WHAT A TREE IS, AND HOW IT GROWS 287 



usually darker in color and is called the heartwood; it no longer has 

 anything to do with the life of the tree, but simply gives to it 

 strength and staunchness. The larger branches, if cut across, 

 shows the same structure as the trunk,— ^the bark on the outside, 

 the cambium layer next, and within this the rings of annual 

 growth. Even the smaller branches and twigs show similar 

 structure, but they are young and have not attained many annual 

 rings. 



The leaves are borne on the outermost parts of the tree. A leaf 

 cannot grow, and if it could would be of no use, unless it can be 

 reached by the sunlight. Therefore the trunk lifts the branches 

 aloft, and the branches hold the twigs far out, and the twigs divide 

 into the fine spray, so as to spread the leaves and hold them out 

 into the sunshine. 



In structure, the leaf is made up of the stem, or petiole and the 

 hlade, or widened portion of the leaf, which is sustained usually 

 with a framework of many ribs or veins. The petioles and the veins 

 are sap channels like the branches and twigs. 



The Way a Tree Grows 



The place of growth on a tree may be found at the tips of the 

 twigs and the tips of the rootlets ; each year through this growth 

 the tree pushes up higher, down deeper and out farther at the sides. 

 But in addition to all of these growing tips, there is a layer of 

 growth over the entire tree — over every root, over the trunk, over 

 the limbs and over each least twig, just as if a thick coat of paint 

 had been put over the complete tree. It is a coat of growth in- 

 stead, and these coats of growth make the concentric rings which 

 we see when the trunks or branches are cut across. Such growth 

 as this cannot be made without food; but the tree can take only 

 liquid food from the soil ; the root-hairs take up the water in which 

 the "fertiHzer" is dissolved, and it is carried up through the larger 

 roots, up through the sap-wood of the trunk, out through the 

 branches to the leaves, where in the leaf -factories the water and 

 free oxygen is given off to the air, and the nourishing elements 

 retained and mixed with certain chemical elements of the air, 

 thus becoming tree food. The. leaf is a factory; the green pulp 

 in the leaf cells is part of the machinery ; the machinery is set in 

 motion by sunshine power; the raw materials are taken from the 



