530 Journal of Agricultural Research voi.xv.no.io 



number it was necessary to add in adjusting the survival by this method 

 was relatively much smaller than in this sample case. 



In cases in which some of the experimental units contained more or 

 larger pots than others, the germination and survival figures for the larger 

 units were reduced proportionally, or were converted for all of the units 

 to a percentage based on the number of seed sown, in order to permit 

 the direct comparison of the figures for the different units. 



OOMYCETES CAUSING DAMPING-OFF 



At least four oomycetes found in America appear capable of causing 

 the damping-off of pine seedlings. Only one of these, Pythium debarya- 

 num Hesse, is believed to be especially important on conifers. Rheo- 

 sporangium apkanidermatus Edson, Phytophthora sp., and an apparent 

 species of Pythium with spiny oogones, are the other oomycetes found 

 attacking pines. As some of those concerned are of doubtful identity, 

 the experimental results obtained with them will not be published until 

 further studies now in progress on them have been completed. 



CORTICIUM VAGUM 



Rhizoctonia was reported as a cause of the damping-off of white pine 

 (Pinus sirobus) in New York in 1901 (6). Preliminary inoculations on 

 conifers were mentioned by the senior writer in an abstract published in 

 1910 {13). No inoculation evidence of its parasitism on conifers has ever 

 been presented. 



The strains of Rhizoctonia which were used successfully in the follow- 

 ing experiments belonged to the common American Rhizoctonia, which 

 causes the damping-off and rootrot of angiosperms, and is now usually 

 referred to Corticium vagum B. and C. (identical with C. vagum var. 

 solani Burt and with Hypochnus solani Prill, and Del. ; 21, p. 286, foot- 

 note). Spores have not been produced in any of the writers' cultures, 

 but the identity of the Rhizoctonia on conifers with the common damp- 

 ing-off fungus on angiosperms is considered established by the following 

 facts : 



1. Widespread distribution and ready growth on various culture 

 media of the strains from conifers. The only other common American 

 Rhizoctonia, R. crocorum (R. medicaginis; 21) will not grow on ordinary 

 artificial media (4). 



2. Successful inoculations on pine seedlings with strains from, or 

 which had been found parasitic on, dicotyledonous hosts. 



3. Observed damping-off of dicotyledonous weed seedlings in patches 

 coextensive with definitely limited damping-off patches of pine seedlings. 



4. Successful inoculations by Edson (7) on dicotyledons with strains 

 which the writers had taken from pines and had found parasitic on 

 them. 



