Water extrusion in the trap bladders ofUtricularia vulgaris

In the trap bladder ofUtricularia vulgaris, a sudden expansion (convex bladder) by opening of the entrance door upon stimulus was followed by slow decreases in bladder width and internal hydrostatic pressure. The decreases were caused by continuous water outflow from bladder lumen. The bladder reached initial resetting state (concave bladder) in about 30 min. The internal pressure reduced to 0.86 bar. This reduction was inhibited by application of sodium azide in the bladder lumen. The total water outflow for 30 min from a bladder, measured using a glass capillary inserted in the bladder, was 630 nl: the rate was 21 nl/min. This rate was also inhibited by sodium azide. In bladder resetting under paraffin oil, it was observed that water emerges from near the free edge of the trap door. From light and electron microscopic observations of the entrance region, it is concluded that the inlet of water outflow is the bifid trichomes which stand on the inner surface of the bladder near the entrance, and the outlet is the outer and middle zones of the pavement epithelium, or threshold, against which the free edge of the door rests.