A Short Periodic Growth Cycle and a Secular Variation in Lemna minor

Abstract

THE rate of frond production in Lemna, when grown under constant conditions in which light, temperature and culture solution were all controlled, was found to be only approximately exponential and certain deviations from the ordinary compound interest law have been established. First, there is a secular variation which takes the form of a wave with a 25–35 day cycle and, secondly, superimposed on the long variation is a short periodic cycle of 4–6 days. The short wave has been followed through 15 successive cycles in one experiment. The length of the cycle of the short, and possible also of the long wave, appears to be correlated with the mean rate of increase in frond number, in that when grown under conditions which give rise to a rapid rate of division the cycle is short, and vice versa.