312 BOTANICAL GAZETTE [NOVEMBER 
the cell and a drawing of the end walls towards each other, But 
the internal pressure is to be counted as almost nothing at the 
angles, while it is still considerable in the middle of each end 
wall. So the margins of the end walls would approach the mid- 
dle of the cell more rapidly than do their central portions, and 
splitting of the common membrane of two adjacent cells would — 
necessarily ensue. Several facts were observed in the cultures ~ 
which seem to support some such hypothesis as the one just a 
stated. I have placed filaments in a solution where they were 
completely plasmolyzed and killed without any change in form. 
In solutions a little less concentrated they are not plasmolyzed 
but round up rapidly and soon die, often in the palmella condi- 
tion. With a still lower pressure the filament cells round up 
more slowly and live. Another fact suggesting this idea is that 
floating filaments can resist a stronger solution, and can resist it 
longer, than sunken ones. The former are to some extent i 
contact with the air, and thus present less surface than the latter : 
to the liquid. Still another observation bearing upo? ae 
hypothesis of partial plasmolysis is that cylindrical cells are : 
the only ones which are able to change their form after ses ' 
have become mature. A spherical cell must remain so till : 
divides, even if it be in a solution of very low pressure. Only a 
two other observations with which I am acquainted bear Bie 
this question: Yasuda (Joc. cit.) says infusoria in pee 
solutions tend to approach the spherical form, and Rlets a 
cit.) notes that the form of Stigeoclonium tenue with which he wa 
working had a tendency to produce round cells ina oe 
solution. The very marked response in the orientation ee 
planes in segmentation may be traceable to the change “ cells 
of the cell, orit may not. The observed fact is that vegetative je 
under low osmotic pressure divide only across their peer 
(across the axis of a lateral outgrowth in the case of a ear 
while under the influence of high osmotic presi ss ulus 
divide in all directions. It is remarkable, too, that hs ee 
determining the position of walls in vegetative wie 
brings about the extreme segmentation which occurs 
