Physiological Structure of the Critical Photoperiod of Lemna paucicostata 6746

The critical day length or the length of the critical photoperiod for the short-day duckweed, Lemna paucicostata 6746 is about 14 h (Oota 1983). With the min-SD method, I found that not the whole critical photoperiod but only its initial and terminal brief fractions, called respectively the LI- and L2-phases, need be illuminated for a given day to be a noninductive day. Inversely, the darkened LI- and/or L2-phase makes the day inductive. The rest of the day can be either darkened or illuminated without modifying the inductive or noninductive property of the day. Thus, the physiological structure of the critical photoperiod for L. paucicostata 6746 closely resembles that of the critical photoperiod for the long-day duckweed, L. gibba G3 (Oota 1981).