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.