the flowering response of sdp to the light quality supplies during the daily photoperiod has also been investigated. For example, white- and red-light grown seedlings of Pharbitis were successfully induced to flower by exposure to an inductive darkness, but FR blue-light grown seedlings failed to flower(Takimotoand Naito, 1962). In Xanthium pennsylvanicum, red light supplied during the intervening light period promoted flowering, whereas FR light was inhibitory(Salisbury, 1965). Similarly, Lemna paucicostata T-101-a strain of SD duckweed-responded as typical SDP when grown under a daily photoperiod of white or red light, but failed to flower when blue or FR light was initially supplied(Ohtani and Ishiguri, 1979). These findings strongly indicate that the photo-activated form of phytochrome is required for production of floral stimuli during inductive darkness(Pfr-requiring reaction). However, the molecular mechanisms underlying the flowering response of SDPs to the light quality supplied during the daily photoperiod remain to be elucidated.