RESPIRATION AND OXYGEN. 



35 



cent. There was a general tendency for the carbon dioxid to in- 

 crease with the depth, but this was not absolute. Habitats at the 

 base of a slope tended to have more CO 2 than those higher up. 



Smolensk! (1877 : 383) concluded that the degree of contamina- 

 tion of the soil is a predominant factor in the amount of CO Z . For 

 example, while he found from 0.1 per cent to 2 per cent in ordinary 

 soil, the amount rose to 10.2 per cent in contaminated soil. Renk 

 (1878; confirmed the results obtained at Munich by Pettenkoffer. 



Moller (1878 : 121) summarized his results from the stud}' of soil- 

 air as follows: The air in purely mineral soil or in absolutely dry soil 

 contains no more carbon dioxid than the atmosphere. Soils with 

 organic constituents possess a constant source of carbon dioxid. 

 The formation of carbon dioxid shows but slight variations when 

 the external conditions are the same. Soil may become so dry that 

 the production of carbon dioxid ceases. On the other hand, a very 

 small amount of water suffices to bring about the production of the 

 same amount of carbon dioxid as when it is saturated. When an 

 air-dry soil is abundantly watered, there results a considerable but 

 temporary increase in the carbon-dioxid content. In a later paper 

 (1879 : 329), a comparative study was made of the carbon dioxid in 

 fallow and cultivated fields and in several kinds of soil. The culti- 

 vated field regularly showed 5 to 6 times as much carbon dioxid as 

 the fallow field, while calcareous soil contained as a rule considerably 

 more carbon dioxid than clay, and both these soils several times as 

 much as sand. 



Audoynaud and Chauzit '1879) obtained somewhat different re- 

 sults from those of Boussingault and Lewy in regard to the compo- 

 sition of soil-air, as shown in table 6. 



TABLE 6. 



The soil-air was much richer in nitrogen and poorer in oxygen 

 than in the studies of Boussingault and Lewy. The authors assumed 

 that the decrease of the oxygen was due not alone to its use in respi- 

 ration or oxidation in the soil, but also to the different osmotic rela- 

 tion of nitrogen and oxygen in the passage through the soil. 



Fodor (1881) found that the amount of CO* in soil-air was very 

 variable, the maximum being 14.3 per cent. He concluded that 



