Germinating barley aleuron cells were studied electron-microscopically. The aleuron grains, after KMnOi-fixation and embedding in Vestopal W, contain a protein matrix, electron-dense, and electron-transparent bodies. Evidence is presented that the electron-dense bodies are globoids which consist of phytin. The nature of the electron-transparent bodies is discussed. During germination the protein matrix disappears and the globoids are decomposed. The rough-surfaced er develops extensively in the first 8 days. It forms protein vesicles which seem to discharge their contents in the vicinity of the cell wall. The latter appears to be subject to chemical change. In the course of the process of germination the er makes connections with the spherosomes. The spherosomes are for the greater part found around the aleuron grains. During germination their contents gradually diminish. In the first 8 days the mitochondria, very undeveloped at the start, obtain more and longer cristae. The cytological changes observed reflect the known physiological activities of the aleuron cells.