Still more widely divided than oak leaves, are such as are called pinnate, in which the separated parts are actually distinct leaflets, some even provided with stalks. Such compound leaves may be seen in almost every garden by looking at a rose-bush. In the cut, we see what appears to be five distinct leaves attached to one twig; but the fact is that they are only leaflets, and, together with the stalk which bears them all, constitute but one complete leaf. Each of these leaflets has a short stalk, connecting it with the main stem, which passes between the pairs, and has an odd leaflet at the end. A rose-bush may have leaves of seven or nine leaflets.
Among our forest trees, hickory, walnut, butternut, locust, and ash have pinnate leaves; and on the honey-locust not only are the leaves pinnate, but on the same tree, may also be found leaves doubly pinnate, and even tripinnate. Compound leaves may be seen also in the pea-vine, which is simply pinnate; but here the place of the absent terminal leaflet is supplied by a tendril.
But if we examine a bean-plant, we do find an odd leaf, together with a pair of leaflets; that is, each leaf is composed of three leaflets. The many varieties of bean-plants are all thus three-leaved. Besides, the woods are full of three-leaved plants, belonging to other kinds of the bean or pulse order of plants. In addition to these and some others, we must not overlook a most extraordinary three-leaved plant, plentiful in almost every forest, and on almost every stone-fence in the country; only too well known by persons who have been poisoned by it, and yet not so well known by most people as it ought to be, for it is often confounded with a plant having digitate leaves.
[Illustration: LEAF OF VIRGINIA CREEPER.]
Here, side by side, the forms of the two leaves can be compared. On the right is the digitate leaf of the beautiful Virginia creeper, entirely harmless; on the left is the pinnate leaf of the poison-vine. The innocent plant is _five_-leaved; the noxious plant is _three_-leaved. But we should also notice particularly that the arrangement of the leaflets is quite different in the two plants. In the poison-vine, we see a pair of leaflets and a terminal odd one; whereas in the Virginia creeper, there is no pairing of leaflets whatever, but the five parts radiate from a centre. All the leaflets come out together from one point at the tip of the leaf-stalk.