Approximately 90 plants of I. balsamea were grown under each of 4 photoperiods: 8-hr., normal (12-15 hrs.), 16-hr., and 20-hr. Measurements of the areas of representative leaves showed that the leaf area was approximately the same under the 3 longer photoperiods but was much less under the 8-hr. photoperiod. The av. ages at budding were 21.8, 22.8, 62.7, and 64.5 days under the 8-hr., normal, 16-hr., and 20-hr. photoperiods, respectively, and the corresponding ages at flowering were 492, 49.6, 92.0, and 92.8 days. Although there is a marked difference in the age at budding under the 2 longer as compared with the 2 shorter photoperiods, the av. length of the period from budding to flowering under the various photoperiods varies only slightly, suggesting that the influence of the length of the photoperiod is primarily on the initiation of the flower buds rather than on their subsequent development. Weekly measurements of the height of the main axis showed that maximum stem development occurred under the 16-hr. photoperiod. Comparison of the form of the growth curves with age at budding and flowering suggests that the effect of the length of the photoperiod on the initiation of flower buds is independent of its effect on stem development.