ANNUAL DISTRIBUTION OF THE ORGANISMS. 13 



Stephanodiscus. 



Stepharwdiscus I have not found at all in Green lake. In 

 Lake Winnebago it may occur from February to July, with 

 a maximum at some time in the spring. In 1900 there were 

 two important periods of large numbers, one the middle of 

 May, and one the last of June. In 1901 the first increase 

 came the last of April and the second the first week in June. 

 Other diatoms were noticed in the plankton, but none in suf- 

 ficient numbers to be of any importance in the total amount. 



Navicula. 



Navicula was found in Green lake a few times and occurred 

 in Lake Winnebago in many of the collections, especially in the 

 winter months. 



Surirella and Pleurosigma. 



Surirella and Pleurosigma were found a few times in Lake 

 Winnebago. 



Nassula. 

 Nassula, also, was noted in the flora of Lake Winnebago. 



COMPARISON OF RESULTS ON ANNUAL DISTRIBUTION OF DIATOMS 

 WITH WORK OF OTHER AUTHORS. 



I find very few recorded facts in regard to the annual dis- 

 tribution of the various genera of diatoms. 



Apstein (Apstein '9 6) finds the two maxima of Melosira 

 much as I do. His maxima for Asterionella do not correspond 

 to my results. 



Whipple (Whipple ? 94), in a discussion of the growth of 

 diatoms in surface waters, comes to the conclusion that the 

 growth of diatoms is directly connected with the phenomena 

 of stagnation, that in deep ponds there are two well defined 

 periods of growth, one in the spring and one in the fall : that 

 in shallow ponds there is usually a spring growth but no regu- 



