APPLE DISEASES 141 
Symptoms. 
The first indication of the disease may appear while the fruit 
still hangs on the tree, and the symptoms consist in the develop- 
ment of a smooth, brownish discoloration in the skin. The 
rotted area increases in size, the general form being retained. 
The pathogene often comes to the surface and shows itself as 
grayish tufts (Fig. 37); these may be arranged in concentric 
circles. The rotting of 
the fruit is finally com- 
plete (Fig. 37). In 
many cases the affected 
fruit becomes jet black 
and the skin assumes an 
ebony aspect. Fruits 
showing such symptoms 
usually exhibit no ex- 
ternal signs of fruiting 
bodies of the causal 
pathogene. The con- 
ditions that determine 
whether an apple affected 
with the brown-rot dis- 
ease will remain brown 
or will become black, as 
already described, are not well understood. The appearance 
of these various characters has been explained in relation to 
weather conditions as follows: — (a) if the weather is warm, 
and the atmosphere has a high relative humidity, the affected 
fruits become brown, and grayish tufts make an early ap- 
pearance; (b) if the relative humidity is reduced, the fruit is 
at first brown, then black, and the tufts are rare or absent; 
(c) if the air is dry and cool, the affected fruit is black and no 
grayish tufts develop. In regions where dry air prevails, this 
type of the brown-rot disease is the more common. Likewise 
Fic. 37. — Brown-rot on apple. 
