302 Journal of Agricultural Research voi. vi, no. 9 



way to that produced by the other methods. A stem-end infection 

 resulting from the inoculation of the broken stolon end under labora- 

 tory conditions is shown in Plate XXXVI, figure 6. In Plate XXXVI, 

 figure 7, is shown an Idaho Rural tuber cut to expose the blackening of 

 the vascular tissue which resulted from the inoculation of the tuber 

 stolon. None of the checks were infected. The fungus was recovered 

 from the decayed tissues each time the attempt was made. 



EXPERIMENTS IN THE FIELD IN 1915 



On August II, in a plot in which disease-free Idaho Rural and Netted 

 Gem seed potatoes had been planted, apparently healthy potato plants 

 were selected. The soil was removed from around the plants in such 

 a manner as to expose the tubers without disturbing their position. 

 Three growing tubers under each plant were then inoculated with F. 

 radicicola, after which the soil was replaced, care being exercised to place 

 moist soil next to the tubers. The methods of inoculation were, respec- 

 tively, as follows: (i) By spraying the tubers with a spore suspension; 

 (2) by wounding each tuber stolon with a needle bearing spores at from i to 

 2 inches from its junction with the tuber; (3) by wounding the upper sur- 

 face of each tuber with a needle bearing spores, and (4) by puncturing each 

 tuber at the stem end with a spore-bearing needle. Ten plants each of 

 Idaho Rural and Netted Gem potatoes were used in each experiment. 

 As a check on each experiment, a similar number of apparently healthy 

 Idaho Rural and Netted Gem plants were selected and a similar number 

 of growing tubers treated in the same manner, except that in the case of 

 experiment i the tubers were sprayed with sterile water, and in numbers 

 2, 3, and 4 a sterile needle was used in place of a spore-bearing needle. 



A fifth experiment was set up in which 10 apparently healthy Idaho 

 Rural and 10 apparently healthy Netted Gem plants, growing in the 

 same plot with those employed in the four experiments just described, 

 were used. In this experiment, the stem of each plant was punctured 

 at the crown with a needle carrying spores of F. radicicola. Checks 

 were prepared in the same manner, except that the stem of each plant 

 was punctured with a sterile needle. 



The soil of the plot in which these experiments were made was very 

 dry and no irrigation water could be applied after the inoculations were 

 made. During the course of the experiments (August 1 1 to September 6) 

 the minimum soil temperature recorded was 66° and the maximum 84° F. 

 The soil temperature was taken at a depth at which the potato tubers 

 were found lying by burying the bulb of a soil thermograph under a 

 potato plant. A little less than a month after making the inoculations 

 an examination of all the plants was made. Table II gives a summary 

 of the experiments and the results obtained from inoculating growing 

 potato plants and tubers with F. radicicola. 



