Abstract: The eastern cottonwood Populus deltoids is an important commercial timber species used for saw-timber, veneer and pulpwood in China. The fast-growing character of P. deltoids has been remarkable for a long time. It is well known that the developmental inherent rhythm occurs during the development of secondary vascular tissue. Synchronously, the cell ergastic substance shows dynamic changes. Using electronic microscopy and cytochemical methods, we studied the distribution changes of the cell ergastic substance and development of secondary vascular tissues. Development of secondary vascular tissue took on an inherent rhythm, showing alternation of dormant and differentiated stages in periodicity of one year, and the formation of secondary phloem and xylem was alternate. In earlier stages, the protein and lipid decreased first. Then the starch grain disaggregated.The accumulation of starch grain, protein and lipid was the least during the development stage of vascular tissue. In the dormant stage, starch grain appeared at the beginning; later on, the accumulation of protein and lipid increased enormously. The distribution of cell ergastic substance was closely related to the developmental inherent rhythm of secondary vascular tissue.