§ 7. But farther, observe in what succession those buds are put round the bearing stem. Let the section of the stem be represented by the small central circle in Fig. 8; and suppose it surrounded by a _nearly_ regular pentagon (in the figure it is quite regular for clearness' sake). Let the first of any ascending series of buds be represented by the curved projection filling the nearest angle of the pentagon at 1. Then the next bud, above, will fill the angle at 2; the next above, at 3, the next at 4, the next at 5. The sixth will come nearly over the first. That is to say, each projecting portion of the section, Fig. 5, expands into its bud, not successively, but by leaps, always to the _next but one;_ the buds being thus placed in a nearly regular spiral order. § 8. I say nearly regular--for there are subtleties of variation in plan which it would be merely tiresome to enter into. All that we need care about is the general law, of which the oak spray furnishes a striking example,--that the buds of the first great group of alternate builders rise in a spiral order round the stem (I believe, for the most part, the spiral proceeds from right to left). And this spiral succession very frequently approximates to the pentagonal order, which it takes with great accuracy in an oak; for, merely assuming that each ascending bud places itself as far as it can easily out of the way of the one beneath, and yet not quite on the opposite side of the stem, we find the interval between the two must generally approximate to that left between 1 and 2, or 2 and 3, in Fig. 8.[2] [Illustration: FIG. 9.] § 9. Should the interval be consistently a little _less_ than that which brings out the pentagonal structure, the plant seems to get at first into much difficulty. For, in such case, there is a probability of the buds falling into a triangle, as at A, Fig. 9; and then the fourth must come over the first, which would be inadmissible (we shall soon see why). Nevertheless, the plant seems to like the triangular result for its outline, and sets itself to get out of the difficulty with much ingenuity, by methods of succession, which I will examine farther in the next chapter: it being enough for us to know at present that the puzzled, but persevering, vegetable _does_ get out of its difficulty and issues triumphantly, and with a peculiar expression of leafy exultation, in a hexagonal star, composed of two distinct triangles, normally as at B, Fig. 9. Why the buds do not like to be one above the other, we shall see in next chapter. Meantime I must shortly warn the reader of what we shall then discover, that, though we have spoken of the projections of our pentagonal tower as if they were first built to sustain each its leaf, they are themselves chiefly built by the leaf they seem to sustain. Without troubling ourselves about this yet, let us fix in our minds broadly the effective aspect of the matter, which is all we want, by a simple practical illustration.