Flower and Seed of Hedyosmum nutans

Abstract

1. The staminate flowers usually occur in long-stalked ovoid catkins which arise in a pair at the base of the cymelike female inflorescence. Each stamen possesses 4 distinct microsporangia. 2. The carpellate flowers occur in sparsely flowered panicles. They have a single pistil, although there is some evidence that 3 carpels enter into the formation of this pistil (5). The perianth of the female flower is initiated before the carpel. It is connected with the surface of the ovary by means of a narrow longitudinal band of tissue which extends along each of its 3 corners; by a similar narrow zone about its base; and by another zone of attachment around the ovary in the apical region just below the base of the style. The perianth persists in the mature fruit and probably constitutes an added protection to the seed. 3. The ovary is 1-celled. Its wall is composed of 15 layers of cells of which the epidermis and the next 3 layers within it are small and but slightly thickened. The cell walls of the fifth, sixth, and seventh layers adjoining the 4 just mentioned are at first unevenly thickened, then, during the ripening of the seed, the entire cavity of each of the cells becomes filled. The inner layer of cells of the ovarian wall next the seed is also considerably thickened in the ripe seed. These 3 thickened layers form the chief protection of the ripe seed. 4. The ovule is pendulous and orthotropic. It bears 2 integuments, the inner being the longer from the outset of development. These are quite thick in the mature seed around the micropylar region, but elsewhere they are unthickened and are scarcely discoverable in the mature seed. 5. A primary archesporium arises from a hypodermal cell of the nucellus, which by dividing produces a tapetal cell and a definitive archesporial cell. The latter divides into three (usually four) potential megaspores. The lower or chalazal one of these is the functional one, the remaining three degenerate and are absorbed. The mature 7-nucleate embryo sac is of the type most characteristic of angiosperms. 6. The endosperm nucleus, embodying two polar nuclei and possibly a male nucleus, begins to divide before the oospore. Its first division is immediately followed by a transverse wall which divides the embryo sac into upper and lower cells. Each of these two cells continues to divide repeatedly, thus forming the thousands of endosperm cells that completely fill the mature seed except for the embryo. The several layers immediately surrounding the embryo are at this time devoid of starch. 7. The fertilized egg begins to divide only after 15-20 endosperm cells have been formed. The synergids and antipodals degenerate by the time of the first division of the oospore. 8. The ripe seed consists of a globular mass of cells with a poorly developed suspensor. The seed coat is not developed appreciably. Its function is obviously performed by the wall of the ovary. 9. At germination the small embryo is for a long time inclosed and nourished by the swelling endosperm. The cotyledons remain in the endosperm until nearly all its starch is exhausted. They are then withdrawn and assume an active photosynthetic function.