Nuclear Differentiation of Male Gametophytes in Gymnosperms

1. The behavior of chromosomes in mitotic nuclei from microspore to matured pollen grain was investigated in 11 phylogenetically distinct species of gymnospermous plants. 2. In the 11 species, the number of cells constituting matured pollen grains varied from one to five and the number of mitotic divisions was from zero to four. The stages and processes of the pollen grain development in the 11 species were substantiated by photomicrographs and shown diagrammatically. 3. In almost of all mitotic divisions in the course of pollen grain development, one of daughter chromosome complements at anaphase moved toward the central region and the other toward the peripheral region of the mother cell. 4. In almost of all mitotic divisions, marked stainable differences were observed between the two daughter nuclei. The one located in the central region of the mother cell was less stained than the nucleus in the peripheral region. There was an exception in Ephedra distachya in that no stainable differences appeared between the generative cell and tube cell nuclei which developed from the daughter nuclei in the antheridial initial cell division. 5. The stages at which stainable differences appeared in the daughter nuclei varied among species from early telophase to interphase, although the stages were constant in the mitoses of one species. 6. The nuclear differentiation accompanied with asynchronous chromatin disorganization is considered to exist widely in spermatophyta.