238 MANUAL OF FRUIT DISEASES 
Symptoms. 
On the upper surface of the leaf the first signs of downy-mildew 
are in the form of small greenish yellow indefinite spots, the 
margins of which gradually merge into the darker green of 
Fic. 61. — Downy-mildew on lower surface of grape-leaf. 
the leaf. In a short time there appears within the spot a net- 
work of small, reddish brown lines, the discolored smaller 
veins. These lines become more pronounced until the whole 
diseased portion is brown, dry and brittle, and eventually 
cracked. These symptoms apply particularly to susceptible 
leaves. On the foliage of the more resistant vines there occurs 
