Nuclear Invagination and Nuclear Vacuole Formation in Several Plants PRELIMINARY STUDIES ON STRUCTURE OF STAMEN HAIRS OF TRADESCANTIA AND ITS SPECIFIC FUNCTION ULTRASTRUCTURE OBSERVATIONS ON THE PLASMALEMMASOMES OF TRADESCANTIA STAMEN HAIR CELLS EFFECTS OF THE ENHANCED UV-B RADIATION ON THE MICRONUCLEUS EVENTS OF TRADESCANTIA POLLEN MOTHER CELLS