PREFACE. 



Part 1 of this bulletin, which covers the plankton algae of Wis- 

 consin, exclusive of the Desmidiaceae and Bacillarieae, appeared in 

 1920. Since this account of the plankton desmids is a continuation 

 of the same investigation and is based upon the same collections, it is 

 unnecessary to repeat the data given on pages 13-19 of Part 1, which 

 describes the location and morphometry of the various lakes from 

 which plankton samples were collected. 



The method of treatment of the various species is the same as that 

 followed in the first section. In addition to the citation of the orig- 

 inal description of the alga there has been a liberal citation of ar- 

 ticles that contain characteristic figures. A list of all stations for 

 each alga is given, following its description, and the same method 

 has been used for designating its frequency at each station as was 

 used in the first part. 



Since all drawings have been made from preparations the vertical 

 and front views are from different individuals. For this reason each 

 drawing has been given a different number. All of the figures of the 

 plates have been drawn from Wisconsin specimens and all dimensions, 

 unless expressly stated, are those of cells as found in the plankton of 

 Wisconsin lakes. Since only varieties of a number of species are 

 represented in the local flora descriptions of the type are taken from 

 other sources. Where illustrations have been drawn of these types 

 they are given as text figures and with an indication of the source of 

 the material. 



The difficulties involved in the determination of the species of 

 Desmidiaceae are well known to all students of the family. In the 

 preparation of this section the Wisconsin specimens have been com- 

 pared with species found in the plankton of various European lakes 

 and the opportunity of studying foreign plankton Desmidiaceae has 

 added greatly to the certainty of determination of members of the 

 local flora. 



In the course of this investigation, through the kindness of Pro- 

 fessor Yapp of the University of Birmingham, I have had free access 

 to the collections and drawings of the late Professor G. S. West. 

 While studying the material at Birmingham Dr. Nellie Carter placed 

 at my disposal her material for the completion of W. & G. S. West's 

 British Desmidiaceae. Dr. A. B, Rendle furnished facilities for ex- 

 amining the herbarium of the British Museum of Natural History and 

 for consulting the rich library of that institution. The privilege of 

 studying the Huitfeld-Kaas collections from Norwegian lakes was 



