HOW TREES GROW.
This is what an elm tree accomplishes in a year's work. In March there are only buds on the twigs, with a leaf scar helot' each one. In April the largest buds cast off their scales. and blossoms open. In Nay the fruit ripens and falls, while the slenderer bolds open into leafy shouts. ln summer these shoots lengthen. They produce leaves set close together. and as they unfold, the stems between these leaves elongate. In October the tree is bare, and the long twigs, each set with many buds. are borne at the points where in March there stood only solitary Jais. The tree has added to the height and the breadth of its crown by the exact length of these new shoots. The prevalent idea that the trunk of a tree lengthens, thus carrying the bases of its branches upward, is erroneous.
Underground, the roots have made a season's growth. They have no buds, nor any regular intervals of branching. as the top has. They lengthen in the direction of least resistance. They branch where branching is possible, or necessary. They interlock and grow fast where they cross. Root hairs form a fine velvety nap for a little space just back of each root tip. These never grow into roots, but wither away as the root tip grows un and deserts them, developing new hairs as it goes.
But the tree's growth is not confined to this pushing' out at its extremities. The trunk grows in thickness, though it is unable to 'elongate. A new layer of woody tissue and one of hark is formed each 'by the cambium which lies under the 4irk. Each branch, out to the plane where the season's shoot started. follows the same rule of increase. The roots, ilk? the brandies, grow' in thickness by annual rings. In some trees, as the black ash, the yearly growths part readily, like the lavers of an onion. In others. as the basswood, one can scarcely count the rings, so uniform is the texture of the woody tissue. This is what makes basswood the wood carver's delight. In oak the annual layers distinctly marked. Each one is composed
of dark porous spring gradually merging into the pale summer wood," which has much smaller pores, and is like horn in hardness and toughness. There are several of these shaded hands to every inch. The number of rings to the inch is a plain record of any tree's rate of growth.
A tree's growing season begins with the thawing of the ground and the warming of the air in early spring. ]'lie roots absorb water supplied to the soil by the thawing of the frozen ground, the melting of snows, and the falling of spring rains. The sap currents rise, gathering on their way to the leaves rich food materials stored during the previous summer. Because they have these resources, the swelling elm buds cast their protecting scales. throw out their blossoms, mature their fruit, and unfold their leafy shoots — all with a rapidity that is incredible. Without stored food it would be impossible for the leaves to open, l'Gr by the leaves tho sap is made ready for use. Leaves take charge of the nourishment of the tree as soon as they open. As soon as it is supplied with foliage, the tree finds its growing season is fully inaugurated.
The taking in of food, its digestion,'' and transportation to the cells that need it belongs to another chapter. The growth of a tree. in height and girth, — depends upon a fundamental property of all living matter. Active well fed cambium cells have a disposition to divide. The mother cell gradually becomes constricted, and divides into two. They may separate, but they usually remain together. By absorbing food, each (laughter cell grows to the size of the mother Consider what this means to the tree. A cambium cell is a thing so tiny as to he seen only under a microscope, but there are millions of them. The second division makes four out of two. Then come eight, sixteen, thirty-two, sixty-four! As long as food holds out, and other conditions remain favorable, there seems to be no limit to the possibilities of cell division.