Flower initiation of chrysanthemum seedlings grown continuously in short days at four levels of irradiance

Chrysanthemum seedlings grown continuously under flower-inducing short-day conditions did not initiate flowers rapidly, but continued to produce leaves. A minimum leaf number seemed necessary before the seedlings responded to the relative length of day and night. The minimum leaf number varied with the initial size of the seedling, genotype and level of irradiance. When growing seedlings — or juvenile cuttings — for the purpose of selecting plants for vegetative propagation, the minimum leaf number required for flowering should be met before the start of the short-day period.