122 PLANKTON OF WISCONSIN LAKES 



102.5 milligrams of pentosans, and 111.8 milligrams of crude fiber. To- 

 gether the crude protein, ether extract, and crude fiber make up 1,535.1 

 milligrams, or 65.3 per cent of the organic matter in the nannoplankton 

 material. This leaves 34.7 per cent of the organic matter to be classed 

 as nitrogen free extract, which is a larger percentage than that noted 

 in the net plankton. 



The total plankton yielded 3,163.8 milligrams of dry organic matter 

 per cubic meter of water in Lake Monona. This material contained an 

 average of 1,821.2 milligrams of crude protein, 170.3 milligrams of 

 ether extract, 150.1 milligrams of pentosans, and 137.6 milligrams of 

 crude fiber. The crude protein, ether extract, and crude fiber made up 

 2,129.1 milligrams of the organic matter, or 67.3 per cent, thus leaving 

 32.7 per cent of the organic matter as nitrogen free extract. 



Organic Matter per Unit op Area 



The plankton material from Lake Monona was obtained regularly 

 from the deeper portion of the lake, that is, where the water reaches a 

 depth of 20 meters to 22.5 meters, the latter being the maximum depth, 

 and the samples of water from which the material was secured covered 

 the lake down to a depth of 18 meters to 20 meters each time. This 

 plankton material, then, represents the deeper part of the lake and the 

 results may, therefore, be compared with similar ones obtained on Lake 

 Mendota. 



The 20 meter contour line of Lake Monona bounds an area of 56,700 

 square meters and the volume of water down to this depth is 1,134,000 

 cubic meters ; between 20 meters and 22.5 meters the volume is 59,000 

 cubic meters, thus making a total of 1,193,000 cubic meters. From this 

 volume and the monthly averages of the organic matter in the total 

 plankton for the two years 1915 and 1916 combined, the results shown 

 in the first part of table 37 (p. 200) have been obtained. The results 

 given for the months of May and November are based on a single set of 

 observations in each of these months, but the other months indicated in 

 the table are represented by three or four sets of observations. 



This table shows a smaller quantity of organic matter in the total 

 plankton in May than in June, while the smallest average was found in 

 July. The August and September averages show a marked increase 

 leading up to the maximum quantity in October. The single set of 

 observations taken in November yielded only a little more than half 

 as much organic matter as the average for October. The October maxi- 

 mum is almost four times as large as the July minimum. 



The amount of organic matter in the total plankton of Lake Monona 

 was smaller in the months of May and July than in the corresponding 

 months in Lake Mendota, but it was larger in the other months. The 



