344 



Eelation of Water to the Behavior of 



humidity, a stronger light intensity, and a wider daily fluctuation in both air 

 and soil temperatures ; excessive nocturnal radiations and convectional currents 

 were also potent factors in the desert. 



Four seasons were apparent in the arid region : A winter rainy season extend- 

 ing from November until April ; a dry fore-summer season, from April until 

 July ; a midsummer rainy season, from July until the middle of September ; and 

 a dry after-summer season, from the middle of September until early in ISTovem- 

 ber. At Chicago rain occurred throughout the year. The annual rainfall from 

 several years' data was about 13 inches at Tucson and 30 at Chicago. The 

 monthly records for both stations are given in Table 1 for the three years during 

 which these experiments were in progress. 



Table 1. 



station. 



Tucson . 



Chicago. 



Year. Jan. 



191011.00 

 191l!l.31 

 1912.0.00 



19103.07 

 1911 1.17 

 19120.84 



Feb. 



T. 

 0.90 

 0.37 



0.89 

 2.27 

 1.57 



Mch. 



Apr. May. I June. 



T. 0.05; T. jo. 22 

 0.25,0.27 0.00 0.07 

 2.120.280.320.61 



0.29 3.84 4.67 0.91 

 1.45 3.03 3.37 2.54 

 2.202.55 3.97 1.78 



July. 



4.20 

 1.57 

 3.00 



1.79 

 2.65 

 3.86 



Aug. 



4.65 

 2.06 

 0.98 



3.08 

 3.72 

 3.59 



Sept. 



0.62 

 2.65 

 0.01 



3.90 

 4.03 

 3,26 



Oct. 



0.08 

 1.23 

 1.78 



1.79 

 3.79 

 3.52 



Nov. 



1.74 



T. 



0.00 



1.31 

 3.27 

 1.45 



Dec. 



0.06 

 0.85 

 0.39 



1.32 

 2.54 

 1.08 



Total. 



12.62 



11.25 



9.84 



26.86 

 33.83 

 29.67 



Note— The rainfall records at Tucson were obtained from a standard Weather 

 Bureau rain-gage at the Laboratory site. The Chicago data were taken from the 

 records of the Weather Bureau. 



MATERIALS. 



The potato beetles were collected in May 1911, near Chicago, as they emerged 

 from hibernation, and were allowed to breed there as a group-culture within a 

 large cage filled with potato plants until late in June. A part of this material 

 was then sent to Tucson, where it became the progenitor of the animals used 

 in the majority of the experiments. Organisms when collected from nature are 

 often hybrids, so that crossing of different generations may have taken place, but 

 for complete breeding-records and life-histories of stocks used see Table 2, which 

 shows that these materials reacted homozygously. A brief description of their 

 activities follows. 



At Tucson Station A these stocks were received on June 26, 1911, and 

 immediately bred as a group-culture, so that 1,328 adults were produced in 25 

 days, giving generation I. After feeding upon the potato plants for a few days, 

 these first-generation individuals were bred as a group-culture and produced 

 generation II, numbering 2,312 progeny, in 26 days. Many of the beetles of this 

 second generation provided the materials for a large number of the hibernation 

 experiments Avhich were carried on in 1911, but many of the emerged animals 

 were allowed to hibernate during the winter of 1911-12 as stock for work during 

 the following year. When, in June, water was added to the soil within the cage, 

 the organisms emerged from hibernation as a group-culture, which in 29 days 

 gave generation III, of 1,743 offspring. From this material 50 females and 

 50 males were mated and allowed to breed at random, giving generation IV, of 

 4,049 progeny, in 26 days. For the above data, see Table 2. 



