SUMMARY AND DISCUSSION 143 



cubic meter of water) multiplied by the total volume of the lake (table 

 1) gives an average standing crop of 159 metric tons of dry organic 

 matter for the entire body of water. Since the lake has an area of 3,940 

 hectares, this crop amounts to a little more than 40 kilograms per hec- 

 tare, or 36 pounds per acre, when expressed in terms of a unit of sur- 

 face. The 84 net catches yield an average of just a little less than 42 

 kilograms of dry organic matter per hectare, or 37 pounds per acre. 



Lake Monona. The 47 catches of net plankton from Lake Monona 

 gave an average of 850 milligrams of organic matter per cubic meter 

 of water, or a little more than two and a half times as much as those of 

 Lake Mendota. In Lake Monona the amount ranged from a minimum 

 of 109 milligrams to a maximum of 3,306 milligrams per cubic meter. 

 No winter catches are included in this series so that the general average 

 may be somewhat higher than it would be if some winter catches had 

 been taken. On the other hand, it may be said that 111 net samples 

 from Lake Mendota taken during the same months of the same years as 

 the catches from Lake Monona yielded a smaller average than the com- 

 plete series of samples, or only 309 milligrams ^s compared with 332 

 milligrams per cubic meter of water. 



The nitrogen amounted to 9.36 per cent of the dry organic matter in 

 the net plankton of Lake Monona, the ether extract 6.02 per cent, the 

 pentosans 5.73 per cent, and the crude fiber 3.62 per cent. The per- 

 centages of nitrogen and pentosans are larger in the net material from 

 Lake Monona than in that from Lake Mendota, but the reverse is true 

 of the percentages of ether extract and crude fiber. The crude protein, 

 ether extract, pentosans, and crude fiber constitute 73.87 per cent of the 

 dry organic matter, leaving 26.13 per cent of undetermined nitrogen 

 free extract. (Table 25.) 



The 21 samples of net plankton from Lake Monona corresponding to 

 the same number of nannoplankton catches yielded a somewhat smaller 

 average amount of dry organic matter than the complete series of net 

 catches, namely, 813 milligrams per cubic meter of water. The per- 

 centages of nitrogen, ether extract, and pentosans are larger in this 

 material, but the percentage of crude fiber is smaller in the complete 

 series of net samples. 



The catches were taken in the deeper water of Lake Monona so that 

 the results may be stated in larger units for the area within the 20 

 meter contour line (see p. 122). The average quantity of dry organic 

 matter in the net plankton is 17.9 grams per square meter of surface for 

 this part of the lake, or 179 kilograms per hectare (160 pounds per 

 acre) for the whole series of net catches. The average is somewhat 

 smaller for the 21 samples corresponding to the nannoplankton series, 

 namely, 171 kilograms per hectare or 153 pounds per acre. The varia- 



