Abstract
Correlation between heading date or air temperature in ripening period and weight of grains were investigated, due to materials get from the experiment of weather influence for rice yield conducted by the agricultural experiment stations which lie in the Tohoku Region, studying cool weather injuries in rice. Means of cultivation in these station were much the same and all seeds examined were produced from the national experiment station "Oushikenchi". The result of the investigation are as follows. a) Rice grains in the Tohoku Region's weather condition easy to reduce its weight as delay of heading and fall of air temperature in the ripening duration. b) Mean temperature of maximum and minimum in 40 days after heading needed for the full developement of grains are about 22°C, and when the temperature goes down to below 20°C weight of grains considerably falls.
