Plant Form
Chapter 36
Plant Body Organization
A vascular plant consists of:
1. Root system, which is underground
-Anchors the plant, and is
used to absorb water and minerals
2. Shoot system, which is above ground
-Consists of supporting stems,
photosynthetic leaves and
reproductive flowers
Each has an apex that extends growth
Roots, shoots and leaves contain three basic
tissue systems:
-Dermal tissue – For protection (Wax and bark)
-Ground tissue – For storage, photosynthesis
and secretion
-Vascular tissue – For conduction
-Xylem – Water and dissolved minerals
-Phloem – Nutrient-containing solution
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Plant Cells
Plant cell walls consist of cellulose
-Primary cell wall
-Found in all cells
-Cellulose fibers parallel to microtubules
-Secondary cell wall
-Found in some cells
-Additional layers of cellulose and lignin
-Increase mechanical strength of wall
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Plant Stem Cells
Meristems are clumps
of small cells with dense
cytoplasm and large nuclei
They act as stem
cells do in animals
-One cell divides producing
a differentiating cell and
another that remains
meristematic
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The Primary Plant Body
Apical meristems are located at the tips of stems and roots
-Give rise to primary tissues which are collectively called the
primary plant body
-Three primary meristems (that come from apical meristem)
-Protoderm  Epidermis
-Procambium  1o vascular tissue
-Ground meristem  Ground tissue
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Secondary Plant Body (increases girth)
Lateral meristems are found in
plants that exhibit secondary
growth
-Give rise to secondary
tissues which are collectively
called the secondary plant
body
-Woody plants have two types
-Cork cambium  Outer
bark
-Vascular cambium 
2o vascular tissue
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Plant Tissues
As mentioned earlier, plants contain three
main types of tissue
-Dermal
-Ground
-Vascular
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Dermal Tissue
*Forms the epidermis, which is usually one cell
layer thick & is outer protective covering
*Covered with a fatty cutin layer constituting the
cuticle (prevents water loss)
*Contains special cells, including guard cells,
trichomes and root hairs
Guard cells are paired sausage-shaped cells
-Flank a stoma, which is the passageway for oxygen and
carbon dioxide...and is the epidermal opening between 2
guard cells
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Dermal Special Cells Continued
Trichomes are cellular or multicellular hairlike
outgrowths of the epidermis
-Keep leaf surfaces cool and reduce evaporation
by covering stomatal openings
-Some are glandular,
secreting substances
that deter herbivory
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Dermal Special Cells Continued
Roots hairs are tubular extensions of individual
epidermal cells in growing roots
-Greatly increase the
root’s surface area
and efficiency of
absorption...of water
and minerals
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Ground Tissue
A tissue that functions in food, water storage,
photosynthesis and secretion...Consist of 3 types of
cells
Collenchyma cells - support for
organs, bend but don’t break
Parenchyma cells - most common
plant cell
-storage,photosynthesis,secretion
-chloroplasts-chlorenchyma
Sclerenchyma cells - tough
thick walls...usually have
Secondary cell walls with
lignin (polymer seen in
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wood)
Vascular Tissue
Xylem
-Constitutes the main
water-and mineral-conducting
tissue...
Water goes in a stream from roots
to shoots and out of the leaves
via transpiration
-Vessels: Continuous tubes
of dead cylindrical cells
arranged end-to-end
-Tracheids: Dead cells
that taper at the end and
overlap one another
-Vessels are shorter &
wider than tracheids
-And conduct water
more efficiently
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Vascular Tissue
Xylem
-Also conducts inorganic ions such as
nitrates, and supports the plant body
-Typically includes parenchyma cells in
horizontal rows called rays
-Function in lateral conduction and
food storage
Note: The diffusion of water vapor from a
plant is termed transpiration
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Vascular Tissue
Phloem
-Constitutes the main food-conducting tissue in
vascular plants
-Contains an elongated living cell with no nuclei
called sieve tube members
-Associated with companion cells
nourishes sieve tube member cells
Phloem transports
sucrose, hormones, and amino acids
Plants synthesize Amino Acids
from Carbon and Oxygen
obtained from air, Hydrogen
from water in the soil. They
form Carbon Hydrate via
photosynthesis and combine it
with Nitrogen obtained from the
soil, leading to synthesis
of amino acids
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Roots
Root cap
-Contains two types of cells that are
formed continuously by the root
apical meristem
-Columella cells: Inner
-Root cap cells: Outer and lateral
-Functions mainly in protection of
the delicate tissues behind it
-Also in the perception of
gravity...columella cells have
amyloplasts (plastids with starch
grain) that collect on the side nearest
the source of gravity...roots bend in
that direction
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Roots
Zone of cell division
-Contains mostly cuboidal cells, with small vacuoles and large
central nuclei
-Derived from rapid divisions of the root apical meristem
-Quiescent center cells divide very infrequently
-Apical meristem daughter cells soon subdivide into the three
primary tissues
Zone of elongation
-Roots lengthen because cells become several times
longer than wide
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Cross Section of the Zone of
Maturation
Zone of maturation
-The elongated cells become differentiated into specific cell types
-Epidermal cells: Have very thin cuticle
-Include root hair and nonhair cells
-Cortex: Interior to the epidermis
-Parenchyma cells used for storage
Casparian strip (made of suberin) forces water through plasma
membrane...membrane itself acts as a water filter
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Modified Roots
Prop roots
Aerial roots
Obtain
water from
air
Keep plant
upright
Pneumatophores
Oxygen uptake
Water storage roots
Weigh over 60 pounds
Buttress roots
Stability
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Stems
Like roots, stems contain the three types of
plant tissue
-Also undergo growth from
cell division in apical and
lateral stems
Shoot apical meristem
initiates stem tissue and
intermittently produces primordia
-Develop into leaves, other
shoots and even flowers
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Stems
Leaves may be arranged in one of three ways
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External Stem Structure
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External Stem Structure
Node = Point of attachment of leaf to stem
Internode = Area of stem between two nodes
Blade = Flattened part of leaf
Petiole = Stalk of leaf
Axil = Angle between petiole/blade and stem
Axillary bud = Develops into branches with
leaves or may form flowers
Terminal bud = Extends the shoot system
during the growing season
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Internal Stem Structure
Vascular tissue arrangement
is directly related to the stem’s ability for
secondary growth
-In eudicots, a vascular
cambium develops between
the primary xylem and phloem
-In monocots, there is no
vascular cambium
-Therefore, no secondary growth
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Bulbous
Underground
stem with
fleshy leaves
Modified Stems
Swollen tip
of rhizome
Underground
stems
Used for
climbing
Grow along
ground
Resemble
leaves
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Leaves
Leaves are the main site of photosynthesis -They are
determinate structures whose growth stops at maturity
A leaf-blade has veins which consist of xylem and phloem
-Microphyll Leaves= Have one vein
-Megaphylls Leaves = Have many veins (most plants)
-Monocot leaves
have parallel
veins
-Eudicot leaves have
netted or reticulate
veins
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Leaves
Simple – undivided blades
Pinnate - paired
leaflets
Palmate - center axis
of leaflets
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Basic Leaf Histology
Epidermis has a waxy cuticle
-The lower epidermis contains numerous
mouth-shaped stomata flanked by guard cells
The mesophyll is the tissue between
the upper and lower epidermis
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