Periodicity Fade-Out; Initiation by External Factors

Abstract

It was mentioned earlier that animals and plants will show an endogenous diurnal rhythm even if they have not been exposed to diurnal cycles of environmental factors during their embryonic development. One more point has to be added: very often these organisms do not show any periodicity at first, but a single stimulus is then sufficient to initiate the rhythm (Bünning, 1931, 1935a, b; Ball and Dyke; Fig. 25 to 27). Since the necessary single stimulus can be compared with the stimulus required for the re-initiation of a rhythm which has faded out, the phenomenon of a rhythm fading out will be discussed first.

„... könne man schließen, die Bewegung des Einschlafens und Erwachens hinge mit einer, dem Gewächse einwohnenden Anlage zu periodischer Bewegung zusammen; letztere würde aber wesentlich durch die erregende Einwirkung des Lichtes in Tätigkeit gesetzt ...“ De Candolle, Pflanzen-Physiologie, Bd. 2, p. 639–640, 1835 (Original: Paris 1832).