DISEASES CAUSED BY FUNGI 



27 



gives rise to root disease and to damping-off of cuttings and 

 seedlings of very many species of plants. According to G. L. 

 Peltier, epidemics are apparently due to a combination of factors, 

 such as the presence of a virulent strain of the fungus, a sus- 



[From Duggar's Fungous Diseases of Plants 

 Fig. 3 HypHAE (Rhizoctonia) Basidia and Spores of Corticium Vagum 



ceptible variety of plant, and optimum conditions of tempera- 

 ture and moisture for infection and development. Under 

 ordinary conditions most of the strains appear to be weak 

 parasites. 



The hyphas freely penetrate soft tissues, and there is usually 

 more or less external mycelium, though never a copious invest- 

 ment as in the previous species. The description given by 

 B. M. Duggar is as follows : 



