33 PLANKTON OF WINNEBAGO AND GREEN LAKES. 



and in August, there may be seen floating about yellowish green 

 masses of a more or less spherical outline, perhaps as much as 

 three inches or more in diameter. These masses, which are com- 

 posed of aggregations of Aphanizomenon mingled with scattered 

 fronds of Gloioirichia and Anabaena, have very little coherence 

 and elude the collector by falling in pieces almost at a touch. 

 As is evident from the discussion of the occurrence of the algal 

 constituents of the plankton, the bloom is not a prominent feat- 

 ure of the deep lakes, in fact in some years the growth of these 

 algae is hardly noticed by the ordinary observer, and of the 

 shallow lakes few seem to produce so large an amount as is seen 

 in Lake Winnebago. Of the lakes under observation, Shawano 

 and Pelican were the only ones that could be compared at all 

 with Lake Winnebago. 



ANNUAL DISTRIBUTION OF THE TOTAL PLANKTON. 



Plates XXI and XXII shows the annual distribution of the 

 total plankton in Green lake and Lake Winnebago during the 

 two years under observation. 



An examination of the curves, while it shows marked similar- 

 ity in the production of the years studied, shows also almost as 

 marked differences. In general it may be said that the sum- 

 mer months are the time of greatest productiveness, although 

 Green lake shows an exception to this. We notice also that the 

 successive years not only differ somewhat in the time of maxi- 

 mum production, but that there is a marked difference in the 

 total amount of plankton. 



In Lake Winnebago in the first year there were four periods 

 of large production, the last of July, the middle of September, 

 and the early part of June. In the second year there was a 

 single maximum which occurred early in September, with not 

 even slight increases at other times 1 . In the third summer there 

 was a pronounced maximum in the last of July, with slight in- 

 creases in September and October. 



In Green; lake there are similar differences. 



