70 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 



weak strains of 0. vagum than in the case of Pythium. In inocula- 

 tions on Pinus banksiana and P. ponderosa in Kansas sand treated 

 with acid followed by lime, the average Corticium was very much 

 more destructive than even the strongest Pythium strains, allowing 

 practically no germination in most cases. On the other hand, in ex- 

 periments in which the inoculum was applied directly to Pinus 

 resinosa and P. ponderosa seedlings, either immediately after germ- 

 ination or after the older parts had become resistant, the Pythium 

 has been the more effective. The inoculation evidence so far avail- 

 able justifies so nearly equal emphasis on the two that it can prac- 

 tical^ be eliminated from the calculations. It is the writer's opinion 

 that the Corticium strains are probably rather less virulent on the 

 average than the Pythium strains, but perhaps better able to main- 

 tain themselves and spread from one seedling to another in most 

 soils. The evidence of Table IX that the Corticium seemed less fre- 

 quent in the damping-off foci is more or less counterbalanced by the 

 apparent larger size of many of the disease patches which it seems 

 to cause in the seed beds. Nearly all the large clean areas such as 

 are shown in figures 7 and 8 have been found to contain abundant 

 Corticium hyphse. The evidence on the whole seems to indicate a 

 very nearly equal importance for the two fungi. The Pythium is 

 probably somewhat the more important for the stations at which 

 most of the cultures in Table IX were made, but the Corticium has 

 received more emphasis from other observers in this country and is 

 indicated by the writer's observations to be more important in the 

 western mountains than any other damping-off fungus. 



The inoculation evidence for Fusarium spp., though less complete 

 than for Corticium and Pythium, is nevertheless rather helpful in 

 indicating their importance rating. None of those so far tested in 

 inoculations at sowing have shown the destructiveness of the aver- 

 age strains of Pythium or of the stronger strains of Corticium ; while 

 this is only in part a test of virulence and in part a test of the 

 ability of the fungus to grow saprophj^tically in the soils used, the 

 indication is that no one Fusarium species is the equal in destructive 

 capacity of either Corticium vagum or Pythium debaryanum, How- 

 ever, when all of the Fusarium species which occur in the seed beds 

 are considered, the group as a whole may prove quite as important 

 or even more important than either of the other two fungi. The data 

 already at hand rather definitely indicate considerable importance for 

 all three. 



DAMPING-OFF FUNGI AS CAUSES OF ROOT-ROT AND LATE 



DAMPING-OFF. 



As has been already stated, root-rot, often with frequent recovery, 

 has been commonly observed in seedlings several weeks old. It has 

 been especially common in the vicinity of old damping-off foci in 



