Plant Structure, Growth, and Development

Page
7

Guard

cells

Vein

Cuticle

Lower

epidermis

Spongy

mesophyll

Palisade

mesophyll

Upper

epidermis

Guard

cells

Stomatal

pore

Surface view of a spiderwort

(Tradescantia) leaf (LM)

Epidermal

cell

(b)

50 µm

100 µm

Vein

Air spaces

Guard cells

Cross section of a lilac

(Syringa)) leaf (LM)

(c)

Slide 50

The Vascular Cambium and Secondary Vascular Tissue

The vascular cambium is a cylinder of meristematic cells one cell layer thick.

It develops from undifferentiated parenchyma cells.

In cross section, the vascular cambium appears as a ring of initials.

The initials increase the vascular cambium’s circumference and add secondary xylem to the inside and secondary phloem to the outside.

Slide 51

Secondary growth produced by the vascular cambium

Vascular cambium

Growth

Secondary

xylem

After one year

of growth

After two years

of growth

Secondary

phloem

Vascular

cambium

X

X

X

X

X

X

P

P

P

P

C

C

C

C

C

C

C

C

C

C

C

C

C

Slide 52

Tree rings are visible where late and early wood meet, and can be used to estimate a tree’s age.

Dendrochronology is the analysis of tree ring growth patterns, and can be used to study past climate change.

As a tree or woody shrub ages, the older layers of secondary xylem, the heartwood, no longer transport water and minerals.

The outer layers, known as sapwood, still transport materials through the xylem.

Older secondary phloem sloughs off and does not accumulate.

Slide 53

Using dendrochronology to study climate

RESULTS

Ring-width

indexes

2

1.5

0.5

1

0

1600

1700

1800

1900

2000

Year

Slide 54

Anatomy of a tree trunk

Growth

ring

Vascular

ray

Secondary

xylem

Heartwood

Sapwood

Bark

Vascular cambium

Secondary phloem

Layers of periderm

Slide 55

Is this tree living or dead?

Slide 56

The Cork Cambium and the Production of Periderm

The cork cambium gives rise to the secondary plant body’s protective covering, or periderm.

Periderm consists of the cork cambium plus the layers of cork cells it produces.