34O ] Trees and How to Know Them 



early fall, new though somewhat smaller wood cells are still pro- 

 duced. During the winter, growth stops entirely. When it resumes 

 once more with "spring wood" next to "fall wood," the contrast 

 between the two kinds of wood produces a line around the trunk. 

 This line we know as the "annual ring." 



How Trees Record Their Autobiographies: In a sense the annual 

 rings are the biography of the tree wide spaces between rings 

 indicate good growing years, whereas narrow spaces tell of seasons 

 of drought or other climatic conditions unfavorable to growth. 

 A series of rings with little space between them at the center of 

 the trunk, changing to wider-spaced rings toward the bark, might 

 also be a clue to improved growing conditions. The thinning out 

 of surrounding trees, for example, would provide more sunlight 

 and the roots would have less competition for the water and 

 minerals of the soil. 



Annual growth rings are common to most of the trees that 

 grow in North America. But in some regions, such as the rainy 

 tropics, there is no distinct growing season. There tree growth is 

 constant, and the wood has a more uniform structure instead of 

 annual rings. When these trees are sawed into boards they do not 

 show the intricate grain that our trees do; what we call the "grain" 

 is simply the annual growth rings sawed lengthwise. 



WATCHING A TREE DEVELOP 



In attaining its height, a tree does not merely stretch up- 

 ward. If you observe one from the time it is a sapling until it is a 

 mature tree, you will see that the height of the lowest limb always 

 stays at exactly the same distance from the ground. It gains height 

 as a result of "leaders" at the top of the tree. 



Buds New Life for the Tree: If you open a bud from the tip end 

 of a branch in wintertime, you will find tiny but perfectly formed 

 stems, leaves, and perhaps clusters of flowers. Many of our familiar 

 trees produce all these in the same bud; others, like the American 

 elm, have twigs and leaves in one type of bud, flowers in another. 

 The buds, folded neatly and tightly, are protected by scales that 

 overlap like shingles on a roof. 



