Abstract
Rice plants was cultured in paddy field in 1952 at eight National Agricultural Experimental Stations located in the main part of Japan from the south to the north (as shown in Fig. 2). These rice plants received almost the same treatments under different climatic conditions. Varieties which were chosen in each Exp. Station were the most common ones in each locality respectively. The process of growth of these rice plants was studied morphologically and the following two types were distinguished in connection with the characteristics of the growth processes. 1) The cool area type, as in the case of Hokkaido : The temperature at transplanting is very low. Earprimordia is initiated by the temperature-effect. Tillering goes on after the ear-initiation. The tendency of dying of lower leaves caused by malnutrition is very weak even at the end of growth. 2) The warm area type, as in the case of Chugoku, Shikoku and Kyushu : The temperature at transplanting is high. Earprimordia is initiated by means of the photo-period-effect. Tillering is vigorous at early stage of growth, so the maximum tiller number period comes about two weeks earlier than the ear-initiation. Many lower leaves die in late period of growth because of malnutrition. In the case of Tohoku (Omagari), the maximum tiller number period and the ear-initiation period came at the same time in 1952 when the summer temperature was rather high, so the southern limit of the location of the cool area type was found there. The northern limit of the location of the warm area type is conjectured to have connection with "the Honshu-Nangan line" which is the demarcation line of the distribution of plants and animals running along the southern coast of the Japan proper. The area between these two limits will be called the transitional zone. The southern limit of the cool area type will move southward when the summer temperature is low and the northern limit of the warm area type goes northward when it is high. These two limits move up and down within the transitional zone according to the summer temperature.
