PLANKTON OF LAKES WAUBESA AND KEGONSA 127 



in 1915 in sample No. 5129. The latter is almost ten times as large as 

 the former. The mean quantity for the entire series of eighteen sam- 

 ples is 785.6 milligrams, which is 47.1 per cent of the average amount of 

 organic matter. This percentage of crude protein is much lower than 

 the means for the net plankton of Lakes Mendota and Monona; the 

 mean for the former is 52.3 per cent and for the latter 58.5 per cent. 

 (See table 25.) This indicates that the net plankton of Lake Waubesa 

 contains a smaller proportion of nitrogenous material than either of the 

 other lakes. Both the maximum and the minimum percentages of crude 

 protein are smaller in Waubesa also than in the other two lakes. 

 (Tables 8 and 31.) 



Ether Extract. The ether extract was determined in twelve of the 

 net plankton samples from Lake Waubesa, namely, the two obtained 

 in 1913, four in 1915, and six in 1916. (See table 47.) The extract 

 varied from a minimum of 2.81 per cent of the organic matter to a 

 maximum of 8.82 per cent, with a mean of 4.64 per cent. The quantity 

 of the extract ranged from 50.0 milligrams to 295.2 milligrams per cubic 

 meter of water, almost a sixfold difference. The average for the twelve 

 determinations is 115.8 milligrams per cubic meter of water. 



Pentosans. The pentosans were determined in six samples of the net 

 plankton from Lake Waubesa. The percentage ranged from 4.05 per 

 cent to 6.77 per cent of the organic matter in these samples ; the mean 

 is 5.90 per cent. The quantity varied from 75.9 milligrams to 264.5 

 milligrams per cubic meter of water, representing more than a threefold 

 variation. The mean quantity for the six determinations is 163.5 milli- 

 grams. J 



Crude Fiber. The amount of crude fiber was ascertained in ten 

 samples. In these catches the crude fiber varied from a minimum of 

 1.82 per cent to a maximum of 10.18 per cent of the organic matter, the 

 mean being 4.70 per cent. The quantity ranged from 17.9 milligrams 

 to 189.6 milligrams per cubic meter of water, thus showing more than 

 a tenfold difference. 



Nitrogen Free Extract. The crude protein, ether extract, crude 

 fiber, and ash were all determined for ten of the eighteen samples of 

 net plankton from Lake Waubesa and together these four items consti- 

 tuted from 53.8 per cent of the dry material in sample No. 691 to 73.5 

 per cent in sample No. 6175. Deducting these percentages from 100 

 leaves a minimum of 26.5 per cent and a maximum of 46.2 per cent for 

 the nitrogen free extract; this is less than a twofold variation in the 

 percentage of the nitrogen free extract. The range of variation in the 

 nitrogen free extract in the net plankton of Lake Monona was much 

 greater, ranging from 15.0 per cent to 49.0 per cent. 



