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PLANT ORGANS
1
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3
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5
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Root
Stem
Leaves
Flowers
Fruits
Seeds

THE ROOTS
 Functions:
o Absorption of nutrients
o Penetrate the soil, growing by elongating near the tip
o Anchorage and support
o Conduction, roots transport water and dissolved nutrients to the shoot
 Structures:
o Root cap
o Root tip
 Classification of Roots in a plant individual
1
...
Secondary
- develops from the primary root
3
...
Rootlet
- develops from tertiary
5
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Root Cap
- Covering the root apical meristem
- Lab: a thimble shaped mass of parenchyma cells which protects the growing portion
of the root tip
...

2
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Calyptogen – give rise to root cap cells
b
...
Periolem – gives rise to cortex
d
...
k
...

Cells produced in this region are destined for one of the three possible fates:
→ Cells toward the tip becomes part of the root cap
→ Cells in the middle remain as cells in the meristem
→ Cells in the upper portion enlarge and differentiate into permanent tissues
3
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4
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o Cross Section of mature roots, the parts identifiable are:




1
...
Cortex
o Surrounds several columns of vascular tissue
o Is made up of undifferentiated parenchymal cells that function for food storage
3
...

4
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Vascular tissues
o Made up of phloem and xylem
o Located in an area generally called the stele
o Is enclosed by pericycle
o Their xylem is arranged radially alternate with shorter bands of smaller cluster of phloem
6
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Notes by: Alexandra Breatriz Silva, Aubrey Olaran and Mary Divine Alegado





Procambial cells develop into lateral meristem called vascular cambium
Vascular cambium – a continuous single layer of cells that give rise to secondary phloem and xylem
...
Stele – smaller in dicot, larger in monocot
2
...
Endodermis – not so prominent in dicot, quite prominent in monocot
4
...
Pith – disappears in dicot, persists in monocot
2
...
Secondary growth – present in dicot, absent in monocot
4
...
Cortex and epidermis – peeled off in dicot, remain as integral part in monocot
Old Dicot
Pith
Disappears
Cambium
Produced
Secondary growth
Present
Cork cambium
Present
Cortex and epidermis
Peeled off



Old Monocot
Persists
None Produced
Absent
Absent
Remain as integral part

Specialized roots
Roots are modified to have specialized function as:
1
...
Orchid roots – for photosynthesis and are provided with velamin as coats (function for water absorption from the air)
3
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Clinging, brace, prop and buttress roots – for support and stability

THE STEM
 The axis of plant that originates above the hypocotyl of the embryo in the seed
...
g
...

o
some stems are specialized for storage, reproduction and other purposes
...

* The falling of leaves is a natural phenomenon, it is the result of the formation of
abscission layer of special cells at the base of the petiole, the point where it is attached to the stem
...

 CLASSIFICATION OF BUDS
o
Terminal bud - found at the tip of the stem which is responsible for elongation;

Notes by: Alexandra Breatriz Silva, Aubrey Olaran and Mary Divine Alegado

o







Lateral bud - those arising from the sides that determine the position of the branches; developed at the axis of the
leaf, hence, called axillary buds
o
Adventitious buds - developed at any point on the stem ; sometimes developed on roots
CLASSIFICATION OF BUDS based on STRUCTURE DEVELOPMENT :
o
branch buds
o
leaf buds
o
flower buds
3 TYPES OF STEM
o
dicotyledonous woody
o
dicotyledonous herbaceous herbaceous
o
monocotyledonous
Sections of Woody Dicot
o
Longitudinal Section of Woody Dicot
From the very tip of the stem, 3 regions are recognized:
 Region of Meristematic activity
 the area of promeristem of primordial stem (youngest part of the apical meristem)
 2 REGIONS OF PROMERISTEM (based of Corpus- Tunica Theory):
→
Tunica - outer enveloping layer of cells which divide at right angles to the surface (anticlinal
division)
→
Corpus- central core, composed of cells which divide parallel to the surface (periclinal division)
 Region of Elongation
 extends from the base of the bud downward through several nodes and internodes
...

consisting of circular row of meristematic cells which form secondary vascular tissues as
the stem grows older, thus resulting growth of stem diameter
...
Bark
all tissues outside the cambium rings
composed of : periderm, cortex, pericycle and phloem
2
...
Heartwood- the central wood which is dark due to depositions
of substances like gums, resins, tannins, and certain pigments
in its cell walls and cell cavities
...

2
...
The
living part of the wood
...
Little secondary growth in herbaceous while extensive in woody dicot
2
...
Pith larger in herbaceous and small or none in woody dicot
4
...
Epidermis – persistent
2
...
Stele – with vascular bundle and ground parenchyma (scattered outside the vascular bundles)
Differences between woody dicot and monocot stem:
1
...

in woody dicot are few and arranged in a ring
b
...
with cambium and open type in dicot because bundle sheath is absent
d
...
Cortex
a
...
indistinct in monocot;
3
...
smaller in dicot
b
...
Epidermis
a
...
persistent in monocot
Structure
Dicot Secondary Growth
Vascular Bundle
few and arranged in a ring
cambium is present and open type
because bundle sheath is absent
Cortex
distinct
Stele
smaller
Epidermis
temporary and replaced by cork

Monocot Secondary Growth
numerous and scattered
cambium is absent and closed type
because bundle sheath is present
indistinct
large
persistent

*In grasses, like rice and bamboo parenchymal cells in the center enlarge greatly, then disintegrates, leaving a hollow pith cavity
but is interrupted by solid plates at the points of nodes or nodal plates
...





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Functions of Stem :
o
support leaves
o
reproduction
o
transport of materials
*The cortex, pith, pith rays are responsible for storage of substances, like water and food (starch is the chief reserve
substance)
*Laticiferous plants yield latex ( a milky juice which is composed of starch, protein, sugar, oil, alkaloids, tannins ,gum, inorganic
salts, etc
...
The basal rooted piece is the stock and the stem piece which is grafted to the stock is
the sclon
...


Notes by: Alexandra Breatriz Silva, Aubrey Olaran and Mary Divine Alegado



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