Leaves—Their Shape and Position

In the summer when the trees are in full leaf, and you have learnt to know them, you should bring in leafy twigs from each tree and note how the leaves grow on the stem, and what shapes they have.

We have already noticed that some trees, such as the horse-chestnut and the maple, have their leaves opposite to each other on the stem, two growing on each joint, while others, such as the elm and the beech for example, have their leaves alternate, one only growing from each joint. But there are many kinds of alternate leaves, and you will enjoy finding them out.

In the elm and the beech every other leaf comes exactly above the one below. Leaf 1 comes on one side of the stem, leaf 2 on the other side, leaf 3 exactly above leaf 1. But if you take a twig of the trembling poplar, or Aspen, it will be leaf 4 which comes above leaf 1. They have crept more slowly round the stem. Then take a twig of oak. You will find that you will have to count six leaves before you find one exactly over the first one. All these differences have their use, and when you are in the lanes, if you look at the trees, you will see how these arrangements bring the leaves into positions where they can best get light and air.

The next thing to look at is the shape of the leaves themselves. Botanists have a great many names to describe the shapes, the edges, the veins, and the divisions of leaves. I can only tell you of a few, so that you may keep your eyes open and notice others.

Leaves which are whole, so that you cannot pull off one piece without tearing it away from the rest, are called simple. The leaves of the elm, beech, sweet-chestnut, lime, oak, willow, sycamore, and many others are simple.

Leaves which are cut into separate leaflets, so that you can pull one off without touching the others, are called compound. The leaves of the horse-chestnut, ash, rose, rowan-tree, and elder are compound. You will remember that you know the divisions are leaflets and not leaves, because there is no growing tip at the end, and there are no buds in the angles. The leaflets grow out from the top of the leaf stalk (horse-chestnut), or from the narrow, green line, up the middle (rose), which is not a stalk, but the midrib of the leaf.

Now take all the simple leaves you have, and see what shapes they are. The best way to find out this is to lay a leaf on your slate and draw a line round it. This is very easy with a beech leaf, or the leaf of a sweet-chestnut. But when you take an oak leaf, you will want to know whether you are to run in and out of the divisions.

Compound Leaves

For the shape of a leaf you are not to do this. You are to begin at the leaf stalk and run round the outside points of the leaf all the way till you come back to the leaf stalk again. If you go round a maple leaf like this you will have a shape something like a kidney. A sycamore leaf will be more heart-shaped, longer, and ending in a blunt tip. An oak leaf will be oblong, longer than it is broad. The leaf of an elm or a beech you will find is shaped like an egg, and so is called oval, while the leaf of the sweet-chestnut is narrow and long. Lastly, if you take a lime leaf it will be heart-shaped, but uneven, one side of the leaf larger than the other. It is called oblique.

Now let us see how much the different leaves are cut. Some, like those of the lilac and ivy, are smooth at the edge. Others are wavy, and the holly has prickles at the end of its waves to protect it. But, if you look at holly leaves near the top of a tree where the cattle cannot reach, you will often find they do not take the trouble to grow prickles.

Shapes and Edges of Leaves

Other leaves have teeth round the edge. The leaf of the sweet-chestnut is toothed like a saw. So is a birch leaf, but if you look closely you will find it has two sets of teeth. The large teeth have their edges cut into small teeth. This leaf has a double-sawed edge. Some leaves again are very deeply cut into divisions or lobes. An oak leaf is cut, sometimes only in a wavy line, and sometimes into quite large divisions. A sycamore leaf has five large pointed divisions or lobes.

Get these two leaves and compare them. You will see that the veins which make the skeleton of the different shapes are not the same. In the sycamore leaf the large veins, or ribs, start from the top of the stalk, and spread out like five fingers, while the little veins start out from them. A leaf like this is called a palm-veined or palmate-veined leaf because the veins are like fingers on a hand. In the oak leaf, on the contrary, one long rib runs up the middle. The smaller ones start from it, like the featherlets of a bird's feather. So an oak leaf is said to be feather-veined or pinnate-veined, from pinna, a feather.

Now take the compound leaves of the horse-chestnut, ash, and rose. In the horse-chestnut the leaflets grow just like the veins of the sycamore. Seven fingers start from the top of the leaf stalk and spread out like fingers, so it is called a palmate leaf. But the ash and the rose have a rib up the middle and the separate leaflets are arranged feather-wise. So these leaves are called pinnate.

There are a great many leaves with shapes between these, and if you collect them and arrange them in an old copy book, you will soon get an idea of the meaning of their names.

Describe the leaves of the oak, horse-chestnut, and elm and their position on the stem. Arrange any simple leaves and compound leaves you can find in a copy book and describe them.