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wards crossing the older bundles, pass outside them. The section above given represents these bundles cut across, and the manner in which they accumulate towards the circumference of the stem.
It has been said that all stems are not erect. It may be added that all stems are not produced above the surface of the soil, for some few have a subterranean habit, and others scarcely creep above it. If we watch the growth of strawberry plants in our garden, we shall observe what are termed " runners" (botanically flagellce), which are stems running along the surface of the soil, rooting at the joints, and still running on. Or, if we attempt to root out the garden-mint, we shall find similar runners under the surface (called in this case soboles), sending down roots at the joints, and sending up leaf-bearing branches to the surface. Yet again, the purple flag or common iris affords an example of another kind of immersed or semi-immersed stem running upon the surface, or near it, and bearing thread-like roots from the under surface and tufts of leaves at the extremities of all the numerous branches. This kind of subterranean stem is a rhizome, though most commonly called a root by all except strict botanists. The most anomalous of all subterranean stems is that of the potato, and we doubt if some botanists have their consciences quite at rest on the subject. The tubers are regarded as swellings of an underground stem, and this opinion is strengthened chiefly by the fact that these tubers are capable of producing buds, a power which true roots do not possess. A negative character of roots may thus be noted: they do not possess scales, which are modified leaves; or buds, which are rudimentary leaves; or nodes, joints, or points, whence buds are developed.
Having disposed of roots and stems, as far as the limits of this work will permit, we next proceed to the leaves, and these are so variable in form, passing into each other by such gentle gradations, that we shall only be able to indicate the most prominent types. If we take the leaf of an oak, a lily, and a hart's-tongue fern, we shall see in each of these, especially if we hold them up to the light, certain thicker portions like threads traversing the leaf: these are usually called the veins. In the oak-leaf the veins are much branched and spread over the leaf in a kind of network: such kinds we will call netveined leaves; in the lily-leaf the veins run parallel, side by side, from the bottom towards the top of the leaf, with finer veins crossing from one to the other of the longitudinal veins: a leaf with such a veining, or venation, we will call a parallel-veined leaf. In the hart's-tongue fern the veins, although all going direct towards the margin of the leaf, divide in a regular manner into tw-o parts like a fork: such leaves as possess this type are called forkveined leaves. Of these three kinds of veining or venation, the net-veined leaves belong to exogens, the stems of which we have already described, the parallel-veined leaves to endogens, and the fork-veined leaves to ferns. As the ferns are not flowering plants, we shall leave them for more special notice hereafter. The veining of leaves is by no means an uninteresting subject; there is a beautiful variety in their mode of distribution through the leaf, and some of the prettiest natural objects ever exhibited under a glass shade are the skeleton leaves of plants. In the growing leaf all the spaces between the veins are filled up with cells, which contain, amongst other things, the green chlorophyl, or colouring matter, of the leaf, and these are covered by the delicate and transparent cuticle or skin. The hairs of many shapes, the glands, stings, scales, or other minute appendages of leaves, are all beautiful and worthy of examination under the microscope, but we must reluctantly pass them by. From the structure of the leaf we must pass to its form.
If it is the reader's good fortune to peruse these pages during any of the summer months, he will not require to go far or search very diligently for a plant of the common scarlet geranium. Let him look at it, and he will observe that the leaves arc attached to the stem by a long stalk. There is the leafy expanded portion, which is the blade, or lamina, and the footstalk, which botanically is called the petiole. On each side of the petiole at its base, where it joins the stem, is a little, scaly, triangular, leaf-like blade, without a footstalk. These are not leaves, but appendages to the leaves, called stipules, to which we shall return presently. Let us go in search of all the different-shaped leaves which we can find, and ascertain how far we can give names to the principal forms, so that by a name which all botanists can understand we may distinguish one kind of leaf from another, as a carpenter knows his Jackplane from his hand-plane or his moulding-plane.
We shall observe that all our leaves may be classed in two groups. The leaves of the geranium, dandelion, daisy, holly, maple, hawthorn, hazel, plum, apple, &c, we place on our left hand: these are all simple leaves. The leaves of the horse-chestnut, the ash, the mountain-ash, the acacia, trefoil or clover, wood-sorrel, &c, we will place on our right hand: these are compound leaves. Now let us examine the great differences in the two groups. In the group of simple leaves on our left hand the blade or lamina of all the leaves, whatever their form, or however deeply they may be cut at the edges, are not cut down to the mid-rib, or great central vein of the leaf; hence we cail them simple. In the other group on our right hand, each leaf is divided into two or more parts or leaflets, which look like smaller leaves clustered together upon the footstalk or petiole. In the clover there are three of these leaflets; in the horse-chestnut, f1ve or seven; in the ash, a great many. But in all these mstances there is but one leaf, which is composed of several leaflets: these are compound leaves.
The simplest form of simple leaves are those of fir trees, which are long and narrow, like needles, sometimes called "pine-needles," three or five bound together at the base in a little bundle. The name by which such leaves are known is acicular, from a Latin word meaning " needle-shaped." In the yewtree the leaves are less needle-shaped, being broader below and coming to a sharp point at the apex; they are awl-shaped, and the term by which they arc distinguished is subulate, which has that meaning. For our next example we leave the large trees and descend to grasses, or little plants which possess leaves resembling the leaves of grasses, such as the grass-leaved stitchwort, in which the leaves arc long and narrow, of the same width throughout, except at the two extremities, and these are said to be linear, or resembling a line. (Plate A, fig. 1.)
Leaves are called lanceolate when their form resembles the head of a lance, broadest in the middle and attenuated towards each end; of such a leaf the lanceolate plantain affords an example. (Fig. 2.)
Egg-shaped leaves, which are broadest near the base and narrowed upwards, are said to be ovate (Fig. 3); but if the footstalk is reversed, and the lamina, though still egg-shaped in outline, has its broadest part at the apex, it is called obovate (Fig. 4). There are constantly to be found forms of leaves which are intermediate, and glide insensibly from one to another of those which we have enumerated; indeed, the forms of leaves are almost infinite, and all we cap
hope to do is to establish a few types. There are. for instance, oval and elliptical leaves, and leaves which are ncrrly round. In all such cases it is better to refer them to the mathematical fonts which they most closely resemble, and call them by their names. Circular or orbicular leaves have generally the petiole or footstalk attached in the centre of the under side of the disc, and are called peltate, not from the form of the leaf, but from the mode in which the petiole is attached (Fig. 17).
The few remaining forms of simple leaves with which we ran associate names are: those which arc kidney-shaped, and hence arc called reniform (Fig. 6); heart-shaped leaves, which are termed cordate when the petiole is attached at its broadest extremity (Fig. 5), but obeordate when the smallest end is attached to the petiole, as in the case of each leaflet of the wood-sorrel (Fig. 7). Other leaves are named after the objects to which they are supposed to bear the closest resemblance, as spoon-shaped, or spathnlate, in the daisy (Fig. 10); arrow-shaped, ox sagittate, in the wake-Robin, and especially m the water-arrowhead (Fig. S); fiddle-shaped, orpanduriform, as exemplified in the fiddle-leaved dock.
All the simple leaves above enumerated have their edges but little, or not deeply, cut. There are, however, very many forms of simple leaves which are irregular, and so deeply cut as at first to resemble compound leaves. Fiveangled leave;, such as those of the ivy, are quinquangular (Fig. 13), and those with a larger number of angles arc described by the number of angles which they possess. Halberd-shaped leaves with two small lobes at the base arc called hastate (Fig. 11). Leaves with lobes at the base are common, and vary much in their form (Figs. 21). Three-lobed leaves in which the leaves are nearly equal are called trilobate (Fig. 9); and with five lobes, palmate, because they resemble the fingers and palm of an open hand (Fig. 14). But the larger number of these deeply-cut leaves are too complex and variable to be named definitely, except by the number and form of their lobes or their incisions.
The group of leaves on our right hand, and which we characterized as compound, must now receive a little attention. The first example which we observe is a temate leaf composed of three leaflets: these leaflets may be obOTate as in clover (Fig. 12), or obeordate as in the wood-sorrel (Fig. 7), or indeed of any other form. If each leaflet is again divided into three parts it is bilernate, or if thrice divided in a like manner, triternate. When there arc five leaflets spreading like five fingers, the leaf is called digitate. By far the largest number of compound leaves are more or less of the pinnate type, such as the leaves of the ash (Fig. 15): the name pinnate is given to them because the arrangement of the leaflets on each side of the petiole or footstalk resembles a feather (Latin "penna"); when the leaflets are in pairs placed opposite to each other on the footstalk (as in the ash), the leaf is said to be oppositely pinnate, but w hen an alternate arrangement is followed it is alternately pinnate.
The arrangement of leaflets may be still more complex by being further subdivided. In this case each leaflet of a pinnate leaf is itself pinnate, and when so divided the leaf is termed bi-pinnate (Fig. 18). If the subdivisions are carried still further, and each leaflet is again divided, the leaf is called tri-pinnate (Fig. 19). When the divisions are carried beyond this, the leaf is called supra-decompot1nd.
Any attempt at describing more intricate forms of compound leaves would tire and bewilder the reader, without adding in the least to his botanical knowledge. The theory and philosophy of leaf-genesis and leaf-structure may be quite as well postponed till the student has acquired more practical botanical knowledge, and then he will find it in more advanced books, and be able to read it with greater pleasure and profit.
It has been stated above, in more especial reference to the geranium leaf,