ell division was found to be the major reproductive manner of Hemiaulus sinensis, an estuarine diatom. The experimental results revealed that this species present a diurnal period-icity in cell division and chlorophyll synthesis. Under a 12hL:12hD condition,the highestpeak of cell division appeared after 8 hour illumination, and the second peak appeared after 2hour darkness ,while chlorophyll synthesis had also got the highest peak after 8 hour illumi-nation and then decreased gradually to the lowest valu...