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