MOVEMENT IN PLANTS. 233 



purposes simultaneously ; if the axis is parallel with the 

 light rays, the plant (also horizontal) is subject to light 



Fig. 53. Clinostat, sup] 



stimulation but not to gravity stimulation ; if the axis is 

 at right angles to the light rays, the plant will show 

 neither geotropic nor heliotropic curvature. 



307. Elimination of Fhototropism. Grerminate seeds 

 (e.g. Cress, Mustard, Sunflower) in two small pots (A, B) 

 in darkness. When the erect shoots are 2 or 3 cm. long, 

 wind up the clinostat and place it, with the axis vertical, 

 in a dark box (heliotropic chamber) with the opening 

 facing the window. Fix A to the plant-holder, so that the 

 seedlings will be carried round in a horizontal plane; 

 place B in the box beside the clinostat. In a few hours 

 the seedlings in B will show a marked curvature towards 

 the light, while those in A will be growing quite erect 

 and continue to grow erect so long as they are rotated. 



308. Elimination of Geotropism in Shoots. Place 

 the clinostat horizontal, and fix the plant-pot horizontally 

 so that the seedlings will be rotated in a vertical plane. 

 To prevent heliotropic curvature, cover the whole with a 

 box, or put it in a dark room. As long as the clinostat is 

 going, the shoots will grow straight forwards horizontally, 

 but if the clock is allowed to stop the shoots will sc-on 

 curve upwards. 



