(diurnal rhythm) An * endogenous rhythm in which physiological responses occur at 24-hourly intervals. For example, some plants exdibit a characteristic change in leaf position on a daily cycle. The opening and closing of stomata and flowers and the frequency of cell divisions also exhibit a circadian rhythm. Such rhythms will persist for several days if the plant is kept in continual darkness. It also appears that, in some species, the photoperiodic response is governed by circadian rhythms (see photophile). |
