| Sorbus amabilis is a beautiful ornamental tree of Rosaeeae which seed have much low germination percentage due to seed dormancy in nature. The seed biology characteristics, seed dormancy mechanism, and the methods to break seed dormancy were studied in this paper. The results were showed as follows:1. The germination percentages reach to 95.00% and 91.67% when seeds with isolated embryos were in 16h light 8h dark and 24 dark conditions. The germination percentages of seeds with bare cotyledons and bare radicle reach to 90.00% and 91.67%respectively, whereas 0% of intact seeds germinated. There is no obvious differences in seed germination when seeds with whole or partial cotyledons. These results indicated that the seed coat were responsible for seed dormancy.2. Effective method of dormancy broken was to soaking seeds in water and exposure to cold stratification at 3～5℃for 75ds, 91.33% seeds germinated. As while, 81.00% of seeds germinated when exposure to GA3 (400mg/L-1) for 24h and exposure to cold stratification at 3～5℃for 90ds. In addition, it was found that seeds treated only by GA3, concentrated sulfuric acid or NaOH can not help to release seed dormancy.3. The SEM and TEM of the seed indicated that the outmost cell walls of the seed coat were thick and keratinized, which may be impermeable. During the release of seed dormancy, this structure disappeared gradually. Meanwhile, it was also found that there were numerous black granules in the cell. These materials were dissolved little and little during cold stratification. While, the mechanical obstruction from seed coat was solved absolutely, and seed dormancy was released ultimately.4. The main causes of seed dormancy of Sorbus amabilis was the mechanical obstruct from seed coat, while the permeability from seed coat has some influence, too. On the basis of this research, seed dormancy type of Sorbus amabilis Cheng ex Yu was physical (PY).
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