The anatomy of roots growing in a water-logged soil may differ considerably from that of roots of the same plant species growing in aerated soil (Me Pherson 1939, Bryant 1934). Generally the volume of the intercellular spaces is increased in the former, often by the breakdown of cells of the root cortex. It has been demonstrated that oxygen diffuses from the leaves through these intercellular spaces into the roots (Barber c.s. 1962; van der Heide c.s. 1963; Greenwood 1967). These anatomical changes may be considered as an “adaptation”, which enables the plants to grow in soils that are poor in oxygen. Besides, in barley, other changes of the properties of the roots may contribute to their capability to grow under these conditions (van der Heide, c.y.).