314 BOTANICAL GAZETTE | NOVEMBER 
action of a concentrated solution is indicated by a comparison of 
the maximum concentrations for zoospore germination in the 
two forms. Zoospores from a palmelloid cell are able to 
produce and maintain filaments at a much higher pressure than 
can those produced from a filament. The two kinds of 
zoospores are physically alike, but are physiologically very 
different. It needs to be said here that in cases where the 
tables record ungerminated zoospores there are also many which 
did germinate to form filaments of several cells. In cultures 
so marked, however, the majority of zoospores failed to germi- 
nate in that way. 
Summary. 
My results are as follows: 
1. The responses of Séigeoclonium (tenue ?), both in fo 
in reproductive activity, which accompany a change in concentra 
tion of the Knop’s solution in which it is growing, are due to 
changes in the osmotic pressure of the medium, and are in 0 
way functions of its chemical composition. 
2. A high osmotic pressure affects the plant i 
(a) it decreases vegetative activity ; (0) it inhibits the production 
of zoospores; (c) it causes cylindrical cells to become spherical’ 
(d) it frees the alga from certain limitations as to the orientation 
of planes of cell division. ‘ 
3. A low pressure has the following effects: 
vegetative activity; (4) it accelerates the production er 
spores; (c) it causes forming cells to become cylindrical; (4) 
it determines the orientation of the planes of cell division. a 
4. A zoospore which has come to rest responds in pee same 
way as a palmelloid cell. 
5. Cells of the palmella form become slightly Ve 
high external pressures of concentrated solutions a aul 
some responses quantitatively different from those 0 
rm and 
n four ways: 
(a) it increases 
FU 
In closing I wish to express my thanks to Profesor 
oa yalua 
Newcombe, of the University of Michigan, for a and 10 
suggestion and advice in the inception of the work, 
