2 PREFACE 



191415-16-17 and all lake areas of the state have been visited during 

 the progress of the investigation. Collections have been made from 

 the lakes around Madison and Ocoiiomowoc during the entire season 

 that they are open. The June, August and early September flora of 

 the northeastern lakes is represented, while the northwestern lakes were 

 visited for two successive seasons during August. Only single collec- 

 tions were made from the northern lakes so that the data for any par- 

 ticular one of them are undoubtedly very fragmentary. 



The limits of the survey are determined by the political boundaries 

 of the state and not by ecological or regional unity. There is a con- 

 tinuation of the southeastern lake group in northeastern Illinois; of 

 the northeastern lake group in the northern peninsula of Michigan ; and 

 of the northwestern lake area in Minnesota. However, variation in 

 depth and surface area together with variation in chemical content of 

 Wisconsin lakes gives a sufficient range of habitat to cover conditions 

 found in almost all other parts of the world if temperature and altitude 

 are excluded. The cosmopolitan nature of phytoplankton, therefore, 

 makes this work of value to the student of these microorganisms in 

 other sections of the United States or even other continents, and he wil] 

 probably find a majority of the species in any region represented in 

 the Wisconsin flora. There is a temptation to include species that have 

 not been observed in order to round out the work for the student in 

 other parts of the world. This practice has been followed in certain 

 algal floras and while it may be helpful to the general student, it causes 

 endless confusion to the phytogeographer. Only those species are in- 

 cluded in this flora which have been collected from the state. 



Descriptions of plankton algae are scattered through a large number 

 of periodical publications and transactions of learned societies, many 

 with only a limited circulation, so that considerable effort has been 

 spent in giving full and correct citations for the original descriptions. 

 When subsequent descriptions have been better or have given more 

 characteristic figures references are also made to them. A great deal 

 of time has also been spent making camera lucida drawings since an 

 accurate figure is frequently more valuable than a description. Draw- 

 ings of the various species of a genus are generally on the same scale, 

 but there has been no attempt to draw the different genera on the same 

 scale. The finer details of cytological structure, such as the nature of 

 the chloroplast or structure of the pyrenoid, are frequently lost in pre- 

 served material ; so all of the Chlorophyceae, with the exception of the 

 Desmidiaceae, the Phaeophyceae, Heterokonteae and the Myxophyceae, 

 have been drawn from living material. 



The original plan for the study of Wisconsin lake algae included those 

 attached to rocky shores or lying among the macroscopic vegetation in 

 the quieter portions of lakes in order to get the relation between the 



