64 



Journal of Agricultural Research 



Vol. XVII. No. a 



square inches in infested soil as against 203 square inches on sterile soil. 

 Examination of the roots in the infested series showed a relatively reduced 

 amount of infection at 9° and 13°, heavy infection between 17° and 24.5^, 

 much less infection again at. 26° and 29°, and no infection at 31°, 35°, 

 and 40°. 



The results of Experiment II are in accord with the results of Experi- 

 ment I, and apparently show in addition that the optimum temperature 

 for the disease lies around 19° and 21°, although heavy infection still oc- 

 curs as high as 24.5°. 



Experiment III. — The same soil was used as in Experiments I and II. 

 This soil was now so heavily infested with nematodes at the higher tem- 

 peratures that the results with T. hasicola were vitiated, and no data were 

 taken. 



Experiment IV. — New soil from the same infested field was used in 

 this experiment, the proper care being taken to sterilize thoroughly the 

 battery jars before filling them with soil. To reduce the harmful effect 

 of the sterilized soils, the pots, after being filled, were allowed to stand 

 moist for a week at room temperature before being placed in the tanks. 

 In this experiment only seven different temperatures were used, which 

 permitted the use of four jars of infested soil and four controls at each of 

 five temperatures, but only two of each at the extremes. The final results 

 are given in Table V. It may be again noted that the greatest amount 

 of injury from disease occurred at the temperatures from 19° to 22° C, less 

 occurred at 24° to 25°, while at 26° to 27° the injury was much reduced. 



Table V. — Influence of soil temperature on development of rootrot 



Temperature. 



Average leaf area (in square inches) of duplicates. 



Experiment III. 



Uninfested 

 soil. 



Infested 

 soil. 



Experiment IV. 



Uninfested 

 soil. 



Infested 

 soil. 



13-15 



15-17 



19-20 



21-22 



24-25 



26-27 



30-31 



63 

 106 

 206 

 212 

 205 

 202 

 256 



28. 5 

 24.9 

 19. 2 

 26. 7 

 71. I 

 168.7 

 243.6 



71 

 87 

 137 

 304 

 430 

 306 



339 



41.7 



13.0 



9-5 



21.4 



197.6 



280. 4 

 327.1 



Experiment V. — ^This experiment was largely a failure, owing to the 

 use of plants that apparently were slightly infected by T. hasicola and 

 also by nematodes. No plants from sterilized soil were available at the 

 time. The results were interesting, however, in that an examination of 

 the roots showed that at the lower temperatures — that is, those favorable 

 to infection — the heaviest infection occurred in the sterilized soil. This 



