Why do they all draw their nourishment from roots as from a mouth dipped into the earth, and distribute the strong bark over the pith?
Why are all the softer parts like the pith deeply encased within, while the external parts have the strong texture of wood, and outside of all is the bark to resist the weather's inclemency, like a champion stout in endurance?
Again, how great is nature's diligence to secure universal propagation by multiplying seed! Who does not know all these to be contrivances, not only for the present maintenance of a species, but for its lasting continuance, generation after generation, for ever?
And do not also the things believed inanimate on like grounds of reason seek each what is proper to itself?
Why do the flames shoot lightly upward, while the earth presses downward with its weight, if it is not that these motions and situations are suitable to their respective natures?
Moreover, each several thing is preserved by that which is agreeable to its nature, even as it is destroyed by things inimical.

Things solid like stones resist disintegration by the close adhesion of their parts.

Things fluid like air and water yield easily to what divides them, but swiftly flow back and mingle with those parts from which they have been severed, while fire, again, refuses to be cut at all.

And we are not now treating of the voluntary motions of an intelligent soul, but of the drift of nature.

Even so is it that we digest our food without thinking about it, and draw our breath unconsciously in sleep; nay, even in living creatures the love of life cometh not of conscious will, but from the principles of nature.