Photoreversibility of Stem Elongation in Melilotus alba Desr 1

IN SWEETCLOVER (Melilotus alba Desr.), as in many other long-day plants, stem elongation and flowering occur more or less simultaneously when the plants are subjected to long-day conditions. In some long-day plants one of these phenomena may be displayed without the other. Thus, Murneek (8) observed an thesis in Rudbeckia plants that had made essentially no stem elongation, and development of tall, leafy, flowerless stems on beet plants is not uncommon. In a short-day plant, grain sorghum, Lane (7) observed that stern elongation and formation of flower primordia occurred at the same time under 10-hour days, but stem elongation preceded initiation of flowers under 14-hour days. The purpose of the research reported herein was to investigate the effects of red and far-red radiation on stem elongation of sweetclover, a long-day plant. The basic photoperiods, given in a fluorescent-lighted growth room, were subcritical for flowering (6) but long enough to permit some stem elongation.