432 Wisconsin Academy of Sciences , Arts , and Letters. 
pure culture by Beyerinck, Grintzesco, Chodat, Tischutkin, 
Andreesen, and myself, so that the variations occurring 
within the limits of a pure culture are well known. Interest 
in the species has increased considerably since Chodat and 
Grintzesco described the remarkable series of transforma¬ 
tions in which the cells are all isolated at one time, and at 
others form branching systems which resemble Dactylo- 
coccus infusionem Nageli. I (1914) have recently discussed 
the question of this Dactylococcus stage and find that it 
never occurs in pure cultures of S. obliquus. On the other 
hand I have isolated an alga with cells shaped like S. obliquus 
but they were always arranged in branching chains as in 
D. infusionem and therefore concluded that the two should 
be regarded as separate species and not different growth- 
forms of the same alga. In this connection it is interesting 
to note that the investigator who first stated that S. obliquus 
and D. infusionem are the same alga (Chodat), brings forth 
no additional data in his recent work (1909, 1913) to show 
that the two are related, but relies on earlier work as evi¬ 
dence. 
It is generally agreed, however, that cultural conditions 
may produce a change in the shape of the individual cells, 
causing them to become less acicular with the increase in 
concentration of the nutrient medium. 
In the different strains of this alga so far isolated, I am 
unable to differentiate between any of them on the basis of 
cell size, whereas in certain other species it is possible to 
distinguish the different strains by cell measurements. The 
arrangement of the cells may be either in a linear series 
(Figs. 63, 64; PI. XXIX) or in an alternating series (Figs. 67, 
68), a fact which I have shown to be due to the manner of 
formation of the young colony by the mother cell. 
GEOGRAPHICAL DISTRIBUTION 
EUROPE. Austria-Hungary (Alexenko, 1888, 1894, 1895; 
Beck, 1887; Brunnthaler, 1900, 1907; Franze, 1892, 1893; Grunow, 
1858; Ianouchkievitch, 1891; Hansgirg, 1883, 1884B, 1886, 1889, 
1890A, 1891, 1892B, 1905; Pascher, 1903, 1906; Pokorny, 1854; 
Riabinine, 1889A, 1889B; Ruttner, 1906; Stadler, 1905). Belgium 
(Conrad et Kufferath, 1912; Paque, 1885; de Wildemann, 1885, 
1890A, 1890B, 1893B, 1895, 1897B). Bulgaria (Petkoff, 1906B). 
Denmark (CJiodat, 1900; W. West, 1891B). England (Bennett, 
