From these ground-hugging trees of the mountain-tops to the great redwoods of our western slopes the mind passes the entire range of tree life. No trees are so great as our redwoods, though in Australia the eucalyptus reaches higher with a comparatively slender trunk. Where the forests are thickest, and the growth of the trees consequently tallest, the eucalyptus towers sometimes four or five hundred feet towards the sky.
The shrinking of mountain trees where the rock affords some warmth and shelter is shown on a larger scale in the forms of trees that stand at the edge of a forest. Where a stream divides the forest we find the trees upon the bank reaching out their branches and spreading luxuriant foliage over the water, because the open air in that direction helps the growth of leaves and twigs. Shade trees by the road-side reach out towards the open space of the road and grow one-sided because the conditions of light and air are better over the road than against the buildings or other trees that are behind them.
The prevailing winds of any country bend the trees largely in one direction. In the vicinity of Chicago, where the return trade winds blow day after day from the southwest, we find the willows of the prairie all bending their heads gracefully to the northeast.
The relations between trees and the fertility of the country around them is a matter of deep interest to man. Portions of France have been productive and afterwards barren because of the abundance of the trees at first and their having afterwards been cut down to supply the wants of man, who desired their material and the ground on which they stood. The rivers of Michigan are not navigable now in some instances where once they were deep with water. The destruction of the forests to supply the lumber and furniture markets of the world has caused less rain to fall, and the snows of winter which formerly lay late in spring beneath the forests now melt at the return of the sun in the early months and are swept with the rush of high water away to the great lakes. Many of the barren wastes in Palestine and other countries, which in olden times blossomed as the rose, have lost their glory with the destruction of their trees.