572 
BOTANY: S. C. BROOKS 
ing the intercellular spaces come into contact with a dilute solution 
which replaces the intercellular sap, a disturbance of equilibrium occurs, 
involving loss of solutes from the cell. Such an 'exosmosis' would 
delay the recovery of a plasmolysed cell. 
The comparative rate of exomosis of electrolytes was studied in 
strips of the peduncles of the common dandelion {Taraxacum officinale 
Weber) and was determined in the following manner: comparable lots 
of tissue were placed for a period of twenty minutes in isotonic solu- 
tions of sodium, calcium and aluminium chlorides, and in an isotonic 
balanced solution containing salts in the following molecular propor- 
tions: NaCl 68.4%, CaCl2 19.8%, MgCU 6.7%, MgS04 3.3% and 
KCl 1.9%, and in distilled water. After removal from these solutions 
the lots of tissue were rinsed and placed in measured amounts of dis- 
tilled water, whose conductivity was determined at suitable intervals. 
It had previously been determined that outward diffusion of the salts 
which had entered the tissue from these solutions was practically com- 
plete in thirty minutes. After thirty minutes the rate of change of 
conductivity of the distilled water bathing the tissue was therefor a 
measure of the rate of exosmosis of electrolytes normally present in the 
cell. 
The rate of exosmosis from tissue previously exposed to distilled 
water or to the balanced solution was less than that from tissue treated 
with sodium chloride, and greater than that from tissue treated with 
calcium chloride. The tissue treated with cerium chloride showed a 
slow exosmosis which after a time became quite rapid, ultimately 
exceeding that from any other lot of tissue. This effect v/as probably 
due to the toxic effect of the cerium, which, like lanthanum, causes an 
increase of permeability following the initial decrease. The data are 
graphically presented in figures 3 and 4. 
It is therefore apparent that exosmosis from living cells is influenced 
by salts such as are frequently used in plasmolytic experiments. In 
Taraxacum, as in Laminaria, sodium increases permeability, while cal- 
cium cerium and lanthanum cause an initial decrease. A balanced 
solution may be prepared, of a constitution such that it will cause no 
appreciable alteration in the permeability of the protoplasm of a given 
plant. 
3. The conclusions derived from the experiments on exosmosis were 
were confirmed and amplified by experiments in which changes in tur- 
gidity were used to measure the rate of penetration of sodium potas- 
sium, calcium, magnesium, aluminium and cerium chlorides, potas- 
sium nitrate, saccharose, and the balanced solution heretofore described. 
