The Potato Beetle in a Desert 



377 



were used as a control. In table 12, the results are given, which shows that 

 group 1 at the beginning of the test was negative, but by 9*^ SO'" a. m., while 

 under the dry bell-jar, all became positive, but when moist conditions were 

 restored in the jar, by 10 a. m. on May 26, they were again negative. In group 2, 

 at the beginning, all were negative and remained thus as long as they were kept 

 under moist conditions, but at 10 a. m. on May 30, all had become positive. In 



Note.— In group 1 the conditions in bell-jar were dry on May 17, 19, and 21, and 

 moist on the other days. In group 2 said conditions were dry on May 26, 28, and 30, 

 and moist on other days. In group 3 said conditions were xmiform throughout. 



group 3, which were the control individuals, a gradual loss of weight occurred 

 until 10 a. m. on May 28, when all were positive. These results showed clearly 

 that reactions to gravity may be reversed through changes in the moisture- 

 content of the surrounding medium. 



RELATION OF TEMPERATURE TO THE OUTGO AND 

 INTAKE OF WATER. 



An interesting discovery was the determination that there was little absorp- 

 tion of water below 12° C. as was shown in a test in which beetles emerging 

 from pupation were collected on July 28 ; they were placed under a bell-jar 

 containing wet filter-paper, where they remain until 13 midnight on July 30, 

 when equal numbers of insects were placed in two bell- jars, in a refrigerator, at 

 a temperature of 10° to 13° C. One bell-jar contained wet filter-paper and the 

 other calcium chloride, but weighings made at frequent intervals showed that 

 in the humidor there was no appreciable loss during the 84 hours in the 

 refrigerator. In another test, desiccated beetles were placed under saturated 

 bell- jars in the refrigerator, but weighings made at frequent intervals gave no 

 evidence of water-absorption. These results showed how much organisms were 

 protected from absorbing water during winter rains, which would otherwise 

 result in their freezing, and further demonstrated that desiccation, occurring 

 slowly at a low temperature, was a factor in the economy of the organism. 



A similar result was obtained with upper temperature limits. It is known 

 that the coagulation temperature of colloids varies with the amount of contained 



