74 Journal of Agricultural Research voi. xiii.no. 2 



station at Jerome, Idaho, on irrigated land never before planted with 

 potatoes, but previously cropped with grain and alfalfa. These two 

 plots consisted of a few hundred hills each. The remaining plots were 

 planted in cooperation with farmers in southern Idaho, as follows: 

 Plots I and 2 on irrigated, previously cultivated land near Blackfoot, 

 Idaho; plot 3 on irrigated, previously cultivated land at Aberdeen, 

 Idaho, on the grounds of the Aberdeen Experiment Station; plot 4 on 

 irrigated alfalfa land, near Twin Falls, Idaho; plot 5 on irrigated alfalfa 

 land near Murtaugh, Idaho; plot 6 on irrigated clover land near Jerome, 

 Idaho; plot 9 on irrigated, virgin desert land, near Jerome, Idaho; plot 

 10 on dry -farming land previously cultivated but never irrigated, on the 

 grounds of the Aberdeen Experiment Station, Aberdeen, Idaho; and 

 plots II to 14 on virgin desert land not subject to irrigation, near Aber- 

 deen, Idaho. Plots I, 4, 5, 6, and 9 consisted of about i acre each; 

 plot 2 of about 0.5 acre; plots 3 and 10 of about 0.2 acre each; and 

 plots II to 14 of about 0.1 acre each. 



The varieties planted in the test plots were as follows: Idaho Rural, 

 Netted Gem, Carmen 3, Early Six Weeks, Irish Cobbler, People's, and 

 Pearl. The seed tubers were selected in such a manner that no seed 

 piece showing any internal or external evidence of disease was used. 

 Every tuber was carefully examined in cutting, and the slightest dis- 

 coloration was sufficient cause for discarding it. No dryrot-infected 

 tubers were used, and all slight bruises were cut out to insure the free- 

 dom of the seed piece from any germs of disease which might be lurking 

 in the bruised tissues. No tubers showing any evidence of common 

 scab or the sclerotia of Rhizoctonia solani were employed. In addition 

 to these precautionary measures, the seed tubers for plots 3, 7, 8, 10, 11, 

 12, 13, and 14, and the Netted Gem of plot 6, were selected from 191 5 

 plantings from hills which showed no evidence of disease. The seed for 

 the other plantings was selected from commercial stock. 



All seed tubers used for the plots were disinfected after cutting for at 

 least two hours in solutions of mercuric chlorid, strength 1:1,000, or 

 stronger. Wherever planting machinery was employed, all parts of the 

 machine were thoroughly scrubbed in a solution of mercuric chlorid 

 (i :50o). The seed for one plot at the Jerome Station (plot 7) was given 

 special treatment as follows : The seed tubers were selected from disease- 

 free hills in 1 91 5. At planting time these tubers were taken to the lab- 

 oratory and thoroughly scrubbed with a solution of mercuric chlorid 

 (i :i,ooo) after which they were cut into seed pieces, only pieces showing 

 clean white tissue being used. The seed pieces were then disinfected for 

 two hours in a solution of mercuric chlorid (1:500) and carried to the 

 field in the disinfecting solution, from which they were picked out by 

 hand. They were then dropped into the row prepared to receive them 

 and were immediately covered. It was believed that in this manner all 



