286 NATURE-STUDY REVIEW [16:7— Oct. 1920 



twigs. The spray is the term given to the outer twigs, the finest 

 divisions of the trunk, which bear the leaves and fruit. The 

 branches are divisions of the bole or trunk which is the body, or 

 stem, of the tree. The bole, at the base, divides into roots, and 

 the roots into rootlets, which are covered with root-hairs. It 

 is important to understand what each of the parts of a tree's 

 anatomy does to help carry on the life of the tree. 



The roots which extend out in every direction beneath the 

 surface of the ground, have two quite different offices to perform: 

 First, they absorb the water which contains the tree food dissolved 

 from the soil ; secondly, they hold the tree in place against the on- 

 slaught of the winds. If we could see a tree standing on its head 

 with its roots spread in the air in the same manner as they are in 

 the ground, we could then better understand that there is as 

 much of the. tree hidden below ground as there is in sight above 

 ground, although of quite different shape, being flatter and in a 

 more dense mass. The roots seem to know in which direction to 

 grow to reach water; thus, the larger number of the roots of a tree 

 are often found to extend out toward a stream flowing perhaps 

 some distance from the tree; when they find plenty of food and 

 water the rootlets interlace forming a solid mat. 



To understand how firm a base the roots form to hold up the 

 tall trunk, we need to see an uprooted tree. The great roots seem 

 to be molded to take firm grasp upon the soil. 



The trunk or bole or stem of the tree has also two chief offices : 

 It holds the branches aloft, rising to a sufficient height in the forest 

 so that its head shall push through the leaf canopy and expose 

 the leaves to the sunlight. It is also a channel by which the water 

 containing the food surges from root to leaf and back again through 

 each growing part. The branches are divisions of the trunk, 

 and have the same work to do. 



In cross- section, the tree trunk shows on the outside the layer of 

 protective bark; next to this comes the cambium layer which is 

 the vital part of the trunk; it builds on its outside a layer of bark, 

 and on its inside a layer of wood around the trunk. Just within 

 the cambium layer is a lighter colored portion of the trunk, which 

 is called the sap-wood because it is filled with sap which moves up 

 and down its cells in a mysterious manner; the sap-wood consists 

 of the more recent annual rings of growth. Within the sap-wood 

 are concentric rings to the very center or pith; this portion is 



