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PREFACE 



The general name plankton is given to the organisms whicl: live li-ea- 

 floating in the deeper parts of lakes and ponds ; the plant individuals 

 being designated the phytoplankton and the animal the zooplankton. 

 Investigations have shown that there is a very special algal flora liv- 

 ing exclusively in the plankton, in addition to the chance wanderers 

 from the littoral, or marginal, region which do not multiply when in 

 the plankton. These will be designated as the euplanktonts and tycho- 

 planktonts respectively in this work. There is still another group of 

 organisms found in lakes, namely those which thrive equally under 

 littoral or pelagic conditions. This group will be referred to as the 

 facultative planktonts. Attempts have been made to differentiate be- 

 tween organisms of these three groups by the Wests, Teiling, and 

 others, although a different terminology has been used. Since the 

 question of a proper habitual classification for any particular species 

 will always be a matter of individual opinion, I have indicated at the 

 end of the description my conception of the natural habitat of the 

 organisms found in the lakes of this state. 



It is only within the past twenty -five years that the phytoplankton has 

 been studied, and our knowledge of the various members constituting 

 this specialized flora has come almost exclusively from European phyco- 

 logists. William West, G. S. West and Pritsch in England; Chodat 

 and Bachmann in Switzerland ; Lemmermann, Schmidle, Schroder and 

 Volk in Germany; von Keissler, Pascher and Woloszynska in Austria- 

 Hungary; and Wesenberg-Lund in Denmark have been the chief stu- 

 dents of European phytoplankton. The central African lakes have 

 been investigated by G. S. West, Schmidle, and Woloszynska. G. S. 

 West and Playfair have studied the phytoplankton of Australia. With 

 the exception of Miss Snow's work on Lake Erie nothing was known 

 concerning the taxonomy of North American phytoplankton at the 

 time the present work was undertaken, the pioneer work on the micros- 

 copy of the Massachussetts and Brooklyn water supplies being of little 

 value to the systematist since determinations were not carried beyond 

 the genus. 



These studies of Wisconsin lakes, carried out under the auspices of 

 the Wisconsin Geological and Natural History Survey, were commenced 

 in the fall of 1913. Field work was continued during the summers of 



