Abstract:The origin and the whole development stage of the juice sac of Citrus sinensis (L.) Obs. "Jincheng" were investigated. Results indicated that the juice sac originates from a single cell of the carpellary endoepiderdris. After the anticlinal and periclinal divisions of the initial cell, a multicellular globular-structure is produced. The globular-structure developes into a column6tructure with the differentiation of a cluster of meristem cells at its apex. As result of the active divisions and growth of the meristem cells, the column-structure expands and widens. At last the column-struCture developes into an expanding sac with a slender stalk that is the juice sac.