536 Journal of Agricultural Research voi. xv.no.io 



tain strains may be slightly specialized to particular hosts, but such 

 variations are hardly of taxonomic value. 



INOCtTLATIONS ON UNSTERIUZED SOIL 



In an experiment in which a very sandy western Kansas soil was 

 treated with 0.5 fluid ounce of sulphuric acid per square foot, followed two 

 days later by 0.9 ounce of air-slaked lime per square foot, a number of 

 strains of Corticium vagum were tested, inoculum on cooked rice being 

 distributed through the drills. Most of the strains either prevented or 

 greatly decreased the germination of both jack and western yellow pines, 

 and the more virulent strains caused the damping-off of practically all 

 of the seedlings which were able to get through the soil surface. In the 

 plots inoculated with strains of C. vagtmi which had indicated any decided 

 degree of virulence in earlier tests the survival ranged from o to 47 seed- 

 lings (44 linear inches of drill, half of each pine, for each fungus strain), 

 while the 16 controls in the same experiments ranged from 59 to 254 

 seedlings for equal lengths of drill, more than half of the controls having 

 survivals better than 1 50 seedlings. The most virulent strain of Pythium 

 debaryanum heavily inoculated in the same way and at the same time 

 resulted in little more parasitic loss than occurred in control plots inocu- 

 lated with saprophytic molds or with nothing at all. The inoculations 

 with Corticium vagum caused as much damping-off as would normally be 

 secured by inoculating autoclaved soil under the most favorable condi- 

 tions for parasitism. The advantage of the C. vagum over the Pythium 

 debaryanum in this case was probably at least in part due to the lack of 

 humus. P. debaryanum apparently prefers soils with a reasonable 

 amount of humus, while C. vagum has been frequently found in damped- 

 o£f seedlings on this same soil and on another very sandy, humus-poor soil. 



In an experiment in which a heavier soil heated in a moist condition to 

 a temperature of 80° to 90° C. for a period of not less than 10 minutes was 

 inoculated with the parasites. Corticium vagum again caused marked 

 decreases in germination, while Pythium debaryanum, had little effect on the 

 number of seedlings which appeared. Outside infections, probably with 

 Fusarium spp., which it was impossible to exclude in this outdoor work, 

 destroyed the seedlings so rapidly after germination that it was impos- 

 sible to obtain evidence on the effect of the inoculum on the seedlings after 

 they came up. The definite superiority of C. vagum over the P. debary- 

 anum in causing germination loss in this case can not be attributed to lack 

 of humus. 



In soil entirely untreated, Corticium vagum was used in two very small- 

 scale inoculation experiments in the Washington greenhouse, inoculum 

 being placed at one and two points in each pot, respectively. In both 

 cases C. vagum definitely decreased the survival. In the first experi- 

 ment Pythium debaryantim had no effect, and in the second affected only 

 germination, while C. vagum both decreased germination and increased 



