DAMPING-OFF IN FOREST NURSERIES. 85 
With Pythium : 
Without saprophytes, 27.5 per cent dainped-off ; coefficient of variability, 
67±7.8 per cent. 
With saprophytes, 16.9 per cent damped-off ; coefficient of variability, 
39 ±2.4- per cent. 
This tendency has been frequently observed in experiments in 
which inoculum is applied to the soil at the time of sowing. Even 
in experiments in which a relatively small proportion of the seed- 
lings are killed, some of the pots are nearly or entirely cleaned out. 
It is taken as an indication that failure of inoculation to give results 
is often due to the inability of the fungus to maintain itself in a 
vigorous condition till the germinating seed is far enough along to 
allow easy infection. It may also be in part due to lack of uni- 
formity of the soil in different pots affecting virulence of parasites 
or resistance of hosts. 
In addition to this experiment on autoclaved soil, a somewhat 
similar experiment was conducted in a nursery in the Kansas sand 
hills on soil which had been treated with sulphuric acid, followed 
by lime raked into the soil. Saprophytes, for the most part the 
same strains that had been used in the experiment in the greenhouse, 
were added to 24 plats, each of one-half square foot, of Pinus bank- 
siana and 24 of P. pondcrosa, with 16 interspersed plats of each 
species serving as controls. The saprophytes were growing on rice, 
part of which was added to the plat with the inoculum in addition 
to the fungous mycelium. Damping-off was rather heavy in this soil 
from accidental infection or from parasites which survived the 
initial acid treatment, no parasites having been artificially intro- 
duced. The loss was probably due to Corticium vagum or Fusarium 
spp. rather than to Pythium debaryanum in this case. In both pines, 
emergence was slightly better in the control plats than in those to 
which the saprophytes had been added, the difference for Pinus banh- 
siana being less than half its probable error and for P. ponderosa 
slightly more than its probable error. Damping-off for the first few 
days after emergence was somewhat less in the controls in one species, 
but higher in the saprophyte-inoculated pots in the other. The 
saprophytes therefore gave no evidence of effective competition with 
the parasites on this acid-lime treated sand. 
While the competition for water which seems to be the form of 
competition most common among green vascular plants is not likely 
to be of significance between fungi such as those which cause damping- 
off, a very little observation of the growth of mixed cultures of the 
parasites and other organisms in Petri dishes is sufficient to make 
one realize that the latter may very considerably decrease the activity 
of certain of the parasites. In nutrient agar most of the fungi and 
bacteria introduced from the soil in attempting parasite isolations, 
