SOIL TEMPERATURES IN PHYTOPATHOLOGY 



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Fig. 2. Graduated temperature tank. This is installed on a greenhouse 

 bench. It has 12 compartments {1-12), each of which can be held at a different 

 constant temperature. Cold water flows into compartment 1 at A through a 

 constant pressure valve. About one-fourth of the intake water is allowed to 

 pass into compartment 2 through the hole B which is 2 inches below the top of 

 the partition and another hole 8 inches below B (not shown in diagram). About 

 I overflows through the waste pipe C. The water passes similarly from com- 

 partment 2 to 3, and from 3 io Jf. with gradually elevated temperatures until in 

 compartment 5 the temperature approximates that of the greenhouse. Com- 

 partments 6-12 are for graduated temperatures above that of the greenhouse. 

 In these the water is static, the higher temperatures being regulated by four 

 devices: first, an asbestos cover D; second, electric heating bulbs E; third, live 

 steam pipes F; fourth, the regular steam heating system of the greenhouse of 

 which the pipes at G lie as close as possible under compartment 12 and slope to a 

 distance of 9 inches from the bottom of compartment 1 at G' . In addition a sheet 

 of asbestos H is laid on the pipes at this lower end to check the radiation. Each 

 compartment has a drain cock J . At lower left corner is sectional view to show 

 detail of wall construction: K, 1 inch board; L, 1^ inch hair-felt; M, galvanized 

 iron lining. 



By proper regulation and manipulation during the past winter it has been 

 possible to hold each compartment within a fluctuation of about 1° at tem- 

 peratures as follows: compartment 1, o°C.; 2, 9°; 3, 13°; i, 16°; 5, 19°; 6, 21°; 

 7, 23°; 8, 26°; 9, 29°; 10, 32°; 11, 36°; 12, 40°. In each compartment were sunk 4 

 battery jars (/) filled with soil for the culture of the experimental plants essen- 

 tially as illustrated in figure 1. 



