黑节草大孢子发生及雌配子体发育研究

Studies on the Megasporogenesis and the Development of the Female Gametophytes in Dendrobium candidum Wall ex Lindl nvva11 cx Lindl

胚珠具内外珠被，珠心仅１～２层细胞。孢原细胞起源于珠心表层下，其不经分裂直接转化为大孢子母细胞，大孢子母细胞减数分裂正常，形成的四个大孢子纵行排列，其中只有合点端的一个能继续发育，此大孢子连续进行３次有丝分裂，其中后２次分裂有很高的同步性。胚囊属于典型的蓼型胚囊。极核在受精前多融合形成次生核。反足细胞位于合点端或稍靠中央，有退化趋势，到受精前已基本消失。

The present paper deals with the megasporogenesis and the development ofthe female gametophytes in Dendrobium candidum Wall ex Lindl.The ovule isbitegminous.The nucellus only consists of one to two layer cells. During early stages onecell, lying directly below the nucellar epidermis,differentiates into a archesporialcell.This cell directly acts as the megaspore mother cell and divides meiotically.This pro-cess consists of two successive divisions and gives rise to four haploid megaspores in a linearrow. The three micropylar megaspores degenerate and the chalazal one develops into themegagametophyte (embryo sac).The functional megaspore enlarges and takes threemitoses.The divisions of the nuclei of the coenocyte are completely synchronous.The em-bryo sac is Polygonum type. Fusion of the two polar nuclei is completed beforeferilization.The ephemeral antipodal cells are at the chalazal pole of sometimes near thechalazal pole. Before fertilization they degenerated.