A developmental study of ovule formation inDendrobiumXJ. Thomas is reported. The ovulary at anthesis is rudimentary and consists of only a placental ridge. Upon pollination the placental ridge undergoes proliferation and ultimately produces embryo sacs. Normally the ovulary requires 6½ to 7 months from the time of pollination to mature. Of the total time, 35–40 days or 1/6 of the period is required for cellular proliferation on the placental ridge and another 1/6 for the formation of embryo sacs. The early developmental stages within the ovulary are subdivided into phases —quiescent, proliferative, nucellar, archesporialandmeiotic.Relative volume changes which occur within the developing cell (nucleo-cytoplasmic ratio) and within the developing ovule during the established phases are also presented.