66 



Journal of Agricultural Research 



Vol. XVII. No. 1 



plants in the inoculated series wilted first at from 22° to 23° C, but no 

 wilting occurred at 31° to 32° or in the inoculated soil. On April 15 

 the experiment was terminated, the stalks and roots were cut and dried, 

 and the roots washed out as carefully as possible and dried. The air- 

 dry weights are shown in Table VI B. 



Table VI. — Influence of soil temperature on the rootrot of tobacco 



A. WHITE BURLEY VARIETY, NORMALLY IISTFESTED SOIL 



B. CONNECTICUT HAVANA VARIETY, ARTIFICIALLY INFESTED SOtI, 



The largest yield of the above-ground portions of the plants in the 

 uninoculated series occurred at 28° to 29°, but was only slightly 

 larger than at 26° to 27° or 31° to 32°. The largest root 'develop- 

 ment occurred at 26° to 27° and 28° to 29°, with a decided falling 

 off at 31° to 32°. In the inoculated soil the largest yield of the above- 

 ground parts was at 28° to 29°, with some falling off at 31° to 32°, 

 though not due to infection. It should be noted here that the greater 

 reduction in yield is at 17° to 18°, the disease apparently less marked 

 at 12° to 13° and at 22° to 23°. Practically this same relation 

 holds for the roots. This, together with other experiments, seems to 

 indicate with considerable certainty that the amount of infection and 

 severity of the rootrot are most marked at temperatures ranging between 

 17° to 23° C. At temperatures below about 15° the extent of the disease 

 is reduced, but this temperature also is too low to permit any growth 

 of tobacco, and consequently is of little practical importance. On the 



