DAMPING-OFF IN FOREST NURSERIES. 



47 



tioned is identical with Pythium debaryanum, causing leak of potato 

 tubers and the damping-off of seedlings of two dicotyledonous 

 families. 



Table V. — Results of inoculations on jack pine and red pine with Pythium 

 dcbanjanum from various hosts. 





Host from which isolated. 



Inoculation results. 





On jack pine. 



On red pine. 





Emerged 



(per 5-pot 



unit). 



Damp- 

 ing-off 

 (per 

 cent). 



Sur- 

 vival 



(per 

 5-p ot 

 unit). 



Emerged 



(per 5-pot 



unit). 



Damp- 

 ing-off 

 (per 

 cent). 



Sur- 

 vival 

 (per 

 pot). 



No. 131 a 



Dicotyledons: 



45 

 45 



36 

 34 



30 

 30 



101 

 62 



23 

 41 



15.6 



No. 810 6 



Do 



7.4 











45 



35 



30 



82 



32 



11.6 









No. 294 c 



50 



28 

 19 



8 



32 

 32 



46 



19 

 13 



79 



62 

 68 



36 



48 

 58 



10.2 



No. 295 c 



Originally potato strain 131, but 

 twice inoculated on and reisolated 

 from sugar-beet seedlings by Ed- 



6.6 



No. 296 d 





5.8 











32 



24 



26 



70 



47 



7.4 









No. 529 



36 



60 



31 



49 



25 

 31 



102 

 108 



26 

 22 



15.0 



No. 530 



Do 



16.8 











48 



40 



28 



105 



24 



16.0 





Conifers: 



Western yellow-pine seedlings 





No. 258 



58 



9 



53 



109 



17 



18.0 



No. 550 



15 



42 



80 



29 



3 



30 



39 

 45 



98 



70 



.2 



No. 555 





5.0 





Average, spruces 



Controls 







29 



55 



17 



42 



84 



2.6 





87 



5 



83 



104 







20.9 



a Furnished by Mrs. C. R. Tillotson: has been used b 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 deb'aryanum 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- 



