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

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Abstract
Buds and developing branches of B. papyrifera were collected weekly from mature trees during 3 successive growing seasons. Material was prepared to show stages of bud inception, development, flushing and female inflorescence inception. Short shoots develop from proximal axillary buds on long shoots, short-shoot terminal buds or 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 3 outer rudimentary leaves. All short-shoot buds possess, in addition, 1-3 embryonic foliage leaves and, distally, 3 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.