A bulb is an underground, modified stem that develops in some flowering plants. Its purpose is to store food and water for the plant through a cold or dry season. Examples of bulbs include the tulip, narcissus, crocus, onion, lily, and garlic. At the start of the new growing season, roots grow from the bottom of the bulb and a bud grows from the stem. The food and water in the bulb tissues nourish the fast-growing bud.
Many bulbs require a period of low-temperature dormancy before they sprout new buds and roots.
Bulbs are usually globular and have concentric layers of fleshy leaves covering the short stem. The fleshy leaves store food and water. Roots emerge from the bottom of the bulb at the beginning of the growing season. The bud grows from the apical meristem at the tip of the short stem. There are two main types of bulbs.