PLANKTON OF LAKE MONONA 115 



centage of crude protein in the organic matter and the second part the 

 amount per cubic meter of water. As might be expected from the nitro- 

 gen results the maximum and minimum percentages were higher in 1915 

 than in 1916 and the mean percentage was nearly 12.0 per cent higher 

 in the former year. In 1915 the crude protein fell below 50.0 per cent 

 of the organic matter in only two of the eight samples, but in 1916 it 

 fell below this figure in eight of the thirteen samples ; in one instance, 

 namely, sample No. 620, it fell as low as 22.4 per cent. The maximum 

 was noted in one sample obtained in 1915 which contained 70.4 per cent 

 of crude protein in the organic matter. 



The mean percentage of crude protein was higher in the nannoplank- 

 ton material from Lake Monona than in that from Lake Mendota. (See 

 table 19, p. 192.) The difference in favor of the former lake was 18.9 

 per cent in 1915 and 12.7 per cent in 1916. The mean for the samples 

 obtained from Lake Mendota in 1917 was substantially the same as that 

 of Lake Monona in 1916 ; the samples collected from the former lake in 

 1917, however, were all obtained by June 1 of that year and the ma- 

 terial was, therefore, not representative of a complete year. As a whole 

 the nannoplankton of Lake Mendota contained a smaller percentage of 

 crude protein than that of Lake Monona. 



In 1915 the mean quantity of crude protein in the nannoplankton 

 material from Lake Monona was a little more than twice as large as 

 that in the nannoplankton from Lake Mendota, while in 1916 it was 

 a little less than twice as large in the former lake. (Compare tables 19 

 and 35.) 



Attention may also be called to the fact that the increase in the 

 quantity of organic matter in the nannoplankton in Lake Monona was 

 accompanied by a rise in the percentage of crude protein both in 1915 

 and in 1916 ; in both years the maximum percentage was found when 

 the organic matter had nearly or quite reached its maximum quantity. 

 (See table 46.) 



The relation between the organic matter and the crude protein in 

 the nannoplankton of Lake Monona for the year 1916 is shown in figure 

 38, in which the amounts of each are given in milligrams per cubic 

 meter of water. In this figure the space between the zero line and the 

 curve marked B represents the crude protein, while the space between 

 B and A, the latter being the curve for the organic matter, represents 

 the other organic constituents of the nannoplankton. The smallest pro- 

 portion of protein was found on May 12, that is, in the first sample 

 obtained in this year, and the largest proportion was noted for the 

 sample obtained on October 12, when the organic matter reached the 

 highest point of the year. Between May 12 and June 14 the organic 

 matter decreased in amount relatively more than the crude protein, 

 but beyond the latter date the two curves are very similar in outline. 



