132 PLANKTON OF WISCONSIN LAKES 



minimum in the former year was 2.90 per cent and in the latter year 

 3.91 per cent, so that there was not as large a variation in the percent- 

 age of nitrogen in the centrifuge material from Lake Waubesa as in 

 that from Lakes Mendota and Monona. (See table 18, p. 192 and table 

 34, p. 199.) 



When expressed in terms of milligrams per cubic meter of water, the 

 quantities of nitrogen were much higher in 1915 than in 1916 ; the mean 

 for the former year was more than one and a half times as large as that 

 for the latter. In 1915 the maximum quantity of nitrogen was two 

 and a half times as large as the minimum, but in 1916 there was an 

 eightfold difference between the maximum and the minimum amounts. 



The nannoplankton of Lake Waubesa showed almost a twofold varia- 

 tion in the ratio of the organic matter to the total nitrogen, ranging 

 from 9.9 to 18.7; this range was larger than that noted for the net 

 plankton. (See table 47.) It is a smaller difference than that noted 

 for the nannoplankton of Lake Monona in which the limits were 8.1 

 and 27.9 ; it is smaller, also, than in the nannoplankton material from 

 Lake Mendota which varied from 9.1 to 23.5. These results also show 

 that the proportion of nitrogen in the organic matter had the widest 

 range of variation in the net plankton of Lake Mendota, while the ma- 

 terial from Lakes Monona and Waubesa possessed the same range, with 

 a larger proportion of nitrogen in the former lake. In the nanno- 

 plankton, however, the proportion was muck more constant in the ma- 

 terial from Lake Waubesa than in that from the other two lakes ; the 

 largest variation was noted in the nannoplankton of Lake Monona. 



Crude Protein. The nitrogen results are summarized in terms of 

 crude protein in table 41 ; the first part of this table shows the varia- 

 tions in the percentage and the second part the changes in the quantity. 

 There was a much larger proportion of crude protein in the material 

 collected in 1915 than in that secured in 1916 ; in the former year the 

 percentage of crude protein in the nannoplankton ranged from a mini- 

 mum of 44.4 per cent of the organic matter to a maximum of 62.5 

 per cent, with a mean of 56.4 per cent for the four catches obtained in 

 this year. In 1916 the extremes were 33.5 per cent and 57.9 per cent, 

 with a mean of 46.3 per cent for the twelve samples of this year ; thus, 

 the mean for 1916 was 10.0 per cent below that of 1915. The crude pro- 

 tein fell below 50.0 per cent of the organic matter in only one of the 

 four samples of 1915, but it reached or exceeded this amount in only 

 one of the dozen catches made in 1916. In two samples secured in 1916 

 the crude protein fell below 40.0 per cent of the dry organic matter. 



The quantity of crude protein varied from a minimum of 1,361.9 mil- 

 ligrams per cubic meter of water to a maximum of 3,471.9 milligrams 

 in the 1915 samples of nannoplankton from Lake Waubesa, while in 



