Abstract
The oscillations in phenylalanine ammonia-lyase activity from Spirodela polyrhiza and phenylalanine ammonia-lyase and tyrosine ammonia-lyase activities from Lemna perpusilla displayed a circadian rhythm under continuous light. Rhythmicity in enzymic activity could not be detected in continuous darkness since under this condition phenylalanine ammonia-lyase activity remains at a fairly constantly low level. Results from our studies of the oscillatory pattern of the respective activities of phenylalanine and tyrosine ammonia-lyase support their "inseparability."