116 



PLANKTON OF WISCONSIN LAKES 



52O0 



4800 



^OOO 



SdOO 



2000 



eoo 



Fig. 38. — The quantity of organic matter and of crude protein in the nanno- 

 plankton of Lake Monona in 1916. Curve A represents the dry organic 

 matter and curve B the crude protein. The amounts are indicated in milli- 

 grams per cubic meter of water. 



Ether Extract. Determinations of the ether extract were made on 

 seven of the eight samples collected in 1915 and on nine of those ob- 

 tained in 1916. In the former year the percentage of the extract varied 

 from 3.34 per cent to 6.27 per cent of the organic matter, with a mean 

 of 4.90 per cent. (See table 36, p. 200.) In 1916 there was a greater 

 range of variation in percentage, namely, from 2.00 per cent to 9.50 per 

 cent, but the mean was substantially the same as that in the previous 

 year, that is, 4.75 per cent. 



