346 A TEXTBOOK OF GENERAL BOTANY 
Relationship. It seems very probable that the Odmycetes have 
been derived from an alga similar to Vaucheria. Some of the 
reasons for this supposition will be apparent if Vaucheria and 
Saprolegnia are compared. The vegetative body is very similar 
in the two cases, except that Saprolegnia lacks chlorophyH, 
whereas this is present in Vaucherta. In both cases the plant 
consists of branched, nonseptate filaments, that is, filaments with- 
out septa, or cross walls. 
Vaucheria is attached to 
the substratum by means 
of a colorless, branched 
filament known as ahold- 
fast. Saprolegnia is at- 
tached in a similar way, 
except that the filaments 
enter the body of the ani- 
mal on which the Sapro- 
legnia is growing. The 
zoosporangium of Sapro- 
legnia has a shape simi- 
lar to that of Vaucheria. 
Fig. 358. Odgonia and antheridia of Sapro- In Saprolegnia there is 
legnia. (x 600) a zoospore for each nu- 
cleus, and each spore 
has two cilia. The zodspore of Vaucheria has a different struc- 
ture, but we have seen that there is reason to believe that it is 
a compound zodspore which can be regarded as formed by the 
fusion of a number of zoospores similar to those of Saprolegnia, 
as the zodspore of Vaucherta has numerous pairs of cilia, each 
of which is opposite a nucleus. The odgonia of the two forms 
are very similar, except that Saprolegnia usually has more than 
one egg, while Vaucheria has a single egg. The general form 
of the antheridia of Saprolegnia is likewise similar to that of the 
antheridia of Vaucheria. Vaucheria, however, produces sperms 
which swim through the water, while in Saprolegnia fertilization 
is by tubular outgrowths from the antheridia. This difference is 

