Floral Initiation in Cestrum Nocturnum. I. A Long-Short Day Plant

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Abstract
Cestrum nocturnum was found to require long day (LD) followed by short day (SD) induction, in that order, for floral initiation. A minimum of 5 LD and an 11.5 hour photoperiod were required for LD induction, and a minumum of 2 SD and an 11.5 hour nyctoperiod for SD induction. Both the LD and SD requirements corresponded to those for long day plants and short day plants, respectively. The strength of LD induction, as determined by the daylength and the number of photocycles, had a quantitative effect upon the number of nodes flowering per plant suggesting that the product of LD induction, L, is a precursor of the floral stimulus. Exposure to high temperature (42[degree]C for 2 hours) after LD induction inhibited floral initiation suggesting that L is a heat labile substance(s). L was not translocated from the leaves after LD induction, whereas translocation of the floral stimulus started within 8 hours after the second nyctoperiod of SD induction. Results for Cestrum were contrasted with existing theories of photoperiodism and synthesis of the floral stimulus in LD plants, SD plants, and intermediate day plants.