Root System: Definition, Types and Functions

The plants that we see today are the result of billions of years of evolution. Today, plants cover almost 30 per cent of the total landmass and account for the 50 per cent of the plant’s productivity (generation of biomass). Plants fulfill many roles in the ecosystem.

They are a source of food, nutrition, and shelter, maintain the integrity of soil (by preventing erosion) and most importantly, they are the main source for balancing the oxygen level in the atmosphere.

Anatomically, plants are very complex organisms and are classified into various types based on certain defining characteristics. Roots are very important structures that provide a variety of functions, but contrary to popular belief, all plants do not have roots. 

Roots are absent in plants like mosses and liverworts.

Read On: Flowering Plants: Structure and Characteristics

Definition of Root

Roots are the important underground part of all vascular plants. This part of the plant is mainly responsible for anchoring it down into the ground and absorbing the essential mineral elements, nutrients, and water from the soil. It is also used to store food.

Root, in botany, that part of a vascular plant normally underground.

Its primary functions are anchorage of the plant, absorption of water and dissolved minerals and conduction of these to the stem, and storage of reserve foods.

The root differs from the stem mainly by lacking leaf scars and buds, having a root cap, and having branches that originate from internal tissue rather than from buds.

However, not all plants have their roots underground; some plants have their roots growing above the ground.

These are called aerial roots. Alike underground roots, these aerial roots are also responsible for absorbing nutrients, anchoring and affixing the plant by supporting them to the structures such as nearby walls, rocks, trellises, etc. 

Few examples of plants with the aerial roots are–Bonsai, Banyan Tree, Mangroves, etc.

What is Root System?

Root System The root system is the part of the plant growing in the soil. This excludes the underground stems which are organs of perennation (survival from year to year by vegetative means). 

There are two kinds of root systems, namely: tap root and fibrous root system. The root system develops from radicle of embryo which normally stays below the ground, and because it never bears leaves or flowers is not divisible into nodes and internodes.

Read On: Ferns: Characteristics, Vegetative Structure, Nutrition, Reproduction and Biological and Economic Importance

Types of Root Systems

Plants have three types of root systems:

1. Taproot, with a main taproot that is larger and grows faster than the branch roots.

2. Fibrous, with all roots about the same size

1. Tap Root System:This system is characteristic of the dicotyledonous plants. There is just one main root known as the tap root growing deep down and giving rise to smaller branches, the lateral roots. Tap roots are firm, if the primary radicle establishes itself to become a permanent and clearly defined organ, then together with its lateral branches it forms a tap root system and the primary radicle become the tap root.

2. The Fibrous Root System: This is characteristic of monocotyledonous plants. In this system, there is a mass of roots arising from the base of the stem. The mass consists of several main roots of approximately the same size. These give off numerous branch roots which in turn give off other branch roots of smaller size. The roots are slender in appearance.

Both the main and branch roots bear a root cap at their tips. The root cap protects the soft growing regions of the root tips. Here the cells are actively dividing to add new cells to the root. A little above the root tips are some unicellular root hairs used for absorption of water and mineral salts from the soil into the plant body.

The root hairs are very numerous and tiny and should not be confused with the very small branch roots seen after an intact plant has been uprooted from the soil. One may need a microscope to observe the root hairs if they have not been damaged by uprooting.

The root begins to thicken above the root hair region. Root produced from parts other than the radicle of a seed is known as adventitious roots. For example, the prop roots of maize which grows from the lower nodes of the stem into the soil.

The roots seen in stem tubers, rhizomes, bulbs and corms are all adventitious roots.

Characteristics of Roots

The general characteristics of roots are as follows:

1. Roots grow inside the ground except for some modified aerial roots

2. Roots lack buds

3. Roots end in caps (stems end in buds)

4. Roots do not bear green pigments or chlorophyll

5. Roots possess unicellular hairs known as root hairs. (Hairs found in some stems and leaves are multicellular)

6. Nodes and intermodals are absent in roots.

Read On: Mosses: Characteristics, Reproduction and Economic Importance

Functions of Roots

The Main Importance Functions of Roots are:

1. For absorption of water and dissolved mineral salts from the soil into the plant body through the root hairs.

2. For anchoring the whole plant firmly to the soil

3. Certain roots become modified to perform some special functions such as food storage, vegetative reproduction, climbing, breathing in water-logged soil and for extra support to the plant.

Modification of Roots

These will be summarized with reference to the particular function the modification serves. Both tap and fibrous roots may be modified for support, food storage or climbing.

Types of Modified Roots

Root-Ilibers:These are roots which become swollen with food reserves. Hence they are called storage organs. Examples are seen in the tap roots of carrot, (Boerhaavia diffusa) and lateral roots of cassava.

Climbing Roots:They are also known as clasping or adhering roots. These are aerial roots growing into cracks, walls, or barks of host plants. By clasping the host for support they are able to climb high.

InFicus pumila, the aerial roots appear in clusters at the nodes.

In Scindapus sp., the clasping roots grow downwards and on getting to the soil they develop lateral roots. In black pepper, the small roots of the plant produce sticky substance that helps to gum it to the host tree or wall.

Breathing Roots:These are special roots possessed by some plants in the swamps for breathing in the air. These breathing roots or pneumatophores, are lateral branches growing above the soil which is often water logged. Good examples are seen in raphia and the white mangrove.

Prop Roots:These are clusters of roots growing from the nodes of a stem straight into the soil for extra support to the plant. Prop roots occur in maize.

Stilt Roots:These are branches from the base of certain trees which grow in muddy places and they help in the support of the plant. In the umbrella tree, for example, the trunk narrows at the base from where the stilt roots develop to provide the necessary support. Stilt roots are also seen in the red mangrove.

Buttress Roots:These are enlarged growths on the upper edges of normal lateral roots of some huge trees such as silk cotton tree. Buttress roots also act as support to the plant as well as providing good hiding places for some forest animals.

Ephiphytic Roots:These are produced by plants growing on another plant with special aerial roots eg. epiphytic orchid. The plants with such roots are not parasitic.

Sucking Roots:These are developed by parasitic plants. Such roots are called haustoria e.g. dodder (cuscuta sp) and mistletoe.

Internal Structure of the Root

Internally, a root consists of an outer cylinder and an inner central cylinder or stele. A transverse section of a root shows the following arrangement of tissues from the circumference to the centre.

Outer Cylinder: Piliferous layer and Cortex, includes the endodermis

Inner Cylinder or Stele: Pericycle and Vascular tissuepith

The outer cylinder consists of a wide zone of loosely packed, thin-walled parenchyma bound on the outside by a single-cell thick piliferous layer.

Roots hairs arise from young cells of the piliferous layer. The endodermis is the innermost layer of the cortex. It is made up of a single-cell thick layer of barrel-shaped cells. Each cell is encircled by a thick waxy band.

The stele consists of vascular tissue made up of alternate phloem and xylem bundles arranged in a ring.

Usually, there are more vascular bundles in a monocotyledonous root than a dicotyledonous one. The pericycle which bounds the vascular tissue on the outer side is a one- or two cell thick layers of thin-walled cells.

The pith which is large in monocotyledonous roots is composed of thin-walled parenchyma.

In most dicotyledonous roots, the xylem fills up the centre of the stele, forming a centrally supporting column. The main supporting tissues in roots are xylem and the turgid parenchyma which makes up the cortex Note: Cambium, a meristematic tissue which gives rise to secondary growth, appears in older dicotyledonous roots but is completely absent in monocotyledonous roots.

Commonly Question Asked

What are the different types of root systems?

The different types of root systems are:

1.     Taproots

2.     Fibrous roots

What are the primary and secondary roots?

Primary roots are the early roots in young plants that consist of taproots, basal roots, and lateral roots. Secondary roots are the side branches of the primary roots.