34 



ALTERNATING GENERATIONS 



only appendages other than rhizoids and occasional hairs are small flat 

 scales borne on the lower surface. The gametophyte is thus of very simple 



form (Fig. 17). The sexual organs are borne 

 in acropetal succession on its upper surface, 

 and are sunk in depressions. The sporophyte, 

 which results from fertilisation of the ovum by 

 spermatozoids motile through water as in Ferns,. 

 is a small spherical body, with no distinction 

 of apex and base (Fig. 18). It consists of a 

 single layer of cells forming a peripheral wall, 

 which is, however, disorganised before the 

 ripeness of the spores. The latter are pro- 

 duced by a tetrad division of the spore-mother- 

 17. cells, which occupy the whole internal space of 



a minima. A, thaiius of the sporogonium (Fig. 1 8 A) ; on germination 



natural size. B. the same in vertical ..... , 



section, showing two sporogonia sunk the spores yield fresh gametophytcs. Thus the 



in the tissue of the thallus. Magnified. , , . . - 



(After Bischoft) two generations are here as distinct from one 



another, structurally and in origin, as in the 



Fern, though both are of small size and simple form. It is to be 

 noted, however, that the sporophyte is throughout its life dependent 



FIG. i8A. 



Riccwcai-fus iitifii/is. The upper tigui > 

 shows the spherical spore-mother-cells 

 surrounded by nutritive material. The 

 Ricciocarpiisiia.ta.ns. Young sporogonia in longitudinal section, lower shews the tetrads formed from 

 surrounded by the archegonial wall. The younger (x 666) shows them: the sp.n.ig.Miial wall (shaded) is 

 the amphithecium (shaded) surrounding the sporogenous cells : in still seen surrounding them, and covered 

 the older (Xs6o) these are separated, as the free, and rounded externally by the ari hegonial w.dlof two- 

 spore-mother-cells. (After Garber.) cell-layers. x666. (After Garber.) 



upon the gametophyte, both mechanically and physiologically, and that it 

 is an almost entirely undifferentiated, spore-producing body. 



