DISEASES OF SPECIAL CROPS 75 



Upon the leaves and twigs the fungus forms a thick 

 velvety coat, varying from dark olive-green to black, in 

 spots at first circular in outline, later irregular and coalesc- 



FiG. 25, — Apple scab. After Craig. 



ing. The irritation and retardation of growth caused by 

 the presence of the fungus induces the leaves to curl and 

 wrinkle in a characteristic manner. 



The injuries by this disease may be enumerated as 

 follows : lessened leaf value, retarded twig and wood 

 growth, premature fall of fruit, retardation of full develop- 



