The material used for this study was collected December May during 2 successive years (1997～1998)from the branches of apparently healthy Populus deltoides growing on the campus of Nanjing Forestry University,Nanjing, China.The samples were taken from three or four trees at 5 day or monthly intervals.The stem and the shoot were fixed in FAA prepared for anatomical studies.The occurrence and development of vascular cambium in Populus deltoides were studied in serial sections of shoot and stem.The results show as follows:(1)The transition from apical meristem to procambium and from procambium to cambium turn toward gradually the apex of stem in process,and the leaf trace is related to vascular tissues closely.(2)The vascular cambium is non stratified,and begins activity before the budding.It marched into the exuberant activity stage in the middle of April,and the cell which derived from the division of vascular cambium differentiated rapidly into vessel forming metaxylem.