ALG^E 55 



later, shows certain interesting analogies with the lower 

 mosses, and is on the whole, the type of the green algse 

 which most nearly approaches them. When the oospore 

 germinates, instead of forming a plant like the original at 

 once, or having its contents divided into zoospores which 

 then germinate, there is first developed a cellular body 

 (Fig. 10, C), which may be considered as a small plant 

 of very limited growth, differing from the normally de- 

 veloped sexual individuals. From each cell of this small 

 plant is produced a single biciliate zoospore, which then 

 develops into a normal individual. This formation 

 from the resting-spore of an individual entirely devoted 

 to the formation of non-sexual spores, from which the 

 sexual plants are finally developed, is very much like 

 what occurs in the life-history of the mosses which 

 probably arose from the Algse by a further development 

 of this alternation of sexual and non-sexual plants. 

 Where there is a marked difference in structure between 

 these phases, such as we find in the mosses and ferns, 

 the terms gametophyte and sporophyte have been ap- 

 plied respectively to the sexual and non-sexual phases. 

 The first indication of this differentiation is seen in such 

 forms as QEdogonium (Fig. 9), where the resting-spore 

 on germination dbes not at once produce a filament like 

 the parent plant, but first divides into four zoospores 

 which, on escaping, give rise to as many new individuals. 

 While the Confervacese probably form the direct 

 line of ascent from the Volvocineae to the mosses, there 

 are several other orders of green algse which, starting 

 from about the same point, show specialization in various 

 directions. Two of these, the Siphonese and Conjugated 

 are obviously related to the other green forms, but a 



