Abstract
The observation of diurnal biological rhythms was first recorded early in the eighteenth century, but it was 200 years before any detailed investigation of the nature of daily plant and animal rhythms was undertaken (Burning, 1964). | As a more virgorous study of biological rhythms developed, it became apparent that the daily rhythmic activity of organisms fell mainly into two categories. The rhythms were either exogenous or endogenous in origin (Frisch, 1960; Burning, 1964; Wolf, 1962; Sollberger, 1965). | Exogenous rhythms in living systems depend on the cyclic variations in light, temperature and other geophysical influences. If a plant or animal were placed in a controlled environment where all external environmental circumstances were relatively constant, the rhythmic behavior of the organism would tend to diminish in time.