Summaries of Addresses of Presidents of Sections: Entrance Mechanisms of the Traps of Utricularia

Abstract

IT is only within the last few years that we have attained an adequate understanding of the way in which the trap (or bladder) of Utricularia works in the catching of prey. It was shown in 1929 that the watertightness of the trap and the emplacement of the edge of the valve or door had not been properly explained. It is now recognised that the free door edge articulates with the threshold in such fashion that no ordinary pressure of water alone, to which it is normally subjected, can press it inwardly. It was already known from the work of Brocher, Withycombe, Merl and Czaja that such water pressures are always present, and are highest when the trap is in the set condition, that is, there is a lower pressure within than outside of the trap, and that this is the result of the physiological activity of the walls, of the trap.