leaves and foliage-leaves is another feature in common. The absence of a reticulum of anastomosing veins can no longer be considered a fatal objection to the suggestion that the Australian type may be a species of Glossopteris. If the view that Blechnoxylon is not a distinct genus is correct, the occurrence of secondary xylem is favourable to the opinion already expressed that Glossopteris is more likely to be a Pteridosperm than a true fern. The data at present available render it advisable to retain Mr Etheridge’s name: the comparison with Glossopteris lacks confirmation.

BLECHNOXYLON

Fig. 344. Glossopteris retifera. (Nat. size. From Arber, after Feistmantel.)

Glossopteris retifera, Feist. Fig. 344.

In some Glossopteris leaves the anastomosing secondary veins form a coarser reticulum, as in the example represented in fig. 344. The name G. retifera was given by Feistmantel[1337] to Indian fronds of this type; similar forms have been described as G. conspicua and G. Tatei. The type illustrated by G. retifera is recorded also from Permo-Carboniferous rocks in Zululand[1338], Natal, the Transvaal, Cape Colony, and the Argentine.

Gangamopteris.

In 1847 McCoy[1339] described a leaf-fragment from Permo-Carboniferous rocks in New South Wales as Cyclopteris angustifolia. The type-specimen of this species, which is now in the Sedgwick Museum, Cambridge, has been re-described by Mr Arber[1340]. Subsequently[1341] McCoy instituted the generic name Gangamopteris for leaves, like that previously referred by him to Cyclopteris, from the Bacchus Marsh Sandstone, of New South Wales, but he did not publish a diagnosis of the genus until several years later[1342]. Feistmantel[1343], who has described many species of Gangamopteris from the Lower Gondwana strata of India, slightly modified the original diagnosis. The genus is represented by sterile fronds only. We know nothing of the stem, and such evidence as is available in regard to the form of the fertile leaves is of a circumstantial kind. It is, however, highly probable that Gangamopteris is not a true fern but a Pteridosperm.

Leaves simple, sessile, varying in shape; obovate or spathulate, broadly lanceolate or rarely linear; the apex is usually blunt (fig. 345) but occasionally gradually tapered. In general appearance a Gangamopteris leaf is similar to that of Glossopteris indica, the chief distinction being the absence of a midrib. Gangamopteris leaves are on the whole larger than those of Glossopteris; many of them reach a length of 20 cm. and some of the large Indian fronds are nearly 40 cm. long. The venation of Gangamopteris shows a greater uniformity in the size and shape of the meshes than that of Glossopteris. The middle of the lamina, especially in the lower part, is occupied by a few vertical veins from which branches curve upwards and outwards towards the edge of the lamina. The secondary veins are connected by frequent anastomoses and agree very closely with those of Glossopteris. The lamina becomes narrower towards the base, which is either cuneate or in some cases slightly auriculate (fig. 345).

As I have elsewhere pointed out[1344], the presence or absence of a midrib is not in itself a character of real taxonomic importance. In the recent fern Scolopendrium vulgare the frond has a prominent midrib, while in S. nigripes there is no median rib. Mr Arber has expressed the opinion that “it is extremely doubtful whether the genus Gangamopteris should not be merged in Glossopteris[1345].” The retention of the two names is, however, convenient, and it would tend to confusion were we to carry to its logical conclusion the view that the recognised distinction between the two genera may not be a mark of generic difference.

Gangamopteris is confined to Palaeozoic strata, a fact which leads White[1346] to speak of the Gangamopteris rather than of the Glossopteris Flora. It occurs in South America, South Africa, Australia, and India, extending as far north as Kashmir; it has been discovered by Amalitzky in Permian rocks of Russia[1347]. The Russian rocks in which Glossopteris and Gangamopteris were found are no doubt of Permian age. In Australia, South Africa, Brazil and Argentina, and in the Indian Coal-fields, Gangamopteris is a characteristic genus of Lower Gondwana rocks. These strata are usually spoken of as Permo-Carboniferous in order to avoid the danger of attempting on insufficient data a precise correlation with European formations.

Feistmantel speaks of Gangamopteris as most abundant in the Talchir-Karharbári beds, though it is represented also in the overlying Damuda series. In Australia the genus occurs in rocks which correspond in position and in their plant fossils with the Talchir-Karharbári beds of India; similarly, in South Africa and South America the Gangamopteris beds are homotaxial with those of India and Australia. The leaf described by Carruthers[1348] from Brazil as Noeggerathia obovata (the type-specimen is in the British Museum) is no doubt specifically identical with Gangamopteris cyclopteroides Feist.[1349] In a paper by Mr Hayden on Gangamopteris beds in the Vihi Valley, Kashmir, evidence is adduced in support of the conclusion that the rocks are “not younger than Upper Carboniferous and may belong to the base of that subdivision or even to the Middle Carboniferous[1350].” It would seem that Gangamopteris was a very widely spread genus during the latter part of the Carboniferous period in the vast Southern Continent to which the name Gondwana Land is often applied, and that it flourished in the Southern Flora during at least part of the Permian period: with other members of the Glossopteris Flora it migrated to the North where it has been preserved in Permian rocks of Northern Russia. The Glossopteris Flora must have had its birth in the Southern hemisphere. The conclusion seems inevitable that the leaves of Glossopteris and Gangamopteris in the shales and sandstones of India, South Africa, South America, and Australia are relics of the vegetation of a continent of which these regions are the disjuncta membra. Darwin wrote to his friend Hooker in 1881, “I have sometimes speculated whether there did not exist somewhere during long ages an extremely isolated continent, perhaps near the South Pole[1351].” It is probable that Gangamopteris is one of the genera which flourished on this continent.

Gangamopteris cyclopteroides, Feistmantel[1352]. Fig. 345.

1876. Feistmantel, Records Geol. Surv. India, Vol. IX. Pt iii. p. 73.

The specimen represented in fig. 345 illustrates the characters of this commonest representative of the genus.

Fig. 345. Gangamopteris cyclopteroides, Feist. (Nat. size. From Arber, after Feistmantel.)

Gangamopteris kashmirensis, Seward.

1905. Seward, Mem. Geol. Surv. India, Vol. II. Mem. ii.

This type agrees closely with G. cyclopteroides in size and in the form of the leaf, but it is distinguished by the flatter form of the arch formed by the lateral veins, by their greater inclination to the margin of the lamina, and by the more acutely pointed apex of the lamina. This species, though not very sharply distinguished from G. cyclopteroides, is important as coming from beds which have been assigned on other than palaeobotanical evidence to an Upper or possibly a Middle Carboniferous horizon[1353].

We have no definite information in regard to the nature of the reproductive organs of Gangamopteris, but such evidence as there is supports the view expressed by Dr White[1354] and shared by some other authors that Gangamopteris and Glossopteris should be assigned to the Pteridosperms. Despite the abundance of Gangamopteris leaves, no fertile specimen has been discovered. This negative evidence may prove to be as correct as that which led Stur[1355] to exclude Neuropteris, Alethopteris and Odontopteris from the ferns. The only evidence of a positive kind is that furnished by Dr David White in his recent Report on the Palaeozoic Flora of South Brazil. This author describes some small Aphlebia-like leaves under two new generic names Arberia[1356] and Derbyella[1357]. The differences between the two sets of specimens, so far as can be determined from the reproductions of imperfect impressions, are slight, and it is by no means clear that a distinction of generic rank exists. These scale-leaves are on the average about 2 cm. in length; the lamina is oval or rounded and has more or less prominent lobes. In Derbyella there are indications of anastomosing veins. The specimens referred to Arberia minasica are, as White points out, very similar to the fossil described by Feistmantel from Lower Gondwana rocks of India as probably a portion of an inflorescence of Noeggerathiopsis[1358]. Feistmantel’s specimen is represented in fig. 346: the curled lobes may have originally borne seeds. In the Brazilian examples the abruptly truncated lobes “bear evidence of separation from reproductive bodies.” An important point is the association of these scale-leaves with Gangamopteris fronds and with gymnospermous seeds of the Samaropsis type. On the leaves assigned to Derbyella aurita circular depressions occur at the base of the lobes which are described as probably due to sporangia.

Dr White’s discovery gives us increased confidence in expressing the view that Gangamopteris bore its reproductive organs on specialised leaves very different from the sterile fronds; it also strengthens the suspicion that the genus is a member of the class of seed-bearing fern-like plants.

Fig. 346. Arberia sp. (= Noeggerathiopsis of Feistmantel). (Nat. size. After Feistmantel.)

Lesleya.

This generic designation was instituted by Lesquereux[1359] for simple oval-linear leaves from the Coal-Measures of Pennsylvania. The leaves so named are probably generically identical with the specimen doubtfully assigned by Brongniart[1360] to the Coal-Measures, and made by him the type of the genus Cannophyllites on the ground of a resemblance to the leaves of the recent flowering plant Canna. Fig. 347 illustrates the form of a Lesleya leaf from the Coal-basin of Gard, named by Grand’Eury L. simplicinervis[1361], a type in which the veins are frequently unbranched and not repeatedly forked as in most examples of the genus (fig. 329, C). The features of the genus are, the oval-linear or lanceolate shape of the presumably simple frond, its entire or, in one species at least (L. Delafondi, Zeill.), finely dentate margin, the stout rachis giving off at a very acute angle numerous dichotomously branched secondary veins. In L. Delafondi (fig. 329, C), described by Zeiller[1362] from the Lower Permian of Autun, the frond may reach a length of more than 20 cm. and a breadth of 8 cm. Similar species are represented by L. ensis[1363] from the coal-field of Commentry, and L. grandis[1364] from Upper Carboniferous rocks of North America. The genus is characteristic of Upper Carboniferous and Lower Permian strata: the form of the leaf and the direction of the secondary veins suggest comparison with Glossopteris, but in Lesleya there are no cross-connexions between the veins. Nothing is known as to the fructification, a fact which naturally evokes the opinion that the genus is a Pteridosperm[1365] and not a true fern. Some years before the discovery of Pteridosperms, Grand’Eury[1366] suggested that Lesleya might be a Gymnosperm; his opinion being based on the woody nature of the rachis and on the simple venation of Lesleya simplicinervis.

Fig. 347. Leslya simplicinervis, Grand’Eury. (Reduced: after Grand’Eury.)

Neuropteridium.

In their monograph of fossil plants from the Bunter Series of the Vosges, Schimper and Mougeot[1367] described some pinnate leaves of ferns as species of the genus Neuropteris. In 1869 Schimper[1368] placed these in a new sub-genus Neuropteridium, in order to draw attention to the fact that their fronds appear to be simply pinnate and not bipinnate or tripinnate as in Neuropteris. The type-species of Neuropteridium is N. grandifolia Sch. and Moug. from the Bunter Sandstones of the Vosges. The genus includes Triassic European species and the widely distributed Permo-Carboniferous species from Brazil[1369] originally described by Carruthers as Odontopteris Plantiana. It is probable that some Carboniferous plants, particularly species from the lower members of the formation, referred to the genus Cardiopteris, are not genetically distinct from the Indian and southern hemisphere type Neuropteridium validum (= Odontopteris Plantiana).

Fronds pinnate, linear; a broad rachis bears pinnules which may be either semicircular or broadly linear with an entire or lobed margin. The longer pinnules may exceed 6 cm. in length. The pinnules agree with those of Neuropteris in being attached by the median portion of the lamina and not by the whole base, which is more or less auriculate. In some cases the repeatedly forked veins diverge from the centre of the pinnule base; in others there is a midrib which persists for a short distance only, and in some species the more persistent median vein gives the segments a closer resemblance to those of Neuropteris. Fructification unknown, with the exception of obscure indications of sporangia (?) on the fertile leaves of a Triassic species.

Fig. 348. Neuropteridium validum, Feist. Nat. size. From the Karharbári Coal-field, India. From Arber, after Feistmantel.

Neuropteridium validum. (Feistmantel[1370]). Fig. 348.

1869. Odontopteris Plantiana, Carruthers, Geol. Mag. Vol. VI. p. 9, Pl. VI. figs. 2, 3.

1878. Neuropteris valida, Feistmantel, Mem. Geol. Surv. India, Foss. Flor. Gondwana Syst., Vol. III. p. 10, pl. II.–VI.

1880. Neuropteridium validum, Feistmantel, Ibid. 2, p. 84.

The specimen represented in fig. 348 illustrates the main features of Neuropteridium validum. This species is referred to by Dr White[1371] as N. Plantianum on the ground of priority, and with a view to perpetuate the name of the English engineer Nathaniel Plant who discovered the species in a Brazilian Coal-field in the province of Rio Grande do Sul. Feistmantel’s specific name is however retained as being much better known. An examination of Mr Plant’s specimen in the British Museum led me[1372] to speak of the Brazilian species as identical with N. validum described by Feistmantel from Lower Gondwana rocks of India. Zeiller[1373] had previously drawn attention to the resemblance between the two sets of specimens. The frond of N. validum may exceed 50 cm. in length. The lower pinnules may be entire and semicircular in form while the upper and larger segments, which may reach a length of 5 or 6 cm., are characterised by broad lobes (fig. 348).

This type is represented in the flora of the Talchir-Karharbári series (Lower Gondwana) of India[1374], in Permo-Carboniferous rocks of Brazil and Argentine[1375], and in the sandstones of Vereeniging on the borders of the Transvaal and Cape Colony. It is a characteristic member of the Glossopteris Flora and occurs in association with Glossopteris and Gangamopteris.

Neuropteridium intermedium (Schimper). Fig. 349.

This species has been figured by Schimper and Mougeot[1376] from the Bunter of the Vosges and more fully described by Blanckenhorn[1377] from the Bunter beds of Commern. The pinnate leaves reach a length of 65 cm.; the lower semicircular pinnules pass gradually into broadly linear segments characterised by an auriculate base and a Neuropteris type of venation (fig. 354, D′, E). In the example reproduced in fig. 349 from one of Blanckenhorn’s figures, the fronds are attached to a short and thick rhizome bearing roots and portions of old petioles.

Fig. 349. Neuropteridium intermedium (Schimp.). (After Blanckenhorn. ¼ nat. size.)

An example of another Triassic species is afforded by Neuropteridium grandifolium Schimp. and Moug., which agrees very closely with N. validum in the size and shape of the pinnules. The occurrence in Lower Mesozoic European rocks of fronds hardly distinguishable from the older southern species may be regarded as favourable to the view already expressed, that some at least of the Permo-Carboniferous plants migrated north of the Equator. The resemblance between the Vosges Triassic species of Schizoneura[1378] and the examples of this genus recorded from the Lower Gondwana rocks of India affords additional evidence of a northern migration.

Our knowledge of the reproductive organs of Neuropteridium is practically nil. There is no doubt that Zeiller[1379] and Blanckenhorn[1380] are correct in regarding the Bunter fronds assigned by Schimper and Mougeot to the genus Crematopteris as the fertile leaves of Neuropteridium intermedium or some other species from the same horizon. These fronds bear crowded pinnules similar to those of Neuropteridium intermedium, N. Voltzii[1381], and other species, exhibiting on the exposed surface numerous carbonaceous spots which may be the remains of sporangia.

Cardiopteris.

Schimper[1382] applied this generic name to Lower Carboniferous fronds of a simple-pinnate habit which had previously been described as species of Cyclopteris. Cardiopteris frondosa may serve as a typical example. This species, originally described by Goeppert as Cyclopteris frondosa (fig. 350), is recorded from Lower Carboniferous rocks in the Vosges district[1383] in Silesia, Moravia[1384], and Thuringia[1385]. The pinnules, which are attached in opposite pairs to a broad rachis, vary in length from 2 to 10 cm. and have a breadth of 2 to 8 cm.; in manner of attachment and venation they agree with those of Neuropteridium validum. The venation is very clearly shown in a drawing of some large pinnules figured by Stur[1386].

The specimen of Cardiopteris frondosa, a portion of which is shown in fig. 350 on a slightly reduced scale, was originally figured by Schimper from an unusually good example in the Strassburg Museum. Schimper’s drawing hardly does justice to the original specimen.

A frond bearing rather narrower pinnules, alternately placed on the rachis, which Fritsch has described as Cardiopteris Hochstetterii var. franconica from the Culm of Thuringia, bears a close resemblance to Neuropteridium validum but differs in the entire margin of the pinnules. An Upper Carboniferous species from Russia described by Grigoriew[1387] as Neuropteris, cf. cordata var. densineura, represents another form of similar habit.

Fig. 350. Cardiopteris frondosa (Goepp.). (¾ nat. size. After Schimper.)

Schuster[1388] has recently proposed a new generic name Ulvopteris for a fragment of a pinna from the Coal-Measures of Dudweiler in Germany bearing large pinnules, which he compares with those of Cardiopteris and species of Rhacopteris. The specimen appears to be indistinguishable from some of those already referred to as conforming to Neuropteridium, and it is difficult to recognise any reason for the creation of a new generic name.

We cannot hope to arrive at any satisfactory decision in regard to the precise affinity between Neuropteridium validum and species referred to Cardiopteris and other genera so long as portions of sterile fronds are the only tests at our disposal. It is difficult to determine whether a specimen consisting of an axis bearing pinnules represents a large pinna of a bipinnate frond or if it is a complete pinnate leaf. There is, however, no adequate reason for supposing that the presumably pinnate fronds from the Gondwana Land rocks are generically distinct from the Lower Carboniferous European species Cardiopteris frondosa. Granting the probability that both genera are Pteridosperms and closely allied to one another, the two generic names may be retained on the ground of long usage and in default of satisfactory evidence confirmatory of generic identity. Cardiopteris would thus stand for a type of frond characteristic of the Lower Carboniferous strata of Europe, while Neuropteridium is retained for the Southern species N. validum, and for others from the Trias of the Vosges.

Aphlebia.

This name was proposed by Presl[1389] for large leaf-like impressions having a pinnate or pinnatifid form and characterised by a confused irregular type of venation, or by a fine superficial striation or wrinkling which simulates veins. Gutbier had previously described similar fossils as Fucoides, and other authors have described Aphlebiae as species of Rhacophyllum, Schizopteris, and other genera[1390]. The term Aphlebia is retained, not as denoting a distinct genus but (i) as a descriptive name for detached leafy structures similar to those figured by Presl, which are now recognised as laminar appendages of the petioles of ferns or fern-like fronds, and (ii) as an epithet for highly modified pinnules which frequently occur at the base of the primary pinnae of Pecopteroid and Sphenopteroid fronds (e.g. Dactylotheca plumosa, fig. 293)[1391].

Modified pinnules, similar in their reduced and deeply dissected lamina to those represented in fig. 293, are frequently found at the base of the primary pinnae of Palaeozoic species of Sphenopteris and other genera of Pteridosperms or ferns, including members of the Coenopterideae. Potonié[1392] gives a list of various types of Aphlebiae in his paper on these organs. A striking case has recently been described by Zeiller in a French Upper Carboniferous species, Sphenopteris Matheti[1393]. It would seem that the larger examples of Aphlebiae are more frequently associated with the compound leaves of Pteridosperms than with those of Ferns[1394].

As examples of the larger types of Aphlebiae reference may be made to Aphlebia crispa (Gutb.)[1395], which reaches a length of nearly 60 cm. and has the form of a more or less triangular pinnate leaf divided into decurrent deeply lobed segments, to a similar species represented by A. Germari (= Schizopteris lactuca Germ.)[1396] which simulates the leaves of endive (Cichorium endivia L.), and to some large forms figured by Grand’Eury[1397] as species of Schizopteris.

Aphlebiae such as that figured by Kidston[1398] as Rhacophyllum crispum, with narrow ultimate segments, might easily be mistaken for the impressions of an alga.

The term Aphlebia may be applied also to the Cyclopteroid pinnules on the petioles of some species of Neuropteris, Odontopteris and Archaeopteris. Goebel[1399] has referred to the application by Potonié and other authors of the term Aphlebioid to the pinnules which serve as bud-protecting organs in recent fronds of Gleichenia (fig. 226, p. 290); he expresses the opinion that it is superfluous and misleading to make use of a special designation for structures which are undoubtedly modified pinnules. In the case of fossils it is, however, convenient to employ the term Aphlebia as a descriptive name for modified pinnules or stipular structures which cannot be connected with definite species of fronds. It is clear that some Aphlebiod leaflets, such as those of Dactylotheca, served as protective organs for the unexpanded pinnae[1400], and in all probability the large Aphlebiae served the same purpose as the fleshy stipules of Angiopteris and Marattia which cover the uncoiled fronds. The pinnatifid scale-leaves of considerable size (fig. 351) which occur in the leaf-axils or as ochrea-like stipules on the fronds of Gunnera (a tropical and subtropical Dicotyledonous genus) bear a very close resemblance to some Palaeozoic Aphlebiae, e.g. Aphlebia crispa (Gutb.). The recent and fossil scale-leaves may be regarded as similar in function as in form; moreover the delicate coiled fronds of Palaeozoic Pteridosperms or ferns, like those of some recent flowering plants, may have been kept moist by a secretion of mucilage. The pinnatifid stipules of Marattia fraxinea (fig. 241, B, p. 317) resemble certain fossil Aphlebiae, and the wrinkled surface of the recent stipules presents an appearance similar to that which in some fossil forms has been erroneously described as veining. It is not improbable that mantle-leaves of such recent ferns as Polypodium quercifolium (fig. 234, M, p. 303) are comparable with some fossil Aphlebiae which may have served as humus-collectors for Palaeozoic epiphytes.

Fig. 351. Scale-leaf of Gunnera manicata. (Slightly reduced. M.S.)

The filiform appendages on the petioles of the recent fern Hemitelia capensis (fig. 235, p. 304) have often been compared with the aphlebioid leaflets of fossil fronds.

Potonié who has discussed the nature of Aphlebiae regards them as vestiges of a once continuous lamina, which formed a winged border to the branched axes of more primitive forms of fronds. It is possible that the pinnules between the pinnae on the rachis of Archaeopteris and the Cyclopteroid leaflets of Neuropteris and Odontopteris may have the morphological significance attributed to them by Potonié. In some cases it is probable that the Aphlebiae, whether vestiges or not, served the purpose of protecting either the whole frond or individual pinnae. Aphlebiae, though especially characteristic of Palaeozoic leaves, are occasionally met with in the form of modified pinnules at the base of the primary pinnae on Mesozoic ferns, e.g. in Coniopteris hymenophylloides[1401].

In some fern fronds the lowest pinnule of each pinna differs in shape or size from the normal ultimate segments, but it would be almost affectation to extend the use of the term Aphlebia to such pinnules. The Jurassic species Cladophlebis lobifolia (Phill.) is a case in point[1402]. In this fern, which some authors speak of, without sufficient reason, as Dicksonia lobifolia[1403], the lowest pinnule is large and different in shape from the others.

Fig.

352.

A. Sphenopteris obtusiloba. Pinnule. (Enlarged. After Zeiller.)

B, C. S. obtusiloba. (⅞ nat. size. After Zeiller.)

D. Pecopteris arborescens. (Slightly enlarged. After Zeiller.)

E. Sphenopteris furcata (= Diplotmema furcatum). (Slightly enlarged. After Zeiller.)

Sphenopteris.

Sphenopteris is one of the many generic names which we owe to Brongniart[1404]. It is the generic designation used for a great number of Palaeozoic and later fronds, most of which are those of true ferns while some Palaeozoic species are undoubted Pteridosperms. The genus, which is purely provisional, includes members of widely different families possessing pinnules of the same general type, such as is represented in some recent species of Davallia, Asplenium, and other ferns.

The fronds of Sphenopteris may be bipinnate, tripinnate, or quadripinnate; the rachis may be dichotomously branched or the branching may be of the pinnate type characteristic of most recent ferns. The pinnules are small; they vary considerably in shape even in a single frond, but the chief characteristics are: the lobed lamina, contracted and often wedge-shaped at the base (fig. 352), the dichotomously branched veins radiating from the base or given off from a median rib at an acute angle. The lamina may be divided into a few bluntly rounded lobes (fig. 352, C) or deeply dissected into linear or cuneate segments (fig. 352, A, B, E).

Examples of Sphenopteroid leaves have already been described under the genera Coniopteris, Onychiopsis, Ruffordia, etc. Among the numerous examples of Sphenopteris species from the Carboniferous rocks mention may be made of Sphenopteris obtusiloba Brogn.[1405] (fig. 352, A–C), which occurs in the Middle and Lower Coal-Measures of Britain[1406]. This type is characterised by the almost orbicular, oval or triangular pinnules which may reach a length of 15 mm.; they are occasionally entire, but more usually divided into 3 to 5 rounded lobes. The forked veins radiate from the base of the pinnule. The rachis may be dichotomously branched. Fructification unknown.

The species S. furcata Brongn.[1407], characteristic of the Middle and Lower Coal-Measures of Britain (fig. 352, E), is referred to under Stur’s genus Diplotmema[1408] in which it is included by some authors solely because of the dichotomous habit of branching of the pinnae.

The pinna represented in fig. 353 illustrates a similar type of pinnule. This species, which is very common in the Calciferous Sandstone of Scotland, was described by Lindley and Hutton as Sphenopteris affinis[1409].

The fronds of Sphenopteris affinis were discovered by Mr Peach[1410] in a fertile condition, but he regarded the reproductive organs as those of a plant parasitic on the Sphenopteris fronds. Kidston[1411] substituted Stur’s genus Calymmatotheca for Sphenopteris on the ground that the sporangia figured by Peach under the name Staphylopteris Peachii bear a close resemblance to the organs which Stur described as valves of an indusium in his species Calymmatotheca Stangeri[1412]. An examination of Stur’s specimens by Miss Benson[1413] and by Prof. Oliver and Dr Scott has confirmed Stur’s interpretation of the appendages at the tips of the fertile pinnae as valves of an indusial or cupular structure. The superficially similar bodies on the fertile pinnae of S. affinis are however true sporangia, and cannot legitimately be included in the genus Calymmatotheca as described by Stur. For this reason Miss Benson institutes a new genus Telangium, the type-species of which, T. Scotti from the Lower Coal-Measures of Lancashire, is based on petrified material. The Scotch species Sphenopteris affinis (= Calymmatotheca affinis of Kidston) is also transferred to Telangium; the sporangia are considered by Miss Benson to be microsporangia. This with other species is no doubt correctly included in the Pteridosperms. A complete frond of Sphenopteris affinis, showing a regular dichotomy of the main axes, is represented by an admirable drawing in Hugh Miller’s Testimony of the Rocks[1414].

Fig. 353. Sphenopteris affinis, Lind. and Hutt. From the Calciferous Sandstone of Burdiehouse (Scotland). (Sedgwick Museum, Cambridge.) M.S.

Some of the Palaeozoic species of Sphenopteris probably represent the fronds of true ferns, but others are known to have been borne by Pteridosperms. S. Hoeninghausi (fig. 290, C, p. 399) is the foliage of Lyginodendron, and Scott[1415] speaks of three species, S. dissecta, S. elegans, and S. Linkii as the leaves of Heterangium. Grand’Eury[1416] has recorded the occurrence in French Coal-Measures of seeds in association with other Sphenopteroid fronds.

Mariopteris, Diplotmema, Palmatopteris.

The discovery of sporangia on the fronds of several Palaeozoic species of Sphenopteris and Pecopteris has led to the institution of new generic names, which indicate an advance in knowledge beyond the stage implied by the use of those provisional designations based solely on the form and venation of the pinnules. Other names have been created by authors in place of Sphenopteris and Pecopteris on the ground that a striking feature in the mode of branching of fronds is sufficiently important to justify generic recognition even in the absence of fertile specimens. As examples of designations based primarily on the branch-system of compound leaves, the genera Mariopteris, Diplotmema, and Palmatopteris may be briefly considered (fig. 354 A–C). Dr Kidston[1417] is of opinion that the creation of new genera for purely vegetative characters of fronds is of no real advantage, and he prefers to retain the older provisional names for species known only in the sterile condition. On the other hand, if we are sufficiently familiar with specimens large enough to enable us to recognise a well-defined morphological character, it may serve a useful purpose to employ a generic designation for features which may have a phylogenetic value. A comparative examination of Palaeozoic, Mesozoic, and recent compound fronds, including both Pteridosperms and true ferns, brings to light certain distinguishing features characteristic of the older types which, as Potonié maintains[1418], point to the derivation of the pinnate habit from a primitive dichotomous system of branching. For a more complete discussion of this question reference should be made to Potonié’s suggestive papers. Among recent ferns Matonia and Dipteris, two survivals from the past, afford instances of fronds with a branching system of the dichotomous type.

Similarly, in Gleichenia, Lygodium, and more rarely in species of Polypodiaceae (e.g. Davallia aculeata, fig. 232) dichotomy is a striking feature of the fronds. In the great majority of recent ferns the fronds have assumed a pinnate habit. Among Palaeozoic fern-like fronds dichotomous branching of the main rachis and of the pinnae is much more common. Potonié draws attention to several other features which distinguish Palaeozoic fronds from the majority of later species: the frequent occurrence of pinnules borne directly on the main rachis (fig. 354, D), and of modified pinnules or Aphlebiae on the rachis and petiole, are characters to which he attributes an evolutionary significance. The main point is that a comparative examination of leaf-form affords evidence in favour of the view that the modern type of frond, with its naked rachis bearing two rows of pinnae, has been derived from a less specialised type in which the distinction between the parts of the leaf is much less evident. The primitive leaf was probably a dichotomously branched axis provided with a continuous lamina which eventually became broken up into separate lobes or pinnules.

As the dichotomy of the frond became less regular, a pinnate habit was acquired, as is clearly seen in many Palaeozoic types which constitute connecting links between forked and pinnate fronds (fig. 354, D). The Aphlebiae may be remnants of the once-continuous lamina on the petiole, and the normal pinnules borne on the rachis may be regarded as the attributes of fronds in which the division of physiological labour had not reached the stage which characterises the leaves of recent ferns.

Mariopteris.

This name, which is due to Zeiller[1419], is applied by him to Palaeozoic fronds characterised by a double bifurcation of the rachis of the primary pinnae. Mariopteris muricata (= Pecopteris muricata Schloth.) may be taken as the type of the genus. This species is common in the Lower and Middle Coal-Measures of Britain and rare in the Upper Coal-Measures[1420]. It is described by Kidston[1421] as one of the most polymorphic and widely distributed Coal-Measure species. The pinnules as seen in fig. 364, B, are of the Sphenopteroid type. No fertile specimens are known, but it is significant that Grand’Eury[1422] has recorded the association of Mariopteris muricata and seeds.

The main rachis gives off alternate naked branches, each of which bifurcates at its apex into two short naked axes, and these are again forked, the ultimate branches having the form of bipinnate pinnae provided with large Sphenopteroid pinnules (fig. 354, B). Zeiller includes in Mariopteris some species which Stur[1423] referred to his genus Diplotmema. Possibly some of the Palaeozoic fronds with a zigzag rachis may have been climbers like Lygodium.

Fig.

354.

A. Palmatopteris.

B. Mariopteris. (A, B, after Potonié.)

C. Diplotmema Zeilleri, Stur. (After Zeiller.)

C′. D. Zeilleri. Pinnule. (× 3. After Zeiller.)

D. Neuropteris macrophylla. (British Museum.)

D′. N. macrophylla. Pinnule. (Slightly enlarged. After Kidston.)

E. N. heterophylla. Pinnule. (Slightly enlarged. After Zeiller.)

F. N. Scheuchzeri. (Slightly reduced. After Kidston.)

G. Alloiopteris Essinghii. (Enlarged. After Potonié.)

Diplotmema.

This generic name is employed by Zeiller[1424] and other authors in a more restricted sense than that in which it was originally used by Stur. The Upper Carboniferous species Sphenopteris furcata Brongn. (fig. 352, E) may serve as the type. This species occurs in the Middle and Lower Coal-Measures of Britain[1425]. The main rachis gives off branches as in Mariopteris, but in Diplotmema each naked lateral branch is forked at its apex into two opposite pinnae bearing deeply dissected Sphenopteroid pinnules. Zeiller[1426] and Stur have recorded fertile specimens of Diplotmema, but in no case have actual sporangia been discovered. In the species Diplotmema Zeilleri Stur (fig. 354, C, C′) two Aphlebiae occur at the base of each secondary axis[1427]. It has been pointed out by Potonié that in Diplotmema furcatum the equal dichotomy of the lateral branches is not characteristic of the frond as a whole. In the case of branches higher on the rachis the dichotomy becomes unequal and the forked axis is gradually replaced by a simple pinna (fig. 354, A). For this type of frond, Potonié proposed the generic name Palmatopteris in place of Diplotmema, which he discards. The long comparatively slender rachis of P. furcata suggests comparison with the liane species of Lygodium[1428].

Fig.

355.

Cephalotheca mirabilis, Nath. Fertile pinnae. (Partially restored. After Nathorst.)

C. mirabilis. Sterile pinnule. Nat. size. (After Nathorst.)

Cephalotheca.

This genus was proposed by Nathorst[1429] for some peculiar bipinnate fertile fronds from the Upper Devonian rocks of Bear Island. The pinnae bear slender forked ultimate segments represented by a few detached fragments (fig. 355, B), associated with the rachises. The fertile pinnae are given off in opposite pairs from the main axis over which they are concrescent (fig. 355, A). A mop-like cluster of sporangia is borne on the lower surface and close to the base of a fertile pinna: the exannulate sporangia are compared with those of Scolecopteris. Nathorst compares Cephalotheca with a Belgian species of Upper Devonian age described by Crépin[1430] as Rhacophyton condrusorum and by Gilkinet[1431] as Sphenopteris condrusorum. A similar fossil is also described by Baily[1432] as Filicites lineatus from the Kitorkan Grits of Ireland.

The position of Cephalotheca cannot be definitely determined from the available data, but it is more probable that it was a seed-bearing Pteridosperm and not a true fern. Zeiller[1433] has recently expressed the same opinion.

Thinnfeldia.

The genus Thinnfeldia, founded by Ettingshausen in 1852[1434] on some Hungarian Liassic specimens, though frequently included in the Filicales, cannot be said to occupy that position by virtue of any well-authenticated filicinean features. It is by no means improbable that many of the species referred to this genus are closely allied to Palaeozoic Pteridosperms.

Thinnfeldia may be briefly defined as follows:

Fronds simple and pinnatifid, pinnate or bipinnate: rachis broad and occasionally dichotomously branched. Pinnules often fleshy or coriaceous; broadly linear, entire or lobed, provided with a midrib from which simple or forked secondary veins are given off at an acute angle: or the laminae may be short and broad without a midrib and traversed by several slightly divergent and forked veins.

No satisfactory evidence of reproductive organs has so far been adduced.

The genus is chiefly characteristic of Upper Triassic, Rhaetic, and Jurassic floras, though it was in all probability represented in Permian floras. Several species, many of which are valueless, are recorded also from Cretaceous and Tertiary formations. Search should be made for fertile specimens or for evidence as to the association of seeds with Thinnfeldia fronds.

Some Permian fossils from Kansas which Sellards[1435] has made the type of a new genus, Glenopteris, appear to be indistinguishable generically from leaves of Lower Mesozoic age universally recognised as typical examples of Thinnfeldia.

Thinnfeldia odontopteroides (Morris)[1436]. Figs. 356–358.

This is a very variable species as regards the shape and size of the ultimate segments and their venation. It is a type of extended geographical range characteristic of Rhaetic or Upper Triassic rocks in Australia, South Africa, India, South America, and various European localities.

Frond bipinnate; the broad rachis may be dichotomously branched. Pinnules with a thick lamina which may be almost semicircular in form, deltoid, broadly oval or broadly linear, and often confluent at the base. Short and broad pinnules occur on some fronds directly attached to the main rachis between the pinnae. The longer and narrower pinnules (fig. 356, C), resembling those of the Palaeozoic genus Alethopteris, have a well-defined midrib, while the smaller segments are characterised by several slightly divergent veins which spring directly from the rachis (fig. 356, A). Epidermal cells polygonal or, above the veins, rectangular in shape; stomata, which are slightly sunk, occur on both the upper and lower epidermis. Fertile specimens unknown.

The portion of a lobed pinnule shown in fig. 356, B, illustrates a form of segment intermediate between the linear type with a midrib and a row of shorter pinnules without a median vein. Fig. 356, D, represents another instance of variation in the arrangement of the veins in segments of different sizes. Various specific and generic names have been assigned to Thinnfeldia fronds of Rhaetic age on the ground of the occurrence of pinnules longer and narrower than those usually associated with T. odontopteroides; but in view of the range of variation met with in a single leaf it is advisable to extend rather than to restrict the boundary of what we are pleased to regard as a specific type.

Fig.

356.

A–D. Thinnfeldia odontopteroides (Morris).

E. Ptilozamites. (E, after Nathorst.)

The name Thinnfeldia lancifolia has been applied by Morris to fossils from Australia which may be identified with T. odontopteroides, and the same designation is employed by Szajnocha and by Solms-Laubach[1437] for Rhaetic specimens from South America. Similar fronds are described by Geinitz[1438] as Thinnfeldia tenuinervis from Argentine Rhaetic strata. Odontopteris macrophylla Curran, T. falcata Ten.-Woods, Gleichenia lineata Ten.-Woods, and Cardiopteris Zuberi Szaj. afford other examples of what are probably closely allied forms[1439].

Fig. 357. Thinnfeldia odontopteroides (Morris). ⅘ nat. size.

Some exceptionally large examples of T. odontopteroides are figured by Feistmantel[1440] from the Hawkesbury series of New South Wales in which the bipinnate frond has a breadth of 25–30 cm. A specimen from the Molteno beds of South Africa, probably of Rhaetic age, represented in fig. 357, illustrates a smaller leaf with pinnules of the linear type, some of which are partially divided into shorter pinnules with forked veins. The example represented in fig. 358, from Cyphergat (S. Africa), shows two equal branches of a rachis with small contiguous segments.

Fig. 358. Thinnfeldia odontopteroides. From a specimen in the British Museum (v. 2490). 1½ nat. size.

Some specimens figured by Zeiller[1441] from the Rhaetic strata of Tonkin as Pecopteris (Bernouillia?) sp. may be portions of Thinnfeldia fronds, and the large leaves which he refers to Ctenopteris Sarreni differ but slightly from the Australian specimens described by Feistmantel as T. odontopteroides.

Thinnfeldia rhomboidalis, Ettingshausen. Figs. 359, 360, C.

Under this name Ettingshausen described the type-specimen of the genus from Lower Lias strata at Steierdorf in Hungary. He assigned the plant to the Coniferae on the ground of a resemblance of the pinnules to the phylloclades of Phyllocladus. Thinnfeldia rhomboidalis bears a close resemblance to T. odontopteroides, but the pinnules are usually longer and narrower, as shown in the English specimen from the Lower Lias of Dorsetshire represented in fig. 359. The darker margin of the pinnules shown in fig. 360, C, gives the impression of a revolute lamina, but a microscopical examination points to a thicker cuticle at the edge of the segments.

Fig. 359. Thinnfeldia rhomboidalis, Ettings. Slightly reduced. From an English Liassic specimen in the British Museum. [M.S.]

The species is recorded from Jurassic rocks of France, Germany, Italy, India, Australia, and elsewhere[1442].

Palaeobotanical literature contains numerous records of Jurassic, Cretaceous and some Tertiary species referred to Thinnfeldia, but many of these are probably not generically identical with T. odontopteroides or T. rhomboidalis. Mr Berry[1443] in a paper on The American species referred to Thinnfeldia concludes that the genus is “a rather indefinite one ... and badly in need of revision.” He regards the Middle and Upper Cretaceous American species as Conifers related to Phyllocladus and probably forming a link between the Podocarpeae and Taxeae: for these forms he proposes the generic name Protophyllocladus. The opinion has been expressed elsewhere[1444] that this “problematical[1445]” genus rests on an unsatisfactory basis; the available data do not justify the use of a name which implies the existence in North American Cretaceous floras of a type related to the New Zealand and Tasmanian Conifer Phyllocladus. We are not in a position to assign a single species of Thinnfeldia to the Filicales or the Gymnosperms.

A leaflet from Jurassic rocks of Poland figured by Raciborski[1446] shows what this author regards as the impression of a circular sorus: no sporangia have been found. A specimen in the British Museum[1447], which is said to come from Rhaetic beds in Queensland, shows a row of contiguous polygonal prominences on each side of the midrib which resemble the sori of a fern; but until sporangia are discovered we cannot determine the precise nature of this apparently fertile frond.

A species described by Fontaine[1448] from the Potomac beds (Wealden-Jurassic) of North America as Thinnfeldia variabilis affords a good example of a plant which cannot be identified with any degree of confidence either as a fern or a seed-bearing type. Mr Berry draws attention to the former application of this name by Velenovský to a distinct Lower Cretaceous Bohemian species and proposes for Fontaine’s plant the name T. Fontainei; he maintains that no one has doubted the fern-nature of the Potomac plant. T. variabilis may indeed be a fern, but the evidence is not such as to preclude legitimate doubts as to the correctness of this suggestion. Solms-Laubach[1449], in referring to Schenk’s view that Thinnfeldia and its allies may represent a group intermediate between Ferns and Gymnosperms, admits that it is a possible supposition; he is, however, inclined to consider Lomatopteris and Cycadopteris, “genera especially comparable with Thinnfeldia” as more probably ferns.

At this point we may conveniently consider a series of genera which occupy an equally uncertain position and bear a very close resemblance to Thinnfeldia.

Fig.

360.

Lomatopteris jurensis. (⅞ nat. size. After Kurr.)

L. Schimperi. (⅞ nat. size. After Salfeld.)

Thinnfeldia rhomboidalis, Ett. (Slightly enlarged. British Museum. No. 52672.)

Lomatopteris.

The generic name Lomatopteris was proposed by Schimper[1450] for some bipinnate fronds originally described by Kurr[1451] from Jurassic rocks of Württemberg as Odontopteris (?) jurensis (fig. 360, A). I have elsewhere expressed the opinion[1452] that this German species may be identical with Thinnfeldia rhomboidalis Ett. Kurr’s type-specimen, a portion of which is reproduced in fig. 360, A, consists of a frond or large pinna characterised by a prominent and broad rachis giving off alternate linear pinnae bearing bluntly rounded, contiguous and basally concrescent pinnules having a thick or revolute border and a central rib. The lateral veins are visible in the ultimate segments of Kurr’s fossil. Saporta[1453] has described several species, which he refers to Schimper’s genus, from French Jurassic strata: it is, however, difficult to recognise some of the examples represented in his illustrations as specifically distinct forms. This author notices the resemblance of Lomatopteris to Thinnfeldia, not only in habit but in the structure of the epidermal cells[1454]. In Lomatopteris and in Thinnfeldia the cells have straight and not sinuous walls and the slightly sunken stomata are surrounded by a ring of epidermal cells. Salfeld[1455] has recently described portions of fronds from Jurassic rocks of South-West Germany, which he identifies as Lomatopteris jurensis. He disagrees with my view that Lomatopteris does not differ sufficiently from Thinnfeldia to be accorded generic autonomy, chiefly on the ground that the folded-over edge of the pinnules is a distinguishing feature of Lomatopteris. There is, however, no difference, in appearance at least, between the leaflets of some species of Thinnfeldia, e.g. T. rhomboidalis from Liassic rocks of England[1456], and those referred to Lomatopteris. In a later paper, Salfeld[1457] describes some Portlandian fragments from North Germany as Lomatopteris Schimperi, identifying them with a Wealden fossil of somewhat doubtful affinity, which Schenk[1458] makes the type of his species. The Portlandian specimens are described as tripinnate, with thick decurrent obtusely terminated pinnules with a revolute edge. The general form of the frond is very similar to that of L. jurensis. Salfeld publishes a photograph of a large specimen which he describes as fertile and a drawing of a piece of a pinna: the latter is reproduced in fig. 360, B. He speaks of sori occurring in two rows, probably attached to lateral veins, in the groove between the midrib and the revolute edge of the lamina. The sporangia are described as “nicht näher bekannt[1459].” An examination of the figures reveals nothing as to the nature of the “sori.” The specimens are considered by Salfeld to afford decisive evidence against the view that Lomatopteris and Thinnfeldia are generically identical. Nothing has so far been published which constitutes a valid argument in favour of retaining Schimper’s generic name.

Cycadopteris.

Zigno[1460] founded the genus Cycadopteris on Italian Jurassic impressions regarded by Schimper as indistinguishable from Lomatopteris. As Solms-Laubach[1461] points out, the supposed sori of Cycadopteris described by Zigno are not convincing. There appear to be no satisfactory reasons for separating Cycadopteris from Lomatopteris, nor do the fronds described under these names exhibit any important differences from Thinnfeldia.

Ptilozamites.

Nathorst[1462] founded this genus on a remarkable series of specimens from the Rhaetic Coal-beds of Scania and assigned it to the Cycadophyta. The species Ptilozamites Heeri may be taken as a representative type. The leaves are linear and simply pinnate. In the example shown on a much reduced scale in fig. 361 the frond is 53 cm. long and 2·1 cm. broad. The upper edge of each pinnule is straight or slightly concave; the lower edge is rounded; the veins are slightly divergent and dichotomously branched (fig. 356, E, p. 539). In some of Nathorst’s specimens the broad rachis is forked as in many Thinnfeldias.

As a comparison of fig. 356, A and E, shows, the pinnules of some specimens of Thinnfeldia odontopteroides are identical with those of Ptilozamites. In the latter genus the rachis is either unbranched or occasionally forked, while in Thinnfeldia the branching may be of the dichotomous or pinnate type. In Ptilozamites the segments appear to be always without a midrib, while a median vein frequently occurs in those of Thinnfeldia. There can be little doubt as to the very close alliance between the Rhaetic species referred to these two genera. The name Ptilozamites should perhaps be retained for such long and narrow fronds as that shown in fig. 361: no species included in Thinnfeldia is known in which the rachis reached so great a length without branching. The habit of Ptilozamites Heeri predisposes one in favour of Nathorst’s opinion that the fronds are Cycadean: we have no information in regard to the nature of the reproductive organs.

Fig. 361. Ptilozamites Heeri, Nath. (⅓ nat. size. After Nathorst.)

Ctenopteris.

This name was instituted by Saporta[1463], at Brongniart’s suggestion, for Liassic species characterised by pinnules like those of Thinnfeldia, but distinguished by the bipinnate habit of the frond. Saporta compares the genus with the Palaeozoic leaves known as Odontopteris, and with Italian Jurassic plants referred by Zigno to his genus Dichopteris.

The name Ctenozamites is applied by Nathorst[1464] to the type of frond which Saporta, Zeiller, and other authors refer to Ctenopteris. Nathorst instituted Ctenozamites for fossils agreeing in the form and venation of the pinnules with his genus Ptilizamites but differing in being bipinnate and not pinnate.

Fronds of Ctenopteris are characteristic of the Jurassic and Rhaetic series; they are known only in the sterile condition. As Zeiller[1465] says, Ctenopteris may be a member of the Cycadofilices, an extinct group founded on Palaeozoic plants combining Cycadean and Filicinean characters, and some of which are now known to be Pteridosperms. It is probable that the genus is not a true fern: it is more likely to be a member of the Cycadophyta or of some generalised extinct group.

Ctenopteris cycadea (Brongniart). Fig. 362.

1828. Filicites cycadea, Brongniart, Hist. Vég. foss. p. 387, Pl. CXXIX.

1832. Odontopteris cycadea, Berger, Verstein. Coburg Geg. p. 23, Pl. III.

1873. Ctenopteris cycadea, Saporta, Pal. Franç. Vol. I. p. 355, Pls. XL. XLI.

Frond bipinnate, broad rachis giving off branches at an acute angle; pinnules broadly linear, slightly falcate, with several slightly divergent forked veins.

A frond very similar to the Lower Lias specimen from Dorsetshire represented in fig. 362 was described by Leckenby as Ctenis Leckenbyi (Bean MS.) from the Inferior Oolite of Yorkshire[1466]. Leckenby recognised the possibility of a Cycadean affinity, but regarded the bipinnate habit as an objection. The branched fronds of the Australian Cycad Bowenia supply an answer to this objection. Several good examples of Ctenopteris cycadea are figured by Schenk[1467] from Rhaetic rocks of Persia. Zeiller’s Tonkin Rhaetic species, C. Sarrani[1468], affords a striking illustration of the difficulty of drawing a clear line of separation between Ctenopteris and some species of Thinnfeldia.

Fig. 362. Ctenopteris cycadea, Brongn. (½ nat. size.) From a specimen in the British Museum. [M.S.]

Ctenopteris is in all probability very closely related to Thinnfeldia and Ptilozamites.

Dichopteris.

This genus was proposed by Zigno[1469] for some large specimens from the Jurassic plant-beds of Northern Italy.

The bipinnate leaves are characterised by the great breadth of the rachis which is dichotomously branched in the distal region (fig. 363); the linear pinnae reach a considerable length. Pinnules relatively small, oblong and slightly contracted at the base; the decurrent and confluent lamina forms a narrow wing to the main axis. Veins slightly divergent and forked, as in Ptilozamites.

Dichopteris visianica, Zigno. Fig. 363.

A specimen of this species in the Padua Museum has a total length of 83 cm. It has been elsewhere suggested[1470] that a fragment figured by Zigno as a fertile example of this type is probably part of a frond of the Osmundaceous fern Todites. Since this opinion was expressed I have had an opportunity of examining the actual specimen at Padua: the circular patches described by Zigno as sori appear to be irregularities in the matrix and not an original feature.

Brongniart[1471] instituted the genus Pachypteris for some imperfectly preserved English Jurassic fossils from Whitby, which he described as P. lanceolata. Specimens have since been described[1472] from the Inferior Oolite rocks of the Yorkshire coast. Brongniart described the pinnules as being without veins or as possessing only a midrib. It is almost certain that the apparent absence of veins in most specimens[1473] is due to the fleshy nature of the segments and that the species P. lanceolata should be transferred to Dichopteris.

Krasser[1474] has described a species from Cretaceous rocks of the island of Lesina, off the Dalmatian coast, as Pachypteris dalmatica which is very similar in habit to the English specimens and to Zigno’s Dichopteris visianica. One of Krasser’s specimens is practically identical with Dichopteris lanceolata (Brongn.), while in others the small pinnules are replaced in some of the pinnae by a continuous lamina with a few distal serrations. The latter form a link between the Dichopteris and Thinnfeldia type of segment. Krasser gives a full résumé of opinions expressed by other authors in regard to the position of Pachypteris (= Dichopteris) and decides in favour of a Cycadean alliance.

Fig. 363. Dichopteris visianica, Zigno. (⅓ nat. size. After Zigno.)

A French Jurassic plant which Saporta[1475] made the type of a new genus Scleropteris, and described as S. Pomelii, appears to be indistinguishable from Dichopteris.

Dichopteris, though conveniently retained as a distinct genus, agrees so closely, in the broad and forked rachis and in the fleshy pinnules, with Thinnfeldia that it would seem reasonable to regard the two genera as members of the same group.

Several authors have drawn attention to the striking resemblance in form and venation between the fronds of the Palaeozoic genus Odontopteris and those of Ctenopteris and Thinnfeldia. In Odontopteris, as in Neuropteris, another Palaeozoic genus, the rachis occasionally bifurcates as in Thinnfeldia and Dichopteris, and the ultimate segments of some species of Odontopteris (fig. 366, A) are practically identical with those of Thinnfeldia and Ptilozamites.

Odontopteris is probably a Pteridosperm. There is no adequate reason for supposing that this group of plants which played a prominent part in the Permo-Carboniferous floras was no longer in existence during the Mesozoic era.

Odontopteris.

Brongniart[1476] instituted the genus Odontopteris for compound fronds from the Coal-Measures characterised by pinnules attached by the whole breadth of the base and traversed by numerous forked veins. Odontopteris is very rare in British Carboniferous rocks and “appears to be restricted to the Middle and Upper Coal-Measures[1477].”

Fig.

364.

Alethopteris lonchitica (Schloth.). ½ nat. size.

Mariopteris muricata (Schloth.). × 2.

Odontopteris cf. alpina (Presl). ⅗ nat. size.

O. cf. alpina. Portion of pinna enlarged.

(A–D. From photographs by Dr Kidston.)]

Fronds large, bipinnate or tripinnate, the main rachis, which may be dichotomously branched, bears long linear pinnae with broadly linear or deltoid pinnules, acute or blunt, attached by the whole of the base; the lower margin of the lamina, which is usually entire and rarely lobed (e.g. Odontopteris osmundaeformis)[1478], is often decurrent on the axis of the pinna. The basal pinnule of each pinna is frequently attached by a contracted base, and the lamina may differ in form from that of the normal segments. Pinnules often occur on the main rachis, and in some species the petiole bears modified pinnules which are larger than the ultimate segments of the pinnae and in some cases Cyclopteroid in shape. The pinnules are traversed by numerous dichotomously branched veins; if a midrib is present it dies out in the basal part of the lamina. In some species (genus Mixoneura) pinnules of the Neuropteroid type, characterised by a well-defined midrib, occur in association with typical Odontopteroid pinnules on the same pinna.

Fig. 365. Odontopteris minor, Brongn. (Rather less than ⅓ nat. size. After Zeiller.) [The pinnules are omitted in the right-hand branch.]

The species represented in fig. 364, C, D, from the Middle Coal-Measures of Barnsley, Yorkshire, illustrates the form and venation of the Odontopteris type of pinnule. Another species, O. Reichiana Gutb.[1479], is also recorded by Kidston from the Lower Coal-Measures of Lancashire. Some unusually good specimens of the type-species of the genus Odontopteris minor, Brongn., have been figured by Zeiller[1480] from the Coal-Measures of Blanzy (fig. 365) which show the dichotomy of the main axis and the occurrence of Aphlebiae on the petiole. The late Dr Weiss[1481] divided Odontopteris into two sections, Xenopteris and Mixoneura, the pinnules of the former having the form shown in fig. 364, D; while in species of the latter sub-genus some of the pinnules are identical in form and venation with those of Neuropteris except that they are attached by the whole breadth of the base. Zeiller[1482] employs Mixoneura as a generic designation. In an American species O. Wortheni Lesq.[1483] the pinnules bear numerous hairs like those on some species of Neuropteris (fig. 373, p. 570). The large size of the fronds of Odontopteris suggested to Weiss[1484] that they were borne on the stems of tree-ferns, but Grand’Eury’s[1485] examination of specimens in the Coal-beds of central France led him to picture the plant as bearing a tuft of leaves on a short subterranean stem. Renault and Zeiller[1486], on the other hand, obtained evidence in the Commentry Coal-field of fronds borne on elongated stems which grew on the ground and were supported by stronger plants. Stur[1487] was the first to suggest that Odontopteris should be excluded from the ferns. Grand’Eury’s[1488] supposed fertile pinnules of Odontopteris do not afford any satisfactory evidence of the sporangial nature of the small swellings which he figures at the ends of the veins. This author pointed out several years ago that the petioles of some species of Odontopteris possess the anatomical features of Myeloxylon, a type of leaf-stalk which is now known to belong to Pteridosperms. In a recent paper Grand’Eury[1489] records the association of Odontopteris fronds with small seeds (Odontopterocarpus), a discovery which leaves little or no doubt as to the Pteridospermic nature of the genus. The fronds of Odontopteris are very similar in habit to those of Neuropteris, another Pteridospermic genus.

The similarity between some Odontopteris and Thinnfeldia leaves, to which attention has already been called, is well illustrated by O. genuina Grand’Eury[1490], a pinnule of which is represented in fig. 366, A. Odontopteris is a fairly widespread genus in Upper Carboniferous and Lower Permian rocks, and is recorded also from Triassic strata: it is represented in the Coal-fields of North America and in several parts of Europe[1491].

In some fronds included in Odontopteris the pinnae are characterised by a broad irregularly lobed lamina which also forms a winged border to the rachis. Examples of this form are afforded by Odontopteris Browni Sew.[1492] from the Burghersdorp Series (Triassic?) of Cape Colony, and O. Fischeri described by Brongniart[1493] from the Permian of Russia. The Russian species would perhaps be more appropriately placed in the genus Callipteris, as Weiss[1494] suggests; the absence of venation in O. Browni renders generic identification unsatisfactory.

Fig.

366.

Odontopteris genuina (Grand’Eury). (× 2⅝. After Renault and Zeiller.)

Callipteridium gigas (Gutb.). (× 2⅝. After Zeiller.)

Callipteris Pellati (Zeill.). (× 1¾. After Zeiller.)

C. lyratifolia (Goepp.). (× 1¾. After Zeiller.)

Callipteris.

Brongniart[1495] instituted this genus for certain species of supposed ferns previously referred to the genera Pecopteris, Alethopteris, and Neuropteris. Callipteris is a characteristic Permian plant which is almost certainly a Pteridosperm. Zeiller has pointed out that such descriptions of fertile specimens as have been written are unsatisfactory. A few years ago, however, Grand’Eury[1496] recorded the occurrence of seeds in association with Callipteris fronds in the Autun district, and in some cases they were found attached to the pinnae and rachis. The seeds are ovoid or spherical (5–10 mm. broad) and smaller than those of Neuropteris. The drawings of fertile segments published by Weiss[1497] afford no indication of reproductive organs. Potonié[1498] figures some pinnules of Callipteris conferta in which the thick lamina is covered with sinuous grooves probably made by some insect larvae: as he suggests, similar markings may have been mistaken for the remains of sori. The occurrence of Callipteris fronds recorded by Weber and Sterzel[1499] in association with Medullosa stems in the Lower Permian of Saxony is in accordance with Grand’Eury’s conclusion.

Fronds reaching 1 metre in length, bipinnate or tripinnate, main rachis frequently exhibiting a combination of dichotomous and pinnate branching. Pinnae linear, usually crowded, decurrent on the rachis; the pinnules on the lower side of the pinnae are continued on to the rachis. Pinnules of the Pecopteroid type, entire or slightly lobed, or of the Sphenopteroid type and more or less deeply dissected (fig. 366 C, D), the lamina of adjacent pinnules concrescent; on the lower pinnae the lamina may be continuous as in an Alethopteris pinnule. A midrib may extend almost to the bluntly rounded apex of the ultimate segments, giving off oblique, simple, or forked veins, the lowest of which arise directly from the rachis; in the Sphenopteroid forms the lateral veins are given off at a more acute angle.

A striking feature of the genus is the occurrence of pinnules on the main rachis, as in Odontopteris. Zeiller has wisely extended the application of Callipteris to fronds possessing this character irrespective of the entire or lobed form of the ultimate segments. He found among the numerous examples of the genus obtained from Autun[1500] and Lodève[1501] transitional forms connecting such species as C. conferta (fig. 367) and C. Pellati Zeill. (fig. 366, C) in which the Pecopteroid pinnules are slightly lobed, with C. lyratifolia (Goepp.) (fig. 366, D), C. flabellifera[1502] (Weiss), and C. Bergeroni Zeill. characterised by deeply lobed Sphenopteroid segments.

Callipteris conferta (Sternberg)[1503]. Fig. 367.

1723. Scheuchzer, Herb. Diluv. Pl. II., fig. 3.

1826. Neuropteris conferta, Sternberg, Flor. Vorwelt, p. 17.

1849. Callipteris conferta, Brongniart, Tableau, p. 24.

This polymorphic species (fig. 367) is one of the most characteristic Permian plants. The oval-linear pinnules, attached by the whole base, occur on both pinnae and rachis; this feature, the thick texture of the lamina, and the linear, obliquely set, pinnae render the fronds easily recognisable. The fronds bore seeds.

Fig. 367. Callipteris conferta. From the Permian of Aschbach, Rhenish Prussia (British Museum, No. 39052).

In a recent account of some Permian plants from Germany, Schuster[1504] refers a portion of a frond to Callipteris conferta (Sternberg) var. polymorpha Sterzel, which is characterised by unusually large and polymorphic pinnules. In size and shape the pinnules recall those of Neuropteridium validum Feist.

Callipteridium.

The name Callipteridium, created by Weiss[1505] as a sub-genus of Odontopteris, is applied by Zeiller and other authors to a few Upper Carboniferous and Permian species characterised by the occurrence of simply pinnate pinnae on the main rachis between the bipinnate primary pinnae. Single pinnules are borne directly on the rachis of the primary pinnae between the pinnate branches. The form and venation of a typical pinnule are shown in fig. 366, B. Callipteridium pteridium, originally recorded by Schlotheim as Filicites pteridius[1506], has been fully described by Renault and Zeiller from unusually large specimens found in the Commentry Coal-field[1507]. This species illustrates the peculiar morphological features of the genus. The main rachis of the tripinnate fronds, several metres long, shows a combination of dichotomous and pinnate branching; from the zigzag and forked axis are given off bipinnate pinnae and, between these, shorter pinnate branches. The pinnules closely resemble those of Callipteris conferta but reach a greater length; the pinnules borne on the rachises of the lateral branches differ from the others in their broader base and more triangular lamina.