236 BOTANICAL GAZETTE [SEPTEMBER 
which these changes occur will depend upon the permeability of the 
protoplasm to the solute and upon the concentration gradient 
causing the diffusion of the solute. 
If a living cell be placed in a fairly concentrated salt solution, 
the salt usually diffuses into the cell (a process known as “endos- 
mosis’’), while the sugars, to which a large part of the intra- 
cellular osmotic pressure was originally due, remain for the most 
part within the cell. Under these conditions the cell will increase 
in volume, until it reaches the same turgidity (that is, the same 
degree of distension due to the tendency of water to enter the cell) 
which it would have possessed had there been no salt at all present. 
The outward diffusion of salts or other substances from the cell 
(‘‘exosmosis”’) is usually negligible, but it is always to be remem- 
bered that such a diffusion may be occurring simultaneously with 
the endosmosis. If a salt after entering the cell forms there osmo- 
- tically inactive compounds, either by adsorption or by chemical 
combination, and does not at the same time cause the liberation 
of an osmotically equivalent amount of some other substance, the 
turgidity of the cell is less than would be expected, and there 1S a 
a decrease in the apparent rate of penetration of the salt. 
If a plant cell be placed in a solution which causes shrinkage, the 
cell I wall will contract elastically fora cortamn distance, and will then 
suffer no fi 1 shrinkage 
ae of the protoplasm will cause it to retract from the cell wall. This 
: - separation of the protoplasm from the cell wall is known as plas- : 
: molysis. It was first observed by, PRINGSHEIM (52) in 1854, and © 
ik 4 by } y NAGELI (37) to to the i y of the protoplast 
_ to the plasmolyzing substance. In ‘this process the protoplasm 
_ may tear away just inside the cell wall, leaving attached to it a 
thin layer of protoplasm to which the central mass remains for 2 — ie 
ee time connected by fine: threads (cf. BowER a Cuca & ant Sie ee | ’ : 
ie cA Hacer 13) and Kisrex > Dig E is | 
