36 



PLANKTON OF WISCONSIN LAKES 



The first part of table 8 indicates some of the general relations of 

 the quantity of crude protein to the quantity of organic matter. It 

 shows the maximum, minimum, and mean percentages of the former in 

 the latter. It will be noted that the amount of crude protein fell as low 

 as 34.5 per cent of the organic matter and it reached a maximum of 70.0 

 per cent, thus giving slightly more than a twofold variation. The seven 

 maxima range from 56.2 per cent to 70.0 per cent, a difference of 13.8 

 per cent, while the minima vary from 34.5 per cent to 52.6 per cent, 

 a difference of 18.1 per cent ; the mean percentages show a variation of 

 15.1 per cent. The organic matter contained the lowest percentage of 

 crude protein in 1912 and the highest in 1913 ; the highest mean per- 

 centage was found in 1915. The high mean percentage of 1915 is ac- 

 counted for by the fact that the crude protein fell below 50.0 per cent 

 of the organic matter in only four of the 34 samples obtained in this 

 year. 



Nitrogen determinations were made on 166 samples and, in this num- 

 ber, the crude protein constituted from 45.0 per cent to 60.0 per cent 

 of the organic matter in 123 samples ; that is, the proportion of crude 

 protein in the organic matter does not vary more than 15.0 per cent in 

 about three-quarters of the samples. Lowering the minimum to 40.0 

 per cent adds 16 more samples to this list. 



The ratio of the crude protein to the organic matter is shown graph- 

 ically in figures 11 to 14, inclusive. The curves marked A in these dia- 

 grams represent the organic matter and those marked B the crude pro- 



-400 



300 



2O0 



too 



Fig. 11. — The amount of dry organic matter, of crude protein and of ether 

 extract in the net plankton of Lake Mendota in 1911. Curve A represents 

 the organic matter, curve B the crude protein and curve C the ether 

 extract. The curves show the number of milligrams per cubic meter of water. 



