Dormancy in deciduous fruit trees and other woody perennials of the temperate zones is a phase of development that occurs annually and enables plants to survive cold winters. It is similar—although not necessarily identical—to dormancy in bulbs, tubers, and seeds. Because of its relation to frost hardiness, horticulturists initially dealt mainly with the induction of dormancy, especially in those parts of the world where cold winters are common. The release from dormancy was studied first by those who were engaged in early forcing of ornamentals. It received little attention in deciduous fruits until early attempts were made to grow temperate fruits in the subtropics or even in the tropics, where cold winters do not exist. In those warm-winter regions, prolonged dormancy became an important obstacle to economic production of temperate crops. The dynamics of dormancy induction and release, ie, the role of the factors involved both within and outside the plants, and the mode of their action, are still not yet fully understood, in spite of the countless publications dealing with dormancy or some of its aspects. Many interesting hypotheses and theories have been suggested, only to be rejected. This subject has been reviewed by Doorenbos (1953), Samish (1954), Vegis (1961, 1964, 1965a, b), Romberger (1963), Leike (1965), Wareing (1969), Wareing and Saunders (1971), Saunders (1978), and Noodén and Weber (1978).

Without a comprehensive theory of dormancy, it will be extremely difficult to improve the management of dormancy release, beit for the promotion or the retardation of growth and development or for the calculation of the actual state of dormancy as an important prerequi-site for the proper timing of various cultural practices. This review is intended to contribute to our understanding of dormancy and of the mechanisms involved in dormancy release, especially in deciduous fruit trees, and possibly in other woody perennials, by incorporating the more recent findings of research on problems of prolonged dormancy in warmer regions into the fund of knowledge from cooler parts