关键词: 龙眼, 花蜜腺, 结构, 发育

Abstract: The structure and development of floral nectaries of Dimocarpus longan were studied with
scanning electron microscopy ( SEM ) , paraffin section, thin resin sections and transmission electron
microscopy (TEM). The floral nectaries ofmale and female flowers of Dim ocarpus longan were located on the
surface of floral recep tacle, which formed a convex disc-like nectary. The nectarywas located at the outer part
of the pistil and stamen and at the inner part of corolla and calyx. The male and female flower nectaries,
composed of epidermis, nectariferous tissue and vascular tissue containing only phloem elements, belong to
typical structural nectaries. The epidermis of floral nectaries was covered with numerous epidermal hairs
consisting of single cellwith thickened wall and cuticle. In addition, some small stomata were observed at the
top surface of nectaries. There were a lot of granulose phenolic compounds within most ep idermis cells. Two
types of cells could be distinguished in nectariferous tissue, one was smaller and had densely stained cyto
p lasm, anotherwas larger and contained phenolic compounds. The former consisted ofmore cells than the lat
er. The nectaries had well-developed vascular tissues, which derived from the branches of the vascular bundle
of floral recep tacle, then they terminated nearby ep idermis. Normally the nectariesps p rimordia ofmale and fe
male flower ofD. longan were found to initiate in surface of recep tacle after other floral organswere differenti
ated. During the development of floral nectaries, especially before and after the nectar secretion, the vacuole
volume ofmost of nectariferous tissue cells changed regularly, which imply that they may be involved in the
p rocess of nectar synthesis and secretion. Some phenolic compounds in specialized cells of nectariferous tissue were disintegrating during nectar secretion, so besides its p rotective function in floral nectaries, the phenolic
compounds were likely to take part in synthesis of nectar.

Key words: Dimocarpus longan Lour., Floral nectary, Structure, Development