Structure of Stigma and Germination of Pollen in Japanese Chestnut (Castanea crenata Sieb. et Zucc.).

The milky-white and needle-shaped styles of Japanese chestnut (Castanea crenata Sieb.et Zucc.) have epidermal cells with thick and hard cell walls covered with cuticle.No distinct stigma-like part was seen macroscopically at the tip of style, but microscopically a shallow cavity was visible.Only pollen grains which land on this cavity germinate and the pollen tube penetrates the style, indicating that this cavity is stigma.Pollen tubes grow down the stylar canal surrounded by vascular bundles and penetrate into the ovary.2. In 'Yamato-Wase', the inner diameter of the stigma remains about 0.05 mm throughout July.The diameters of pollen grains are 0.012 to 0.013 mm in four cultivars, including 'Yamato -Wase'.3. Pollen germination on the stigma and pollen tube growth began as the style ceased to elongate and for about a week thereafter.If pollinated while the styles are still elongating, pollen germination and/or pollen tube growth were retarded.In open-pollination, pollen germination also occurred at the time styles ceased to elongate.Open-pollination excelled artificial-pollination both in the number of pollen grains which germinated and pollen tubes which grew.4. The largest numbers of pollen tubes per style were 2 ~3 and 4~5 at upper part of the style, and 1~2 and 3~4 at the lower part in artificial-and open-pollinated flowers, respectively.In open-pollinated central female flower, the pollen tubes which reached the ovary was found 9 days after cessation of style elongation.Three days later, 10 to 30 pollen tubes were observed at the upper part of the ovary, 5. From 18 to 26% of pollen grains of `Ginyose' used for the artificial-pollination germinated on agar medium.No difference was found in their germinability among pollination dates.緒