The universe is a vast system of exchange. Every artery of it is in motion, throbbing with reciprocity, from the planet to the rotting leaf. The vapor climbs the sunbeam, and comes back in blessings upon the exhausted herb. The exhalation of the plant is wafted to the ocean. And so goes on the beautiful commerce of nature. And all because of dissimilarity--because no one thing is sufficient in itself, but calls for the assistance of something else, and repays by a contribution in turn.