Abstract
The saturating photon flux density (400 to 700 nanometers) for induction of flowering of the long day plant Anagallis arvensis L. was 1,900 micromoles per square meter per second (6,000 foot-candles) when an 8-hour daylength was extended to 24 hours by a single period of supplementary irradiation. The saturating photon flux density for photosynthetic CO(2) uptake during the same single supplementary light period was lower, at about 1,000 to 650 micromoles per square meter per second (3,000 to 2,000 foot-candles).The per cent flowering and mean number of floral buds per plant were significantly reduced when the light extension treatment was given in CO(2)-free air, and glucose (10 kilograms per cubic meter in water) relieved this effect. Glucose solution also significantly increased flowering of plants given supplementary light treatment in atmospheric air under a photon flux density of 80 micromoles per square meter per second. Increasing the CO(2) concentration to 1.27 grams per cubic meter of CO(2) in air during the supplementary light period did not increase flowering.It is concluded that high photon flux densities promote flowering of Anagallis through both increased photosynthesis and the photomorphogenic action of high irradiance.