A Persistent Diurnal Rhythm in Photosynthetic Capacity

Abstract

IN 1939, Meyer¹ discovered a daily rhythm in the rate of photosynthesis in Ceratophyllum, a fresh-water angiosperm. In 1957, similar rhythms were found in natural populations of marine phytoplankton^2,3. Four years later, Hastings et al.⁴, working on the photosynthetic-capacity rhythm in the marine dinoflagellate Gonyaulax, demonstrated that these rhythms would persist for a few days in the laboratory in the absence of day–night environmental cycles, that is, in continuous dim illumination and constant temperature. Negative evidence was presented by Blinks and Givan⁵, who performed experiments which suggested the absence of photosynthetic rhythms in 13 species of marine littoral algae. In view of the different results, we have undertaken comparative investigations in an attempt to establish the distribution of persistent rhythms in marine flora.