PLANKTON OF LAKE MONONA 117 



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

 amount of the ether extract varied from 47.9 miligrams to 201.5 milli- 

 grams in 1915, with a mean of 125.9 milligrams, and from 51.8 milli- 

 grams to 154.2 milligrams in 1916, with a mean of 95.5 milligrams. 

 Thus, the average amount was slightly more than 30.0 milligrams per 

 cubic meter of water larger in 1915 than in 1916. 



Pentosans. Only four samples were analyzed for the pentosans, all 

 collected in 1915. (See table 46, p. 212.) The average amount in these 

 four samples was 140.4 milligrams per cubic meter of water, which was 

 4.36 per cent of the organic matter in these samples. 



Crude Fiber. Quantitative determinations of the crude fiber were 

 made on six samples collected in 1915 and on five obtained in 1916. In 

 the former year the average amount was 57.2 milligrams per cubic 

 meter of water, which was 2.23 per cent of the organic matter in these 

 samples. (See table 46.) The five samples of 1916 yielded an average 

 of 126.7 milligrams of crude fiber per cubic meter of water, or a little 

 more than twice as much as was found in 1915 ; this was 10.0 per cent 

 of the organic matter in these five samples. 



Nitrogen Free Extract. The crude protein, ether extract, crude 

 fiber, and ash were all determined for only 11 of the 21 samples of nan- 

 noplankton from Lake Monona. In these samples the four items con- 

 stituted from 77.0 per cent to almost 86.0 per cent of the dry weight of 

 the material, leaving only 14.0 per cent to 23.0 per cent for the nitrogen 

 free extract. This is a much smaller range of variation than was noted 

 for the net plankton, in which the maximum percentage of nitrogen 

 free extract was approximately 49.0 per cent, with a minimum of 

 about 15.0 per cent. 



Ash. In general the percentage of ash was not as high in the centri- 

 fuge material from Lake Monona as in that from Lake Mendota. In 

 the former lake the ash averaged about 49.0 per cent of the dry material 

 which was obtained with the centrifuge, while in the latter lake the 

 average was about 56.0 per cent. In Lake Monona the ash varied from 

 a minimum of slightly less than 29.0 per cent to a maximum of almost 

 67.0 per cent. (See table 46.) Both of these percentages are smaller 

 than the maximum and minimum of Lake Mendota (table 44). The 

 average percentage of ash was somewhat smaller in the catches obtained 

 from Lake Monona in 1915 than in those collected in 1916, because the 

 bowl water was added to the samples of the latter year. Thus, in the 

 former year, the ash was derived from the plankton organisms and from 

 the silt which was removed from the water by the centrifuge, while 

 in the latter year there was an additional source, namely, the bowl 

 water. 



