ATMOSPHERE 159 



TABLE XXXV 



SHOWING VARIATION OF SAND TEMPERATURE WITH DEPTH AND MOISTURE CONTENT- 

 AIR 36 C. 



It will be noted from the table that temperature decreases with depth 

 and with increasing moisture. 



4. PLANTS AND ANIMALS 



Cowles (120) mentions the importance of soil bacteria which increase 

 with the increase of the humus, and the development of substances toxic 

 to the plants producing them (121,1 140). Little is known of the effect of 

 animals upon the soils in which they live but if excretory products ever 

 accumulate in any quantity, they probably have a detrimental effect, 

 especially upon the animals which produce them (114). On the other 

 hand, many burrowing animals bury organic material and bring mineral 

 soil to the surface. The digger wasps add much to the sand by burying 

 many insects for their young. Earthworms contribute to soil forma- 

 tion (30). Cowles states further on the authority of Transeau (122) that 

 humus accumulation alters soil aeration. It follows that the atmosphere 

 available to subterranean animals differs in different soils. 



III. ATMOSPHERE 



Animals living fully exposed to the atmosphere are usually those most 

 dependent upon the various physical factors of the air, viz., light, 

 temperature, pressure, humidity, currents, electrical conditions, etc. 



I. LIGHT 



Animals are either positive or negative to the actinic rays of the 

 spectrum (45, 123). Considerable work has been done by plant 

 ecologists, on the measurement of light with photographic papers, but its 

 bearing on plant problems is questioned by some because the nonactinic 

 portion of the spectrum is most important in the process of photosyn- 

 thesis. It appears that these measurements are of much greater signifi- 

 cance for animals than for plants. Zon and Graves (124) have brought 



