The study deals with the role of the rough endoplasmic reticulum in the pollen mother cells ofBerberis vulgarisfrom telophase I to the tetrad stage of meiosis. At the time of cell plate formation, among the various vesicles and vacuoles concerned derived from Golgi structures and containing callose material, globules of an electron-dense and amorphous material appear in the area of the cell plate. Initially such globules are associated with short cisternae of rough endoplasmic reticulum, which have a characteristic electronopaque content. As the formation of the cell plate progresses, analogous globules become deposited on the surface of the newly formed plasmalemma as well as on the plasmalemma surrounding the pollen mother, cell. It would appear that these deposits of electron-dense and amorphous material, so abundant at the tetrad stage represent the exine material of the pollen grain wall.