344 ] Trees and How to Know Them 



the end of the branch shows up as a knot. In cases where the 

 branch was quite dead when it dropped from the tree, the knot 

 is a dead one and falls out readily, leaving a knothole a boon to 

 many a child who wishes to peep through a board fence. 



The Underground Life of Trees 



Trees vary in many respects, but all kinds are alike in being 

 made up of two main parts. Every tree has a trunk and a crown 

 or head which is made up of branches and spray (the term used 

 for its great mass of twigs) . We can easily see this part of the tree, 

 but there is another big section which is concealed. 



Below the Surface: The root system of a tree is often so extensive 

 that its size would equal that of the crown if this upper part were 

 somewhat compressed. The roots of some species grow almost 

 straight down; other species have roots extending outward close 

 to the surface of the ground. Certain oak trees have been found 

 with roots two or three times as widespread as their branches! 



Sometimes roots that have pushed partly above the surface help 

 a child to picture the extent of a root system or he may come 

 upon an uprooted stump to which roots are still attached. City 

 youngsters occasionally see work being done on pavements or 

 watch the installation of pipes under sidewalks which uncovers 

 or cuts into the roots of shade trees. They may well be impressed 

 by the amount of abuse the trees will take, yet there are limits to 

 the damage that a tree can stand. 



Repairing Injured Roots: Often the injured roots require treat- 

 ment. Sometimes it is enough to trim away the ragged edges; in 

 other cases the broken sections should be removed completely. If 

 any considerable amount of root material is taken away when a 

 tree is transplanted, the crown should also be trimmed. This re- 

 duces the needs of the foliage for food and water at a time when 

 the root system can no longer do its full part in providing them. 



