Tree Study 7^9 



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



WOOD-GRAIN 

 This is the way thai the sap-river ran 

 From the root to the top of the tree 



Silent and dark, 



Under the bark, 

 Working a wonderful plan 

 That the leaves never know. 

 And the branches that grow 

 On the brink of the tide never see. 



— John B. Tabb. 



THE WAY A TREE GROWS 



jHE places 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 grow- 

 ing 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 instead, 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 "fertilizer" 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 air 

 and from the sap containing food from the soil; the finished product is 

 largely starch. Thus, it is well, when we begin the study of the tree, to 

 notice that the leaves are so arranged as to gain all the sunlight possible, for 

 without sunlight the starch factories would be obUged to "shut down." It 

 has been estimated that on a mature maple of vigorous growth there is 

 exposed to the sun nearly a half acre of leaf surface. Our tree appears to us 

 in a new phase when we think of it as a starch factory covering half an acre. 

 Starch is plant food in a convenient form for storage, and it is stored in 

 sap-wood of the limbs, the branches and trunk, to be used for the growth of 

 the next year's leaves. But starch cannot be assimilated by plants in this 

 form, it must be changed to sugar before it may be used to build up the 

 plant tissues. So the leaves are obliged to perform the office of stomach and 

 digest the food they have made for the tree's use. In the mysterious 

 laboratory of the leaf-cells, the starch is changed to sugar; and nitrogen, 

 sulphur, phosphorus and other substances are taken from the sap and starch 

 added to them, and thus are made the proteids which form another part of 



