The first business of the budding stem, is to get every pair of buds set accurately at right angles to the one below. Here are some examples of the way it contrives this. A, Fig. 13, is the section of the stem of a spray of box, magnified eight or nine times, just where it throws off two of its leaves, suppose on north and south sides. The crescents below and above are sections through the leaf-stalks thrown off on each side. Just above this joint, the section of the stem is B, which is the normal section of a box-stem, as Fig. 5 is of an oak's. This, as it ascends, becomes C, elongating itself now east and west; and the section next to C, would be again A turned that way; or, taking the succession completely through two joints, and of the real size, it would be thus: Fig. 14. [Illustration: FIG. 13.] [Illustration: FIG. 14.] The stem of the spotted aucuba is normally hexagonal, as that of the box is normally square. It is very dexterous and delicate in its mode of transformation to the two sides. Through the joint it is A, Fig. 15. Above joint, B, normal, passing on into C, and D for the next joint. [Illustration: FIG. 15.] [Illustration: FIG. 16.] 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 rounded and softened into irregularities; A, Fig. 16, becoming, as it buds, B and C. The dark diamond beside C is a section through a bud, in which, however small, the quatrefoil disposition is always seen complete: the four little infant leaves with a queen leaf in the middle, all laid in their fan-shaped feebleness, safe in a white cloud of miniature woollen blanket. § 13. The elementary structure of all important trees may, I think, thus be resolved into three principal forms: three-leaved, Fig. 9; four-leaved, Figs. 13 to 16; and five-leaved, 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. Quatrefoil, Fig. 13: Type, Horse-chestnut. Cinqfoil, Fig. 5: Type, Oak.