A UMNOLOGICAIy STUDY OF THE FINGER LAKES. 
587 
favorable for their activities, the demand for carbon dioxide exceeds the supply of free 
gas and some of the half-bound carbon dioxide is consumed. This makes the water 
alkaline to phenolphthalein, since it leaves an excess of normal carbonate. The degree 
of alkalinity is measured by the amount of carbon dioxide that would be required to 
convert this normal carbonate to bicarbonate, and it is dependent upon several factors, 
chief among which are the free exposure to the atmosphere, decomposition, respira- 
tion, the abundance and activity of the algae, and the weather conditions. Thus it 
will be seen that the status of the carbon dioxide in the epilimnion is the resultant of 
the activities of those agents which furnish a supply to this stratum and those which 
consume this gas. 
The epilimnion in all of the Finger Lakes was alkaline, thus showing that not only 
the free, but also some of the half-bound carbon dioxide, had been consumed by the 
chlorophyl-bearing organisms. (See table xviii, p. 602, and fig. 9-18.) The degree of 
alkalinity varied in the different lakes, ranging from a minimum of about 0.5 cc. in 
Canadice Lake to a maximum of 3.0 cc. in Canandaigua Lake; in five lakes the average 
amount was about 2.5 cc. In the carbon dioxide curves the alkaline stratum is indi- 
cated by that portion which lies to the left of the zero line and the degree of alkalinity 
is shown by the quantity of carbon dioxide required to make the water neutral. 
The free carbon dioxide content of the thermocline depends upon the conditions 
which are found there for photosynthesis. In some lakes this stratum lies so near the 
surface that light conditions are favorable for this process and in such cases not only 
the free, but a large portion of the half-bound carbon dioxide may be removed by chloro- 
phyllous organisms, thus making the stratum strongly alkaline. But in a large majority 
of cases conditions in this stratum are not favorable for photosynthesis and the water 
contains free carbon dioxide. This was true of all of the Finger Lakes. 
The hypolimnion is a zone of decomposition, so that its water generally contains 
an abundance of free carbon dioxide. In the process of respiration also a certain 
amount of this gas is contributed to the water and some may reach this stratum from 
underground waters. The largest amount is found at the bottom of the lake, where 
decomposition is greatest owing to the presence of a large amount of organic material. 
The maximum quantity found in the bottom waters of the Finger Lakes varied from 
i.o cc. per liter in Cayuga Lake to 7.1 cc. in Hemlock Lake. 
PLANKTON. 
Methods of observation . — Plankton catches were obtained in the Finger Lakes at the 
same time that samples of water were procured. They were made either by means of a 
pump and hose or with a vertical closing net. The former method was used at all 
depths in Canadice, Conesus, and Hemlock Lakes, and in the upper 30 meters and 50 
meters, respectively, of Cayuga and Seneca Lakes, while the latter method was employed 
below these depths in the last two lakes and at all depths in the other five lakes. For 
the purpose of counting, a catch was diluted to 10 cc., of which 2 cc. were removed 
with a “stempel” pipette, and the Crustacea and rotifers therein were counted. When 
