Shoot development in Betula papyrifera. VI. Development of the reproductive structures

Abstract

Reproductive buds and developing inflorescences were collected weekly from mature trees during three successive growing seasons in northwestern Ontario. Material was prepared to show all stages of inflorescence and flower development and meiosis. Male inflorescence induction, involving the long-shoot bud apex and one or two proximal axillary apices, occurred in early May, before bud burst. Female induction involved the short-shoot bud apex and occurred in late June – early July. Both male and female partial inflorescences resembled a simple dichasium. The male flower consisted of usually two stamens and two or three tepals variably arranged. Meiosis occurred in late July – early August. Each female flower consisted of two stigmas, two connate tepals that were not noticeable at maturity, and a parietal placenta bearing two unitegmic ovules. Meiosis occurred in mid-June, after pollination in mid-May. It is concluded that developmental data do not help elucidate whether the inferior portion of the gynoecial wall is cauline or appendicular and whether the placenta is derived from axial or carpellary tissue. It is suggested that the trigger(s) evoking male and female inflorescence induction may be different and that the metabolic prerequisites for induction and early development would be supplied by winter-stored material for male development and by current metabolic processes for female development.