248 



Journal of Agricultural Research vo1.xxii,no.s 



plant at 27° to 28° as compared with 25° to 26°. It is interesting to note 

 that infection was reduced more abruptly at 27° to 28° in the artificially- 

 inoculated soil than in that naturally infested. This may be due to the 

 age of the inoculum, a smaller percentage of the spores being functional 

 in the former soil, or perhaps to the presence of a smaller amount of 

 inoculum. 



Table VI. — Relation of soil temperature to infection of onion seedlings by Urocystis 



cepu lae 



" stand reduced by damping-off fungi. 



Table VII. — Relation of soil temperature to infection of onion seedlings by Urocysti^ 



cepulae 



Experiment 3. 



Naturally infested soil 

 pleted Jan. 10, 1920 



Begun Dec. 20, 1919; com- 

 Soil moisture held at 25 per 



cent or two-thirds the water-holding capacity. 

 Air temperature, 13° to 2?° C: relative humiditv. 



Air temperature, 13 

 4S to 75 per cent 



Soil temperature. 



"C 



19 to 22 



23 to 26 



26 to 27 



27 to 28 



Total num- 

 ber of 

 plants. 



44 



100 

 86 



Smutted 

 plants. 



Per cent. 



93 

 96 



S7 

 12 



Experiment 4. 



Artificially inoculated soil. Begun Dec. 18, 1919; 

 completed Jan. 12, 1920. Soil moisture held at 13 

 per cent or two-thirds the water-holding capacity. 

 Air temperature, 13° to 25° C; relative humidity, 

 AS to 75 per cent. 



Soil temperature. 



C. 



23 to 26 

 26 to 28 

 29 to3i , 



Total num- 

 ber of 

 plants. 



50 

 40 



Smutted 

 plants. 



Per cent. 



98 



12 

 O 



