SHOOT APICAL MERISTEMS OF PICEA-SITCHENSIS SEEDLINGS ACCELERATE IN GROWTH FOLLOWING BUD-SET

First-year seedlings of P. sitchensis were induced to set buds by transferring them from long days (17 h) to short days (10 h at 20.degree. C, 12 h night at 12.degree. C). After 20 short days, the seedlings stopped growing in height, the shoot apical domes began enlarging and the transverse growth rates of the shoot apical dome tissues increased. For about 25 days thereafter primordia were produced faster within the developing buds than at the apices of seedlings which had been kept in long days to prevent bud-set. Accelerated primordia production after bud-set enables the largest possible buds to be formed during the frost-free period before winter.