123 



THE FUNGI WHICH CAUSE PLANT DISEASE 



fusion of two nuclei as is general among the Ascomycetes. The 

 spore-nuclei arise by repeated mitoses of the primary nucleus. 



Affected leaves, fruit and twigs become swollen and much dis- 

 torted; wrinkled, curled, arched, puckered. In woody twigs the 



mycelium often induces 

 unnatural, profuse, 

 tufted branching result- 

 ing in "witches brooms" 

 though such structures 

 often arise from irrita^ 

 tion due to other causes. 

 Many attempts have 

 been made to arrange the 

 species in natural genera; 

 some based on the num- 

 ber of ascospores,*' ^** others largely on the biologic groxmds of an- 

 nual or perennial mycelium.' Giesenhagen ^° whose classification 

 is followed here, recognizes two genera, Exoascus being merged 

 into Taphrina. 



Key to Genera of Ezoascacee 



Asci cylindric, clavate or abbreviate-cylin- 



dric, produced above the epidermis of 



the host 1. Taphrina, p. 126. 



Asci saccate, in epidermis 2. Magnusiella. 



Fig. 86. — Taphrina showing mitoses in the young 

 ascus leading to the development of spore- 

 nuclei. After Ikeno. 



Taphrina Fries 



Mycelium annual or perennial; asci 4 to 8-spored, or by germina- 

 tion of the ascospores, multispored, borne on the surface of blisters 

 and other hypertrophied areas, cylindric to clavate, or a modifica- 

 tion thereof. Of this genus Giesenhagen '" recognizes four series 

 of species which are arranged in three subgenera. 



Subgenus 1. Taphrinopsis, — one series (Filicina) 



The asci are slender clavate, narrowed at each end, rounded 

 above, broadest in the upper fourth. Parasitic on ferns. None of 

 the five species is of economic importance. 



