Abstract
This experiment was carried out to elucidate the roles of leaves and roots in the bulb formation and development of onion plants, using the methods of defoliation and root-cutting with potted Senshu-Ki variety.
(1) In the experiment on the continuous removal of leaf blade tips, it was shown that a rapid increase in plant height followed by a remarkable bulb thickening under long photoperiod was not always required as an essential process of bulbing.
The bulb formation was retarded by continous severe removal of leaf blades, but not by slight one, and the bulb development was inhibited by the removal of leaf blades in proportion to leaf area of removed leaves.
(2) Defoliation of alternate expanded leaves prior to bulb formation induced the retardation of scale leaf formation, and that during the bulb development inhibited the thickening of bulbs, The effect of defoliation was severer in the early stage than in the later stage, and the more the leaves were defoliated, the less the bulb enlarged.
It was noticed that the defoliation of all leaf blades or leaves except the lower half part of bulb induced the emergency of foliage leaves instead of scale leaves even under long photoperiod. Thus, it was clearly suggested that the foliage leaves were developed with the nutrition supplied from roots
(3) Removal of about half number of roots just below the crown before bulb initiation induced the promotion of scale leaf formation, and the same treatment during the bulb develoment resulted in the inhibition of bulb thickening. It was observed that the uniform fall over of tops was significantly promoted by root cutting
(4) The promotive effects of root-cutting on the initial thickening of bulb and on the fall over of tops were affected by soil moisture. In other words, the former effect was strengthened in wet soil and the latter one in dry soil. These tendency were also ascertained in the subexperiment with the combination of root-cutting and soil moisture content.
