Plant Organ

ROOT

Roots are the principal water-absorbing organs of a plant.

Roots can also be aerial or aerating (growing up above the ground or especially above water)

Function:

To absorb or take in water and minerals from the ground

To hold the plant in place. To store food for the plant

) Prop roots: Prop roots grow from the stem to the ground. They give extra support to the plants.

b) Buttress roots: Buttress roots are large roots on all sides of a tall or shallowly rooted tree. Typically they are found in rain forests where soils are poor so roots don't go deep. They prevent the tree from falling over and help gather more nutrients. They are there to anchor the tree and soak minerals and nutrients from the ground, a function that would prove difficult if the tree was unsoundly rooted.  

Modified/Specialized Roots

Aerial Roots: 

Aerial roots are roots above the ground. They are almost always adventitious. They can absorb water from the air.They are also used to hold on to their support. They are found in diverse plant species, including epiphytes also known as air plants, which includes the orchids, tropical coastal swamp trees such as mangroves.

Clasping roots:  Clasping roots grow from the nodes of the soft stem to cling on to other

plants

Storage roots: Storage roots are swollen with nutrients and water to prepare for unfavourable conditions. Some are swollen main roots. Examples: carrot. Others are swollen branched roots or adventitious.

Respiratory roots: Some plants in swampy areas have branch roots that grow upwards, through the mud and into the air. The exposed parts of the roots are spongy and they take in air for respiration.

Parasitic Roots Some plants live on other plants and get food materials from their hosts. Parasitic roots are used to absorb food materials form their hosts.

Specialized Roots

Aerial root: Aerial roots are adventitious roots formed on above the ground surface of the earth or water. They function as prop roots or anchor roots.

E.g. Epiphytes (orchids), mangroves, banyan tree (Ficus benghalensis), ivy (Hedera helix) etc.

Buttress root: Buttress roots are form of prop root that develop board like growth on the upper side of the tree and assist with support of the trunk against lateral forces. It serves as effective tension members to prevent uprooting. Many tropical tress are buttress roots e.g. Ceiba pentandra

Contractile roots: Contractile roots is a specialized thickened root and it serves to pull down a rhizome, bulb, corn, etc., to an appropriate level in the soil e.g. Crocus, Allium species

Fibrous roots: Fibrous root is a specialized root system in which both primary and lateral roots are divided with equal diameters. Most of the monocots are fibrous roots consisting of an extensive massive of similar size of roots e.g. Coconut palm, Trifolium repens, grass roots

Fleshy roots: Fleshy roots store nutrient reserves in the fleshy roots. Their roots are larger in diameter and soft to the touch

E.g. Beta vulgaris, carrot Haustorial roots: It penetrates into the

host tissues for nutrient absorption. Plants with haustorial roots have a tendency to suck the life out of plants around them. e.g. Viscum album, Cuscuta, Rafflesia

Pneumatophorous roots: Pneumatophorous roots contains spongy aerenchyma tissues of plants living in swampy soils

Still roots: Still roots are adventitious support roots (mangroves). They grown from lateral branches, branching in the soil surface

Tuberous roots: These types of roots are thick, soft and round in shape and they contain more storage tissue than most roots. e.g. Sweet potatoes

Taproot: A taproot is a primary root that grows downward into the ground. From main root it creates a central root from which others develop. e.g. dandelions, radishes, and carrots.

Internal Structure of the Root of a Typical Dicotyledonous Plant Root structure:a) Epidermis: Outer layer of cells ("skin"). Protection.b) Root Hair: An extension of specialized root epidermal cells increasing surface area for absorption of water & minerals.c) Cortex: Region between epidermis & vascular cylinder. Supports plant parts & stores food.d) Endodermis: Layer of cells just outside vascular cylinder.e)Pericycle: Cylindrical layer of cells inside endodermis. Origin of cork & secondary (side) roots.

f) Vascular Cylinder: Arrangement of vascular tissues as a central cylinder in roots. This is shown as the large circular area in the middle of both diagrams.g) Xylem: Living (outer) vascular system carrying water & minerals throughout plant.h) Phloem: Living (inner) vascular system carrying dissolved sugars and organic compounds throughout plant.

External Structure

a) Root Hairs: Outward extensions of epicermal cells which extend between soil particles to collect water and solutes (minerals).Region of Maturation: Older section of root tip where the root begins adding cells to increase the width, and where root hairs form.

b) Region of Maturation: Older section of root tip where the root begins adding cells to increase the width, and where root hairs form.

c) Region of Elongation: Region of root tip where cells get longer, thus lengthening the root. This is the only place where the root grows longer.

d) Region of Rapid Growth: Region where cells divide rapidly by mitosis.

e) Apical Meristem: Cells near the tip that can divide by mitosis to make any type of plant cell.

f)Root Cap: Dome-shaped mass of cells at the tip which protect the meristem cells from damage (as root extends through soil).

Kinds of Root Systems› Taproot System

has prominent primary root› Fibrous (diffuse) System

Primary root is lost and replaced by numerous adventitious roots arising from the lower portion of the stem

Slender in form and are more or less equally prominent

Tap root system

Tap root is common in dicots; the first or primary root grows straight down and remains dominant root of a plant; often fleshy and adapted to store food (e.g., carrots, beets)

The fibrous root system of monocots is a mass of slender roots and lateral branches that hold the plant secure in the soil.

Fibrous root system