233 
oct. 30,1916 Spongospora subterranea and Phoma tuberosa 
treatments with a hot solution of these for a short time being more effi¬ 
cient than with a cold solution for a longer time. 
The relative efficiency of the various disinfectants, according to the 
data obtained for the two years, is shown in Table VIII. 
Table VIII .—Average results in controlling powdery-scab obtained from different dis¬ 
infectants used in the tests of 1914 and 1915 
Treatment. 
Average 
percent¬ 
age of 
hills in¬ 
fected. 
Average 
percent¬ 
age of 
tubers 
infected. 
Formaldehyde (2:30), 46°-5o° C., 5 minutes.. 
4 - 75 
7 - 58 
8- 00 
1.20 
Check, clean seed. 7 . 
Mercuric chlorid (4:15), 44°-45° C., 5 minutes... 
*•73 
2.83 
1-50 
Mercuric chlorid (2:15), 1% hours... 
8. 50 
8. 70 
10.90 
10.95 
13.80 
18.00 
Mercuric chlorid (1:15), 1 y* hours. 
Copper sulphate (5 per cent), hours. 
Mercuric chlorid (4:15), so°-s4° C., 5 minutes. 
Formaldehyde (1:30), 1% hours.. .7 . 
2.85 
Mercuric chlorid+~ethyl alcohol (2:15), hours; i,oooc. c.of alcohol in 3K gallons of 
water. 
Formaldehyde (2:30), hours. 
20* 20 
5-39 
10.60 
Cut and rolled in sulphur. 
Atomic sulphur (5 per cent), 1^ hours. 
Checks, powdery-scab seed. 
64.60 
25* 12 
varietae response 
Tor a number of years the Office of Cotton and Truck Disease Inves¬ 
tigations has carried on experiments on varietal susceptibility of potatoes 
to the lateblight fungus (Phytophfhora infestans) and in this connection 
has made an extensive collection of European and American varieties 
reputed to be more or less resistant to lateblight. The study of powdery- 
scab also suggested the selection of resistant varieties as a possible means 
of control, and accordingly it was decided to use the above collection in 
the experimental plots infected with powdery-scab. In addition to this 
collection of standard varieties, a collection of seedlings also was used in 
the experiment. 1 
A piece of ground with a uniform soil type and infected with Spongos¬ 
pora subterranea was selected and 25 hills each of the different varieties 
of seedlings were planted, the Green Mountain variety being planted in 
alternate hills as controls. Table VIII gives the varieties tested and 
the results of the tests, including the percentage ratio of infection in the 
varieties tested and the checks. 
1 These seedlings, which have not yet been distributed to farmers and seedsmen, were obtained through 
the courtesy of Prof. William Stuart, of Horticultural and Pomological Investigations, Bureau of Plant 
Industry, by whom they were developed. 
