On rhythmic movement of the diatom Amphora ovalis

The vertical migration, motility and cell division rhythms of the diatom Amphora ovalis Kütz from Lake Kinneret, Israel, have been studied under laboratory conditions and results compared with comparable rhythms of other unicellular algae. The vertical migration rhythm exhibits two peaks during the light period, both when the cells are kept in continuous light or continuous dark. There is a single peak of motility occurring in the first half of the natural light period and a single peak of cell division in the latter half of the dark period. Rephasing of the rhythm by means of delayed start up time is illustrated and the possible interaction of phototactic and geotactic rhythms discussed.