A CYTOPHOTOMETRIC STUDY OF EMBRYOGENESIS IN TWO DIPLOID ANGIOSPERMS IN WHICH POLYPLOID DIVISIONS OCCUR AS A NORMAL PATTERN IN DEVELOPMENT

Although polyploid divisions occur normally in various parts of the seedling during germination in a number of diploid angiosperms, their time of origin has not been established. Their presence, however, very early in germination and the paired association of chromosomes in many of the polyploid divisions indicate their possible origin during embryogenesis or during the subsequent dormancy phase. To determine this, cytophotometric studies were undertaken of the interphase nuclei in different parts of the embryo during the various phases of embryogenesis and dormancy in two angiosperms, Anchusa capensis, the summer forget-me-not, and Spinacia oleracea, the common spinach, in which polyploid divisions occur early in germination as a normal feature in development. In Anchusa capensis, where the polyploid divisions were restricted to a particular time and place in germination, cytophotometric analysis showed that the polyploid cells arose at the time of conversion of the globular-shaped embryo to the heart-shaped embryo. In Spinacia oleracea, where divisions occur throughout the growth of the root and are found in both primary and secondary roots, these polyploid cells did not arise during embryogenesis but during germination and during continued growth. The origin of polyploid cells in Anchusa capensis at the time of conversion of the globular embryo to the heart-shaped embryo indicates that this is a possible critical phase in plant embryogenesis