GROWTH AND DORMANCY IN LUNULARIA CRUCIATA (L) DUM .4. LIGHT AND TEMPERATURE CONTROL OF RHIZOID FORMATION IN GEMMAE

The first sign of initiation of growth in dormant gemmae of L. cruciata is the formation of rhizoids. Gemmae in the cup cannot 'germinate' until exposed to substrate conditions allowing the outward diffusion of a growth inhibitor. Rhizoid production depends on temperature and light. With long light periods rhizoids are formed over a wide range of temperatures. Transference to darkness after 2 h white light causes about 50 per cent of gemmae to produce rhizoids, and these are formed only between 20 and 25 °C. Outside these temperature limits the percentage of gemmae with rhizoids soon drops to zero. Although rhizoid production is prevented in total darkness, gemmae remain alive for well over 6 months. Red light for as little as 5 s promoted, and far-red light inhibited, rhizoid formation in the dark. Coumarin and indol-3yl-acetic acid can substitute for light and partly reverse the effect of far-red irradiation. © 1969 Oxford University Press.