450 BOTANICAL GAZETTE [JUNE 
fact that water distilled in a metal still produces such results in 
Spirogyra, while pure distilled water does not. 
The cause of these effects lies in an increase in the permeability 
of the plasma membrane (and likewise of internal cell membranes), 
as the result of which some or all of the substances which main- 
tain the osmotic pressure of the cell diffuse out; the protoplasm 
then shrinks as the result of loss of water from the vacuoles, which 
in consequence become smaller, as is shown in figs. 3-5. This is 
often followed by an apparent “coagulation” of the protoplasm, 
which is sometimes evidenced by the assumption of an irregular 
outline. Most of the characteristic features of cytolysis as described 
for animal cells are lacking. In some cases, however (particularly 
in cells which are not surrounded by a cell wall), they occur. 
These effects might naturally be ascribed to the absorption of 
water by the protoplasm, but they cannot be due to this cause, 
for observation shows that the cells do not increase in size as they 
would if water were absorbed. In some cases a few of the cells 
burst when transferred to distilled water, but the majority do not 
_ burst or even swell noticeably. This is probably due in some cases 
to the fact that swelling is prevented by the cell wall, for some 
cells which lack the cell wall (for example, spores of Polysiphonia) 
may swell in distilled water. Moreover, it was found that isotonic 
solutions of cane sugar produce the same effects as distilled water 
although not as rapidly. 
The increased permeability must be due, therefore, to the loss 
of certain substances upon which the maintenance of the normal 
permeability depends. The most important of these are undoubt- 
edly the inorganic salts. If the concentration of salts be lowered 
beyond a certain point, the permeability of the membrane increases 
very rapidly. This is shown by experiments in which the increase of 
permeability is directly measured by electrical means. In sea 
water plus an equal amount of distilled water the cells do not shrink, 
but with the addition of three volumes of distilled water they may 
begin to shrink in seven hours or less, and with increasing amount 
of distilled water shrinkage takes place more and more rapidly. 
These remarks apply only to balanced solutions such as sea water. 
