44 GERLOFF, FITZGERALD, AND SKOOG 



have similar requirements, and experiments now in progress indi- 

 cate that diis is true for Microcystis aeruginosa, nitrogen supply 

 must be an important factor in controlling the growth of blue- 

 green algae under natural conditions. Furdiermore, the high 

 nitrate requirement togedier with the direct relationship between 

 yield and added nitrate over a wide range indicate that Cocco- 

 chloris Peniocystis in all probability does not fix atmospheric nitro- 

 gen as some blue-green algae have been shown to do. 



A question might be raised regarding the applicability of 

 results obtained in culture flasks in the laboratory to conditions 

 existing in lakes and streams. The results with Coccochloris Peni- 

 ocystis indicate that the laboratory data cannot be applied directly 

 to field conditions. For example, the maximum inorganic nitrogen 

 concentration in die lakes and streams near Madison, Wisconsin, 

 where blue-green algae grow in great abundance is far below the 

 13.6 ppm. necessary for maximum growth in the laboratory ex- 

 periments. Not only the concentration of the essential elements, 

 but also the volume of the solution from which the algae can ex- 

 tract them must be important in determining the suitability of a 

 particular environment for the growth of blue-green algae. Never- 

 theless, data obtained in the laboratory on the qualitative growth 

 requirements of blue-green algae and the relative proportions of 

 the essential elements necessary for maximum growth should be 

 of considerable value in determining the requirements for opti- 

 mum growth of these organisms in lakes and streams. 



Acknowledgements 



This work was supported in part by the University Research Commit- 

 tee on funds from the Wisconsin Alumni Research Foundation and in 

 part by a research grant from the Division of Research Grants and Fel- 

 lowships of the National Institute of Health, U.S. Public Health Service. 



