Initiation, Structure and Sprouting of Dormant Basal Buds in Betula pubescens

Abstract

The morphological basis for sprouting in Betula pubescens E hrh ., is studied with special reference to the initiation, structure and number of buds at the base of the tree and their development into sprouts. The material consists of seedlings of varying ages and stumps of mature trees. The dormant basal buds begin life as axillary buds at the seedling stage, positioned in accordance with the leaf arrangement. These primary basal buds are initiated in the axils of retarded leaves, and it is perhaps partly for this reason that they remain in a protracted state of dormancy. This dormancy is no more than a superficial feature, however, as, unlike the axillary buds higher up the stem, they are engaged in constant growth. They also differ structurally from ordinary axillary buds, possessing a growth point and a few scales after the first growing season, but no foliage leaf primordia, and gaining more scales as they age, normally one whorl per year. Similarly the vascular connection of a dormant basal bud grows year by year in accordance with the radial growth of the tree, thus ensuring that the bud does not become buried within the wood. The basal buds normally increase in number as the seedling grows, the primary buds branching to form clusters of secondary buds located in the axils of their scales. This branching requires a some degree of bursting of the buds. The resulting clusters are also found to vary in structure. Felling causes the majority of the dormant basal buds to burst, but only a certain number develop into sprouts. These sprouts differ morphologically from seedlings, especially in their pattern of ramification.