72 



BULLETIN" 934, U. S. DEPARTMENT OF AGRICULTURE. 



weak point in the results is, of course, the insufficiency of the 6-pot 

 and 9-pot groups as bases for probable-error determination. The 

 indicated relative ability of these different fungi to cause root-rot 

 is about the same as their relative ability to cause the damping-off of 

 sprouting seed and young seedlings, as indicated by the results of the 

 earlier experiments in which inoculations were made at the time of 

 sowing. The fact that only the very strongest available strains were 

 used and that the pots were rather heavily inoculated is to be kept 

 in mind in considering these results. As in the seedlings examined 

 in the nursery beds, when a root system was partly rotted it was 

 only the younger portions of the roots that were affected. The evi- 

 dence obtained from this experiment needs to be amplified by experi- 

 ments with other coniferous hosts, other strains of the fungi, and 

 under other conditions. The experiment just described furnishes 

 the only evidence available on the relation of the important fungi 

 Pythium debaryanum and Corticium vagumio the root-rot of conifers 

 and is therefore presented as a preliminary contribution. 



TABLE X. Results of root inoculations of older pine seedlings with damping-off 



fungi. 



a Forrelative virulence of these strains on younger seedlings as compared with other strains of the same 

 species, note their position in figures 11 and 14. 



b For performance of these strains in inoculations at time of sowing, see an earlier publication (68, 

 table 2). 



The figures in column 7 give information as to the percentage of 

 late damping-off resulting from the inoculations. A certain per- 

 centage of the early type of damping-off appeared in some of the 



