Geotropic Curvature of Avena Coleoptiles in Solutions of Various Osmotic Values

Isolated Avena coleoptiles are placed with their bases in mannitol solutions of various osmotic values. In this way the water uptake is inhibited. The coleoptiles are irradiated with red light and turned through 90 °. Considerable geotropic curvatures are developed in solutions which prevent growth to a large extent. Red light enhances the geotropic response also under these conditions, but a red, far-red reversal of the red effect does not take place. The tips of the horizontal coleoptiles appear not to reach the vertical position, but end up growing at a constant angle to the vertical.