Abstract
The top whorl of branches on each year's leader on mature P. sitchensis (Bong.) Carr. had more needles and longer needle internodes than branches lower down on the leader. All branches developed as buds for similar periods of time from April to October, but top branch buds developed larger apical meristems which generated needle primordia more rapidly than lower branch buds. In mid-August, top branch buds produced at least 13 primordia per day compared with only 5 per day in basal buds. In the next year, when these preformed buds extended, top branches produced about one and a half times as many cells per needle internode as basal branches, as judged by observing the pith. In both years, cell division was the important growth process affected by 'dominance' mechanisms between branch buds.
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