While in the horse-chestnut, a larger tree, and, as we shall see hereafter, therefore less regular in conduct, the section, normally hexagonal, is much trees may, I think, thus be resolved into three principal forms: three-leaved, Fig. 9; four-leaved, Figs. 13 to 16; and fiveleaved, Fig. 8. Or, in well-known terms, trefoil, quatrefoil, cinqfoil. And these are essential classes, more complicated forms being usually, it seems to me, resolvable into these, but these not into each other. The simplest arrangement (Fig. 11), in which the buds are nearly opposite in position, though alternate in elevation, cannot, I believe, constitute a separate class, being only an accidental condition of the spiral. If it did, it might be called difoil; but the important classes are three: Trefoil, Fig. 9: Type, Rhododendron. § 14. The coincidences between beautiful architecture and the construction of trees must more and more have become marked in the reader's mind as we advanced; and if he will now look at what I have said in other places of the use and meaning of the trefoil, quatrefoil, and cinqfoil, in Gothic architecture, he will see why I could hardly help thinking and speaking of all trees as builders. But there is yet one more subtlety in their way of building which we have not noticed. If the reader will look carefully at the separate shoots in Plate 51, he will see that the furrows of the stems fall in almost every case into continuous spiral curves, carrying the whole system of buds with them. This superinduced spiral action, of which we shall perhaps presently discover the cause, often takes place vigorously, producing completely twisted stems of great thickness. It is nearly always existent slightly, giving farther grace and change to the whole wonderful structure. And thus we have, as the final result of one year's vegetative labor on any single spray, a twisted tower, not similar at any height of its building: or (for, as we shall see présently, it loses in diameter at each bud) a twisted spire, correspondent somewhat in principle to the twisted spire of Dijon, or twisted fountain of Ulm, or twisted shafts of Verona. Bossed as it ascends with living sculpture, chiselled, not by diminution but through increase, it rises by one consistent impulse from its base to its minaret, ready, in spring-time, to throw round it at the crest at once the radiance of fresh youth and the promise of restoration after that youth has passed away. A marvellous creation nay might we not almost say, a marvellous creature full of prescience in its infancy, foreboding even, in the earliest gladness of its opening to sunshine, the hour of fainting strength and falling leaf, and guarding under the shade of its faithful shields the bud that is to bear its hope through winter's shieldless sleep? Men often look to bring about great results by violent and unprepared effort. But it is only in fair and forecast order, "as the earth bringeth forth her bud," that righteousness and praise may spring forth before the nations. 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 shieldthe 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. Fig. 17. § 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;* this figure being the enlargement of a typical section FIG. 18. 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 encour aging 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. FIG. 19. 19, the actual form will always be c, or an approximate to it; * 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. 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. с FIG. 20. 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 |