An Endogenous Rhythm in the Rate of Carbon Dioxide Output of Bryophyllum

Abstract

SUMMARY A technique is described for recording automatically, with the aid of an infra red gas analyser, the rate of C02 output or absorption by plant material under controlled conditions. An examination of the rate of C02 output by excised leaves of 16 species of succulent plants in darkness and in a C02-free atmosphere revealed clearly defined rhythms in only Bryophyllum fedtschenkoi, B. daigremontianum, and B. calycinum (pinnatum). Further investigation of the rhythm in leaves of B. fedtschenkoi revealed that: (i) day length has no effect upon the period of the rhythm in subsequent darkness, the phase being set at the time the lights are extinguished ; (2) normal air suppresses the rhythm; (3) removal of the epidermis and cutting the mesophyll into pieces i cm2 does not affect either the phase or period of the rhythm ; (4) continuous illumination at an intensity of 3,000 lux inhibits the rhythm which restarts when the lights are extinguished. The phase of the rhythm can be set at any time of day according to the time at which the lights are extinguished. The time which elapses between the onset of darkness and the first peak decreases as the length of the light treatment is increased. The endogenous nature of the rhythm is fully established. The results are compared with those of other researches.