THALLOPHYTA 331 
cilia occurs in connection with a nucleus, the zoospore is re- 
garded as a compound structure composed of many uninuclear, 
biciliated zodspores. 
The zoédspore with the surrounding wall 

Fre. 339. Celastrum, a colonial nonmotile green alga 
Left, colony; right, portion of a colony, two cells of which are giving rise to 
daughter colonies. (x 750) 
is known as a zoosporangium. The zodspore escapes by the 
rupture of the wall of the zodsporangium. After swimming 
about for a while 
the zoospore comes 
to rest, develops a 
cellulose wall, and 
grows into a new 
plant (Fig. 341). In 
this process the zoo- 
spore produces two 
tubular filaments, 
one of which devel- 
ops a holdfast by 
which the plant be- 
comes attached to 
the substratum. 
Sexual reproduc- 
tion is by means of 
eggs and spermato- 
zoids. The eggs oc- 
cur singly in odgonia, 

Fic. 340. Vaucheria 
First three figures, formation and escape of zoéspore ; 
fourth figure, section of a portion of zodspore, show- 
ing two cilia opposite each nucleus. (The first three 
figures redrawn after Goetz from Oltmanns ; the last 
figure redrawn after Strasburger from Oltmanns) 
