232 
Journal of Agricultural Research 
Vol.'VII, No. 5 
Table VII .—Results of experiments in controlling powdery-scab by seed treatment in IQ15 
Plot 
No. 
Treatment. 
Hills. 
Tubers. 
Total 
num¬ 
ber. 
Num¬ 
ber 
sound. 
Num¬ 
ber 
in¬ 
fected. 
Per¬ 
cent¬ 
age of 
infec¬ 
tion. 
Total 
num¬ 
ber. 
Num¬ 
ber 
sound. 
Num¬ 
ber 
in¬ 
fected. 
Per¬ 
cent¬ 
age of 
infec¬ 
tion. 
1 
Check, clean seed. 
56 
47 
9 
16.0 
282 
263 
19 
6. 7 
2 
Check, infected cut seed. 
64 
22 
42 
65.6 
443 
349 
93 
21.0 
3 
Formaldehyde (2:30), hours. 
66 
49 
17 
25- 7 
392 
364 
28 
7 *i 
4 
Mercuric chlorid+ethyl alcohol (2:15), 
hours; 1,000 c. c. of alcohol in 
gallons of water. 
72 
59 
13 
18.0 
363 
346 
17 
4.6 
Check, infected seed.. 
28.6 
6 
Atomic sulphur (5 per cent), iK hours. 
84 
39 
45 
53-5 
469 
388 
81 
17.2 
7 
Mercuric chlorid (4:15), so 6 C., 5 min- 
utes. 
65 
55 
10 
15-3 
332 
321 
11 
3-3 
8 
Check, infected cut seed. 
56 
9 
47 
83-9 
428 
304 
124 
28. 9 
9 
Check, clean seed. 
73 
61 
12 
16.4 
449 
43 i 
18 
4.0 
10 
Wet and rolled in sulphur. 
.57 
37 
20 
35 *o 
366 
33 2 
34 
9. 2 
11 
Formaldehyde (1:30), 1%, hours. 
93 
82 
11 
11. 8 
486 
474 
12 
2.4 
12 
Check, infected cut seed. 
7 i 
49 
22 
31-0 
374 
329 
45 
.12. 0 
13 
Formaldehyde^:^), 50° C., 5 min- 
utes. 
78 
72 
6 
7 - 7 
366 
359 
7 
1.9 
*4 
Mercuric chlorid (1:15), hours. 
69 
63 
6 
8.7 
386 
380 
6 
1* 5 
15 
Copper sulphate (5 per cent), 1 % hours 
49 
40 
9 
18.3 
327 
300 
27 
8. 2 
16 
Check, infected whole seed. 
88 
19 
69 
78.4 
780 
506 
274 
35 -1 
17 
Mercuric chlorid (2:15), 1 X A hours. 
100 
85 
15 
15.0 
39 i 
37 ° 
21 
5-3 
18 
Check, clean seed. 
138 
124 
14 
10.1 
643 
629 
2.1 
As will be seen in Table VII, 10.1 per cent of the progeny of the hills in 
plot 18 became infected, and as in all probability the seed was free from 
infection and the disease is not indigenous to virgin land, the question 
arises as to the source of the infection. In the case of the healthy control 
plots the probable source of infection was the adjoining infected controls, 
soil water, animal life, and cultural methods being the probable agencies 
by which the disease was spread. Considering the results from each 
plot individually and in relation to those in adjoining plots, it would 
seem reasonable to believe that in the case of the healthy checks adjoin¬ 
ing those planted with untreated seed, the latter served as centers of 
infection. In 8 out of 10 cases more infection occurred in the rows next 
to the untreated checks than in the rows farther away. 
Although the infection of the healthy checks diminishes the value of 
the seed-treatment experiment, it serves to emphasize the infectiousness 
of the disease and to some extent indicates the rate and means of spread 
where conditions are favorable for its growth. In the light of the devel¬ 
opments on the healthy plots in 1915 it is easily understood that the 
two cases of infection in the clean control plots in 1914 were doubtless 
carried from the infected to the healthy controls. 
As in the case of the experiments in 1914, those in 1915 show, in addi¬ 
tion to the spread of the organism in the soil, that seed disinfection has 
a beneficial effect in diminishing the amount of infection and that treat¬ 
ment with mercuric chlorid and formaldehyde are the most effective, 
