Ontogenetic Studies on the Juvenile Leaves of Phoenix dactylifera L

Abstract

The ontogeny of seedling leaves or eophylls of Phoenix dactylifera was studied from foliar initiation to the stage of laminal maturation. During germination, the embryonal axis is carried deeper into the soil by the elongating cotyledonary sheath. As soon as the root and shoot apices become active the elongation stops. The first foliar organ produced by the shoot apex is a prophyll, a structure that has a sheath but no lamina. The second product of the shoot apex is the first eophyll, which is simple, lanceolate, plicate and devoid of haut. The plications arise by the process of schizogenous splitting of cells of the laminal meristem and not by differential growth or by 'invagination' as reported by earlier authors working on other palm genera. The eophyll differs from the adult leaf in the mode of splitting and in the number of plications produced. The adaxial splits occurring in the eophyll start from the epidermis and proceed inwards, whereas they are internal for the most part and leave a continuous sheet of tissue (haut) in the adult leaf. The first eophyll develops only one split on either side of the rachis-petiole axis on the adaxial side followed by a similar splitting on the abaxial side. This limits the number of plications to a minimum. Ontogeny of the vasculature of the eophyll is traced from early stages.