MILDEWS, RUSTS AND SMUTS 
5 
NOTES ON THE GENERA 
PYTHIUM 
The exceedingly minute organisms constituting this 
genus are remarkable for their lack of differentiation be¬ 
tween the vegetative and reproductive portions. A more 
or less vaguely branched mycelium traverses the host, and 
here and there throughout its length produces at the tips 
of branches, or intercalary—that is at intervals in the length 
of a hypha, the various reproductive bodies. All the 
species are aquatic, or grow in very damp places, where the 
zoospores can disperse in a film of moisture. Some are 
destructive parasites, often attacking plants in the seedling 
stage, and causing the injury known as “ damping off." 
CYSTOPUS 
The conid'al condition of all the species form white, 
flattened, or slightly raised patches of variable size, on 
living leaves. The patches are at first white, and present 
a polished appearance, but finally become powdery when the 
chains of conidia rupture the epidermis of the leaf. The 
oospores are formed in the tissues of the leaf, and can only 
be seen when sections of the diseased parts are prepared. 
C. candidus is very abundant on the weed called Shepherds’ 
purse, which, under the influence of the parasite, usually 
becomes much twisted and distorted. 
PHYTOPHTHORA 
Most of the species are destructive parasites to cultivated 
plants, the most important being P. infestans, the cause of 
the too well known potato disease. All the species form a 
very delicate white, or greyish, mould on the leaves or stem 
of the host-plant. The haustoria are not so short, and 
vesicular or pear-shaped as in allied genera, but grow out 
like ordinary threads of mycelium, and are more or less 
elongated. The oospore is smooth in P. omnivora, the only 
species in which it has been observed. 
BASIDIOPHORA 
There is only one species in this genus, which is readily 
recognised by the simple, stout conidiophores, swollen 
at the tip, the swollen portion bearing a number of very 
short, stout outgrowths, each of which supports a single 
large conidium. The wall of the oosphere is very thick and 
hard. 
