432 VEGETABLE PHYSIOLOGY 
The more complete differentiation of the gametes into 
male and female can be observed among several of the 
families of the Algw. In some species of Hctocarpus and 
Cutleria the gametes are much like those of Ulothrix, but 
some are smaller than the others. The larger ones come 
to rest soonest, and loge their cilia; one of the smaller 
more motile ones then fuses with each of the larger. We 
can in this case speak of the larger as female and the smaller 
as male. The differentiation is still very rudimentary, 
as in the event of no fusion taking place the female cell can 
still develop into a new plant. 
Fia. 170.—Oocontum or Fucus, con- Fie. 171.—AN OOSPHERE oF Fucus 
TAINING EIGHT OOSPHERES. (After SURROUNDED By ANTHEROZOIDS. 
Thuret.) (After Thuret.) 
The most complete differentiation of the gametes can 
be traced in the higher members of the Algw. The females 
become larger and cease to develop cilia, the males remain 
small and motile. The former are then called oospheres 
and the latter antherozoids or spermatozoids. A good 
example of this stage of differentiation is afforded by Fucus 
(figs. 170 and 171). 
The structures or organs in which the gexual cells of 
these plants are formed are known as gametangia. When 
the gametes are distinctly male and female the gametangia 
in which they are developed are termed antheridia and 
oogonia respectively, 
