THE GREAT GROUPS OF A~LGM 
241 
about itself. This firm wall indicates that the oospore is 
not to germinate immediately, but is to pass into a resting 
condition. Spores which form heavy walls and pass into 
the resting con- 
dition are often 
spoken of as "rest- 
ing spores," and it 
is very common 
for the zygotes 
and oospores to 
be resting spores. 
These resting 
spores enable the 
plant to endure 
through unfavor- 
able conditions, 
such as failure of 
food supply, cold, 
drought, etc. 
When favorable 
conditions return, 
the protected rest- 
ing spore is ready 
for germination. 
When the 
oospore of Edogo- 
nium germinates 
it does not develop directly into a neAV filament, but the 
contents become organized into four zoospores (Fig. 206, F), 
which escape, and each zoospore develops a filament. In 
this way each oospore may give rise to four filaments. 
It is evident that Edogonium is a heterogamous plant, 
and is another one of the Conferva forms. Conferva bodies 
are not always simple filaments, as are those of UlotJirix 
and Edogonium, but they are sometimes extensively branch- 
ing filaments, as in Cladophora, a green alga very common 
FIG. 207. Cladophora, a branching green alga, a very 
small part of the plant being shown. The branches 
arise at the upper ends of cells, and the cells are 
ccenocytic. CALDWELL. 
