Root, in botany, that part of a vascular plant normally underground. Its primary functions are anchorage of the plant, absorption of water and dissolved minerals and conduction of these to the stem, and storage of reserve foods. The root differs from the stem mainly by lacking leaf scars and buds, having a root cap, and having branches that originate from internal tissue rather than from buds.
snake gourd flower
angiosperm: Root systems
The roots anchor a plant, absorb water and minerals, and provide a storage area for food. The two basic types of root systems are a primary…
Types Of Roots And Root Systems
The primary root, or radicle, is the first organ to appear when a seed germinates. It grows downward into the soil, anchoring the seedling. In gymnosperms and dicotyledons (angiosperms with two seed leaves), the radicle becomes a taproot. It grows downward, and secondary roots grow laterally from it to form a taproot system. In some plants, such as carrots and turnips, the taproot also serves as food storage.
Two types of root system: (left) the fibrous roots of grass and (right) the fleshy taproot of a sugar beet.
Two types of root system: (left) the fibrous roots of grass and (right) the fleshy taproot of a sugar beet.
Encyclopædia Britannica, Inc.
Grasses and other monocotyledons (angiosperms with a single seed leaf) have a fibrous root system, characterized by a mass of roots of about equal diameter. This network of roots does not arise as branches of the primary root but consists of many branching roots that emerge from the base of the stem.
Some roots, called adventitious roots, arise from an organ other than the root—usually a stem, sometimes a leaf. They are especially numerous on underground stems, such as rhizomes, corms, and tubers, and make it possible to vegetatively propagate many plants from stem or leaf cuttings. Certain adventitious roots, known as aerial roots, either pass for some distance through the air before reaching the soil or remain hanging in the air. Some of these, such as those seen in corn (maize), screw pine, and banyan, eventually assist in supporting the plant in the soil. In many epiphytic plants, such as various orchids and Tillandsia species, aerial roots are the primary means of attachment to non-soil surfaces such as other plants and rocks.
A number of other specialized roots exist among vascular plants. Pneumatophores, commonly found in mangrove species that grow in saline mud flats, are lateral roots that grow upward out of the mud and water to function as the site of oxygen intake for the submerged primary root system. The roots of certain parasitic plants are highly modified into haustoria, which embed into the vascular system of the host plant to feed the parasite. The nodular roots of many members of the pea family (Fabaceae) host symbiotic nitrogen-fixing bacteria, and many plant roots also form intricate associations with mycorrhizal soil fungi; a number of non-photosynthetic mycoheterotrophic plants, such as Indian pipe, rely exclusively on these fungi for nutrition.
Pneumatophores of the black mangrove (Avicennia germinans) encrusted with salt and a young seedling projecting above the surface of the water.
root nodules
Pneumatophores of the black mangrove (Avicennia germinans) encrusted with salt and a young seedling projecting above the surface of the water.
Thomas Eisner
root nodules
The roots of an Austrian winter pea plant (Pisum sativum) with nodules harbouring nitrogen-fixing bacteria (Rhizobium). Root nodules develop as a result of a symbiotic relationship between rhizobial bacteria and the root hairs of the plant.
John Kaprielian, The National Audubon Society Collection/Photo Researchers
Morphology And Growth
Roots grow in length only from their ends. The very tip of the root is covered by a thimble-shaped root cap, which serves to protect the growing tip as it makes its way through the soil. Just behind the root cap lies the apical meristem, a tissue of actively dividing cells. Some of the cells produced by the apical meristem are added to the root cap, but most of them are added to the region of elongation, which lies just above the meristematic region. It is in the region of elongation that growth in length occurs.
