Root Modification 2p1k6x

Modifications of Roots •   • Roots are modified into different forms to perform specific functions other than their normal functions. • Modification in roots is found in both tap root system and adventitious root system.

• Modification in root occurs when there occurs a permanent change in the structure of the root system. • This change in structure of the tap root or the adventitious root system is for carry out certain specific functions additional to anchorage and absorption. • The change in the structure of the roots is for adaptation to their surrounding environment.

Tap Root Modifications Tap roots are modified in to different structures, these modified structures carry out specific functions like food storage. Such roots are referred to as modified tap roots. They are different types of modified tap roots like Fusiform, Napiform, Conical, Tuberous or tubercular roots, pneumatophores.

• Fusiform : Fusiform is a modified tap root. The primary root of the system is swollen at the middle and tapers gradually at both the ends forming a spindle shaped structure. Example of fusiform roots is radish.

Napiform : The base region of the root is swollen becoming almost spherical in shape, and then it abruptly tapers towards the lower end, forming a tail-like structure. Example of Napiform roots are turnip and beet.

• Conical: In the conical form of root modification the roots are swollen and are broad at the base, the apex part gradually tapers forming a con like structure like in carrot.

Tuberous or tubercular : In the case of tuberous roots, the roots are thick and fleshy. They do not form any definite shape. Example: Sweet potato, yam.

• Pneumatophores : The pneumatophore roots grow vertically up, they protrude out of water or marshy sol like conical spikes. These roots occur in large number around the trunk of the tree. Pneumatophore roots are many pores for breathing through which exchange of gases takes place for respiration. Example of pneumatophores are Rhizophora. 

Adventitious Root Modifications Adventitious roots are the roots that are produced from any portion of the plant other than the radicle. The root system may be changed to different forms for special functions like storage, mechanical and vital functions. 

• For Storage Of Food • Tuberous root : The adventitious roots in this are grown from the nodes of the running stem. These roots are modified are swollen into irregular forms and are known as tuberous roots. They are produced in single number. Example: Sweet Potato.

Fasciculate root : The tuberous roots are developed from the base of the stem in cluster.

• Nodulose root : The adventitious roots in this case arise from the underground stem. Some roots that are  slender become swollen near the apex and they form nodule like structures. Example: mango-ginger.

• Moniliform or Beaded roots : In this case, the roots are swollen at frequent intervals. This formation gives a beaded or moniliform type of appearance. This form of root formations is seen in many grasses, Basella, etc.

• Annulated roots : This type of roots has ringlike swellings ina series and appears in the form of a number of discs placed one above the other. Examples are Cephalis ipecacuanha (Ipeca). 

Prop roots : Here the plants have tap roots system. the horizontal branches of the stem of the plant gives rise to aerial roots. These aerial roots hang vertically downwards. These roots on reaching the ground, they grow and act like pillars. They provide mechanical to the plant. Example Ficus bengalensis.

•

Stilt Roots : These plants have their own roots system like in screwpine. They are not strongly anchored tothe soil. Hence, these plant develop adventitious roots from near the base of the stem. These roots grow obliquely downwards. They act like stilt and they provide mechanical to the plant. Example - the maize plant produces adventitious roots form the lower nodes which also act in a similar way. 

•

Climbing roots : This type of root system is found in climbers. Adventitious roots are developed from the nodes and are aerial roots. These aerial roots twist and clasp the and help in climbing. Example Betel, Pothos, etc. 

•

Clinging roots : This type of roots are seen in orchids. These roots arise from the stem base of the plant. They enter crevices of the to fix the epiphyte. They provide the plant with mechanical . 

•

Root buttresses : Some trees have great plant-like roots that radiate

Root  The part of a plant that attaches it to the ground or to a , conveying water and nourishment to the rest of the plant.

Modifications of Roots Roots sometimes have special functions to perform and in such cases their form and structure differ from those of normal roots. The modified roots may be underground or aerial.

Underground Root Modifications

Taproot and adventitious roots may undergo certain modifications to perform the function of storage and vegetative propagation.

Tap Root Modifications (for storage of food) In some plants the tap roots store reserve food for which they become swollen and assume different shapes. There are three types : (i) Fusiform: (ii) Napiform: (iii) Conical: (iv) Tuberous or tubercular: (v) Pneumatophores:

(i) Fusiform: It is a modified tap root. The primary root is swollen in the middle while both the ends gradually taper forming a spindle shaped structure, e.g., Radish (Raphanus sativus). (ii) Napiform: The hypocotyls region is considerably swollen, becoming almost spherical and then abruptly tapering towards the lower end, e.g., Turnip (Brassica campestris var. rapa) and beet (Beta vulgaris). (iii) Conical: The roots swell, becoming broad at the base and gradually taper towards apex forming a cone like structure, e.g., Carrot (Daucus carota).

(iv) Tuberous or tubercular: In this case, the root is thick and fleshy but does not form any definite shape, e.g., Mirabilis jalapa. (v) Pneumatophores: These roots grow vertically up and come out of the water or marshy soil like conical spikes. They occur in large numbers around the tree trunk. Such roots are provided with numerous pores (breathing pores) through which air is taken for respiration, e.g., Rhizophora.

Fusiform root - In radish the modified tap root is thickened in the middle and tapers towards both ends. e.g., Raphanus sativus (Radish) Napiform root - In beetroot the modified tap root is greatly swollen at the base, but abruptly narrows into a tail-like portion. e.g., Beta vulgaris (Beetroot) Conical root - In carrot the modified tap root is conical. It is broad at the base and gradually tapers towards its apex. e.g., Daucas carota (carrot)

Adventitious Root Modifications

• Tuberous or tubercular root, e.g., Ipomoea batotas (Sweet potato) Here, the modified adventitious root is swollen without any definite shape. It is always produced singly and not in clusters. • Fasciculated roots e.g., Asparagus, Dahlia In Dahlia and Asparagus a number of adventitious roots arise as a cluster, from almost the same level at the base of the stem.

Tuberous root

Fasciculated roots

Adventitious Root Modifications • Nodulose roots e.g., Curcuma amada, (mango ginger)Here, the root becomes swollen at its tip. • Moniliform roots e.g., Momordica. Here, the roots show beadlike swellings at frequent intervals. • Annulated roots E.g., Ipecac. Here, the adventitious roots have a series of ring-like swellings on

Annulated roots

Moniliform roots

Nodulose roots

Aerial Root Modifications

Aerial roots are adventitious roots which develop from the aerial parts of the plant to perform various functions. A. For Mechanical B. For Vital Functions

For Mechanical • Prop roots • Stilt roots • Climbing roots

For Vital Functions •Haustoria or sucking roots

•Respiratory roots or breathing roots or pneumtophores. •Floating roots •Epiphytic roots

Prop roots e.g., Ficus benghalensis (Banyan): In banyan the adventitious roots arise fromthe horizontal branches and grow vertically downwards. After reaching the soil they become thick and woody. Thus, they function as pillars giving mechanical to the branches. Hence, they are also known as

Stilt roots e.g. Pandanus : In Pandanus the adventitious roots arise from the lower part of the main stem and grow obliquely towards the soil. They serve to keep the plant erect by giving additional .

Climbing roots or clinging roots e.g., Piper betel, Pothos, etc : These roots arise from the nodes and help in attaching the climbing stem firmly to a like a tree or a wall, by various mechanisms.

Haustoria or sucking roots e.g. Cuscuta : Parasites like Cuscuta develop a kind of root which penetrates into the tissue of the host plant and help to draw nutrients from the host by sucking it. The parasitic plants are not completely equipped to prepare their food. Hence, such plants have to depend on host plants for nutrients.

Respiratory roots or breathing roots or pneumtophores e.g., Avicennia, Rhizophora. A number of plants growing in marshy water-logged soils which contain almost no air, develop some branches which grow vertically upwards into the air. These roots are called breathing roots or pneumatophores. Each such root is provided towards the upper end with numerous pores through which gases diffuse in and out.

Floating roots e.g., Jussiea: In Jussiea which is an aquatic plant, special spongy roots called floating or respiratory roots arise from the plant. They are adventitious and enclose a tissue called aerenchyma. These roots usually develop above the level of water and serve to store up air and help in buoyancy of the plant. In addition, the floating roots may also perform the respiratory function.

Epiphytic roots e.g., Vanda: In epiphytes like orchids which grow on other plants, special adventitious roots called epiphytic roots are produced. The outer region of the root is made up of a special tissue called the velamen. This tissue absorbs moisture from the air and makes it available to the plant. These roots do not penetrate the host tissue like parasitic roots.

Summary of Root Modifications

The Plant Body: Stems FUNCTION OF STEMS • Stems leaves and branches. • Stems transport water and solutes between roots and leaves. • Stems in some plants are photosynthetic. • Stems may store materials necessary for life (e.g., water, starch, sugar). • In some plants, stems have become adapted for specialized functions.

Stems  a display of  leaves. Stems orient the leaves  toward the light with  minimal overlap among the  leaves.

Asclepias ­ milkweed

Modified & Specialized Stems

Food Storage Stems - Asparagus

Photosynthetic Stems Cacti - stout fleshy stems that are modified for food and water storage and photosynthesis.

Tuber • Tubers accumulation of food at the tips of underground stolons • The "eyes" of a potato are the nodes of a starchladened stem

Corms

Crocus corms

• A corm is a swollen, vertical stem with a papery covering. • Gladiolus and Crocus are examples of plants that form corms.

Bulb • Bulbs - large buds with a small stem at the lower end surrounded by numerous fleshy leaves, adventitious roots at base • Examples include onion, tulip, and lily

Rhizomes • Rhizomes horizontal stems that grow below the ground with adventitious roots • Examples of plants that can produce rhizomes are irises, ferns, and grasses.

Rhizomes • Other plants, like ginger, produce large, thick rhizomes called pachymorphs. The pachymorph rhizome of Ginger

Thorns • Honey locust (modified stem) • Black Locust (modified leaf stipules)

Tendrils

Grape Tendrils

Stolons • Stolons or runners horizontal stem that grows above the ground with long internodes • Examples of plants that can produce stolons are strawberry and airplane plants