Oct., 1923] ROBBINS-ISOELECTRIC POINT FOR PLANT TISSUE 437 
has been established by these experiments, it would appear very difficult to 
explain the phenomena which have been described on the basis of the con¬ 
ception of the cell as an osmotic chamber and of the theories of permeability 
of the plasma membrane which have been suggested. It would appear of 
extreme importance to reinvestigate the problems of water absorption and 
permeability, particularly with relation to salts and dyes, from this stand¬ 
point, bearing in mind that other constituents of the cell than proteins may 
react with dissolved material. 2 
Some substantiation of the conception that plant tissue may have an 
isoelectric point is afforded by the work of Osterhout on the conductivity 
of the tissue of Laminaria. Osterhout (19) found that alkali increased the 
conductivity of the tissue. Acid (20) was found to produce first a sharp 
decrease in conductivity, followed by a rapid increase. While no measure¬ 
ments were made on the hydrogen-ion concentrations of the solutions used, 
this result would be analogous to the changes which would take place in the 
conductivity of a protein which was originally in a solution more alkaline 
than the isoelectric point. 3 In the presence of alkali, the formation of 
greater and greater quantities of metal proteinates, accompanied by in¬ 
creased conductivity, would result. The addition of acid would first cause 
a decrease in the quantity of metal proteinates and probably produce an 
exosmosis of bases. When the isoelectric point was reached the minimum 
conductivity would be found. Further increase in acid would increase the 
amount of protein combined with anions and result in increased con¬ 
ductivity. It would appear advisable to reinvestigate the experiments 
which have been performed by Osterhout on the effect of salts and other 
conditions on the conductivity of plant tissue from the standpoint of the 
quantities of material which can conduct electricity rather than of the ease 
with which the electrolytes can move through the protoplasm. 
The conception that protoplasm acts like an ampholyte with an iso¬ 
electric point in water absorption and in the absorption of solutes is one 
which, if substantiated by further investigation, would be of far-reaching 
importance. It would bear directly on the problem of water- and salt- 
absorption by plant cells, of the excretion of water by cells, the translocation 
of salts from one part of the plant to another, and conceivably on the rest 
period of plants in such cases as are apparently due to protoplasmic condi¬ 
tion. (See Eckerson, 7.) 
Whether we are correct or not in proposing the existence of an isoelectric 
point for plant tissue, 4 it would appear that the demonstration that there is a 
2 The analogy between the absorption of water by animal tissue and by proteins has 
been most completely presented by M. H. Fischer, in “ Oedema and Nephritis,” 3d ed. 
3 This has been suggested by W. O. Fenn. Similarity in the behavior of protoplasm 
and gelatine. Proc. Nat. Acad. Sci. 2: 537-543. 1916. 
4 From the effect of salts in acid and alkaline solutions on the absorption of dyes by 
Elodea, an isoelectric point of between pH 3.8 and pH 4.1 was proposed for the protoplasm 
of that plant by J. Endler. See Ueber den Durchtritt von Salzen durch das Protoplasma. 
