. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. S6o FILICALES primitive. It will be seen that this species has a stelar structure of the axis of a type which also indicates its relatively primitive character in the genus. The sorus of Oligocarpia from the upper Carboniferous corresponds in its arrangement to that of Gkichenia (Fig. 312). O. Gutbieri and lindsaeoides show uniseriate sori with varying number of the sporangia, as in G. flabellata; but 0. Brongniartii has accessory sporangia occupying. Fig. 312. I. Oligocarpia Brongniartii,$>tiir. ^
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. S6o FILICALES primitive. It will be seen that this species has a stelar structure of the axis of a type which also indicates its relatively primitive character in the genus. The sorus of Oligocarpia from the upper Carboniferous corresponds in its arrangement to that of Gkichenia (Fig. 312). O. Gutbieri and lindsaeoides show uniseriate sori with varying number of the sporangia, as in G. flabellata; but 0. Brongniartii has accessory sporangia occupying. Fig. 312. I. Oligocarpia Brongniartii,$>tiir. ^=asterile ; 5=afertile pinnule {\) ; C = asorus more strongly magnified. (After Stur.) II.—two sori of the same species. X35. (After Zeiller.) III. Oligocarpia Gutbieri, Gopp. ' ^(=position of the sori on a segment of the last order. X30. B=a. sorus. X60. (After Stur.) Oligocarpia lindsaeoides (Ett.), Stur. A= position of the sori on a segment of the last order. #30. i?=asorus. C=a sporangium. X60. (After Stur, from Potonie's Lehrbuch.') the centre of the sorus, as in G. dichotoma. There is, however, a difference of opinion as to the annulus, and it is upon this that the ultimate deter- mination must rest: Zeiller recognises an annulus similar to that of the Gleicheniaceae; but Solms Laubachl does not assent to this, asserting that the supposed annulus is due to an effect of lighting of the specimen under observation. Zeiller nevertheless adheres to his Whatever 1 Fossil Botany, p. 146. 2Potonie, Lehrbttch, p. 102. Mr. Kidston has shown me specimens of Oligocarpia Gtitbieri in which the line of dehiscence was clearly seen running radially down the central face of the sporangium. The annulus could not be reduced to a single row of cells. Probably the type had a pluriseriate annulus like other Palaeozoic Ferns (compare Kidston, Phil. Trans., Ser. B, vol. 198, p. 188; also Scott, Progressus Rei Botanicae, vol. i., p. 184). It may, however, be remarked that a divis
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