Abstract: A natomic observation was made in the terminal bud of Clematis heracleifolia，C. terniflora var. mandshurica，C. hexapetala and C. fusca during flower bud differentiation with the paraffin-cut section. The results showed that flower bud differentiation of the four species of Clematis could be divided into five stages. The primordia of all floral organs initiated and developed centripetally without differentiation or degradation of calyx or petal obviously. It also included the whole inflorescence formation during the flower bud differentiation of C. heracleifolia，C. hexapetala and C. terniflora var. mandshurica. After the complete morphology differentiation of floral organ，it took about 10–12 d for the flowers of C. terniflora var. mandshurica and C. fusca，12–14 d for that of C. hexapetala and 15–17 d for that of C. heracleifolia to develop from the initiation to the end.

Key words: Clematis, flower bud differentiation, the paraffin-cut section