72 
BULLETIN 934, U. S. DEPARTMENT OE AGRICULTURE. 
weak point in the results is, of course, the insufficiency of the 6-pot 
and 9-pot groups as bases for probable-error determination. The 
indicated relative ability of these different fungi to cause root-rot 
is about the same as their relative ability to cause the damping-off of 
sprouting seed and young seedlings, as indicated by the results of the 
earlier experiments in which inoculations were made at the time of 
sowing. The fact that only the very strongest available strains were 
used and that the pots were rather heavily inoculated is to be kept 
in mind in considering these results. As in the seedlings examined 
in the nursery beds, when a root system was partly rotted it was 
onry the younger portions of the roots that were affected. The evi- 
dence obtained from this experiment needs to be amplified by experi- 
ments with other coniferous hosts, other strains of the fungi, and 
under other conditions. The experiment just described furnishes 
the only evidence available on the relation of the important fungi 
Pythium debaryanum and Corticium vagum to the root-rot of conifers 
and is therefore presented as a preliminary contribution. 
Table X. — Results of root inoculations of older pine seedlings with damping-off 
fungi. 
Number of— 
Seedlings which developed root-rot 
(percent). 
Host and inoculating fungus. 
Pots. 
Seed- 
lings. 
Tops still health j*. 
Killed. 
Root recovery. 
Average 
of in- 
dividual 
pots. 
Total. 
Started. 
Not 
started. 
1 
2 
3 
4 
5 
6 
7 
8 
Pinus pondercsa: 
Pythium debarvanum, strains 295, 550, 
and 810.a 
Corticium vagum, strains 147, 213, and 
747. a 
Fusarium moniliforme, strains 249, 251, 
and 260. & 
9 
9 
9 
3 
6 
3 
9 
9 
8 
3 
6 
3 
71 
56 
64 
18 
41 
18 
140 
146 
128 
39 
115 
51 
27 
16 
19 
17 
2 

3 
3 


- 

25 
34 
27 
39 
15 
17 
16 
16 
11 
5 
3 

53±4.5 
51 ±3. 5 
42±6.2 
50 
22±6.5 
23 
18±4.0 
21±2.4 
12±3. 7 
4 
4±2.0 

4 
4 




12 
13 
2 

6 
2 
56 
54 
45 
56 
17 
17 
Pinus resinosa: 
31 
33 
13 
5 
10 
2 
a For relative virulence of these strains on younger seedlings as compared with other strains of the same 
species, note their position in figures 11 and 14. 
b For performance of these strains in inoculations at time of sowing, see an earlier publication (68, 
table 2). 
The figures in column 7 give information as to the percentage of 
late damping-off resulting from the inoculations. A certain per- 
centage of the early type of damping-off appeared in some of the 
