白桦雌雄花发育周期的时序特征

Temporal Characteristics of Developmental Cycles of Female and Male Flowers in Betula platyphylla in Northeastern China

以20—30年生白桦的雌雄花序为材料，研究东北地区白桦花发育的生殖周期和发育时序特征。结果表明：雌花序出现于4月中下旬，5—10d后开始受粉，持续1周左右；大孢子母细胞于5月中旬开始减数分裂．3．4d后形成大孢子，功能大孢子继续发育，成熟胚囊在5月底产生，并进行受精，6月初开始胚胎发育，8月中下旬种子成熟。雄花序出现于5月底，比雌花序晚1个月左右；小孢子母细胞于7月中旬开始减数分裂，8月中旬结束，历时近1个月；白桦的雄配子体发育很特殊，在当年不形成成熟的雄配子体，以单核小孢子状态宿存于雄花序中越冬，直到第2年4月中下旬才发育成熟，形成具有2核或3核的成熟花粉，随即散粉。雌花受粉时的花粉来源于前1年出现、宿存越冬、第2年4月底开始散粉的雄花。通过比较，建立东北地区白桦雌雄花生殖周期时序特征表，并对白桦雌雄花发育的时序特点进行讨论。

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.