NORTH AMERICAN PARASITIC EXOASCE.E. 107 



Exoasciis dcfonuau^ I'^ckl. 



Bessey '85. Kiiowles '87. 



Kelieriiiiin "85''. Saccardo '89. 



"85/'. Webber '90. 



.Vrthur "85. Pazschke '9'j. 



IJessey '86. Briosi e Ca\ara "91. 



Scribner '87. Ilalsted '92. 

 Kellernian cV CarltDii '87. 



Exoascns defonnaiis Berk. 



Ellis cV E\ erhart '93. 



Exoai^nis (fcfoniiaiis (Berk ) Fuckek 



Sadebcck "93. 



This species causes the famihar "leaf curl" of the peach. 

 Until a comparatively recent date it has been customar\- to 

 refer all leaf and sprout affections of fruit trees to the defor- 

 mans, as has been the case with diseased carpels and E. pntui. 

 In both instances variations sufficient to render necessary fur- 

 ther specific separation are now recognized. To the species 

 Exoasciis dcfoniKiiis (Berk.) Fuckek Sadebeck refers all dis- 

 eases of Pnniiis pcrsica, which, at the time of writing his last 

 monograph, he considered to be the only American host. I 

 sent him leaves of Pniiins rli/rdsa, which he has decided was 

 suffering from an attack of the same fungus. The mycelium 

 is perennial and is found in the young shoots of early spring, 

 in the bark, but never in the medullar^■ rays: it penetrates 

 among the parenchyma of the leaves and develops a sub- 

 cuticular hymenium. In consequence of the parasitic influ- 

 ence yery striking abnormal growths occur; infected leaves 

 become curled and often cartilaginous. The microscopic 

 changes of leaf-structure are well illustrated in an article by 

 E. L. Knowles. mentioned in the bibliographv of the species. 

 The ■• witches' broom'' formations haye been described in a 

 previous page. Sadebeck sa\'s the fungus does not spread in 

 the leaves of the later sprouts. June and July twigs always 

 have a perfectly healthful appearance, e'/en if the disease has 

 been yery \iolent in the spring. The asci are cylindrical, 

 usually rounded at the top. in size 9-10x35 40/. The stalk- 



