REGULATION OF THE GROWTH POTENTIAL OF DOUGLAS FIR SEEDLINGS DURING DORMANCY

Abstract

S ummary The three experiments indicated that individual buds were the receptors for the growth stimulus produced by extended photoperiods during the autumn and winter. No evidence of transport of growth stimulatory materials from active to dormant bud was noted. Buds whose chilling requirements were fully satisfied initiated growth in response to favourable temperatures rather than to long photoperiods. Initiation of activity by lateral cambia required material exported from both expanding buds and mature foliage. No significant correlation between shoot and root growth was found. Although neither active buds nor applications of exogenous IAA or GA stimulated roots growth, both root elongation and initiation were found to be dependent upon some substance or substances, presumably hormones or carbohydrates, exported from mature foliage. Findings indicated that seedling physiology during the dormant period may be controlled by a changing balance in growth inhibitors and promoters.