232 L. R. JONES 



The results obtained by various investigators on the stinking 

 smut of wheat {Tillaetia tritici), including Hecke (13) and 

 Munerati (14) in Europe, Heald and Woolman (15) and Hum- 

 phrey in America, point clearly to temperature of the soil at 

 time of seed germination as a factor controlling infection. 

 Humphrey (in correspondence) sums up the conclusions that 

 '4t seems now to be an established fact that soil temperatures 

 of 0° to 5°C. are decidedly unfavorable to successful infection as 

 are also temperatures higher than 22°C., with 15° to 22°C. as 

 the optimum for the development of the smut." In accord 

 with this conclusion the farmers of the Pacific Northwest are 

 finding that "by sowing their winter wheat either very early 

 (warm soil) or very late (cold soil) they can reduce the loss 

 from smut to an almost negligible percentage." Munerati has 

 pointed out similar variations of infection wdth date of planting 

 spring wheats in Italy. 



The writer's interest in the possible relation of soil tem- 

 perature to infection with oat smut was first aroused in Ver- 

 mont over twenty years ago (16) upon finding that the smut 

 was less abundant in Vermont than in the western States even 

 when heavily smutted seed was used, and he at that time at- 

 tempted to secure comparative data as to soil temperatures dur- 

 ing the germination period. This problem has received experi- 

 mental treatment by several investigators including Brefeld (17), 

 Tubeuf (18), and Hecke (13) in Europe and G. M. Reed and 

 A. G. Johnson (correspondence) in America. While the results 

 point clearly to soil temperature as an important factor they are 

 not fully in accord, the variations being apparently in part at 

 least dependent upon whether constant or variable temperatures 

 are used. 



Although it is only in these two groups of parasites that we 

 have sufficient data to justify any generalization, there can be no 

 doubt that further study will bring out constantly increasing 

 evidence of the importance of soil temperature as influencing 

 either the occurrence or severity of the attacks of soil parasites 

 of other* types. 



Balls (19) has shown that Rhizoctonia can attack cotton at 



