_FIRST READING._
By far the greater number of plants have leaves of an oval shape, and
we have only to go through our forests and gardens to see them on every
hand. Exceedingly varied are they indeed, from very narrow to very
broad oval, some with toothed, some with smooth edges, and some even
deeply notched; and yet to such an extent does this tendency toward a
rounded form prevail, that there seems scarcely a plant in whose leaves
a trace of the oval may not be found.
The apple tree gives us a good specimen of an oval leaf; and an immense
number of plants have leaves resembling it in shape. In many plants,
the leaves are almost the very counterpart of those of the apple-tree;
in some, they are narrower, and in others, still narrower, till we come
to very slender blades like those of the grasses; and then, beyond
still, to the needle-like leaves of the pines. On the other hand,
plants are to be found with leaves broader than the apple-leaf; and so
on, rounder and rounder, until we come to such plants as the nasturtium
and the water-lily, whose leaves are almost as round as circles.
[Illustration: LEAF OF APPLE.]
There are certainly to be met with most remarkable departures from
the oval shape, and we need but refer to such leaves as those of the
buckwheat, to find that roundness seems to be entirely absent.
[Illustration: BUCKWHEAT LEAF.]
This style of leaf, of which there are many variations, is apparently
built on the model of the heart-shaped leaf, of which the morning-glory
affords a familiar example. It will be noted, however, that instead of
the curvilinear flow of outline, in which a tendency to oval roundness
is plainly visible, the hastate leaf of the buckwheat is angular
throughout.
[Illustration: MORNING-GLORY LEAF.]
Another marked characteristic of most leaves is, that they terminate
in a point, either sharp to extreme slenderness, or blunt to broad
roundness; for even in a circular leaf there is one point which is its
extremity, and to which the margin from either side approaches by a
convexity. To this pointedness of leaves the exceptions are exceedingly
rare. A plant found in some parts of our own country--the magnificent
tulip-tree--presents, perhaps, the most extraordinary of all.
[Illustration: LEAF OF TULIP-TREE.]
Now this leaf comes out of a bud-case which is actually oval. The young
leaf is folded double inside of its bud-case; and, besides, its small
stalk is bent over so as to bring the little leaf to hold its end
downwards. We can see this curious arrangement very well, just after
the bud has opened, and the young leaf has come out. However, it soon
straightens up, holds its little head aloft, and looks like a pretty
little flag. After this it spreads apart into the full leaf, and stands
up like a banner. If the bud be held up to the light, the young leaf
can be seen nicely folded up inside, with its head snugly bent down.
There is nothing prettier, or more curious, to be seen in the woods,
than the young buds of the tulip-trees, when they are about to open, or
after they have unfurled their little flags; and all summer long, even
from earliest spring, the tulip-trees are continually unfolding their
buds.
[Illustration: OPENING LEAF-BUD OF TULIP-TREE.]
[Illustration: EARLY LEAF-BUD OF TULIP-TREE.]
There are leaves broader above than below, and some, instead of ending
in a point, have a notch or indentation of some sort. Oak-trees give
us many fine and varied samples of notched and lobed leaves. And yet
the leaf of the chestnut-oak is not at all notched, being simply ovate,
pointed, and toothed. The leaves of the bur and the pin oaks, on the
contrary, are lobed and notched, and are therefore characteristic
oak-leaves, while those of the chestnut-oak are not so, because almost
all oaks have leaves more or less scalloped or deeply indented.
Great as is the variety in the shapes of oak leaves, any one of them
would almost surely be at once recognized as belonging to an oak-tree
by its peculiar scallopings. But suppose a person had never seen or
heard of a chestnut-oak leaf, would he be likely to recognize such a
leaf simply by its outline? There is still another oak with simple
leaves; and they are not even toothed, but entirely smooth all around
the edge. Looking at that tree, which is called the willow-oak,
scarcely anyone would suppose it to be an oak unless he could see its
flowers or its fruit, the acorns.
[Illustration: CHESTNUT-OAK LEAF.]
[Illustration: BUR-OAK LEAF.]
[Illustration: PIN-OAK LEAF.]
This fact brings us to consider a very important point in the study of
a plant. It is not the leaf which tells us what kind of plant it is:
it is the flower and the fruit. Whatever be the shape of the leaf, if
the plant bears acorns it is an oak. If a tree has cherries and cherry
blossoms, it is a cherry.
It is true that, in many families of plants, leaves, by their shape
alone, announce at once the kind of plant to which they belong; at the
same time there is a large number of plants that cannot be known by
their leaves, but only by their flowers and fruits. It is by flowers
and fruits that plants are classified; and the more nearly alike these
are in two plants, the more closely are those plants related. The
flower and the fruit proclaim the nature of the plant. “A tree is
known by its fruit.”