50 SCHOOL AGRICULTURE 



acteristic form. The tree is the "whale" of the vegetable world 

 in size, and the "man" of that world in point of highest devel- 

 opment. 



Identifying the Trees. Before we can go far into the study 

 of trees, we must be able to call them by their names. We 

 must know them at sight as we know our friends. It may 

 not be necessary for us to be able to tell just how we know 

 the maple from the ash when we are children, the form, fea- 

 tures and general appearances will guide, but later we shall 

 need to use a "key", based on structural features of leaves or 

 other parts of the tree. 



Life Processes of the Tree. The two great life processes 

 of the tree, as well as of all plants, are to get nourishment 

 and to reproduce its kind. The tree gets its food through its 

 roots and its leaves from the soil and the air. The solid food 

 from the soil must go into solution and be carried upwards 

 from the roots through the sap-wood to the leaves. The gas 

 food must be taken in through the leaves. All this food, the 

 minerals from the soil and the carbon from the air, is pre- 

 pared for the different parts of the tree, in the leaves by the 

 aid of the sunlight. The prepared food is then carried down- 

 ward through the inner, soft bark, to where it is needed to 

 make root, trunk, branch, leaf, flower, and fruit. Girdling a 

 tree, therefore, checks this downward flow of food and not the 

 upward flow of crude sap. 



The trees, except those of the palm tribe, grow in girth by 

 adding ring upon ring of wood cells to their trunks and 

 branches, and in height, not by lifting its whole trunk and 

 crown, but by adding on to the tips of its twigs. Trees re- 

 produce by seeds, sprouts and sometimes by cuttings. 



Structure. A tree like every other living thing is com- 

 posed of tissues made up of minute cells, varying in shape, 

 size and thickness of cell wall. The bulk of the bole of the 

 tree is not living, but dead tissue, composed of empty cells. 

 It is for this reason that a tree may have its heart rotten or 

 gone, and still live and grow. The living part of the tree 

 trunk is on the outside of the wood, between bark and wood. 

 The growing tissue of this live part is called the cambium. 

 Growing cells are also grouped at the tips of the roots and 

 at the tips of the shoots. The thick outer bark of the tree is 

 dead tissue, which sooner or later loosens and sloughs off. 

 In the center of a young tree and of an old tree whose heart 

 has not rotted, is the pith, soft, thin-walled cells in which food 

 Js stored. The pith extends in radiating rays out to the bark. 



