Plant Tissues

Chapter 26

Jin Hoe
Huh

March 28,
2005

Angiosperms – flowering

plants

• The angiosperms are seed-bearing

vascular plants

• In terms of distribution and

diversity, they are the most
successful plants on Earth

• The structure and function of this

plant group help explain its success

Flowerin

g Plant

Life Cycle

Double fertilization

Meiosis

Meiosis

microspores

Female gametophyte

pollination

Mitosis
without
cytoplasm
ic division

Two
sperms
enter
ovule

Diploid

Haploid

Plant Life Histories

• Annuals complete life cycle in

one growing season

• Biennials live for two seasons;

flowers form in second season

• Perennials grow and produce

seeds year after year

Shoot
Syste
m

Root
Syste
m

Root system

- anchors the plant
- penetrates the soil and
absorbs water and
minerals

- stores food

Shoot system

- produces sugars by
photosynthesis

- carries out
reproduction

Shoot and Root
Systems

water &
minerals

sugar

SHOOT SYSTEM

ROOT SYSTEM

Shoot and root
systems are
interdependent

Plant Tissue
Systems

VASCULAR TISSUES

GROUND TISSUES

SHOOT SYSTEM

ROOT SYSTEM

EPIDERMIS

• Ground tissue

system

• Vascular tissue

system

• Dermal tissue

system

Meristems – Where Tissues

Originate

• Regions where cell divisions

produce plant growth

• Apical meristems

– Lengthen stems and roots
– Responsible for primary growth

• Lateral meristems

– Increase width of stems
– Responsible for secondary growth

Apical Meristems

activity at
meristems

new cells
elongate
and start to
differentiate
into primary
tissues

procambium



primary

vascular tissues

protoderm



epidermis

Cells that form at

apical meristems:

ground meristem



ground tissues

Lengthen shoots and
roots:
SAM and RAM

Lateral Meristems

vascular cambium



secondary vascular

tissues

periderm



cork cambium

thickening

Increases girth of older roots and stems

Cylindrical arrays of cells

Simple Tissues

Made up of only one

type of cell

Parenchyma

Collenchyma

Sclerenchyma

collenchym

a

parenchy

ma

sclerenchym

a

Morphology of three simple tissue

types

Parenchyma: A Simple

Tissue

• Comprises most of a plant’s soft primary

growth

• Cells are pliable, thin walled, many sided
• Cells remain alive at maturity and retain

capacity to divide

• Mesophyll is a type of parenchyma that

contains chloroplasts

Collenchyma: A Simple

Tissue

• Specialized for support for primary

tissues

• Cells are elongated, with walls

(especially corners) thickened with
pectin

• Makes stems strong but pliable
• Cells are alive at maturity

Sclerenchyma: A Simple

Tissue

• Supports mature plant parts
• Protects many seeds
• Cells have thick, lignified walls and are

dead at maturity

• Two types:

– Fibers: Long, tapered cells
– Sclereids: Stubbier cells

Complex Tissues

Composed of a mix of cell types

Xylem

Phloem

Epidermis

Xylem

• Conducts water

and dissolved
minerals

• Conducting cells

are dead and
hollow at
maturity

vessel
member

tracheids

Phloem:

A Complex Vascular Tissue

• Transports sugars

• Main conducting

cells are sieve-
tube members

• Companion cells

assist in the
loading of sugars

sieve plate

sieve-tube

member

companion

cell

Epidermis:

A Complex Plant Tissue

- Covers and protects
plant surfaces

- Secretes a waxy,
waterproof cuticle

- In plants with
secondary growth,
periderm replaces
epidermis

Monocots and Dicots –

same tissues, different

features

Parallel veins

Netlike veins

3 pores

1 pore

4 or 5
floral
parts

3 floral
parts

1 cotyledon

2 cotyledons

Vascular
bundles
dispersed

Vascular
bundles
in ring

Shoot

Developme

nt

ground
meristem

primary
xylem

pith

procambriu
m

corte
x

procambrium

protoder
m

shoot
apical
meristem

primary
phloem

Bud = undeveloped shoot of

meristematic tissue

Internode

Leaves

Axillary bud at node

Longitudinal section of terminal bud

Roots also have meristems

Internal Structure of a

Dicot Stem

- Outermost layer is epidermis
- Cortex lies beneath epidermis
- Ring of vascular bundles
separates the cortex from the
pith
- The pith lies in the center of
the stem

Internal

Structure

of a

Monocot

Stem

• The vascular
bundles are
distributed
throughout the
ground tissue
• No division of
ground tissue into
cortex and pith

Dicots

Dicots and Monocots have different stem and root anatomies

Ground tissue

system

Vascular tissue

system

Dermal tissue

system

Monocot

s

Leaf Gross Structure

petiole

blade

axillary
bud

node

blade

sheath

node

DICOT

MONOCOT

Adapted for

Photosynthesis

• Leaves are usually thin

– High surface area-to-volume ratio
– Promotes diffusion of carbon dioxide in,

oxygen out

• Leaves are arranged to capture sunlight

– Are held perpendicular to rays of sun
– Arrange so they don’t shade one another

Leaf Structure

UPPER

EPIDERMIS

PALISADE

MESOPHYLL

SPONGY

MESOPHYLL

LOWER

EPIDERMIS

one stoma

cuticle

O

2

CO

2

xylem

phloem

Mesophyll:

Photosynthetic Tissue

• A type of parenchyma

tissue

• Cells have chloroplasts
• Two layers in dicots

– Palisade mesophyll
– Spongy mesophyll

Parenchyma

Collenchyma

Leaf Veins: Vascular

Bundles

• Xylem and phloem –

often strengthened with

fibers

• In dicots, veins are netlike

• In monocots, they are

parallel

Root Systems

Root

Structure

• Root cap covers tip
• Apical meristem

produces the cap

• Cell divisions at the

apical meristem cause
the root to lengthen

• Farther up, cells

differentiate and mature

root

apical

meristem

root

cap

Internal Structure of a

Root

• Outermost layer is epidermis

• Root cortex is beneath the epidermis

• Endodermis, then pericycle surround

the vascular cylinder

• In some plants, there is a central pith

pericycle

phloe

m

xylem

root

hair

endoderm

is

epidermi

s

cortex

Root Hairs and Lateral

Roots

• Both increase the surface

area of a root system

• Root hairs are tiny

extensions of epidermal cells

• Lateral roots arise from the

pericycle and must push
through the cortex and
epidermis to reach the soil

new
lateral
root

Secondary Growth

• Occurs in perennials
• A ring of vascular cambium

produces secondary xylem and
phloem

• Wood is the accumulation of these

secondary tissues, especially xylem

Secondary Growth

Woody Stem

periderm (consists of
cork, cork cambium,
and secondary cortex)

secondary
phloem

BARK

HEARTWOOD

SAPWOOD

vascular cambium

Annual Rings

• Concentric rings of secondary xylem
• Alternating bands of early and late

wood

• Early wood

– Xylem cells with large diameter, thin walls

• Late wood

– Xylem cells with smaller diameter, thicker

walls

Types of Wood

• Hardwood (oak, hickory)

– Dicot wood
– Xylem composed of vessels,

tracheids, and fibers

• Softwood (pine, redwood)

– Gymnosperm wood
– Xylem composed mostly of tracheids
– Grows more quickly