CHAPTER IV 



THE STRUCTURE AND REQUIREMENTS OF TREES 



To be able fully to appreciate trees, their mode of life, 

 their enemies and their care, one must know something of 

 their structure and life requirements. 



Structure of trees: Among the lower forms of plants 

 there is very little distinction between the various parts — 

 no differentiation into root, stem, or crown. Often the 

 lower forms of animal and vegetable life are so similar 

 that one cannot discriminate between them. But as we 

 ascend in the scale, the various plant forms become more 

 and more complex until we reach the tree, which is the 

 largest and highest form of all plants. The tree is a living 

 organism composed of cells like any other living organism. 

 It has many parts, every one of which has a definite pur- 

 pose. The three principal parts are: the stem, the crown, 

 and the root. 



The stem: If we examine the cross-section of a tree, 

 Fig. 86, we will notice that it is made up of numerous 

 rings arranged in sections of different color and structure. 

 The central part is known as the pith. Around the pith 

 comes a dark, close-grained series of rings known as the 

 heartwood, and outside the heart-wood comes a lighter 

 layer, the sap-wood. The cavibium layer surrounds the 

 sap-wood and the hark covers all. The cambium layer 

 is the most important tissue of the tree and, together with 

 part of the sap-wood, transports the water and food of 



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