Photoperiodic Responses of Hemp Plants, Especially Their Morphogenetic Changes in Leaf Shape

Abstract

Hemp plants (variety "Tochigi No. 1") grown in their early stages of growth from the time of germination under long-day condition, were exposed to different successive short-days, and thereafter were grown under the condition of long-day or natural-day length. 1. It was a similar result as reported formerly in soybean that the hastening of flowering and the inhibition of stem growth were proportionate to the strength of photoperiodic induction due to the initial exposure to short-day, and that the reversal of growth to vegetative phase under the long-day condition was proportionate to the weakness of photoperiodic induction. 2. It was worth notice especially that in the leaves except the juvenile ones the number of leaflets desreased under the infludnce o short-day and increased under the influence of long-day. As to the number of serration in the margin of leaves, a similar change was brought about also. It was ascertained that these decreases or increases were reversible under the influence of day-length. Furthermore, such morphogenetic changes in leaf shape were graded according to the degree of photoperiodic induction. Consequently, these marked systematic changes in leaf shape under the influence of day-length correspond to the vegetative or reproductive growth behavior under the influence of day-length. 3. As to the decrease of the number of leaflets under the influence of short-day, male plants were more densitive than female plants. 4. Regarding phyllotaxy, the relation between opposite arrangement and alternate one was not affected by day-length.