Abstract: Eucommia ulmoides Oliv. is a typical dioecious species, a plant with an approximately equal propertion of the staminate and pistillate trees, suggesting that the gene responsible for sex determination couldbelocated on file sex chromosomes. Nevertheless heteromorphous sex chromosomes were not found in their ovary and anther cells. Homologous chromosome pairing and division regularly occurred during meiosis of the pollen mother cells and occasionally chromosome bridges, chain and ring tetmvalents were observed in a few ceils.However, the length and maximum diameter of the apical buds in the staminate trees were significantly more than those in the pistillate, trees throughout the hudding process from mid-Deoeinber to mid-April ( P < 0.01 ).In contrast, the gutta content of the leaves in the pistillate trees was significantly much nvore than that in thestanfinate trees (P < 0.01 ). And in beth staminate and pistillate trees, however, the gutta content graduallydecreased, in the same propertion between the staminate and pistillate trees, from April to October with the seasonal change and the growth of leaves. These indicated that the size of the buds and the mount of the leafgutta content in E. ulmoides were sex dependant. Since beth of the gutta content and bud-size were quantita- tire characters which were usually contrelled by multiple genes unlikely being all located on the sex chromo-somes, it might be possible that some of the important genes controlling these two characters could be linkedwith the genes responsible for sex determination.

Key words: Eucommia ulmoides, Sexuality, Apical buds, Gutta content