60 EXPERIMENTAL PLANT PHYSIOLOGY. 



which, so far as they are capable of growth, finally result in the 

 placing of the leaves in a horizontal position, but parallel to the 

 shoot and one another. (Fig. 55.) 



EXPERIMENT 72. 



EFFECT OF RED AND BLUE LIGHT. 



Of two equally sensitive seedlings, place one in a chamber (Fig. 

 55), with one side of yellow glass, and the other in a similar chamber, 

 with one side of blue glass. The heliotropic movement is much more 

 marked in the blue light. Instead of the colored plates, use glass 

 vessels with parallel walls, filled, one with a solution of bichromate 



FIG. 55. 



Shoot of Sunflower which has been in a horizontal position several days. 



(After Oels.) 



of potassium, the other with a solution of ammonia-copper-oxide. 

 Only small plants can be used in the experiment. 



EXPERIMENT 73. 



HELIOTROPIC REACTION OF PLANT WITH GRAVITY NEUTRALIZED. 



If the influence of gravity is removed from a plant as in Experi- 

 ment 67, and the light allowed to fall parallel to the axis of the 

 plant, the roots and shoots will be seen to take opposite direc- 

 tions in a plane parallel to its rays. 



EXPERIMENT 74. 



THERMOTROPISM. 



Grow seedlings of Corn in a pot, and place in a position where 

 the light will be received perpendicularly. At a distance of 40 cm. 

 place a sheet of smoked tin which is kept warm by a spirit-lamp. 

 In twenty-four hours the shoots will have inclined toward the 

 source of the heat. Repeat the experiment with Peas. 



