GRAPE DISEASES 245 
in an irregular fashion. As described for the canes the outer 
cells are injured, which accounts for a halting in the growth of 
affected portions. Sometimes this irregularity of development 
results in a cracking of the fruit, in which case the berries either 
become entirely dry and never ripen, or are greatly reduced in 
size and quality. The fruits are not attacked by the pathogene 
after they enter the ripening-period. On older, but still im- 
mature,. berries brown spots appear; subsequently mildew 
becomes perceptible. The peduncles and pedicels also show 
the mildew. Very commonly on these parts the pathogene 
makes profuse growth. By harvest time the peduncles are 
dwarfed and withered. The development of the grayish mildew 
is followed by the appearance of black perithecial bodies as 
described for the other susceptible organs. 
Cause of powdery-mildew. 
Sexual fruit-bodies, perithecia, of the causal fungus, Uncinula 
necator, probably remain on the canes and leaves or in the 
soil until the return of summer. Within each perithecium 
twenty-five to fifty ascospores are found. These are liberated 
from their asci, and are carried to the growing shoots and leaves. 
The ascospores are not all ejected at the same time; some may 
not be discharged until a year later. Itis thought that in many 
cases the fungus hibernates by means of the asexual (conidial) 
stage; this opinion is based largely on the scarcity of the peri- 
thecia in certain regions. 
Whether the fungus begins its spring activities by means of 
ascospores or conidia, the result is a mildewed spot. The 
whitish mildew is composed of mycelium and conidiophores. 
When a spore falls on a leaf it germinates, and a copious develop- 
ment of mycelium results. Haustoria are sent into the epider- 
mal cells for nourishment. As a result of this action the cells 
turn brown, as described under Symptoms. From the mycelium 
elongated, erect conidiophores extend into the air; each bears 
a chain of conidia. The conidia are light and are easily dis- 
