134 PLANKTON OF WISCONSIN LAKES 



organic matter in milligrams per cubic meter of water in the various 

 samples and curve B indicates the amount of crude protein in this 

 material. That is, the space between the zero line and curve B shows 

 the proportion of crude protein, while the space between B and A rep- 

 resents the other constituents of the organic matter. With one excep- 

 tion the two curves possess a similar outline; during the second and 

 third weeks in July there is a decrease in the crude protein which is 

 correlated in time with a moderate increase in the organic matter. 



Ether Extract. The quantity of ether extract was determined in 

 twelve of the sixteen samples of nannoplankton from Lake Waubesa. 

 The percentage of extract varied from a minimum of 1.48 per cent to 

 a maximum of 8.13 per cent of the dry organic matter, almost a sixfold 

 difference. Both of these percentages were found in material collected 

 in 1916. (Table 42.) A much smaller range of variation was found in 

 the 1915 samples, the difference between maximum and minimum being 

 less than two per cent. The mean for the twelve samples on which de- 

 terminations were made, amounts to substantially four per cent of the 

 organic matter in these samples. 



The quantity of ether extract varied from 61.5 milligrams to 308.0 

 milligrams per cubic meter of water, with a mean of 121.0 milligrams 

 for the twelve samples. The mean quantity in the 1915 catches was 

 more than twice as large as that in the 1916 material. 



Pentosans. The pentosans were determined in the four samples col- 

 lected in 1915, but not in any of the catches made in 1916. In these 

 four samples the pentosans varied from 4.55 per cent to 6.72 per cent of 

 the dry organic matter. (See table 48, p. 214.) The quantity of pen- 

 tosans in this material ranged from a minimum of 193.0 milligrams to 

 a maximum of 346.0 milligrams per cubic meter of water ; the mean for 

 the four samples was 237.0 milligrams. 



Crude Fiber. Twelve samples of nannoplankton were analyzed for 

 the crude fiber. The percentage of this material in these samples varied 

 from a minimum of 0.83 per cent to a maximum of 10.43 per cent of 

 the organic matter ; the mean for all determinations was 4.45 per cent. 

 (Tables 25 and 48.) 



Quantitatively the amount ranged from 49.7 milligrams to 332.6 mil- 

 ligrams per cubic meter of water, with a mean of 135.5 milligrams. 

 The smallest quantity was found in sample No. 597 and the largest in 

 No. 6150. 



Nitrogen Free Extract. The chemical analyses were complete enough 

 to ascertain the percentage of nitrogen free extract in a dozen samples 

 of nannoplankton from Lake Waubesa. In these catches it ranged 

 from a minimum of 15.0 per cent in sample No. 666 to a maximum of 

 29.0 per cent of the dry weight of the material in sample No. 597, 



