IN SEARCH OF A BIOLOGICAL HOUR

We focus here on a prominent subset of rhythms within the ultradian do main that have periods between 30 and 240 min as a candidate for a <<b iological hour.>> Smooth histograms produced from reported periods obt ained from two surveys of literature display prominent peaks centered near 95 min, with a range from about 50 to 130 min. The list of variab les having these periodicities is extensive and diverse (e.g., circumn utation movements of plants and the REM/non-REM sleep cycle of human b eings). The periodicity displayed by many of these examples is somewha t irregular, perhaps because of other changing biological components a nd/or environmental factors such as stress. For example, results from our experiments showed that when Phaseolus vulgaris L. shoots were sub jected to stress caused by staking, the ultradian periodicity of circu mnutation was initially lengthened and later restored to its <<normal> > length.