| Abstract: | The presence or absence and the distribution of the starch during embryogenesis of Pinus tabulaeformis have been investigated by using the usual histochemical methods. The embryogenesis of the pine may be divided into six stages. In the course of embryo development the accumulation of starch has been observed in the nueellus, the megaspore mother cell and the megaspore, in the female gametophyte, in the pollen grain and in the embryo itself. The larger starch region, however, is only seen in the free apex of the ovule, the female gametophyte and the root cap-suspensor region of the embryo. During embryogenesis the starch region in the free apex of the nucellus appears before the pollination and persists until the late stage of the development of the young embryo. In the female gametophytc the starch region appears about the time of fertilization or at the early stage of proembryogenesis. It is always surrounding the developing young embryo, moves progressively toward the chalazal end of the female gametophyte after the development of the young embryo and then disappears when the embryo is approaching maturity. The starch region in the embryo itself appears in the basal region of the young embryo before the differentiation of the root initials and then develops into the root cap suspensor starch region and finally disappears until the complete development of the embryo and the seed maturity. The starch region, therefore, is the main site for supplying the carbonhydrate for the developing pine embryo. Many young embryos are distributed in the narrow and long embryonal cavity of the female gametophyte during the stage of cleavage polyembryony. But usually only one of them which can obtain the sufficient saeeharide material becomes the dorminant embryo. It is, therefore, considered that the carbonhydrates may be one of the important factors involving the embryo selection. In the mature seed, with the exception of a few residual starch grains scattered in the root cap-suspensor region, no starch grains are found in other organs or 9issues of the embryo. Hence, we may conclude that the starch grains participate actively in the carbonhydrate metabolism and finally they are almost entirely consumed off and they are, therefore, not the reserve material of the pine seed. |
