In a study of the effect of photoperiod upon the growth and flowering of Calistephus chinensis (var. Queen of the Market) it has been shown that a one-hour night break of low intensity red light given to plants growing in eight hours daylight can have a number of morphogenetic effects. In the young plant, such a treatment increased the total area of the leaf surface and the area per unit weight of leaf material, i.e. the specific leaf area. This effect enabled the treated plants to make greater use of the incident light, for after nine weeks they were at least 25 per cent heavier than comparable plants which had not had the benefit of the night-break treatment. This treatment also caused flower induction and concomitant stem extension, but transfer back into eight-hour days after an inductive period accelerated further flower development and restricted stem extension of both the main axis and the laterals. If flower development was delayed by continuing night breaks or by delaying the onset of induction then more flowers were eventually formed, but in the very prolific treatments flower size was reduced. The experiment also indicated that the partition of available dry weight between leaves, stems, and roots followed a definite pattern dependent only upon total plant dry weight. The diversion of dry weight into flowers was strongly accelerated by transfer into eight-hour days after induction but the remaining dry matter still appeared to be distributed between the vegetative parts along the general pattern determined by total vegetative weight. Finally the experiment showed that a wide range of plant forms bearing varying amounts of flowers could be obtained by appropriate transfers between treatments.
No takes yet. Share an insight, caveat, or question.
HUGHES et al. (1965) studied this question.