The lecture notes provide an understanding of the different types of roots and their morphology. different types of roots have been clearly explained with their pictures and labeled diagrams included, enjoy the reading Asangalwisye deo SJUT

1. In vascular plants, the roots are the organs of a plant that typically lie below the surface of the
soil, roots can also be aerial or aerating, that is, growing up above the ground or especially above
water. Furthermore, a stem normally occurring below ground is not exceptional either.
Therefore, the root is best defined as the non-leaf, non-nodes bearing parts of the plant's body.
There are important internal structural differences between stems and roots. Characteristics of
roots involves, non-green due to absence of chlorophyll not divided into nodes and internodes
absence of leaves and buds positively geotropic (grow towards gravity) positively hydrotropic
(grow towards water) and negatively phototropic (grow away from light)
The root system is the descending (growing downwards) portion of the plant axis. When a seed
germinates, radicle is the first organ to come out. It elongates to form primary or the tap root. It
gives off lateral branches (secondary and tertiary roots) and thus forms the root system. It
branches through large and deep areas in the soil and anchors the plant very firmly. It also plays
another vital role in absorbing water and mineral salts from the soil and transporting them
upwards.
The root system of a plant constantly provides the stems and leaves with water and dissolved
minerals. In order to accomplish these roots must grow into new regions of the soil. The growth
and metabolism of the plant root system is supported by the process of photosynthesis occurring
in the leaves. Photosynthetic from the leaves is transported via the phloem to the root system.
Root structure aids in this process. This section will review the different kinds of root systems
and look at some specialized roots, as well as describe the anatomy of the roots in monocots and
dicots.
Mainly there are two types of root system, the tap root and the fibrous root system
A. TAP ROOT SYSTEM
It is the root system that develops from the radicle and continues as the primary root (tap
root) which gives off lateral roots. They provide very strong anchorage as they are able to
reach very deep into the soil. It is the main root system of dicots e.g. gram, China rose,
and neem.it is characterized by having one main root (the taproot) from which smaller
branch roots emerge. When a seed germinates, the first root to emerge is the radicle, or
primary root. In conifers and most dicots, this radicle develops into the taproot.

2. Taproots can be modified for use in storage (usually carbohydrates) such as those found
in sugar beet or carrot. Taproots are also important adaptations for searching for water,
as those long taproots found in mesquite and poison ivy.
A PICTURE SHOWING THE STRUCTURE OF TAPROOT SYSTEM

3. B. FIBROUS ROOT SYSTEM
In this root system, the primary root is short lived. A cluster of slender, fiber-like roots
arises from the base of the radicle and plumule which constitute the fibrous root system.
They do not branch profusely, are shallow and spread horizontally, hence cannot provide
strong anchorage. Fibrous root system is the main root system of monocots, e.g. maize,
grasses, and wheat
Characterized by having a mass of similarly sized roots, in this case the radicle from a
germinating seed is short lived and is replaced by adventitious roots. Adventitious roots
are roots that form on plant organs other than roots. Most monocots have fibrous root
systems. Some fibrous roots are used as storage; for example sweet potatoes form on
fibrous roots. Plants with fibrous roots systems are excellent for erosion control, because
the mass of roots cling to soil particles
A PICTURE SHOWING THE STRUCTURE OF A FIBROUS ROOT SYSTEM

4. Mainly there are two types of roots, tap root and adventitious root
I. TAP ROOT.
The first root that is formed by the elongation of the radicle of the embryo in the seed is
called tap root. It has three different forms, fibrous tap root, tuberous tap root and
biennial plants
 Fibrous tap root are found in herbaceous annual plants, such as bean and pea, tap
root elongates and gives off branches, long and slender tap root is called fibrous
nodulated roots. In medicago the tap root bears small swellings of nodules (these
bacteria fix nitrogen and forms nitrates), these bacteria provide nitrates to plants
and in return get protection and shelter from roots
A PICTURE SHOWING TAP AND FIBROUS TAPE ROOT
 Tuberous tap root
When the tap roots are thick and store reserve food, they are called as tuberous
roots. Occurs in biennial plants examples: carrot, radish, turnip and beet, oak,
dandelion

5. A picture showing tuberous tap root
 Biennial plants
These plants live for two seasons in the first season they produce leaves only and
store up the surplus food in the tap root in the nest season, they use that stored
food for flower production, after they die. Conical tap root: it is swollen form the
top and tapering from the ends e.g. English radish and English carrot. Napiform
tap root: this type of root is very much swollen form the tap and abruptly tapers
from the lower side. E.g. turnip and beet
A PICTURE SHOWING A BIENNIAL PLANT

6. II. ADVENTITIOUS ROOT
Roots which arose from the stem, leaves, other than radicle part is called adventitious
root. Various forms of adventitious roots are present. Subterranean or underground
adventitious roots, partly subterranean adventitious roots, aerial roots, parasitic roots, and
aquatic roots
 Subterranean or underground adventitious roots. They arose from the part of stem,
which is in contact with soil. They may be of fibrous or adventitious type
o Fibrous adventitious root: They are long and slender commonly creeping
on underground stem. E.g. grasses, ginger
A picture of a ginger
o Tuberous adventitious root: They are swollen and fleshy, containing stored
food. They are present in Dahlia, sweet potato and many orchids .In dahlia
and sweet potato some roots remain fibrous, while others enlarge greatly
to form tubers
A picture of sweet potato

7.  Partly subterranean adventitious roots. They are present partly above or partly
below the ground. They may be classified into stilt roots, prop roots, aerating
roots
o Stilt roots. when the roots arise from the lower portion of the stem and
grow obliquely down into the soil where they develop in the normal
manner they are called stilt roots they fix the plant firmly in soil and keep
it erect examples : maize , sugar cane, bamboo ,palms
A picture of a sugar cane
o Prop roots. These roots grow vertically downward in the air from which
they absorb moisture on reaching the soil they absorb water and minerals
from it, after this they behave as stouter and form props and pillars which
support the branches, banyan tree ( Ficus bengalensis), and rubber tree (
Ficus elastic )
A picture of banyan tree

8. o Pneumatophore roots/aerating roots. Such roots are found in plant growing
in mangroves or swamps near the sea-shore. Pneumatophores arise
vertically upwards and come out of soil and water. They bear small pores
called pneumatophores or lenticels for exchange of gases, e.g. Heritiera.
A photo showing pneumatophore
 Aerial roots. They are exposed to air and carry specific functions. They are of two
types, clinging or climbing roots and absorbing roots
o Clinging or climbing roots. They are developed from stem, They are
sensitive to touch and support, they secrete a fluid and when they are
exposed to air, that dries up , helps plant to support sometimes they form
disc like structure , to ensure the firm attachment with the host Ivy
(Hedera helix) Long pepper ( Pipper longum)

9. A picture showing climbing roots
o Absorbing roots. These are present in epiphytes in tropical rain forest, they
have long adventitious roots which hang freely in air and absorb moisture
from air, and these roots are covered by dead, spongy tissue called as
velamen. That absorbs and store water
A picture showing absorbing root
 Parasitic roots. In parasitic flowering plants, various roots arise from the stem of
the plant where it is near to its host. They are also called as haustoria they
penetrate into the stem and become connected with its conducting tissue they

10. absorb the manufactured food from the host and pass it to the stem of parasitic
plant Cuscutta.
A picture of parasitic root
 Aquatic roots. In many water plants, clusters of fibrous adventitious roots arise
from the stem and dangle (swing) in water. They are usually without root hairs
A picture showing aquatic root
ROOT STRUCTURE AND THEIR FUNCTIONS
Root Tip: the end 1 cm of a root contains young tissues that are divided into the root cap,
quiescent center, and the sub apical region.
Root Cap: root tips are covered and protected by the root cap. The root cap cells are derived
from the root cap meristem that pushes cells forward into the cap region. Root cap cells
differentiate first into columella cells. Columella cells contain amylopasts that are responsible for
gravity detection. These cells can also respond to light and pressure from soil particles. Once

11. columella cells are pushed to the periphery of the root cap, they differentiate into peripheral
cells. These cells secrete mucigel, a hydrated polysaccharide formed in the dictyosomes that
contains sugars, organic acids, vitamins, enzymes, and amino acids. Mucigel aids in protection
of the root by preventing desiccation. In some plants the mucigel contains inhibitors that prevent
the growth of roots from competing plants. Mucigel also lubricates the root so that it can easily
penetrate the soil. Mucigel also aids in water and nutrient absorption by increasing soil: root
contact. Mucigel can act as a chelator, freeing up ions to be absorbed by the root. Nutrients in
mucigel can aid in the establishment of mycorrhizae and symbiotic bacteria.
Quiescent Center: behind the root cap is the quiescent center, a region of inactive cells. They
function to replace the meristematic cells of the root cap meristem. The quiescent center is also
important in organizing the patterns of primary growth in the root.
Sub apical Region: this region, behind the quiescent center is divided into three zones. Zone of
Cell Division - this is the location of the apical meristem (~0.5 -1.5 mm behind the root tip).
Cells derived from the apical meristem add to the primary growth of the root. Zone of Cellular
Elongation - the cells derived from the apical meristem increase in length in this region.
Elongation occurs through water uptake into the vacuoles. This elongation process shoves the
root tip into the soil. Zone of Cellular Maturation - the cells begin differentiation. In this region
one finds root hairs which function to increase water and nutrient absorption. In this region the
xylem cells are the first of the vascular tissues to differentiate.
A DIAGRAM SHOWING A LONGITUDINAL SECTION OF A ROOT TIP

12. Mature Root: the primary tissues of the root begin to form within or just behind the Zone of
Cellular Maturation in the root tip. The root apical meristem gives rise to three primary
meristems: protoderm, ground meristem, and procambium.
Epidermis: the epidermis is derived from the protoderm and surrounds the young root one cell
layer thick. Epidermal cells are not covered by cuticle so that they can absorb water and mineral
nutrients. As roots mature the epidermis is replaced by the periderm.
Cortex: interior to the epidermis is the cortex which is derived from the ground meristem. The
cortex is divided into three layers: the hypodermis, storage parenchyma cells, and the
endodermis. The hypodermis is the suberinized protective layer of cells just below the
epidermis. The suberin in these cells aids in water retention. Storage parenchyma cells are thin-
walled and often store starch. The endodermis is the innermost layer of the cortex. Endodermal
cells are closely packed and lack intercellular spaces. Their radial and transverse walls are
impregnated with lignin an suberin to form the structure called the Casparian Strip. The
Casparian Strip forces water and dissolved nutrients to pass through the symplast (living portion
of the cell), thus allowing the cell membrane to control absorption by the root.
Stele: all tissues inside the endodermis compose the stele. The stele includes the outer most
layers, pericycle, and the vascular tissues. The pericycle is a meristematic layer important in
production of branch roots. The vascular tissues are made up of the xylem and phloem. In
dicots the xylem is found as a star shape in the center of the root with the phloem located
between the arms of the xylem star. New xylem and phloem is added by the vascular cambium
located between the xylem and phloem. In monocots the xylem and phloem form in a ring with s
the central portion of the root made up of parenchymatous pith.

13. A picture showing cross section of a matured root
FUNCTIOS OF PLANT ROOTS
Despite being inconspicuous because they are normally hidden underground, the plant root
system performs various functions which are essential to growth and development. The extent of
underground expansion of this plant structure serves as limitation in the growth of the plant.
Thus potted plants usually exhibit slow growth but once the roots leak out from the bottom of the
pot and penetrate into the ground, growth rate accelerates. The functions of the plant root system
include:
1. Anchorage and support. The plant root system anchors the plant body to the soil and provides
physical support. Redwood trees (a gymnosperm) about 100 meters tall have stood erect for
thousand years only because millions of individual fibrous roots dig into the ground, even though
the depth of penetration is only up to about 5 meters. In general, however, taproot system
provides more effective anchorage such that they are more resistant to toppling during storms.
2. Absorption and conduction. The plant root system absorbs water and nutrients from the soil in
mineral solution, mainly through the root hairs. They are capable of absorbing inorganic
nutrients in solution even against concentration gradient. From the root, these are moved upward.

14. Plants with a fibrous root system are more efficient in absorption from shallow sources.In the
desert plants called phreatophytes like the mesquite, the roots seek permanent underground water
reserves. These plants are water indicators and knowledge of such plants has been put to use by
digging wells where they grow.
3. Storage. The root serves as storage organ for water and carbohydrates as in the modified,
swollen roots of carrot, sweet potato (camote) and yam bean (sinkamas). Fibrous roots generally
store less starch than taproots. Some roots are capable of storing large amounts of water; the
taproots of some desert plants store more than 70 kg of water
4. Photosynthesis. Some roots are capable of performing photosynthesis, as in the epiphytic
orchids and aerial roots of mangrove trees.
5. Aeration. Plants that grow in stagnant water or other watery places have modified roots called
pneumatophores to which oxygen from the air diffuses.
6. Movement. In many bulb- and corm-forming plants, contractile roots pull the plant downward
into the soil where the environment is more stable.
7. Reproduction. The plant root system also serves as a natural means of perpetuating a species.
In mature agoho or horsetail tree (Casuarina equisetifolia) and certain plants, clonal seedlings or
offshoots are commonly seen growing profusely around the trunk from horizontally growing
roots. Likewise, new plants emerge from left-over tuberous roots after harvest in fields grown to
sweet potato (Ipomaea batatas) and yam bean (Pachyrhizus erosus). As a rule, plants with a
fibrous root system are easier to transplant than those with tap roots.

15. MODIFICATIONS OF ROOTS
In some plants, the roots change their shape and get modified to absorb and transport water and
minerals from the soil to different parts of the plant. They are also modified for support, food
storage, and respiration. The root modifications to perform two major functions- Physiological
and Mechanical.
i. Modification of tap roots.
a) For food storage
In some plants, the roots become fleshy due to the absorption of food material, the aerial parts of
these plants worn out due to unfavorable conditions. When the conditions are favorable again
new buds emerge either from the fleshy root or from a small bit of stem above. The taproots of
carrot and turnip get swollen to store food.
Depending upon their shapes, they are classified as;
 Conical roots are broad at the base and conical at the apex, example, carrot
 Fusiform roots are swollen in the middle and tapering towards both the ends, example,
radish
 Napiform roots are spherical at the base and taper towards the apex, example, turnip
 Tuberous roots have no specific shape. They appear thick and fleshy, example, 4’O clock
plant.
b) For better Respiration
In some halophytes such as Rhizophora that grow in swampy areas, the roots emerge out of the
ground and grow upwards to get oxygen for respiration. The root tips of these plants have minute
pores called lenticels through which they respire
c) Nodulated Roots

16. Roots of the leguminous plants are modified into root nodules which contain nitrogen-fixing
bacteria such as Rhizobium. They help in fixing the atmospheric nitrogen into nitrates and make
it available to the plant
ii. Modification of Adventitious Roots
a) For food storage
Adventitious roots are modified into:
 Simple Tuberous Roots are swollen and do not assume any shape. For example., sweet
potato
 Nodulose Roots are single beads. They become swollen at the apex and have a definite
shape, example., ginger
 Fasciculated Tuberous Roots is the cluster of adventitious roots for food storage. They
have a definite shape, example., Dahlia
 Moniliform Roots are swollen and constricted, example., grasses
 Annulated Roots has an appearance of discs placed one over the other, example., Ipecac
b) For support
 Prop Roots: These roots develop from the branches of the tree, hang downwards, and
penetrate into the ground thereby supporting the tree. Example, roots of the banyan tree.
 Stilt Roots: These roots grow obliquely from the basal node of the stem. Example, roots
of the sugarcane.
 Climbing Roots: These roots arise from the nodes and attach themselves to some support
to climb over it. Thus they provide support to the plant. Example., Money plant
 Clinging Roots: These roots enter the crevices of some support and fix the plant.
Example., epiphytes orchids

17.  Buttress Roots: These are vertically elongated basal part of the stem which spread in
different directions in the soil. These are horizontally compressed and appear like planks.
Example, Bombax
c) For special functions.
 Epiphytic Roots: These roots are aerial hanging and spongy. They have a porous wall and
absorb moisture from the atmosphere. These aerial roots possess a special sponge-like
tissue known as velamen. Velamen absorbs and stores moisture from the air since these
plants do not have direct contact with the soil.
 Sucking Roots: These are microscopic roots developed by the roots to
absorb nutrients from the host. These are also known as parasitic roots or haustoria
because these are found in non-green parasitic plants. These roots arise from the nodes
and penetrate into the host tissue. They then enter into the conducting tissue from where
they obtain the required food material.
 Floating Roots: These arise from the nodes of the aquatic plants and help in floating and
respiration. Example, Jussiaea. These roots are very spongy in nature and look like a
mass of white cotton. The plant floats due to its buoyancy. They dry when taken out of
the water.
 Assimilatory Roots: These are also known as photosynthetic roots. These, when exposed
to the sun, develop chlorophyll and manufacture food. Example, In Tinospora, the roots
hang as green threads from the nodes during the rainy season. They assimilate carbon
dioxide in the presence of sunlight.
 Mycorrhizal Roots: The symbiotic association of a fungus with higher plants is called
mycorrhizal root. The fungus absorbs nutrients from the soil for the plant, and the plant,
in turn, provides organic food to it. Example, Pinus
 Reproductive Roots: In some plants such as sweet potato, the adventitious roots give rise
to buds which develop into leafy shoots. Root cuttings are the main mode of
reproduction.

18. Lastly, Plant root systems secure the uptake of water and nutrients from soil, provide anchorage,
and integrate signals from the rhizosphere. The basic architecture of the root stock is determined
by an endogenous genetic program, whereas its developmental plasticity allows the root system
to adapt to changing environmental cues. In general, the cellular organization of angiosperm
roots is similar. Nevertheless, the simple structure and transparency of Arabidopsis thaliana roots
made this dicotyledonous species a premier model for the genetic dissection of plant root
development. The Arabidopsis root comprises only 15 different cell types. In transverse
orientation, root cells are organized in concentric cell files around the central cylinder. Among
those, the outermost cell layer of the central cylinder, the pericycle, gives rise to newly emerging
lateral roots, while the outermost cell file of the root, the epidermis, connects the root with the
soil environment. Longitudinally, roots are organized in a meristematic zone at the root tip,
distally followed by the elongation and differentiation zones. The four to seven quiescent center
cells in the Arabidopsis root tip keep the surrounding meristematic cells in their undifferentiated
state. As new root cells are produced by division of meristematic cells, older cells are displaced
away from the meristem into the elongation and differentiation zones. Hence, roots provide a
developmental gradient in which cell age correlates with the distance from the root tip with the
youngest cells in the meristematic zone around the root tip. The stereotypic cell lineage found in
Arabidopsis allows each tier of cells to be clonally traced back in the Arabidopsis root to its
founder cell.
The root system of Arabidopsis consists of a single primary root preformed during
embryogenesis and lateral roots initiated from pericycle cells of the primary root during
postembryonic development. In contrast, monocot cereals such as maize or rice form different
root types during development. In addition to a single embryonic primary root, an extensive
shoot-borne root system forms the major backbone of the cereal root system during
postembryonic development. Histological differences between Arabidopsis and cereals are
reflected, for instance, by distinct numbers of cells and cell tiers and different modes of root hair
patterning.

19. REFERENCES
Heywood, V.H. (1972). Plant Taxonomy. London. Edward Arnold Publisher's.
Hotchkiss, Neil. (1970). Common Marsh, Underwater and Floating-leaved Plants of the United
States and Canada. Toronto, Ontario. General Publishing.
Jeffrey, C. (1982). An Introduction to Plant Taxonomy. New York. Cambridge University Press.
Jones, Samuel B., and Arlene E. Luchsinger. (1986). Plant Systematics. New York. Mcgraw-Hill
Book.
Kuijt, Job. (1969). The Biology of Parasitic Flowering Plants. Los Angeles, California.
University of California Press.
Walters, Dirk R. (1977). Vascular Plant Taxonomy - A Study Guide. Dubuque, Iowa.
Kendall/Hunt Publishing.