The How and Why Library/Trees/Section II
II. Summer: "In the Tree Tops"
Summer is the leafy season. But the time to begin to study leaves is in the early spring. On nearly all trees the leaf comes as soon as the blossom falls. The first leaves are very small, and they are not green but pink, red, yellow, gray or white. They have been wrapped up in bed clothes all winter. It takes several days of warm sunshine for them to turn green and to grow up. The leaf of the red maple tree, true to its name, is red. On the sugar maple it is a yellow-green, on the silver maple a shining green-white. When they grow to full size these maple leaves all have much the same form. In different members of a plant family there is a resemblance, as in a human family. You can learn to call each one by its "given," as well as by its family name, by looking out for the differences.
When you see a tree with a leaf that would lie in a three to five inch circle, but that is cut down part way into five lobes, you would be safe in thinking that tree a maple. The lobes of the red maple are sharply notched and parted. In the sugar or rock maple, the leaf lobes and partings are more rounded. It is a darker, smoother leaf, too, and grows more thickly on an evenly balanced, round-headed tree. The red maple has straggling branches, and the leaves are thin so light sifts through them, giving the tree an airier look than any other maple.
The leaf of the silver maple is smaller, a sage green above, a cottony white below. It does not sift light, but seems to reflect it like a mirror, as the white underside turns up in every breeze. There are other maples, but these are the best known. The leaves of all-trees and of low plants, too, are alike in being brighter and smoother on the upper side. The underside is paler and rougher, and the veins stand out more plainly. This is because the upper side is a sort of rain and dust coat and sun-umbrella, for the breathing pores underneath. It is the lower side of a leaf that is the most interesting to study under a microscope.
All of the willows have long, slender leaves. Each leaf is a narrow, thin, delicately veined blade that grows by itself, and alternately, along a slender stem, making a sort of feathered branch. The pussy willow leaves are a bright green. The black willow leaf is broader, saw-notched, and it tapers toward both stem and tiplike a canoe. It is bright green above and silvery underneath. The leaf of the white willow is a gray green lined with silver, and it droops from yellow stems. The crack willow, whose twigs snap so easily, has a green leaf lined with a waxy coating. The weeping willow has long, sad, gray "weeping" leaves.
The leaves of the alders are darker and broader than those of the willows, and the undersides are hairy. The poplars all have broad, heart-shaped leaves of emerald green satin, many of them silvery underneath. They are always in motion, so they shimmer in the sun in quite a dazzling way. The tall, slim, Lombardy poplars seem robed in dark green, flowing satin.
After the maples and willows, very likely you know oak trees best. The oak leaf is very irregularly shaped, like the oak tree. It is a long, oval or pear-shaped leaf, usually narrowest at the stem end, and is deeply notched and lobed. It is a strong, tough leaf as glossy above as if varnished, and rough underneath, with woody veins standing out like a net-work of cords. The scarlet, the red and the black oaks have about five, sharply notched lobes with broad partings, and each lobe is often notched again. The white oak has seven or nine narrow, rounded lobes, with very deep rounded partings cut down almost to the midrib. The bur oak has five or seven broad round lobes and narrow partings. In the swamp oak the leaf is deeply and irregularly scalloped. The chestnut oak leaf is oval with shallow scallops, and the smaller live oak leaf has wavy edges.
The oaks ring all the changes from many sharp, almost spine-tipped lobes to wavy edges. And they are very puzzling, for they are not all alike even on one tree, nor in different seasons. The best way to be sure of an oak tree is to study the acorns. Oaks can be as tricky as they like about leaves, but they stick each to its own pattern, in making acorns. So, in the fall, when the acorns drop, you can study the oaks again.
After these tantalizing oak leaves, it is always such a comfort to turn to the American elm. That tree can always be depended upon to make a certain leaf. Along its high branches, that curve over in great plumes, the elm sets an oval or egg-shaped leaf about three inches long, narrowest at the tip and just a little pointed. The elm leaf grows singly, on opposite sides of twigs, each a little advanced beyond the last, and making a neat, feathered spray. The leaf is strong, saw-notched, short stemmed and firmly set, smooth above, rough underneath. From the midrib the veins slant upward, makingevenly spaced broad V's, about a quarter of an inch apart from stem to tip. You might think these veins were laid off with a ruler. Isn't that a satisfactory kind of leaf? You could almost draw it without seeing it, couldn't you?
The leaf of the beech tree is something like that of the elm, but thinner, softer, often fringed as well as saw-notched along the edges, and it is irregularly net-veined, not strongly feather-veined like the elm. The tree, too, is so different that you could not mistake them. The beech is a broad, low-branching tree, leafed all over as heavily as the maples.
The orchard fruit trees, wild and tame, all have rose-like leaves. Apple tree leaves are a soft green above, lighter and furry underneath. They grow in tufts around the fruit and along the stems. The cherry leaf is smaller, darker, brighter, and more blade-like than the apple leaf. The foliage of the pear tree is larger and thicker; of a peach a long, slender, bright green blade like a very large, rather curly willow leaf. On the thorny canes of the briar berries are broad, spiny compound leaves that tell very plainly their kinship to the rose. In open spaces of the woods, the wild grape spreads its tent of broad, deep lobed and toothed leaves. They are very glossy and dark green above, hairy and pale underneath. And among them are curling tendrils and bunched clusters of little green fruit.
In every forest you will see several trees that have what are called pinnate leaves. Such leaves have three or more pairs of leaflets set on opposite sides of a central stem, with a single leaf at the tip. So, in a pinnate leaf, there are always an odd number of leaflets, five or seven in the rose, about nine in the leaf of the white ash tree. This is a beautiful shade tree, of hard wood, ranking with the rock maple and the elm. The leaf is quite nine or ten inches long, and the leaflets long oval blades very bright and clean. The mountain ash, or rowan tree, has as long a leaf but with a greater number of narrow leaflets, giving the tree a feathery, almost fern-like look. The honey locust, too, has this feathered leaf of many drooping leaflets.
Many of the nut trees have these beautiful drooping pinnate leaves. The black walnut is hung all over its high crown with long plume-like leaves with from seventeen to twenty-five slender leaflets. The leaf of the butternut, or white walnut tree, has from seven to nine. The horse chestnut, buckeye and hickory trees have palmate leaves. That is, the broad oval leaflets are all set around the tip of a common leaf stem, spreading in a circle, like the ribs of a palmleaf fan. The largest, middle leaflet of the horse chestnut leaf is often ten or twelve inches long, and four or five wide.
It is a wonderful thing to see a horse chestnut burst into leaf in April. This tree has thick stems and big, scaly leaf buds like little pine cones. The outer scales are brown, and water-and-frost-proofed with gum. Inside is layer after layer of green scales each lapping over the next. Inside of all these is a tender, pink, leafbud baby, snuggled in a blanket of fleecy white wool. Now watch and see one of these undone, for all the leaves of all trees come out in much the same way. You can study Mother Nature's way of wrapping up and taking out her leaf-bud babies in the horse chestnut best, because its buds are so large. One by one the cover scales are turned back as the baby stretches too big for its cradle. Then, on a warm day, five crumpled pink toes wriggle through the fleecy blanket. Suddenly, the bed clothes are kicked off, the pink toes spread into five leaflets and the whole tree tumbles, green in a day, into the sunlight. But it takes the leaves days and days to grow up.
The paper or canoe birches have the prettiest fairy-like leaf in the world! It is a broad oval, three or four inches long, with finely toothed edges. The pointed tip is often curved over a little, in a graceful, tricksy way. This is a way many leaves have of being a little out of balance. If you fold any leaf along the midrib you will find the two sides are never exactly alike. This is just as it is in the faces of little boys and girls. One cheek has the dimple, one eyebrow is lifted or eyelid drooped more than the other. It is these little things that keep any two faces, even of twins, from being exactly like any other, and gives every face what we call character, or individuality.
The birch leaf has this little tilt at the tip, now on one side, now on the other, with a little hollow cut out below it. A thin, fluttery, transparent leaf, scantily scattered over the lace-like twigs of the slender white-barked trees, it glances like a butterfly and sifts sunlight. A group of birches always have a dryad, wood-fairy look. Step softly when you come upon them in some shy retreat in a forest. They look as if a snapping twig might startle them into taking flight.