Abstract: Semi-thin sectioning and electron microscopy were used to observe and analyze the development processes in the bisexual flower and unisexual male flower of Xanthoceras sorbifolia Bunge. The results show that: (1)At the early microspore development stage, there is no obvious difference between these two different kinds of flowers. At the uninuclear phase of microspore development when the cell walls thicken, lip cells do not form in the bisexual flower, but develop in the unisexual male flower. At the mature microspore stage, the lip cells form completely and the anther forms a double heart-shape in the unisexual male flower. However, the anther has not broken completely and can not disperse pollen. (2)In the bisexual flower, the ovary has two rooms, the cells are closely packed, the stigmas are cylindrical with papillate cells, and there is a hollow canal inside the style. However, in the unisexual male flower, the development of stigmas cease without the formation of a hollow canal inside the style, the ovarian rooms shrink, and the embryo sac degenerates. (3)The tapetum cells of the unisexual male flower contain many protein bodies, amyloplasts, vacuoles, and Ubisch bodies, and the tapetum cells completely disappear at the later microspore development stage. However, these organelles become less abundant in tapetum cells of the bisexual flower, and the tapetum cells do not completely disappear. (4)The pollen cell wall thickens without germination apertures in the bisexual flower, whereas in the unisexual male flower there are three germination apertures on the pollen grains, and many vacuoles, protein bodies, and liposomes accumulate in the pollen grains.

Key words: Xanthoceras sorbifolia Bunge, bisexual flower, unisexual male flower, abortion, anatomy, ultrastructure