DAMPING-OFF IN FOREST NURSERIES. 41 
formed, a few tests indicate that the fungus is very short lived, 
sometimes dying in a month. On media on which spores are pro- 
duced, transfers any time before the sixth month, and often as late 
as the tenth month, start immediate growth on fresh media. This 
is true even for strains which produce few or no oospores. The im- 
mediate commencement of growth from cultures 3 or 4 months old 
is taken as an indication that the new growth results from the 
asexual spores, as oospores are commonly believed to require a rest- 
ing period of five or more months before they are able to ger- 
minate (5, 38). 
INOCULATION ON STERILIZED SOIL. 
PytMum debaryanum has been used in inoculation in pots of 
recently autoclaved soil in 16 different series of tests. In 10 of these, 
fragments of agar cultures were scattered over about one- fourth 
of the area at the side of each pot when seed was sown ; in 2 of these 
10 and also in 2 other tests some pots were inoculated over their 
entire surface. In every one of these 12 heavily inoculated series 
positive results were indicated by smaller emergence and where any 
considerable number of sprouting seeds escaped the fungus by heavier 
damping-off loss in the inoculated pots than in the controls. In 
some cases the fungus killed all or practically all of the seed or 
seedlings in the inoculated pots before they emerged from the soil. 
In a total of 7 series, part or all of the pots received lighter in- 
oculations, consisting of one or two small fragments of an agar 
culture placed just below the surface of the soil at the edge of each 
pot. In 5 of these success was indicated. In the sixth and seventh 
also of these lightly inoculated sets, there was more damping-off in 
the inoculated pots than in the controls, but the difference was neg- 
ligible. The damping-off caused by light inoculations was in general 
distinctly less than that resulting from broadcast inoculations. To 
sum up the evidence: Sixteen separate experiments were conducted 
with PytMum debaryanum on pine seedlings in autoclaved soil, and 
in every one fewer seedlings survived in the inoculated pots than in 
the checks ; the difference in most of the experiments was large. 
Of the successful inoculation experiments — that is, those in which 
the difference between the inoculated pots and the checks seemed 
significant — 9 series included jack pine (Pinus banksiana) , 7 series 
western yellow pine (P. ponderosa, Colorado and New Mexico seed), 
and 3 series red pine (P. resinosa) . In addition to the pines, Doug- 
las fir (Pseudotsuga taxifolia, Colorado seed) was grown in two large 
plats in one of the earlier series, one being inoculated over its entire 
surface with PytMum debaryanum. Because of the poor quality 
of the seed in the test on Douglas fir, too few seedlings were obtained 
to furnish a decisive test, but the difference in the emergence in the 
inoculated plat and the control affords preliminary evidence that 
