. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 546 FILICALES. Fig. 303. Senftcnbergia (Pecopteris) elegans, Corda. A=^ small piece of sporophyll (-J). 5=a spor- angium px5')* (After Zeiller, from Engler and Prantl, Nat. Pflanzenfam.) The sporangia of Mohria are radially constructed, the apex and base being opposite (Fig. 302 d, e). In the other genera the sporangia are more or less curved, so as to be dorsiventral: this curvature is slight in Aneimia and Schizaea (Fig. 302 a, b, f, g), but very marked in Lygodium (Fig. 302 c). Here it will be well
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. 546 FILICALES. Fig. 303. Senftcnbergia (Pecopteris) elegans, Corda. A=^ small piece of sporophyll (-J). 5=a spor- angium px5')* (After Zeiller, from Engler and Prantl, Nat. Pflanzenfam.) The sporangia of Mohria are radially constructed, the apex and base being opposite (Fig. 302 d, e). In the other genera the sporangia are more or less curved, so as to be dorsiventral: this curvature is slight in Aneimia and Schizaea (Fig. 302 a, b, f, g), but very marked in Lygodium (Fig. 302 c). Here it will be well to introduce a brief notice of certain fossil sporangia which have been referred to this affinity, w\ <5ni, \ f '/''W ^or tney ne^P t0 an understanding of the structure of those of living forms. The best known of these is Senften- bergia (Pecofteris) elegans, Corda, from the upper Carboniferous (Fig. 303): it corresponds to Schizaea both in the disposition of the solitary sporangia and in their form and mode of dehi- scence ; but the annulus is composed of several cell-rows, and the terminal " plate " has not been observed. Zeiller points out, however, that this is not an absolute difference from living forms, for various species of Lygodium (a genus which has itself been traced back to the Cretaceous Period), have a partially double series of cells of the annulus, while the " plate" in living forms is often so small that a similar one in a fossil- impression might well escape A second example is the genus Klukia, the fructification of a Pecopterid from the Jurassic, of which several species have been described by Here the arrangement of the sporangia, their struc- ture, and line of dehiscence are as in Schizaea, there being only a single series of cells of the annulus (Fig. 304). In both of these genera of fossils it is to be noted that the sporangia are intra-marginal, on the lower surface of the pinnule, but without any indusi
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