. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARATTIACEAE 513 view of its origin, since its sporangial structure is closely similar to that of Angiopteris, while such elongated sori are absent from the corresponding fossil types. A similar elongation of a synangial sorus of the Marattia- type, so as to extend the full length of the vein, would give the condition seen in Danaea (Fig. 283 j, k, or better in Fig. 2S6 a) ; here also the sporangia are disposed as in Marattia, but differing in the minor fact. Fig. 283. Sori and sporangia. A, B = Angio
. The origin of a land flora, a theory based upon the facts of alternation. Plant morphology. MARATTIACEAE 513 view of its origin, since its sporangial structure is closely similar to that of Angiopteris, while such elongated sori are absent from the corresponding fossil types. A similar elongation of a synangial sorus of the Marattia- type, so as to extend the full length of the vein, would give the condition seen in Danaea (Fig. 283 j, k, or better in Fig. 2S6 a) ; here also the sporangia are disposed as in Marattia, but differing in the minor fact. Fig. 283. Sori and sporangia. A, B = Angiopteris crassipes, Wall, /?=sorus. />' = two sporangia, one in surface view from without, the other cut longitudinally. C, D — Arcli- augio/jteris Henryi, Christ et Giesen. C=som$. D— two sporangia in section. E, F= Marattia/raxinea, Sm. E —synangium ; i?=the same in section. G, H'= Kaulfjtssia aescztlifolia, Bl. t7 = part of the lamina seen from below, with three synangia ; the numerous small circles on the leaf-surface are stomata. /V = section through a synangium. y, K= Danaea elliptica, Sm. y = two synangia; 7v" = section through a synangium. (A, B, E, G, J after Bitter. C, D after Christ and Giesenhagen. ' F, H, K after Hooker-Baker. From Engler and Prantl, Nat. Pllauzctifam.). that the valley between the rows of them is almost levelled up, and the sorus thus forms a solid cake. It will be shown shortly that developmental details support the view that such elongation has actually taken place, while the fact is worthy of note that the length of the sorus varies greatly in different species of Danaea. And lastly, in Kanlfussia the synangial association of the sporangia together in the circular sorus is on the plan of Marattia and Danaea (Fig. 283 G, h). The origin of the numerous sori by fission from the Danaea-typc as the lamina expanded has already been. Please note that these images are extracted from scanned page images that may have been digitally enhanced
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