35 



When tubers with sclerotia attached are planted, the dormant threads 

 of the sclerotia grow rapidly and branch in all directions. These branches 

 are able to attack the living tissues of the young stems and set up a decay 

 already noted. 



An examination of many hundred plants in the field showed in every 

 case of injured stems the presence of sclerotia and the mould-like growth 

 of the mycelium on the tubers. We were unable to find the fruiting stage 

 of the fungus, but such has been observed upon living plants as "a mem- 

 branous layer enclosing the stem for several inches above the surface of 

 the ground. This layer is composed of rather loosely interwoven threads, 

 and on account of this character it is difficult to say if the plant is properly 

 placed under the genus Corticium, or whether it might not with equal 

 propriety be considered a species of Hypochnus" (Duggar). 



Forms of Rhizoctonia allied to the one found on potato have been 

 observed on sugar beet, bean, carrot, cabbage, garden pea, lettuce, 

 pumpkin, radish, tomato, watermelon, and upon many species of orna- 

 mental plants and weeds. 



Treatment. — The only available remedy is to treat the "seed" pota- 

 toes with formalin as for scab. It is also not advisable to grow potatoes 

 two years in succession on the same soil, for tubers left in the soil may 

 inoculate healthy seed tubers of the following season. Moreover, the use 

 of barnyard manure tends to the development of the fungus, while the 

 presence of lime retards to all appearances the growth of the fungus. 



