Monocot vs Eudicot
Monocot vs Eudicot
Internal Structure of Stems
• Vascular bundles of xylem and phloem run through ground
tissues of stems, leaves, and roots
• The bundles conduct water, ions, and nutrients between
different parts of the plant, and also function in support
• vascular bundle
• Multistranded, sheathed cord of primary xylem and
phloem in a stem or leaf
Internal Structure of Stems
• In herbaceous and young woody eudicot stems, a ring of
vascular bundles divides ground tissue into cortex and pith
• Monocot stems have vascular bundles distributed throughout
ground tissue
Primary Structure: Eudicot Stem
Fig. 25.8a.1, p. 402
A Cross-section of
an alfalfa stem.
The cylindrical
arrangement of
vascular bundles
is a characteristic
of eudicot stems.
Primary
Structure:
Eudicot Stem
Fig. 25.8a.3, p. 402
sieve tube
in phloem
vessel in
xylem
companion cell
in phloem
meristem
cellPrimary
Structure:
Eudicot
Stem
Primary Structure: Monocot Stem
Fig. 25.8b.1, p. 402
B Cross-section
of a corn stem.
The vascular
bundles in
monocot stems
are not arranged
in a cylinder.
Primary Structure:
Monocot Stem
Fig. 25.8b.3, p. 402
sieve tube
in phloem
collenchyma
sheath cell
vessel in
xylem
companion cell
in phloem
air
spacePrimary
Structure:
Monocot
Stem
Primary Growth of a Stem
• Most primary growth occurs by cell divisions of apical
meristem in terminal buds (naked or encased in bud scales)
• Meristem cells differentiate into dermal tissues, primary
vascular tissues, and ground tissues
• A lateral bud is a dormant shoot that forms in a leaf axil
• Lateral buds give rise to branches, leaves, and flowers
Primary Stem Growth (Eudicot)
Fig. 25.9a-c, p. 403
A Shoot tip,
tangential cut.
immature leaf
B Same tissue region
later, after the shoot tip
has lengthened above it.
C Later still, different
lineages of cells are
differentiating
and forming complex
tissues.
pith
apical meristem
cortexphloemxylem
Primary Stem Growth
(Eudicot)
Leaf Growth
B Same
tissue region
later, after the
shoot tip has
lengthened
above it.
A Shoot tip,
tangential cut.
immature leaf
apical meristem
C Later still,
different
lineages of
cells are
differentiating
and forming
complex
tissues.
pithcortex
phloemxylem
pith
vascular
tissues
forming
lateral bud
forming
epidermis
forming
apical
meristem
youngest
immature
leaf
immature
leaf
Leaf
Development
A Closer Look at Leaves
• Leaves are metabolic factories where photosynthetic cells
make sugars
• Leaves vary in size, shape, surface specializations, and
internal structure
Similarities and Differences
• Leaf shapes and orientations are adaptations that help a plant
intercept sunlight and exchange gases.
• A typical leaf has a flat blade and, in eudicots, a petiole (stalk)
attached to the stem
• Leaves of grasses and other monocots are flat blades, with a
base that forms a sheath around the stem
• Simple leaves are undivided; compound leaves have blades
divided as leaflets
Fig. 25.10ab, p. 404
node
BA
blade
petiole
sheath
axillary
bud
stem
blade
node
Leaf Forms: Eudicots and Monocots
Fig. 25.10cd, p. 404
elliptic odd pinnate
C
D
elliptic
acuminate odd pinnate lobed odd bipinnate
pinnatisectlobedpalmate
Simple and Compound Leaves
Fine Structure
• Leaves contain mesophyll and vascular bundles between
their upper and lower epidermis
• A leaf’s internal structure is adapted to intercept sunlight and
to enhance gas exchange
• Many leaves also have surface specializations
Leaf Cell Surface Specialization
• Hairs on a tomato leaf: Lobed heads are glandular structures
that secrete aromatic chemicals that deter plant-eating insects
Epidermis
• Epidermis covers every leaf surface exposed to air
• A translucent, waxy secreted cuticle slows water loss from the
sheet-like array of epidermal cells
• Water vapor and gases cross the epidermis at stomata
• Shape changes of guard cells close stomata to prevent
water loss, or open stomata to allow gases to cross
Mesophyll
• Mesophyll consists of photosynthetic parenchyma with air
spaces between cells that allow gas exchange
• Plasmodesmata connect the cytoplasm of adjacent cells
• In leaves oriented perpendicular to the sun, mesophyll is
arranged in two layers: palisade and spongy mesophyll
• Monocot leaves that grow vertically intercept light from all
directions; their mesophyll is not divided into two layers
Veins: The Leaf’s Vascular Bundles
• Leaf veins are vascular bundles of xylem and phloem,
typically strengthened with fibers
• In eudicots, large veins branch into a network of minor veins
embedded in mesophyll; in monocots, veins are similar in
length and run parallel with the leaf’s long axis
• vein
• A vascular bundle in the stem or leaf of a plant
Eudicot and Monocot Leaves
Fig. 25.12, p. 405
stomata
phloem
vascular
tissue
palisade
mesophyll
epidermis
xylem
spongy
mesophyll
1
2
3
4
5
Anatomy of a Eudicot leaf