Indeterminate shoot extension and heterophylly in Acersaccharum

Abstract

Shoots of Acersaccharum Marsh., with at least three long internodes were of two types: long determinate shoots (LDS) usually quickly expanding three or four pairs of preformed leaves and then developing terminal buds; and indeterminate shoots (IS) similarly expanding usually four pairs of preformed leaves and then several pairs of neoformed leaves before developing their terminal buds. The neoformed leaves were smaller, of different shape, and took longer to complete expansion than the preformed leaves. The mature form of the preformed leaves was related to the degree of development of the leaves in the overwintering buds. The last pair of preformed leaves was sometimes intermediate in morphology between earlier preformed and neoformed leaves. The last two pairs of lateral buds on IS were generally formed close together below the terminal bud because internode extension between the last two pairs of neoformed leaves was minimal. On LDS, there was a long internode between the last two pairs of preformed leaves, thus, only one pair of lateral buds was situated close to the terminal bud.