The Estimation of the Osmotic Potential of Plant Sap by Refractometry and Conductimetry: A Field Method1

Abstract

The refractive index and electrical conductivity of the leaf sap of 17 plant species were measured and the osmotic potentials contributed by electrolytes and soluble metabolites estimated from certain simplifying assumptions. The sum of these two estimates agreed remarkably well with the total osmotic potential of the sap as measured by cryoscopy. A detailed description is presented of the equipment employed, and the field applicability of the refractometry-conducti-metry method of estimating the osmotic potential is pointed out.