The relation of the refractive index of plant cell sap to its osmotic pressure

Abstract

Parallel measurements of the osmotic pressure (cryoscopic method) and the refractive index of cell sap were carried out on 246 samples from seven plant species. At the same time both values were ascertained as well as their relation for aqueous solutions of some sugars, organic acids and inorganic salts. The relations found with these model solutions are different for different substances. The quantitative composition of osmotically active components of cell sap changes in the course of ontogenesis and as a result the relation of refractive index and osmotic pressure also changes. By this comparison it has been shown that a reliable and more or less linear relation of the two values, which is advantageous for practical application, is only valid for a limited period in the ontogenesis of the experimental plant. The determination of the osmotic pressure of cell sap from the refractive index, the main advantage of which is its quickness and the small volume of sap required (0-02 ml.), is reliable if we construct empiricallyad hoc the appropriate correlation graph for the experimental plant for a limited ontogenetic period.