Studies on the Physiology of Rice. VI. Effect of Photoperiod on Development of the Shoot Apex

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Abstract
Seedlings of winter rice, Rupsail, were subjected to 8-hr. photoperiods in 24-hr. cycles for 1, 2, 3, or 6 wks. and to interposition of a wk. of natural daylengths in the 3d, 4th, or 5th wks. of the 6 wks. of short-day treatment. Short days induced earliness accompanied by increased tiller production. With 1 wk. none, with 2 wks. 3%, with 3 wks. 67%, and with 4 wks. 100%, of the plants flowered. Interposition of natural daylengths delayed the flowering of the primary axis and also the tillers. Although 4 wks. of short days were sufficient for 100% flowering of the primary axis, 2 more wks. were needed to induce flowering of the tillers. The tiller buds formed during the period of short-day exposure received the stimulus and flowered earlier than the late tillers. With short-day treatment the shoot apex elongated and pushed up from the soil level. Stages of transition from the vegetative to the reproductive condition were illustrated. Changes in the shoot apex took place in the 3d wk. of the photoinductive treatment.