Under the Maples by John Burroughs

One of our seven wise men once said to me, "Have you observed that in the inorganic world things go by even numbers, and in the organic world by odd? " I immediately went down to the edge of a bushy and swampy meadow below our camp and brought him a four-petaled flower of galium, and a plant-stalk with four leaves in a whorl. In another locality I might have brought him dwarf cornel, or the houstonia, or wood-sorrel, or the evening-primrose. Yet even numbers are certainly more suggestive of mechanics than of life, while odd numbers seem to go more with the freedom and irregularity of growing things.

One may make pretty positive assertions about non-living things. Crystals, so far as I know, are all even-sided, some are six and some eight-sided; snowflakes are of an infinite variety of pattern, but the number six rules them. In the world of living things we cannot be so sure of ourselves. Life introduces something indeterminate and incommensurable. It makes use of both odd and even, though undoubtedly odd numbers generally prevail. Leaves that are in lobes usually have three or five lobes. But the stems of the mints are four-square, and the cells of the honey bee are six-sided. We have five fingers and five toes, though only four limbs. Locomotion is mechanical and even numbers serve better than odd. Hence the six-legged insects. In the inorganic world things attain a stable equilibrium, but in the living world the equilibrium is never stable. Things are not stereotyped, hence the danger of dogmatizing about living things. Growing Nature will not be driven into a corner.