THE PLANT BODY
Meristems
In flowering plants cells originate from
regions of active cell division known as
meristems.
 The cells arising from meristems give
rise to the many different cell types that
make up a plant

Types of Meristems
Primary Meristems (also called Apical
Meristems) result in primary growth growth in length
 Secondary Meristems result in
secondary growth which in growth in
width (increase in diameter)

Apical meristems
Also known as primary meristems
 Found at the tips of all roots and stems
 Contribute to the increase in length of
the plant which is called primary growth
 Give rise to the leaves, and non-woody
stems and roots

Secondary Meristems

Some plants have additional meristems
that result in increases in diameter
which is secondary growth.
• Vascular cambium
• cork cambium
Multicellular Organisms
In multicellular organisms, certain cells
are specialized in structure and function
 Tissues are specialized cells that
perform specific functions
 Plants composed of three basic tissues
categories

• Dermal
• Ground
• Vascular
Dermal Tissue
Dermal tissues are the outermost layers
in a plant
 They protect the plant
 Two types of dermal tissues

• Epidermis
• Periderm
Epidermis



Outermost layer In
young plants and
non-woody plants
Single layer of
flatten cells
Cells secrete cutin
which makes up the
cuticle and
prevents water loss
Cuticle
Epidermal
Cell
Trichomes



Hairs (trichomes)
may be present on
the epidermis.
Sometime abundant
enough so leaves
look fuzzy
Trichomes may also
be glandular
Hair
Gland
Guard Cells and Stomata
Pores known as stomata (singular
stoma) occur on epidermis
 Gases exchange occurs through
stomata
 A pair of sausage-shaped cells, guard
cells, regulate the opening and closing
of the stomata

Guard Cells and Stoma
Guard Cell
Stoma (opening)
Periderm
In woody plants when the tree increases
in diameter, the epidermis cracks and is
replaced by periderm
 The periderm consists:

• Cork cells
• Cork cambium
Cork Cells
Outer bark on mature trees
 Dead cells with walls containing
suberin, a waterproofing fatty
substance.
 Prevents water loss from underlying
tissues
 Produced by cork cambium

Ground tissues
Major tissue of non-woody plant organs
 Perform a variety of functions
 The three types of ground tissue:

• Parenchyma
• Collenchyma
• Sclerenchyma
Parenchyma
Almost any shape or size
 Loosely arranged with intercellular
spaces
 Many different functions:

• Photosynthetic cells in leaves and green
stems
• Storage cells in plant organs for starch,
sugar, or water
Parenchyma Cells
Intercellular
spaces
Parenchyma Cells
Collenchyma
Support tissue in young plant organs
 Found in stems, leaves, and petals
 Elongated cells with unevenly thickened
primary cell walls with the walls thickest
at the corners
 Found tightly packed together just
below the epidermis

Collenchyma Cells
Cross
section
showing
uneven
wall
thickening
Longitudinal view
Sclerenchyma

Two cell types
• fibers
• sclereids.
Non-living at maturity
 Thickened secondary walls

Fibers
Elongate cells
 Function in support
 Leaf and stem fibers from many plants
used for cloth and rope.

Sclereids
Various shapes
 Functions

• mechanical support and
• protection

Account for the hardness in nut shells
and the grit of pear fruit
Sclerenchyma
Fiber
X-section of fiber showing
thick secondary wall
Sclereid
x-section
showing
thick
secondary
wall
Sclereids
Sclereids
Vascular tissues
Xylem - conducts water and minerals
from the roots upward
 Phloem - transports organic materials
(sugars) synthesized by the plant

Xylem

Cells conducting water - non-living
• Tracheids - long thin cells with tapering
walls and numerous pits
• Vessel elements - short, wide, with
horizontal end walls with large openings
• Both cells have secondary walls
Fibers - non-living - provide support
 Parenchyma cells - metabolic activity

Tracheids and Vessels
Xylem Cells from Oak Wood
Primary and Secondary Xylem
Primary xylem develops from the
apical meristem
 Secondary xylem develops from the
vascular cambium.
 In trees secondary xylem is very
extensive

Phloem

Cell Types in phloem
•
•
•
•

Sieve Tube Members - transport sugars
Companion Cells - loading and unloading
Fibers - support
Parenchyma - metabolic activity
Primary and Secondary phloem
Sieve Tube Member
• Living cells with
only thin primary
walls
• End walls have
sieve plates (large
pores with large
plasmodesmata)
End wall
with sieve
plate
Companion cells
• Specialized parenchyma cell
develops alongside a sieve tube
member
• Plasmodesmata connect it to sieve
tube member
• Loading and unloading sugars for
transport
Plant Tissues and Cells



Tissue Type
Dermal
Cell Types
Function
Epidermis
Periderm
Ground
Parenchyma
epidermal cells
cork cells
protection
protection
parenchyma cells
storage,
photosynthesis
support
support,
protection
Collenchyma
Sclerenchyma
collenchyma cells
sclereids, fibers
Plant Tissues and Cells


Tissue Type
Vascular
Xylem
Phloem
Cell Types
tracheids
vessel elements
fibers
parenchyma
sieve tube
member
companion cells
fibers
parenchyma
Function
water
conduction
support
metabolism
transport
sugars
loading
support
metabolism
Plant Organs

Stems
• Support leaves
• Conduct water and sugars

Roots
• Anchor the plant
• Absorb water and minerals

Leaves
• Photosynthesis
• Transpiration
Herbaceous Dicot Stem
Cross-section
Vascular bundle
P
X
Pith (parenchyma
cells)
Cortex (parenchyma cells)
Epidermis
Monocot Stem
Epidermis
Vascular bundle
Scattered
Vascular Bundles
Ground
Tissue
Roots
Stele
Epidermis
root
hair
Xylem
Cortex
Endodermis
Phloem
Leaf
Epidermis
X
P
Palisade Mesophyll
(parenchyma)
Spongy mesophyll
(parenchyma)
Veins
Leaf from Ligustrum
Secondary Growth in Dicots
5 Year Old Woody Dicot Stem
Periderm (cork)
Cortex
Secondary phloem
Vascular Cambium
5 Years of Secondary Xylem
One
annual
ring
Three Year Old Tree
Dendrochronology
Study of tree rings has added many
fields of study
 Can tell us about past climates
 Can be used to date from archeological
sites artifacts
 Tree ring research lab at the University
of Arizona http://www.ltrr.arizona.edu/

Summary
Growth, replacement of cells, and
asexual reproduction all depend on cell
division
 Tissues are groups of cells that perform
a common function
 Stems, roots and leaves are made up of
three basic tissue types: dermal,
ground, and vascular
