1. ANATOMY OF ROOT
By
Dr. Gunmala Gugalia
Associate Professor
Dept. of Botany, Sangam University
Bhilwara, Rajasthan(India)
2. SIX ANATOMICAL CHARACTERISTICS OF THE
ROOT.
The characteristics
are: 1. Root Cap
2. Epidermis
3. Cortex
4. Endodermis
5. Pericycle
6. Vascular System.
3. Root: Anatomical Characteristic #
1. Root Cap:
The root cap consists of parenchymatous cells in various
stages of differentiation. It is protective in function.
The root cap is apparently the site of the perception of gravity;
thus it appears to be capable of controlling the production in
the meristem of the growth- regulating substances involved in
geotropism or their movement.
2. Epidermis:The epidermis is also known as epiblema or
piliferous layer. In most of roots, root hairs develop from some
of the epidermal cells at a little distance from the apical
meristem
4.
5. 3. Cortex:
In most roots the cortex is parenchymatous.
In some roots, the cells of the cortex are very regularly
arranged, both radially and in concentric circles.
Conspicuous intercellular spaces may be present, and
especially evident in aquatic species, where they form a type of
aerenchyma.
The cortical cells often contain starch, and sometimes
crystals. Sclerenchyma is more common in the roots of
monocotyledons than those of dicotyledons.
The innermost layer of the cortex is usually differentiated as
an endodermis.
6. 4. Endodermis:
The endodermis comprises a single layer of cells
differing physiologically and in structure and function from
those on either side of it.
In the young endodermal cells a band of suberin,
Casparian strip, runs radially around the cell and is
thus seen in the radial walls in transverse sections of
roots.
The thin-walled passage cells often remain in the
endodermis in positions opposite the protoxylem which is
known as passage cells
8. 5. Pericycle:
The pericycle is usually a single layer of
parenchymatous cells lying just within the
endodermis and peripheral to the vascular tissues.
The pericycle has a capacity for meristematic
growth, and gives rise to lateral root primordia,
parts of the vascular cambium, and usually the
meristem which produces cork, the phellogen.
The pericycle is sometimes called
pericambium.
9. 6. Vascular System:
The vascular system of the root as seen in transverse section consists
of a variable number of triangular rays of thick-walled, lignified
tracheary elements, alternating with arcs of thin-walled phloem.
In the root, the xylem and phloem do not lie on the same radius.
The xylem may form a solid central core, or there may be a
parenchymatous or sclerenchymatous pith, as in the roots of many
monocotyledons.
Roots with 1, 2, 3, 4, 5 and many arcs of xylem are respectively called
monarch, diarch, triarch, tetrarch, pentarch and polyarch.
The xylem is exarch, i.e., protoxylem lies towards periphery and
metaxylem towards the centre.
10. The xylem is always centripetal in its development.
The phloem bundle consists of sieve tubes, companion cells
and phloem parenchyma.
The protoxylem consists of annular and spiral vessels and
meta-xylem of reticulate and pitted vessels.
The parenchyma found in between xylem and phloem bundles
is known as conjunctive tissue.
The pith may be large, small or altogether absent.
12. DIFFERENCE BETWEEN DICOT AND MONOCOT
ROOT
1. Cortex is comparatively narrow.
2. The epiblema, the cortex and
even the endodermis are peeled
off and replaced by cork.
3. Older root has a covering of cork.
4. Endodermis is less thickened and
casparian strips are more
prominent.
5. Passage cells are generally
absent in endodermis.
6. Pericycle produces lateral roots,
cork cambium and part of the
vascular cambium.
1. Cortex is very wide.
2. Cork is not formed. The cortex
and the endodermis persist. Only
the epiblema is peeled off.
3. Older root has a covering of
exodermis.
4. Casparian strips are visible only
in young root. The endodermal
cells later become highly
thickened.
5. Thin walled passage cells
generally occur in the
endodermis opposite the
protoxylem point.
6. Pericycle produces lateral roots
only.
Dicot Root Monocot root
13. DIFFERENCE BETWEEN DICOT AND MONOCOT
ROOT
7. The number of xylem and phloem
bundles varies from 2-5 or
sometimes 8.
8. Xylem vessels are generally
angular.
9. Conjunctive tissue is
parenchymatous.
10. Conjunctive parenchyma forms
the cambium.
11. Secondary growth takes place
with the help of vascular
cambium and cork cambium.
12. Pith is either absent or very
small.
7. Xylem and phloem bundles are
numerous and are 8 or more in
number.
8. Xylem vessels are oval or
rounded.
9. Conjunctive tissue may be
parenchymatous or
sclerenchymatous.
7. Conjunctive parenchyma does
not produce cambium.
10. Secondary growth is absent.
11. A well-developed pith is present
in the center of the root.
Dicot Root Monocot root
