Lectures on the physiology of plants . lt;?, developed entirely in its points come out still more clearlyin the germination of the spores of the genusSelagincUa. The sporangia here arise in theaxils of the leaves at the ends of the foliageshoots. Fig. 434 A shows the fertile shoot ofa Sclaginella looked at from the outside; B isthe same in longitudinal section. The sporangiasituated in the leaf-axils are obvious at once,and it is observed that those on the right sidecontain only four (only three are visible) largespores, whereas the sporangia on the left sideIf the macrospores a
Lectures on the physiology of plants . lt;?, developed entirely in its points come out still more clearlyin the germination of the spores of the genusSelagincUa. The sporangia here arise in theaxils of the leaves at the ends of the foliageshoots. Fig. 434 A shows the fertile shoot ofa Sclaginella looked at from the outside; B isthe same in longitudinal section. The sporangiasituated in the leaf-axils are obvious at once,and it is observed that those on the right sidecontain only four (only three are visible) largespores, whereas the sporangia on the left sideIf the macrospores and microspores are sownseparately on a suitable damp substratum, both develope, it is true, but no subse-quent fertilisation occurs : the unfertilised macrospores give rise to prothallia witharchegonia, it is true, but no embryo arises in these. This fact, which can beconfirmed in the case of the most different Cryptogams, is in so far of great value asit is not always feasible to observe directly the entrance of antherozoids into the. Fig. 432.—Marsilia salvcitrix. Longi-tudinal section of macrospore, prothallium,and embryo (X about 60) : am starch-grainsin spore ; i inner membrane, ruptured above ;ex epispore, with prismatic structure; ccavity beneath the protruded diaphragm onwhich the basal layer of the prothallium issituated ; pt prothallium ; ivh its root-hairs ;a archegonium ; y foot of embryo; w its root;s its stem-apex ; * its first leaf, which distendsthe prothallus ; si gelatinous envelope of thespore ; at first it forms the funnel above thepapilla, and it still envelopes the prothallium(50 hours after sowing). contam numerous microspores. EMBRYOLOGV OF SELAGINELLAE, ETC. 749 oosphere; the suppression of the fertilisation and development of the embryo whenthe access of antherozoids is prevented, however, is a certain proof of the necessityof the union for the formation of an embryo. The processes of reproduction which alone interest us here can be rajjidly appre-he
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Keywords: ., bookcentury1800, bookdecade1880, booksubjectplantph, bookyear1887
