Preliminary Results in Measuring the Hardiness of Plants.

The injury of plants occasioned by winter conditions has been a subject of great interest and importance to plant breeders and agriculturists. The development of hardy strains has been, and is, one of the principal means of comiibating losses caused by injury from cold, although cultural methods, as well, lhave been adapted to help the plant survive the rigors of its climatic environiment. Recog,nition of the degree of hardiness has necessitated field trials commonly requiring extended periods of time, during which weather conditions may be too mild to test the relative hardiness in one season, while so severe in the next that hardy as well as tender varieties and strains are severely injured. It is quite evident that a rapid means of measuring relative degrees of resistance to cold of strains and varieties of plants, grown with various cultural procedures, would hasten progress in the work of plant breeders, as well as facilitate investigations of the physical and chemical nature of the hardening process, and its relation to the resistance of plants to low temperatures and other climatic conditions. No attempt will be made to review the literature on hardiness or reactions of plants to freezing in reference to changes in permeability, colloidal structure or compositional variations. It seems to be generally accepted that the inijury, or killing of tissue, by cold, or by any other means, involves the disorganization of the substances essential for carrying on the processes of life. With such disorganization, it is well recognized that the cell loses its capacity to regulate the diffusion of its soluble contents. Upon this basis, it was assumed that the degree of injury from low temperature, to overwintering and other plant structures might be correlated with the exosmosis of electrolytes and other materials following exposure to cold. Such outiward diffusion of electrolytes can readily be estimated by conductivity measurements. Other investigators have applied conductivity metlhods to problems involving the viability of seeds, and the injury of plant and animal tissues. To test this hypothesis, alfalfa roots of three varieties of known hardiness (Grimm, Utah Common, and Hairy Peruvian) were frozen under con-