108 ILLINOIS BIOLOGICAL MONOGRAPHS [502 



PLATE XIX 



Explanation of Plate 



Figure 455. Showing the equipment used in the experiments on modification 

 of tiger beetle color and color patterns. 



The experiments were conducted in four chambers ; two, A and B, which 

 were of galvanized iron, rested with their bottoms in a concrete tank of running 

 water. Trey were wrapped with cheese cloth and sprayed with jets of water on 

 two sides which kept the mean temperature at 21° C. throughout the summer. 

 The other two, C and D, were heated from above with electric lights, blackened 

 in C and separated from the main chamber by a copper jacket in D. These were 

 were heated to a point io c C. above the temperature of the greenhouse except 

 during the middle of the day. The switch shut off the heat at about 35° C. air 

 temperature and the sun continued to heat the chamber so that the maximum 

 soil temperature sometimes reached 40° C. or more by midafternoon. Air was 

 drawn through the tanks by filter pumps and, in the case of the control tanks, 

 through sulfuric acid for the dry one and water for the moist one, but this 

 intake was not maintained for the high temperature tanks at all times because 

 of mechanical difficulties. The moisture in the moist chambers was maintained 

 by frequent additions of water to the soil, while in the dry chambers as little 

 water as possible was added. H , sulphuric acid bottles ; S, mercury switch ; T, 

 thermostat ; B, batteries ; IV, water bottles ; SP, spray nozzles ; C, cloth cover. 



