Bulbs are the most common and best understood to the average gardener. In fact, when we talk about the others (Corms, Rhizomes, & Tubers) we often refer to them as bulb like. The bulbs most commonly known are tulips, caladiums, onions, garlic, narcissus, crocuses, hyacinths and daffodils. A true bulb is like an onion — it grows in layers and often is covered with the same papery skin that covers the onion.
Bulbs that have this skin usually are easy to handle and not easily damaged. Those, like lilies, that lack the papery tunic are much more easily damaged and need to be handled with care.
At the very heart of that bulb is the flower itself — in miniature — but there and just waiting to emerge. It is covered by scales — the layers of an onion in most cases — but in some cases, as with the lily, the scales are loose and swollen, looking more like thin buds of garlic. A basal plate — a hairy looking plate with the beginnings of roots, holds these scales together. Thanks to this plate, not only does the bulb stay together, but we can also tell which end of the bulb is up.
A bulb produces offsets — little bulbs attached to the larger bulb — as a way of reproducing itself. Dig them up and it will look like a big bulb-hen mothering baby bulb-chicks. (Debbie Van Bourgondien "The Bulb Lady")