40 THE NATURE AND WORK OF PLANTS 



substances distributed equally in all directions frc m 

 it. To secure this the branches drive their tips 

 horizontally or nearly so, taking a course nearly 

 parallel to the surface of the soil. The positions 

 attained by these secondary roots may be seen if a 

 young bean or tomato plant is carefully dug from 

 the ground, noting the position of the main roots 

 and the branches as they are exposed to view. 



45. Sensitiveness of the roots to moisture. — Both 

 lateral and main roots may encounter other forces, 

 which cause them to bend away from the direc- 

 tions taken in response to gravity as described in 

 the previous paragraphs. The action of -unevenly 

 distributed moisture may be shown as follows : Place 

 some germinating peas in a deep cigar box full of 

 garden soil. They should be planted in the ordi- 

 nary manner near the middle of the box. Give the 

 seedlings barely enough water to keep the soil moist 

 at one end of the box. Pour the necessary amount 

 from a cup on the soil just inside one end and allow 

 it to diffuse toward the plants. The quantity should 

 be so small that the soil in the other end of the box 

 will become quite dry. After a growth of two weeks 

 turn the box upside down, shake out the plant, and 



