DAMPIXG-OFF IN FOREST NURSERIES. 
47 
tioned is identical with Pythium debaryanum, causing leak of potato 
tubers and the damping-off of seedlings of two dicotyledonous 
families. 
Table V.— Results of inoculations on jack pine and red pine with Pythium 
debaryanum from various hosts. 
Host from which isolated. 
Inoculation results. 
On jack pine. 
On red pine. 
Emerged 
(per 5-pot 
unit). 
Damp- 
ing-off 
(per 
cent). 
Sur- 
vival 
(per 
5-p ot 
unit). 
Emerged 
(per 5-pot 
unit). 
Damp- 
ing-off 
(per 
cent). 
Sur- 
vival 
(per 
pot). 
No. 131 a 
Dicotyledons: 
45 
45 
36 
34 
30 
30 
101 
62 
23 
41 
15.6 
No. 810 6 
Do 
7.4 
45 1 35 
30 
82 
32 
11.6 
Sugar-beet seedlings 
No. 294 c 
50 8 
28 ' 32 
19 32 
46 
19 
13 
79 
62 
68 
36 
48 
58 
10.2 
No. 295 c 
Originally potato strain 131, hut 
twice inoculated on and reisolated 
from sugar-beet seedlings by Ed- 
son 
6.6 
No. ''96 d 
Sugar-beet seedlings 
5.8 
Average, sugar beet 
32 24 
26 
70 
47 
7.4 
Fenugreek seedlings d 
No. 529 
36 31 
60 49 
25 
31 
102 
108 
26 
22 
15.0 
No. 530 
Do 
Average, fenugreek 
Conifers: 
Western yellow-pine seedlings 
Sitka spruce seedlings 
16.8 
48 40 
28 
105 
24 
16.0 
No. 258 
58 9 
53 
109 
17 
18.0 
No. 550 
15 80 
42 29 
3 
30 
39 
45 
98 
70 
.2 
No. 555 
Engelmann spruce seedlings 
5.0 
Average, spruces 
29 55 
17 
42 
84 
2.6 
87 5 
83 
104 

20.9 
a Furnished by Mrs. C R. Tillotson: has been used 6 Furnished by Dr. L. A. Hawkins: cause of leak, 
successfully on sugar-beet seedlings by Dr. H. A. c Furnished by Dr. H. A. Edson. 
Fdson. d Diseased material furnished by Prof. W. T. Home. 
VARIATIONS IN VIRULENCE OF PYTHIUM STRAINS ON PINE. 
In Pythium debaryanum strains, as in the case of Corticium 
vagum, there appeared to be a considerable difference in the parasitic 
activity of different strains used in the same experiment. Figures 
14, 15, and 16 show graphically the results from inoculations with 
different strains of P. debaryanum in all the experiments in which 
it was possible to compare directly the activity of different strains. 
All the inoculations involved at the time of sowing the addition to 
the soil of cultures on nutrient media in recently autoclaved 3-inch 
pots. In experiment 31C the inoculum fragments were scattered over 
the whole pot, in 31D at only one point in each pot, and in the others 
were distributed over about one-fourth of the pot's area. As noted 
elsewhere, the variations observed in the results may have been due 
in part to differences in the ability of the different strains to main- 
