Complex Reaction in Hyoscyamus niger upon Night Interruption with Red Light

Abstract

IN general, long-day plants form rosettes in short days (in white light), and flower stalks in long days. The dependence on the wave-length of radiation of this photoperiodic reaction can be determined in three different ways: (a) by growing plants exclusively in light of narrow wave-length bands, at high intensity, (b) by extending short white days with a coloured light treatment, and (c) by interrupting the long night, in a short-day treatment, with coloured light. Most results on the spectral dependence of the photoperiodic reaction have been obtained with the night interruption technique. These results appear rather clear-cut, which is the main reason why the two other possible modes of approach have only been used incidentally. Moreover, the results obtained from the other methods were not taken too seriously if they disagreed with the results of night-interruption experiments.