290 
Journal of Agricultural Research 
Vol. XXIII, No. 4 
10. Tubers showing closed-pustule stage of powdery scab collected by 
the writer at Vancouver, B. C., in the fall of 1920. They were thoroughly 
washed after digging and stored for winter in a laboratory refrigerator. 
Isolations were made in March, 1921. (One of these tubers is shown in 
PI. 3, A. ) 
11. Irish Cobbler tubers from Maine, crop of 1920, showing immature 
sori of powdery scab. Isolations were made in the winter of 1920-21. 
(One of these tubers is shown in PI. 3, B.) 
12. The same material as in the preceding sample, but isolations were 
made from mature sori. 
Isolations were made from each of these samples and the results are 
presented in Table I. 
Table I .—Results of isolations from the skinspot pustules and the sori of powdery scab 
Number of the sample. 
Number 
of spots 
from 
which 
isola¬ 
tions 
were 
made. 
Number 
of spots 
which 
yielded 
no 
growth. 
Number 
of spots 
which 
yielded 
OosPora 
pustu¬ 
lans. 
Number 
of spots 
which 
yielded 
miscel¬ 
laneous 
fungi 
and 
bacteria. 
Remarks. 
1. 
27 
3 
I 
23 
6 spots yielded Fusarium spp. 
2. 
60 
3 
49 
8 
3 out of 5 tubers (42 spots) yielded 
1 exclusively Oospora pustulans . 
3 . 
15 
5 
6 
i 4 
i 
No isolations were made from the 
: open pustules shown on the 
! photograph. 
4 . 
24 
2 
10 
12 
Samples showed no mature sori of 
I powdery scab. 
5 . 
.6 
0 
S 
1 
Sample similar to the preceding 
one in appearance. 
6. 
6 
0 
3 
3 
Do. 
6 
0 
6 
0 
Do. 
8. 
34 
2 
6 
26 
1 sample (12 spots) yielded no 
culture of Oospora pustulans. 
9 .. 
60 
0 
0 
60 
The predominant culture in this 
case was Co lleto trichum atra- 
mentarium (Berk, and Br.) 
Taub. 
10. 
12 
10 
0 
2 
1 Phoma sp. and 1 Verticillium sp. 
11. 
12 
7 
0 
5 
Only 1 sorus yielded Phoma sp. 
12. 
3 i 
3 
0 
28 
16 sori yielded Phoma sp. and the 
remainder miscellaneous fungi. 
Total^of 1 to 9 
238 
15 
86 
137 
Oospora pustulans 36.1 per cent. 
(undoubted 
skinspot). 
Total of 2/3, 5, 6, 
and 7 (English 
material). 
93 
8 
69 
16 
Oospora pustulans 74.2 per cent. 
Total of 1, 4, 8, 
and 9 (Ameri 
can and Danish 
material). 
145 
7 
17 
121 
Oospora pustulans 11.72 per cent. 
These results of isolations made from various lots of material in 1920 
and 1921 show that Oospora pustulans is by no means the only invader of 
the skinspot pustules, since it comprised 36.1 per cent, or slightly above 
one-third, of the total isolations from the undoubted skinspot material. 
