282 



Bulletin 2'j(i. 



flowers and young fruit may also be affected, but as these soon drop from 

 the trees this is seldom observed by the grower. The affected leaves 

 not only curl and thicken but become sickly yellow in color often tinted 

 with red. After a few weeks these leaves fall from the trees (Fig. 84), 

 in severe cases leaving them nearly or quite denuded of foliage, and 

 that at a time of year when the tree can ill aft'ord to lose them. It 

 is true that a new crop of leaves is soon produced, but this effort of 

 nature to repair the loss is disastrous in that it is a heavy drain on 

 the vitality of the tree. 



Fig. 80. — A comparison of twigs; a, heallhy twig; b and c, twigs in which 

 the Leaf-Curl fungus is wintering; d, twig killed by the fungus. 



Etiology.— This malady, liks most diseases of trees, is caused by a 

 fungus that lives as a parasite in the affected parts. The name applied 

 to this particular fungus is Exoascus deformans. This name, which at 

 first appears rather formidable, is really descriptive. " Exoascus " 

 refers to the fact that the spore sacs or asci of the fungus are borne free 

 and uncovered over the diseased surface of the leaf (Fig. 81), while 

 the last name, " deformans," refers to the characteristic deformity 

 of the leaf produced by this particular species (Fig. 79). 



Just how this parasite enters the young leaves and shoots is not 

 known. Certain it is that entrance into the host is effected very early 



