SOME CRITICAL COMMENTS ON THE METHODS EMPLOYED IN THE EXPRESSION OF LEAF SAPS

Abstract

Treatment of leaves of Pinus rigida by grinding to a shredded pulp or by freezing with an ice-salt mixture, or with solid CO2, gave press-juices similar in amount and in osmotic value provided the leaves were in the summer condition (Aug.). But when these three methods were applied to leaves in the winter condition (Jan.) the ice-salt method gave a smaller volume of juice with a much lower osmotic value. A field method for collecting and freezing leaves by solid CO2 and a press with a capacity of 100 grams of leaf tissue for obtaining juice at known pressures are described. Papers reporting results on this subject should state the water content of tissue, exact method of preparing and pressing, pressure used, and volume of sap obtained.