96 PLANKTON OF WISCONSIN LAKES 



H 



and in November-December, 1916. In the former year, curve A pre- 

 sents a conspicuous peak in October corresponding to a similar peak 

 in C, but which is not represented in B; in the latter year, curve A 

 possesses a broad, prominent peak in November-December, 1916, and 

 in January, 1917, which more closely resembles the one found in C at 

 this time. 



Expressing the relation of the amount of organic matter in the net 

 plankton to that in the corresponding sample of nannoplankton in the 

 form of a ratio also serves to bring out more clearly some of these 

 quantitative differences. Taking the samples collected on December 

 12, 1916, in which the organic matter of the two is most nearly equal in 

 amount, the following ratio is obtained, net plankton: nannoplank- 

 ton— 1 :1.1 ; on the other hand, the samples which show the greatest 

 difference, those collected on April 21-23, 1915, give a ratio of 1 :24.6. 

 Each year the largest differences were found during the vernal maxi- 

 mum of the nannoplankton; the nannoplanktonts thus appear to re- 

 spond more promptly to the more favorable conditions which obtain 

 after the ice disappears than the organisms in the net plankton. That 

 is, the small forms multiply and develop more rapidly than the larger 

 ones. 



The ratios of the mean quantities of organic matter in the net plank- 

 ton and in the nannoplankton are the same for 1915 and 1916, namely, 

 1 :4.8, while that for the samples collected in 1917 is somewhat higher, 

 that is, 1 :5.9. The latter year, however, is incomplete ; if the January 

 samples, in which the net plankton is unusually large, are omitted, the 

 ratio then becomes 1 :7.8. In comparison with this, the samples ob- 

 tained between February and June, 1916, give a ratio of 1 :7.7, or sub- 

 stantially the same as that of the same period in 1917. Thus, it ap- 

 pears that, with the exception of the January samples, the normal ratio 

 of the organic matter in the net plankton to that in the nannoplankton 

 is shown by the material collected in 1917. In general, then, it may 

 be said that, for the entire year, the nannoplankton of Lake Mendota 

 yields an average of about five times as much organic matter as the 

 net plankton; but, at certain times, the amounts may be almost equal, 

 while at other times the nannoplankton may yield about twenty-five 

 times as much organic matter as the net plankton. 



Moore, Edie, "Whitney, and Dakin 1 obtained from three to six times 

 as much organic matter from sea water with a Chamberland filter as 

 with No. 20 silk bolting cloth. 



1 Biochemical Journal, Vol. 6, 1912, pp. 255-296. 



