22 
MILDEWS, RUSTS AND SMUTS 
shaped; tufts of mildew formed by the conidiophores 
more or less effused, rather dense, usually more or less 
grey in colour ; conidiophores either sohtary or tufted, 
usually emerging through the stomata, cylindrical, generally 
repeatedly forked above, the ultimate branchlets either 
straight or curved, pointed; conidia elliptical, without 
a papilla or wart at the tip (except in one species), colourless 
or tinged dingy violet, germinating by the protrusion of a 
branch of mycelium, or germ-tube; oosphere subglobose, 
with a thin, almost or quite colourless wall; oospore with 
a somewhat thick wall, which is often ornamented with 
raised lines, etc., coloured. 
The species included in this genus form a thin, whitish 
or greyish mildew on the leaves and other parts of living 
plants. Known amongst allies by the elongated, slender, 
often branched haustoria, and by the absence of a papilla 
or wart at the tip of the conidium. 
All the species are true parasites, and many prove very 
destructive to cultivated plants. 
KEY TO THE SPECIES 
A. Divaricatae 
Branches of the conidiophores all straight, or scarcely 
curved. 
Parasitic on petals of plants belonging to the order Dip- 
saceae . violacea. 
Parasitic on plants belonging to the order Valerianaceae. 
Valerianae. 
Parasitic on plants belonging to the order Liliaceae. 
schleideni. 
Parasitic on plants belonging to the order Chenopodiaceae 
schactii. 
Parasitic on plants belonging to the order Polygonaceae, 
Rumex . rumicis. 
Parasitic on plants belonging to the order Caryophylla- 
ceae, Silene and Dianthus . dianthi. 
Parasitic on plants belonging to the order Caryophyllaceae, 
Arenaria . arenariae. 
Parasitic on plants belonging to the order Polygonaceae, 
Polygonum . polygoni. 
Parasitic on plants belonging to the order Galiaceae. 
calotheca. 
Parasitic on plants belonging to the order Caryophyllaceae, 
Cerastium, Stellaria . alsinearum. 
