AUTOBASIDIOMYCETES 471 



The spores, white in mass, are hyaline, ovate, averaging 6-8 x 

 5-6 fi, with a prolongation at the base. The fungus has been 

 grown in pure cultures, and inoculation experiments from such 

 pure cultures have yielded the typical disease, this in turn show- 

 ing the characteristic mycelium. The mycelium in culture makes 

 the best growth at from 25° to 30 C. The fungus spreads rapidly 

 by means of the vigorous mycelium, and the sporophores are pro- 

 duced so infrequently that spores would seem to play a minor part 

 in the distribution of the species. 



Control. As a result of his studies, Fulton cites the following 

 conditions as favoring the growth of the organism. 



1. Slowness of germination and early growth of the canes. 



2. Improper cultural procedures. 



3. Unsuitable soil. 



4. Bad drainage. -<■"••' 



5. Unfavorable seasonal conditions. 



6. A stubble crop. 



These facts make it evident that prevention should be concerned 

 with general methods of sanitation, such as the destruction of all 

 infected waste material, the rotation of crops, selection and disin- 

 fection of seed cane, and also the planting of the more resistant 

 varieties. 



XII. ROOT ROT OF FRUIT TREES 



Clitocybe parasitica Wilcox 



Wilcox, E. M. A Rhizomorphic Root-Rot of Fruit Trees. Okla. Agl. Exp. 

 Sta. Built. 49 : 1-32. pis. 1-11. 1901. 



For some years attention has been called to a destructive disease 

 of apple trees in Missouri, Oklahoma, and adjacent states, character- 

 ized primarily by the death of the root system. There is commonly 

 associated with this disease an invasion of the root system by the 

 mycelium of some one of the mushrooms. Wilcox has concluded 

 that the disease in Oklahoma is caused by a fungus described as 

 a new species, Clitocybe parasitica. He has found this fungus 

 constantly associated with the root rot of the apple, and also with 

 a similar disease of peach and cherry, as well as of certain native 

 species of oak. Other observers have apparently not been able 

 to conclude that a Clitocybe is the cause of the disease prevalent 



