542 Journal of Agricultural Research voi. xv, no. io 



Pythium and Corticium in experiment 31 indicates much less damage 

 by F. monUijorme to germinating seed. While some of the strains of 

 Corticium and Pythium also do little or no damage to germinating seed 

 in inoculations by the writer's standard methods, they are in most cases 

 strains whose general virulence is low, and which are not able to kill 

 many seedlings after germination. The indications are that C. vagum 

 is rather better able to kill germinating seed than seedlings which have 

 recently appeared above the soil ; that P. debaryanum is at least approxi- 

 mately as well able to cause germination loss as normal damping-off ; 

 and that F. monUijorme is distinctly less able to cause germination loss 

 than it is to cause subsequent damping-off. 



The relation of heavy inoculation to positive results with F. monUi- 

 jorme is indicated, first, by the negative results in the two nontabulated 

 experiments in which inoculation was light, the weakly positive results 

 in experiment 57 in which inoculation wasi fairly heavy, and the unques- 

 tionable results in the heavier inoculations in experiments 31 and 60; 

 and second, by the difference in results between the heavily inoculated 

 and the parallel lightly inoculated pots in experiment 60. It is not 

 possible to say whether the increased damping-off in the heaviest inocula- 

 tions was simply due to the development in the soil of a larger amount of 

 mycelium and consequently more points of contact between hyphae and 

 seedlings, or whether in the cases in which large amounts of nutrient sub- 

 stratum were added with the fungus, there was an actual temporary 

 increase of virulence resulting. It appears from experiment 60 that 

 broadcast inoculations with spore suspensions were distinctly more 

 effective than inoculation with a small fragment of a culture at a single 

 point at the edge of each pot. The single point inoculations resulted in 

 no more damping-off than occurred in the controls. Broadcast inocula- 

 tion over the entire pot and including nutrient substrata were definitely 

 successful in all four of the 5-pot units on which it was used. These 

 heavy inoculations were clearly more effective tlan the inoculations over 

 smaller areas or those made with spore suspensions. In comparing 

 these heavily inoculated units with each other and considering both ger- 

 mination loss and subsequent damping-off, it appears that inoculation 

 with cultures on steamed rice is more effective than with cultures on 

 prune agar, and that the greatest total loss occurred following the use 

 of both media in the inoculum. The apparent increase in damping-off 

 with increase in the amount and richness of the media, though by no 

 means final proof, is believed to indicate that the presence of the nutrient 

 substrata actually increased the virulence of the parasite, as well as 

 assisting it to become thoroughly distributed throughout the pot. The 

 possibility that the substrata added may have decreased the resistance 

 of the seedlings must also, of course, be considered. 



