银杏( Ginkgo biloba L. ) 大孢子的发生和形成

研究观察银杏（Ginkgo bilobaL.）大孢子母细胞发生和大孢子的形成过程，结果表明银杏大孢子发生在4月中旬，从孢原细胞到雌配子体游离核时期，要经历几个不同的发育阶段，未成熟的大孢子母细胞近菱形的，并被一层较厚的细胞壁近围绕，初期一个大细胞核位地细胞的中央，各种细胞器散布在细胞质中，将要成熟时，大孢子母细胞以胚珠纵轴的方向伸长，当大孢子母细胞的长度宽度的3－4倍时，即进入成熟阶段，并出现较大的液泡，随后大孢子母细胞开始发生减数分裂，形成一纵列四分体大孢子，但到后来只有合点端的一个是具功能的，珠孔端的3个大孢子逐渐退化消失，具功能的大孢子进行有丝分裂，形成众多雌配子体游离核。

THE FORMATION OF MEGASPORE AND THE GENESIS OF FEMALE GAMETOPHYTE OF GINKGO BILOBA

The megaspore of Ginkgo biloba occurred in the middle of April and went through several different developmental stages from archesporium cell to free nucleus of female gametophyte. The immature megaspore mother cell of Ginkgo biloba was approximately lozenged and had a thick wall. A large nucleus aws situated at the center of the cell and organelles were scattered over the cytoplasm during initial stage. As approaching maturity the cell gradually enlarged and elongated in the direction of length axis of the ovular when the length of the megaspore mother cell was 3-4 thmes large than width, the megaspore mother cell was ripe and had big vacuole, soon afterwards the megaspore mother cell began meiosis and the megaspore tetrad formed along the ovular axis. Three megaspore facing the micropylar pole gradually degenerated and one megaspore had function near the chalaza. The nucleus of the function near the chalaza. The nucleus of the functional megaspore was in the process of mitosis and formed free nuclei of the female gametophyte.