_SECOND READING._
Although the flower and its fruit tell us what the plant is, and leaves
do not with any certainty, there is yet a strong similarity, as well
in texture as in shape, in the leaves of most of the plants comprised
within any one family. Especially in texture is this marked similarity
observable; and, perhaps, in most cases the peculiar structure of the
leaf, aside from its shape, is indicative of the order to which the
plant belongs. The leaves of the grasses are very much alike; so are
the leaves of the sedges;--and though it is true, also, that in some
instances a sedge-leaf might be mistaken for a grass-leaf, it must be
remembered that the sedge family and the grass family have some points
of similarity.
Again, if we should come upon a plant belonging to the common potato
or nightshade family, we should be almost sure to recognize the
family resemblance at the very first glance, provided we were already
familiar with a number of plants included in that order. Yet the
leaves of the nightshade family vary considerably in shape, and it is
therefore decisively the texture and peculiar appearance of the leaves,
that announce the kinship of the plant. And thus we are led back to
the consideration of the willow-oak and chestnut-oak leaves, which,
entirely unlike the typical oak-leaf in shape, are yet very much like
all other oak leaves in texture and other essential structure.
[Illustration: LEAF OF THE ROSE.]
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 POISON-VINE.]
[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.
Plants there are with digitate leaves, having three, five, seven, nine,
or more leaflets. Clover has digitate leaves of three leaflets, while
the leaves of the buck-eye and horse-chestnut have five, seven, and
nine leaflets. The pretty little wood-sorrel plant of small yellow
flowers, has three most beautiful, inverted, heart-shaped leaflets,
radiating from the tip of the little leaf-stalk.
[Illustration: LEAFLET OF WOOD-SORREL.]
In leaves like those of the maple we see the main veins radiating from
a point at the top of the stalk. Such leaves are therefore much like
the digitate kind, only they are not completely divided into separate
leaflets.
[Illustration: MAPLE LEAF.]
Sassafras leaves offer forms something different. On the same tree
may be seen oval, two-lobed, and three-lobed leaves. Thus on one and
the same plant, we see leaves strikingly different in form; yet the
texture, the color, and the veining are exactly after the same pattern
in them all, so that a sassafras leaf, whether oval or cleft, can at
once be easily known.
Recalling to mind the leaf of the apple, buckwheat, morning-glory,
oak, rose, Virginia creeper, maple, and sassafras, we have pretty good
models after which nearly all leaves are built, approximating to one or
other of these, with certain variations peculiar to the species.
Another important matter regarding the leaves of plants, is their
relative position on the stems. There are two principal and very
marked arrangements of leaves. Leaves are either opposite one another
on the stem, or they are alternate or not opposite. There are whole
orders of plants with none but opposite leaves, as the mint family. In
other orders, the leaves of every plant are alternate. And again, in
some orders, and even on the same plants, are found both opposite and
alternate leaves, as in the composite or sunflower family; and a single
wild sunflower plant itself has opposite leaves below, and alternate
leaves above.
Of our forest trees, there are very few species with opposite leaves.
If you see that the branches and leaves of a tree do not stand one
opposite another on the stem, you can at once be sure that it is not an
ash, a maple, or a buck-eye, because all these trees do have opposite
leaves. On the other hand, there are many trees having alternate
branches and leaves, such as the oak, chestnut, elm, hickory, walnut,
butternut, tulip-tree, alder, beech, birch, poplar, willow, mulberry,
linden, locust, and others.