A UMNOLOGICAIv STUDY OF THF FINGER LAKES. 
585 
air it will be found to contain some free carbon dioxide. The amount, however, 
is small because it is absorbed only in proportion to its partial pressure. The decay of 
organic matter yields considerable carbon dioxide and, under favorable conditions, the 
water may become charged with fairly large amounts derived from this source. This 
is true especially of the bottom water. Spring waters are generally charged with free 
carbon dioxide, so that they contribute their quota. 
Fig, 15. — Dissolved gases, Cayuga Lake, Aug. ii, 1910. For 
explanation see fig. 9, p. 580. 
Fig. 16. — Dissolved gases, Owasco Lake, Aug. 13, 1910. For 
explanation see fig. 9, p. 380. 
The quantity of free carbon dioxide in the epilimnion is subject to variations. 
The water of this stratum is kept in circulation by the wind and this process tends to 
maintain a normal amount of this gas; but the quantity derived from the respiration 
and the decomposition which take place in this layer tends to raise it above the satu- 
ration point. On the other hand, this region is preeminently the zone of photosyn- 
thesis and in this process carbon dioxide is consumed and oxygen is liberated. When 
this stratum is fairly well stocked with chlorophyllous organisms and conditions are 
