Poplars 



79 



1800 feet. It would be 

 difficult to tell how far 

 all the roots of a big 

 cottonwood tree would 

 reach if placed end to 

 end. Figure 46 shows 

 the roots of a cotton- 

 wood tree less than one 

 year old. This tree 

 grew in sandy soil. In 

 arid parts of the South- 

 west the mesquite has 

 been known to send its 

 roots to a depth of 60 feet 

 in search of water. In 

 ordinary soils the roots of 

 trees must remain nearer 

 the surface, where they 

 can get air as well as water. If the soil is not drained 

 and water completely fills the spaces between the soil par- 

 ticles, the roots of most trees will die for lack of oxygen, 

 Functions of roots. The roots of most trees do not 

 serve, like those of the silver poplar, to reproduce the 

 tree, but they have other very important functions. They 

 anchor the tree in its place, and they gather from the soil 

 and supply to the tree the water and mineral materials 

 that it needs. Roots excrete substances which help to 

 dissolve limestone and other mineral materials in the soil. 

 In this way they secure more mineral matter for the tree. 

 If the ground on one side of a tree is well watered and 

 on the other side dry, the roots grow toward the water. 



Wm. H. Moon Co. 

 FIG. 47. Young Lombardy poplars. 



