GERMINATION-REGULATING MECHANISMS IN SOME DESERT SEEDS VIII. ARTEMISIA MONOSPERMA1

Abstract

Germination of achenes of Artemisia monosperma is absolutely dependent on light, irrespective of temperature. Full saturation by light was obtained with 24 meter-candle seconds and more than half with 0.1 meter-candle second. Nevertheless, even with saturating irradiation, action of light was cumulative, requiring repeated short irradiation, the number depending on temperature, separated by a minimal interval. Responsiveness to light increased with progress of incubation. The cumula-tiveness and the increase in responsiveness are discussed. A gradual achievement of an equilibrium between an inactive precursor and a substance which participates in the light-induced reactions, is postulated. The stage of equilibrium, as well as the rate at which it is reached are temperature-dependent. Light-independent reactions which are triggered by irradiation may be reversed by incubation at supra-optimal temperatures, or by desiccation, and full promotion may be restored after re-imbibition or after return to optimal temperatures, by an additional irradiation. The ecological significance of the germination responses is also discussed.