60 



Bulletin 186. 



4 



] 



The latter is a matter which inust be determined largely by cross 

 inoculations, together with morphological studies. Inoculation 

 experiments have been in progress for two years, but they are not 

 yet in shape to be fully reported ; hence a presentation of the 

 results will be deferred. 



Characters of the Fungus. 



Hhizoctonia is a form genus established to include certain sterile 

 fungi occurring upon the roots of plants. The members of this 

 genus, however, may be readily located by certain distinguishing 

 characters of the mycelium. In pure culture, moreover, a very 

 characteristic form of growth is to be found. The young hyphse 

 growing in diseased tissue or in pure culture show a distinctive 

 manner of branching ; but as this character is in general the same 

 for all, a description of the beet fungus will suffice for this account. 



The young branches are inclined to the 

 direction of growth of the parent branch 

 at an angle more or less acute. And the 

 former are somewhat narrowed or con- 

 stricted where united with the latter, 

 as in Fig. 15. At a distance of a few 

 microns from these places of union, a 

 septum is invariably formed. The young 

 hyplu^ are often strongly vacuolate ; but 

 later they usually become uniformly 

 granular and more deeply colored. The 

 branching also seems to have occurred 

 more nearly at right angles to the main 

 liypha, and the constriction at the place 

 of union may not be so marked. (See 

 Fig. 16.) On the beet root a short, 

 tufted, or somewhat sporodochia-like 

 growth of the mycelium may also occur. 

 The hyphae of these tufts are brown, 

 closely septate, constricted at the septa, 

 and often branching in an irregular or dichotomous fashion, as in 

 Fig. 17. Such hyphae may eventually break up into hyphal lengths 



15. 



■Young liypJm of the 

 Rhizoctonia. 



