Hardy woody species which cold acclimate late or slowly are often injured by early autumn frosts. Adapted hardy species characteristically stop growing and acclimate to some extent prior to autumn frosts. In nature this first stage of acclimation appears to be induced by shortening photoperiods in a number of woody species (4, 23, 24). Because growth cessation is associated with cold acclimation in woody plants, a considerable amount of work has been done to determine whether growth retarding chemicals can induce cold acclimation in the absence of inductive photoperiods. The growth retardants tested have been found to have only slight and often inconsistent effects on hardiness (7, 8, 13, 15). Such findings have stimulated interest in elucidating the effective endogenous system(s) which induce acclimation in hardy species (7, 8). Several researchers have recently reported that short-day-induced leaves are the source of translocatable hardiness promoting factor(s) (4, 5, 10). The existence of such a factor(s) is of practical interest because it (they) may prove to be a relatively simple compound(s) which could be applied exogenously to induce acclimation in the absence of inductive environmental stimuli. There is, as yet, no evidence to indicate whether or not the promoting factor(s) is genotype specific. A considerable amount of research has been done on the environmental control of cold acclimation (1, 4, 10, 24), the natural patterns of acclimation (4, 22), and the metabolic changes associated with acclimation (14) in red-osier dogwood (Cornus stolonifera Michx.). In nature, acclimation usually proceeds in two distinct stages which appear to be induced by short days and low temperatures (4, 21, 22), respectively. Climatic races collected from various sites in North America were found to differ greatly in the timing and rate of cold acclimation when they were grown in a uniform environment field plot in Minnesota (18). In the field at St. Paul, Minnesota (45° North latitude), a clone from Dickinson, North Dakota (47° North latitude), was found to begin cold acclimating as much as 8 weeks earlier in the autumn than a clone from Seattle, Washington (47° North latitude) (20). Both races eventually acclimate to below -196 C, but the Seattle race is often injured severely by the first frost in the autumn at St. Paul. The influence of gibberellic acid and abscisic acid on cold acclimation has been studied in the hardy tree, Acer negundo (8). Based on these results, Irving has suggested that abscisic acid may be the hardiness promoting factor (6).