INFLUENCE OF METHYL-DERIVATIVES OF COUMARIN ON MITOTIC-ACTIVITY AND ULTRASTRUCTURE OF MERISTEMATIC CELLS OF ALLIUM-CEPA ROOT-TIPS

7-Methoxy-, 7-methyl- and 6-methylcoumarins retarded mitosis in Allium cepa root promeristem and caused chromosomal aberrations. Chromosomes became shorter and thicker, and often were lost during anaphase, form ing micronuclei during interphase. Chromatid bridges were observed in anaphase and telophase, leading to the formation of a restitutional nu cleus, often of irregular shape. Abnormal fragmopasts, often discontin uous, prevented normal cytokinesis. There was increased vacuolization and the mitochondria contained an electron-dense matrix. Parts of the cytoplasm, which were surrounded by ER cisternae, cortained mitochondr ia and pieces of ER membrane. Autophagous vacuoles showed a lower dens ity of cytoplasm, but still contained numerous pieces of ER cisternae.