44 Nature of Aquatic Environment 



example, the absorbing power of pure water at various 

 temperatures for oxygen from the normal atmosphere 

 at 760 mm. pressure: 



The primary carbon supply for the whole organic 

 world is the carbon dioxide (CO2) of the atmosphere. 

 Chlorophyll-bearing plants are the gatherers of it. 

 They alone among the organisms are able to utilize the 

 energy of the sun's rays. The water existing as vapor 

 in the atmosphere is the chief agency for bringing these 

 gases down to earth for use. Standing water absorbs 

 them at its surface but slowly. Water vapor owing to 

 better exposure, absorbs them to full saturation, and 

 then descends as rain. In fresh water they are found in 

 less varying proportion, varying from none at all to con- 

 siderable degree of super saturation. Birge and Juday 

 report a maximum occurrence of oxygen as observed in 

 the lakes of Wisconsin of 25.5 cc. per liter in Knight's 

 Lake on Aug. 26, 1909 at a depth of 4.5 meters. This 

 water when brought to the surface (with consequent 

 lowering of pressure by about half an atmosphere) 

 burst into lively effervescence, with the escape of a 

 considerable part of the excess oxygen into the air. 

 ('11, p. 52). They report the midstimmer occurrence 

 of free carbon dioxide in the bottom waters of several 

 lakes in amounts approaching 15 cc. per liter. 



The reciprocal relations of CO2 and — Carbon dioxide 

 and oxygen play leading roles in organic metabolism, 

 albeit, antithetic roles. The process begins with the 

 cleavage of the carbon dioxide, and the building up of 

 its carbon into organic compounds; it ends with the 

 oxidation of effete carbonaceous stuffs and the reappear- 

 ance of CO2. Both are used over and over again. 



