Development of Pinus thunbergii cones after pollination was very slow until February of the next year (Fig. 1). Physical characterization and nitrogen distribution of cones in this period are given in Figs. 2 and 3. It takes thirteen months from pollination to fertillization in Pinus thunbergii, so cone development after pollination seemed to be very limited. Rapid development of cones began at March of the next year, three months before fertilization (Fig. 1), and non-pollinated cones (parthenocarpy) also developed at the same time (Fig. 4). Rapid development of cones did not occur as the result of ferti-lization, but seemed to be closely connected with winter bud development. Physical characterization and nitrogen distribution of cones after fertilization are given in Figs. 5_??_8. Nitrogen of cone scales increased to the middle of July, and then decreased as the formation of seeds proceeded (Fig. 7). Cone scales seemed to be the reserve tissues of nutritive substances transferred from leaves and branches to seeds. Cone scale development began before seed formation, but declined by the deficiency of sound seed yields (Fig. 10). Cone scales however developed even in case of non-pollination (Fig. 11), so cone drop and cone scale development seemed to be induced by the effect of other factors different from fertilization and seed formation.