There is a rest period for buds of deciduous fruit trees during which they do not expand into shoots or flowers even though environmental conditions for growth are favorable. Buds enter this period of rest shortly after they are formed in the late spring or early summer and develop only microscopically until after they are exposed to the chilling temperatures of winter. Cold temperatures bring about physiological changes in the bud which end the rest period and enable the buds to expand when conditions for growth become favorable in the spring.