A short-day duckweed,Lemna paucicostata6746, was exposed to continuous darkness at 26°C, and the changes in the floral parameters (3) due to far-red and/or red light pulse given at various times of the dark period were studied.Parameters a (vegetative growth rate) andφ(flowering ratio) were respectively decreased and increased with a far-red light pulse given at the outset of the dark period. The decreased a and the increasedφremained almost unchanged until the 7th hour, but returned to their initial levels thereafter. The far-red light actions on a andφwere reversed by subsequent exposure to red light. Parameter P1(pre-flower induction period) was extended by 1 day when far-red and/or red pulse was given at about the 7th hour of the dark period. A far-jed pulse given at the outset of the dark period only affected parameter P2(flower induction period). Although the sensitivity of P2to red light increased with time, its sensitivity to far-red light remained constant and at about the 7th hour was equally sensitive to far-red and red lights. Both red and far-red pulses given later than the 7th hour were increasingly ineffective on P2. The red/far-red reversibility occurred only for the action on P2of the far-red pulse applied during the early dark period. Parameter P4(flower production period) varied rhythmically in length with a far-red puke, the maximum shortening and extension being induced by the pulse given at about the 7th and 19th hours, respectively. The sensitivity of P4to red light also changed rhythmically with an inverse phase angle to the rhythmic response to farred light, and the far-red and red light actions were reversed respectively by subsequent red and far-red lights.These findings suggested that multiple timing devices including an hourglass-type clock and a circadian clock are involved in duckweed flower
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