158 DISEASES OF CULTIVATED PLANTS 



is somewhat erratic in its appearance, and during certain 

 seasons it covers both surfaces of the leaves of gooseberries 

 with a delicate greyish-white mildew. Less frequently the 

 fruit is also attacked. When the mycelium is well 

 established on the leaf, it becomes covered with a mass of 

 conidia, giving to it a mealy appearance. The ascigerous 

 condition is usually produced in abundance later in the 



FiG. 40. Microsphaera grossulariae. i , gooseberry leaf 

 with patches of mildew ; 2, a perithecium with its append- 

 ages ; 3, tip of an appendage ; 4 and 5, asci containing 

 spores. Fig. i nat. size ; the remainder highly mag. 



season, and is readily recognised under the microscope by 

 the elaborate tips of the appendages. 



Mycelium delicate, greyish-white on both surfaces of the 

 leaf; perithecia usually in small, scattered groups, dark 

 brown, appendages once or twice as long as diameter of 

 peridium, 4-6 times forked at the tip; asci 3-10, ovate, 

 containing 3-6 spores of variable size, 20-30 X 12-15 /x. 



As a rule this parasite cannot be considered as injurious. 

 Spraying with potassium sulphide is effective if commenced 

 when the leaves are unfolding. 



