FILMING. 



371 



487. The archegonia 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. 254). 

 The archegonia of the other Fili- 

 cinae do not differ much as to struc- 

 ture, but like the antheridia, they 

 are not confined to the under sur- Fig- 254._ Yo nng archegonium 



fnpp nf +lif> nvnf-'hillinm of Pteris aerrulata, showing a few 



m ' cells of the prothallium, contain- 



488. After fertilization the ing chlorophyll, and the axial row 



of cells and the germ-cell, filled 



germ-Cell divides (111 the knOWll with dense and granulated pro- 

 . . __ toplasm. Highly magnified. 



cases) into four parts, as in Equi- After Sachs. 



setince, 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. 255 and 256). 



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 Ophioglossacecs, the single spo- 

 rangia occur in the tissues of the greatly 

 modified leaves. The spores are all of one 

 255-prothai- kind, excepting in the Rhizocarpem, in 

 nd young plant of which there are two sizes, viz., micro- 



.ris, seen from below, spores and macrospores. The sporangia 



p, the prothallium ; A, * u T7 / zr-7 \ i. j> 



root- hairs of prothallium; oi the true Jjerns (Filices) have a ring of 



b, first leaf of young nil n T-I 



plant; w f , the first root cells belonging to their walls, peculiarly 

 the th s e econ l d n ?oot ant x s.~ 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. 



