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UNIVERSITY OF CALIFORNIA EXPERIMENT STATION. 



As the disease progresses these patches run together until a large 

 part of the surface of the leaf may be covered with a grayish white 

 mildew. The leaf ceases to grow and curls up towards its upper sur- 

 face. (See figure on cover.) 



Fig. 2. White patches of Oidium on upper surface of young leaf. 



As the shoots lengthen, the canes may be attacked in the same way. 

 The patches of mildew appear usually near the bases of the canes and 

 are difficult to see until they acquire the gray tint. In severe cases, the 

 fungus may completely cover the whole surface of the cane, but it is 

 usually confined to patches. If these patches are rubbed the fungus 

 comes off completely. The places where it has been, however, will turn 

 dark later owing to injuries to the superficial cells of the bark. (See 

 % 3.) 



Fig. 3. Blackening of canes due to Oidium. 



