ABSTRACT
This study investigated male and female gametophytes in Ginkgo biloba, while a droplet of fluid was present in the fertilization chamber and found that the central cell, the generative cell and the neck mother cell divided simultaneously prior to fertilization. In male gametophytes, the generative cell divided to yield two sperm cells. Concomitantly, the two neck mother cells of the archegonium increased in size then divided asymmetrically resulting in two big cover cells and two small base cells. Each cell had a fixed end in direct contact with an adjacent jacket cell and a free end overlapping its counterpart. This unique arrangement could allow for their free ends to swing into the fertilization chamber as a result of the force from the interior of the archegonium where a polar periclinal division had occurred to produce a canal cell and an egg. The subsequent withdrawal of the content of the archegonium may facilitate the entry of sperm into the archegonium. The neck apparatus closed after the fertilization occurred. The concurrence of the above divisions and the delicate structure of neck apparatus suggest that the gametophytes undergo a synchronization process to become receptive at the time of fertilization. However, the formation of neck cells and the opening time of neck apparatus of the archegonia within the same ovule were slightly different, which could lead to the formation of zygotes at a temporally distinct interval. The earlier formed zygote may progress as the only mature embryo in the ovule.