PREFACE 3 



benthos and the plankton, but it soon became apparent that limitations 

 of both time and space precluded an adequate presentation of the lit- 

 toral flora; attention, therefore, has been confined to phytoplankton 

 since the second season's work. The great amount of material 011 the 

 phytoplankton has necessitated dividing the work into two portions; 

 the material included in the present volume, and the Desmidiaceae and 

 Bacillareae which are reserved for a later one. A considerable amount 

 of work has been done already on these two groups and it is hoped that 

 the complete report can be published shortly. 



Phycologists are generally agreed on the broader principles of algal 

 classification but naturally differ on minor details. The classification 

 here adopted for the Myxophyceae is used almost universally. The 

 group of flagellates with brown chromatophores is frequently consid- 

 ered more animal than plant. One section, the Chrysomonadineae, 

 where there are golden brown chromatophores, seems to be sufficiently 

 related to the Phaeophyceae to warrant placing them in a description 

 of plankton algae and in the arrangement of the group I have followed 

 Pascher's classification. Since Luther's establishment of the Hetero- 

 konteae, the question of whether to recognize this group as a separate 

 class or a division of the Chlorophyceae has arisen. The evidence 

 seems fairly clear, however, that the origin of the group is from a 

 primitive flagellate of the Chloramoeba type and since this phylogenetic 

 starting point is so markedly different from the phylogenetic starting 

 point of the Chlorophyceae (the Polyblepharidaceae) I feel that the 

 two should be considered distinct classes. The classification used is 

 that of G. S. West, although it should be noted that he considers the 

 Heterokonteae a division of the Chlorophyceae. I have also, with a 

 few exceptions, followed West's arrangement of the Chlorophyceae. 

 It is hoped that the keys found in this work will prove usable. They 

 are based solely upon characters of the species described herein; so 

 will be of no value for those not mentioned. 



During the seasons of 1916 and 1917 the field work was assisted by a 

 grant of money from the United States Bureau of Fisheries ; and the 

 extension of these studies to the lakes of northwestern Wisconsin has 

 thus been made possible. 



The University of Wisconsin, 

 Department of Botany, 

 February, 1919. 



