266 FIRST YEAR COURSE IN GENERAL SCIENCE 



plant needs them. It is their function to take water from 

 the ground into the roots for the plant's work of food making. 

 If the roots are allowed to become dry, the root hairs, being 

 small, are soon rendered unfit to take water from the soil, 

 and the plant droops and usually dies. 



Most shade trees have a long primary root. This helps to 

 hold the tree in an upright position, even if strong winds push 



FIG. 140. PRIMARY AND SECONDARY ROOTS 



The figure at the left is a seedling morning-glory; at the right, a seed- 

 ling oak. 1. Compare the roots in the two seedlings as to kind and number. 

 2. Which of these plants lives more than one year? 3. What relation is 

 there between the answers to 1 and 2? 



against its spreading crown. The elm tree is an exception in 

 this respect, and as a result, it is much oftener overthrown in 

 a gale than is the maple, the oak, or the chestnut. 



Roots serve a useful purpose in holding particles of soil 

 together. The cutting of a forest from a hillside is likely 

 to result in the rapid washing away of the soil and in floods. 

 Large tracts of valuable land have been ruined in this way, 



