Permeability of Membranes as Related to Their Composition

The role of different substances in seed coats in regulating their permeability to water was studied. 2. Membranes were extracted with water, alcohol, acetone, ether, and calcium chloride, and their permeability measured before and after such treatments. 3. Cross-sections of the seed coats were made and tested microchemically to determine the nature of the substances present, and the effect upon them of the different methods of treatment employed in the experiment. A chemical analysis of the seed coat of the peanut and of the extracted materials was made to determine the content of tannins, lipoids, and proteins. 4. Extraction with hot water increased the permeability of the peanut and almond seed coats, the percentage increase ranging from 135 to 500 per cent. Such treatment removed from the peanut membrane the tannins and a part of the lipoid materials. 5. Extraction with hot water did not measurably increase the permeability of the grapefruit and squash seed coats; but these membranes before such treatment were so resistant to the passage of water that an increase could have resulted from the hot water extraction without being detected by the apparatus under the conditions of the experiment. 6. Extraction with hot lipoid solvents increased the permeability of all membranes studied except the seed coat of the grapefruit. The percentage of increase ranged from 15 to 871 per cent. 7. Extraction with acetone at room temperature also increased the permeability of all the seed coats except that of the grapefruit. The percentage increase ranged from 53 to 313 per cent. 8. After a membrane had its lipoid content removed, its permeability was decreased by impregnating it with the lipoid material that had been extracted; but in no case was the permeability reduced to the low point exhibited by it before the process of extraction. 9. Calcium chloride treatments increased the permeability of the membranes, but the cause of this increase could not be determined. 10. The substances found to be factors in determining the permeability of the membranes to water were lipoids, tannins, and pectic substances. Suberized layers were not found to be significant in the membranes studied, and the presence of soluble proteins could not be detected.