A Contribution to the Life History of Aster

Abstract

The embryo sac arises from the lowest cell of an axial row of four cells. The eight-nucleate embryo sac is formed in the usual manner. Great variation is shown in the form of embryo sacs, both in different species and in the same species. The polar nuclei fuse ordinarily before fertilization, but may fuse after it. The endosperm nucleus is marked by its very large size, its almost spherical shape, its large nucleolus, and its position below and in contact with the oosphere. The antipodals show a remarkable growth before the time of fertilization and persist very late in the development of the embryo. From one to nineteen nuclei were found in a single antipodal cell. The lowest antipodal cell in A. undulatus and A. Novae-Angliae is often very much enlarged. The fertilization of an antipodal egg is clearly demonstrated in Aster. Double fertilization was observed in A. undulatus. The sperm nuclei assume the structure of ordinary nuclei at the time of their fusion with the egg and the endosperm nucleus. The d...