14 MILDEWS. RUSTS AND SMUTS 
\nicotianae, Breda de Harm. Conidia pear-shaped, 36 x 
25 (JL. Parasitic on plants belonging to Solanaceae 
{N icotiana).'] 
Phytophthora omnivora, De Bary. Spots on the leaves 
often somewhat vague and indistinct ; conidiophores 
either solitary or in tufts, emerging through the stomata, 
or bursting through the epidermis, simple, small, often 
bearing only one or two conidia, not swollen at the point 
of origin of the conidia, which are lemon-shaped, colourless, 
50—70 X 35—38 [JL; oospores globose, smooth, brown, 
25—30 [JL diam. 
Syn. Peronospora cactorum, Cohn and Lebert. 
Peronospora sempervivi, Schenk. 
Peronospora fagi, Hartig. 
Many different kinds of plants are attacked by this 
parasite, more especially in the seedling condition. In 
Biis country it is perhaps most abundant on the cotyledons 
of the beech {Fagus sylvatica), but also occurs on cultivated 
plants. It has been recorded as attacking plants belonging 
to the following genera : Fagus, Melocactus, Cereus, Sem- 
pervivium, Cleome, Clarkia, Schizanthus, Cactus, Acer, 
Fraxinus, Rohinia, Lepidium, Fagopyrum, Oenothera, 
Epilohium and Salpiglossis. 
Hartig ; Unters. aus dem Forsthot. Institut, 1880, p. 33. 
De Bary ; Beitr. zur Morphol. und Phys. der Pilze, 1881, 
p. 22. 
Phytophthora infestans, De Bary. Spots formed on the 
leaves are at first pale yellowish-green, then brown, be¬ 
coming blackish when old, the edge of the spot often 
fringed with the white conidiophores, which emerge through 
the stomata either singly or in small tufts, or in some 
instances they burst directly through the epidermis ; coni¬ 
diophores variable in length, somewhat slender and spar¬ 
ingly branched, swollen at intervals upwards, at points 
corresponding to the origin of the conidia ; conidia elliptical 
or lemon-shaped, with a very short stem at the base, wall 
thin, colourless, 20—32 X 15—24 p, producing zoospores 
on germination. Oospores unknown, 
Syn. Botrytis infestans, Mont. 
This fungus is the cause of the terrible scourge known as 
“ Potato disease,’' which was first observed in 1840, and by 
1845 had become general throughout Europe. Notwith¬ 
standing the absence of oospores, the fungus is able to 
reproduce itself by two methods, and to perpetuate its 
