Circadian Rhythms and the Time Measurement in Photoperiodism

Abstract

By means of diurnally periodic oscillations (the physiological clock) the cell is brought alternately into two period parts with properties differing both quantitatively and qualitatively. Each of these parts lasts approximately eleven to thirteen hours. The basic importance of this oscillation lies in the fact that the cell is thus brought to certain extreme physiological states. Various physiological functions are possible only when these extremes are reached. One of these extreme states is characterized by a high synthetic capacity and the other by a high catabolic capacity. We may illustrate the importance of the oscillator for cellular chemical reactions by means of a diagram (Fig. 1). Many of these processes (A, B, C, etc.) are already known, and I shall not bother to go over them again now. If the oscillator is not functioning--that is, if the clock is not running--several of these processes cease or operate at submaximal rate...