Abstract: The male flowers of Populus lasiocarpa survive the winter in PMCs stage. Meanwhile, a large number of starch grains accumulate in the outer wall layers show a successive decrease in starch grains content in them, but retaining rich starch grains in the inner ones. Finally, all of the starch grains disappear from the wall layers and high concentration of soluble polysacchaddes is further synthesized and maintained in tapetum and PMCs. Tapetal cells always contain rich DNA, RNA and protein. The changes of the content and the distribution of RNA are similar to those of the protein during microsporogenesis.Callose spots are deposited among PMCs at leptotene stage. Gradually the spots connect with each other to form plates which completely surround the PMCs at metaphase I . By metaphase Ⅱ and anaphase Ⅱ, the callose plates deposit at its maximum of thickness. With the formation of tetrads, callose deposition starts on the center of the tetrads, and then extends rapidly along the four cells, separating them from each other. A great majority of tetrads are tetrahedral, seldom isobilateral.