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.
