142 DISEASES OF CULTIVATED PLANTS 



removed. It is perfectly certain that a tree bearing a con- 

 siderable number of large brooms continues to flourish just 

 the same as if such structures were absent. 



Cherry leaf blister, caused by Exoascus minor (Sadeb.). 

 Diseased leaves become slightly thicker in substance, change 



FlG. 35. Exoascus alni-incanae, causing 

 enlarged scales of alder catkins. 



to a pink or red colour, and are more or less curled up. The 

 surface is covered with a delicate white bloom when the 

 spores are produced. Diseased leaves soon die and decay. 

 The mycelium hibernates in the buds. 



As the mycelium is perennial in the living plant, pruning 

 all diseased shoots is the only remedy. 



