How shall we tell a leaf stem from a twig? Leaf stems do not look like the twigs of the tree. A little practice in looking closely and comparing these leaf stems and twigs will ob viate any confusion of the two. The leaf has a bud at its base, and it breaks off easily at this joint.
Among the fine, feathery leaves that are so beautiful and light that they give great beauty to the tree tops are those of the honey locust. These leaves are of the feather type, the slender stems, with double rows of tiny leaflets. Very often we find among the single feather forms, leaves of greater size, which have branched stems. This branching multiplies the number of leaflets, and gives us, on the same trees, what the bota mists call once compound, and twice compound leaves. The simple feather and the branched feather forms add greatly to the beauty and luxuriance of the foliage of the honey locust.
The common black locust of the roadside has single leaf stems with oblong leaflets set in oppo site rows upon it. Ash trees have the same feather type of leaves, the leaflets usually pointed and oval, and always an odd one at the tip. They are all larger than leaves of the locusts.
In the maple family there is a broad, simple blade, about as wide as it is long. It is a family trait to have three main veins running out from the end of the leaf stem, into the blade. Each of these veins has side branches, and they are connected with a network of smaller veins. Be tween the tips of these three main veins the leaf is usually notched, so as to divide it into thirds. In the red maple these notches are shallow V's cut out, leaving triangular points. In the silver maple the leaves are cut by deeper clefts, which reach more than half-way to the leaf stalk. The three lobes are cut with jagged points into an uneven margin. The sugar maple has its three lobes separated by wide, deep clefts, and its mar gins are irregularly wavy. The box elder, which is a maple, is cleft so deeply that the blade is split into three distinct leaflets, each with its own short stem. This makes a compound leaf of it. It is the only maple with a leaf of more than one blade.
The tree which shows the greatest difference in the form of its leaves is the sassafras, whose oval leaves grow on the same stem with mittens and double mittens—a mitten pattern with a thumb on each side. The hawthorns have small oval leaves with variously cleft borders. There are over a hundred kinds of hawthorns in our woods, and each kind has a leaf different from all the rest; yet a single tree will often show leaves that differ so much from the others in form that we might easily suspect, if some one brought them to us, that each grew on a different tree from all the rest.
Many oak trees have the same habit of leaf variation, so that even a forester has to examine many leaves with care, and with them the buds and the acorns, to make sure that he has called the oak by its right name.
The behaviour of the leaves of a tree depends largely on the length and flexibility of their stems. If they are long, and slender, and supple, the tree top is in a continual flutter when the wind blows. If they are thick and stiff, they do not catch the breeze as readily, and their blades lie com paratively still when other trees near by may be twinkling and trembling. Leaves with deeply cut borders, like some oaks and maples, flutter much more than leaves like the basswood, whose borders are unbroken. Oak leaves that are deeply cut will rarely lie down flat. The curving bays in its borders cause the leaf to curl, so that no matter what face is presented, the wind gets under and strikes some surface, and sets the leaf to dancing.
The flat leaf stems of the trembling aspen, one of the poplar family, are very flexible, and they are flattened at right angles to the blades of the leaves. When a breeze comes by, it may strike the edge of the leaf, but if so, it catches the flat leaf stem broadside. If it comes from any other direction the leaf trembles, because one of the blades is sure to receive the force of the wind. So the tree top is in one constant tremor, even when the breeze is scarcely sufficient to dis turb broad-leaved trees which are near neighbours of the aspens.
Whatever the form and size and shape of its leaf, the tree depends upon its foliage mass for all the life it enjoys, and for all the growth it makes. The soil and the air feed the tree. The leaves and the sun do the work of digesting the food. In the porous wood and bark are the channels through which sap mounts upward to the leaves, and another set of channels which carry the prepared food back, leaving it wher ever needed, along the way from tip of twig to tip of root. Whatever is not needed is stored away, to be dissolved as needed and carried to the points where the need is. In spring it is the growing buds that chiefly need this stored food. Its presence explains the miracle of the bursting of blossoms and leaves when spring comes.
One by one the trees of your own yard may be learned by name this summer. The leaves are your sure guide. Trees stay where they are. Once we recognise their leaves and call them by name, we may depend upon finding them still standing the next day we pass them, and their leaves are still held out as the sign of recogni tion. Every time we pass yonder red maple let us glance at its three-pointed leaf, and fix its shape indelibly in the mind. When we have done this a dozen times, I am sure that we shall be able to pick out all the red maples in town; and if we journey far from home we may find and recognise the same kind of trees by the same sign. More and more as we grow older, we find out that half the pleasure of travelling is the occasional meeting with old friends, be they peo ple or trees.