104 SHADE-TREES IN TOWNS AND CITIES 



them makes the upward growth of stem and leaves. The 

 materials for the growth are supplied by the cotyledons or 

 seed leaves. The seedling, although diminutive and most 

 simple, possesses all the organs of the fully developed tree ; 

 namely, roots in the soil, the stem rising out of it, and the 

 leaves in the light and open air. It now draws in moisture 

 and food materials from the soil by its roots, conveys them 

 through the stem into the leaves, where these materials 

 together with the other crude food which the leaves imbibe 

 from the air, are assimilated into grov/ing tissue. 



Growth in Height. In the autumn, after the leaves have 

 fallen from the seedling, the bare stem represents the height 

 and thickness of the first season's growth. If the seedling 

 is carefully examined, it is seen that just above the points 

 where the leaves were attacked during the growing season 

 are the buds, from which the growth of stems and leaves 

 will be continued. The shoot from the terminal bud will pro- 

 long the height of the central stem, and the lateral buds will 

 form the branches. Growth in height ceases for the season as 

 soon as the shoot develops from the bud, and this is usually 

 indicated when the terminal leaves are fully grown. The 

 tree adds no other way to the length of limb and trunk. 



There is a general impression that trees add to their 

 height by the gradual lengthening of the trunks and limbs. 

 If this were true, nails driven into the trunk one above 

 the other, would gradually become farther apart, and wire 

 fences nailed to trees would rise in the air. 



Growth in Diameter. While the growth of a tree in 

 height is the result only of the shoots developing from the 

 buds, the growth in diameter of the trunk, main branches, 

 and twigs is a process affecting every part of the entire plant. 



Separating the bark from the wood is a colorless, muci- 



