ANNUAL DISTRIBUTION OF THE ORGANISMS. H 



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CHAPTER II. 



ANNUAL DISTRIBUTION OF THE ORGANISMS OF 

 THE PLANKTON. 



Asterionella gracillima. Heib. 



Asterionella occurs in botli 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 (Roth) 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 tb^ first of May. 



