MLlalNM 



sn 



Fig. 254. — Young archegonium 

 of Pteris semUata^ showing a few 

 cells of the prothallium, contain- 

 ing chlorophyll, and the axial row 

 of celle and the germ-cell, filled 

 with dense and granulated pro- 

 toplasm. Highly magnified. — 

 After Sachs. 



487. — The ai'chegonia of the Ferns are cellular projec- 

 tions from the anterior portion of the under surface of the 

 prothallium. The germ-cell is sit- 

 uated at the base of an axial row 

 of cells ; the latter dissolve, and thus 

 form a canal, which becomes open 

 by the separation of the apical cells 

 of the archegonium wall (Fig. 354). 

 The archegonia of the other Fili- 

 cinse do not differ much as to struc- 

 ture, but like the antheridia, they 

 are not confined to the under sur- 

 face of the prothallium. 



488. — After fertilization the 

 germ-cell divides (in the known 

 cases) into four parts, as in Equi- 

 setincB, and by the growth and development of these the 

 young plant of the asexual generation is produced. The 

 young plant is at first very simple, the 

 first leaves being much smaller and less 

 divided than those which appear later 

 (Figs. 355 and 356). 



489. — The spores are developed upon 

 the leaves. They are contained in spo- 

 rangia, which occur singly or in clusters 

 upon the surface, or on the margins of 

 the more or less modified leaves ; in one 

 order, the OpMoglossaceoB, the single spo- 

 rangia occur in the tissues of the greatly 

 modified leaves. The spores are all of one 

 kind, excepting in the RMzocarpea, in 

 Jantof which there are two sizes, viz., micro- 

 spores and macrospores. The sporangia 

 of the true Ferns (Filices) have a ring of 

 cells belonging to their walls, peculiarly 

 thickened, forming an elastic ring, which 

 ruptures the mature sporangium ; in the 

 other orders there is no such elastic ring, and the dehiscence 

 is usually by the simple splitting of the dried wall. 



Pig. 255. — Prothal 

 linm and young plant of 

 Adiantum Capillus-Ven- 

 eris, seen from below. 

 p, the prothallium \ h, 

 root-hairs of prothallium; 

 b, first leaf of young 

 plant ; w', the first root 

 of the young plant ; w", 

 the second root. X 3.— 

 After Sachs. 



