The Potato Beetle in a Desert 



365 



shown in figure 4, while the transpiration and reaction curves of Leptinotarsa 

 decemlineata and Catalpa lanigera are given in figure 5. The upper diagram 

 contrasts for the potato beetle its transpiration rate with the percentage posi- 

 tive to light, while the lower half of the cut does the same thing for Catalpa 

 lanigera. This experiment was similar to the former ones, in that the insects 

 were subjected to the environmental conditions out-of-doors at the foot of 

 Tumamoc hill. 



For other data and comparisons Table 9 should be consulted; the results 

 given show that the evaporation curve as measured by the porous-cup atmometer 

 and the transpiration curves of the insects are similar, as was previously found 

 to be true. Moreover, the positive reaction curve of the potato beetle was the 



55.0% 

 2 

 ^ 42.5% 



'|30.0% 



II 

 M 17.5% 



V 



> 



o 



5.0 * 



3 8.21 



c 



■| 6.2% 



"a 



c 



^ 4.2% 

 II 



> 



a 



2.2t 



Units 12 3 4 5 6 7 



100% 



75%- 



50% u .3 



25% 



90X 



65% S 

 I 



40% 



15% 



9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 

 Fig. 5. 



0% 5 



reciprocal of its transpiration curve. In the same way the reaction curve of 

 C. lanigera was associated with its transpiration curve imtil 9 a. m., when all 

 reactions became negative. The Lachnosternse appeared here only with a 

 negative reaction, regardless of their transpiration curve, which agreed with 

 the curve of evaporation. 



These results prove, in the first instance, that the evaporating power of the 

 air was the determining factor in the transpiration of these animals, a result 

 similar to that obtained by Livingston (1906) for plants; secondly, that there 

 existed from the base to the top of associated plants, in an arid region, an 

 extreme zonation, in which great differences were found in the evaporating 

 power of the air, and that this in turn controlled the rate of transpiration ; and 

 finally, that the evaporating power of the air surrounding the organisms deter- 

 mined their behavior through transpiration. Moreover, many animal organisms 

 of the desert exhibited great localization in their distribution and the ruling 

 feature of the environmental complex, whether it entailed a habitat of trees, 

 among rocks, or in soils, was that of the moisture-relation. 



