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Internal and External Stem Anatomy
Internal and External definitions of each stem anatomy including diffe...
Course
Bachelor of Science in Biology (BSBiol)
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Saint Louis University (Philippines)
Academic year: 2022/2023
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Stem Anatomy and Modified
Stems
Stem
➔ bears the leaves and reproductive
structures
origin: epicotyl portion of the
embryo axis
Function:
1. Support of leaves and reproductive
structures
2. Carbohydrate production
3. Mineral storage
4. Transport medium between roots and
leaves
Kinds of stem
• Herbaceous stem
– soft and green
– little growth in diameter
– compose of primary
tissues
– covered by epidermal
tissues
– naked buds (without
scales)
– chiefly annuals
• Woody stem
– tough and not green
– with considerable growth
in diameter
– both primary and
secondary tissues present
– covered by bark
– buds covered by scales
– chiefly perennial
External structure of a Woody
Stem (twig):
a. Node
– site where leaves
and buds arise
b. Internode
– region between
successive nodes
c. Lenticels
– raised pore in
surface; replace the
stomata for gas
exchange
d. Buds
– undeveloped
shoot; meristematic;
protected by scale
leaves
e. Scars
– marks left on stem:
bundle scars, leaf
scars, fruit scars,
flower scars, etc...
Internal Structure of the
Herbaceous Stem
Primary Tissues in Stem
Regions:
1. Epidermis:
- outer single layer of epidermal cells, with
guard cells,
different type of trichomes and cutinized
- function: protection, restrict transpiration
2. Cortex or ground tissue
- region between epidermis and vascular
tissue
- tissue composition:
- Parenchyma – chlorenchyma
- Collenchyma
- Sclerenchyma
Endodermis – with suberin, impervious to
water and
dissolve substances; evident in
underground stems
3. Vascular bundle
– vascular tissues
• xylem
• phloem
– surrounded by protective sclerenchyma
fibers
Internal Anatomy Of
Monocot and Dicot stem
• Representative specimens:
Monocot plant: Zea mays
(corn plant)
Dicot plant: Helianthus sp.
(sunflower)
Corm:
- swollen base of an aerial
shoot covered with dry leaves
- for vegetative propagation
(asexual reproduction)
Stem Internal Anatomy in
Different Vascular Plants
Primary tissue arrangement in:
• Pinus stem
• Fern stem
• Equisetum stem
• Lycopodium stem
Pinus young stem
- wavy in outline
(1)Epidermis
- single-layered, with cuticle
(2) Cortex
- outer region:
- multi-layered hypodermis
of lignified sclerenchymatous
cells
- inner cortex:
-parenchymatous cells
containing chloroplasts and
resin canals
-endodermis and pericycle is
inconspicuous
Pinus young stem
(3) Stele (vascular cylinder)
- Siphonostele: Ectophloic -
Eustele
- vascular bundles forming a
ring with pith at the center
- vascular bundles are
separated from each other
by narrow medullary rays
- phloem consists of sieve
tubes, albuminous cells and
phloem parenchyma
- xylem consists of tracheids
Fern stem (rhizome)
(i) Epidermis:
• Narrow cells with thickened brown outer
walls.
(ii) Cortex:
• Outer cortex/hypodermis
– thick walled scelerenchymatous tissue
• Inner cortex/ground tissue
– thin walled parenchymatous tissue
– embedded with many meristeles.
– in between the meristeles two patches of
sclerenchymatous
tissue are present
– one patch lies above and one lies below
the inner meristeles
(iii) Stele:
• siphonostele:
amphiphloic – dictyostele
• Two Concentric Cylinders of
Vascular Bundles
– inner cylinder: consist
of two meristele
– Outer cylinder: consist of several
meriststeles
– Each meristele is
surrounded by a single
layer of endodermis
and one or two layers
of pericycle
- phloem surrounds the xylem
tissue
Equisetum Stem -Internode of
Aerial Sterile
Shoot c.:
- wavy in outline because of the
presence of ridges and grooves
(1)Epidermis
- cells with silica deposits of
silica in their cell walls (stem
appears hard and rough to
touch)
- Presence of sunken stomata in
each groove
- the guard cells covered
completely by subsidiary cells.
(2) Cortex
- Sclerenchyma
- Present below each ridge and below the
grooves in
between chlorenchyma
- For mechanical support
- Chlorenchymatous tissue
- Present inner to the sclerenchyma below
each ridge
- photosynthetic in function.
- Parenchyma tissue of several layers
- Vallecular canal
- large air canal in the parenchymatous
cortex
- Endodermis with casparian strips
- Pericyle (single layer) below the
endodermis
Vallecular canals
- For respiration (plant grows
in water-logged soil) and to
reduce weight and increase
stem strength
(3). Stele
- Vascular bundles present below the
ridges
alternate to the vallecular canals of the
cortex.
- present in a ring
- number of vascular bundles and
vallecular canals
is equal to the number of ridges and
grooves,
respectively
- Stele is ectophloic siphonostelic type.
- Each vascular bundle consists of xylem,
phloem
and some parenchyma.
- carinal canal (water- containing cavity)
- Present in each Vascular bundle.
- Protoxylem is endarch lying opposite to
carinal
cavity
- It consists of annular and spiral
tracheids.
- Two strands of metaxylem are present.
- Phloem is present in between two
strands of
metaxylem and made up of phloem
parenchyma
and sieve tubes
- Pith is present in the form of pith cavity,
located in
the centre of the aerial shoot
C. Internode of Aerial Fertile
Shoot:
- The structure is exactly similar with that
of
aerial sterile shoot, except a few following
minor differences:
1. Absence of stomata.
FERN STEM
EQUISETUM
AERIAL STEM LYCOPODIUM
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Internal and External Stem Anatomy
Course: Bachelor of Science in Biology (BSBiol)
53 Documents
Students shared 53 documents in this course
University: Saint Louis University (Philippines)
Was this document helpful?
Stem Anatomy and Modified
Stems
Stem
➔bears the leaves and reproductive
structures
origin: epicotyl portion of the
embryo axis
Function:
1. Support of leaves and reproductive
structures
2. Carbohydrate production
3. Mineral storage
4. Transport medium between roots and
leaves
Kinds of stem
•Herbaceous stem
– soft and green
– little growth in diameter
– compose of primary
tissues
– covered by epidermal
tissues
– naked buds (without
scales)
– chiefly annuals
•Woody stem
– tough and not green
– with considerable growth
in diameter
– both primary and
secondary tissues present
– covered by bark
– buds covered by scales
– chiefly perennial
External structure of a Woody
Stem (twig):
a. Node
– site where leaves
and buds arise
b. Internode
– region between
successive nodes
c. Lenticels
– raised pore in
surface; replace the
stomata for gas
exchange
d. Buds
– undeveloped
shoot; meristematic;
protected by scale
leaves
e. Scars
– marks left on stem:
bundle scars, leaf
scars, fruit scars,
flower scars, etc...
Internal Structure of the
Herbaceous Stem
Primary Tissues in Stem
Regions:
1. Epidermis:
- outer single layer of epidermal cells, with
guard cells,
different type of trichomes and cutinized
- function: protection, restrict transpiration
2. Cortex or ground tissue
- region between epidermis and vascular
tissue
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