Investigation of Hyoscyamus Niger L., A Long-Day Plant, for Endodiurnal Periodicity in Flowering Response

Abstract

Flowering in Hyoscyamus, which resulted from exposures to several light-dark cycles of different durations in different treatments (all light periods were the same duration), revealed an inhibition of flowering in plants exposed to cycles of 24- and 30-hours'' duration. In longer or shorter cycles flowering was promoted. Darkness may be either inhibitory or promotive in Hyoscyamus. Since a similar phenomenon (displaced by 12 hours) has been found already in Glycine max, a short-day plant, the classical terms "long-day" and "short-day" may have to be revised since they do not constitute accurate causal descriptions. A discussion of the results relative to endogenous rhythms is given.