Megagametophyte and Embryo Development of Betula platyphylla in Northeastern China

This paper describes megasporogenesis, megagametogenesis, and the process of embryonic development of the female inflorescence in 20-year-old Betula platyphylla. Megaspore mother cells undergo meiosis, which results in the formation of 4 megaspores in a row. The chalazal-most cell develops into an 8-nuclei embryo sac after 3 rounds of mitosis. A mature embryo sac is produced after cellularization and nuclear migration. The other cells of the tetrad undergo degeneration. The mature embryo sac consists of an egg apparatus, a central cell, and 3 antipodal cells. The embryo sac is a monosporic Polygonum type. The zygote develops into a mature embryo going through proembryo, globular, heart, and torpedo stages. The suspensor is developed fully at the stage of globular embryo and consists of 3 cells, which are degenerated later. The organization and development of the female flower and the type and synchrony of embryogenesis in Betulaceae are also discussed.