138 PLANKTON OF WISCONSIN LAKES 



48.) In net sample No. 598 the organic matter was about 17.0 per cent 

 larger than in nannoplankton sample No. 597, while nannoplankton 

 sample No. 5129 yielded only about two-thirds as much organic matter 

 as net sample No. 5128. Four net samples from Lake Monona also 

 yielded a larger amount of organic matter than the corresponding nan- 

 noplankton samples, which makes a total of six sets of catches showing 

 this phenomenon. All of the nannoplankton samples from Lake Men- 

 dota yielded a larger amount of organic matter than the corresponding 

 net samples. 



In the four sets of samples that were obtained in Lake Waubesa in 

 1915, the dry organic matter of the total plankton ranged between a 

 minimum of 6,538.0 milligrams in samples No. 5174 and No. 5175 and a 

 maximum of 9,489.7 milligrams in samples No. 5152 and No. 5153. 

 (Tables 47 and 48.) In 1916 the quantity varied from 1,272.1 milli- 

 grams in samples No. 650 and No. 651 to 6,378.3 milligrams per cubic 

 meter of water in samples No. 6150 and No. 6151 ; this represents a five- 

 fold variation in the quantity of organic matter obtained in the sam- 

 ples of this year. The maximum amount was found on the same date in 

 both years, October 2, but the maximum for 1915 was almost one and 

 a half times as large as that of 1916. The dry organic matter con- 

 stitutes only about one-tenth of the weight of the living organic matter 

 because most of the organisms in the plankton contain at least 90.0 per 

 cent of water in the living state ; the 1915 maximum, therefore, repre- 

 sents approximately 95 grams of living organic material per cubic meter 

 of water. 



The Waubesa maximum of dry organic matter in the total plankton 

 noted in 1915 was not only the largest for this lake, but it was also 

 much larger than the maxima for Lakes Mendota and Monona. It was 

 a little more than one and a half times the maximum of Lake Monona, 

 6,088.8 milligrams per cubic meter of water, and almost three times as 

 large as that of Lake Mendota, which was 3,327.3 milligrams per cubic 

 meter. The minimum amount of organic matter in the total plankton 

 of Lake Waubesa, 1,272.1 milligrams per cubic meter of water, was 

 about one-third larger than the minimum of Lake Mendota, 906.0 milli- 

 grams, and also about a third larger than the minimum of Lake Monona, 

 926.2 milligrams. 



The mean quantity of organic matter in the total plankton of Lake 

 Waubesa amounted to 4,938.3 milligrams per cubic meter of water. 

 (Table 25.) This material contained 2,401.2 milligrams of crude pro- 

 tein, 227.5 milligrams of ether extract, 284.7 milligrams of pentosans, 

 and 218.1 milligrams of crude fiber. The crude protein, ether extract, 

 and crude fiber amounted to 2,846.8 milligrams, or 57.6 per cent of the 

 organic matter ; this leaves 42.4 per cent of the organic matter as nitro- 

 gen free extract. 



