1. The autotetraploid rye (Secale cereale) shows gigantism in cell size as well as in the plant as a whole. 2. The meiotic metaphase shows a maximum number of quadrivalents of 4, and the mean number per cell is 1.05. No multivalents were found in 28.6 per cent of the cells. 3. Chiasma frequency of the autotetraploid rye in comparison with that of the diploid is discussed. 4. Bridges of the first division have been observed. The coefficient of hybridity is 0.00229. 5. Lobed pollen grains have been found, and this is ascribed to failure of cell-wall formation. On the average, the seed setting is 23.8 per cent. 6. Cross pollination shows that only 4n x 2n sets seed and that 2n x 4n is entirely incompatible, owing to the failure of pollen-tube growth.