§ 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.