A flower bulb is really an underground storehouse and flower factory.
Within the flower bulb is just about everything the plant will need to sprout and flower at the appropriate time. Split a flower bulb in half and you will see this clearly. In the center of the basal part of the flower bulb are the leaves, cradling a baby bud. In many species, this bud already has the appearance of a flower while still inside the flower bulb! Surrounding the bud are fleshy white layers known as “scales”. In true bulbs, it is these scales which contain all the food the flower bulb will need to flower and thrive.
Not all flower bulbs are true bulbs
Technically speaking, many popular "bulb" flowers are not produced from true flower bulbs at all. Crocuses and gladioli, for example, are really corms, while such favorites as dahlias and begonias are really tubers. The main distinguishing trait is their method of storing food. In corms, most of the food is stored in an enlarged basal plate rather than the fleshy scales which in corms are much smaller.