Abstract: Through the preliminary observation of some external characteristics of three lines (Ehl-jioou-narn, Ehl-jioou-aai, Taih-yiin No. 1) of rice (Oryza sativa L.), we know that when the differentiation of the shoot apex takes place, the distance between two adjacent pulvini of the last 3,4 leaves of the plant becomes prominently elongating. Rice and some other graminae such as wheat, millet, etc. are characterized by this morphological feature. The differentiation of the shoot apex of rice initiates at a definite "double Οleaf" period, passes through the first, second and third "elongating periods of distance between pulvini" successively and then emerges. There is no great externally morphological difference during the differentiation of the shoot apex among the early maturing or the late maturing varieties of rice. In growing plant, any central young leaf ("Ο leaf) will make a chance to coincide with "Οleaf", forming "double Ο leaf". During the stage of vegetative growth, the "double Ο leaf" plant has two central young leaves, denoted by "-1 leaf" and "-2 leaf", the blades of which are more slender; while during differentiation of the shoot apex the "double Οleaf" plant has only one central young leaf with comparatively broad blade so that it is possible to make a distinction from that of vegetative stage. According to this characteristic, the floresence of any variety of rice may be estimited.