Bulb is an underground modification of stem.
(i) It is highly condensed stem, represented by a short convex or slightly conical disc.
(ii) There are large numbers of fleshy scaly leaves surroundings a terminal bud at the center of the disc.
(iii) There are few scaly leaves which bear buds in their axil.
(iv) The fleshy leaves store the food while the scaly leaves are protective in function.
(v) The roots are adventitious arisng from the lower side of the stem. Common example is Allium sepa (onion).