1. The author presumed the temperature for flower bud formation, comparing the leaf-stage for bolting of the onions sown in autumn, with the temperature of spring.
2. The onions which reached to the leaf-stage for bulb-division, were able to form flower buds only with low temperatur: that is below 5°C on the mean temperature, below 10°C on the max-imum, and below 0°C on the minimum.
3. The onions which reached to the leaf-stage for bulb-division, were retarded growth and ob-structed bulb-division for a time by replanting. In this case, the flower bud formation occurred at 10°C on the mean temperature, 13°C on the maximum and 2_??_3°C on the minimum.
4. It seemed that the period of low temperature which the onions needed for flower bud formation was about 4_??_5 days.