Discussion on the embolism repairing in xylem of woody plants

Wood sections of species of plants were made and observed under microscope.When a dehydrated section was rewetted,the air inside its conduits contracted under the force of surface tension for several seconds to form elongated or round bubbles.The elongated bubbles in the smaller conduits shortened till vanished.The authors also discovered that the bubbles outside conduits appeared gradualy one after another and they originated mainly from the cross sections of the wood rays.The smaller ones collapsed and the larger ones grew up gradually.The bubbles in the larger conduits extended at first,and then collapsed and disappeared. It was suspected that air might transfer from the bubbles with short radii to those with large ones,both inside and outside conduits.There are two possible mechanisms to explain the phenomena.First,based on the capillay equation,air can move from the smaller bubble to the larger one.Another reason is that the dissolving air from the smaller bubbles can enter into the adjacent bubbles with larger curvature radii.Therefore,it is suggested that after cavitation events,instead of air moving from xylem into ambient atmosphere,two mechanisms could induce air to transfer from the smaller conduits into the regions with lower pressures.Thus,the embolized conduits in the smaller conduits are repaired.