Investigations on the flower induction were carried out with Silene armeria L., a plant species flowering under all conditions after a treatment at LD, 5° C or 32° C. Two strains E 1 and L 1 differing in their photoperiodic and temperature requirements, were used in the present research, which completes former investigations (VAN DE VOOREN 1969a, b, 197 1 a, b).High temperaturePlants under short day conditions at 32° C are induced to flower bud formation. A quantitative juvenility for 32° SI), interaction between 32° SD and L 20° , partial induction by 32° SD and desinduction of this partial induction in SD 20° exist in both strains, but E 1 is more sensitive than L 1 .High temperature action on flower induction is maximal during the middle of a 16 h dark period for both E 1 and L 1 . Maximal action in E 1 is more precisely 7 h after the onset of darkness, independent on the length of the dark period for 8-16 h photoperiods. There is no action for 20 and 24 h photoperiod.No influence of temperatures on flower induction during SD is apparent in the range 10°-30°C and an increasing response in the range 35°-50° C.LightLight intensity is an important factor in flower induction. Increasing light intensities during SD or CL increase the flowering response. The optimal light intensity during CL is rather low in E 1 and has not been reached in L 1 in our experiments.Photoperiodic response curves at 20° and 32° C for E 1and L 1For photoperiods from 8 to 18 h more numbers of cycles necessary for 50% flowering are needed for 20° C than for 32° C. The curves run parallel for both E, and L, at photoperiods from 18 to 24 h. In this range E 1 needs an equal number and L 1 decreasing numbers of cycles.HypothesisThe mechanism of flower induction is a balance between two processes:1. A deblocking process in high intensity light, increasing light intensities accelerating it with an optimum, temperature insensitive.2. A reblocking process in darkness, starting about 4 h after the onset of darkness° reaching its maximum after 6-7 h and decreasing for about 5 h, temperature sensitive, temperatures higher than 30°-35° C slowing it down increasingly. Incandescent light postpones the onset of darkness and hence the reblocking.When these 2 processes are out of balance and more deblocking than reblocking occurs, a critical level or disappearance of the block is reached and flower induction is completed.ModelsModels, based on the foregoing hypothesis, are presented for induction by LD 20° high intensity light, LD 20° - high+low intensity incandescent light, 32° SD. These models fit well and can be used to predict time of flowering under specific conditions
