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
Root trainer support vigorous root growth when the plant is put in the ground. The other lateral roots of the plant grow to compensate for this—so a stronger root ball forms, which improves the sapling's chances. When raising multiple seedlings, the root trainers are commonly placed in trays or racks. The size of each trainer depends upon the species but, for broad-leaved trees, the capacity is about a cup. Vertical ribs inside the trainer are positioned to train the roots to grow downwards and so prevent root spiralling. Owing to numerous problems (stability, restricted growth, etc.), the issue of root circling in