320) A TEXTBOOK OF GENERAL BOTANY 
individuals held together by a gelatinous envelope (Kig. 321). 
When conditions again become favorable to the motile stage, 
the cells acquire cilia and swim out of the jelly. 
Reproduction. Chlamydomonas reproduces vegetatively by the 
formation of zodspores, a method which is characteristic of many 
green alge. Zod- 
spores are motile 
spores. In the for- 
mation of zoospores 
in Chlamydomonas 
the contents of the 
cell divide rapidly 
into two, four, or 
eight parts (Fig. 
322). These ac- 
quire the structure 
of mature individu- 
als and are set free 
trom the mother cell 
by the conversion 
of the wall of the 
latter into mucilag- 
is 7 4 inous material. The 
eee 5) mature motile indi- 
viduals are simply 
enlarged zoospores. 
Sexual reproduc- 
tion takes place by 
means of gametes, which are formed in the same way as zodspores 
and have the same general structure, but are frequently smaller 
and more numerous (Fig. 323). Two of these fuse together to 
form a single cell known as a zygospore. A zygospore is a spore 
formed as a result of the fusion of two similar gametes. The 
zygospore surrounds itself with a thick wall and undergoes a 
period of rest. When conditions are favorable, the contents of 
zygospores are transformed into zoéspores, which enlarge and 

Fig. 823. Chlamydomonas longistigma 
Above, division into daughter cells; lower figures show 
the conjugation of gametes. (Redrawn after Dill) 
