INTERNAL STRUCTURE: CROSS SECTION OF A YOUNG DICOT ROOT
Specimen: Helianthus Annus (Sunflower)
Guide Questions:
1. What is the exarch pattern of the xylem of your specimen?
Ans. In our specimen, the xylem is towards the inside and is polygonal or angular in shape. The more it
is towards the center, the little size it become.
2. Why is the xylem composed of tracheary elements only at this point?
Ans. In order to specialized for transporting water and conducting salt.
3. Fill up the table below:
Structure
Description of Cells
Epidermis
It can be seen at the outermost layer. We
also saw in our specimen that it is compactly
arranged. This provides protection to the
roots and helps in the absorption of water
and minerals from the soil.
Parenchyma
Parenchyma makes up the ground tissue
found in the cortex of dicot roots. The cells
have thin walls and are usually orb-shaped.
The cortex of monocot roots can contain
sclerenchyma in addition to parenchyma.
Endodermis
We saw the endodermis in our specimen at
the inner most layer of the cortex. It is a
single layer that seems like a barrel-shaped
cells.
Pericycle
We saw the pericycle next to the
endodermis. It represents the outer
boundary of vascular strand. It is an
important layer because a part of vascular
cambium is formed by the pericycle.
Primary xylem
The primary xylem was located at the middle
of the dicot root. It is formed during the
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primary growth coming from the
procambium of apical meristems.
Vascular cambium
We’ve saw it between the xylem and phloem.
This is the main growth tissue in the stems
and roots most specifically in dicots.
Primary phloem
Can be seen around the xylem, it is separated
by vascular cambium. It is formed by the
apical meristem same goes in xylem.
Figure 1. Helianthus Annus under 4x lens
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Figure 2. Helianthus Annus under LPO
Epidermis
INTERNAL STRUCTURE: CROSS SECTION OF A MONOCOT ROOT
Cortex
Stele
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Figure 2. Helianthus Annus under HPO
Epidermis
Casparian Strip
Pericycle
Endodermis
Parenchyma
Xylem
Phloem
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INTERNAL STRUCTURE: CROSS SECTION OF A MONOCOT ROOT
Specimen: Zea May (Corn)
Guide Questions:
1. Why do young and old monocot roots have little difference in terms of structure?
Ans. Older monocot roots show a covering of exodermis than that of a young monocot. After the
loss of epidermis, the external cells of the overall cortex are suberized with the material called
suberin and then it will become a thick-walled layer called exodermis.
2. Since monocots do not produce peridermal layers, what is the use of the pericycle?
Ans. Pericycle in monocot plants helps support the root and protects its vascular structure, stores
nutrients and facilitates root growth.
3. Fill up the table below:
Structure
Description of Cells
Epidermis
In our specimen, we saw the epidermis at the
single outermost layer with no cuticle. It is
densely arranged cells and few cells may see
unicellular root hair emerging.
Pith
Unlike dicot roots, a monocot root has a pith
in the stele. In monocot, well-developed pith
is observed. It comprises of the parenchyma
in the mid-region of the root.
Endodermis
It is the innermost layer of the cortex. Barrelshaped cells arranged in a ring-like manner.
Pericycle
It can be seen at the outermost layer of the
stele and it contains cells that can divide and
give rise to lateral roots.
Primary xylem
They are stacked end to end in the center of
the plant, forming a vertical column that
conducts water and minerals absorbed by
the roots upward. It occurs in the form of
solid core extending towards the pericycle.
Monocot root contains xylem and phloem in
another manner, forming a circle.
Primary phloem
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Phloem is located below the pericycle
towards the exterior side. It is found below
the endodermis and is a single layer of
parenchymatous cells. It is organized in
thinner rows of cells around the primary
xylem rows.
Figure 3. Zea May under 4x Lens
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Figure 3. Zea May under LPO
Cortex
Stele
Epidermis
Figure 4. Zea May under HPO
Primary Xylem
Pericycle
Phloem
Endodermis
Pith
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Epidermis
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INTERNAL STRUCTURE: LONGITUDINAL ZONES OF THE ROOT
Specimen: Allium Cepa (Onion)
Guide Questions:
1. Fill up the table below:
Zone/region
Root cap
Embryonic, apical meristem region
Embryonic, quiescence region
Elongation
Maturation, root hair region
Maturation, Primary permanent tissue
zone
Description of Cells
The root cap is a tiny tissue that serves
as a barrier against environmental stress
and aids in the perception of gravity
located at the tip of the root.
A root apical meristem is a tiny area at
the tip of a root where all cells can divide
repeatedly and where all primary root
tissues are derived.
A quiescent center is a region in a root's
apical meristem that contains cells that
divide more slowly than other
meristematic cells.
Between the meristematic zone and the
maturation zone of the root tip is the
elongation zone. Rapid cell lengthening
and the final round of divisions are what
cause the endodermis to form.
Root hair is affixed to the roots in the
maturation zone. By increasing surface
area, the tiny root hairs help plants
absorb water as well as minerals from the
soil.
The zone of maturation is where the
xylem and phloem of the root have fully
developed.
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Figure 1: Internal Structure: Longitudinal Zones of the Root in 4x Lens
Zone of Maturation
Zone of Elongation
Zone of Cell Division
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Figure 2: Zone of Maturation in 10x
Epidermis
Stele
Cortex
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Figure 3: Zone of Elongation in 10x
Protoderm
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Figure 4: Zone of Cell Division in 10x
Apical meristem
Quiescent center
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Figure 5: Zone of Maturation in 40x
Stele
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Figure 6: Zone of Elongation in 40x
Procambium
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Figure 6: Zone of Cell Division in 40x
Root cap
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