Piperazine, a chemical used as buffer component, greatly promoted adventitious root formation in cuttings of sunflower (Helianthus annuus L.), pea (Pisum sativum L.), mung bean (Vigna radiata L.) and to a lesser extent in bean (Phaseolus vulgaris L.) seedlings. Piperazine was more effective in acidic pH. The studies with piperazine analogues showed that any substantial modification of the structure caused the chemical to be less effective, or even inhibitory. Histological studies in sunflower hypocotyls demonstrated that piperazine did not alter the timing of the initial cell division. In the presence of piperazine, sunflower hypocotyls failed to develop primary phloem fibres. Piperazine at the concentrations that promote rooting did not kill or damage the tissue at the base of the hypocotyl. Compared to controls, piperazine treatment did not alter the proportion of primordia that eventually developed into actively elongating roots. Six days after treatment 45% of the control roots in the basal section were actively growing, compared to 51% in the piperazine. There was little evidence suggesting that the piperazine-induced promotion of rooting was caused by the removal of basal dominance in which piperazine killed the basal part of hypocotyl.