Abstract
Twenty-two strains of planktonic blue-green algae belonging to the genera Anabaena, Aphanizomenon and Oscillatoria were grown under controlled conditions at 20°C under continuous light. Growth rates were found to be positively correlated with size but less than half the variation in growth rates observed could be associated with changes in the surface/volume ratio. Cultures of the same species often showed wide variation in cell morphology and growth rates. The maximum growth rate observed was K = 2·74 doublings day-1 for a culture of Oscillatoria limnetica.