Trees Every Child Should Know: Easy Tree Studies for All Seasons of the Year

by Julia Ellen Rogers

The reason is this: the life of the trees is in the green layer which we see on the surface of all green shoots, and which we can discover under the older bark of twigs, which has turned brown. Following the twig back from its tip, all of the leafy part is green. Behind it the smooth twig is no longer green, but a thumb nail easily strips off the layer of brown, and reveals the green under bark. Go a little further back, and gradually the outer bark thickens, and it is more difficult to get at the soft under layer. After a while, we shall need a knife to reach it, for old bark is hard and tough.

When the bark gets so thick that the sun cannot reach the green layer, the colour fades out. The living part of the trunk of the tree is the soft, juicy layer between the bark and wood. Through this portion of the tree the sap rises from the roots, and finally reaches the leaves. This sap needs to be changed before it can be useful to the tree as food.

The leaves are the places where these changes take place. Through little doorways in the under sides of the leaf air passes in. With it goes carbonic acid gas, an important food element. The soft green leaf pulp, which is the green juice of a bruised leaf, has a wonderful work to do. It cannot do this work unless the sun is shining upon it. On a bright day every leaf is making starch, and sending it down through the twigs and branches as food. This starch is contained in the sugary sap that flows back constantly from the leaves to the farthest root tips. It is made in the leaves out of the sap brought up from the roots and the carbonic acid gas which the leaves absorb from the air.

As long as the leaves do their work, the tree is able to grow, and to blossom, and to ripen its seeds. When the leaves have done their work the summer has passed; the tree lets go the leaves, and rests without growing all winter.

It is not easy to explain the work of the leaves, nor even to understand the wonderful work accomplished there all through the summer. When we eat, our food must go into the stomach to be changed by the processes called digestion. It is hours before the digested food is poured into the blood and carried to all parts of the body. The tree takes its food from the air, and from the soil. Neither the dirty water that rises as sap to the leaves, nor the gas which enters the leaf doorways from the air, is useful as food to the growing tree until they have been combined and changed. The leaves are, then, in a sense, the stomachs of the trees, for in them the raw foods must be “digested” before they are ready to be poured into the life blood that flows down through all the live parts of the tree. Now they are fit to feed the growing cells, which are always hungry.

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.