Simplified Plant Tissues
Lesson Plan 4
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Plant Organs

The 3 primary organs found in plants are:
• Leaves
• Stems
• Roots


Since flowers are thought to have evolved
from leaves, they are called “reproductive
structures”.
Leaves, stems, roots, and flowers are all
made up of various tissues.
Plant Tissues

Plant Tissues fall into two large categories:
• Meristematic, or
• Permanent (Non-Meristematic)
Meristematic Tissues


Meristems are places in plants where cell
division is occurring.
During cell division, one cell becomes two
cells. Each new cell can also divide.
Meristematic Tissues

In this class we will discuss three kinds of
meristems:
• Apical Meristems
• Intercalary Meristems
• Lateral Meristems
Apical Meristems

In plants belonging to
the DICOT class,
apical meristems are
located in BOTH the
shoot tips and root tips.
A shoot is simply a
young, leaf-bearing
stem.
 In plants belonging to
the MONOCOT class,
apical meristems are
located ONLY in the
root tips.
Microscopic View of an
Apical Meristem
Apical Meristems

Apical meristems
cause PRIMARY
GROWTH.
 As cells in apical
meristems divide and
elongate, shoot tips
and root tips grow
longer. This increase
in length is called
primary growth.
Apical Meristem in
a Root Tip
Apical Meristems
•Primary growth of shoots
and roots occurs as the cells
of the apical meristem divide
and elongate.
Apical Meristems

A bud is a dormant
apical meristem.
 When conditions are
favorable for growth,
buds “break” and
begin pushing out new
growth.
Bud Break
Buds

Buds come in 3 basic types:
• Vegetative-produce stems and leaves.
• Flower-produce only flowers.
• Mixed-produce stems/leaves and flowers.
Mixed Buds
Mixed buds of Amelanchier x grandiflora
Mixed Buds of Cornus alternifolia
1
2
3
4
Pussy Willow
vegetative
bud
flower bud
Pussy Willow is a plant
which bears separate
vegetative and flower
buds. In the image to the
left you can see vegetative
buds producing green
leaves and flower buds
producing male flowers
(the species is dioecious).
Also, note that the two
different types of buds are
indistinguishable from
one another.
Lantanaphyllum Viburnum
flower bud
vegetative bud
Viburnum x rhytidophylloides, Lantanaphyllum Viburnum,
also bears separate vegetative and flower buds. However,
the two types of buds are distinctly different from one
another in appearance.
Intercalary Meristems


In addition to the apical meristems located
in their root tips, plants in the MONOCOT
class have special meristems called
intercalary meristems.
Intercalary meristems are located on
monocots where the leaf bases connect to
the stem of the plant.
Intercalary Meristems
Monocots, like grasses, have intercalary
meristems which allow the leaves to grow
back after mowing.
Lateral Meristems

In addition to the
apical meristems
located in the shoot
and root tips, plants in
the DICOT class have
lateral meristems.
 Lateral meristems
cause SECONDARY
GROWTH.
 Secondary growth
causes stems and
roots to grow larger in
diameter.
Lateral Meristems cause an
increase in stem diameter
Lateral Meristems
Think of a lateral meristem
as being a cylinder, several
cell layers thick, of
actively dividing cells.
Lateral Meristems




MONOCOTS do not have lateral
meristems.
Lateral meristems come in two basic types:
Vascular cambium; meristematic tissue
located between the xylem and phloem. The
vascular cambium makes new xylem and
phloem cells.
Cork cambium; meristematic tissue located
just below the bark in woody dicot stems.
The cork cambium makes new bark cells.
Lateral Meristems
Phloem
Vascular Cambium
Cross Section of a
Woody Dicot Stem
Xylem (Wood)
Lateral Meristems
Cork (Bark)
Cork Cambium
Vascular Cambium
Woody Dicot Stem
Permanent Tissues

Permanent tissues are non-meristematic.
 The following permanent tissues will be
discussed:
•
•
•
•
•
•
epidermis
xylem
phloem
cortex
pith
fibers
Epidermis

The epidermis can be
from one to several
cell layers thick.
 It covers all the parts
of a plant; shoots,
stems, leaves, and
roots.
 In woody dicots the
epidermis is called the
bark or cork.
Agave Epidermis
Epidermis

The epidermis
covering the leaves of
plants contains
thousands of tiny pores
called stomata. The
singular of stomata is
stoma.
 Stomata are usually
found on the underside
of leaves.
 An apple leaf contains
39,000 stomata per
square centimeter!
Stoma in Fuchsia
Epidermis

In most plants the cells
of the upper and lower
leaf epidermis secrete
a waxy substance that
covers the leaf and
prevents water loss.
 This waxy secretion is
called a cuticle.
Cuticle
Leaf with Cuticle
Epidermis

In many plants, the cells of
the upper and lower leaf
epidermis are modified to
form small hairs.
 These small hairs are called
pubescence.
 Lambs Ear is an example of
a herbaceous perennial that
has pubescent leaves.
Leaf Hair
Cortex



The cortex is a tissue found in both the
stems and roots of monocots and dicots.
The cortex is made up of thin-walled cells.
Vascular bundles are surrounded by the
cortex.
Cortex
Vascular Bundles
Dicot Stem
Monocot Stem
Dicots-Cortex and Pith

In this dicot stem cross
section the cortex,
vascular bundles, and
pith have been
identified.
 The pith is located in
the center of dicot
stems.
Cortex
Vascular Bundle
Pith
Monocots-Cortex

In this monocot stem
cross section the
cortex and vascular
bundles have been
identified.
 Monocots do not have
a pith.
Cortex
Vascular Bundle
Xylem



Xylem
Phloem
fibers not shown
Xylem tissue conducts water
and dissolved mineral
nutrients.
It is composed of columns
of vessel cells (tracheids in
gymnosperms), stacked one
upon another, and fibers.
Vessel cell walls are pitted
and allow water passage
between the xylem and
surrounding tissues. Mature
xylem cells are dead.
Phloem



Xylem
Phloem
fibers not shown
Phloem tissue conducts the
food produced by the leaves in
a downwards direction to
stems and roots (from source
to sink).
Phloem is composed of sieve
tubes, companion cells, and
fibers.
The end walls of the sieve
tubes are called sieve plates.
Fibers

Fiber Cell - the cell
wall is stained dark red.
Fiber cells have thick
walls. A cluster of
fiber cells is called a
fiber.
 Fibers are associated
with the xylem and
phloem of both
monocots and dicots.
 Fibers provide
strength and support to
xylem and phloem.
Fibers
A cluster of many fiber cells
make up a fiber
Fibers
Phloem
Xylem
Cortex
Fibers
Vascular Bundles in
Corn
The End