Though hidden below ground and often ignored by gardeners, roots are vital to a plant’s survival and growth. They absorb water and nutrients and help transport them throughout the plant; they store food for future use; and they anchor the plant in the soil.
As they seek water and nutrients, roots grow through the soil away from the center of the plant. This growth takes place in the apical meristem, a region at the root tip where cells are actively dividing and elongating. Just behind the tender root tip, which is protected by the root cap, is a zone of cells that produce many tiny projecting root hairs. These are in direct contact with the soil and increase the surface area available for absorption of water and nutrients.
If exposed to sunshine or dry air, the root hairs quickly shrivel and die. When plants are dug for transplanting, the root hairs inevitably suffer some exposure, and the plant wilts as a result. Gardeners therefore try to plant and transplant leafy (nondormant) plants quickly, minimizing the contact of roots with air.
Plants are anchored in the soil by fibrous roots, taproots, or (sometimes) a combination of both. A fibrous root system has many branching roots that grow fairly close to the soil surface. The taproots of some large trees and shrubs, in contrast, grow deep into the soil and develop horizontal branches that hold the plant firmly in place.
Adventitious Roots and Stems
Adventitious roots are roots that grow in unexpected positions, such as from leaves or the sides of stems; strawberry stems (“runners”), for example, form adventitious roots as they spread across the ground. Propagation by stem or leaf cuttings is based on a plant’s ability to form adventitious roots from its stems or leaves. Ground layering is another propagation method that depends on the development of adventitious roots.
Adventitious stems (adventitious shoots) are, likewise, stems growing in an unusual position–from a root, for instance. The suckers formed by raspberry plants are upright adventitious stems arising from horizontal roots.
Propagation by root cuttings involves the formation of adventitious stems from pieces of root.