240 
Journal of Agricultural Research 
Vol. VII, No. s 
Table XI shows the comparative value of the treatments on plots 
similar in other respects: 
Tabi<£ XI .—Comparative effect of different soil treatments on powdery-scab and on the 
yield of potatoes 
Plat 
No. 
Treatment. 
Percent¬ 
age of 
powdery- 
scab. 
Bushels 
per acre. 
I 
Sodium nitrate. 
16.95 
24.7 
i 3 8 -3 
205. 8 
2 
Control with commercial fertilizer. 
3 
Old horse manure. 
l8. 2 
165. 9 
4 
Control with no fertilizer. 
23. 8 
123. 2 
5 
New horse manure. 
II. 05 
108. 8 
6 
Acid phosphate. 
20. ' I 
143. 2 
204. 8 
’ 114.9 
7 
9 
Ammonium sulphate and acid phosphate. 
Potassium chlorid. 
17. I 
11.5 
10 
Ammonium sulphate. 
12. 7 
I 37 - 5 
11 
Sulphur drill. 
10.1 
140.9 
13a 0 
12 
Sulphur broadcast. 
7-35 
13 
Calcium carbonate. 
J 7 ‘ 3 
104. 4 
As shown by Table XI, ammonium sulphate and acid phosphate gave 
nearly the same yield as the checks fertilized, and in addition dimin¬ 
ished the amount of infection by Spongospora subterranea 7.6 per cent. 
In the plots treated with potassium chlorid there was less infection than 
in any of the plats receiving'other fertilizer ingredients, or only 11.5 
per cent. This is attributed to the slow growth of the plants in the 
early part of the season and their continued growth until killed by frost. 
The potassium chlorid apparently prolonged the growing season, and it 
may be that the crop in a measure escaped the infection period, which, 
as already shown, was in August. 
While these experiments extended through only one season and conse¬ 
quently only tentative conclusions can be drawn, they demonstrated 
that sulphur at the rate of 900 pounds per acre applied broadcast reduced 
the amount of infection by Spongospora subterranea , and all of the fer¬ 
tilizer ingredients tested reduced the amount of infection from 5 to 12 
per cent when applied alone. 
DRY-ROT ASSOCIATED WITH SPONGOSPORA SUBTERRANEA 
Although Spongospora subterranea has been known in Kurope since 
early in the forties of the last century, no mention has been made of a 
dry rot commonly associated with and following the disease. This rot 
differs markedly from the many rots which have already been described 
and which are common to the potato tuber, and a discussion of it neces¬ 
sarily involves the description of several types of rot not heretofore 
distinguished and a study of their causes. This is the rot to which the 
senior writer in his brief mention (7) of the shriveling and shrinking 
