81 



Lakes, determiuecl that the vast amouut of algai collecting at the top of the 

 thermoclme, at certain times, so increased the process of photosynthesis, 

 that 300 per cent, oxygen saturation occurred. It is also to be remembered 

 that the lowering of the thermocline in August increased the depth of the 

 epilimnion one meter. 



Four factors must be taken into consideration in accounting for the 

 rapid decrease of organisms below the epilimnion : First, the lower temper- 

 ature (20° C. at the top of the thermocline and 9.6° C. at the bottom during 

 July, 21.1° C. and 10.7° C. respectively being the average temperatures for 

 August) ; second, the decrease in the amount of oxygen from 4.25 c. c. per 

 liter of water at six meters to 2.50 c. c. at the bottom of the thermocline ; 

 third, the decrease in the amount of food; and. fourth, the limited .-imonnt 

 of sunlight. 



In the hypolimnion the jihysicnl cdnditious were so uniform that the 

 lilanktoii was very evenly dislrilmted in this stratnui. 



SEASONAL DISTRIBUTION OF THE PLANKTON. 



Six weeks is too short a time to olitaln results of much value concern- 

 ing seasonal distribution. However, the data collected indicate the follow- 

 ing facts : The plankton, as a whole, increased in amount in August. Cerd 

 tium, Fragilaria, Microcystis, and Lynr/hya increased gradually to August 

 13th, the date of the last observation. Diaptomus reached its maximum 

 August 1st; Nauplii and Aiiahaciui on August 8th. The Cladocera and JRo- 

 tifcra increased rather suddenly in August and were most numerous on the 

 date of the last collection. 



THE EFFECTS OF WIND UPON DISTRIBUTION. 



As mentioned earlier in this paper, six stations were established to de- 

 termine whether or not the plankton of the whole lake at a given level was 

 homogeneous at all times. Repeated catches at different stations under ordi- 

 nary conditions Indicate that the plankton at the different levels was uni- 

 form. 



SUMMARY. 



Oxygen sufficient for respii'ation occurs at all levels of the lake, and 

 probably is not a limiting factor. 



Carbon dioxide was present in sutficient quantities for photosynthesis. 



6—1019 



