§ 1. We have hitherto spoken of each shoot as either straight or only warped by its spiral tendency; but no shoot of any length, except those of the sapling, ever can be straight; for, as the family of leaves which it bears are forced unanimously to take some given direction in search of food or light, the stalk necessarily obeys the same impulse, and bends itself so as to sustain them in their adopted position, with the greatest ease to itself and comfort for them. In doing this, it has two main influences to comply or contend with: the first, the direct action of the leaves in drawing it this way or that, as they themselves seek particular situations; the second, the pressure of their absolute weight after they have taken their places, depressing each bough in a given degree; the leverage increasing as the leaf extends. To these principal forces may frequently be added that of some prevalent wind, which, on a majority of days in the year, bends the bough, leaves and all, for hours together, out of its normal position. Owing to these three forces, the shoot is nearly sure to be curved in at least two directions;[1] that is to say, not merely as the rim of a wine-glass is curved (so that, looking at it horizontally, the circle becomes a straight line), but as the edge of a lip or an eyebrow is curved, partly upward, partly forwards, so that in no possible perspective can it be seen as a straight line. Similarly, no perspective will usually bring a shoot of a free-growing tree to appear a straight line. § 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.