ALG 55 
later, shows certain interesting analogies with the lower 
mosses, and is on the whole, the type of the green alge 
which most nearly approaches them. When the odspore 
germinates, instead of forming a plant like the original at 
once, or having its contents divided into zoédspores 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 zodspore, 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 Algez 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 insuch 
forms as CEdogonium (Fig. 9), where the resting-spore 
on germination does not at once produce a filament like | 
the parent plant, but first divides into four zodspores 
which, on escaping, give rise to as many new individuals. 
While the Confervacee probably form the direct 
line of ascent from the Volvocines to the mosses, there 
are several other orders of green alge which, starting 
from about the same point, show specialization in various 
directions. Two of these, the Siphonez and Conjugate 
are obviously related to the other green forms, but a 
