Maple syrup is one of the few agricultural products distinctive to North America and a 100 percent natural food rich in electrolytes, minerals, vitamins, and antioxidants, with no fat or cholesterol, low sodium, and no more calories than sugar. The amount of sap needed to produce syrup is determined by dividing 86 by the sap's sugar content, so sap with 2 percent sugar content would require 43 gallons of sap to make 1 gallon of syrup, a calculation known as the Rule of 86. Sap flows through the sapwood, the actively growing cells that conduct water and nutrients from the roots to the branches, and its flavor is influenced by genetics, environmental factors, and tree health. Canada has developed a flavor wheel identifying 91 unique flavors detectable in maple sap. Sugar water flows from sugar maple trees only when temperatures rise above freezing by day and fall below freezing at night, and the liquid that comes from the tree is crystal clear and only slightly sweet. Tapping does no lasting damage to the tree, and tap holes heal completely within about 6 months. The sugar maple is the state tree of New York, Vermont, Wisconsin, and West Virginia. Canada produces about 80 percent of the world's maple sugar supply, the United States the remaining 20 percent, with Vermont producing 35 percent of that U.S. share, and Japan is the largest importer. Maple syrup boils at 219 degrees Fahrenheit, 7 degrees above the boiling point of water. Thomas Jefferson started a maple plantation at Monticello in 1791 and advocated maple sugar over cane sugar. The Algonquin Indians called maple sap sinzibukwud, meaning drawn from wood. The tapping season typically lasts about six weeks, depending on weather and when tapping began, and once tree buds begin to open, the sap develops an off flavor and is no longer suitable for making maple syrup.