THE TREE 19 



nual rings can be seen. The age of tropical trees cannot be told 

 by the annual rings. The size of the tree however will give 

 some indication of the age. 



The width of the annual rings varies in different species. 

 The wider the annual rings the faster has been the growth of 

 the tree. In the same tree the width of the annual rings will 

 usually vary from year to year. A favorable, moist year will 

 produce a \vide annual ring and a dry, unfavorable year a 

 narrow ring. In general trees grow slowly in diameter during 

 the first few years of their life. The rate then increases until 

 middle life when the trees usually produce their widest annual 

 rings. The rate of growth then falls off and in old trees the 

 width of the annual rings may be so small as not to be seen 

 with the naked eye. 



Height Growth in Trees. The growth of trees in height 

 and the growth of branches in length is produced by the 

 development in the spring of the terminal buds formed the 

 previous season. It is a kind of stretching process or the 

 filling out with water or sap of cells already formed in the 

 buds. New cells are also formed by cell division and the buds 

 quickly lengthen into twigs or shoots. These new shoots do 

 not grow in length after the first season. The next year they 

 will grow in thickness only. From the terminal bud formed 

 on the end of the twig a new shoot will be produced to in- 

 crease the length of the tree or branch. The growth of the 

 roots in length and thickness is much similar to the growth of 

 branches. It will thus be seen to be impossible for a fork in 

 the trunk of a young tree to rise as the tree grows older. 

 A fork once formed in a tree always remains at the same 

 height above the ground. The trunk of a tree does not stretch. 

 If this were not so, \vire fencing nailed to a young tree would 

 gradually be carried upward. 



