156 FUNGI. 
species as P. effusa. The conditions which control this form 
of germination cannot be indicated, since some conidia which 
germinate after this manner will sometimes be found mixed 
with others, the majority of which furnish zoospores. It may 
be that the conidia themselves are in some sort of abnormal 
condition. 
In all the species examined the conidia possess the power of 
germination from the moment of their maturity. The younger 
they are the more freely they germinate. They can retain this_ 
power for some days or weeks, provided they are not entirely 
dried. Dessication in an ordinary temperature seemed sufficient 
to destroy the faculty of germinating in twenty-four hours, when 
the conidia had been removed from the leaves on which they 
were produced. They none of them retained the faculty during 
a few months, hence they cannot preserve it during the winter. 
The germs of Peronospora enter the foster plant if the spores 
are sown upon a part suitable for the development of the 
parasite. It is easy to convince one’s self that the mycelium, 
springing from the penetrating germs, soon takes all the 
characters that are found in the adult state. Besides, when 
cultivated for some time, conidiiphorous branches can be seen 
growing, identical with those to which it owes its origin. Such 
cultivation is so readily accomplished that it can be made upon 
cut leaves preserved fresh in a moist atmosphere. 
In the species of Peronospora that inhabit perennial plants, or 
annual plants that last through the winter, the mycelium hidden 
in the tissues of the foster-plant lasts with it. In the spring it 
recommences vegetation, and emits its branches into the newly- 
formed organs of its host, there to fructify. The Peronospora 
of the potato is thus perennial by means of its mycelium con- 
tained in the browned tissue of the diseased tubers. When in 
the spring a diseased potato begins to grow, the mycelium rises 
in the stalk, and soon betrays itself by blackish spots. The 
parasites can fructify abundantly on these little stalks, and in 
consequence propagate themselves in the new season by the 
conidia coming from the vivacious mycelium. 
The diseased tubers of the potato always contuin the myce- 
