Abstract: In order to explore the reason for poor fruit set in sweet cherry grown in Shanghai area，the development of flower organs was investigated with 5-year-old sweet cherry(Prunus avium L．)trees which were planted in tlle research orchard of Shanghai Jiaotong University．Results showed that floral diferentiation and appearance of stamen and pistil during their development were normal for sweet cherry in Shanghai area.The microscopic observations revealed that poNen developed well and polen germination rate reached about
50％.However．98.2％ of ovary failed to develop，among which tllere was 26.3％ of ovaries witllout ovule, and 71.9％ of ovaries witll ovule but witllout embryo sac.The result indicated tllat undeveloped ovule and embryo sac are tlle main reason for poor fruit set of sweet cherry in Shanghai area．

Key words: Cherry, Sweet cherry, Flower organ, Pollen, Ovary, Ovule, Fruit set