Oct. 30, 1916 
235 
Tabl£ X .—Results of tests of potato seedlings for resistance to powdery-scab in 1915 
Seedlings. 
Control tubers (Green 
Mountain). 
Infection 
in terms 
of p. ct. 
seed X100 
p. ct. G. M. 
Collection No. 
Num¬ 
ber 
plant¬ 
ed. 
Num¬ 
ber in¬ 
fected. 
Per¬ 
centage 
of in¬ 
fection. 
Num¬ 
ber 
plant¬ 
ed. 
Num¬ 
ber in¬ 
fected. 
Per¬ 
centage 
of in¬ 
fection. 
1357 . 
79 
0 
O 
130 
18 
12. 1 
0 
1488. 
IOI 
0 
O 
44 
3 ° 
40. 5 
0 
99 2 ... 
98 
0 
0 
S 2 
2 
3 - 7 
0 
2892. 
12 5 
0 
O 
58 
5 
7*9 
0 
628. 
99 
0 
O 
36 
2 
5*2 
O 
2 3 r 5 . 
59 
O 
O 
98 
9 
8.4 
0 
2387. 
128 
O 
O 
42 
4 
8.7 
0 
2193 . 
90 
I 
I. I 
21 
6 
22. 2 
4-955 
I 5 22 . 
129 
3 
2 . 2 
26 
12 
3 1 * 5 
6. 984 
1124..*. 
160 
7 
4. 2 
34 
26 
43*3 
9. 700 
22402. 
151 
2 
*■3 
148 
23 
13*4 
9. 702 
2426. 
141 
3 
3 -o 
63 
13 
17. 1 
n. 696 
42 59 . 
119 
5 
4. 0 
43 
20 
3 1 * 7 
12. 618 
1429 . 
1055 . 
4755. 
i 74 
TI 3 
112 
7 
18 
19 
3-8 
* 3 - 7 
I 4 - 5 
28 
15 
72 
5 
14 
52 
i 5 - 1 
48. 2 
41.9 
15. 166 
28. 423 
24. 606 
3760. 
II 3 
3 
2. 5 
54 
4 
6.9 
36. 232 
2294. 
116 
1 
0. 8 
103 
.2 
1.9 
42. 105 
295 P. 
126 
37 
22. 7 
27 
19 
4 i .3 
54. 964 
1212. 
109 
1 
°* 9 
194 
3 
i* 5 
60. 000 
1034. 
144 
21 
12. 7 
m 
32 
18. 9 
67. 196 
2870. 
171 
20 
10. 4 
53 
8 
x 3 * 1 
79 - 389 
13660. 
105 
21 
16. 6 
42 
11 
20. 7 
80. I93 
49 2 7 . 
48 
14 
22. 5 
79 
24 
2 3 - 3 
96. 567 
4227 . 
213 
88 
29. 2 
80 
27 
25. 2 
ii5- 873 
968I . 
36 
5 
12. 2 
95 
9 
8.6 
141. 86l 
15284 . 
89 
72 
44 - 7 
25 
10 
28. 5 
156. 842 
14329 . 
107 
117 
52. 2 
108 
53 
32.9 
158. 663 
I 3 8 9 6 . 
IIO 
12 
9*7 
46 
3 
6. 1 
159. 0l6 
1449 . 
90 
114 
55-8 
109 
22 
16. 8 
33 2 - 143 
As will be seen by a comparison of Tables IX and X, the response to the 
disease was very similar in the standard varieties and the seedlings, except 
that the extremes of infection were greater in the latter, ranging from o 
to 55.8. Seven of the seedlings showed no infection, while the checks 
were infected in every case, the infection varying from 1.5 to 48.2; or in 
the rows of the nine cases referred to, from 3.7 to 40.5. Although the 
tubers of these nine varieties were free, the roots showed a goodly number 
of galls, which indicates either that the roots and tubers do not resist the 
disease to the same degree or that the tubers merely escaped the disease. 
As already explained, infection in 1915 took place only for about two 
weeks during the growing season—that is, between August 1 and 15— 
. and in case the tubers had not set by this time or had not reached a sus¬ 
ceptible stage, infection was avoided. It was also observed that, so far 
as the amount of infection is concerned, it made no difference whether 
the variety was early or late. That there is a close correlation between 
