204 MANUAL OF FRUIT DISEASES 
seasons nearly complete defoliation occurs. This loss of foliage 
interferes with the maturing of both the wood and buds, 
and as a result the succeeding crop is injured. Perhaps the 
cumulative effects constitute the worst feature. 
Symptoms. 
During the month of June, lesions appear as small brown 
spots (Fig. 53) on the upper and lower surfaces of the leaves. 
The spots may number few 
or several toa leaf. Each dis- 
eased area enlarges until it 
has reached a diameter of 
about one-eighth of an inch, 
and the center becomes pale 
with small black fruiting 
bodies of the pathogene, while 
the border remains brown 
(Fig. 53). Older lesions are 
frequently confluent. From 
the last of June to August 
the affected leaves turn vel- 
Fic. 53.— Mycospherella leaf-spot low and fall prematurely, 
on currant. This happens on red and white 
currants particularly. The 
leaf-spot lesions are distinguished from those of the anthrac- 
nose by their larger size, sharp outline, and pale, dead center. 
Cause. 
The causal organism, Mycospherella Grossularia, is a fungus 
which has been known since 1842. It was first described from 
Europe. When the affected leaves fall to the ground, the fungus 
is carried with them. It begins to develop perithecia, but these 
do not reach maturity before winter comes. With the advent 
of spring these bodies complete their growth. Within each 
many ascospores are formed. These are discharged with force 
into the air, are caught by the air currents, and are carried to 
