. Bulletin. Forests and forestry -- United States. 18 A PRIMER OF FORESTRY. THE GROWTH OF A TREE. The addition of new material in the way described in tlie preceding pages is the foundation of growth. Ex- cept in the buds, leaves, fruit, and the twigs less than a year old, this material is deposited in a thin coat over the whole tree between the wood and the bark. The new twigs grow in length by a kind of stretching, but only during the first year. Thus it is only by means of these youngest twigs that a tree increases in height and in spread of branches. After the first year their length is fi
. Bulletin. Forests and forestry -- United States. 18 A PRIMER OF FORESTRY. THE GROWTH OF A TREE. The addition of new material in the way described in tlie preceding pages is the foundation of growth. Ex- cept in the buds, leaves, fruit, and the twigs less than a year old, this material is deposited in a thin coat over the whole tree between the wood and the bark. The new twigs grow in length by a kind of stretching, but only during the first year. Thus it is only by means of these youngest twigs that a tree increases in height and in spread of branches. After the first year their length is fixed, younger twigs stretch out from the buds, and the older ones grow henceforth only in thickness. (See fig. 9.) The fresh coat of new material mentioned above covers them year by year. There are two layers in this coat, separated by a third one of tender forming tissues called the cambium, in which the actual making of the new substance goes on. The inner side of the cambium layer forms new wood, the outer side new bark. Be- sides the true cambium, which forms both wood and bark, there is another cambium which makes the corky outer bark, and nothing else. This cork cambium may encircle the whole tree, like the true cambium, as in the Eed Cedar, or it may form little separate films in the bark, but in either case it dies from time to time, and is re-formed nearer the wood. (See figs. 10-13 and Pis. Y and Yl.). Fig. 18.—Cross section of a fallen Black Oak. Milford, Pa. The slabs shown in figs. 19 and 22 were sawed lengthwise from this tree, beginning where the black lines arc seen on the cross Please note that these images are extracted from scanned page images that may have been digitally enhanced for readability - coloration and appearance of these illustrations may not perfectly resemble the original United States. Division of Forestry. Washington : G. P. O.
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