THE PARASITIC EXOASCEAE. 



163 



are somewhat curled up, and the asci appear on their lower 

 surface.! 



Exoascus cerasi Fuck, occurs very commonly on cherry 

 trees (Frunus Cerasus and P. avium) both in Europe and America.^ 

 It produces witches' brooms, which may be large, upwardly 

 directed, bush-like, and very conspicuous structures, with 

 numerous thickened and elongated twigs (Fig. 3); or they may 

 be small, hanging bunches of twigs with upturned free ends. 

 The leaves are somewhat wavy, slightly crumpled, and reddish ; 

 on their lower epidermis they bear asci, and fall off prematurely. 



Fig. 58. — Normal twig of Cherry from a tree in blossom, as in Fig. 57. 

 (T. Tubeuf phot.) 



The brooms are visible at a considerable distance in the winter 

 (Fig. 56), while they are even more conspicuous during the 

 flowering season (Fig. 57). At the latter time, before the 

 leaf-buds open, the cherry trees are normally covered with 

 white blossom, while the brooms bear leaves only, and rarely 

 blossom. Hence they produce little or no fruit. Each tree 



1 Wehmer {Bot. Zeitung 1896) discusses the formation of these witches' 

 "brooms. (Edit.) 



- E. Rathay, "Uber die Hexenbesen d. Kirschbaumen." — Sitzungsber. d. K. K. 

 Akad. zu Wien, 1881. 



