As a part of a study of organ and cellular senescence in plants, we are delineating the structural and functional changes which occur in the cotyledons of germinating peas. As might have been expected from earlier reports that cotyledon cells are capable of performing oxidative phosphorylation, incorporation of labeled amino acids into protein (4) and de novo synthesis of certain enzymes (5), examination by electron microscopy showed the presence of all structures normally present in plant cells. In addition, a major fraction of the cell volume was found to be occupied with relatively large roughly spherical bodies, with no visible internal structure. The data presented here indicate that the reserve globulins are localized in these structures. These structures are easily isolated as a pellet following centrifugation of a pea cotyledon homogenate. The presence of similar protein bodies in peanut cotyledons has already been reported (1, 3).