68 



PROBLEMS OP LAKE BIOLOGY 



limnology of which preclude them from the 

 European system of classification (Fig'. 1). 

 Oligotrophic lakes, or those with predomi- 

 nating oligotrophic features, are known 

 which show eutrophic plankton; for exam- 

 ple, Mountain Lake in Virginia, Lake Nipi- 

 gon in Canada, Lake West Okoboji in Iowa, 

 and certain lakes in northern Wisconsin 

 and Michigan. 



At the same time we find dystrophic 

 plankton in eutrophic lakes and eutrophic 

 lakes with practically no plankton at all. 

 These statements, insofar as my own obser- 



used to classify phytoplankton types and to 

 relate them to lake types. Why, for exam- 

 ple, does a certain eutrophic lake persis- 

 tently have an algal population dominated 

 by Lynghya Birgei, while a stone's throw 

 away is one overwhelmingly populated by 

 Aphanizomenon flos-aquael Or, why does 

 one lake have a predominating diatom flora, 

 and one just across the way have no dia- 

 toms, but mostly members of the Conju- 

 gatae ? 



These and other similar questions are 

 often answered through the discovery that 



Fig. 3. An old lake, passing from eutropliy to heteiotropliy. 



vations are concerned, are based upon phy- 

 toplankton collections made during the 

 summer months only and should be qualified 

 accordingly. 



When, and if, a classification of North 

 American lakes should be formulated it 

 should be based upon correlation coefficients 

 of phytoplankton species and limnological 

 features, and should rest as far as possible 

 on a mathematical background. I believe 

 this is possible and infinitely desirable, al- 

 though patience and painstaking work 

 would be required. 



The planktonologist turns to limnology 

 for an explanation of geographical and local 

 distribution. Limnological data have been 



there are certain limnological correlations. 

 It is my thesis tliat these correlations are 

 not, in many cases, the answers w^e are look- 

 ing for, but are the clues to the solution of 

 ecological problems. The real questions are 

 only apparently or partly answered by these 

 correlations, and many of our published 

 studies are forced to use the phrases "it 

 seems," or "it is possible." 



Notwithstanding the enormous amount of 

 accumulated information, I believe that 

 many more culture studies must be made 

 and the problems carried into the labora- 

 tory where the experimental method of re- 

 search may be added to the extensive field 

 work now being carried on. 



