DAMPING-OFF IN FOREST NURSERIES. 71 



which Corticium vayum appeared to be the active parasite, but 

 beyond this indication of the causal relation of C. vagum it was liot 

 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 1J 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 PytJwwn 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 2^ 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 



