Effects of a Night Break of Red Fluorescent Light on Leaf Growth of Callistephus chinensis (var. Queen of the Market)

Abstract

THE results described here are from the initial part of an experiment on the effects of short days of 8 h of natural light with and without an interruption of 1 h red fluorescent (cadmium borate) light in the middle of the 16 h dark period. The plants were grown first in seed boxes and then in pots, on trolleys in a glasshouse (13° C night min, 19° C day min), and had natural daylight from 8 a.m. to 4 p.m. G.M.T. They were then pushed into two dark compartments for the night. The treatments began immediately the seed was sown. The disposition of pots on the trolleys and the orientation of the trolleys were re-randomized weekly and the night break compartment was changed over each week. Thus although some position effect was confounded with treatment the former component should have been small. The total radiant energy during the night break (4.6 × 10⁻² cal/cm²; Kipp solarimeter) was about 0.5 per cent of the visible component of natural radiation in the glasshouse for an 8-h day during January. While the night break light was on the temperatura rose gradually to 2° C above the unilluminated compartment and returned to normal again in about 30 min. The oscillation of temperature due to the on-off cycle of the thermostat was ± 0.5° C, so the small rise has been ignored.