Abstract: 【Objective】In this paper, Erythronium japonicum, a spring ephemeroid plant from the Changbai Mountains, China, was used as a study species for the morphological differentiation and growth of underground buds, to reveal the individual development pattern in summer dormancy.【Method】The bulbs of E. japonicum were collected at regular intervals in the growing season and during summer dormancy. Then, bulbs were fixed in formalin-acetic acid-alcohol(FAA). Underground bud organogenesis and growth rhythms were observed and studied using ananatomical lens, scanning electron microscopy(SEM), and paraffin method.【Result】Our results showed that the bulbs of E. japonicum were renewed in the full-blossom period. The aboveground parts wither from mid to the end of May. Instead of becoming dormant, the bulbs continue to grow, producing flowers and leaves. Aboveground floral morphogenesis was completed by the end of June. The underground bud differentiation of E. japonicum went through five stages, including leaf primordia differentiation, flower primordia differentiation, perianth primordia differentiation, stamen primordia differentiation, and pistil primordia differentiation. The whole process took approximately 1.5 months. When the buds finished morphogenesis, they continuedin underground growth, and went into dormancy with the mature flower formed. During the entire summer dormancy, the buds grew in length and diameter following an exponential model. Allometric analyses of growth rates in length and diameter indicated that diameter increased at a slower rate than length overall.【Conclusion】The bulbs of E. japonicumwere renewed in the full-blossom period. They did not undergo dormancy, but rather completed the underground bud morphogenesis. Growth of bud length and diameter in E. japonicum followed the exponential model with significantly slower rates in the early organogenesis stages and faster rates before winter dormancy. There was a significant allometric relationship with periodicincreases in elongation and diameter increase.