81 



Lakes, determiued that the vast amount of algse collecting at the top of the 

 thermoeliue, 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 dviring 

 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 amount 

 of sunlight. 



In the hypdiimnion the ]>hysical conditions were so uniform that the 

 l-.lankt()n was very evenly distributed in this stratum. 



SEASONAL DISTRIBUTIOX OF THE PLANKTON. 



Six weeks is too .short a time to obtain 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. Cera 

 Hum, Fragilaria, Microcystis, and Lynghya increased gradually to August 

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

 August 1st; Nauplii and Anahacna on August 8th. The Clatloccra and Ro- 

 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 respiration occurs at all levels of the lake, and 

 probably is not a limiting factor. 



Carbon dioxide was present in sufticient quantities for photosynthesis. 



6—1019 



