Morphology and Development of Populus deltoides Branches in Different Environments

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Abstract
The structure of axillary buds of P. deltoides Bartr. ex Marsh. and the development of branches from these buds were studied under conditions promoting vigorous growth, inducing dormancy and dormancy release, and inhibiting axillary bud break. Bud growth and branch development continued without interruption on vigorous plants but buds were inhibited on less vigorous plants growing under less favorable conditions. Bud growth declined and then ceased during dormancy induction. Both dormant and apically inhibited buds had mature protoxylem connections with the main stem; therefore, bud inhibition could not be directly attributed to lack of vascularization. Under all growth conditions, specific leaves on every branch were smaller at maturity than adjacent leaves. Anisophylly was present in primordia within the bud and it was accentuated during leaf expansion. Small anisophyllous leaves experienced higher percentages of both leaf abortion and senescence than adjacent leaves. The presence of anisophylly throughout ontogeny, its persistence on all branches under all growth conditions and its relation to demonstrated patterns of vascular organization, all suggest a definite role for nutritional and/or hormonal gradients.

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