Abstract: The microsporogenesis in Pinus thunbergii occurs in early to middle March, and the development of pollen in late March to early April. A mature pollen grain consists of four cells. The starch grains aggregate in the equators during meiosis Ⅰ to Ⅱ. The callose materials appear first in inner side of the wall of meiocyte and then in the equator. Sometimes the 3-or 4-sac- cate pollen grains have been found. In the ontogeny of pollen in Pinus thunbergii following events are noteworthy. (1) During meiosis the equatorial aggregation of starch grains in me iocyte becomes conspicuous. (2) During formation of tetrad the callose wall appears in regular activity. It is noteworthy that there is itself feature for the accumulation of callose in Pinus thunbergii. After formation of prothallial cells the callose appears mainly in the area between body and saccus. So the prominent symmetry of distribution of callose occurs in the pollen grains. But almost no callose accumulation takes place i,n tenuity in distal face of pollen grain. On the contrary, there are certain callose accumulation around the prothallial cells in the proximal face, forming the polar distribution of callose in pollen grains.

Key words: Callose, Microsporogenesis, Ontogeny, Pinus thunbergii, PoLlen