<P> The onion (Allium cepa L., from Latin cepa "onion"), also known as the bulb onion or common onion, is a vegetable that is the most widely cultivated species of the genus Allium . Its close relatives include the garlic, shallot, leek, chive, and Chinese onion . </P> <P> This genus also contains several other species variously referred to as onions and cultivated for food, such as the Japanese bunching onion (Allium fistulosum), the tree onion (A. × proliferum), and the Canada onion (Allium canadense). The name "wild onion" is applied to a number of Allium species, but A. cepa is exclusively known from cultivation . Its ancestral wild original form is not known, although escapes from cultivation have become established in some regions . The onion is most frequently a biennial or a perennial plant, but is usually treated as an annual and harvested in its first growing season . </P> <P> The 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 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 cause rotting . Some varieties of A. cepa, such as shallots and potato onions, produce multiple bulbs . </P> <P> Onions are cultivated and used around the world . As a food item, they are usually served cooked, as a vegetable or part of a prepared savoury dish, but can also be eaten raw or used to make pickles or chutneys . They are pungent when chopped and contain certain chemical substances which irritate the eyes . </P>

Where is the food produced in the onion plant