The Circadian Rhythm of Photoperiodic Responsiveness in Kalanchoe

Abstract

In Kalanchoë we know about several rhythmic phenomena which are more or less endogenous. Among them are diurnal changes of osmotic values [1], water uptake [1, 2], fresh weight [3], turgor pressure [1], guttation [4], CO2 metabolism [5, 6, 7], acidity [3], phosphatase activity [8], substances active in root growth [3], heat resistance [9, 10], and responsiveness to temperature [11] and light [12 to 19]. All of them have an equal diurnal frequency but not in every case equal phase relations. The opening and closing movements of the flowers, for instance, are mainly due to changes in the turgor pressure of the petals. Therefore, there is a simultaneous oscillation of them coinciding with alternations of the osmotic values and the fresh weight of the flowers. On the other hand, the total acidity of the petals and the water uptake of the flowers oscillate synchronously with the velocity of the flower...