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.)