1170 Wisconsin Academy of Sciences, Arts and Letters. 
Systematic Discussion 
The nomenclature for the systematic classification of the 
Protococcales is one which offers considerable difficulty, even 
when the form under consideration isi fairly well known. The 
Brussels Congress of 1910, according to the report of Farlow 
and Atkinson (16), decided that Ralfs’ “British Desmidieae” 
(1848) should be taken as the starting point for systematic 
work in the Desmidiaceae. In this work Scenedesmus and 
Pediastrum are classed as Desmidaceae. Whether it was the 
intention of the Congress that we should base our nomenclature 
for the systematic classification of these two genera on this 
work is a matter that is perhaps open to question, but in my 
work I have followed Ralf’s classification. 
The species of Scenedesmus studied were S. acutus Meyen 
and S. quadricauda (Turp.) Breb. The classification of the 
species of Pediastrum is a more difficult matter. Although Ralfs 
recognizes' the danger of using the: arrangement of the cells in the 
colony as a specific character, his system of classification is, 
based both on the shape of the cell and on the number of cells 
in the colony. Little reliance can be placed on this latter char¬ 
acter, since there is great variation, within specific limits, in 
both the number and the arrangement of the cells. Certain 
species are described by Ralfs in which the chief determining 
character is the fact that the number of cells is not a multiple of 
two. These so-called species are merely abnormal forms. The 
species of Pediastrum that I have obtained in my cultures 
agrees more nearly with the description of P. Boryanum 
(Turp.) Mengh. than with that of any other species. Obser¬ 
vations were also made on Pediastrum tetras (Ehrenb.) Ralfs. 
Senn (85) has gathered together the widespread literature 
on Coelastrum and monographed the genus. LEis work is espec¬ 
ially authoritative in that he had several species under cultiva¬ 
tion and so was able to determine the variation in appearance 
within each species. The species that I have had in my cul¬ 
tures is Coelastrum microporum IN’aeg. 
