I 



PLANKTON OF LAKE MONONA iq? 



fall below 10.0 per cent of the organic matter, while it reached or ex- 

 ceeded this percentage in but one sample collected in the other years. 



Crude protein. The results for crude protein are shown in table 

 31, p. 198. The highest percentages for the different years varied from 

 60.4 per cent in 1912 to 73.2 per cent in 1915, a difference of approxi- 

 mately 13.0 per cent ; the minima ranged from 42.7 per cent in 1911 to 

 62.6 per cent in 1915, a difference of almost 20.0 per cent. With the 

 exception of 1915 the range of variation in the mean is less than 5.0 

 per cent; the mean percentage of 1915, however, is from 9.5 per cent 

 to 13.1 per cent higher than those of the other years. This is a smaller 

 range of variation than in the net plankton from Lake Mendota where 

 there is a difference of 15.1 per cent in the mean percentages of the 

 different years. In general the net plankton of Lake Monona has a 

 distinctly higher percentage of crude protein than that of Lake Men- 

 dota. Only three of the annual means for Lake Mendota exceed the 

 minimum for Lake Monona. (See table 7, p. 187.) The mean per- 

 centage of crude protein in the 41 samples from Lake Monona, on which 

 nitrogen determinations were made, is 56.4 per cent, while that for 166 

 samples from Lake Mendota is 52.4 per cent, just 4.0 per cent smaller. 



The largest amount of crude protein was found in 1912, namely, 

 1,888.7 milligrams per cubic meter of water and the smallest amount 

 in 1911, or 112.5 milligrams. The latter year also yielded the smallest 

 mean of the five years in which observations were made on Lake 

 Monona. 



Ether extract. The percentage of ether extract in the net plankton 

 ranged from a minimum of 2.79 per cent in sample No. 330, July 30, 

 1913, to a maximum of 11.16 per cent of the organic matter in sample 

 No. 659, June 23, 1916. (Table 45.) The mean percentages for the 

 different years fall between 4.77 per cent and 9.62 per cent. The mean 

 for the 35 determinations is 7.23 per cent. This percentage is much 

 lower than that of the net plankton of Lake Mendota ; the highest mean 

 of Lake Monona, 9.62 per cent, is distinctly lower than the lowest mean 

 for the various years on Lake Mendota, namely, 11.27 per cent. (See 

 table 32, p. 199.) 



The amount of ether extract per cubic meter of water varied from 

 a minimum of 12.6 milligrams in sample No. 114, July 27, 1911, to a 

 maximum of 171.8 milligrams in sample No. 5167, October 15, 1915. 

 The mean quantities for the different years ranged from 27.5 milli- 

 grams in 1911 to 105.6 milligrams in 1916. Only two determinations 

 were made on the samples collected in 1916 and they were made on 

 samples which contained a large amount of organic matter, so that they 

 cannot be regarded as representative of the whole series of net catches 

 obtained in 1916. The mean quantity for the 35 determinations on 



