THE TREE. 6 



up of two parts, the outer or corky la^r which is dead 

 bark and the inner or live bark. These vary much in ap- 

 pearance and thickness on different kinds of trees. For 

 instance, on the White Birch the corky layer is pure white, 

 very thin and tough, while on our White Pine it is very 

 dark brown and often an inch or more in thickness and 

 quite brittle. 



The Sapwood is the portion of thewood next to the bark. 

 It varies much in thickness in different species and in trees 

 of the same species; the most rapidly grown trees contain 

 the largest amount. It is the most active portion of the 

 wood in the growing tree, and contains considerable plant- 

 food and more water than the heartwood. 



The Heartwood is the wood in the centre of the trunk and 

 is generally distinguished from the sapwood by its more 

 compact structure and darker color, though in some cases 

 it may be lighter colored than the sapwood. It is also 

 harder and more valuable for fuel, shrinks less in drying, 

 and is more durable in contact with the soil than the sapn 

 wood. There is very little movement of the sap in the 

 heartwood. 



The Roots furnish water and nourishment that the 

 plant receives from the soil, but only the young roots have 

 the power of taking up the soil water; the older roots are 

 most useful in holding the tree in place. It is common to 

 classify roots into surface roots and tap-roots, depending 

 on their shape and the depth they go in the ground. Some 

 trees have nearly all surface roots, as the Birch and Spruce, 

 others have nearly all tap-roots, which often go to a great 

 depth on dry land, as those of the Bur Oak, White Oak, 

 Black Walnut, and Butternut. Most of our trees have a 

 combination of the two kinds, as the Maple, Hackberry, 

 and Ash. Seedling trees of most kinds have a decided tap- 

 root when young, but in many species it ceases to grow 

 downward when a few years old. This is true of the Red 



