Studies on the bolting of onion. I

Relation between the flower bud formati on and the bulb division

Abstract

1. The experiment was carried out on the bolting in relation to leaf-stage and nutritional conditions of the onions sown in autumn. The results were as follows. Under same nutritional conditions, the more advanced the leaf-stage, the more boltings occured; but under poor nutritional conditions there were more boltings on the lower leafstage as compared with under adequate nutritional conditions.
2. The onion not bolted, produced bulb-division .after growing to the certain stage, while the onion bolted produced bulb-division with flower bud formation. In any case, there were considerable variations in the leaf-stage to produce bulb-division, but lowest leaf-stage for division seemed to be the ecological characteristic in each variety. Yama-guchi-kodaka divided at 12th. leaf-stage, and Awaji-chu-kodaka, 13 th. leaf-stage.
3. But it was found that bulb-division was -obstructed by the poor nutritional conditions and low temperature. In such conditions, therefore, the variation curve of the leaf-stage for bulb-division tended to move to higher leaf-stages.
4. The leaf-stage for bolting was one-leaf lower than leaf-stage for bulb-division. In the bolting bulb, the division bud was formed with the flower stalk and in the divided bulb, the division bud was formed within the leaf-sheath which corresponded to the flower stalk. So, there was oneleaf difference between both stage from the ana-tomical point of view.
5. For bolting, it seemed necessary that the onion plant, on the leaf-stage for bulb-divison, formed flower bud under lower temperature condition. Further, besides low temperature, such conditions, were necessary, as poor nutrition, extreme lower temperature which tended to obstruct bulb-division. And it was found that onion bulbdivided without flower bud formation under good nutritional condition and temperature in which buld-division was possible.