Changes in the cells comprising the abscission zones of Lycopersicon esculentum and Nicotiana tabacum flower pedicels were observed, apparently associated with the separation of the flowers from the plants. Special attention is devoted to changes which occurred in the fine structure of intracellular components of the abscission cells. Microbodies with crystalloid cores in cells comprising the abscission tissue of the pedicels were observed to undergo structural changes. These changes occurred prior to the cell-wall degradation which resulted in cell separation. At the time of cell separation, the number of microbodies present in the abscission cells was greatly diminished. The changes in the fine structure of the crystalloid core may represent the release of latent enzymes into an active form which then induces cell separation in the abscission tissue. Other structures in the cells in which changes occurred are the endoplasmic reticulum (ER) and the nucleolus. Prior to, and during cell-wall disintegration, an abundance of rough ER was observed within the abscission cells. The occurrence of rough ER may represent an increase in the synthesis of protein for export from the cells of the abscission region and/or for the synthesis of certain enzymes associated with the degradation of cell walls in the abscission zone itself. In some abscission cells, prior to the cell-separation phase, nucleoli were observed which appeared as though they had segregated spatially. In such cases, the amorphous zone was the only nucleolar component observed. The possible significance of these observations is discussed.