Abstract: The early events of the 'differentiating laticifers in the primary system of the young shoot of Hevea brasiliensis were studied by electron microscopy with emphasis on the initiation of the characteristic components,of the laticifer. The smallest rubber particles with diameter 40- 60 nm recognizable in the y6ung laticifer appeared as electrondense globules in the cytoplasm and as the particles enlarge they became electron-transparent in their central region while the periphery of the particles remained electron-dense and one or more electron-dense protrusion (s) can sometimes be seen on.the particles. Lutoids which constituted a dispersed lysosomal vacuole were found to origin from extensions of endoplasmic reticulum. There were three types of lutoids with different inclusions apperaring one after another in laticifer during its development. The lutoids with dark microfibrils appeared first, then replaced by the lutoid with bright microfibrils and in mature laticifer only the lutoids with fine fibrils were able to be found. There were no F-W complexes but normal proplastids in laticifer at the initial stage of its development. Some abnormal laticifers were detected that appered to remain in early stage of differentiation and did not form typical ones.

Key words: Hevea brasiliensis, Laticifer, Differentiation, Ultrastructure