BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VIII. BASICS OF PLANT MORPHOLOGY AND ANATOMY

Root Morphology and Anatomy

Root Modifications

Adapting to various habitats and diverse ecological conditions during evolution, roots have undergone significant modifications. Many ROOT Metamorphoses are known: storage, aerial, symbiotic (Fig. 57).

Storage roots serve as sites for nutrient storage, causing them to become thick and fleshy during growth. Both primary, lateral, and adventitious roots can be involved in this transformation. They become greatly thickened due to the proliferation of phloem or xylem parenchyma. These include fleshy roots (root crops) and root tubers.

Root crops are characteristic of many plants, such as radishes, carrots, and chicory. They consist of a greatly thickened primary root, the stem portion - hypocotyl (root collar), and the crown (often the epicotyl), which bears a rosette of leaves. The full development cycle of such roots lasts two years; by the end of the first year, they accumulate a significant reserve of nutrients and thicken considerably.

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Fig. 57. Root metamorphoses:

A - aerial prop roots of a maize stem; B - root tubers of dahlia;

C - root nodules on lupine.

Root tubers or root knobs are fleshy thickenings of adventitious or lateral roots that predominantly store CARBOHYDRATES. This type of root is characteristic of dahlias, certain orchids, sweet potatoes, and yams.

Aerial roots are partially or entirely located in the air.

Prop roots serve for better anchoring of the plant in the substrate.

Stilt roots are characteristic of mangrove vegetation growing in the tidal zone of sea shores. By origin, these roots are adventitious, growing downwards from the trunk and lower branches toward the ground. They serve the plant for support and nourishment. A similar function is performed by the adventitious roots of maize. The stilt roots of the banyan fig, known as prop roots, are exceptionally well developed.

Plank roots (buttress roots) are typical of trees in tropical rainforests and are lateral in origin. They develop triangular, board-like outgrowths at the Base of the trunk, thereby increasing the plant's supporting surface.

Respiratory roots (pneumatophores) are characteristic of marsh plants, notably the bald cypress. They exhibit negative geotropism and grow vertically upwards, rising above the soil surface.

They possess a system of openings and well-developed aerenchyma, which allows them to supply air to other parts of The Root System. In addition, they bring thin, thread-like feeding roots up to the upper, more fertile soil layers.

Aerial absorbing roots are adventitious roots located in the air that can absorb water and nutrients from it thanks to a specialized tissue called velamen. They are characteristic of tropical forest epiphytes, particularly certain orchid species.

Climbing roots are also located in the air, but their main function is to anchor the plant to a support. They are typical of ivy and wild grapes.

Haustoria (sucking roots) are pseudo-roots that arise in parasitic and hemiparasitic plants; by penetrating the Tissues of the host plant, they enable the absorption of nutrients. These occur in parasitic plants such as toothwort and dodder, as well as hemiparasitic plants like mistletoe and yellowrattle.

Contractile roots are capable of longitudinal contraction due to a high degree of parenchymatization, elastic Cell walls, radial cell expansion, and longitudinal compression. They are found in tulips, crocuses, gladioli, and others. These roots enable the gradual pulling of the underground Organs deeper into the soil.

Mycorrhiza is a type of root modification that results from a symbiotic association between a flowering plant and Fungi (pine, oak, heather, blueberry). The plants have become so specialized for this coexistence that their rootlets are deformed and often lack a root cap and root hairs. In mycorrhizal plants, this function is performed by fungal hyphae that encase the root tip in a sheath or colonize the Cells of the epiblema and cortical parenchyma.

Another root modification is the root nodules found in legumes. These modifications arise As a result of colonization by symbiotic Bacteria. Their secretions stimulate the division of parenchyma cells, causing the bacterial tissue to proliferate extensively and form nodules on the root system of legumes. With the participation of symbiotic bacteria, atmospheric nitrogen is fixed into salts of nitric and nitrous acids, which can then be assimilated by the flowering plants.