MITOSIS IN THE COENOCYTIC GREEN-ALGA BOERGESENIA-FORBESII (HARVEY) FELDMANN (SIPHONOCLADALES, ULVOPHYCEAE)

Mitosis in vegetative cells of the siphonocladalean alga Boergesenia f orbesii (Harvey) Feldmann was investigated mainly by electron microsco py. The mitotic spindle was centric and closed. The interphase nucleus contained a spherical nucleolus. The nucleolus was slightly dispersed at prophase, but nucleolar materials remained during nearly all stage s of mitosis. Kinetochores were evident on chromosomes. The polar regi ons of nuclear envelope had no fenestrae during mitosis. Anaphase sepa ration of the chromosomes was asynchronous. Elongation of interzonal s pindle at telophase separated the two daughter nuclei widely. The ultr astructural features of mitosis in B. forbesii revealed by the present investigation are compared with those of other siphonous and siphonoc ladous algae in the Ulvophyceae.