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 This lateral section of a root tip is divided into three areas: an upper area of maturation, a middle area of elongation, and a lower area of cell division at the root tip. In the area of maturation, root hairs extend from the main root and cells are large and rectangular. The area of elongation has no root hairs, and the cells are still rectangular, but somewhat smaller. A vascular cylinder runs through the center of the root in the area of maturation and the area of elongation. In the area of cell division the cells are much smaller. Cells within this area are called the apical meristem. A layer of cells called the root cap surrounds the apical meristem.
A longitudinal view of the root reveals the zones of cell division, elongation, and maturation. Cell division occurs in the apical meristem.

The root has an outer layer of cells called the epidermis, which surrounds areas of ground tissue and vascular tissue. The epidermis provides protection and helps in absorption. Root hairs , which are extensions of root epidermal cells, increase the surface area of the root, greatly contributing to the absorption of water and minerals.

Inside the root, the ground tissue forms two regions: the cortex and the pith ( [link] ). Compared to stems, roots have lots of cortex and little pith. Both regions include cells that store photosynthetic products. The cortex is between the epidermis and the vascular tissue, whereas the pith lies between the vascular tissue and the center of the root.

 The micrograph shows a root cross section. Xylem cells, whose cell walls stain red, are in the middle of the root. Patches of phloem cells, stained blue, are located at the edge of the ring of xylem cells. The pericycle is a ring of cells on the outer edge of the xylem and phloem. Another ring of cells, called the endodermis, surrounds the pericycle. Everything inside the endodermis is the sclera, or vascular tissue. Outside the endermis is the cortex. The parenchyma cells that make up the cortex are the largest in the root. Outside the cortex is the exodermis. The exodermis is about two cells thick and is made up of sclerenchyma cells that stain red. Surrounding the exodermis is the epidermis, which is a single cell layer thick. A couple of root hairs project outward from the root.
Staining reveals different cell types in this light micrograph of a wheat ( Triticum ) root cross section. Sclerenchyma cells of the exodermis and xylem cells stain red, and phloem cells stain blue. Other cell types stain black. The stele, or vascular tissue, is the area inside endodermis (indicated by a green ring). Root hairs are visible outside the epidermis. (credit: scale-bar data from Matt Russell)

The vascular tissue in the root is arranged in the inner portion of the root, which is called the vascular cylinder ( [link] ). A layer of cells known as the endodermis separates the vascular tissue from the ground tissue in the outer portion of the root. The endodermis is exclusive to roots, and serves as a checkpoint for materials entering the root’s vascular system. A waxy substance called suberin is present on the walls of the endodermal cells. This waxy region, known as the Casparian strip , forces water and solutes to cross the plasma membranes of endodermal cells instead of slipping between the cells. This ensures that only materials required by the root pass through the endodermis, while toxic substances and pathogens are generally excluded. The outermost cell layer of the root’s vascular tissue is the pericycle , an area that can give rise to lateral roots. In eudicot roots, the xylem and phloem are arranged alternately in an X shape, whereas in monocot roots, the vascular tissue is arranged in a ring around the pith.

 The cross section of a dicot root has an X-shaped structure at its center. The X is made up of many xylem cells. Phloem cells fill the space between the X. A ring of cells called the pericycle surrounds the xylem and phloem. The outer edge of the pericycle is called the endodermis. A thick layer of cortex tissue surrounds the pericycle. The cortex is enclosed in a layer of cells called the epidermis. The monocot root is similar to a dicot root, but the center of the root is filled with pith. The phloem cells form a ring around the pith. Round clusters of xylem cells are embedded in the phloem, symmetrically arranged around the central pith. The outer pericycle, endodermis, cortex and epidermis are the same in the dicot root.
In (left) typical eudicots, the vascular tissue forms an X shape in the center of the root. In (right) typical monocots, the phloem cells and the larger xylem cells form a characteristic ring around the central pith.

Root modifications

Root structures may be modified for specific purposes. For example, some roots are bulbous and store starch. Aerial roots and prop roots are two forms of aboveground roots that provide additional support to anchor the plant. Tap roots, such as carrots, turnips, and beets, are examples of roots that are modified for food storage ( [link] ).

 Photos shows a variety of fresh vegetables in a grocery store.
Many vegetables are modified roots.

Epiphytic roots enable a plant to grow on another plant. For example, the epiphytic roots of orchids develop a spongy tissue to absorb moisture. The banyan tree ( Ficus sp.) begins as an epiphyte, germinating in the branches of a host tree; aerial roots develop from the branches and eventually reach the ground, providing additional support ( [link] ). In screwpine ( Pandanus sp.), a palm-like tree that grows in sandy tropical soils, aboveground prop roots develop from the nodes to provide additional support.

Questions & Answers

Application of nanotechnology in medicine
what is variations in raman spectra for nanomaterials
Jyoti Reply
I only see partial conversation and what's the question here!
Crow Reply
what about nanotechnology for water purification
RAW Reply
please someone correct me if I'm wrong but I think one can use nanoparticles, specially silver nanoparticles for water treatment.
Damian
yes that's correct
Professor
I think
Professor
what is the stm
Brian Reply
is there industrial application of fullrenes. What is the method to prepare fullrene on large scale.?
Rafiq
industrial application...? mmm I think on the medical side as drug carrier, but you should go deeper on your research, I may be wrong
Damian
How we are making nano material?
LITNING Reply
what is a peer
LITNING Reply
What is meant by 'nano scale'?
LITNING Reply
What is STMs full form?
LITNING
scanning tunneling microscope
Sahil
how nano science is used for hydrophobicity
Santosh
Do u think that Graphene and Fullrene fiber can be used to make Air Plane body structure the lightest and strongest. Rafiq
Rafiq
what is differents between GO and RGO?
Mahi
what is simplest way to understand the applications of nano robots used to detect the cancer affected cell of human body.? How this robot is carried to required site of body cell.? what will be the carrier material and how can be detected that correct delivery of drug is done Rafiq
Rafiq
if virus is killing to make ARTIFICIAL DNA OF GRAPHENE FOR KILLED THE VIRUS .THIS IS OUR ASSUMPTION
Anam
analytical skills graphene is prepared to kill any type viruses .
Anam
what is Nano technology ?
Bob Reply
write examples of Nano molecule?
Bob
The nanotechnology is as new science, to scale nanometric
brayan
nanotechnology is the study, desing, synthesis, manipulation and application of materials and functional systems through control of matter at nanoscale
Damian
Is there any normative that regulates the use of silver nanoparticles?
Damian Reply
what king of growth are you checking .?
Renato
What fields keep nano created devices from performing or assimulating ? Magnetic fields ? Are do they assimilate ?
Stoney Reply
why we need to study biomolecules, molecular biology in nanotechnology?
Adin Reply
?
Kyle
yes I'm doing my masters in nanotechnology, we are being studying all these domains as well..
Adin
why?
Adin
what school?
Kyle
biomolecules are e building blocks of every organics and inorganic materials.
Joe
anyone know any internet site where one can find nanotechnology papers?
Damian Reply
research.net
kanaga
sciencedirect big data base
Ernesto
Introduction about quantum dots in nanotechnology
Praveena Reply
hi
Loga
what does nano mean?
Anassong Reply
nano basically means 10^(-9). nanometer is a unit to measure length.
Bharti
how did you get the value of 2000N.What calculations are needed to arrive at it
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Source:  OpenStax, Principles of biology. OpenStax CNX. Aug 09, 2016 Download for free at http://legacy.cnx.org/content/col11569/1.25
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