16 PLANKTON OF WINNEBAGO AND GREEN LAKE 8. 



ber. It reaches its greatest abundance in July and August. 

 The numbers in September are ordinarily very small. Yet I 

 have found it in Pelican lake in great numbers in the latter part 

 of September. 



Aphanizomenon. 



ApJianizomenon occurs in Lake Winnebago associated with 

 Anabaena, its period of growth being very similar although it 

 does not appear so early nor remain so long. While I have not 

 counted Anabaena and Aphanizomenon , and so cannot state 

 their maximum period with any exactness, I get the impression 

 that Anabaena reaches its maximum earlier than Aphanizomr 

 enon. It is found in other shallow lakes associated with Ana- 

 baena. 



Oscillaria. 



Oscillaria is not a constituent of the plankton in either Green 

 lake or Lake Winnebago. In some of the shallow lakes, how- 

 ever, it is very abundant at certain times in the summer. This 

 is notably so in Shawano lake where it seems to assume the 

 importance that Anabaena and Aphanizomenon do in Lake 

 Winnebago. 



Lingbyj,. 



Lingbya is associated with Anabaena and Aphanizomenon 

 in Lake Winnebago, especially in July, sometimes in large 

 numbers, but is of less importance than the other two genera. 



Gloiotrichia echinulata Richt. 



Gloiotrichia has no importance in the plankton of Green 

 lake. In Lake Winnebago it is found in great numbers in 

 July and August. In the summer of 1899 (Plate I) there 

 was a rapid increase from the first of July to the middle, fol- 

 lowed by a decrease, from which there was again a -rise to a 

 maximum about the twelfth of August. In 1900 there was a 

 single maximum early in July. The total production of 

 GloiotricJiia in 1899 was much greater than in 1900. 



