July i, 1921 
Pathogenicity of Corticium vagum on the Potato 
469 
Unsterilized soil was again used in one series of 16 cans, 2 cans at each 
temperature. A second series was provided with steam-sterilized soil. 
As in experiment 2 both types of soil were represented in the controls. 
As the Irish Cobbler potatoes used for seed were free from sclerotia, 
two small Early Ohio tubers well covered with sclerotia and without 
treatment were placed in the bottom of each can and covered with approx¬ 
imately 1 inch of soil. Three halves of Irish Cobbler tubers, previously 
treated, were then placed on this surface and covered to the regular depth 
of 5 inches. All the controls were arranged in exactly the same way 
except that the potatoes used were treated before planting. Observa¬ 
tions made 42 days after planting are recorded in Table III. 
The plants, on the whole, exhibited a more severe type of injury in the 
sclerotia-inoculated soil than was obtained with the pure culture of the 
fungus in experiments 1 and 2. The range of temperature through which 
lesions occurred was approximately the same as that found in experi¬ 
ment 2. The greatest degree of severity was found at 15 0 and 18 0 C. 
Table III .—Effect of growing Irish Cobbler potatoes in soil inoculated with sclerotia of 
Corticium vagum and held at various temperatures 
EXPERIMENT 3 
Temperature 
(° C.). 
Number 
of sets 
planted. 
Number 
of stems 
grown 
in un¬ 
inocu¬ 
lated 
soil. 
Stems grown in inoculated soil. 
Total 
number. 
Number 
slightly 
injured. 
Number 
severely 
injured. 
Number 
cut off. 
Number 
unin¬ 
jured. 
Per¬ 
centage 
injured. 
Inten¬ 
sity of 
injury 
(points). 
9 . 
3 
8 
34 
6 
5 
23 
32.3 
79-3 
11.6. 
3 
5 
4 i 
8 
5 
28 
31-7 
75 - 6 
* 4-7 . 
3 
8 
49 
I 
II 
14 
25 
53*0 
132.6 
18. 
3 
13 
54 
4 
14 
15 
21 
61. 0 
142. 2 
21. 
3 
14 
38 
7 
7 
3 
21 
44.6 
78. 2 
23-7 . 
3 
8 
34 
11 
7 
2 
14 
5 °. 0 
82. 2 
% 
8 
38 
4 
34 
10. 5 
21. 0 
* / . 
O 
■20 .... 
O 
3 i 
. 
O 
V 
O 
i 
The type of lesions produced on the stems in this experiment was iden¬ 
tical with those obtained in the previous experiments from a pure culture 
of the organism. In no case were lesions found without the presence of 
the typical hyphae characteristic of the sterile stage Corticium vagum. 
The control plants were found to be free from both lesions and fungus. 
The Early Ohio tubers used to introduce the inoculum had not passed 
through their dormant period. Sprouts from these made a growth of 
from % to 3 inches during the five weeks. When harvested, a number of 
these slow-growing stems showed distinct lesions only at the growing 
point. Further examination indicated that such lesions were initiated 
in the sinus or reentrant angle of the hook-shaped bud, at which point 
considerable quantities of mycelium were collected (PI. 89, A). The 
