58 



BULLETIN 934, U. S. DEPARTMENT OE AGRICULTURE. 



either of the groups of pots compared is seriously affected by parasites, the 

 most convenient index of the comparative activity of the fungi used. In such 

 a comparison as that between the Rheosporangium pots and the controls in 

 experiment 68 (Table VII), accidental variations in emergence, of course, over- 

 shadow the slight effect of the fungus, and the definitely determinable per- 

 centage of loss after emergence is the only value which can serve as a basis for 

 any definite conclusion. 



Table VII. — Results of inoculations on pine seedlings with initial and reisolated 

 strains of Rheosporangvum aphanidermatus compared with parallel inocula- 

 tions with Pythium debar pa num. 





Reisolation source. 



Num- 

 ber of 

 pots. 



Num- 

 ber of 

 strains. 



Results. 



Experiment number, host, and 

 inoculating fungus. 



Emerged 



(per 5-pot 



unit). 



Damp- 



ing-off 



(per 



cent). 



Survival 

 (per 5-pot 



unit). 



No. 66, Pinus banksiana: 

 Rheosporangium — 



Strain229 



Edson from beet 



.....do 



5 

 5 

 10 

 15 

 15 



1 

 1 

 2 

 3 

 3 



63 

 80 

 78 

 63 



72 



9 



52 

 43 

 43 

 42 



58 



Strain 351 



39 



Strains 403 and 404 



Strains 405, 406, and 407... 

 Strains 417, 430, and 433... 



Strai n 229 from beet 



Strain 351 from beet 

 Strain 351 from pine 



44 

 36 

 41 





50 



10 



70±2. 7 



40 



42±3. 8 











25 

 235 



47 



75 

 43 



15 

 33 



64 







29 





do 





No. 67, Pinus banksiana: 

 Rheosporangium — 



Strain 229 



5 

 5 

 10 

 15 

 15 



1 

 1 

 2 

 3 

 3 



107 

 88 

 91 

 92 



83 







6 

 8 

 4 

 3 



107 



Strain 351 



83 



Strains 403 and 404 



Strains 405, 406, and 407 .. . 

 Strains 417, 430, and 433 .. . 



Strain 229 from beet 

 Strain 351 from beet 

 Strain 351 from pine 



84 

 88 



80 





50 



23~ 

 235 



10 



90±2. 4 



4 



86±2. 9 











47 



87 

 51 



5 



26 



83 







38 





Edson from beet 



do 





No. 68, Pinus resinosa: 

 Rheosporangi urn — 



Strain 229 



5 

 5 

 10 

 15 

 15 



1 

 1 

 2 

 3 

 3 



105 

 124 

 102 

 105 

 100 





 

 1 

 5 

 3 



105 



Strain 351 



124 



Strains 403 and 404 



Strains 405, 406, and 407. . . 

 Strains 417, 430, and 433. . . 



Strain 229 from beet 



Strain 351 from beet 



Strain 351 from pine 



101 

 100 

 97 





50 



10 



105 ±2. 3 



2 



102±2.5 











IS 

 235 



47 



104 



86 





 27 



104 







63 









A frequency graph based on the survivals of the 50 individual pots 

 inoculated with Rheosporangium in experiment G8 yields a rather 

 interesting asymmetrical curve (fig. 17). The shape of the curve 

 is taken as indicating that in a large number of the pots the inocula- 

 tion produced no effect, while in the smaller number of pots in which 

 the inoculation apparently " took," the loss was rather heavy. This 

 is a rather common phenomenon in inoculations which are only 

 partly successful, part of the pots being free or practically free from 

 loss, while others are nearly cleaned out. It will be seen again in 



