Volume 74 (1961) Issue 876 Pages 303-309
Effects of isolation and bisection of the leaf primordium by tangential incisions upon its dorsiventral development were studied for the first leaf of Sesamum indicum L. Incisions were made on the shoot apices of three stages, i. e., dormant, 1 day- and 2 day-cultured embryos, and in three positions, i. e., in the median plane of the shoot apex, along the adaxial border of the leaf primordium and in the middle of the leaf primordium. When the incisions were made in the median plane of the shoot apices of the dormant and the 1 day-grown embryos, the leaf primordia developed dorsiventrally. When the leaf primordia were isolated along their adaxial border from the apical meristem, they developed as centric organs in higher proportions after the operation at earlier stages than after that at later stages. When the leaf primordia were bisected tangentially, the abaxial half developed only as a centric organ, whereas the adaxial half formed every time a dorsiventral leaf. From above results, it is inferred that the principal factor determining leaf dorsiventrality is the effects from the apical meristem, and that the intrinsic factor, if any, of the leaf primordium itself may be very faint or of secondary nature in its function. Moreover, it is suggested that dorsiventrality may become gradually intensified in the course of plastochron and perfect establishment of dorsiventrality may be attained at the end of the first plastochron.