The term bulb refers to a short, vertical, underground shoot that has modified leaves or thickened leaf bases used as food storage organs by a plant. The leaf bases generally do not support leaves, but contain food reserves to enable the plant to survive adverse conditions. The leaf bases may overlap and surround the center of the bulb as with lilies, or may completely surround the inner regions of the bulb, as with the onion. A modified stem forms the base of the bulb, and plant growth occurs from this base. Roots emerge from the underside of the base, and new stems and leaves from the upper side.
Cultivated plants that form true bulbs include: