ANNUAL DISTRIBUTION OF THE ORGANISMS. 



CHAPTER II. 



ANNUAL DISTRIBUTION OF THE ORGANISMS OF 

 THE PLANKTON. 



Asterionella gracillima Heib. 



Asterionella occurs in both lakes through the entire year. 

 In Lake Winnebago there seems to be a minimum in June, 

 July, and August, but no very pronounced maximum period. 



In Green lake there is a similar paucity of numbers in the 

 summer months and a strong maximum in February, March, 

 and April. This winter maximum was first noticed in 1900 

 when Asterionella was found in such numbers as to make a 

 layer of water two feet in thickness almost opaque, the water 

 having a milky appearance. This winter increase was con- 

 firmed in the two succeeding winters, and it would seem to be a 

 fair inference that its maximum in Green Lake occurs regu- 

 larly in the winter. 



Cyclotella flocculosa (Koth) Kg. 



Cyclotella is never found in any numbers in Green lake. I 

 have found it only in November, January, February, and May. 



In Lake Winnebago, in the years under observation, Cyclo- 

 tella was at its maximum of development in the fall months, 

 September, October, and November. In 1900 there was an in- 

 crease in May, and in 1901 in the last of April. I think, then, 

 that we may say that Cyclotella in Lake Winnebago has two 

 maxima, the principal one in the fall with its greatest develop- 

 ment about the first of November, and the other one less pro- 

 nounced about tbi> first of May. 



