138 DISEASES OF CULTIVATED PLANTS 



EXOASCUS (FCKL.) 



The species often produce witches' brooms, or distortions 

 of the fruit or leaves. Mycelium perennial in the tissues. 

 Asci produced on the leaves or fruit. 



Many species are very destructive parasites. 



Peach leaf-curl, due to Exoascus deformans (Fckl.), attacks 

 the leaves of peach and almond. Diseased leaves are much 



FIG. 32. Exoascus deformans. i, peach leaves curled by 

 the fungus ; 2, section showing asci on the surface of a 

 leaf; 3, spores producing secondary spores by budding. 

 Fig. i reduced ; remainder highly mag. 



puckered, crumpled, and twisted, at first pale green, becoming 

 more or less rosy and covered with a delicate whitish bloom, 

 due to the presence of numerous asci. 



The mycelium hibernates in the bark, medullary rays, and 

 pith of young shoots, and extends along with the growing 

 parts, from which it passes into the leaf-buds, and infects the 

 leaves each succeeding season. 



