Photo: Teresa Arago (flickr)
A bulb is actually just a swollen underground storage unit during the winter months as it sleeps underground. Plants that grow from bulbs are, for example, daffodils, tulips and lilies.
True bulbs like these are made up of a short basal stem covered with fleshy leaf scales wrapped around a growing point. The scales are attached to the bottom of the bulb which is called the basal plate and the roots grow out of this plate. In most bulbs the protective fleshy leaf scales that make up the interior of each bulb are enclosed by an outer coat of dry papery scales.
Corms are more squat in shape than bulbs and are solid with no fleshy scales inside, and they have a fibrous outer coat. Corms do have a basal plate, however, from which their roots grow. Examples of flowers that grow from corms are crocus and gladioli.
Tubers are bigger than both bulbs and corms and are swollen, irregularly shaped underground stems with nodes or eyes that produce their roots. Tuberous begonias and anemones grow from tubers.
Irises are another type of plant that grows from underground stems and theirs are called rhizomes. Their storage units grow horizontally and lie close to the surface of the soil.
All of the different types of storage units are distinguishable by their shape and form and by where there roots emerge into the soil. But at this time of year all are lying in the cold earth waiting for it to warm up in the spring so that they can send forth their flowers.