A series of experiments and data have been pre sented, indicating that the degree of resistance of plants to injury by cold weather may be measured by the diffu sion of electrolytes and other substances from chilled or frozen tissues into water after such tissues have thawed. The amount of diffusion has been determined with alfalfa roots by conductivity measurements, which have been supplemented by colorimetric tests for chlorides. Within the limits of this investigation there exist cor relations between known hardiness of alfalfa roots and the degree of retention of electrolytes by the tissue after freezing.