The Crack in the Sidewalk

Walk down any sidewalk in Chicago or Charlotte, and eventually you will spot it — a thin green shoot splitting through inches of concrete. A dandelion or blade of grass, seemingly fragile, fracturing a surface that was engineered to bear the weight of trucks. Botanists have measured the force a germinating seed can exert: hundreds of pounds per square inch of pressure, generated by nothing more than a hull of cellulose and the life locked inside it.…