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Plant structure, growth and
development
Chapter 35
Plant Tissues
•
There are three categories of plant tissues
– Dermal tissues
• form the outer covering of the plant
• serve a protective function
• herbaceous plants – epidermis
• Woody plant – periderm (outer bark)
– Vascular Tissues
• Function to transport materials through the plant body and provides support
– Xylem – transport of water and dissolved minerals
– Phloem – transport of dissolved sugars
• Arranged into vascular cylinder in the root or vascular bundles in stems and
leaves
– Ground Tissues
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Neither dermal or vascular
Pith – internal ground tissue (in vascular cylinder or stem)
Cortex – ground tissue located towards the outside of the plants organs
Functions for storage, photosynthesis
Cell types composing
plant tissues
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Simple tissues
– Collenchyma
• Cell walls of irregular
thickness
• Flexible support
– Parenchyma
• Cell walls very thin to
facilitate movement
of particles through
cell
• Storage,
photosynthesis
– Sclerenchyma
• Very thick cell walls
(primary and
secondary cell walls
made of lignin)
• Dead at maturity
• Sclerenchyma fibers
and sclerids
• Rigid support
Cell types composing
plant tissues
• Complex tissues
– Xylem
• Tracheids and vessels
– Modified
sclerenchyma fibers
– Dead at maturity
(hollow)
– Phloem
• Sieve tubes and
companion cells
• Companion cells alive
• Sieve tubes dead at
maturity (sclerenchyma
fibers)
Plant organs
•
Plant organs may
be divided into two
systems
– Shoot system
• Above ground
(usually)
• Stem
• Leaf
• Flower
– Root system
• Taproot
(primary)
• Lateral roots
(secondary)
• Adventitious
roots (arise from
stem)
Growth of plant parts
•
Plant exhibit localized growth at
meristems
– Apical meristems – produce primary
tissues and increase the length of
plant parts
• Found at the tips of roots (root
apical meristem) and in buds on
stems (terminal buds and axillary
buds)
– Lateral meristems are found in
woody plants and increase the girth
of plant parts
• Vascular cambium – produces
secondary xylem and phloem
• Cork cambium – produces cork
cells that will form periderm (outer
bark)
The root system
• Functions of the root
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Absorption of water and nutrients
Anchorage
Storage
Soil erosion
Other root modifications:
Root modifications
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Prop roots
– Adventitious
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Storage roots
Aerial roots
Buttress roots
Pneumatophores
– Exchange
gases
Root anatomy
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Zone of cell division
– Root apical meristem
– Protected by root cap
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Zone of elongation
Zone of maturation
– Contains mature
tissues
– Root hairs
• Cytoplasmic
extension of
epidermal cells
• Increase surface
area
•
Layers of typical root
– Epidermis
– Cortex
– Vascular cylinder
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Be sure to know the difference
between monocot and eudicot
roots
Epidermis
Cortex
Vascular cylinder
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Endodermis
Pericycle
Pith (in monocots)
Xylem/phloem
Development of lateral (secondary)
roots from pericycle
•
Notice that
the vascular
cylinder of the
original root
and the lateral
root are
connected
The stem
• Part of shoot system
• Functions for support of leaves and flowers
• Modifications allow for other functions as well
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Bulbs
Stolons
Rhizomes
tubers
Stem anatomy
(external)
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Node
Internode
Axil
Axillary bud
Terminal bud
Bud scale
– Modified leaf to
protect apical
meristem
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Terminal bud
scar
Leaf scar
Stem anatomy
(internal)
•
Be sure to note differences
between monocots and eudicots
Secondary growth to produce woody tissues
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All woody plants exhibit
primary growth to produce
new shoots (herbaceous)
Secondary growth at
lateral meristems is
responsible for the
production of woody
tissues and increases the
girth of plant
– Vascular cambium
– Cork cambium
• Wood (secondary xylem)
– Heartwood vs.
sapwood
• Cork cells form periderm
outer bark
• Secondary phloem
forms inner bark
Secondary growth to produce woody tissues
The leaf
• Primary function of
photosynthesis
• Form = function
– CO2 + H2O Æ C6H12O6 + O2
– Other function of leaves (leaf
modifications)
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Tendrils
Spines
Storage
Bracts
Reproductive leaves (asexual)
Leaf anatomy (external)
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Axil
Petiole
Blade
veins
Leaf types
• Simple – one blade per leaf
• Compound – blade divided into leaflets
– Palmate
– Pinnate (once –pinnate and twice pinnate)
Leaf anatomy
(internal)
Epidermis
cuticle
guard
cells
stoma
Mesophyll
palisade
spongy
Vein
bundle
sheath
xylem
phloem