40 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



maxima. These correspond to the maxima of Eurycercus lam&l- 

 latus. Eurycercus is a very bulky form, and when it is present 

 in considerable numbers is a large element in the total plankton. 

 A careful analysis of the summer collections shows, however, 

 that while Eurycercus was an important factor in these maxima, 

 it was by no means alone responsible for them. They were 

 rather caused by a general increase in a number of forms of 

 Crustacea, accompanied by a large development of the plants. 



In the maximum of June, 1900, Daphnia pulicaria, another 

 bulky form, also* reached its maximum development for the year. 

 But at this time, too, other forms are as important in making 

 up the total. There was a general increase of most of the Crus- 

 tacea., — among others Diaptomus oregonensis being very promi- 

 nent. Many of the plants, too-, were present in considerable 

 numbers, especially Asterionella. 



In the summer of 1900 the maximum early in September was 

 coincident with a maximum of Daphnia hyalina. But 

 this was not in itself sufficient to produce the maximum. The 

 real determining cause was the enormous number of Anabaena, 

 Clathrocystis, and an unnamed alga. The winter maximum was 

 characterized by an almost total lack of Crustacea and algae, 

 while rotatoria, diatomaceae> and protozoa in small numbers 

 formed the bulk of the plankton. 



In the summer of 1901 there was one pronounced maximum 

 the last of July. At this time there was a large number of Crus- 

 tacea, but the size of the collections was mainly caused by the 

 enormous numbers of Anabaena, Lingbya, and Aphanizomenon. 



In Green lake the maximum of Aug. 1, 1899, was due to the 

 large number of several of the entomostraca, especially of Diap- 

 tomus minutus and Daphnia. The increase of the first of Octo- 

 ber was due mostly to the Crustacea, Diaptomus minutus and 

 Cyclops prasinus being important elements, while the increase 

 in Bosmina is another factor. The rise the last of November 

 is due mainly to the very large number of Bosmina, combined 

 with large numbers of Asterionella and Sphaerella. 



The striking feature of the Green lake curve for the year 



