THE PARASITIC EXOASCEAE. 



103 



are somewhat curled up, and the asci a[)pear on their lower 

 surface.! 



Exoascus cerasi Fuck, occurs very commonly on cherry 

 trees (Fninus Ccrasus and P. avium) both in Europe and America.- 

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

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

 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 otf pi'i'iuaturely. 



, as in Fig. 



The brooms are visible at a considerable distance in the winter 

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

 lowering 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 fniit. P^ach tree 



' Wehmer (Bot. Zeituwj 1896) discusses the formation of these witches' 

 brooms. (Edit.) 



- E. Rathay, " Uber die Hexenbesen d. Kirschbiiumen."— 5(7;«HrMf>*. 'Z. A'- K. 



Akad. zii Witn, 1881. 



