208 COLORATION IN LEPTINOTARSA. 



ferent soils is high or low, and the deviations are the same as those found in 

 the experiments with moisture. 



I conclude, therefore, that clay soils (glacial clays, glacial tills, etc.) are 

 productive of melanic tendencies in color variation ; that from fine-grained 

 soils rich in humus we have average or slightly melanic conditions ; while 

 sandy soils poor in humus and coarse sands produce albinic tendencies. 



These results correspond well with conditions found in nature. Over the 

 northeastern part of the United States and Lower Canada, in the region of 

 glacial soils which contain a high percentage of clay, the general tendency of 

 coloration in decemlineata is melanic. In the prairie country and in the re- 

 gion of residual soils, in the middle latitudes of the United States, average or 

 slightly melanic conditions are found, while in the west and southwest, in the 

 sandy soils poor in humus, the tendency is albinic. Soil acting upon color- 

 ation through the contained moisture may, therefore, be an important factor 

 in geographical and place variation, as also in distribution and ecology. 



Experiments with Light. 



It is frequently stated that light has an important influence upon coloration, 

 and there is frequently assumed to exist a sort of bio-photography of the 

 environment upon the animal ; but with the exception of the results of the 

 experiments of Poulton and his pupils upon Lepidoptera there is not to my 

 knowledge any evidence of value on this subject. 



For several years (1897 to 1904) I have experimented with decemlineata 

 to determine the action of light upon coloration. All separate colors of light 

 or different intensities thereof parallel rays, cross-rays, and absolute dark- 

 ness have been used, but with none have I been able to obtain any variations 

 in color in decemlineata. I therefore conclude that in this beetle at least 

 light that is, its action in different wave-lengths and intensities certainly 

 has no effect upon color-pattern variations. The beetle responds to light, 

 but in other ways, and not by changes in coloration. 



Experiments with Atmospheric Pressure. 



Experiments with altered atmospheric pressure, wherein alpine conditions 

 were simulated, have been tried, but not with any success. While it is easy 

 to produce rarefication of air and the conditions of temperature and moist- 

 ure found in alpine regions, it is not possible to produce the same kind of 

 atmosphere, nor the intense sunlight. These experiments were continued for 

 three years, but although as far as atmospheric pressure was concerned it 

 was possible to obtain conditions equal to an altitude of 22,000 to 23,000 feet, 

 the beetles showed no resulting modifications of coloration. When, however, 

 opportunity came to transport them to an altitude of 9,000 feet, a marked 

 change was noticeable, which indicates that something was lacking in the 

 environmental elements in the experiment made in the laboratory. 



