Roots are the characteristic underground organs of angiosperms* (In some aquatic angiosperms, e.g., Ceratophyllumn, Lemna, Myriophyllum and Wolfia roots are absent. On the other hand in Podostemon the main plant body is root which carries out assimilation and reproduction) and most other vascular plants gymnosperms and pteridophytes). The root system of plant develops from the hypocotyl of the embryo of a seed. The basal end of the hypocotyl the radicle, grows out to form the first or primary root of the plant. This forms the original root system of the seedling in all angiosperms and is called seminal root. In dicotyledons this root survives whereasS in monocotyledons the seminal roots die early and are replaced by adventitions roots. The root is an important basic organ of the plant because of its two major functions absorption of water and minerals from the soil and fixation of plant in the soil. Roots are usually sub-cylindrical, tapering towards the tip. In comparison to stem, roots are much more crooked (bent) because of their growth in between the soil particles.
Table of Contents
“A TREE WITH STRONG ROOT LAUGH AT STROMS”
Characteristics of Root protect part
(I) Root forms the descending organ of the which plant axis, normally growing away from the light (i.e., negatively phototropic). Root growth is generally directed (i.e., positively gravity, towards geotropic) except for the breathing roots (pneumatophores) of plants growing in marshy and saline soils which project out of the soil surface.
(2) Normally roots lack chlorophyll and, hence, are non-green. However, roots of certain plants, which are exposed to light for long periods, turn green.
(3) Roots show much variability in their shape and structure. It is related either environmental to their function or conditions.
(4) Roots do not bear buds, leaves and flowers. They lacknodes and internodes.
(5) Root hairs are always unicellular.
(6) The root apex is protected by a root cap. Thus in real sense, the root apex is not apical but sub-apical.
(7) The branch roots (lateral roots) are produced endogenously from pericycle.
Regions or Parts of Root
The root shows Tolowing four regions (These usually merge into one another, without distinct boundaries between them). The zones successively from the apex to the base, are as follows:
(1) Root cap,
(2)Region of cell division or apical meristem
(3)Region of elongation and
(4) Region of maturation.
what is Root cap describe about root cap?
The apex of each root is covered by a cushion of walled cells known as root cap. Multiple thin root cap is present in Pandanus, In aquatic plants (e.g., Pistia, Eichhornia, etc.) the root apex 1s apex 1sec closed within a sac-like structure called root The primary function of root cap 1s
what is pocket. Describe about pocket?
The primary function of root cap protect the root apex which is the main grow part of the root. It also secretes certain substance which help the root in penetrating the soil. Region of root apical meristem It lies just behind the root cap. It is the main wing region of the root where active cell is ions take place It is composed of densely alasmic, thin walled parenchymatous cells with no intercellular spaces. Iis region extends a few millimeters in length.
Region of elongation. What is Region of elongation? describe about Region of elongation?
Region of elongation It is 1-10 millimeters in length. This region is characterised by the rapid elongation of cells; divisions Occur in relatively small number of cells. The region of elongation is responsible for growth in length of the root.
Region of maturation. Describe about Region of maturation?
Region of maturation It is usually one to several centimeters long. Here the cells, having fully expanded, mature into final form. Epidermal cells of this region give out small, thin, cylindrical unicellular outgrowths, known as root hairs. These are the main absorbing organs of the root. Root hairs are in abundance in this part (sometimes several hundred root hairs are present per square millimeter of the epidermal Surface) and, hence, it is also called root hair region.
So, now we are going to know about what are the roots types and what is tap roots? what is adventitious roots? what are the Difference between Tap root system and adventitious root system? What are Difference Between prop roots and stilt roots? What are the Functions of Roots? What are the Modifications of Roots? What are the Modifications of Tap Roots? What are the Modifications of Adventitious Roots?
Types of Roots
On the basis of place of origin two types of roots are distinguished:
(1) Tap roots and
(2) Adventitious roots.
The root developing directly from the radicle is known as primary root. In most of the plants primary root persists and becomes stronger to form tap root. Tap root usually produces lateral branches called secondary roots.
Branches of the secondary roots in turn are called tertiary roots and so on. The branching results in small, younger branches near the tip and older and longer away from the tip. this arrangement is called acropetal.
Roots developing from any part of the plant, other than radicle, are known as adventitious roots On the basis of nature of development, the adventitious roots are further divided into the following three types.
- Fibrous roots. In this type the primary root does not persist for long. It is soon replaced by a cluster of slender, thread ike roots originating from the base of the stem, e.g., Triticum vulgare (wheat) Oryza sativa (rice), Allium cepa (onion) etc.
- Foliar roots. Roots developing from the leaf are known as foliar roots. They originate either from the petiole (e.g., Pogostemon, patchouli) or from the margins of the leaf blade (e.g., Bryophyllum).
- True adventitious roots. These roots develop from the nodes and internodes of the stem, e.g prop roots of banyan (Ficus), climbing roots of money plant (Pothos) and roots from the stem cuttings (Coleus)
Difference between Tap root system and adventitious root system.
Tap root system
- It develops from the radicle.
- It possesses primary, secondary and tertiary roots.
- The primary root persists throughout the life of the plant.
- It is always underground.
- It penetrates deep into the soil.
Adventitious root system
- It may develop from any part other than radicle; (e.g., stem, leaf, etc.)
- No such distinction occurs, all roots are alike.
- Primary root is short lived and is replaced by adventitious roots.
- These roots also develop in the aerial parts of the plant.
- Usually do not penetrate very deep into the soil.
Modifications of Roots
Roots are modified into a number of forms to carry out specific functions.
Modifications of tap root
- Fusiform roots. The primary root is swollen in the middle and gradually tapers at both the ends, i.e., towards the apex and the base; e.g.,Raphanus (radish) roots. The primary root
- Napiform roots the primary root’s becomes almost spherical and tapers abruptly at the lower end; e.g., Brassica rapa (turnip), Beta vulgaris, (beet root);: 5B)
- Conical roots. These roots are just like a cone broad at the base and gradually tapering towards the apex; e.g.,Daucas carota (carrot)
- Tuberous or tubercular roots. These roots are fleshy but do not maintain any specific
shape; e.g., Manihot esculenta (tapioca, Fig. 5D).
- Pneumatophores or knees. These special roots, called pneumatophores or knees, develop in mangrove plants, i.e., plants growing in saline marshes. These roots grow vertically upward and are negatively geotropic (Fig. 6A). Air enters these roots through minute breathing pores called pneumathodes, present on the tips of vertical roots. These plants include Rhizophora, Heritiera, Avicenia, etc., and are found in Sundarbans of West Bengal.
Modifications of adventitious roots
- Tuberous roots. These adventitious roots are swollen without any definite shape e.g., Ipomoea batatas (sweet potato).
- Fasciculated roots These are tuberous roots arising in cluster from the base of the stem;e.g., Dahlia (Dahlia, Fig. 7B), Ruellia (Menow weed), A.sparagus (Asparagus), etc.
- Moniliform or beaded roots These adventitious roots are swollen at frequent intervals. This gives the root a beaded appearance, eg Portulaca (Rose moss) Momordica (bitter gourd, Cyperus (Guinea rush).
- Nodulose roots. These roots become swollen at their tips due to accumulation of food (e.g., Maranta sp. (Arrowroot); Curcuma amanda (Mango ginger).
- Annulated roots. This type of root has many ring-like Swellings placed one at the top of other, (e.g., Cephaelis ipecachuanha: Ipecac;.
- Prop roots In trees like banyan (Ficus benghalensis) and India rubber plant (Ficus elastica) many adventitious roots arise from the horizontal branches of the stem and grow vertically downward . They become thick pillar like and provide mechanical support to the giant trees.
- Stilt roots. These are small stout roots growing obliquely from the basal nodes of the main stem. Like prop roots, they also provide mechanical support. Stilt roots are found in Zea mays (maize), Saccharum officinarum, (sugarcane); PandanuS tectorius (screwpine), etc.
- Climbing roots These roots arise from the nodes and internodes of many climbers. They help the plants in fixing themselves to their Support, e.g., Pothos (money plant), Piper betle (betel).
- Floating roots In Jussiaea, an aquatic plant, tufts of spongy, soft and light roots arise from the nodes in addition to ordinary adventitious roots. These roots have innumerable air spaces and thus help in maintaining buoyancy and facilitate respiratfon.
10 epiphytic roots. Epiphytes (plants growing on other plants) have two types of roots-clinging roots which cling to the host for support and aerial roots which hang downwards. The latter are green in colour and have special outer covering called velamen. It helps in the absorption of moisture from air e.g., Vanda sp. (orchid)
- Assimilatory roots. Aerial adventitious roots of some plants develop chlorophyll and become assimilatory in function, i.e., synthesize food, e.g., Tinospora, Trapa (water chestnut) and aerial or hanging roots of some orchids.
- Parasitic roots or sucking roots. Parasitic plants develop roots which penetrate into the tissue of the host plant to absorb nutrition. Thus these roots function as haustoria; e.g., Cuscuta (Dodder, Orobanche) etc.
- Reproductive roots. In some plants exposed part of the roots develop adventitious buds which can grow into new plants e.g.. Murraya, Trichosanthes dioica, (palwal) and guava. Thus these roots help in multiplication.
Difference Between prop roots and stilt roots.
- Prop roots arise from the horizontally placed aerial branches.
- These roots grow vertically downward and enter the soil at right angle.
- These roots act just like pillars and provide support to the horizontally growing aerial branches.
- When young, the prop roots absorb water (hygroscopic).
- Prop roots grow in thickness and sometimes it becomes difficult to differentiate them from the main stem.
6.These are usually quite long.
- These roots develop from the lower nodes of the main stem.
- These roots grow obliquely at an angle to the main stem.
- These roots are just like the ropes of a tent or stay wires of electric poles and provide support to the main stem.
- Young stilt roots do not absorb water (non-hygroscopic).
- Stult roots do not grow in thickness.
- These are comparatively short.
Functions of Root
The following are the major functions of the root
- Fixation. One of the primary functions of root is to provide anchorage to the plants. The tap root and its lateral branches spread out in all directions deep in the soil, thus fixing the plant firmly. Besides this, the prop roots and stilt roots provide mechanical support to the plant.
- Absorption. Root is the main absorbing organ of the plant. Water and minerals are of absorbed by the younger parts of the root especially the root hair region.
- Conduction. Roots are also concerned With upward transport or conduction of water and minerals to the stem and leaves.
- Storage. Roots of many plants store large amount of food. It is utilized by the plant itself during growing season and also eaten by mankind.
- Aeration. Saline and waterlogged soils are usually poor in oxygen. Plants growing in such habitats have special roots (i.e., pneumatophores which help in gaseous exchange. Besides this, roots of aquatic plants have large intercellular spaces to store air.