VASCULAR CRYPTOGAMS 17 



lowermost portion of the lowest cell remains of a comparatively large 

 size, and is the central cell containing the oosphere. When mature, the 

 two canal-cells deliquesce into mucilage, which swells up considerably, 

 drives apart the four apical lid-cells or stigmatic cells of the neck, and 

 is ejected ; an open canal being thus formed to allow the access of the 

 antherozoids to the oosphere, which always takes place in moisture, the 

 ejected mucilage assisting also in this process. 



The tfMm#rappear as roundish papillae on the margin, or dispersed 

 over the under surface of the prothallium ; in some cases they are im- 

 bedded in its tissue. Each antherid consists of a comparatively small 

 number of cells ; when mature the cell-walls are ruptured under water, 

 and from each escapes a swarming antherozoid. The antherozoids are 

 spirally coiled threads of protoplasm, the body of which is formed from 

 the nucleus of the mother-cell, with a number of fine vibratile cilia 

 on the anterior coils. There is generally attached to each anthero- 

 zoid, as it escapes from its mother-cell, a vesicle of protoplasm contain- 

 ing starch-grains, formed out of the cytoplasm of the mother-cell, which, 

 adhering to one of its posterior coils, is dragged along with it during its 

 swarming, but becomes detached before its entry into the neck of the 

 archegone. In the heterosporous families the antherid is of very simple 

 structure, and is either produced directly within the microspore, or after 

 the preliminary formation of a few cells, which must be regarded as a 

 rudimentary prothallium. 



The form and size of the non-sexual generation or sporophyte vary 

 within very wide limits, from the filmy, moss-like Hymenophyllacese 

 (Filices) to the arborescent tree-ferns (Filices), and must be described 

 more in detail under the various families. It arises in the archegone, 

 from the oosperm or fertilised oosphere. The first effect of impregnation 

 is that the oosphere invests itself with a cell-wall of cellulose, thus 

 becoming the oosperm, which then divides into a small number of 

 undifferentiated cells, in which condition it is known as the embryo. In 

 the earliest subsequent divisions of the embryo may be recognised the 

 rudiments of the first root, of the first leaf or cotyledon, and of the apex 

 of the stem ; while at the same time a lateral outgrowth termed \hefoot 

 is formed at the bottom of the venter, and draws from the prothallium 

 the first nourishment for the young plant. The venter at first grows 

 vigorously, enveloping the embryo, until this latter finally protrudes 

 free, leaving the foot still attached to it for some time as a nutritive 

 organ. The primary root soon disappears, and in some Hymenophyl- 

 laceae, and in Salvinia and Psilotum, is not followed by others ; but in 

 the great majority of cases other true roots succeed in acropetal suc- 

 cession, and the prothallium then disappears. The cotyledon always 



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