Following previous studies (KITANO and FUTSUHARA 1981), the effects of temperature on culm elongation of the dwarf mutant, Fukei N0.71 and its original cultivar, Fujiminori were evaluated in the present investigation under eight different tempeature conditions cornposed of the combination of two temperatures, high (30°C-25°C) and low (23°C-18°C), and three growth periods (vegetative, early reproductive, and late reproductive or culm elongation stage). Fukei N0.71 showed a larger response to the treatments in culm elongation than Fujiminori, the culm elongation of the former being reduced significantly by high temperature treatment in the culm elongation stage. On the other hand, under low temperature conditions in this stage, it grew as tall as Fujiminori. To elucidate the dwarfing mechanism of Fukei N0.71, some histological observations were carried out on the elongated internodes of Fukei No.71 and Fujiminori grown under high and low temperature conditions. When Fukei No.71 was grown under high temperature, it showed a tendency for a decrease in the number of parenchyma cells in the longitudinal direction and an increase in number in the transverse direction of each elongated internode. It was also observed that partially non-uniform parenchyma cells occurred only in Fukei No.71 when treated with high temperature. These results suggest that the dwarfness expressed under high temperature condition in Fukei N0.71 is induced by abnormal cell differentiation from intercalary meristems of the internodes.