9 6 



PLANT DISEASES 



as very delicate white patches on both surfaces of the 

 leaves, being usually most abundant on the under side; 

 during damp weather the patches increase in size, often 

 covering the entire surface of the leaf and presenting a 

 mealy appearance, due to the presence of numerous white 



Fig. 15. Microsphaera grossulariae. i, gooseberry 

 leaf with fungus ; 2, a perithecium with its appendages, 

 x 75 ; 3, tip of an appendage, x 300 ; 4, 5, asci contain- 

 ing spores, x 400. 



conidia, which, as usual in the Erysipheae, are produced 

 in erect chains, the terminal ones falling off as they become 

 mature, young ones at the same time forming at the base 

 of the chain. By this method enormous quantities of 

 conidia are produced throughout the summer months, and 



