1900] CHANGE OF FORM IN GREEN ALG 311 
protoplasm may so decrease the lability that rapid growth is 
impossible. 
What may be the mechanics of this rounding up of cylin- 
drical cells when placed ina concentrated solution is one of the 
most important problems suggested by. the present research. 
The fact that the dead cellulose membrane is almost entirely 
reshaped during this process, without being dissolved, renders it 
probable that the change in form is directly caused by some 
turgor change within the cell. In arounding cell the membrane 
moves and changes its form and, since it is entirely inert, the 
source of this motion must be either in the activity of the proto- 
plasmic body itself, or it must be in the turgor pressure of the 
mass of liquid within. But since protoplasm and cellulose wall 
ra be parted so readily during plasmolysis, the first alternative 
iswell-nigh untenable. If the wall be forced into the spherical 
shape by a change in the pressure from within, this must be 
brought about by a change in the mass of the contained liquids. 
Now, this slight change in mass which might produce a change 
in the turgor of the cell is most probably due to an alteration in 
the amount of cell sap within the vacuole. When the surround- 
™g medium suffers change in concentration, a change in the 
Yolume of the vacuole may come about through the protoplasmic 
“, either secreting liquid or acting merely as a semipermeable 
Membrane, 
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When filaments are placed in a concentrated solution their 
behavior Suggests at once partial plasmolysis. Water may be 
“tracted, the turgor pressure on the walls may be decreased, 
- by the forces of surface tension and cohesion the proto- 
: ag May tend to round itself up into a sphere. If this be set 
. oo a explanation of the lateral bulging which accompa 
— longitudinal shrinking of the cellulose envelope. If wei 
Protoplasm tended to assume a spherical form within the cylin- 
_ | Mall, the pressure upon this would be decreased first at the 
pe At the same time it would be relatively increased sail 
. ral walls near their middle. Thus would come — 
Sing of the lateral walls outward, and hence a shortening f 
