ACKNOWLEDGMENTS 



I wish to express my appreciation to those who have given much 

 valued assistance. Special acknowledgments are due the late Dr. 

 Edward A. Birge, who generously gave much of the financial support 

 necessary for the preparation of the manuscript and illustrations, I 

 am grateful to him not only for material assistance but also for help- 

 ful advice and for the lively interest he showed during the entire 

 project. Also I wish to express my indebtedness to the late Professor 

 Chancey Juday for the help he contributed from his long experience 

 and familiarity with limnological problems and also to Drs. C. E. 

 Allen, Stanley Cain, Francis Drouet, Robert T. Hatt, C. M. Palmer, 

 the late Gilbert M. Smith, Clarence E. Taft, Wm. Randolph Taylor, 

 Lewis H. Tiffany, and the late Edgar N. Transeau, all of whom 

 either made or confirmed identifications of some of the species 

 listed herein, or gave helpful advice on certain portions of the work. 



Dr. Hannah Croasdale, Dr. Ruth Patrick, and Miss Hilda Harris 

 assisted in checking a number of bibliographic references. Mr. 

 Thomas Cobbe helped in the preparation of some of the plates, and 

 Mr. H. Ward Prescott did most of the photographic work involved. 

 Dr. Croasdale helped to prepare Latin diagnoses which appear in 

 preliminary reports (Prescott, 1944; Prescott, Silva, and Wade, 1949). 



Further, I wish to express my appreciation of facilities provided 

 by the following laboratories and libraries where various portions 

 of this study have been carried on: Trout Lake Limnological Lab- 

 oratory, Trout Lake, Wisconsin; University of Michigan Biological 

 Station and the University of Michigan Library; Woods Hole Marine 

 Biological Laboratory and Library; Farlow Herbarium and Refer- 

 ence Library; Albion College Biological Laboratory and Library; 

 University of Minnesota Herbarium and Library; Chicago Natural 

 History Museum Cryptogamic Herbarium; University of California 

 Herbarium and Library; the library of the late Dr. Gilbert M. 

 Smith; the University of Wisconsin Library; the John Crerar Li- 

 brary; the Lloyd Library; and the Library of the Academy of 

 Natural Sciences of Philadelphia. 



I wish to make grateful acknowledgment of grants in aid which 

 directly or indirectly facilitated this study from the American Asso- 

 ciation for the Advancement of Science, the Wisconsin Geological 

 and Natural History Survey, the Horace H. and Mary A. Rackham 

 Fund, the Michigan State College Research Fund, the Muellhaupt 

 Fellowship, and the Brittingham Trust Fund. 



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