xii PHYSIOLOGY OF GROWTH AND MOVEMENT 159 



EXPT. 152. Germinate a few Peas in damp sawdust. Place one on 

 damp soil. Place another with the radicle and plumule in a horizontal 

 position on a piece of 

 glass which is covered 

 with damp blotting 

 paper. Note 



(i) The radicle of 

 the Pea in the damp 

 soil bends downwards 

 and the plumule up- 

 wards. 



(ii) The plumule of 

 the Pea on the piece 

 of glass grows straight 

 upwards, but the root 

 grows along the piece 

 of glass until it reaches 

 the edge, when it turns 

 so as to make nearly a 

 right angle with the 

 rest of the root, and 

 then grow down- 

 wards. 



(iii) This shows that 

 the root is positively 

 geotropic and the stem 

 negatively geotropic. 



EXPT. 153. Make 

 a hole in the bottom 

 of a glass tumbler for 

 drainage. This can 

 be done by striking a 

 blow at the centre 

 with a sharp pick. 

 The tumbler may 

 crack, but if it holds 

 together anyhow it 

 will do. Fill with 

 soil (p. 13). and put a 

 quick growing plant 

 in it. Expose to light. 

 Note 



(i) No roots will be 



seen near the glass (Fig. 162), or, if they should appear there, they will 

 soon bend away from the light. 



Cover the tumbler with brown paper to prevent the light from affect 

 ing the roots. Examine in a few days. 



(ii) The soil near the glass is packed full of roots. 



(iii) If the plant and soil are turned out, and a sharp knife is used to 



FIG. 162. Photograph of a plant grown in a tumbler to 

 show the distribution of the roots. The white roots 

 are close to the side of the tumbler. During the 

 growth of the plant the tumbler was covered with 

 brown paper. The plant produced both flowers and 

 fruits. 



