CHAPTER VI 



THE CARE OF STREET-TREES 

 HOW A TREE GROWS 



Evolution of a Tree. Success in the care of trees neces 

 sarily depends upon the knowledge of their requirements to 

 maintain life and their mode of growth. Let us, therefore, 

 for a moment trace the evolution of a tree. The tree's begin 

 ning is long before it becomes established in the soil, and 

 shows the differentiating parts of root system, stem, and 

 crown. Its birth really occurs on the parent-tree from which 

 the seed comes. The seed contains the rudiments of all 

 the parts of the mature tree. 



The Seedling. In Plate 25, Fig. 4, is shown a common 

 lima bean dissected. The thick fleshy parts, which form the 

 initial leaves on germination, are called cotyledons. These 

 are attached to the very short initial stem. Below that is 

 the initial root, which on germination turns downward and 

 penetrates into the soil. As the root continues its growth, 

 the stem adds to its length, and, in seeking the light, brings 

 the seed up out of the ground. In the case of the lima bean 

 the cotyledons become the first pair of leaves. Many seeds 

 of trees germinate in the same way. 



In the case of the seeds of other trees, as the white maple, 

 for example, the cotyledons are not lifted out of the soil and 

 transformed into actual leaves. The growth below the co 

 tyledons is nearly all root. The rudimentary bud between 



102 



