Chapter 35
Plant Structure and Growth
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1
Monocots Vs. Dicots
(Eudicots)
•Formerly, angiosperms were divided
into two groups:
–Monocots-one cotyledon.
–Dicots-two cotyledons.
•There were also many other features
that distinguished the two groups.
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Current Research on the
Topic
•Current research suggests that
monocots form their own clade.
•The remaining angiosperms are
divided among many lineages
–Most of which are known as eudicots.
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Monocots Vs. Eudicots
• One cotyledon
• Parallel veins
• Scattered vascular
tissue
• Fibrous roots
• Floral organs in multiples
of three
 Two
cotyledons
 Webbed veins
 Vascular tissue in a ring
 Taproot present
 Floral organs in
multiples of 4 or 5
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Cell Organization
•Tissues are groups of cells with a
common function.
•Tissues (or many different types)
comprise organs--they carry out
particular functions.
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3 Basic Organs
• Three basic organs
evolved to take
advantage of this
– 1. Roots
– 2. Stems
– 3. Leaves
• They are organized
into a root system
and a shoot system.
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Plant Tissue
•Plants have 3 tissue
systems:
–1. Dermal
–2. Vascular
–3. Ground
•Each plant organ has
the three tissue types.
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1. The Dermal Tissue System
•It is the outer protective covering, it’s
the first line of defense against
physical damage and pathogens.
•Non-woody plants consist of a tightly
packed tissue called the epidermis.
•Woody plants consist of protective
tissues called periderm (eventually
forming bark).
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1. The Dermal Tissue System
•The epidermis also forms the cuticle
which assists in protection, disease
prevention, and prevention of water
loss.
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2. The Vascular Tissue System
•Carries out long-distance transport of
materials between roots and shoots.
•The 2 tissues are:
–A. Xylem
–B. Phloem
•Together, they’re the stele
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Stele
• The vascular tissue of a root or
stem is called the stele.
– In angiosperms, the stele of the
root is in the form of a solid
vascular cylinder.
– The stele of the stem and leaves
is arranged into a vascular
bundle--strands consisting of
xylem and phloem.
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A. Xylem
•Xylem conveys water and dissolved
minerals upward from roots to shoots.
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A. Xylem
•The two types of water conducting
cells of xylem.
–A. Tracheids
–B. Vessel Elements:
•These are dead at functional maturity.
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A. Tracheids
• Are found in the xylem of all
vascular plants.
• Most angiosperms, a few
gymnosperms, and a few
seedless vascular plants
have vessels.
• When the cell dies, a nonliving conduit remains
through which water flows.
• The secondary cell walls
contain lignin.
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B. Vessel Elements
•Usually wider, shorter
and thinner than
tracheids.
•They are long
micropipes and are
aligned end to end.
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B. Phloem
•Phloem transports organic nutrients
from where they are made to where
they are needed (from leaves to root
tips, developing leaves and fruits).
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B. Phloem and Sieve Tubes
•The sugar conducting
cells of phloem are
alive at maturity.
•The sugar and other
organic nutrients flows
through sieve tubes.
•The end walls of sieve
tubes have sieve plates
which have pores that
allow fluid to move
from tube to tube.
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Companion Cells
•Sieve tubes have companion cells
that help to load sugars into sieve
tube members.
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3. Ground Tissue
• The ground tissue systems provides
for storage, photosynthesis and
support.
• The ground tissue system comprises
tissues that are neither dermal nor
vascular.
• Pith is ground tissue internal to the
vascular tissue.
• The cortex is ground tissue external
to the vascular tissue.
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Meristems
•Contain perpetually embryonic cells.
•There are two main types:
–1. Apical
–2. Lateral
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1. Apical Meristem
•These are located at the tips of roots
and in the buds of shoots.
•These enable primary growth (length).
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2. Lateral Meristem
•After the primary growth from the
apical meristem has stopped, the
remaining growth is mostly all
secondary (girth).
•It increases the girth of the plant.
–A. Vascular cambium
–B. Cork cambium
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A. Vascular Cambium
•Adds layers of
vascular tissue to the
woody plant.
•Secondary xylem
(wood)
•Secondary phloem
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A. Vascular Cambium
•Viewing a transverse
section of a woody
plant:
–The vascular cambium
appears as a ring with
interspersed regions of
fusiform initials and ray
initials.
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Fusiform Initials
•Produce elongated cells--tracheids,
vessel elements, fibers of xylem, sieve
tube members, companion cells,
parenchyma and fibers of phloem.
•These run parallel to the root axis.
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Ray Initials
•These are shorter and run
perpendicular to the stem/root axis.
•These consist of parenchyma cells
and provide a way for H2O and
nutrients to flow between secondary
xylem and secondary phloem.
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B. Cork Cambium
•Replaces the epidermis with periderm
which is thicker and tougher.
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Primary and Secondary
Growth
•Viewing a transverse section, the
vascular cambium appears as a ring.
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Primary and Secondary
Growth
•There are interspersed regions of
fusiform initials and ray initials.
•When these initials divide they
increase the circumference of the
cambium.
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Primary Growth
•Recall, primary
growth produces
the main plant
body.
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Secondary Growth
•Secondary growth
continues over the
years and layers of
wood accumulate
(secondary xylemtracheids, vessel
elements and
fibers.)
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Secondary Growth
•They have thick,
lignified cell walls
that give wood its
hardness.
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