Abstract
Practical studiess on the injurie of cool weather in rice plant. Report II Ripening optimum outdoor temperature and critical heading date for it. As before reported, the average temperature of maximum and minimum in 40 days after heading necessary for full development of rice grain in the Tohoku Region's weather condition is over 22°C. In order to gain the temperature, the date of heading must be earlier than August 16 in the average year at the Fujisaka Experimental Farm in Aomori-Prefecture, and August 26 at the Obanazawa Experimental Farm in Yamagata-prefecture. Namely, these date can be called the critical heading date for full development of grains.
