Several attempts have been made to establish various leguminous plants as forage and cover crops on pasture land in Hawaii. Korean Lespedeza (Lespedeza stipulacea Maxim) and the common Lespedeza (L. striata Thunb. H and A) were among those tried. These two species are widely grown throughout the central and southern parts of the United States, where they attain good vegetative growth and are from one to two feet in height. In contrast, when they are grown in Hawaii, these plants attain a height of only a few inches before maturing. Their inability to develop a good vegetative growth in Hawaii suggested that their failure was concerned with the relationship of the plants to the relative length of day. Based on this supposition, a series of experiments was conducted to determine the critical day length for flowering in Lespedeza. Smith (2) reported that Lespedeza can be grown under 14 hours of photoperiod without fruiting. However, the effect of increasing the duration of the light period up to the critical photoperiod for the initiation of flowering has not been investigated. Four light-tight chambers were constructed. The plants were grown in wooden soil boxes 3 ? 4 ? 1.5 ft. in size which were placed on galvanized pipe frames fitted with rollers. The boxes were rolled out of the light-tight chambers each morning at 7:30 a.m., and the plants were exposed to normal conditions of sunlight intensity until 4:30 p.m. The length of the various photoperiods was adjusted by exposing the plants in the chambers to additional light from fluorescent lamps regulated by time switches. In each experiment, the treatments were started as soon as the seeds began to germinate. A field test was conducted during the longer days of the year to corroborate the results obtained in the chambers.