July i, 1921 
Pathogenicity of Corticium vagum on the Potato 
473 
tubers used for soil inoculation, the latter were treated five minutes in 
a mercuric-cholrid solution (1 to 1,000). They were then washed free 
from the mercuric chlorid and planted. Tubers from the same lot, treated 
two hours in the standard solution, were planted for control. Three 
half tubers were planted in each can. 
The plants were harvested June 15, 32 days after planting. 
Under these more natural conditions lesions again occurred at from 
9 0 to 27 0 C. No typical lesions were found in the soil held at 30°. The 
difference in intensity of injury at the various temperatures was even 
more distinctly marked than was found in the preceding experiments. 
At 24 0 and 27 0 the lesions were limited both in depth and area. Severe 
cortical injury resulted at 21 0 , and at 15 0 and 18 0 the entire cortex of 
many of the stems was totally destroyed (PI. 91, A, B). Below 15 0 this 
type of critical injury again definitely decreased. 
At the soil temperature of 21 0 G. and below, the growing points of 
many of the shoots were destroyed. As is shown in Table VII, this type 
of injury was slight at 21 0 but became very prominent at 18 0 and 15 0 . 
The highest percentage of stems showing the destruction of the primordia 
was found at the low temperature of 12 0 (PI. 90; 91; fig. 5). In this 
latter respect experiment 5 differed from all previous experiments. The 
relation, however, was so definite as to indicate that similar results 
might be obtained in many cases under natural conditions in the field. 
Table VII .—Effects of growing Irish Cobbler potatoes at various temperatures in soil 
inoculated with sclerotia of Corticium vagum 
EXPERIMENT 5 
Temperature (°C.). 
Number 
of sets 
planted. 
Number 
of stems 
grown in 
uninocu-, 
lated soil. 
Stems grown in inoculated soil. 
Total 
num¬ 
ber.® 
Num¬ 
ber 
slightly 
injured. 
Num¬ 
ber 
severely 
injured. 
Num¬ 
ber 
cut off. 
Num¬ 
ber 
unin¬ 
jured. 
Per¬ 
centage 
injured. 
Inten¬ 
sity of 
injury 
(points). 
9*4 .••• 
3 
II 
6l 
8 
17 
36 
40. 9 
109. 6 
12.2. 
3 
II 
65 
3 
14 
31 
17 
73-0 
190.9 
* 5 -° . 
3 
13 
62 
2 
16 
24 
20 
62. 4 
158. 6 
18.2. 
3 
8 
64 
4 
22 
23 
15 
76.4 
182. 5 
21.4. 
3 
9 
51 
11 
20 
3 
17 
66.6 
ii 7 - 5 
24-4 . 
3 
16 
49 
13 
15 
21 
57 - 1 
87.7 
27. 1. 
3 
II 
47 
5 
4 
40 
19. 1 
27.7 
30-3 . 
3 
38 
47 
2 
1 
44 
6 -3 
8-5 
° The number of stems was determined on the basis of all stems arising from the tuber directly or as sec¬ 
ondary shoots at or near the base of the primary stem (PI. 90, 91). Comparatively few stems succeeded in 
getting through the soil at the lower temperatures. 
TEMPERATURE RESPONSE OF THE POTATO PLANT IN UNINOCU¬ 
LATED SOIL 
The available data on the temperature requirements of the potato 
secured by Orton (9, 10) and Smith (15) from a study of the regional 
distribution of the plant and as expressed in terms of yield and general 
