Abstract: The changes in endogenous ABA, IAA and zeatin levels of control,NAA-treated and NAA+BA-treated cuttings(bud,bark) of Populus alba,P.tomentosa and P.davidiana during rooting process were investigated by using HPLC and GC.The experiments showed that the rooting ability of hardwood cuttings was determined by both presence of latent root primodia and balance of endogenous hormones bark.The high IAA/ABA ratio and zeatin content in bark of P. alba allowed the latent root primodia to resume their growth, and the cuttings could root and survive spontaneously.For P.tomentosa, because of its low IAA/BA ratio and zeatin content,approprite amount of exogenously applied NAA and BA was needed for stimulating latent root primodia to grow.P.davidiana had no ability to form bark-or-ignated adventitious roots, although treated with NAA and BA, the cuttings needed longer time to developl callus-originated adventitious roots. Finally, the action mode of exogenous NAA and BA in rooting process of cuttings was discussed.

Key words: Hardwood cutting, Root promotion, NAA, BA, Endogenous IAA, ABA, Zeatin