120 PLANKTON OF WISCONSIN LAKES 



to confine the discussion of the net plankton to those samples which were 

 obtained at the same time as the samples of nannoplankton ; that is, 

 only those collected in 1915 and in 1916 are considered here. 



In 1915 the quantity of dry organic matter in the net plankton 

 varied from a minimum of 404.0 milligrams per cubic meter of water in 

 sample No. 564 to a maximum of 2,161.8 milligrams in sample No. 5167 

 (table 45). In 1916 the minimum and maximum amounts were 109.3 

 milligrams and 1,226.1 milligrams, respectively, in samples No. 6123 

 and No. 659. In the former year the variation was somewhat more than 

 fivefold, while in the latter year it was a little more than elevenfold. 



The dry organic matter in the nannoplankton of Lake Monona ranged 

 from 723.0 milligrams in sample No. 563 to 3,746.5 milligrams per cubic 

 meter of water in sample No. 5166 (table 46). In 1916 the minimum 

 amount was 672.1 milligrams, noted in sample No. 648, and the maxi- 

 mum was 5,696.2 milligrams per cubic meter of water in sample No. 

 6158. In the former year the maximum was just a little more than five 

 times as large as the minimum, while in the latter year it was about 

 eight and a half times as large. 



A comparison of the organic matter in the net plankton with that in 

 the corresponding samples of nannoplankton shows that the latter was 

 smaller in amount than the former in four samples. These nanno- 

 plankton samples are Nos. 543, 583, 658, and 672 and the corresponding 

 net samples are Nos. 544, 584, 659, and 673 ; in the other seventeen sam- 

 ples of nannoplankton the organic matter was larger in amount than in 

 the corresponding net samples. (Tables 45 and 46.) The minimum 

 ratio is shown by samples No. 658 and No. 659 in which the quantity 

 of organic matter in the nannoplankton is only two-thirds as large as 

 that of the net plankton, the ratio being 1 : 0.66 ; in the other three of 

 these samples the nannoplankton yielded somewhat more than four- 

 fifths as much organic matter as the corresponding net catches. In sev- 

 enteen of the samples the quantity of organic matter was larger in the 

 nannoplankton catches than in the corresponding net plankton catches ; 

 in four of these samples the nannoplankton yielded somewhat less than 

 twice as much organic matter as the net plankton, while sample No. 

 6134 contained approximately twenty-eight times as much organic mat- 

 ter as the corresponding net sample, No. 6135, and sample No. 6122 

 almost twenty-three times as much as No. 6123. These results differ 

 from those obtained on Lake Mendota in two respects, namely, all of the 

 nannoplankton samples from Lake Mendota yielded a larger amount 

 of organic matter than the corresponding catches of net plankton, but 

 the maximum excess of the former over the latter was not quite as large, 

 being only about twenty-five times as large instead of about twenty- 

 eight times. 



