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



Inoculations at two points in each pot : 



Experiment 26A. Jack pine, 3 pots inoculated, 4 controls; inoculated, 

 emergence 29 per cent, as compared with 39 per cent in the controls ; 

 subsequent damping-off the same in both. 

 Inoculations at four points in each pot : 



Experiment 58B. Jack pine, 5 pots inoculated, 5 controls; inoculated, 

 emergence 51 per cent, damping-off 10 per cent, survival 46 ; controls, 

 emergence 43 per cent, damping-off 22 per cent, survival 34. 



Experiment 59A. Jack pine, 5 pots inoculated, 5 controls; inoculated, 

 emergence 55 per cent, damping-off 2 per cent, survival 54 ; controls, 

 emergence 50 per cent, damping-off 8 per cent, survival 46. 



Of these experiments, No. 29 was in the original fine sandy soil 

 of a nursery in Nebraska in which Pythium is commonly found 

 native and damping-off losses are usually heavy. Experiments 58 A 

 and 59 were conducted on soil from the same source which had been 

 kept dry in the laboratory for five years; experiments 25, 27, 31, 

 and 58 A were on greenhouse mixtures of sand and soil. In experi- 

 ments 31, 58 A, 58B, and 59 parallel inoculations were made on auto- 

 claved portions of the same soil, with definitely positive results in 

 three of the four cases. In the heated soil the results were positive, 

 not only because of smaller losses in the controls but because the losses 

 in the inoculated pots were actually heavier in the sterilized soil than 

 in that untreated. 



Inoculations broadcast : 



Experiment 31. Jack pine, 8 pots inoculated, 8 controls; inoculated, 

 emergence 31 per cent, damping-off 39 per cent, survival 129; con- 

 trols, emergence 38 per cent, damping-off 26 per cent, survival 196. 



Experiment 59. Jack pine, 5 pots inoculated, 5 controls; inoculated, 

 emergence 58 per cent, damping-off 22 per cent, survival 45 ; controls, 

 emergence 44 per cent, damping-off 2 per cent, survival 43. 



Even with these broadcast inoculations the results on untreated 

 soil were too indefinite to allow the drawing of positive conclusions. 

 In both experiments much heavier losses than these resulted from 

 inoculations on steamed soil. It is evident that experiments on steril- 

 ized soil do not always show what can be expected on ordinary soil. 

 The same thing is indicated by the results of Edgerton with tomato 

 wilt (36). 



CONCLUSIONS AS TO THE PARASITISM OF PYTHIUM DEBARYANUM. 



Pythium debaryanum has been found in low-altitude nurseries in 

 all the species of conifers from which a serious effort has been made 

 to obtain it, and its parasitism has been indicated in autoclaved soil 

 on all of the conifers on which inoculation has been attempted. 

 Therefore, although the work reported has been limited to a relatively 

 small number of hosts, it seems likely that it will be found able to 

 cause damping-off in most of the species of the Abietoidese which 

 suffer seriously from the disease. Just how active as a parasite it is 



