STUDIES ON EXOSMOSIS 
S. C. Brooks 
In experiments on permeability where the turgidity of plant cells 
or their osmotic pressure (as judged by that of a solution just concen- 
trated enough to plasmolyze them) is used as a criterion, there is an 
important source of error, which is usually overlooked. This lies in 
the possibility that osmotically active substances may diffuse out o£ 
the cell. 
It was noted as early as i860 by Knop, in connection with water 
cultures, that plant organs bathed by distilled water may give off 
substances to it. This phenomenon, usually termed exosmosis, may 
take place when tissues which are not normally in contact with water 
are placed in contact with distilled water or dilute solutions. Thus 
Wachter (7), found that strips of onion bulb scale gave off sugars to 
distilled water, and that this exosmosis was hindered by o.i to 0.4 M 
solutions of potassium and sodium chlorides and potassium nitrate. 
Recently True and Bartlett (4, 5, 6) have made a thorough in- 
vestigation of the intake and outgo of salts from roots of field peas 
grown in distilled and river water, and in solutions (mostly 0.001 M) 
of various salts singly and in combinations. A somewhat similar 
investigation by Merrill (i, 2) included the study of the effects of salt 
concentrations as high as o.i M} 
In all these experiments solutions were used whose concentration 
was far below that necessary to cause plasmolysis, and the effects 
were observed after periods up to fifty days, at which time the pure 
salt effects might be obscured by the readjustments of the organism 
to its change in environment. They do not, therefore, enable us to- 
distinguish the immediate effects of salts on the plasma membrane,, 
nor do they help us to determine the possible role of exosmosis in 
experiments whose duration is a matter of a few hours at most, as is 
the case in most experiments in which the turgidity of cells or their 
recovery from plasmolysis is used as a criterion of their permeability. 
1 It is not known to what extent the results (in all the cases here cited) may be 
due to the death of superficial cells of the roots. 
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