176 



however that the most severe attack of the disease will re- 

 sult in the death of the tree during the first year. 



FUNGUS CAUSING THE DISEASE. 



The fungus causing this disease is one of the lower As- 

 comijcetes, a group characterized bv the formation of 



"ascus." 



its spores in small sacs of "asci," singular 

 This fungus is very closely related to the hJxoascus de- 

 formans causing the w(41 known leaf-curl disease of 

 peaches. Unlike the latter our fungus does not possess 

 a perennial mycelium and is carried over from one year 

 to another entirely through the agency of the ascospores. 

 These germinate in the spring and form a mycelium that 

 spreads out beneath the cuticle of the leaves of the host 

 to form there a more or less extensive network of hyphsp. 

 Vvorn. this vegetative mycelium the asci arise in large 

 numbers. These areniore or less cylndrical in form and 

 are packed closelv together side bv side. See Fisf 1. 



Fig. 1. — Cross section of a portion of a diseased leaf, sliowing the 

 young asci of the fungus. Each division of the scale is equiva- 

 lent to 10 mu. 



