DAALIMXC-OFF IN FOKKST NURSERIES. 



47 



tioned is identical with Pythium debaryanum, causing leak of potato 

 tubers and the damping-off of seedlings of two dicotyledonous 

 families. 



TABLK V. Results of iunc-Hliiti-oH* on jack i>inc <in<I red pine with P nthium 

 <l( Ixirira n-niH from nirious hosts. 



n Furnished by Mrs. C. R. Tillotson; has been used t> Furnished by Dr. L. A. Hawkins: cause of leak, 

 successfully on sugar-beet seedlings by Dr. H. A. c Furnished by Dr. H. A. Edson. 

 Edson. d Diseased material furnished by Prof. W. T. Home. 



VARIATIONS IN VIRULENCE OF PYTHIUM STRAINS ON PINE. 



In Pythium debaryanum strains, as in the case of Corticium 

 vagum, there appeared to be a considerable difference in the parasitic 

 activity of different strains used in the same experiment. Figures 

 14, 15, and 16 show graphically the results from inoculations with 

 different strains of P. debaryanum in all the experiments in which 

 it was possible to compare directly the activity of different strains. 

 All the inoculations involved at the time of sowing the addition to 

 the soil of cultures on nutrient media in recently autoclaved 3-inch 

 pots. In experiment 31C the inoculum fragments were scattered over 

 the whole pot, in 31D at only one point in each pot, and in the others 

 were distributed over about one-fourth of the pot's area. As noted 

 elsewhere, the variations observed in the results may have been due 

 in part to differences in the ability of the different strains to main- 



