Further Studies on Cold Resistance in Evergreens, with Special Reference to the Possible Role of Bound Water

Abstract

A pressure dehydration method of distinguishing between bound and free water in plant tissues is described. A modified form of the calorimetric procedure of determining the amount of free water in a system, suitable for use with plant tissues, is outlined. An improved form of the equation for calculating the amount of free water from the calorimetric data is also derived. The total amount of water in leaves of the pitch pine (Pinus rigida Mill.) was about 5% less in winter than in summer. Larger amounts of sap can be expressed from these leaves in summer than in winter, but this difference represents almost entirely a correlation with the difference in total water content. No evidence could be obtained by the pressure dehydration method of any significant increase in amount of bound water in pine leaf tissues in winter as compared with summer. The calorimetric determinations showed greater amounts of both bound and free water per gm. of dry matter in leaves of this sp. in summer than in winter. The differences between summer and winter values were statistically significant. Apparently there is a positive correlation between the total hydration of the tissues and the amounts of both bound and free water per gm. of dry matter. No evidence was obtained, therefore, that increase in bound water plays any role in the cold resistance of this sp.