Chapter 29
Plant Tissue
Overview of the Plant Body
• Although no one species of the 295,000
species of plants can be considered
typical, the focus here is on angiosperms
Shoots and Roots (Figure 29.2)
• Shoots consist of stems, leaves, and
flowers (reproductive structures)
– Water, minerals, and organic substances are
transported
– Stems are frameworks for upright growth and
to display flowers
– Parts of the system store food.
Continue…
• Root system absorbs water and minerals
from soil and conducts them upward
• Root store food
• Anchor and support the plant
Three plant tissue system
• 1- Ground Tissue: makes up the bulk of
the plant body (food and water storage)
• 2- Vascular tissue system: contains two
kinds of conducting tissues that distribute
water and solutes through the plant body.
• 3- Dermal Tissue system: covers and
protects the plant’s surfaces.
Where Do Plant Tissues Originate?
• Meristems are localized regions of selfperpetuating, embryonic cells.
• Two kinds of meristems
– 1- Apical meristems: at tips of roots and stems
is responsible for growth and elongation
• Growth originating at the root and shoot tips is
labeled primary growth
Continue…
• Lateral meristem: are responsible for the
increase in diameter of older roots and
stems.
– Vascular Cambium and cork cambium are two
kinds of lateral meristems
– These are responsible for secondary growth
which adds to wood parts of the trees.
Types of Plant Tissues
• Simple Tissues:
– 1- Parenchyma makes up most of the soft,
moist primary growth of plants
• Thin walled pliable cells stay alive and retain the
capacity to divide
• Various types of participate in photosynthesis
(mesophyll), storage, secretion, and other tasks.
– 2. Collenchyma: cells are thickened and help
strengthen the palnt (e.g. strings of celery)
• It commonly arranged at strands or cylinders
beneath the dermal tissue of stems and stalks
• The primary cells walls of collenchyma become
thickened with cellulose and pectin at maturity.
– 3. Sclerenchyma: cells provide mechanical
support and protection for mature plants
• Secondary walls are thick and often impregnated
with lignin, which strengths and waterproofs the
cell walls
• Form fibers such as hemp and flax
– Sclereids form strong coats around seeds as in a peach
pit
Complex Tissues
• Vascular tissues function in the distribution
of substances throughout the plant
– Xylem uses two kinds of cells (dead at
maturity) to conduct water and minerals
absorbed from the soil
• Vessel members: are shorter cells joined end to
end to form a vessel with perforation plates at the
end of each member
• Tracheids are long cells with tapered, overlapping
ends
Continue…
– Phloem: transports sugar and other solutes
throughout the plant body.
• Phloem contains living conducting cells called
sieve tube members which bear clusters of pores
in the walls through which the cytoplasm of
adjacent cells is connected
• Companion cells: adjacent to the sieve tubes
members, help to load sugars produced in leaves
and unload them in storage and growth regions
Continue…
• Dermal Tissue System: called the
epidermis covers all primary plant parts
– Waxy Cuticle covers the external surfaces of
the plant to restrict water loss and resist
microbial attack.
– Stomata openings between pairs of guard
cells permit water and gaseous exchange with
the air
– Periderm replaces the epidermis when roots
and stems increase in diameter and become
woody.
Monocots and Dicots
• Through the rest of chapter we will be
talking about monocots and dicots
• Moncots have one cotelydons (seed leaf)
and Dicots have two cotelydons (seed
leaf)
• Common monocots include: grasses, lilies,
irises and palms.
• Common dicots include: trees and shrubs
Primary Structure of Shoots
• Leaves develop from leaf primordia along
the apical meristems of stems
– A node is the point where a leaf or leaves
attach to the stems
– Internode is the region on the stem between
the two nodes.
Continue…
• Buds develop in the leaf axils (the upper
angle where leaves attach to the stem)
– A bud is underdeveloped shoot of mostly
meristematic tissue covered by modified
leaves (bud scales)
– Buds give rise to stems, leaves, and flowers
Internal Structure of Stems
• A vascular bundle is a multistranded cord
of primary xylem and phloem running
lengthwise through the ground tissue of
shoots.
Similarities and Differences
Among Leaves
• Leaves are metabolic factories equipped
with photosynthetic cells.
• Deciduous trees drop their leaves as
winter approaches
– Evergreen retain their leaves
• Leaves vary enormously in shape, size, texture, and surface
features.
– Monocots leaves tend to have a flat surface – like a knife
blade, the base of which encircles and sheaths the stems
– Dicots leaves have broad blade attached by a petiole to the
stem; the blade may be lobed or composed of leaflets
– Simple leaves: undivided leaves
• Oak
– Compound leaves: divided leaflets
• Locust
• Leaves represent a large surface area that is exposed to
sunlight and carbon dioxide
Leaf Fine Structure
• Epidermis covers every leaf surface
exposed to air (waxy layer)
– A cuticle layer minimizes water loss.
– Stomata are located mostly on the lower
epidermis
Continue…
• Mesophyll consisting of photosynthetic parenchyma
cells extends throughout the interior of the leaf
– Air spaces, which connect to the stomata,
participate in gaseous exchange
– Palisade mesophyll cells lies closer to the epidermis
and are columnar in shape compared to the spongy
mesophyll below them
• Leaf veins are vascular bundles of xylem and phloem
that form a network for movement of water , solutes,
and photosynthetic products
Primary Structure of Roots
• Taproots and Fibrous Root Systems
– In most dicots, the primary root emerges from
the seedling, increases in diameter, and
grows downward.
• Lateral roots emerge sideways along its length
• Primary root plus lateral roots form from the
taproot system
Continue
– Monocots: the taproot is replaced by
adventitious roots that arise from the stem
• The roots and their branching form a fibrous root
system
• Fibrous roots do not penetrate as deeply.
Internal Structure of Roots
• Cells in the apical meristem divide and
then differentiate into root epidermis,
ground tissues, and vascular tissues
behind the meristematic region
– The root cap protects the apical meristem and
pushes through the soil
– Cells are torn loose as the root grows
Continue…
• Protoderm gives rise to the root epidermis with
its extensions called root hairs for the outer
absorptive interface with the environment
• Vascular tissues form a vascular cylinder
arranged as a central column
– The column is surrounded by root cortex (ground
tissue), which has abundant air spaces
– The endodermis- the innermost layer of the cortex
–surrounds the vascular cylinder and helps control
water movement into it
Woody and Nonwoody Plants
• Seasonal growth cycles proceed from
germination, to seed formation to death.
– Annuals complete life cycle in one season,
they are nonwoody , or herbaceous plants
such as corn.
– Biennials such as carrots, live two seasons:
vegetative growth first , flower and seed
formation second season
• Perennials live many years and have secondary
growth (roses, grape vines, and apple trees)
• Woody plants such as dicots and gymnosperms
show secondary growth by producing large
amounts of secondary xylem
Vascular Cambium
• Vascular Cambium is a cylinderlike lateral
meristem.
– It produces a secondary xylem on its inner
face and secondary pholem on its outer.
– The secondary growth displace the cells of
the vascular cambium toward the stem
surface
• Secondary xylem and phloem form at the
vascular cambium of the roots
Formation of Bark
• In response to rupture of the outer cortex (by
girth expansion), cork cambium produces the
periderm – a corky replacement of the
epidermis
– Periderm and secondary pholoem constitute of
bark
– Periderm consist of cork, secondary cortex, and
cork cambium
• Lenticels are small channels through the corky
surface of bark that allow for exchange of
gases
Heartwood and Sapwood
• Heartwood lies at the center of older
stems and roots.
– It depository for resins, oils, gums and tannins
– It makes tree strong and able to defy gravity/
• Sapwood is secondary growth located
between heartwood and the vascular
cambium
– Wet, pale in color and is not strong
– Rich in the sugar-rich fluid of the phloem
Early Wood, Late Wood, and Tree Rings
• In regions with cool winters or dry spells, the
vascular cambium is inactive during part of the
year
– Early wood (start of the growing season) contains
xylem with large diameters and thin walls
– Late wood contains xylem with small diameter and
thick walls
– Growth rings appear as alternating light bands or
early wood and dark bands of late wood
Continue…
• Hardwood: (OAK) has vessels, tracheids,
and fibers in its xylem
• Softwood (CONIFERS) have no vessels or
fibers
Limits to Secondary Growth
• Some trees live in habitats too harsh and
remote for most invaders
• Most trees use a strategy of
compartmentalization to wall off invaders,
building a fortress of thickened cells walls
around wounds or deploying toxic
compounds
•The End