A lylMNOIvOGICAIv STUDY OF THE FINGER LAKES. 
589 
Some of the plankton algae appear to be able to live saprophytically, and such forms 
could maintain themselves in this manner in the deeper water. Oscillatoria seems to 
show this tendency most frequently, and one of its usual distributions was shown in 
Keuka Lake, where the maximum number was found in the 15-20 meter stratum. (See 
table XIX, p. 606.) In general, however, the presence of large numbers of phytoplank- 
tonts below the thermocline is to be regarded as an indication of their senility. 
The curves for zooplankton show two general types of vertical distribution. In one 
type the lower, as well as the upper, strata of the lake are well populated, as in Canadice 
and Hemlock Lakes (fig. 18, 19). A similar distribution was noted also in Keuka and 
Fig. 20. — Vertical distribution of plankton organisms in Hemlock Lake, Aug. 23, 1910. Scale, i vertical space=i meter; i hori- 
zontal space=5 Crustacea, nauplii, and rotifers per liter of water and 150 algae and diatoms. Predominant forms: Diapiomus, 
Ceratium, Coelosphasrium, and Aslertonella. The column at the right marked O shows the quantity of dissolved oxygen at 
the various depths as indicated, and T represents the temperature. 
Owasco Lakes. All of the various forms of plankton animals were not distributed 
throughout the depth of these lakes, since some of them habitually occupy the warmer 
water of the epilimnion, while others are confined chiefly to the thermocline and the 
hypolimnion. In the latter stratum the crustacean population consisted almost entirely 
of Diaptomus and Cyclops and their nauplii, while Polyarthra platyptera had the widest 
vertical distribution among the rotifers. In general, the forms which have a wide 
vertical distribution reach their maximum numbers either in the upper or the middle 
strata of the lake. The presence of a fairly large population in the lower water is 
dependent upon two factors, viz, an adequate amount of both dissolved oxygen and food 
60289° — Bull. 32 — 14 38 
