DAMPING-OFF TN FOREST NURSERIES. 



59 



figure 1$. This suggests, further, that part of the lack of activity 

 was due to the failure of the fungus to maintain itself vigorously 

 in the soil till the pines reached a stage of sprouting in which they 

 could be readily attacked. Direct inoculations after the seed starts 

 to sprout are therefore desirable .to supplement the experiments 

 reported. The survivals in the controls did not show any such 

 asymmetrical distribution. 



While the Rheosporangium has given rather definite evidence of 

 parasitism on Pinus Ijanksiana under favorable conditions, the 

 activity of the strains available has been much less than that of the 

 Pythium debaryanum strains. In view of the fact that the fungus 

 has not so far been isolated from pine it can be concluded to have no 

 general importance 

 in pine seed beds. Its 

 very rapid growth on 

 prune agar makes it 

 very easy to isolate 

 when present. 



If) 19 22 ZS 2. 



&EEDUMGS &UWW/NG PER POT 



PHYTOPHTHORA SPP. 



Phytophthora fagi 

 R. Hartig has been 

 commonly reported 

 as the cause of death 



Ol Seedlings Ol Va- FIG. 17. Diagram showing the results of inoculation of 



HoUS plants in Eu- Pinus resinosa seedlings with Rheosporangvum aphanider- 



-, -,' matus, as indicated by the number of seedlings surviving 



ro P e > l in inoculated pots (solid line) and control pots (broken 



ifers and herbaceous line). The shape of the curve for the inoculated pots is 



i, 11 taken as indicating that a large proportion of them 



were entirely unaffected by inoculation, while those which 



beech (5, 8, 15, 55, were at all affected suffered considerably. This is a 



K^> K>- KQ YQ ifi/l \ frequent result in inoculations with weak parasites added 

 30, o < , oy, < o, j at the time of sowlng the smh 



It has been grouped 



with the rather indefinite Phytophthora omnivora and with P. 

 cactorum, the enemy of cactus, ginseng, and other plants. Wil- 

 son (147, p. 54) considered it distinct, but Rosenbaum (114). 

 in his biometric comparison of Phytophthora cactorum and a 

 single strain of P. fagi, failed to find significant morphological 

 differences. If P. fagi is even physiologically different from 

 the American strains of P. cactorum, its introduction into the 

 United States is to be guarded against. There is certainly no 

 fungus in the United States causing the damage to coniferous 

 seedlings which European reports have attributed to P. fagi there. 

 As P. fagi attacks roots, it presumably can be carried in soil as well 

 as on plant parts. 



