It is astonishing how soon and unexpectedly flowers appear, when the fields are scarcely tinged with green. Yesterday, for instance, you observed only the radical leaves of some plants; to-day you pluck a flower.
—Henry David Thoreau
In science as in anything else, history and tradition can be powerful teachers. So here's a vivid lesson: Today, flowers and trees are awakening much earlier than they did 150 years ago, and there's proof in the journals of Henry David Thoreau.
Thoreau, best known for authoring "Walden," was a prolific chronicler and admirer of nature. He kept detailed logs describing the first days when a plant or a tree flowered, which are now being used to document the changing face of Concord, Mass., as the earth grows warmer. Boston University botanist Richard Primack and National Park Service scientist Abe Miller-Rushing have spent a decade comparing Thoreau's observations with their own.