DAMPING-OFF IN FOREST NURSERIES. 
15 
table tend to confirm field observations that, as compared with other 
species, Pinus resinosa is more susceptible to the later forms of 
damping-off than to germination loss. 
Further indication that the killing of germinating seed before 
emergence may be important enough to help explain cases of poor 
germination is obtained by an entirely different method, as follows: 
At the Wind River Experiment Station of the United States Forest 
Service counts of the seedlings emerging and of those which later 
died were made on a number of untreated plats by forest officers, 
who kindly permitted the writer to use the data obtained. The 
counts were made separately on 10 plats each of noble fir {Abies 
nobilis) and silver fir {Abies concolor). The plats of each species 
had been sown with equal quantities of seed. It appeared on in- 
spection of the figures that the plats which showed the poorest emer- 
FlG. 
-The area shown in figure 7 after the bed had been weeded and damping-off had 
practically ceased. (Photographed by S. C. Bruner.) 
gence were also the ones which suffered the most subsequent loss. The 
coefficient of correlation between the number of seedlings emerging 
and the percentage of subsequent loss in the same plats was found 
to be —0.49 + 0.16 for the noble fir, and — 0.50±0.16 for the silver 
fir, an average of — 0.49±0.11 for the two species, confirming the 
conclusion drawn from inspection of the figures. In other words, 
poor emergence and heavy subsequent loss were in general associated. 
The simplest explanation of this association appears to be to suppose 
that both poor emergence and subsequent loss were largely due to 
the same cause, namely, the damping-off parasites. Another possible 
explanation of the correlation would be to neglect parasites as im- 
portant causes of the poor emergence in certain plats and to suppose 
that the higher subsequent loss in such plats was clue to heat injury, 
the less dense stands affording less shade to the bases of the seedlings 
composing it. As damping-off is in general so much more important 
than heat injury as a cause of death after emergence and the dif- 
ference in the degrees of shade between the plats with the denser 
