Recall that the first structure to emerge from a germinating seed is the radicle, or primary root (see fig. 1.16). In most di-cots, the radicle enlarges and forms a prominent taproot that persists throughout the life of the plant. Many progressively smaller branch roots (also called secondary or lateral roots) grow from the taproot. This type of root system consisting of a large taproot and smaller branch roots is called a taproot system and is common in cone-bearing trees and dicots (fig. 7.1). In plants such as sugar beet and carrot, fleshy taproots are the plant's "food" pantry; they store large reserves of carbohydrates. (The use of the word food here means a substance that provides both energy and chemical building blocks for a plant. A plant gets no energy from the soil, thus, a plant does not absorb food from the soil. Although a plant absorbs minerals through its roots, a plant's "food" is produced through photosynthesis in its leaves.)
Roots conform to the general biological principle of form and function, which is the idea that the form of a structure often reveals, and is directly related to, its function. For instance, the large, fleshy taproot of a dandelion or carrot has a form that is adapted to store many food reserves, one of its main functions. Not all taproots evolved a function for storage. For example, the long taproots of poison ivy (Rhus toxicodendron) and mesquite (Prosopis) absorb water from deep in the ground. As you read this book, try to determine how the form of a plant part could be advantageous to the part itself and to the plant as a whole.
Because taproots of most dicots grow faster than branch roots throughout the life of the plant, many plants have long taproots. Indeed, engineers digging a mine in the southwestern United States uncovered a mesquite root 53 meters down (as deep as a 15-story building is tall). If you'd like to see firsthand how big roots can get, visit the Roto-Rooter Monster Root Hall of Fame in Des Moines, Iowa. There you can see "Moby Root," a 31-meter specimen pulled out of a drainage pipe of a parking garage in 1994.
Was this article helpful?