LEAVES OF ALL SHAPES AND SIZES
The leaf of the tree is its visiting card. We shall learn to know trees by their leaves, as easily as if the name were written across the face of the leaf. Some leaves have a single blade of green, and for this reason the botanist calls them simple leaves. This blade has a stem that unites it with the twig. A compound leaf is one whose stem bears more than one blade. These small blades are called leaflets. There are two types of compound leaves, one feather-like, having a main stem with leaflets arranged in two rows on opposite sides of this stem. Such a leaf is feather-like. The other type has a leaf stem with all the leaflets attached at one end. The horse chestnut is the best example of this type. The leaves spread from the end of the stalk somewhat as the fingers rise from the palm of your hand.
The biggest leaves with single blades to be found in our forests grow on trees of the magnolia family. The silver-lined leaves of the large-leaved cucumber tree are over a foot in length, sometimes two and one-half feet, down South. These great leaves are about one-fourth as wide as long, and at the base each one broadens and extends backward into two rounded ear-like lobes. This gives the tree the name, ear-leaved magnolia. The whole leaf flaps in the wind, like the ear of an elephant, and, of course, the wind lashes it into strings and soon robs it of its beauty.
The Northern cucumber tree is another magnolia whose leaves are tropical-looking. This is the hardiest of the magnolia family, and its heart-shaped leaves are six to ten inches long. They are not large for a magnolia of the South, but they look larger because they grow among the small-leaved trees of the Northern states.
The tulip tree has a large leaf of peculiar form. It is broad like a maple leaf at the base, but at the tip it is cut off square as if with a pair of shears, forming a right angle with its straight sides. Sometimes the leaf is notched, as if a V-shaped piece were cut out of the square tip. These leaves are long-stemmed, their blades polished, and they flutter on the twigs with the lightness of a poplar leaf. Once we have in mind the form of the leaf of the tulip tree, we shall never forget it, for it is different from all other leaves.
The catalpa tree, which lifts its great blossom clusters above the foliage in late June, is another of the few large-leaved trees of the North. The single blade is heart-shaped, six to eight inches long, and more than half as broad. These leaves usually have plain margins, but sometimes they are wavy and notched near the base so as to produce faint side lobes. The blades hang on long, stout stems.
Among the feather-leaved trees, the walnuts and butternuts, the sumachs, and the ailanthus, furnish examples. A black walnut leaf is often two feet long, with a dozen or more leaflets on the longest ones. These leaflets are always set opposite in pairs, with an odd one on the tip of the leaf stem. Butternut leaves have the same form, but the leaves are longer. They range from fifteen to thirty inches, and have from ten to twenty leaflets, but always an odd number. The peculiar gummy feeling of these hairy leaves, and their pungent butternut odour when bruised, make it easy to know the tree wherever we meet it, through the long summer.
The hickories are cousins of the walnuts, but their leaves, though of the feather form, have larger and fewer leaflets than any walnut tree. A shagbark hickory leaf has one or two pairs of little leaflets on the stem, and above them three of larger size. The pignut has the same habit of clustering its three largest leaves at the tip of the leaf stem, and tapering off at the base with one or two pairs of decreasing size.
The largest of all the compound leaves have branched stems to which leaflets are attached. The main leaf stem’s side branches may yet branch again, forming a twice-branched framework that is set with leaflets, not large, but so numerous as to make the whole leaf surprisingly large. The greatest of these twice-compound leaves is borne by that astonishing, spiny-stemmed Hercules’ club. A single leaf is often four feet long, and nearly a yard wide. There are no leaflets on the main stem; they are on the side branches.
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 obviate any confusion of the two. The leaf has a bud at its base, and it breaks off easily at this joint.
The sugar maple trees are tapped in February; they bloom in May after the leaves come out; they ripen their keys in October, when the foliage turns to red and yellow.
Leaves of black willow have frills at their bases. Twigs of pussy-willows, cut and brought indoors, can be forced into bloom in midwinter
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 botanists 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 opposite 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. Between 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 margins 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 comparatively 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 disturb 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 wherever 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 recognition. 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 people or trees.