Shoot development in Betula papyrifera. I. Short-shoot organogenesis

Abstract

Buds and developing branches of Betula papyrifera were collected weekly from mature trees during three successive growing seasons. Material was prepared to show stages of bud inception, development, and flushing and female inflorescence inception. Short shoots develop from (i) proximal axillary buds on long shoots (ii) short-shoot terminal buds, or (iii) axillary buds on flowering short shoots. An axillary bud apex forms a terminal bud after bud burst. An axillary bud possesses one outer rudimentary leaf, but all other short-shoot buds have three outer rudimentary leaves. All short-shoot buds possess, in addition, one–three embryonic foliage leaves and, distally, three primordial rudimentary leaves which form the outermost appendages of the succeeding terminal bud. Rudimentary leaf stipules form the cataphylls. Foliage leaf primordia are initiated in May – early June and rudimentary leaves arise in late June – July. If a bud apex is initiated in year n, female inflorescence induction occurs in late June of year n + 1 or any succeeding year. An axillary bud develops on a short shoot as a consequence of flowering; it is initiated concurrently with inflorescence development and its development is completed during flowering and seed maturation. Short- and long-shoot buds can be distinguished, upon dissection, in mid-July when buds are forming. Hence, determination of potential long and short shoots occurs the year before bud burst.