DAMPING-OFF IN FOREST NURSERIES. 71 
which Corticium vagum appeared to be the active parasite, but 
beyond this indication of the causal relation of G. vagum it was not 
known which of the damping-off fungi were able to attack the roots 
of seedlings too old to be killed by damping-off. To throw light on 
this point, seedlings of Pinus ponderosa and P. resinosa grown in 
autoclaved soil in the greenhouse and approximately \\ months old 
were inoculated with different fungi. There had been a certain 
degree of early damping-off in these pots, but it had apparently 
ceased before the inoculations were made. The inoculum used con- 
sisted of cultures on rice introduced through the drainage holes at 
the bottoms of the pots. The strains of Pythium debaryanum and 
Corticium vagum used were the ones which had given maximum 
results in earlier inoculation experiments at the time of sowing. The 
strain of Fusarium ventricosum was the only one available, and the 
Fusarium moniliforme strains were all of approximately equal viru- 
lence, the three used having given as much evidence of parasitism 
as any of the strains of this species in the earlier damping-off experi- 
ments. Three pots of each pine were inoculated with each strain. 
Two 3-pot units of each pine were set aside as controls and inoculated 
with sterile rice. In addition, three pots of each pine were kept in 
the same bench without the addition of any inoculum, for comparison 
with the controls with rice. The results of this experiment, taken 
a month after the inoculations were made, with the seedlings averag- 
ing 2J months old, appear in Table X. The roots of the living seed- 
lings were washed out carefully with water to permit examination. 
The results in so far as they indicate root-rot of the oldest seedlings 
are best shown by the figures in columns 4 and 5. These seedlings 
were so far advanced that the fungi had not been able to kill them, 
and nearly all would probably have recovered if they had not been 
dug up. It will be noted from .column 4 of Table X that a consider- 
able portion of the Pinus ponderosa seedlings with root-rot had al- 
ready made their recovery apparent by pushing out adventitious 
roots above the decayed portion at the time they were examined. 
For Fusarium ventricosum there was only the merest indication of 
ability to attack pine roots at this stage. For F. moniliforme the 
evidence is somewhat better, more pots being included and the dif- 
ference in healthy-topped seedlings with injured roots between the 
inoculated pots and the controls being approximately twice its indi- 
cated probable error for each species. The percentage of root-injured 
seedlings in the Pythium debaryanum pots exceeded that in the con- 
trols in each species by between three and four times the probable 
error of the difference, while the difference in percentage between 
the Corticium- vagum pots and the controls is approximately four 
times its probable error in the case of Pinus ponderosa and five and 
one-half times its probable error in the Pinus resinosa pots. The 
