WATER MOLDS 187 
basally rooted. All its vegetative portion is continuous; 
the reproductive portions only are separated from the 
rest of the plant-body by partitions. 
274. The propagation is very much the same as in 
Green Felt. It may be briefly described as follows for 
Saprolegnia: The protoplasm in the end of a branch 
becomes somewhat condensed, a partition forms, cutting 
off this portion from the remainder of the filament, and 
the whole of its contents becomes converted by inter- 
nal cell division into zoospores provided with two cilia. 
These soon escape from a fissure in the wall and are active 
for a few minutes, after which they come to rest and their 
cilia disappear. In one or two hours they germinate by 
sending out a filament, from which a new plant is quickly 
produced. 
275. The sexual organs also bear a close resemblance 
to those of Green Felt. The oogones are spherical, or 
nearly so (in most of the species), and contain from one 
to many eggs, which are fertilized by means of antherids, 
which usually develop as lateral branches just below the 
oogones. Fertilization takes place by the direct contact 
of the antherid and the passage of its contents into the 
oogone by means of a tubular process from the former. 
In some species there is no transfer of the contents of 
the antherid, and in others again there are no antherids. 
These eggs must therefore develop without fertilization, 
indicating that sexuality is disappearing in these plants. 
Eventually each egg becomes covered with a wall of 
cellulose and is thus transformed into a resting spore, 
which later germinates by sending out a tube, as in 
Green Felt. 
276. The Downy Mildews (Peronosporaceae) and 
White Rusts (Albuginaceae) live parasitically in the 
tissues of higher plants. They are composed of long 
