THE RHIZOCTONIA DISEASE OF POTATOES. 209 



Rhizoctonia injury similar to that observed in the field, including 

 typical lesions on the stems below ground and on the basal ends 

 of the tubers. 



About a month after the plants came up large clusters of 

 small tubers could be seen just at the surfaces of the pots and 

 in one case aerial tubers were formed in the axils of the leaves 

 to a considerable height. It is of interest to note that this par- 

 ticular plant was inoculated without any injury to the stem or 

 tuber. . Check plants, the tubers of which were both punctured 

 and untouched, remained healthy. 



Inoculation of young, living potato stems. On account of 

 limited space in the greenhouse only 3 pots were used in this 

 experiment. When the young plants had reached the height of 

 from one to one and one-half inches above the soil in the pots 

 they were uncovered to their junction w^ith the seed-piece and 

 small particles of pure cultures of Rhizoctonia were applied to 

 the surface of the base of the shoot, after which the stem was 

 carefully recovered with soil. After two months the plants 

 were dug up and examined. One was apparently healthy while 

 the others showed the characteristic clusters of numerous, small 

 tubers close to the stem at or near the surface of the soil. One 

 of these showed the typical brown lesions on the stem below 

 the surface. 



Planting diseased tubers in sterilized soil. Whenever dis- 

 eased tubers or those showing Rhizoctonia sclerotia were planted 

 in sterilized pots of soil the fungus practically always appeared 

 on the growing plant or tubers in some form or other. In such 

 instances tubers bearing sclerotia were produced almost invari- 

 ably. Stem lesions, clusters of little potatoes near the surfaces 

 of the pots with or without browning of the surface of the stem 

 end of the young tubers or other injury usually occurred. Less 

 frequently, though by no means uncommonly, the Corticium or 

 fruiting stage of the fungus appeared on the plants in the green- 

 house. 



Attempts were made on a small scale to determine if par- 

 ticular forms of the disease could be transmitted to the crop 

 That there was a possibility of this was indicated by the results 

 obtained when the tubers from Nebraska and Wisconsin were 

 planted. In one instance a badly pitted tuber of the type 

 already described on page — was planted in one pot and in 



