The Potato Beetle in a Desert 369 



thrice daily, but only a few small sprays were used each time, so that the air 

 within the tube was free from dampness, a condition which would have increased 

 the evaporation rate and assisted in making the environmental situation un- 

 favorable. The environmental conditions in this case were normal, in so far as 

 the food-supply was a factor; but the other surroundings were modified, at 

 least as to the high rate of evaporation (Table 10 for tube 2) . Both tubes 1 and 

 2 were planned to give the ascertained differences in evaporation-rates ; accord- 

 ingly tube 1 produced a lower and tube 3 a higher rate, but the food relations 

 for both were approximately normal. 



No plants were used in tubes 3 and 4, but each tube was wrapped with several 

 thicknesses of coarse absorbent paper ; at the beginning of the test the soil within 

 each was saturated with water, but no water was added during the experiment. 

 Around the outside of tube 4 was placed a coil of lead-tubing drilled full of 

 holes, and this was connected to a carboy of water. This device kept the 

 absorbent paper surrounding the tube saturated and, furthermore, a large piece 

 of oil-cloth was wrapped to the height of 15 cm. aroimd the base of the tube 

 and beneath the absorbent paper. This oil-cloth was extended out in all direc- 

 tions for about 60 cm. from the bottom of the cage, so that the dripping water 

 did not come in direct contact with the soil in the tube. On the other hand, no 

 water was added to tube 3, so that this cage was kept dry during the experiment. 

 These conditions, therefore, produced a high rate of evaporation in tube 4 and a 

 low one in tube 3 (Table 10) . The results for each of these tests follow. 



The 1,000 beetles used in this experiment were grown imder the same environ- 

 mental conditions and from the same parents, and, moreover, these animals had 

 emerged as adults from the pupa state synchronously; so they were then as 

 nearly uniform physiologically as it was possible to obtain them. The con- 

 clusions showed for tube 1 with plenty of food and moisture, when the indi- 

 viduals were counted at the end of the experiment, that there was no hiberna- 

 tion ; 28 were found dead upon the soil. In tube 2, with plenty of food, but in 

 which the air was kept dry, the census, when taken at the end of the test, showed 

 that 157 had successfully hibernated and that 93 had died. At the end of the 

 experiment tube 3, which contained dry air and no food plants, showed 129 

 beetles in hibernation and 121 dead ones. Tube 4, which was supplied with 

 moisture but with no food, at the end of the test gave no evidence of hibernation ; 

 73 of the 250 beetles originally present were found dead upon the soil. These 

 results proved that newly emerged adults of the fall generation can not be 

 caused to hibernate under normal conditions, but that if the surrounding 

 medium was dry a type of hibernation reaction did result through desiccation. 

 Such deductions are possible, since the evaporation rates in Table 10 show that 

 a low rate retarded hibernation and a high one accelerated this behavior. 



It is also true that this entrance into hibernation may be of the normal type, 

 which always occurs under normal conditions in the winter generation. Low 

 temperature, however, was an important factor at Chicago, but this kind of 

 hibernation also took place in the pure winter-generation stock, even under high 

 temperatures. This behavior was further studied in the second generation of 

 the year under the following set of experimental conditions. 



At Tucson Station A this type of hibernation reaction in beetles of the winter 

 generation (Tucson A, g. II) was observed to appear under a normal environ- 

 mental complex in the fall of 1911, but all other hibernations (Tucson A, g. IV) , 

 25 



