Hemp came to America on the Mayflower–woven into the ship's sails and rigging. It covered Conestoga wagons trudging west. According to legend, Betsy Ross stitched it into that famous flag, and Levi Strauss sewed it into the first pair of gold miner's jeans. Hemp was a cash crop for rope, twine, canvas and cellulose in the United States until 1937, when it was outlawed by the federal government, largely because major chemical companies—competing for the war industry with synthetic fibers–lobbied for the Marijuana Tax Act.…