Transformation of Chitinase Gene into Populus simonii×P. nigra and Chitinase Activity of Transgenic Plants Effects of Defoliations on the Chlorophyll Contents and Biomass of the Poplar (Populus simonii×P. nigra) and Larix gmelinii Seedlings Rapid Propagation and Regeneration System of Populus simonii×Populus nigra STUDY ON THE TRANSFORMATION OF POPULUS SIMONII×P.NIGRA WITH SALT RESISTANCE GENE BET A In Vitro Germination and Cytology Analysis of Populus simonii×P. nigra Pollen Activities of POD, PPO and PAL in Poplar(Populus simonii×P. pyramidalis ‘Opera 8277’)Leaves Exposed to Different Volatiles