108 PLANKTON OF WISCONSIN LAKES 



Lake Monona material is 61.5 milligrams per cubic meter of water. 

 This average is about one and a half times as large as that of the net 

 plankton of Lake Mendota ; while the percentage of ether extract aver- 

 ages lower in the material from the former than in that from the 

 latter lake, the amount per cubic meter of water is greater in Lake 

 Monona because th<? quantity of organic matter is much larger than 

 in Lake Mendota. 



Pentosans. The pentosans were determined for only 20 samples of 

 net plankton from Lake Monona and 13 of these were on material col- 

 lected in 1913; therefore, no comparisons of the different years can 

 be made. (See general table No. 45). In the 20 samples on which 

 determinations were made the percentage of the pentosans varied from 

 a minimum of 3.07 per cent to a maximum of 10.6 per cent. The latter 

 was found in sample No. 345, August 27, 1913, which contained a large 

 amount of Microcystis ; this form, in fact, constituted by far the greater 

 part of the net material. The average percentage for the 20 samples 

 on which determinations were made, amounted to 8.23 per cent of the 

 organic matter as compared with an average of 3.5 per cent for 92 

 analyses of material from Lake Mendota. 



The quantity of pentosans varied from a minimum of 11.2 milligrams 

 per cubic meter of water to a maximum of 228.3 milligrams. The 

 latter was found in sample No. 238, October 15, 1912; this sample 

 contained a larger amount of organic matter than usual and it con- 

 tained very large numbers of Microcystis and Melosira. The 20 

 analyses of material from Lake Monona yielded an average of 70.0 

 milligrams per cubic meter of water, while the material from Lake 

 Mendota gave an average of 11.7 milligrams for 92 samples, a sixfold 

 difference. 



Crude Fiber. The crude fiber was determined for 26 samples of net 

 plankton from Lake Monona; 16 of the catches belonged to the series 

 obtained in 1913. In general the percentage of crude fiber was com- 

 paratively low; it ranged from a minimum of 1.56 per cent of the 

 organic matter in sample No. 340, August 20, 1913, to a maximum of 

 9.74 per cent in No. 308, May 30 and June 4, 1913. The average for 

 all of the analyses was 5.0 per cent as compared with an average of 6.82 

 per cent for the net plankton of Lake Mendota. 



The quantity of crude fiber in the net plankton of Lake Monona 

 varied from 7.2 milligrams per cubic meter of water to 92.5 milligrams. 

 The 26 analyses yielded an average of 42.6 milligrams, or almost twice 

 as much as the net plankton of Lake Mendota; while the percentage 

 was lower in the former lake, the total yield was larger because the 

 quantity of organic matter was larger than in Lake Mendota. 



