QUARTERLY CHRONICLE OF MICROSCOPICAL 
SCIENCE. 
BOTANY. 
Sexual Reproduction of Thallophytes (Supplement). 
Every microscopist is familiar with the members of the Proto- 
coccoid group of algze, but it is astonishing how very vague our 
knowledge of the life history of the greater part of them still 
remains. Speaking in general terms, it exhibits three dis- 
tinct stages:—1l, a non-motile vegetative phase, in which 
ordinary cell-division may take place ; 2, a motile condition, 
in which the protoplasm of the quiescent cells divides into a 
small number of portions—macrozoospores (which germinate 
asexually), or by a continuation of the process into a large 
number of portions—microzoospores (which conjugate, but 
otherwise in most cases appear incapable of germination) ; 
3, a resting stage, in which the green colour of the chloro- 
phyll gives place toa red hue. ‘The non-motile conditions 
have been placed by systematic algologists in the genera of 
Protococcacee and Palmellacee, and have been mostly limited 
by insecure diagnostic characters such as the degree of dif- 
fluence of the mother-cell-wall, or the manner in which the 
daughter-cells remain for a time aggregated. On the other 
hand, the motile phases have to be sought in Volvocinee 
amongst the species ef the genus Chlamydomonas. 
It will be convenient to sum up briefly what appears to be 
the present state of our knowledge as to three of the most 
common types. 
Chlamydococcus.—Cohn’s study of Ch. (Protococcus) plu- 
vialis! still remains the most complete account of the life 
history of any member of the group. As I have already 
stated (p. 303), Velten has described what he believed to 
be the conjugation of the macrozoospores. Rostafinski has, 
however, obtained further confirmation? of his own state- 
ment that what Velten saw were merely zoospores destroyed 
by a parasitic monad. One of Velten’s figures (fig. 9) Ros- 
1 Ray Soe. ‘ Bot. and Phys. Mem.,’ 1853, p. 517. 
*«Mém. Soc. Sc. Nat. de Cherbourg,’ 1875, p. 144. 
