Nodal explants of the LSD plantCestrum diurnum, each consisting of a short piece of stem with leaf and axillary bud, produced flower primordia in culture on White's basal medium after removal from stems grown on 16‐hr day and subjected to 8‐hr daily photoperiods. No flower primordia formed in the absence of leaves or with leaves excised during the rapidly expanding phase of growth. The presence of 1/16 of a leaf blade was, however, enough to provide for floral initiation. Young mature leaves induced flower initiation equally well whether the leaf was erect, with only the stem portion in contact with the agar culture medium, or inverted, with the leaf blade making contact, whereas, when erect, fewer older leaves induced flower initiation and tended, in addition, to abscise. In a survey involving light intensity (1–1000 ft‐c) and number of daily cycles (1–9) flower primordia were induced to form on 1 ft‐c with 1 short day, increasing percentagewise to an optimum of about 81 ft‐c in 7 days. The number of flowers per bud was little affected by light intensity but increased progressively with the number of daily cycles.