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- 



Fig. 8. 



-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 due 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 



