Home >> Science & Nature >> Nature

Types of Modified Stems

For most people, the word "stem" conjures up the image of what holds up a plant, like a flower, or, in some cases, holds up a champagne glass. Children learn about stems, roots and leaves as parts of plants from a very early age. Later on, in more advanced biology classes, the information turns to such matters as modified stems. Stem modification has created certain recognizable features in plants that the average person may not known are stems.

Above Ground: Stolons, Cladodes and Shoots
- Some of the modified stems grow above ground. Stolons are also called "runners." They are most easily seen in the way grass grows. A thin stem grows along the ground. At nodes that touch the earth, roots and leaves sprout. Cladodes, or cladophylls, are stems that have flattened out like leaves to help with photosynthesis. One example is the green part of a cactus. Two forms of shoots grow above ground: the tendril or twining shoot and the searcher shoot. Both of these stems curl around objects to support the main plant.
Above Ground: Succulent Stems, Thorns, Spurs and Offshoots
- Other above ground stems include the succulents. These stems are found in desert plants; they hold copious amounts of water. Thorns are stems modified into short points for protection against herbivores. Thorns are not to be confused with spines, which are modified leaves. Spurs are slow-growing short branches often found on fruit trees, where they will bloom and carry the fruit. Offshoots occur on monocots (a type of flowering plant). A branch will laterally form and grow away from the main plant, and ultimately create other plants from it.
Below Ground: Bulbs, Pseudobulbs and Rhizomes
- Stems have modified themselves over time to help a plant below ground as well. One form that people should easily recognize is the bulb. A bulb consists of a tiny stem squashed down and enclosed by papery leaves or leaf bases. Bulbs come in two types: a concentric or tunicate bulb, like the onion, or a nontunicate or scale bulb, like the Easter lily. Roots form yearly; they are not part of the main plant. Pseudobulbs look much like bulbs, only they can be found above ground and also may be leaves. Finally, the rhizome makes a J-shape just beneath the ground, allowing roots to grow off, such as those on an iris.
Below Ground: Corms, Tubers and Crowns
- The corm regulates itself. Its root system can run very deep, such as those of the crocus, and can pull the plant deeper into the earth if necessary. Corms are thick and bulbous. The old corms are nearer the bottom of the complex rather than the top (making it necessary for the roots to pull it down deeper). A corm has dry, scalelike leaves. Tubers grow at the end of rhizomes; they are swollen compartments meant to store food for future growth. Crowns are modified stems found just at the surface, either above or below, where new shoots are produced.

Nature