(Kadman-Zahavi and Ephrat, 1973). These findings suggest that the relative amount of Pfr at the end of the light period is important forthe flowering-inducing capacity during darkness. Inthe present study, the inhibitory effect of NB-B and NB-FR was observed only following a daily photoperiod with monochromatic blue, and was canceled by supplementation with red light(Fig. 2 and Table 3). It is well known that blue and red light establish in vitro photoequilibria for phytochrome(Pfr/Pr+ Pfr) of 0.3-0.5 and 0.8, respectively(Butler et al., 1964). In the present study, the estimated phy- tochrome photoequilibria(Pfr/Pr+ Pfr) maintained during the daily photoperiods under B-SD and B+R-SD conditions were 0.54 and 0.85, respectively(Fig. 2A and Table 3; Sager et al., 1988). There- fore, it is likely that the ratio of Pfr/Pr maintained throughout the blue photoperiod was much lower than that maintained under the blue +red photoperiod. It is possible that the red-light-activated Pfr strengthened the floral-inducer activity, resulting in a higher