RESPIRATION AND OXYGEN. 



Table 15. 



49 



When the CO2 ranged from 0.055 to 0.067 per cent in the open 

 lake, it varied from 0.066 to 0.084 per cent in a closed bay contain- 

 ing Caslalia, Potamogeton, and Carex. 



Bergmann (1921 : 50) has estabhshed a relation between the vari- 

 ation in carbon dioxid and oxygen-content of water and the condi- 

 tion of the sky. In one pond with clear water, Uttle vegetation, 

 and a white sandy bottom, the oxygen averaged 6.2 c.c. and the 

 carbon dioxid 0.46 c.c. on clear days, and 5.5 c.c. and 0.17 c.c. on 

 cloudy days. In one filled with vegetation and with a muck bot- 

 tom, the oxygen averaged 4.7 c.c. and the carbon dioxid, 0.7 c.c. on 

 clear days. In bog ditches the general average was about 4 c.c. of 

 oxygen on clear days and 5.1 of carbon dioxid on clear days, and 2.7 

 c.c. and 4.5 c.c. respectively on cloudy ones. Where algse and other 

 vegetation were present, as in the last two cases, there was a much 

 wider variation in the gas-content of the water between day and 

 night, or between clear and cloudy days. 



Summary. — Since the amount of oxygen in water is usually deter- 

 mined in cubic centimeters per liter or in percentages of saturation, 

 and the carbon dioxid often in parts per milhon, it is difficult to 

 estabhsh comparisons with soil-air. This is directly possible only 

 from the researches of Morren and Morren, who found the carbon 

 dioxid in the gas of a vivarium to vary from 1.27 to 24 per cent and 

 the oxygen from 18 to 60 per cent. The maximum amount of CO2 

 caused the death of animals and must have had a similar effect upon 

 the plants. Whipple and Parker stated that the amount of oxygen 

 varied from about 9 c.c. in midwinter to about 6 c.c. in midsummer, 

 which approximates saturation at both times. The water of ponds, 

 reservoirs and rivers is usually somewhere near saturation, and often 

 exceeds it. Tap-water is more rarely saturated, the averages being 

 61 and 85 per cent. Volk found the water of the Elbe to be generally 

 above saturation in September, the amount being greater in the 

 Upper than in the Lower Elbe. Birge and Juday noted 8 c.c. of 

 oxygen in the water of Lake Mendota at the spring overturn, and 

 from 5 to 8 c.c. in the surface 5 feet during June to September, the 

 surface itself often showing supersaturation. Chambers found 3.2 

 c.c. of oxygen in the water of a lagoon in June, and 7.8 c.c. in July, 

 while Bergman observed an average of 3.4 c.c. in bog water and of 

 7.4 c.c. in a lake fed by springs. Whipple and Parker obtained an 



