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INTRODUCTION ^'^ ^ V' 



Interest in the algae of the State of Illinois, as indicated by the 

 published literature, extends back to the middle of the past century; 

 since early in the present century, this interesting group of plants 

 has been studied in the State by some of the best-known and most 

 critical workers in this country. To the present date, algal species 

 have been reported in the published literature from only 64 of the 

 102 counties, and among these only 10 counties are represented by 

 as many as 50 species and only 4 by 100 or more species (see map, 

 p. 2). Despite this seemingly inadequate knowledge of Illinois algae, 

 more than 90 papers have appeared as a more accurate testimonial 

 to the interest and attention which the algae of the State have re- 

 ceived, directly or indirectly. Although many of these reports are 

 but brief notes resulting from limited investigations, there are a few 

 of outstanding interest, which have resulted from intensive studies 

 of localized areas over periods of many years, and which have had a 

 major influence on the subsequent course of algological and limno- 

 logical research in this and other countries. 



Beginning in 1938, the writer made a study, submitted as a thesis 

 for the Ph.D. degree in botany at Northwestern University, of dis- 

 tribution of algae about the southern end of Lake Michigan in certain 

 counties of Wisconsin, Illinois, Indiana, and Michigan. In the course 

 of this study, a review of the Illinois literature was made and a check- 

 list of the algae previously reported compiled, a classified summary 

 of which was subsequently published (Britton 1940). More recently, 

 believing this list to be of interest especially to algologists of the Mid- 

 dle West and particularly to students of algology of Illinois, the data 

 have been reorganized and expanded into this catalog of all algae 

 known by the writer, from published or unpublished sources, to occur 

 in the State. Previously unpublished records include those of the 

 writer, as well as a large number made available through the courtesy 

 of Dr. E. N. Transeau of The Ohio State University and Dr. F. 

 Drouet of the Field Museum of Natural History. 



The records included are based on reports from the various algal 

 habitats within the State boundaries and from waters occurring at 

 and forming these boundaries. All records from the Mississippi, Ohio 

 and Wabash Rivers where they adjoin the State are included as 

 Illinois records without regard to the point where the collections were 

 made relative to the midstream State boundary. Reports of algae 

 from Lake Michigan have been included only if based on collections 

 obtained within the lakeward boundaries of Cook and Lake Coun- 

 ties. 



Reference to the Illinois map (p. 2) reveals that of the 64 counties 



