Bulbs have some characteristics to distinguish them from tubers and corms. Most bulbs such as daffodils, tulips and hyacinths often have a papery skin or tunic on the outside like an onion. The tunic helps protect the bulb from drying. Some bulbs like for example lilies do not have a tunic which means that they dry out faster of get more easily bruised.
- Bulbs are more or less rounded with a narrow point at the top. The leaves and flower stems appear from this point.
- At the bottom bulbs are flat, called the basal plate. That is where the roots grow.
- New bulbs, called offsets or daughter bulbs, are formed from the basal plate. The offsets grow out to full bulbs themselves.
- Bulbs are made up of rings, called scales, which are modified leaves that store food.
Corms look very much like bulbs but if you cut them open you will see that they do not have rings they are solid on the inside. At the end of the growing season one or more new corms are formed to replace the mother corm. Examples of corms are the crocus, freesia, gladiolus and crocosmia.
Tubers do not have a tunic or a basal plate. Tubers have several growing point, called eyes. Some tubers have their eyes on top like begonias or caladiums. With some tubers it is hard to distinguish the top from the bottom like anemones and potatoes. If you are not sure which end is top and which end is bottom you can plant them sideways and let the tuber find its way. Tubers usually do not make offsets or produce new tubers. Tubers usually get bigger every year and make more eyes.
Tuberous roots are modified, enlarged and specialized roots that store food. The tuberous roots cluster together, joined at the bottom of a stem. The stem contains the new growing point, a piece of root alone will not grow. Examples of plants with tuberous roots are dahlias, daylilies and sweet potatoes.