PHOTOPERIODIC RESPONSES OF CERTAIN GREENHOUSE ANNUALS AS INFLUENCED BY INTENSITY AND WAVELENGTH OF ARTIFICIAL LIGHT USED TO LENGTHEN THE DAYLIGHT PERIOD

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Abstract
Expts. on the effect of intensity of incandescent lamp radiation and wavelengths of artificial radiation used during the winter to prolong the day, using pansy (Viola tricolor), stock (Matthiola incana), and China aster (Callistephus chinensis), are reported. The intensities used were 100, 10, 1, 0.3, and 0.1 foot candles. The wavelength bands included blue, green, yellow, orange-red, red, extreme red, and infra-red. Little difference in response was secured between 100 and 10 foot candles and a very definite photoperiodic effect was produced by 0.3 foot candle and as low as 0.1 foot candle with China aster. An increase over the control in dry weight was produced by all 3 spp. under all the intensities. Orange and red radiation (650-720 m[mu]) caused the most marked photoperiodic responses. The earliest blooming with pansy and stock and the largest number of flowers with all 3 were occasioned by the orange-red. Little effect in flowering time was observed in the case of pansy and stock with blue, green, and yellow radiation. With aster, all wavelengths of additional light brought about earlier flowering than in the control plants.