关键词: 白桦, 花发育, 周期

Abstract:

The reproductive cycle and temporal characteristics of flower development for the female and male inflorescences of 20 to 30-year-old Betula platyphylla in northeastern China were studied. Results showed that female inflorescence occurs in the middle and last ten days of April, beginning to be pollinated several days later and lasting about one week. Megasporocyte begins the meiosis at the middle ten days of May, and comes into being megaspores at 3～4 days later. Then functional megaspore continues to develop, mature embryo sac forms at the late May and begins to fertilize, embryogenesis begins at the early June, and a seed ripens at the middle and last ten days of August. Male inflorescence is formed at the late May, which is later about one month than female inflorescence. Microsporocyte begins the meiosis at the middle ten days of July, and ends at the middle ten days of August, lasting about one month. The development of male gametophyte in B. platyphylla is obviously different from that of female gametophyte. The flowers don’t form the mature male gametophyte at this year, overwintering in male inflorescence with monocaryon microspore, and develop to maturation until the middle ten days of April at the next year, forming the mature pollen with 2～3 nucleus, and then disseminating pollen. The pollen pollinating female flowers comes from the overwintering male flowers at the previous year. The temporal characteristics table of reproductive cycles of female and male flowers of northeastern B. platyphylla was established, and the temporal characteristics of female and male flowers in B. platyphylla were discussed.

Key words: Betula platyphylla, flower development, cycle