BulbsBulbs are plant storage organs generally grown underground, consisting of a short stem (the basal plate), from which grow overlapping, swollen leaves or leaf bases. The top growth emerges from the bulb center. Here's an example:

CormsCorms are not made up of leaves, but a vertical swollen compact stem, and as such are solid. The corm is protected by a tunic of old leaf petioles. Here's an example:

Tubers

Tubers are, simply, enlargements in the underground stem or lateral root of a plant that are used for food storage. These vary greatly in appearance, but all have the same function. Here's an example:

From: gardening.stackexchange.com