126 PLANKTON OF WISCONSIN LAKES 



dry material, with an average of 89.2 per cent for the eighteen samples. 

 The results for organic matter in 1916 are shown in figure 39, in 

 which the curve marked A indicates the quantity per cubic meter of 

 water in the various samples. This curve shows that there was a slight 

 decrease in the organic matter between May 24 and June 15; the 

 amount noted on the latter date was the smallest obtained in the various 

 samples from this lake. A small peak in July and another in August 

 represent moderate increases at these times, but the large increase came 

 during the latter part of September. The maximum point was reached 

 in the sample collected on October 2. The two samples collected later in 

 October showed a marked decline in the quantity of organic matter so 

 that the autumnal peak is sharp and prominent ; the amount was only 

 about 12.0 per cent larger on October 30 than on September 7. 



Nitrogen. The quantity of nitrogen was determined in all of the 

 samples of net plankton from Lake Waubesa. The percentage varied 

 from a minimum of 5.82 per cent in one sample collected in 1916 to a 

 maximum of 8.57 per cent in a catch obtained in 1913. The mean 

 percentages were substantially the same in 1915 and 1916, but that of 

 1913 was somewhat higher than the other two. (See table 38, p. 200.) 



A maximum of 343.7 milligrams of nitrogen per cubic meter of water 

 was noted in one of the 1915 samples and a minimum of 36.1 milligrams 

 in a 1916 catch. The smallest mean was found in the material collected 

 in 1916 and the largest in that of 1915, the latter being almost three 

 times as large as the former. 



The ratio of the quantity of organic matter to the quantity of total 

 nitrogen in the net plankton of Lake Waubesa ranged from 10.2 to 16.3, 

 these extremes being found in two samples collected in 1916, namely. 

 No. 6141 and No. 6117. (Table 47, p. 213.) These results show that 

 the net plankton of Lake Waubesa contained a smaller proportion of 

 nitrogen than that of Lake Monona, in which the ratio ranged from 8.5 

 to 14.6 ; in the net plankton of Lake Mendota the ratios showed a wider 

 variation, ranging from 8.7 to 17.4. 



Crude Protein. The nitrogen results are given in terms of crude 

 protein in table 39, p. 201 ; the first part of this table shows the varia- 

 tions in the percentage of crude protein in the organic matter, while 

 the second part gives the maximum and minimum quantities. The 

 maximum percentage, namely, 53.6 per cent of the organic matter, was 

 found in one of the samples collected in 1913, while the minimum was 

 noted in a sample collected on October 23, 1915, which contained 32.1 

 per cent of crude protein. 



The quantity of crude protein ranged from a minimum of 225.6 

 milligrams per cubic meter of water to a maximum of 2,148.1 milli- 

 grams ; the former was found in 1916 in sample No. 663 and the latter 



