Aug. 21, 1916 Control of Powdery Dryrot of Potatoes 821 



plants out of the fifty which resulted from the planting of the inoculated 

 seed pieces showed vascular infection, but F. trichothecioides could not 

 be recovered. 



2. Twenty-five Idaho Rural tubers, first disinfected by dipping in 

 formaldehyde, were placed in moist chambers and allowed to develop 

 sprouts. On July 10, when the sprouts were from one-eighth to one-half 

 inch long, they were sprayed with a spore suspension of the fungus. 

 As a check, twenty-five Idaho Rural tubers were treated in the same 

 manner, but the sprouts were sprayed with sterile water. After a little 

 more than a month each sprout was carefully examined. No evidence 

 of infection was found either in the sprouts sprayed with the spore 

 suspension or in the checks. 



3. On July 11 further attempts to infect growing potato plants were 

 made as follows : 



a. Ten apparently healthy Idaho Rural plants were selected. The soil 

 was removed to expose as many of the tubers as possible without dis- 

 turbing their position. In all, twenty-five tubers were uncovered and 

 punctured with a needle inoculated with the spores of the fungus, after 

 which the soil was replaced. As a check, a similar number of plants of 

 the same variety were selected and twenty-five tubers punctured with 

 a sterile needle. This experiment was duplicated with Netted Gems. 



b. Ten apparently healthy Idaho Rural plants were selected. The 

 soil was removed to expose as many of the tubers as possible without 

 disturbing their position. Twenty-five tubers thus uncovered were 

 sprayed with a suspension of the spores of the fungus, after which the 

 soil was replaced. To prevent the rapid drying off of the sprayed tubers, 

 the soil when replaced was moistened. As a check, ten other apparently 

 healthy Idaho Rural plants were selected and twenty-five tubers 

 sprayed with sterile water. The soil was moistened upon being replaced. 

 This experiment was duplicated with Netted Gems. 



c. Ten apparently healthy Idaho Rural plants were selected. The soil 

 was removed to expose as many of the tubers with their stolons as possi- 

 ble without disturbing their position. The stolons of twenty-five tubers 

 thus uncovered were then punctured with a needle inoculated with the 

 spores of the fungus, after which the soil was replaced, care being exer- 

 cised to place moist soil next to the inoculations. As a check, ten other 

 plants of the same variety were selected and twenty-five tuber stolons 

 punctured with a sterile needle, after which the soil was replaced. This 

 experiment was duplicated with Netted Gems. 



d. Ten apparently healthy Idaho Rural plants were selected and the 

 stem of each plant punctured at the crown with a needle inoculated with 

 the spores of the fungus. As a check the stems of ten plants were punc- 

 tured with a sterile needle. This experiment was duplicated with 

 Netted Gems. 



