Jones—'Relation of Soil Temperature to Disease in Plants. 439 
Apparatus and Methods op Investigation 
In all cases attention has been restricted to cases of parasitism 
of subterranean parts. The primary object has been to determine 
the influence of various soil temperatures upon the development of 
disease. At the outset the attempt was made to do this by growing 
the plants in ordinary flower pots in greenhouses held at different 
temperatures or in favorable places out of doors, recording the 
temperatures and observing the results. Although valuable evi¬ 
dence was thus secured by Gilman in his pioneer work with cabbage 
yellows, the method was not sufficiently accurate for continued use. 
Text 'Fig. 1 . The first and most simple form of constant temperature 
apparatus used in the soil temperature experiments: A is a large earth¬ 
enware jar with a constant flow of tap water entering through the tube D, 
regulated by the faucet E. B 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. 
The next step was to grow the experimental plants in a battery 
jar which, being water tight, could be immersed in a larger jar of 
water of which the temperature could be lowered to the desired 
point by allowing cold tap water to trickle through it at a con¬ 
trollable rate (text fig. 1). This sufficed to give W. H. Tisdale 
more accurate data relative to the influence of the lower range of 
temperatures upon the flax-wilt disease. When it was proposed 
to push the work more aggressively with a larger series of plants 
