Photoperiodic Initiation of Flower Primordia in Japanese Morning Glory, Pharbitis Nil Chois

The studies of photoperiodic responses in Japanese morning glory, undertaken some time ago under the guidance of Dr. Kwan Koriba in the Botanical Institute of Kyoto University, came for the time being to a conclusion.In the present brief article the main results are summarily reported.1) The Japanese morning glory, Pharbitis Nil Chois, is known as one of the most sensitive short day plants'>2>5;6>.The strain used in the present study has been obtained from Dr. H. Kihara.The plants remain under continuous illumination strictly vegetative for months, and may attain a large size without differentiating a single flower primordium.When transferred to short day conditions, the strain responds very readily to photoperiodic stimulus by initiating flower buds.Even seedlings, having only cotyledons, which did not yet fully expand the foliage leaves are capable of responding to photoperiods.Under favorable conditions even a single relatively long dark period will induce the plants to initiate flower primordia.No more consecutive dark periods are necessary, and the buds in the axils of the developing leaves differentiate into flower primordia.If the stimulus given is not strong enough, the induction is reversible.After the growing point has given rise to several axillary flower primordia, it becomes again vegetative and continues to develop foliage leaves with vegetative axillary buds.In such a case the number of flower primordia initiated can be used as a measure of photoperiodic response.When long dark periods are given repeatedly, the terminal bud begins to form bracteal leaves and, since its growing point is used up to form a terminal flower primordium, the apical growth of the stem stops.The number of plants with terminal flower buds can also be used as another measure for the intensity of photoperiodic induction.2) When a topped plant is deprived from all leaves except for the just expanded one, the axillary bud of this leaf begins to grow into a lateral shoot.If such a plant is subjected to long dark periods, the developing axillary shoot differentiates lateral flower buds only or, in addition, also a terminal flower bud, according to the intensity of the stimulus given.In favorable conditions a topped