Abstract: Populus deltoides Barter. var. deltoides cv. "Harvard" (I-63/51) and Populus deltoides Barter. var. deltoides cv. "Lux" (I-69/55) are two clones selected from Populus deltoides Barter. deltoides in the state of Mississippi (at 33° north latitude) and the state of Illionis (at 36° north latitude) of America respectively by the Poplar Research Institute of Casale Monferrato in Italy. These clones exhibit rapid growth and disease-resistance, but as originated from southern sources, they are susceptible to early low temperatures. Clones I-63, I-69 and I-72 were introduced into Jiangsu Provinee in 1972. Thereafter, these clones were further introduced into North Jiangsu, the Dongting Lake Plain, the Beyang Lake Plain and the Zhangjiang-Hanshui Plain.Results of experiments show that the above new clones adapt themselves readily to the climate conditions in districts to the south of Zhangjiang River. With an average temperature of 16°-17℃ (extremes being 5℃ and 38℃), a temperateure accumulation index of 120°-140℃ (above 5℃) and a yearly rainfall of 1,000 mm, the lower reaches of the Zhangjiang River provide an even more fevourable land for these clones to grow and flourish,?21