Knowledge of the level of cold stress resistance and how this resistance is inherited in sour cherry is essential to cultivar development and future germplasm collection. Twig and flower bud samples of two sweet cherries (Prunus avium L.), 12 sour cherries (Prunus cerasus L.), and one ground (Prunus fruticosa Pall.) were collected once a month from Aug. 1990 to Mar. 1991, preconditioned, and subjected to freeze tests and differential thermal analysis. LTEs were detected in all stems of P. cerasus investigated and were strongly correlated to xylem ITs in December to March. LTEs were strongly correlated to phloem-cambium ITs in November. Xylem ITs were the selected method for evaluating sour cherry cold resistance in December to March. Phloem-cambium ITs were the selected method for November. The degree of hardiness of the phloem-cambium in late fall and early spring is a factor determining P. cerasus germplasm geographic distribution and commercial production. The principal component (PC) analyses, of the phloem-cambium and cortical tissues, depict gradations between minimum survival temperatures of the two presumed progenitor species of sour cherry, sweet cherry and ground cherry suggesting that cold is a major selective force, contributing to sour cherry population variation.