Failure of Photoreversible Control of Flowering in Pharbitis nil

Abstract

1. Flowering of seedlings of Japanese morning-glory, Pharbitis nil Chois., grown in nutrient solution or in soil is inhibited by far-red and repromoted by red irradiations at the beginning of 16-hour dark periods and inhibited by both red and far-red irradiations at the middle of such dark periods. Older plants are not responsive to red or far-red irradiations at the beginning of the dark period, but, at the middle, red inhibits flowering and far red repromotes it. 2. Seedlings irradiated at the beginning of the dark period flower if at least one cotyledon is either not irradiated with far red or is irradiated with red after far red. Flowering of seedlings following irradiation at the middle of the dark period occurs only if one cotyledon is not irradiated. 3. Action spectra for control of flowering by irradiation of cotyledons were measured at the start and near the middle of inductive dark periods adequate to promote flowering. The energies required at the beginning of the dark period for half-saturatio...