234 



L. R. JONES 



Cornell, to endeavor to perfect methods of securing data as to 

 such temperatures under controllable experimental conditions. 



In the earUer work at Wisconsin the endeavor was to grow 

 the plants m greenhouse rooms of differing temperature. It is, 

 however, ahiiost impossible to maintain house temperatures 

 within narrow enough limits for the results desired. Therefore, 

 we have turned to the use of the constant temperature water 

 jacket surrounding the culture pot or jar. Tisdale, in his work 

 on the flax wilt to which reference has previously been made, 



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'/ /y ' / / ^ / /• .' ^ r f 7 ? 7 /^ T27^ 



Fig. 1. Constant temperature culture jars, yl is a large earthenware jar with 

 a constant flow of tap-water entering through the tube T>, regulated by the 

 faucet E. 5 is a smaller glass jar resting on a support C and containing soil in 

 which the experimental plants may be grown at approximately constant soil 

 temperature. F, Control culture jar at room temperature. 



adopted the simple method illustrated in figure 1, using a single 

 culture jar sunken in a larger receptacle through which cool tap 

 water trickled just rapidly enough to maintam the desired tem- 

 perature. Wishing to secure simultaneously a series of con- 

 stant temperatures we have since expanded this idea, under the 

 supervision of R. E. Hartman, who is investigating the relation 

 of soil temperatures to the development of tobacco and its 

 infection with the root parasite Thielavia hasicola. The essen- 

 tial method is illustrated in figure 2. In this way, Hartman 

 has maintained fairly constant temperatures at points between 



