20 
MILDEWS, RUSTS AND SMUTS 
more especially the grape vine {Vitis vinifera), many other 
species of Vitis and Ampelopsis are also attacked. 
This destructive parasite, which has been the ruin of 
numerous vineyards in Europe, is a native of the United 
States. It was introduced into France about the year 1878, 
along with American vines that were imported to replace 
those destroyed by the Phylloxera, also a pest of American 
origin. The mildew attacks the foliage, young shoots, 
tendrils, flowers and young fruit of the Vine, but usually 
appears first, and is most abundant on the leaves, which are 
often killed within a fortnight of the appearance of the 
disease. During the autumn the winter form of fruit, 
or resting-spores, are produced in great numbers in the tis¬ 
sues of diseased leaves. When the leaves decay, the resting- 
spores are not injured, but remain in the soil until the fol¬ 
lowing spring, when they germinate, producing two or 
three conidiophores, similar to those present on the leaves 
during the summer. The conidia present on these conidio¬ 
phores infect the vines early in the season, being carried 
by wind, etc. 
Plasmopara nivea, Schroet. Spots on the upper surface 
of the leaf, yellowish-green, then brownish and becoming 
dry, the conidiophores form rather dense, white patches on 
corresponding areas on the under surface of the leaf; 
mycelium stout, often contorted, haustoria numerous, 
pear-shaped ; conidiophores tufted, emerging through the 
stomata, 150—300 x 8—10 (jl, tapering upwards, simple 
or with 3—5 alternate, primary branches near the tip, 
these branches bear 3—5 tapering branchlets at the tip, 
or bear i—3 short lateral branches, which are divided into 
2—3 short, stout, tapering branchlets at the tip, colourless ; 
conidia broadly elliptical, with a vague apical papilla, 
colourless, 21—32 x 12—22 p,, producing zoospores on 
germination ; oospore globose, yellowish-brown, smooth 
or slightly wrinkled, 28—^40 p, diam. 
Syn. Botrytis nivea, Unger. 
Peronospora nivea, Unger. 
Peronospora umhelliferarum. Gasp. 
Parasitic on living leaves of various umbelliferous plants, 
Goutweed (Aegopodium podagraria), Anthriscus sylvestris, 
Angelica sylvestris, Pimpinella magna, P. saxifraga, Sium 
latifolium, Pastinaca sativa, Petroselinum sativum, Peu~ 
cedanum palustre, Daucus carota, Conium maculatum, 
