Lake Maxinkuckee, Physical and Biological Survey 105 



THE PLANKTON 



By CHANCEY JUDAY, University of Wisconsin 



Between the 2nd and the 29th of August, 1899, some observa- 

 tions were made on the plankton of Lake Maxinkuckee as a part 

 of the field investigations of the U. S. Fish Commission at that 

 lake. 



The net used in making the observations had an opening of 

 471.5 sq. cm. The filtering cone was made of Dufour's No. 20 

 bolting cloth. The area of the cone was 3,910 sq. cm., thus making 

 the ratio of the opening of the net to filtering area 1 to 8.2. Lack 

 of time prevented experiments for the determination of the coeffi- 

 cient of the net, as the plankton work was only one of several 

 duties assigned the writer. 



Three main stations were selected. No. I was located just 

 north of the center of the lake in the deepest part. No. II was in 

 the southwestern part in a small basin called the Kettlehole. This 

 basin has a maximum depth of 43 feet (12.8m.) and is separated 

 from the main basin of the lake by a considerable area where the 

 water scarcely exceeds 10 feet (3m.) in depth. During the time 

 of these observations, the bottom temperature in the Kettlehole 

 was lower than the bottom temperature in the deepest part of the 

 lake. This was selected for the purpose of determining whether 

 these local peculiarities would have any marked effect on the quan- 

 tity of plankton. No. Ill was about midway between the other 

 two stations in water only 20 feet (6m.) deep. For purposes of 

 comparison in horizontal distribution, one series of hauls was 

 made at each of five other stations. 



In making the hauls, the net was lowered to the desired depth 

 and then raised to the surface with a velocity as nearly uniform 

 as possible. The material was washed into the bucket of the net 

 and then transferred to 95 per cent, alcohol. 



Because of the small amount of time available for this work,' 

 the centrifuge method was used in measuring the quantity of 

 plankton. This method, however, is open to the serious objection 

 that the material is treated as if it were a homogeneous mass, and 

 this is obviously not the case. This same objection applies equally 

 to the gravity method, in which the material is allowed to settle 

 a certain number of hours. Both must be supplemented by the 

 counting method in order to show the part played by each species 

 in the plankton life of a body of water. In settling the material, 

 the centrifuge was given a speed of 3,000 revolutions per minute 

 and this speed was continued for a period of one minute. 



