§ 2. It is evident that the more leaves the stalk has to sustain, the more strength it requires. It might appear, therefore, not unadvisable, that every leaf should, as it grew, pay a small tax to the stalk for its sustenance; so that there might be no fear of any number of leaves being too oppressive to their bearer. Which, accordingly, is just what the leaves do. Each, from the moment of his complete majority, pays a stated tax to the stalk; that is to say, collects for it a certain quantity of wood, or materials for wood, and sends this wood, or what ultimately will become wood, down the stalk to add to its thickness.

§ 3. “Down the stalk?” yes, and down a great way farther. For, as the leaves, if they did not thus contribute to their own support, would soon be too heavy for the spray, so if the spray, with its family of leaves, contributed nothing to the thickness of the branch, the leaf-families would soon break down their sustaining branches. And, similarly, if the branches gave nothing to the stem, the stem would soon fall under its boughs. Therefore, by a power of which I believe no sufficient account exists,[2] as each leaf adds to the thickness of the shoot, so each shoot to the branch, so each branch to the stem, and that with so perfect an order and regularity of duty, that from every leaf in all the countless crowd at the tree’s summit, one slender fibre, or at least fibre’s thickness of wood, descends through shoot, through spray, through branch, and through stem; and having thus added, in its due proportion, to form the strength of the tree, labors yet farther and more painfully to provide for its security; and thrusting forward into the root, loses nothing of its mighty energy, until, mining through the darkness, it has taken hold in cleft of rock or depth of earth, as extended as the sweep of its green crest in the free air.

§ 4. Such, at least, is the mechanical aspect of the tree. The work of its construction, considered as a branch tower, partly propped by buttresses, partly lashed by cables, is thus shared in by every leaf. But considering it as a living body to be nourished, it is probably an inaccurate analogy to speak of the leaves being taxed for the enlargement of the trunk. Strictly speaking, the trunk enlarges by sustaining them. For each leaf, however far removed from the ground, stands in need of nourishment derived from the ground, as well as of that which it finds in the air; and it simply sends its root down along the stem of the tree, until it reaches the ground and obtains the necessary mineral elements. The trunk has been therefore called by some botanists a “bundle of roots,” but I think inaccurately. It is rather a messenger to the roots.[3] A root, properly so called, is a fibre, spongy or absorbent at the extremity, which secretes certain elements from the earth. The stem is by this definition no more a cluster of roots than a cluster of leaves, but a channel of intercourse between the roots and the leaves. It can gather no nourishment. It only carries nourishment, being, in fact, a group of canals for the conveyance of marketable commodities, with an electric telegraph attached to each, transmitting messages from leaf to root, and root to leaf, up and down the tree. But whatever view we take of the operative causes, the external and visible fact is simply that every leaf does send down from its stalk a slender thread of woody matter along the sides of the shoot it grows upon; and that the increase of thickness in stem, proportioned to the advance of the leaves, corresponds with an increase of thickness in roots, proportioned to the advance of their outer fibres. How far interchange of elements takes place between root and leaf, it is not our work here to examine; the general and broad idea is this, that the whole tree is fed partly by the earth, partly by the air;—strengthened and sustained by the one, agitated and educated by the other;—all of it which is best, in substance, life, and beauty, being drawn more from the dew of heaven than the fatness of the earth. The results of this nourishment of the bough by the leaf in external aspect, are the object of our immediate inquiry.

§ 5. Hitherto we have considered the shoot as an ascending body, throwing off buds at intervals. This it is indeed; but the part of it which ascends is not seen externally. Look back to Plate 51. You will observe that each shoot is furrowed, and that the ridges between the furrows rise in slightly spiral lines, terminating in the armlets under the buds which bore last year’s leaves. These ridges, which rib the shoot so distinctly, are not on the ascending part of it. They are the contributions of each successive leaf thrown out as it ascended. Every leaf sent down a slender cord, covering and clinging to the shoot beneath, and increasing its thickness. Each, according to his size and strength, wove his little strand of cable, as a spider his thread; and cast it down the side of the springing tower by a marvellous magic—irresistible! The fall of a granite pyramid from an Alp may perhaps be stayed; the descending force of that silver thread shall not be stayed. It will split the rocks themselves at its roots, if need be, rather than fail in its work.

So many leaves, so many silver cords. Count—for by just the thickness of one cord, beneath each leaf, let fall in fivefold order round and round, the shoot increases in thickness to its root:—a spire built downwards from the heaven.

Fig. 36.

And now we see why the leaves dislike being above each other. Each seeks a vacant place, where he may freely let fall the cord. The turning aside of the cable to avoid the buds beneath, is one of the main causes of spiral curvature, as the shoot increases. It required all the care I could give to the drawing, and all Mr. Armytage’s skill in engraving Plate 51, to express, though drawing them nearly of their full size, the principal courses of curvature in even this least graceful of trees.

§ 6. According to the structure thus ascertained, the body of the shoot may at any point be considered as formed by a central rod, represented by the shaded inner circle, a, Fig. 36, surrounded by as many rods of descending external wood as there are leaves above the point where the section is made. The first five leaves above send down the first dark rods; and the next above send down those between, which, being from younger leaves, are less liable to interstices; then the third group sending down the side, it will be seen at a glance how a spiral action is produced. It would lead us into too subtile detail, if I traced the forces of this spiral superimposition. I must be content to let the reader peruse this part of the subject for himself, if it amuses him, and lead to larger questions.

§ 7. Broadly and practically, we may consider the whole cluster of woody material in Fig. 36 as one circle of fibrous substance formed round a small central rod. The real appearance in most trees is approximately as in b, Fig. 36, the radiating structure becoming more distinct in proportion to the largeness and compactness of the wood.[4]

Fig. 37.