Studies in Permeability. 
III. The Absorption of Acids by Plant Tissue. 
BY 
MILDRED HIND. 
With eleven Figures in the Text. 
I N the first of these studies it has been shown that cells of potato tuber 
absorb hydrogen ions from aqueous solutions of hydrochloric acid with 
considerable rapidity. In this paper an account is given of more detailed 
experiments made to determine to what extent this rapid absorption is 
a characteristic of acids in general. 
Earlier work (4) appears to indicate that with strong acids it is the 
concentration of the hydrogen ion which is the determining factor of the 
action of acid on plants, while with organic acids the anion is stated to 
influence the action (6). So far, the methods which have been used have 
given little information as to the extent to which acids are actually absorbed 
by plant tissue, nor have these methods yielded results of any great 
accuracy. In the experiments recorded in this paper the methods of 
physical chemistry advocated and described in previous papers of this 
series have been used. 
Again, so far there has not been produced much evidence as to the 
substances which are responsible for the absorption of acids. For instance, 
Czapek (1, 2, 3) seems to be of the opinion that the action of acids on the 
fat emulsions of the plasma is responsible for the effects produced ; on the 
other hand, Loeb (5, 7), Pauli (11), and Osterhout (9) think that protein 
substances are active in many of the phenomena of permeability. Some 
experiments have accordingly been made in the course of this work in 
regard to the action of acids on various plant substances, but however 
suggestive the results of these experiments may be, it is of course impossible 
to draw from a few isolated experiments any definite conclusions in regard 
to the structure and function of cell membranes. 
This work was undertaken at the suggestion of Mr. Stiles and Mr. 
Jorgensen, whom I would here thank for their advice during its progress. 
[Annals of Botany, Vol. XXX. No. CXV 1 II. April, 1916.] 
