Abstract: Using the histochemical and cytological method of Bromine-Iodine-Glacial aceticacid fluid, we have observed the location, time, and processes of rubber formation inthe pericarp of Decaisnea fargesii and the ontogenetic changes of the epidermal cellsin these processes of the same plant. The following results are presented: 1. The formation of rubber is limited in the protoplasm of the secretory epidermis of pericarp. Generally, about ten days after blooming and fertilization, the rubbergranules begin to appear in the epidermal cells which are located in the depressionsof the young pericarps. And then, following the formation and development of thesecretory epidermis, the rubber granules increase progressively and stop till 60 daysold. when the secretory epidermis lyses into laticiferous canals, the formation of rubbergranules disappears. The rubber is stored up within the laticiferous canals. 2. During the course of fruiting, the epidermal cells of the carpel wall differentiate into the pericarpial epidermis and the secretory epidermis. To adapt it-self to its peculiar functions, each part forms its own particular feature, which isprominently different from the other. The cells of the secretory epidermis in cluding dense protoplasm, enlarge rapidly, and retain their vigorous activity. During thisperiod, they form rubber granules successively. Finaly when these cells are full of granules, they lose their vital functions andlyse into laticiferous canals. 3. The limitation of distribution and formation period of the rubber in Decaisnea fargesii is closely correlated with the ontogenetic processes of, its secretoryepidermis. This characteristics has never been observed, in other rubber plants. Decaisnea fargesii may provide a satisfactory material for the study of the mechanismof rubber biosynthesis. We hope that the present observation will provide some useful information for the improvement of rubber yield in this plant.