Teddy Roosevelt's head sculpted from butter. The Liberty Bell replicated in oranges. The Sioux City Corn Palace of 1891 encased with corn, grains, and grasses and stretching for two city blocks--with a trolley line running down its center. Between 1870 and 1930, from county and state fairs to the world's fairs, large exhibition buildings were covered with grains, fruits, and vegetables to declare in no uncertain terms the rich agricultural abundance of the United States. At the same fairs--but on a more intimate level--ice-cooled cases enticed fairgoers to marvel at an array of butter...