CULTIVATION. 265 
long for quotation here, except his observations on the devclop- 
ment of the threads of Peronospora infestans on the cut surface 
of the tubers of diseased potatoes. When a diseased potato is 
cut and sheltered from dessication, the surface of the slice covers 
itself with the mycelium and conidiiferous branches of Perono- 
spora, and it can easily be proved that these organs originate 
from the intercellulary tubes of the brown tissue. The mycelium 
that is developed upon these slices is ordinarily very vigorous ; 
it often constitutes a cottony mass of a thickness of many milli- 
metres, and it gives out conidiiferous branches, often partitioned, 
and larger and more branched than those observed on the leaves. 
The appearance of these fertile branches ordinarily takes place 
at the end of from twenty-four to forty-eight hours; sometimes, 
nevertheless, one must wait for many days. These phenomena 
are observed in all the diseased tuborcles without exception, so 
long as they have not succumbed to putrefaction, which arrests 
the development of the parasite and kills it. 
Young plants of the species liable to attack may be inoculated 
with the conidia of the species of Peronospora usually developed 
on that particular host, in the same manner that young cruci- 
ferous plants, watered with an infusion of the spores of Cystopus 
candidus, will soon exhibit evidence of attack from the white 
rust. 
It is to the cultivation and close investigation of the growth 
and metamorphoses of the minute fungi that we must look for 
the most important additions which have yet to be made to our 
knowledge of the life-history of these most complex and interest 
ing organisms. 
