THE PARASITIC EXOASCEAE. 



161 



Exoascus alpinus -lohan. and Ex. nanus Johan. Both occur 



on Biiidii iKnui, and induce formation of hypertrophied twi^s. 



Fig. 56.— Witcha' Broom of the Cheny. Exoascus cerasi on Prunus Cenmus. The 

 whole left side forms a large broom. A smaller example occupies the summit of 

 the crown, while another hangs do^^^lwards to the right. In winter condition, 

 (v. Tubeuf phot.) 



The mycelium of Re. nanus hibernates in twigs, and penetrates 



L 



