DIURNAL AND CIRCADIAN PERIODICITY OF MITOSIS AND GROWTH IN MARINE MACROALGAE .1. JUVENILE SPOROPHYTES OF LAMINARIALES (PHAEOPHYTA)

In juvenile sporophytes of Laminaria schinzii, Laminaria sinclairii an d Plerygophora californica grown at 12 h light per day the majority of nuclear divisions took place during the dark interval. In P. californ ica it was ascertained that the rhythm in nuclear division persisted i n continuous light for at least six cycles and thus was controlled by the circadian system. Under light-dark conditions, a night peak occurr ed for division and a morning peak for growth rate. Maxima of the free -running division rhythm preceded maxima of the free-running growth rh ythm by about 6 h. Sporophytic cells of L. saccharina with a generatio n time of up to 3 days continued to grow between two cell divisions so that thallus expansion rhythmicity may reflect mainly the growth beha viour of non-dividing cells.