MORPHOLOGY 
colorless Vaucheria. The representative genus Saprolegnia contains 
saprophytic species found on dead bodies of crustaceans, water insects, 
etc., and also parasitic species attacking fishes, frogs, etc. One species 
that attacks the eggs and young of fishes is very destructive in hatcheries. 
The asexual reproduction resembles that of Cladophora, sporangia 
developing as terminal cells and producing vast numbers of biciliate 
zoospores, which escape through a termi- 
nal pore (figs. 155, 156). The oogonium 
is a spherical cell, borne terminally or 
laterally, and contains one to several 
eggs. The antheridium is tubular in 
form, arising from another hypha or 
from the same one, and grows up in 
contact with the oogonium in various 
ways, sometimes curving about it. A 
small fertilizing tube sent out by the 
antheridium pierces the wall of the 
oogonium, reaches an egg, and through 
it the contents of the antheridium are 
discharged (fig. 157). Fertilization re- 
sults in heavy-walled oospores, which 
upon germination form new hyphae 
directly. 
Parthenogenesis. Saprolegnia is notable for 
the frequent and perhaps usual occurrence of 
parthenogenesis. All stages of abortion of the 
FIGS. 155-157. Saprolegnia: 
155, terminal cell producing zoo- 
spores; 156, free zoospores; 157, fcr- 
tilization, showing oogonium con- male apparatus have been observed: as, for 
taining several eggs, and antheridial example, the antheridial tube reaching the 
tube piercing the oogonial wall. egg but remaining closed ; the tube piercing 
the wall of the oogonium but not reaching the 
egg; the suppression of an antheridial tube; or even the suppression of the 
antheridium. In all these cases the eggs develop as if fertilized, and produce new 
plants. 
Experiments. The culture of Saprolegnia under experimental control has 
succeeded in determining the conditions that favor vegetative activity, zoospore 
formation, and gamete formation. If well nourished, the plant vegetates in- 
definitely ; if it is starved, as by removal to pure water, zoospore formation is in- 
duced; if the temperature is lowered, or if the plant is transferred to a solid substra- 
tum, conditions forbidding swarm spores, oogonia are formed. 
MonoUepharis. This is a form similar to Saprolegnia in many respects, being 
an aquatic saprophyte on decaying plants ; but it is chiefly interesting as the only 
