Abstract
Winter flowering chrysanthemums which are reta-rded by artificial illumination bear generally some-what deformed flowers, having fewer number of ray-flowers, exposing flower center, then of lower marketable value. In this study, the authors tried to increase number of ray-flowers in the center of flower head by re-illumination after flower bud had differentiated in the chrysanthemums which had been retarded by artificial illumination.
Plants which had been retarded by artificial illu-minaton, were re-illuminated for various length of days after having been grown for certain periods under natural day (short day). Six varieties were used in 1952, and three in 1953.
The results showed that 15 to 20 days of re-illumination were most effective to increase the num-ber of ray-flowers when it was started about ten days after the plants had been transfered to natural day under favorable conditions. Under more adverse conditions the re-illumination treatment must be started a few days later. Shorter, earlier, or later treatments were less effective.
By these treatments, time of flowering was reta-rded as many days as those the plants were received of re-illumination.
