Chapter IV: The Leaf

§ 1. Having now some clear idea of the position of the bud, we have next to examine the forms and structure of its shield--the leaf which guards it. You will form the best general idea of the flattened leaf of shield-builders by thinking of it as you would of a mast and sail. More consistently with our classification, we might perhaps say, by thinking always of the arm sustaining the shield; but we should be in danger of carrying fancy too far, and the likeness of mast and sail is closer, for the mast tapers as the leaf-rib does, while the hand holding the uppermost strap of the buckler clenches itself. Whichever figure we use, it will cure us of the bad habit of imagining a leaf composed of a short stalk with a broad expansion at the end of it. Whereas we should always think of the stalk as running right up the leaf to its point, and carrying the expanded, or foliate part, as the mast of a lugger does its sail. To some extent, indeed, it has yards also, ribs branching from the innermost one; only the yards of the leaf will not run up and down, which is one essential function of a sailyard.

§ 2. The analogy will, however, serve one step more. As the sail must be on one side of the mast, so the expansion of a leaf is on one side of its central rib, or of its system of ribs. It is laid over them as if it were stretched over a frame, so that on the upper surface it is comparatively smooth; on the lower, barred. The understanding of the broad relations of these parts is the principal work we have to do in this chapter.

§ 3. First, then, you may roughly assume that the section of any leaf-mast will be a crescent, as at _a_, Fig. 17 (compare Fig. 7 above). The flat side is the uppermost, the round side underneath, and the flat or upper side caries the leaf. You can at once see the convenience of this structure for fitting to a central stem. Suppose the central stem has a little hole in the centre, _b_, Fig. 17, and that you cut it down through the middle (as terrible knights used to cut their enemies in the dark ages, so that half the head fell on one side, and half on the other): Pull the two halves separate, _c_, and they will nearly represent the shape and position of opposite leaf-ribs. In reality the leaf-stalks have to fit themselves to the central stem, _a_, and as we shall see presently, to lap round it: but we must not go too fast.

§ 4. Now, _a_, Fig. 17, being the general type of a leaf-stalk, Fig. 18 is the general type of the way it expands into and carries its leaf;[1] this figure being the enlargement of a typical section right across any leaf, the dotted lines show the under surface foreshortened. You see I have made one side broader than the other. I mean that. It is typically so. Nature cannot endure two sides of a leaf to be alike. By encouraging one side more than the other, either by giving it more air or light, or perhaps in a chief degree by the mere fact of the moisture necessarily accumulating on the lower edge when it rains, and the other always drying first, she contrives it so, that if the essential form or idea of the leaf be _a_, Fig. 19, the actual form will always be _c_, or an approximate to it; one half being pushed in advance of the other, as at _b_, and all reconciled by soft curvature, _c_. The effort of the leaf to keep itself symmetrical rights it, however, often at the point, so that the insertion of the stalk only makes the inequality manifest. But it follows that the sides of a straight section across the leaf are unequal all the way up, as in my drawing, except at one point.

§ 5. I have represented the two wings of the leaf as slightly convex on the upper surface. This is also on the whole a typical character. I use the expression "wings of the leaf," because supposing we exaggerate the main rib a little, the section will generally resemble a bad painter's type of a bird (_a_, Fig. 20). Sometimes the outer edges curl up, _b_, but an entirely concave form, _c_, is rare. When _b_ is strongly developed, closing well in, the leaf gets a good deal the look of a boat with a keel.

§ 6. If now you take this oblique form of sail, and cut it into any number of required pieces down to its mast, as in Fig. 21, A, and then suppose each of the pieces to contract into studding-sails at the side, you will have whatever type of divided leaf you choose to shape it for. In Fig. 21, A, B, I have taken the rose as the simplest type. The leaf is given in separate contour at C; but that of the mountain ash, A, Fig. 22, suggests the original oval form which encloses all the subdivisions much more beautifully. Each of the studding-sails in this ash-leaf looks much at first as if he were himself a mainsail. But you may know him always to be a subordinate, by observing that the inequality of the two sides which is brought about by accidental influences in the mainsail, is an organic law in the studding-sail. The real leaf tries to set itself evenly on its mast; and the inequality is only a graceful concession to circumstances. But the subordinate or studding-sail is always _by law_ larger at one side than the other; and if he is himself again divided into smaller sails, he will have larger sails on the lowest side, or one more sail on the lowest side, than he has on the other. He always wears, therefore, a servant's, or, at least, subordinate's dress. You may know him anywhere as not the master. Even in the ash leaflet, of which I have outlined one separately, B, Fig. 22, this is clearly seen; but it is much more distinct in more finely divided leaves.[2]

§ 7. Observe, then, that leaves are broadly divisible into mainsails and studding-sails; but that the word _leaf_ is properly to be used only of the mainsail; leaflet is the best word for minor divisions; and whether these minor members are only separated by deep cuts, or become complete stalked leaflets, still they are always to be thought of merely as parts of a true leaf.

It follows from the mode of their construction that leaflets must always lie more or less _flat_, or edge to edge, in a continuous plane. This position distinguishes them from true leaves as much as their oblique form, and distinguishes them with the same delicate likeness of system; for as the true leaf takes, accidentally and partially, the oblique outline which is legally required in the subordinate, so the true leaf takes accidentally and partially the flat disposition which is legally required in the subordinate. And this point of position we must now study. Henceforward, throughout this chapter, the reader will please note that I speak only of true _leaves_, not of _leaflets_.

§ 8. LAW I. THE LAW OF DEFLECTION.--The first law, then, respecting position in true leaves, is that they fall gradually back from the uppermost one, or uppermost group. They are never set as at _a_, Fig. 23, but always as at _b_. The reader may see at once that they have more room and comfort by means of the latter arrangement. The law is carried out with more or less distinctness according to the habit of the plant; but is always acknowledged.

In strong-leaved shrubs or trees it is shown with great distinctness and beauty: the phillyrea shoot, for instance, Fig. 24, is almost in as true symmetry as a Greek honeysuckle ornament. In the hawthorn shoot, central in Plate 52, opposite, the law is seen very slightly, yet it rules all the play and fantasy of the varied leaves, gradually depressing their lines as they are set lower. In crowded foliage of large trees the disposition of each separate leaf is not so manifest. For there is a strange coincidence in this between trees and communities of men. When the community is small, people fall more easily into their places, and take, each in his place, a firmer standing than can be obtained by the individuals of a great nation. The members of a vast community are separately weaker, as an aspen or elm leaf is thin, tremulous, and directionless, compared with the spear-like setting and firm substance of a rhododendron or laurel leaf. The laurel and rhododendron are like the Athenian or Florentine republics; the aspen like England--strong-trunked enough when put to proof, and very good for making cartwheels of, but shaking pale with epidemic panic at every breeze. Nevertheless, the aspen has the better of the great nation, in that if you take it bough by bough, you shall find the gentle law of respect and room for each other truly observed by the leaves in such broken way as they can manage it; but in the nation you find every one scrambling for his neighbor's place.

This, then, is our first law, which we may generally call the Law of Deflection; or, if the position of the leaves with respect to the root be regarded, of Radiation. The second is more curious, and we must go back over our ground a little to get at it.

§ 9. LAW II. THE LAW OF SUCCESSION.--From what we saw of the position of buds, it follows that in every tree the leaves at the end of the spray, taking the direction given them by the uppermost cycle or spiral of the buds, will fall naturally into a starry group, expressive of the order of their growth. In an oak we shall have a cluster of five leaves, in a horse-chestnut of four, in a rhododendron of six, and so on. But observe, if we draw the oak-leaves all equal, as at _a_, Fig. 25, or the chestnut's (_b_), or the rhododendron's (_c_), you instantly will feel, or ought to feel, that something is wrong; that those are not foliage forms--not even normally or typically so--but dead forms, like crystals of snow. Considering this, and looking back to last chapter, you will see that the buds which throw out these leaves do not grow side by side, but one above another. In the oak and rhododendron, all five and all six buds are at different heights; in the chestnut, one couple is above the other couple.

§ 10. Now so surely as one bud is above another, it must be stronger or weaker than that other. The shoot may either be increasing in strength as it advances, or declining; in either case, the buds must vary in power, and the leaves in size. At the top of the shoot, the last or uppermost leaves are mostly the smallest; of course always so in spring as they develope.

Let us then apply these conditions to our formal figure above, and suppose each leaf to be weaker in its order of succession. The oak becomes as _a_, Fig. 26, the chestnut shoot as _b_, the rhododendron, _c_. These, I should think, it can hardly be necessary to tell the reader, are true normal forms;--respecting which one or two points must be noticed in detail.

§ 11. The magnitude of the leaves in the oak star diminishes, of course, in alternate order. The largest leaf is the lowest, 1 in Figure 8, p. 14. While the largest leaf forms the bottom, next it, opposite each other, come the third and fourth, in order and magnitude, and the fifth and second form the top. An oak star is, therefore, always an oblique star; but in the chestnut and other quatrefoil trees, though the uppermost couple of leaves must always be smaller than the lowermost couple, there appears no geometrical reason why the opposite leaves of each couple should vary in size. Nevertheless, they always do, so that the quatrefoil becomes oblique as well as the cinqfoil, as you see it is in Fig. 26.

The normal of four-foils is therefore as in Fig. 27, A (maple): with magnitudes, in order numbered; but it often happens that an opposite pair agree to become largest and smallest; thus giving the pretty symmetry, Fig. 27, B (spotted aucuba). Of course the quatrefoil in reality is always less formal, one pair of leaves more or less hiding or preceding the other. Fig. 28 is the outline of a young one in the maple.

§ 12. The third form is more complex, and we must take the pains to follow out what we left unobserved in last chapter respecting the way a triplicate plant gets out of its difficulties.

Draw a circle as in Fig. 29, and two lines, AB, BC, touching it, equal to each other, and each divided accurately in half where they touch the circle, so that AP shall be equal to PB, BQ, and QC. And let the lines AB and BC be so placed that a dotted line AC, joining their extremities, would not be much longer than either of them.

Continue to draw lines of the same length all round the circle. Lay five of them, AB, BC, CD, DE, EF. Then join the points AD, EB, and CF, and you have Fig. 30, which is a hexagon, with the following curious properties. It has one side largest, CD, two sides less, but equal to each other, AE and BF; and three sides less still, and equal to each other, AD, CF, and BE.

Now put leaves into this hexagon, Fig. 31, and you will see how charmingly the rhododendron has got out of its difficulties. The next cycle will put a leaf in at the gap at the top, and begin a new hexagon. Observe, however, this geometrical figure is only to the rhododendron what the _a_ in Fig. 25 is to the oak, the icy or dead form. To get the living normal form we must introduce our law of succession. That is to say, the five lines A B, B C, &c., must continually diminish, as they proceed, and therefore continually approach the centre; roughly, as in Fig. 32.

§ 13. I dread entering into the finer properties of this construction, but the reader cannot now fail to feel their beautiful result either in the cluster in Fig. 26, or here in Fig. 33, which is a richer and more oblique one. The three leaves of the uppermost triad are perfectly seen, closing over the bud; and the general form is clear, though the lower triads are confused to the eye by unequal development, as in these complex arrangements is almost always the case. The more difficulties are to be encountered the more licence is given to the plant in dealing with them, and we shall hardly ever find a rhododendron shoot fulfilling its splendid spiral as an oak does its simple one.

Here, for instance, is the actual order of ascending leaves in four rhododendron shoots which I gather at random.

Of these, A is the only quite well-conducted one; B takes one short step, C, one step backwards, and D, two steps back and one, too short, forward.

§ 14. LAW III. THE LAW OF RESILIENCE.--If you have been gathering any branches from the trees I have named among quatrefoils (the box is the best for exemplification), you have perhaps been embarrassed by finding that the leaves, instead of growing on four sides of the stem, did practically grow oppositely on two. But if you look closely at the places of their insertion, you will find they indeed spring on all four sides; and that in order to take the flattened opposite position, each leaf twists round on its stalk, as in Fig. 35, which represents a box-leaf magnified and foreshortened. The leaves do this in order to avoid growing downwards, where the position of the bough and bud would, if the leaves regularly kept their places, involve downward growth. The leaves always rise up on each side from beneath, and form a flattened group, more or less distinctly in proportion to the horizontality of the bough, and the contiguity of foliage below and above. I shall not trouble myself to illustrate this law, as you have only to gather a few tree-sprays to see its effect. But you must note the resulting characters on _every_ leaf; namely, that not one leaf in a thousand grows without a fixed turn in its stalk; warping and varying the whole of the curve on the two edges, throughout its length, and thus producing the loveliest conditions of its form. We shall presently trace the law of resilience farther on a larger scale: meanwhile, in summing the results of our inquiry thus far, let us remember that every one of these laws is observed with varying accuracy and gentle equity, according not only to the strength and fellowship of foliage on the spray itself, but according to the place and circumstances of its growth.

§ 15. For the leaves, as we shall see immediately, are the feeders of the plant. Their own orderly habits of succession must not interfere with their main business of finding food. Where the sun and air are, the leaf must go, whether it be out of order or not. So, therefore, in any group, the first consideration with the young leaves is much like that of young bees, how to keep out of each other's way, that every one may at once leave its neighbors as much free-air pasture as possible, and obtain a relative freedom for itself. This would be a quite simple matter, and produce other simply balanced forms, if each branch, with open air all round it, had nothing to think of but reconcilement of interests among its own leaves. But every branch has others to meet or to cross, sharing with them, in various advantage, what shade, or sun, or rain is to be had. Hence every single leaf-cluster presents the general aspect of a little family, entirely at unity among themselves, but obliged to get their living by various shifts, concessions, and infringements of the family rules, in order not to invade the privileges of other people in their neighborhood.

§ 16. And in the arrangement of these concessions there is an exquisite sensibility among the leaves. They do not grow each to his own liking, till they run against one another, and then turn back sulkily; but by a watchful instinct, far apart, they anticipate their companions' courses, as ships at sea, and in every new unfolding of their edged tissue, guide themselves by the sense of each other's remote presence, and by a watchful penetration of leafy purpose in the far future. So that every shadow which one casts on the next, and every glint of sun which each reflects to the next, and every touch which in toss of storm each receives from the next, aid or arrest the development of their advancing form, and direct, as will be safest and best, the curve of every fold and the current of every vein.

§ 17. And this peculiar character exists in all the structures thus developed, that they are always visibly the result of a volition on the part of the leaf, meeting an external force or fate, to which it is never passively subjected. Upon it, as on a mineral in the course of formation, the great merciless influences of the universe, and the oppressive powers of minor things immediately near it, act continually. Heat and cold, gravity and the other attractions, windy pressure, or local and unhealthy restraint, must, in certain inevitable degrees, affect the whole of its life. But it is _life_ which they affect;--a life of progress and will,--not a merely passive accumulation of substance. This may be seen by a single glance. The mineral,--suppose an agate in the course of formation--shows in every line nothing but a dead submission to surrounding force. Flowing, or congealing, its substance is here repelled, there attracted, unresistingly to its place, and its languid sinuosities follow the clefts of the rock that contains them, in servile deflexion and compulsory cohesion, impotently calculable, and cold. But the leaf, full of fears and affections, shrinks and seeks, as it obeys. Not thrust, but awed into its retiring; not dragged, but won to its advance; not bent aside, as by a bridle, into new courses of growth: but persuaded and converted through tender continuance of voluntary change.

§ 18. The mineral and it differing thus widely in separate being, they differ no less in modes of companionship. The mineral crystals group themselves neither in succession, nor in sympathy; but great and small recklessly strive for place, and deface or distort each other as they gather into opponent asperities. The confused crowd fills the rock cavity, hanging together in a glittering, yet sordid heap, in which nearly every crystal, owing to their vain contention, is imperfect, or impure. Here and there one, at the cost and in defiance of the rest, rises into unwarped shape or unstained clearness. But the order of the leaves is one of soft and subdued concession. Patiently each awaits its appointed time, accepts its prepared place, yields its required observance. Under every oppression of external accident, the group yet follows a law laid down in its own heart; and all the members of it, whether in sickness or health, in strength or languor, combine to carry out this first and last heart law; receiving, and seeming to desire for themselves and for each other, only life which they may communicate, and loveliness which they may reflect.

FOOTNOTES:

[1] I believe the undermost of the two divisions of the leaf
represents vegetable tissue _returning_ from the extremity. See
Lindley's _Introduction to Botany_ (1848), vol. i. p. 253.

[2] For farther notes on this subject, see my _Elements of Drawing_,
p. 286.