onion plant has a fan of hollow, bluish-green leaves, and its bulb at the base of the plant begins to swell when a certain day-length is reached. The bulbs are composed of shortened, compressed, underground stems surrounded by fleshy modified scale (leaves) that envelop a central bud at the tip of the stem. In the autumn (or in spring, in the case of overwintering onions), the foliage dies down and the outer layers of the bulb become more dry, and brittle. The crop is harvested and dried and the onions are ready for use or storage. The crop is prone to attack by a number of pests and diseases, particularly the onion fly, the onion eelworm, and various fungi which can cause rotting. Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs..

potato, (Solanum tuberosum), annual plant in the nightshade family (Solanaceae), grown for its starchy edible tubers. The potato is native to the Peruvian-Bolivian Andes and is now cultivated on every inhabited continent and is one of the world’s main food crops, valued for its high yields and adaptability to diverse climates. Potatoes are consumed in a variety of forms, including as cooked vegetables, as processed foods such as french fries and potato chips, and as ingredients such as potato starch and potato flour, which are used in cooking, baking, and food manufacturing. They are also used to make vodka and aquavit. The tubers are highly digestible and supply vitamin C, potassium, thiamin, and niacin; when eaten with their skins, they also provide dietary fiber.