PLANKTON OF LAKE MONONA 121 



In 1915 the organic matter of tlie total plajikton of Lake Monona 

 ranged from a minimum of 1,127.0 milligrams per cubic meter of water 

 in samples No. 563 and No. 564 to a maximum of 5,908.3 milligrams in 

 samples No. 5166 and No. 5167. (Tables 45 and 46.) In 1916 the mini- 

 mum amount of organic matter in the total plankton was 926.2 milli- 

 grams per cubic meter of water in samples No. 648 and No. 649 and the 

 maximum quantity was 6,088.8 milligrams in samples No. 6158 and No. 

 6159. In the former year the variation in quantity was somewhat more 

 than fivefold and it was almost sevenfold in the latter year. The 

 minimum amount of organic matter in the total plankton was much 

 smaller in 1916 than in 1915, but the maximum quantity was somewhat 

 larger in the former year. 



The above quantities indicate only the dry weight of the organic mat- 

 ter ; the live weight would be approximately ten times as much. Thus, 

 the live weight of the organic matter in the total plankton obtained 

 on October 12, 1916, samples No. 6158 and No. 6159, for example, was 

 approximately 61 grams per cubic meter of water. The total live 

 weight of these organisms would include the ash also. 



Table 25 shows the mean quantity and the chemical composition of 

 the net plankton and the nannoplankton of Lake Monona. The 47 sam- 

 ples of net plankton yielded an average of 850.2 milligrams of dry or- 

 ganic matter per cubic meter of water. This material contained 497.5 

 milligrams of crude protein, 51.2 milligrams of ether extract, 48.7 

 milligrams of pentosans, and 30.8 milligrams of crude fiber. The crude 

 protein, ether extract, and crude fiber made up 579.5 milligrams, or 

 68.2 per cent, of the organic matter. The remainder of the organic 

 matter, 31.8 per cent, constituted the nitrogen free extract. 



The 21 samples of net plankton obtained in 1915 and in 1916, which 

 correspond to the nannoplankton catches, yielded a smaller mean quan- 

 tity of dry organic matter than the whole series of samples, namely, 

 only 813.8 milligrams per cubic meter. The proportion of crude pro- 

 tein, ether extract, and pentosans was somewhat larger in these 21 

 samples than in the complete series; the crude protein, ether extract, 

 and crude fiber amounted to 594.0 milligrams in the former, or sub- 

 stantially 73.0 per cent of the mean quantity of organic matter in these 

 catches. These three items, therefore, constituted 4.8 per cent more of 

 the organic matter in the 21 samples of net plankton than they did in 

 the 47 samples. Thus, the nitrogen free extract in the former amounted 

 to 27.0 per cent of the organic matter as compared with 31.8 per cent 

 in the latter. 



The nannoplankton material gave an average of 2,350.0 milligrams 

 of dry organic matter per cubic meter of water and this contained 

 1,310.0 milligrams of crude protein, 113.3 milligrams of ether extract, 



