Roots have several key functions including water and mineral absorption, transport, anchoring the plant, and storing food. There are three main types of root systems: taproots, lateral roots, and adventitious roots. Roots develop from root caps, epidermis, cortex, endodermis, pericycle, and vascular cylinders. Lateral and adventitious roots develop from the pericycle. Roots differ from shoots in their development, structure, and vascular tissue organization.

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Functions
• absorption of
water and
minerals
• transport of
water and
minerals
ROOTS • anchorage of the
h f h
plant to the soil
• holds soil
particles in place
• storage of food
Types of root systems Origin of ROOTS
1. taproot/ primary root‐ from the radicle
• e.g. gymnosperms and dicots,
• Ultimate lateral branches
Origin of ROOTS
10 state of growth
2. lateral roots/branch roots –
absorption of water
from the pericycle
feeder roots‐‐remain short
• secondary root – from
pericycle of and fragile and short‐lived
main/tap/primary root
/ /
• tertiary root‐ from pericycle 3. adventitious roots‐ roots that
of secondary root arise from unusual places
• quaternary root‐ from
pericycle of tertiary root
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Primary State PRIMARY STATE
• Root cap
1. ROOT CAP
• Epidermis
• Protects the root meristem
• Exodermis
• assists the root in the
• Cortex penetration of soil during its
• Endodermis growth
• Pericycle • With mucilage
• Vascular • Consists of living parenchyma
Cylinder cells containing starch and
are believed to be involved in
gravity perception
PRIMARY STATE Velamen
2. EPIDERMIS • multiseriate (in Orchids);
• closely packed elongated cells with thin walls,
uncutinized • during dry weather, the cells are filled with air;
• If it persists, may become cutinized or suberized, during rain, they become filled with water;
or lignified
or lignified • f
functions: mechanical protection and
i h i l i d
• typically uniseriate prevention of excessive loss of water from the
• with root hairs which are typically short‐lived cortex
3. Cortex
• Degree of differentiation is
related to the longevity of
the cortex
• With schizogenous
intercellular spaces
a. Exodermis
• Differentiated as a
protective tissue
• May have casparian strip
suberin lamella cellulose
layers and be lignified
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b. Endodermis
• Universally present in roots
• With casparian strip
• Casparian strip is part of the primary wall;
composed of lignin or suberin or both;
• In the 2nd stage • In the third stage,
suberin lamella covers the entire wall on the a thick cellulose layer is
inside of the cell deposited over the
casparian strip is separated from the suberin lamella
cytoplasm
• The thick wall+ original
wall (with casparian
strip)
may become lignified
4. Pericycle
• Consists of thin‐walled parenchyma
• Concerned with meristematic activities
• Origin of lateral roots and phellogen
• Origin of part of the vascular cambium
• The wall modifications
The wall modifications
appear first on the face of the phloem
strand and then spread toward the xylem
• Passage cells
opposite the xylem allow a limited transfer of
material between the cortex and the vascular
cylinder
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• In monocots may undergo sclerification in Vascular System
older roots • Typically has an exarch
• In gymnosperms typically multiseriate xylem
• Typically differentiation of
5. Vascular cylinder—(+assoc. parenchyma) phloem is centripetal
• More clearly delimited from cortex than the
More clearly delimited from cortex than the (p
(protophloem pole near
p p
shoot: the periphery of pericycle)
a. Not interrupted by leaf gaps
b. This tissue is surrounded by the pericycle Pith consists of parenchyma,
c. Endodermis surrounds the pericycle may become sclerified
Development Roots without 20 growth
MONOCOTS– completion of 10 growth
• Sclerification of parenchyma cells associated
with the vascular elements
• Development of thick 20 walls in the
endodermis
d d i
• Differentiation of exodermis
• Cortex is retained and no periderm develops
• The protective tissues are the epidermis and
the exodermis(replaces epidermis if former is
destroyed)
Roots with 20 growth
• Vascular cambium develops partly between 10
xylem and 10 phloem
• Partly, vascular cambium develops from the
y, p
pericycle
• Pericycle divides periclinally and the
outermost gives rise to the phellogen
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Protective tissue: Development of lateral roots
• Persisting thick‐walled epidermis (Ranunculus) • In gymnosperms and angiosperms, originate
• Exodermis (Compositae) from the pericycle
• Dead and collapsed but persisting cortex • Endodermis may participate in the initial
(Linaria, Polygonum) growth of the branch root
• Subdivided and suberized endodermis
Subdivided and suberized endodermis • The derivatives of the endodermis combined
The derivatives of the endodermis combined
(Gentiana) with those of the cortex may form a rootcap‐
• Polyderm (Potentilla) like structure called pocket
• Periderm of deep seated origin (Saxifragaceae)
• In lower vascular plants
Development of Adventitious roots
the branch roots originate from the
endodermis
• Most of them arise endogenously
• If parent plant has more than 2 xylem poles,
• Plants with adventitious roots:
lateral roots emerge opposite the xylem or
p
phloem lower vascular – main root system
• if diarch, monocots
in between X and P dicots –propagated by means of rhizomes
or runners; water plants
• Most of them arise endogenously
• In young stems, adventitious roots derived
from interfascicular parenchyma, phloem, in
perivascular position
position
• In older stems from the vascular ray;
sometimes from the cambial zone
• parenchyma vascular elements
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Little water enters the rootcap and the apical meristem 10 roots or roots with limited 20 growth
cortex
Maximum rates of absorption of water
10xylem is mature and endodermis has casparian with 20 growth
strip
parenchymatic and some sclerenchymatic cells of X
and P
Maximum accumulation of salts
close to the apical meristem
The hypocotyls and base of the taproot is fleshy
Root hairs (Daucus, Beta)
Formation of many branches in the branched type of
root system
Many adventitious roots in fibrous root system
(penetrate the soil less deeply but binds the soil more
( t t th il l d l b t bi d th il
tightly)
Root hairs play a part in binding the soil
The leaf primordia arise directly from the apical
meristem of the shoot and the branches more or less
directly; and both are exogenous
Apical meristem of the root is
subterminal because it is covered
by the root cap
Apical meristem of the shoot is
terminal
i l
The epidermis of the root has
more varied ontogenetic origin
than that of the shoot
(dermatogen;
dermatocalyptrogen; protoderm)
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The lateral roots arise independently of the apical Vascular system of the shoot differentiates largely or
meristem and are endogenous entirely in relation to the leaves
The vascular system of the root develops as an axial
structure independent of the lateral organs
Leaf gaps and pith are characteristic of the vascular The relation between the regions of the primary body
system of stems except in certain lower vascular plants and the apical initials is often more precise in the root
than in the shoot;
There are no leaf gaps in the root and frequently no
pith
The 10 vascular tissues of the shoot more or less SHOOT 10 xylem differentiation is centrifugal in the
discrete bundles (units combining xylem and phloem) shoot (endarch xylem)
while in the ROOT centripetal in the root (exarch xylem)
Root the xylem alternates with the phloem lower vascular the 10 xylem is exarch in both root
and stem,
in ferns commonly mesarch in the stem
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The boundaries between the tissue systems are quite
precise in the root.
Endodermis and pericycle are universally present in
roots
The root has shorter elongation region than the shoot
and frequently develops no extensible types of
protoxylem elements (with annular and helical 20
t l l t ( ith l d h li l
walls)
Roots have a lower percentage of the area of the bark
occupied by fibers
Roots have smaller number of fibers in the xylem
Differences are quantitative rather than qualitative
The 20 vascular tissues of the root higher proportion
of living to non living cells
Roots have higher bark to wood ratio
Larger vessels of more uniform size although
sometimes fewer in number
A poor differentiation of growth increments
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First periderm arises in the pericycle while in the stem A larger ratio of area of living cells to area of nonliving
in the peripheral layers of the axis cells in both the phloem and the xylem
More starch and less tannic substances
region of the plant axis where some features are
intermediate or transitional between those of the
shoot and the root
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