Internodes of floating rice begin to elongate during vegetative growth and then elongate rapidly in response to flooding. After floodwaters recede, the upper parts of the elongated shoots stay erect due to gravitropic bending of the leaf-sheath pulvini of shoots and continue to grow upwards. We have characterized the gravitropic response of leaf-sheath pulvini of floating rice using isolated stem segments with pulvini. When stem segments with five upper pulvini excised from plants during vegetative growth were gravistimulated, the stem segments with the uppermost to the fourth pulvini displayed a gravitropic curvature, and a maximum curvature response occurred in the segments with the second highest pulvinus. In response to gravistimulation, the segments started to bend upwards after a lag time of 37 min, showed a maximum bending rate of 2.4 degrees per hour at 6-7 h after gravistimulation, and ceased bending after almost 48 h. The bending of the stem segments occurred in response to the orientation of the segments at angle values of as low as 1°or 2°in relation to the gravitational force. The stem segments excised from vegetatively growing plants showed a slightly stronger graviresponse than those excised from reproductively growing plants. The strong response of the pulvini of vegetatively growing shoots to gravistimulation is considered to be one of the characteristics of kneeing in floating rice.