Polyploid lines were constructed from several diploid ecotypes of Arabidopsis thaliana by colchicine treatment. To confirm their ploidy by counting the chromosome number of the respective cells under a microscope, meiotic chromosomes of pollen mother cells were surface-spread on slide glasses and visualized by DAPI staining. It was clearly indicated that the tetraploid lines assumed by flowcytometry had 20 chromosomes, since 10 pairs of bivalents were observed on the metaphase I plate, and 2 sets of 10 chromosomes on metaphase II plates. As far as we analyzed through light microscopic observation, homologous chromosomes normally synapsed at the pachytene stage, congressed on the metaphase plate at metaphase I, and segregated reductionally to daughter cells at the anaphase I, and sister chromatids were separated to produce tetrads during meiosis II. Putting these results together with their fertility, the constructed tetraploid lines were concluded to undergo meiosis as normally as wild-type diploid plants, though the chromosome number was doubled
