Root plant to fuel the process. In return, the plant takes nitrogen compounds produced from ammonia by the bacteria. The term root crops refers to any edible underground plant structure, but many root crops are actually stems, such as potato tubers. Edible roots include cassava, sweet potato, beet, carrot, rutabaga, turnip, parsnip, radish, yam and horseradish. Spices obtained from roots include sassafras, angelica, sarsaparilla and licorice. Sugar beet is an important source of sugar. Yam roots are a source of estrogen compounds used in birth control pills. The fish poison and insecticide rotenone is obtained from roots of "Lonchocarpus" spp. Important
PTC tasting in some vegetables from the cabbage family ("Brassicaceae") such as broccoli and Brussels sprouts. This variability of PTC tasting came to the attention of Albert Blakeslee at the Carnegie Institute of Genetics on Long Island, New York. Blakeslee believed that PTC tasting was genetically determined. In 1932 he published a population study that showed that PTC tasting is inherited as a dominant Mendelian trait. For seven decades, Blakeslee's genetic description of the PTC tasting was widely accepted: "tasters" having one or two copies of a taster allele, but "nontasters" being recessive homozygotes. Then, in 2003, Dennis Drayna and his colleagues