GRAPE DISEASES 233 
volved. After about a week the berry is a hard and shriveled 
mummy (Fig. 59). 
Although the berries, of all susceptible parts of the vine, are 
most severely affected, the disease may first be observed on the 
leaves (Fig. 60). In June or early in July black-rot appears on 
the leaves in the 
form of reddish 
brown, somewhat 
circular spots. 
Close observa- 
tions show that 
the first evidence 
of the trouble on 
the leaves is a 
slight blanching 
of the affected tis- 
sue. The small 
veinlets form the 
margin of the spot 
so that, while the 
shape of the le- 
sion tends to be 
circular, the out- 
line is finely cren- 
ulate (Fig. 60). 
Soon the center 
of the affected 
area becomes 
ashen-gray, but at this stage the margin is still brown. By 
the time the spot is just visible to the unaided eye the 
margin appears asa black line. Two or more spots may coalesce 
to form large irregular areas. The fruiting bodies of the patho- 
gene protrude through the cuticle of the leaf. These structures 
are black and are arranged promiscuously or in more or less 
concentric rings (Fig. 60). 
Fic. 60. — Black-rot lesions on grape-leaf. 
