2007 plant histology
P.1
Plant Anatomy and Histology
Anatomy of Dicotyledonous Angiosperms
1. young stems
(Pericyle)
2.
young roots
(with Casparian strip)
(meristematic parenchyma)
2007 plant histology
3.
P.2
woody stems
cork
cortex
pith
phloem
Vascular
cambium
Annual rings of xylem (wood)
4.
leaves
Medullary Rays
2007 plant histology
P.3
Plant Histology:
Characteristic features, functions and distribution of plant tissues
Tissue
Cell Wall
Cell features
Main functions
Distribution
Living or
dead
protoplasm
A. Ground tissues
- making up the bulk of the plant
- 3 types: parenchyma, collenchyma, sclerenchyma
1. Parenchyma
- most abundant ground
tissue
- composed of mature,
undifferentiated cell,
though specialization
according to position in the
plant may occur
- with living protoplasm
Primary cell
wall only
May be
transversed by
plasmodesmata
More or less
isodiametric*,
sometimes
elongated
-
As packing ground tissue
With turgidity for support
in herbs and seedlings
Metabolically active
Intercellular spaces allow
gaseous exchange
Food and water storage
Deposition of waste
Transport of materials
through cells or cell walls
Cortex, pith,
medullary rays and
packing tissues in
xylem and phloem
Some modified parenchyma:
-
-
- epidermis
Usually covered
Elongated and
with cuticle
flattened
made of cutin
-
-
- mesophyll
(spongy and palisade
mesophyll)
-----
sponge m.:
Isodiametric,
irregular
palisade m.:
column-shaped
-
Transparent for light
penetration in green stems
and leaves.
Cuticle provides protection
from desiccation and
infection.
Single layer of cells
Hairs and glands may have
Covering entire
additional functions.
primary plant body.
Stomata between guard
cells facilitate gaseous
exchange
Root hair cells facilitate
water and mineral
absorption.
Photosynthesis (contains
chloroplasts)
Storage of starch
-
- endodermis
- root pericycle
And deposits of
As epidermis
suberin
----
----
Selective barrier to
movement of water and
mineral salts (between
cortex and xylem) in
roots.
- with possible role in
geotropic response in
stems
In roots it retains meristematic
activity producing lateral roots
and contributing to secondary
growth if this occurs.
Between the upper
and lower epidermis
of leaves.
NB: the pericycle in the stem is made of sclerenchyma and has a different origin.
Surrounding vascular
tissue (innermost
layer of cortex)
In roots between
central vascular tissue
and endodermis
Living
2007 plant histology
P.4
2007 plant histology
Tissue
P.5
Cell Wall
Cell features
Main functions
Distribution
Living or
dead
protoplasm
A. Ground tissues
- making up the bulk of the plant
- 3 types: parenchyma, collenchyma, sclerenchyma
2. Collenchyma
3. Sclerenchyma
- both types have evenly
thickened cell walls
- Sclereids / stone cells
- Fibres
usually closely packed with
little or no air space
between them
Extra deposition
of cellulose,
pectins and
hemicelluloses
at corners
making cell wall
unevenly
thickened
Secondary cell
wall with lignin
----
----
Elongated and
polygonal with
tapering ends
Walls are
generally flexible
and allow certain
degree of
stretching.
-----
Outer region of stem
cortex(hypodermis)
-
Little or no intercellular
space)
Provide support (a
mechanical function) to
supplement the effects of
turgid parenchyma.
(Not in root and
moncots.)
Mechanical support and
protection
Roughly
isodiametric,
though variations Or mechanical protection
occur
Narrow,
elongated,
polygonal
with tapering ends
In dicotyledonous
leaves as solid masses
living
running the length of
the midrib
----
---Widely distributed
throughout the plant
Or outer surface of
seeds and fruits (e.g.
pear)
Commonly associated
with vascular tissues
(e.g. pericycle --- the
sclerenchyma
sheath outside
phloem of vascular
bundle in stems
also often in the outer
cortex as
collenchyma
Dead
2007 plant histology
P.6
2007 plant histology
Tissue
P.7
Cell Wall
Cell features
Main functions
Distribution
Living or
dead
protoplasm
B. Vascular Tissues
Inner layer of bundle
in stem
1. Xylem
Outer layer of bundle
in root
-
Transport water and
minerals (resistance to
water flow is greater than
xylem vessels)
-
Provide mechanical
support
-
Hollow vessels allow
continue conduction of
water column with
minerals over long
distance.
Tube-like with
tapering end walls
- Tracheids
With pits on
thickened
lignified
secondary cell
wall
-
- Vessels elements
-
Vessel
elements with
no end wall
fused to form
long hollow
vessels
Thickened lignified wall
offer resistance to
collapse during
transpiration and
mechanical support for
the plant.
with annular thickenings.
The presence of lateral
border pits allows
transverse transport of
water and minerals to
neighbouring xylem
vessels.
-
-
Xylem fibres
(Sclerenchyma fibres)
----
----
Parenchyma
----
----
-
Important in
ferns and
gymnosperms.
Relatively fewer
in angiosperms
dead
Characteristic
conducting units of
angiosperm xylem
(not in non-flowering
plants)
Hexagonal vessels allow
close packing for greater
strength.
Mechanical support only
----
-------
Dead
Living
2007 plant histology
P.8
2007 plant histology
Tissue
P.9
Cell Wall
Cell features
Main functions
Distribution
Living or
dead
protoplasm
B. Vascular Tissues
2. Phloem
Sieve tube element
Companion cells
- highly specialized
parenchyma cell
Phloem fibres
(Sclerenchyma fibre)
Parenchyma
-
Continuous sieve tube for
translocation of soluble
organic compounds over
long distance.
-
Minimum resistance to
the flow of organic solutes
due to the reduced
cytoplasm, degeneration
of nucleus and perforation
of sieve plates
Elongated and
Primary cell
tubular elements
wall, with
joining end to end
perforated sieve
forming the sieve
plate
tubes
-
Through
plasmodesma(ta), the
activity of sieve tube
elements is closely
dependent on their
adjacent companion cells.
-
Communication with the
cytoplasm of sieve tubes
by plasmodesmata,
Primary cell
wall
Elongated and
narrow cells
----
----
----
----
Outer layer of
vascular bundle in
stem
Inner layer of
vascular bundle in
root
Play a role in metabolic
activities of itself and the
associated sieve element
(hence with numerous
mitochondria to provide
energy for active loading
of substances into phloem
elements.
Mechanical support
----
In angiosperm
only.
Associated with
sieve tube
In dicots but not in
monocots.
Living but
no nucleus
Nucleated
living cell
Dead
living
2007 plant histology
Tissue
C. Meristematic tissues
P.10
Cell Wall
Thin primary
cell wall
Cell features
Main functions
Retain the ability to divide by
mitosis producing daughter
Isodiametic, small
cells which grow and form the
size with dense
rest of the plant body.
cytoplasm and
large nucleus
(the daughter cells after
differentiation form the
Closely packed
permanent tissue, ie.cells
with no or no
which have lost the ability to
intercellular space
divide.)
Formation of primary tissues
and
- Apical Meristem
Increase in the length
- Vascular cambium
(Lateral Meristem)
Living or
dead
protoplasm
-----
living
Shoot and root tips,
leaf bud primordial
Formation of secondary xylem
Vascular bundles
(wood) and phloem
Formation of periderm
 outer cork (to replace
epidermis) & inner
secondary cortex
- Corks cambium
(Lateral Meristem)
* isodiametric = equally expanded on all sides
* primary cell wall – mainly composed of cellullose, pectins and hemicelluloses
Apical meristem
Epidermis
Distribution
Ground tissue
(cortex and pith)
- Parenchyma
- Collenchyma
- Sclerenchyma
- Cork cambium
Vascular tissues
- Xylem
- Phloem
- Vascular cambium
- Pericyle
Outside of cortex