Botany - B.Ye. Yakubenko 2017

Part One. Plant Anatomy and Morphology
Chapter III. Vegetative Plant Organs
3.3. Root Metamorphoses

Adapting to environmental conditions and specific Functions, roots have undergone significant modifications in the course of evolution. A wide variety of ROOT modifications are known:

Storage roots are roots that, In addition to performing primary functions, store nutrients and become thickened due to the proliferation of storage parenchyma. These include root crops and root tubers. In root crops, nutrients accumulate in the main root, such as in the roots of beets, radishes, turnips, parsley, carrots, and others. In root tubers, nutrients accumulate in adventitious roots, as seen in dahlias, sweet potatoes, and peonies.

Prop roots are adventitious roots that form in the lower part of the stem and help anchor the plant in the soil. Such roots develop on the stems of corn. A specialized type of these is stilt roots, characteristic of mangrove vegetation. In tropical plants, particularly those growing in tidal zones, buttress roots form to support the stems.

Aerial roots are adventitious roots that develop in epiphytic plants (those growing on tree trunks) and absorb Water and nutrients from the air, as seen in certain tropical orchids.

Climbing roots are also aerial roots, but their primary function is to attach the plant to a support. They are found in ivy and pumpkins.

Sucking roots, or haustoria, occur in parasitic and semi-parasitic plants. They penetrate into the host plant's Organs and absorb organic nutrients. Such roots are characteristic of plants of the genera Viscum (mistletoe) and Cuscuta (dodder).

Respiratory roots (pneumatophores) develop in plants growing in excessively waterlogged habitats where plants experience oxygen deficiency. These roots emerge from the substrate and absorb oxygen from the air. They are found in swamp pine and bald cypress.

Root and Bacteria Symbiosis. The roots of certain plants, particularly legumes, can enter into a symbiotic relationship with bacteria of the genus Azotobacter. Through root hairs and microcracks, bacteria penetrate the root cortex parenchyma, multiply, and stimulate Cell Division; the parenchyma proliferates, and nodule-like growths appear on the roots. The bacteria residing in the root have The ability to fix and accumulate atmospheric nitrogen, which is otherwise inaccessible to higher plants, binding it into usable compounds. Part of the nitrogen is utilized by the plants, while the greater portion remains in the soil, enriching it with nitrogen. Therefore, legumes are excellent preceding crops for other plants and can be used as "green" manure.

Mycorrhiza is a symbiotic association between plant roots and Fungi. The fungus colonizes young rootlets, enveloping them with its filaments (hyphae) or penetrating inside the root. If the hyphae envelop the root only externally, such mycorrhiza is called ectotrophic; it develops on the roots of oak, pine, birch, hazel, and others. In the course of evolution, such plants have lost their root hairs and feed exclusively through mycorrhiza. This mode of Nutrition is called mycotrophic.

If the fungus penetrates inside the root, such mycorrhiza is termed endotrophic. It is characteristic of plants from the heather family (Ericaceae), strawberries, and alfalfa. In ecto-endotrophic mycorrhiza, the fungus both envelops the root externally and penetrates its interior; this type is less common and is typical of certain gymnosperms.