A Little Bit More
The study of underground plant structures is surprisingly complex. Here is a greatly simplified summary of some of the many structures that are commonly called "bulbs".
Bulb - the term "bulb" is regularly applied to any root-like swelling on a plant, but technically it is a specific kind of structure. A true bulb is a very short underground stem wrapped in thickened, fleshy scales that are actually modified leaves. The scales are the chief sites of food accumulation. Food stored in the leafy scales of a bulb is used up by the initial growth of the new shoot (that's why the overlooked onions on a pantry shelf shrivel as they sprout).
Corm - A corm is an underground, vertical, compressed stem with reduced scale leaves. It differs from a bulb in that the stem, not the leaves, stores food for the shoot. Some examples include gladiolus, crocus, and tuberous begonias.
Rhizome - A rhizome is a slender, elongated, underground stem that is usually horizontal in position. It is rich in accumulated food in the form of starch. Rhizomes are often confused with roots. Examples include sweet flag, cattail, many violets, iris and water lilies.
Tuber - A tuber is a greatly enlarged and swollen portion of a rhizome. The most familiar examples are the common potato and sweet potato. Tubers are marked by "eyes" over their surface, each of which bears a minute, scale-like leaf with several minute buds.
Bulb, rhizome, corm, tuber - different in structure, but delightfully equal in the pleasure their flowers and foods can bring.
Activities
Growing bulbs
Objectives: See how quickly a bulb can produce a plant from its stored food
Materials: pot, soil, and bulb(s) (tulip, amaryllis, daffodil)
Almost all of us have had a plant or two in our homes or offices to brighten the room. But usually the plant we choose is a typically rooted plant that takes a long time to develop. If we begin a plant from seed or a cutting it may never even produce a flower at all. If you obtain one of the plants that grow from a bulb, you can enjoy the dramatic changes of the plant, as well as the resulting flower, in a very short period of time.
This activity will require you to purchase a few bulbs but it really is worth the expense. You should be able to purchase bulbs from a local nursery (be sure you have instructions for indoor growth) or log on to the www.urbanext.uiuc.edu/bulbs/planting.html website for ordering and instructions over the internet. Watching a bulb develop into a mature plant sporting a flower is both interesting and just plain fun. You may want your students to document each day's change in the plant. Take advantage of the dramatic changes that will be taking place by developing your own activity around your plant's growth. Keep in mind too that temperature will play a role in the plant's development - warmer temperatures speed growth.
Alternative - If growing bulbs won't work for your situation, you can bring a grocery bulb to your students as an alternative. Bring in a garlic bulb to your students and carefully dissect it for them to see. Garlic bulbs consist mostly of individual segments called cloves. Each clove consists of a bud - the beginnings for a new plant - surrounded by several thick leaves that provide the energy for new growth until the plant can make its own food.
Key Concepts
Structures and Functions, Growth and Development
Questions
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