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Plant
Morphology
shoot tip
(terminal bud)
lateral (axillary) bud
flower
node
internode
node
EPIDERMIS
leaf
VASCULAR TISSUES
seeds
(inside fruit)
GROUND TISSUES
withered
cotyledon
SHOOT SYSTEM
ROOT SYSTEM
primary root
lateral root
root hairs
root tip
root cap
activity at
meristems
new cells
elongate
and start to
differentiate
into primary
tissues
new cells
elongate
and start to
differentiate
into primary
tissues
activity at
meristems
SHOOT APICAL MERISTEM
Source of primary growth (lengthening)
THREE PRIMARY MERISTEMS
Protoderm
epidermis
Ground meristem
ground tissue
Procambium
primary vascular tissues
ROOT APICAL MERISTEM
Apical meristem near all root tips gives rise to
protoderm, ground meristem, and procambium
These give rise to the root’s primary tissue
systems: epidermis, ground tissues, and
vascular tissues
immature leaf
shoot apical meristem
procambium
protoderm
procambium
ground meristem
epidermis
cortex
primary phloem
procambium
primary xylem
pith
Fig. 35.19
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
cuticle
upper
epidermis
leaf vein
xylem
palisade
mesophyll
phloem
spongy
mesophyll
lower
epidermis
water, minerals
products of
photosynthesis
oxygen and
water vapor
cuticle-coated cell
of lower epidermis
one stoma
carbon
dioxide
pit in cell wall
one vessel
member
cytoplasm
absent
(cells dead
at
maturity)
sieve plate
sieve-tube
member
companion
cell (living)
vascular cambium
produced by pericycle
epidermis
cortex
endodermis
pericycle
primary procambium
xylem
primary
phloem
vascular cambium
produced by
procambium
secondary
xylem
secondary
phloem
vascular
cambium
pericycle
derivatives
vascular ray
cortex,
epidermis
slough off
crushed
primary
phloem
Pattern of activity at vascular cambium
outer surface
of stem or
root
division
One of the
cells of
vascular
cambium
at the
start of
secondary
growth
division
One of the two
daughter cells
differentiates
into a xylem
cell (coded
blue), and the
other remains
meristematic
One of the two
daughter cells
differentiates
into a phloem
cell (coded
pink), and the
other remains
meristematic
The same pattern
of cell division and
differentiation into
xylem and phloem
cells continues through
the growing session
direction of growth
secondary
phloem
vascular cambium
cork cambium
secondary
xylem
thickening
LATERAL MERISTEMS
Two lateral meristems in older stems and roots of woody
plants produce secondary growth (increases in diameter):
Vascular cambium
Cork cambium
secondary vascular tissues
periderm (replaces epidermis)
periderm
secondary
phloem
BARK
vascular cambium
HEARTWOOD
SAPWOOD
Fig. 36.11
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 36.10
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Hakea gibbosa leaf, longitudinal section
thick cuticle
closed stoma between
two guard cells
(side view)
palisade mesophyll cell
air space
Driving force of
evaporation
into dry air
Cohesion in xylem
of roots, stems, and
leaves
Water uptake in
growth regions
Water uptake
from soil by roots
K+
ABA
signal
K+
Ca+ +
Ca+ +
malate
stoma (open)
Water has moved in
malate
stoma (closed)
Water has moved out
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upper epidermis
photosynthetic
cell
sieve tube
companion cell
lower epidermis
Section from a leaf
Translocation along a distribution path
sieve tube
Section from a stem
sieve tube of the phloem
SOURCE
Active transport
moves solutes
into sieve tubes
Pressure pushes
bulk
solutes by bulk
flow
flow between
source and sink
Solutes unloaded
into sink cells,
lowering their
water potential;
water follows
WATER
Water moves
in, increasing
turgor pressure
Pressure and
solute
concentrations
decrease
between source
and sink
SINK
• In most plant tissues, two of the three
cellular compartments are continuous from
cell to cell.
– Plasmodesmata connect the cytosolic
compartments of neighboring cells.
– This cytoplasmic continuum, the symplast,
forms a continuous pathway
for transport.
– The walls of
adjacent plant cells
are also in contact,
forming a second
continuous
compartment, the
apoplast.
Fig. 36.6b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 36.7
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
in root cortex;
water molecules
pass through
and between
walls of cells
Casparian strip
vascular cylinder
exodermis
root hair
epidermis
newly forming
vascular cylinder
cortex
Casparian strip (gold)
within all the abutting walls
of cells of the endodermis
water and solutes
Waxy, water-impervious
Casparian strip in abutting
walls of endodermal cells
• Parenchyma cells perform most of the
metabolic functions of the plant,
synthesizing and storing various organic
products.
– For example, photosynthesis occurs within the
chloroplasts of parenchyma cells in the leaf.
– Some cells in the stems and roots have
colorless plastids that store starch.
– The fleshy tissue of
most fruit is composed
of parenchyma cells.
Fig. 35.11a
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Collenchyma cells have thicker primary
walls than parenchyma cells, though the
walls are unevenly thickened.
– Grouped into strands or cylinders, collenchyma
cells help support young parts of the plant
shoot.
– Young cells and petioles often have a cylinder
of collenchyma just below their surface,
providing support without restraining growth.
– Functioning collenchyma cells are living and
flexible and elongate with the stems and
leaves they support.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Fig. 35.11b
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Sclerenchyma cells also function as
supporting elements of the plant, with thick
secondary walls usually strengthened by
lignin.
– They are much more rigid
than collenchyma cells.
– Unlike parenchyma cells,
they cannot elongate and
occur in plant regions that
have stopped lengthening.
Fig. 35.11c
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Many sclerenchyma cells are dead at
functional maturity, but they produce rigid
secondary cells walls before the protoplast
dies.
– In parts of the plant that are still elongating, the
secondary walls are deposited in a spiral or
ring pattern, enabling the cell wall to stretch
like a spring as the cell grows.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• Vessel elements and tracheids in the xylem
are sclerenchyma cells that function for
both support and transport.
• Two other sclerenchyma cells, fibers and
sclereids, are specialized entirely in
support.
– Fibers are long, slender and tapered, and
usually occur in groups.
• Those from hemp fibers are used for making rope
and those from flax for weaving into linen.
– Sclereids, shorter than fibers and irregular in
shape, impart the hardness to nutshells and
seed coats and the gritty texture to pear fruits.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
• A major difference between plant and most
animals is that the growth and development
of plants is not just limited to an embryonic
or juvenile period, but occurs throughout
the life of the plant.
– At any given instance, a typical plant consists
of embryonic organs, developing organs, and
mature organs.
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings