PLANKTON OF LAKES WAUBESA AND KEGONSA 137 



trif uge catch ; several other forms, however, showed a marked increase 

 in number at this time and these increases together with that of Aphano- 

 capsa were sufficient to yield a maximum of organic matter. 



The number of forms represented in the centrifuge material from 

 Lake Waubesa in 1916 increased as the season advanced, just as noted 

 in Lake Monona. On May 24, for example, ten different forms were 

 present in the centrifuge catch, and the number varied from seven to 

 ten until July 25, when it rose to fifteen. In the catch taken on Sep- 

 tember 19, the various forms number twenty and a maximum of twenty- 

 five was found on October 30. 



Total Plankton of Lake Waubesa 



In the 18 samples of net plankton from Lake Waubesa, the dry or- 

 ganic matter varied from a minimum of 471.1 milligrams to a maximum 

 of 4,232.5 milligrams per cubic meter of water, almost a tenfold varia- 

 tion in quantity. The whole series of net catches yielded an average of 

 1,665.8 milligrams of organic matter per cubic meter of water, of which 

 785.0 milligrams consisted of crude protein, 115.8 milligrams of ether 

 extract, 98.3 milligrams of pentosans, and 78.3 milligrams of crude fiber. 

 (Table 25.) The crude protein, ether extract, and crude fiber amounted 

 to 979.1 milligrams per cubic meter of water, or 58.7 per cent of the 

 organic matter. This leaves an average of 41.3 per cent of the organic 

 matter as nitrogen free extract. 



In the 16 samples of net plankton corresponding to the same number 

 of samples of nannoplankton, the mean quantity of organic matter was 

 somewhat smaller than in the entire series of net catches, namely 1,639.2 

 milligrams per cubic meter of water. In this material the crude pro- 

 tein, ether extract, and crude fiber made up 56.9 per cent of the organic 

 matter, leaving 43.1 per cent of nitrogen free extract. The latter is 

 nearly two per cent larger in these samples than in the complete series. 



The organic matter of the nannoplankton varied from a minimum 

 of 801.0 milligrams to a maximum of 6,143.2 milligrams per cubic meter 

 of water. The mean quantity for the 16 samples was 3,299.1 milli- 

 grams, of which 1,635.0 consisted of crude protein, 132.0 milligrams of 

 ether extract, 183.1 milligrams of pentosans, and 146.8 milligrams of 

 crude fiber. The crude protein, ether extract, and crude fiber accounted 

 for 1,913.8 milligrams, or 58.0 per cent of the organic matter; this 

 leaves 42.0 per cent of the organic matter in the nannoplankton of Lake 

 Waubesa as nitrogen free extract. The percentage of extract is a little 

 larger in the net plankton than in the nannoplankton. 



The quantity of dry organic matter in two net samples from Lake 

 Waubesa, No. 598 and No. 5129, was larger than that in the correspond- 

 ing samples of nannoplankton. No. 597 and No. 5128. (Tables 47 and 



