THE SPECTRAL DEPENDENCE OF FLOWERING AND ELONGATION 1)

Experiments with Salvia occidentalis (SDP) and Hyoscyamus niger (LDP) demonstrated that at least two photoperiodic reactions are involved in the process leading to a long-day effect. The main-light-period reaction is more sensitive to near infra-red and blue light than to red or green light. The effect of near infra-red and blue light can be antagonized by red light. The nightbreak reaction, promoted by red light, is nullified by a relatively short exposure to near infra-red or blue light. Experiments with various plant species on the elongation of internodes have shown that at relatively low intensities red light is more inhibitive than blue light. At relatively high intensities blue light is the most inhibiting spectral region. The inhibiting effect of red light on the elongation of hypocotyls of light-grown gherkin seedlings is antagonized by a subsequent exposure to near infra-red or blue light. The inhibiting effect of red light on the hypocotyl of dark-grown gherkin seedlings is much more pronounced when the seedlings are pre-irradiated with white or blue light.