AbstractDifferent methods (physiological, electrophysiological and biochemical) were used in order to show, during a 24 h period, a change in sensitivity ofBidens pilosusseedlings to the pricking of one of the cotyledons. The sensitivity is maximum in the morning and in the evening; it decreases during the light period (day) and the dark period (night). The minimum of the sensitivity occurs in the middle of the day and 3 to 4 h after the beginning of the night.