Text-book of structural and physiological botany . Aspidiumy^\\ annulus: with hori-zontal annulus ; III. Os--1711 tnda regalis, royalfern, with incompleteannulus (all greatly magnified). Fig. 441.—Reproduction of a Fern, Pteris serrulata; prothallium proceeding from the spore ; a spore, brhizoids, xy antheridia (x 80) ; II. an archegonium nearthe period of opening, a central cell (x 400); III. theyoung plant springing from the cordate prothallium ; wfirst leaf, r first root (natural size). gium in a horizontal or oblique direction (Fig. 440 11. iii).On germinatin
Text-book of structural and physiological botany . Aspidiumy^\\ annulus: with hori-zontal annulus ; III. Os--1711 tnda regalis, royalfern, with incompleteannulus (all greatly magnified). Fig. 441.—Reproduction of a Fern, Pteris serrulata; prothallium proceeding from the spore ; a spore, brhizoids, xy antheridia (x 80) ; II. an archegonium nearthe period of opening, a central cell (x 400); III. theyoung plant springing from the cordate prothallium ; wfirst leaf, r first root (natural size). gium in a horizontal or oblique direction (Fig. 440 11. iii).On germinating, the spore first gives rise to a green thalloid special Morphology and Classification, 315 leaf-like often kidney-shaped structure, lying flat on thesurface of the ground, the prothallium or pro-embryo ( III.), which puts out root-hairs \^hizoids~\ from its underside, and forms the archegonia and antheridia among the former are produced the ciliated antherozoids (); from the latter, which agree in almost all points with. Fig. 442.—Antheridia of Adianttmt capillus-veneris, maidenhair-fern : I. not yetmature; II. the antherozoids fully developed; III. the antherozoids escapingfrom the burst antheridium ; / prothallium, a antheridium, ^ antherozoids, bmother-cell of an antherozoid ( X 500). the archegonia of Mosses, the young plant is developed,after the fertilisation of the oosphere by the antherozoids;the prothallium then disappearing.^ An alternation of generations is very strongly marked inFerns; the first [sexual] generation includes the formation ofthe prothallium and sexual organs; the second [non-sexual] 1 [The central cell of the archegonium divides first into foiir cells,of which the two lowest subdivide and become imbedded in the sub-stance of the prothallium. The two upper of the four cells also sub-divide, one developing into the rhizome, the other into the first rootletof the young Fern.—Ed.] 316 Striicttcral and Physiological Botajty. g
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