Smithsonian Report, 1939. — Meier 



Plate 4 



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■^'t- 







Courtesy of U. S. Piil>lic Hp.ilth Service. 



NUISANCES IN Water supplies 

 1 Stauraslrum, a desmid; 2, Anabaena, a blue-green agla; 3, Rivutaria, a blue-green alga. Greatly magnifleil. 



