78 PLANKTON OF WISCONSIN LAKES 



cubic meter of water. The details of the analyses are shown in the 

 general table, No. 44, p. 207. 



The highest percentage of ether extract, calculated on an ash free 

 basis, was found in a sample obtained in 1915, namely, 15.77 per cent. 

 In 1917 the maximum was only 7.07 per cent, less than half of the 

 preceding maximum, but the latter is not representative of an entire 

 year since the observations were discontinued on June 1, 1917. The 

 minimum percentage was highest in 1915 and lowest in 1917 and the 

 same was true of the mean percentage. There was slightly more than 

 a fivefold difference between the maximum and minimum of 1915, al- 

 most sixfold in 1916, and more than threefold in 1917. 



When stated in terms of milligrams per cubic meter of water, as in- 

 dicated in the second part of this table, the largest quantity of ether 

 extract was found in 1915 and the smallest in 1917. The mean quantity 

 was lowest in 1917 and highest in 1915, the latter being about 40.0 per 

 cent higher than the former. 



The curves marked C in figures 30 and 31 give a graphic representa- 

 tion of the quantity of ether extract in the various samples. These 

 curves show that, in general, the extract constituted a relatively small 

 proportion of the organic matter. The largest amount was found dur- 

 ing the vernal pulse of the nannoplankton, after which there was a 

 gradual decline to the summer level, which was reached about the first 

 week in June. Thus, the decrease was more gradual than in either 

 the organic matter or the crade protein. With two exceptions the quan- 

 tity remained well below 100 milligrams per cubic meter of water 

 during the summer season. In 1915 the curve shows a distinct peak 

 during the early part of August which is correlated with similar peaks 

 in the organic matter and the crude protein at this time. In 1916 the 

 quantity rose slightly above 100 milligrams about the middle of July, 

 and again during the autumnal rise in late September and early Octo- 

 ber. In the latter part of 1915 there is no marked rise corresponding 

 to the early autumnal increase of organic matter, but a prominent peak 

 covers the second part of November which is correlated with a peak 

 in the organic matter. 



In comparison with the net plankton (table 43) the nannoplankton 

 shows a distinctly lower percentage of ether extract; the mean of the 

 latter averages only about a half to two-thirds as high as the former. 

 This is probably due to the larger proportion of fat in the Crustacea of 

 the net plankton. Owing to the presence of a larger quantity of nanno- 

 plankton, however, the total amount of ether extract in it is markedly 

 greater than that in the net plankton. In 1915, for example, the mean 

 percentage of ether extract in the net plankton is one and seven-tenths 

 times as much as that in the nannoplankton, yet the mean quantity of 

 the latter is two and a half times that of the former. 



