DISCUSSION OF RESULTS. 55 



The stations where these collections were made were chosen 

 much at random, with the exception of those in Cedar lake, 

 which were for the most part in the limnetic region. In many 

 cases the stations of a given date were widely separated. In 

 lakes Poygan and Winneeonne they were scattered from one 

 end of the lake to the other. In Lake Winnebago most of them 

 were within two or three miles of the laboratory at Stony Bleach. 

 The route traversed on July 18, however, must have covered 

 16 or 18 miles. 



In looking over the table, the amount of uniformity is cer- 

 tainly very striking. This is especially true of the collections 

 in Cedar lake on Aug. 4, 1899, when five collections varied only 

 from 119 to' 130.9. These collections were all made in the lim- 

 netic region, and the depths at the different stations did not 

 vary greatly. 



The collections made in Cedar lake on March 24, 1900, were 

 made through the ice-, and the depth at the different stations 

 varied from six meters to thirty-one meters. Collections 0.18, 

 0.19, and 0.20 were made at a depth of thirty-one meters, the 

 depths at the other stations being as follows : 0.16 thirty meters, 

 0.17 twelve, and 0.22 six. There would seem in these collections 

 to be a connection between the depth and the amount of plank- 

 ton. This is perhaps, as would be expected, for the tempera- 

 ture conditions in winter are practically uniform for all depths, 

 and as temperature is one of the most important factors limit- 

 ing distribution we might infer that increasing depth, under 

 such conditions, would tend to increase the amount of plankton. 



Winter collections made on Green lake at other dates, not 

 listed in the foregoing table, seem to confirm this generalization 

 that during the winter months in a deep lake the amount of 

 plankton varies, in a general way, with the depth. 



These facts in regard to the winter plankton led me to look 

 over my notes to see whether there was evidence of any similar 

 difference in the summer. My only available collections for 

 this purpose were those made on Green lake, for the collections 

 from Lake Winnebago were nearly all taken from what was 



