(1)In 1938, at KONOSU Exp.Station, 134 recommended varieties of low-land rice in Japan weregrown in natural, short day length (8 hours), hightemperature (glass house) and high temp.-short dayconditiorls.By the response of heading time of rice plant under these 4 treatments, examinated varieties weredivided in 2 groups, the former group is high sensitive to temperature and low sensitivity for davlength and the latter group shows high sensitivity forday-length and low sensitivity for temparature. Thefirst group contains almost early varieties and the2nd group are consisted with the later varieties