A STUDY OF PERMEABILITY BY THE METHOD OF TISSUE 
TENSION 
S. C. Brooks 
A number of investigators have shown that recovery from plas- 
Tnolysis is not wholly satisfactory as a criterion of the permeability 
•of protoplasm to a plasmolyzing agent because of the possible in- 
jurious mechanical effect of the plasmolysis itself.^ It is evident that 
this difficulty disappears if instead of plasmolysis and recovery we 
•use as a criterion the shrinkage and the elongation of young, highly 
^stretched tissues, taking care that the shrinkage does not proceed 
far enough to cause a retraction of the protoplasm from the cell walls. 
This is most conveniently done with tissues in which the changes in 
turgidity are indicated by a bending of the tissue, due to great differ- 
ences in the elasticity of the cell wall in its different layers. 
In rapidly elongating plant tissues there is usually a very con- 
siderable pressure exerted by the protoplasts against the cell walls 
which confine them. If all the cell walls of the stem are thin and 
elastic, the whole stem will be kept in a stretched condition by this 
pressure. The presence of thick walled cells, such as fibro-vascular 
or epidermal cells, which are not easily stretched by internal pressure, 
will, if they are symmetrically distributed, prevent this elongation of 
the tissue. If now we cut such a stem or peduncle in such a way that 
these two types of tissue are unsymmetrically distributed, the whole 
tissue will curl so that the elastic tissue forms the longer, or convex 
side. The distension of the elastic tissues, and therefore the degree 
of curvature, will vary with the turgidity of the tissues. A hypertonic 
solution will withdraw water from the cells, and consequently reduce 
the turgidity and the degree of curvature, while a hypotonic solution 
will have the opposite effect. The penetration of the protoplasm by a 
salt with whose solution such a tissue had come into osmotic equi- 
librium would lead to an increase in the turgidity, and hence in the 
curvature of the tissue. De Vries (8), in the investigation of the iso- 
tonic coefficients of various substances by this method, observed such 
1 Cf. Bower (i), Chodat and Boubier (3), Hecht (4), and Kuster (5). 
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