Then there is the beauty of form, size, position, and arrangement. Of the one hundred and fifty thousand or more known species of trees, the leaves of each have a characteristic shape. The leaves of no two species are precisely alike in form. More than this is also true. No two leaves upon the same tree are in this respect alike. While there is a close resemblance among the leaves of a given tree, so that one familiar with trees would not be in doubt of their belonging to the same tree, though he should see them only when detached, yet there is more or less variation, some subtle difference in the notching or curving of the leaf-edge perhaps, so that each leaf has a form of its own. These differences of shape in the leaves are a constant source of beauty.
What a variety of size also have the leaves, from those of the birches and willows to those of the sycamores, the catalpas and the paulownias. On the same tree also the leaves vary in size, those nearest the ground and nearest the trunk being usually larger than those more remote. How different as to beauty would the trees be if their leaves were all of the same size; how much less pleasing to the sight.
Then what a wide difference is there in the position of the leaves on the trees and their relative adjustment to each other? Sometimes they grow singly, sometimes in pairs, sometimes in whirls or clusters. Some droop, others spread horizontally, while others still are more or less erect. The leaves of some trees cling close to the branches, others are connected with the branches by stems of various length and so are capable of greater or less movement. The leaves of poplars and aspens have a peculiarly flattened stem, by reason of which the slightest breath of wind puts them in motion.
These are some of the most obvious characteristics of the leaves, and by which they are made the source of so much of the beauty of the world in which we live. It will be a source of much pleasure to anyone who will begin now, in the season of swelling buds and opening leaves, to watch the leaves as they unfold and notice their various forms and colors and compare them one with another. There is no better way of gaining valuable knowledge of trees than this, for the trees are known by their leaves.