<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> 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>
where is the food produced in the onion plant
where is the food produced in the onion plant
bulb at the base
bulb at the base