422 MANUAL OF FRUIT DISEASES 
land are more severely diseased than those on light, well-drained 
soil. Plants exposed to the sun are said to be more affected 
than those which are growing under shade; it appears that 
shade has a preventive effect, a phenomenon not easily ex- 
plained. Moisture alone increases the amount of leaf-spot, 
yet during an excessively rainy season plants remain quite 
free from the disease. This freedom from leaf-spot during 
a very wet season has been explained on the grounds that 
cloudy weather offers much the same conditions as those of 
shade. In a year of continued drought the disease is likewise 
less common. In general, conditions most favorable to the 
disease are hot, bright days with occasional showers or heavy 
dews. 
Symptoms. 
The disease makes its appearance on the leaves (Fig. 123), 
calyx and fruit-pedicels. In the beginning, the spots are very 
small, deep purple or red, and are usually first evident on the 
upper surface of the leaves. These areas rapidly increase in 
size, and at the same time the color of the central portion 
changes from a purple to a reddish brown; eventually the 
lesions become grayish or whitish in the center (Fig. 123). 
The border remains purplish, shading off to a reddish brown 
coloration towards the healthy. The single lesions vary from 
% to ¢ of an inch in diameter, but several spots may coalesce 
to form a large irregular blotch. Severely affected leaves 
turn brown, this discoloration beginning at their tips; finally 
such leaves shrivel and die. The lesions on the other suscep- 
tible organs are similar to those on the leaves. 
Cause. 
The leaf-spot disease of strawberries is produced by the 
fungus Mycospherella Fragarie. The mycelium of the fungus 
grows in and between the cells, and through the action of these 
threads upon the host-cell contents there is a response expressed 
in the spots as described. After a short time the hyphe 
