Abstract:Rooting mechanism for Populus tomentosa was studied by using 14C-α-NAA trace technique in this paper. Obsergations on ~(14)C-activities from 14C-microautoradiograph showed that the acting location of NAA was in cortical parenchyma cells which would produce meristematic cells. The role of NAA in the formation of root primordium is the induction of cortical cells to differentiate meristematic cells which possess meristematic ability. The root primordium distributed mainly in the parts of cuttings treated with NAA, which did not relate to the polarity of cutting icself. 590ppm NAA will be good for producting roots since adventitious root formation can be promoted obviously while its growth can not be inhibited by NAA. On the average, 8 adventitious roots per cutting will be induced from cuttings treated with 500ppm NAA for 40 days at soil tempematures of approximately 20℃, which have an average length of 4.5cm.