May IS. 1919 Influence of Soil Environment on Rooirot of Tobacco 5 1 



evident that in uninf ested soil the optimum moisture content of this soil 

 type for the growth gf tobacco lay close to three-fourths saturation and 

 that full saturation was more favorable than the one-half and one-fourth 

 saturation. Although still no great differences existed between the 

 infested and uninf ested soils at one-fourth, one-half, and three-fourths 

 saturation, the plants in the uninf ested soil at full saturation were about 

 10 times as large as those in the infested soil at the same saturation. 



The data taken upon the growth of the plants in these experiments are 

 recorded for the most part as the total leaf area of each plant taken at 

 intervals of about one week. These determinations were made by plac- 

 ing the leaves over a standard leaf -area chart on which areas for varying 

 sizes and shapes of leaves had been previously determined with a plani- 

 meter. These areas, expressed in square inches, were determined at the 

 end of this experiment, on March 28, and are given under experiment 2, 

 Table II. The results appear to justify the conclusion that a fairly 

 constant ratio exists between the growth on infested and uninfested soil 

 at the three lower saturations. This ratio is approximately i to 3^. 

 On the soils at full saturation, however, the ratio of growth on infested 

 soil to that on uninfested soil is about i to 40. The evidence from 

 this experiment therefore shows that a very considerable amount of 

 disease can occur in a relatively very dry soil and that it does not appear 

 to be proportionately increased in a relatively moist soil, but that a wet 

 or saturated soil, which still permits a good growth of tobacco when 

 uninfested, causes a rapid decrease in yield when infested with T. basicola. 



Table; 2. — Influence of the moisture content of the soil on the amount of tobacco rootrot 



In a following experiment, which was conducted on the same soil in 

 the greenhouse, the above results were practically duplicated so that 

 the data will not be presented here. A third experiment was conducted 

 during the growing season in a shelter out of doors, permitting atmos- 

 pheric relations more nearly normal than those occurring in the green- 

 house during the winter season. The experiment w^as run in the same 

 manner as the foregoing one, except that a change of soil w^as made, 

 another batch from the same source was used in order to avoid nematode 

 injury. The crocks were set to White Burley on July 5. On July 12 

 all the plants appeared to have a good start except those at one-fourth 



