Lecture 8: Secondary growth; TIMBER!

Question 1

What does anticlinal division promote?

Answer 1

breadth; perpendicular to the meristem

Question 2

What does periclinal division promote?

Answer 2

depth; new cell wall parallel to the outside

Question 3

true or false; secondary growth is rare for monocots

Answer 3

true

Question 4

What is the purpose of the vascular cambium?

Answer 4

• adds secondary xylem (wood) and secondary phloem, increasing vascular flow and support for the shoot system

Question 5

What does vascular cambium develop into

Answer 5

wood

Question 6

What does cork cambium develop into

Answer 6

bark

Question 7

what are the two lateral meristems of secondary growth?

Answer 7

cork cambium
vascular cambium
- overall increases the girth of the stem

Question 8

What is the purpose of the cork cambium

Answer 8

produces tough, thick covering
- consisting mainly of wax impregnated cells that protect the stem from water loss and from invasion by insects, bacteria, fungi

Question 9

true or false; secondary growth occurs simultaneously with primary growth

Answer 9

true

Question 10

true or false; secondary growth occurs both inwards and outwards

Answer 10

true

Question 11

What is bark made of?

Answer 11

all the tissues outside the vascular cambium

Question 12

What does the bark consist of in trunks?

Answer 12

bark = phloem+ cortex+ periderm

Question 13

What does the bark around roots consist of?

Answer 13

bark = phloem + periderm

Question 14

true or false; in woody roots, cortex dies and is sloughed off

Answer 14

true

Question 15

What is the Cork Cambium

Answer 15

• cork tissue functions as a barrier that helps protect the stem. root from water loss; physical damage; pathogens
• produces protective covering on secondary plant body

Question 16

Where does the cork cambium originate in stems?

Answer 16

-originates from layer immediately beneath epidermis

Question 17

Where does the cork cambium for roots originate?

Answer 17

pericycle

Question 18

Where is the cork located? And what is its’ function?

Answer 18

outside from the cork cambium

• consists of cork cells that accumulate to the exterior of the cork cambium
• as cork cells mature they deposit a waxy material called suberin in their walls then die
• because they are lined with suberin and wax
• protective layer of the plant

Question 19

what is the phelloderm?

Answer 19

• thin layer of parenchyma cells that forms the interior of the cork cambium
• living parenchyma

Question 20

true or false; cork cells are dead at maturity

Answer 20

true

Question 21

Why are cork cells impermeable to water and gases

Answer 21

they are lined with suberin and waxes

Question 22

What is the consequence of the stem/root splitting as it gets older?

Answer 22

it loses its meristematic activity and differentiates into cork cells
- a new cork cambium forms to the inside, resulting in another layer of Periderm; older layers of periderm are sloughed off

Question 23

the formation of bark depends on?

Answer 23

the phelloderm, cork cambium and cork

Question 24

What are lenticels

Answer 24

these are ‘dots on the periderm’

• the inter cellular spaces allow gas exchange between the cells and the atmosphere
• raised circular or oval areas

Question 25

What are the downfalls of periderms?

Answer 25

pathogens can enter through them

Question 26

Why is respiration via the periderm necessary?

Answer 26

allows the release of stored energy

Question 27

Describe the vascular cambium

Answer 27

- one cell thick (in atypical woody stem; the VC consists of a continuous cylinder of undifferentiated parenchyma cells) - highly vacuolated - dense initials

Question 28

What is residual procambium?

Answer 28

fascicular cambium

Question 29

What do you call parenchyma between vascular bundles

Answer 29

interfascicular cambium

Question 30

How does the VC divide?

Answer 30

Periclinaly

Question 31

What are the two types of meristematic cells that the VC consists of?

Answer 31

fusiform initials | ray initials

Question 32

What is the orientation of fusiform initials?

Answer 32

vertical

Question 33

Where is the secondary phloem

Answer 33

outside

Question 34

Where is the secondary xylem

Answer 34

inside

Question 35

What is the orientation of ray initials?

Answer 35

horizontal

Question 36

What are ray cells made of

Answer 36

parenchyma

Question 37

What are the shape of fusiform cells

Answer 37

longer/ wide

Question 38

ray intials

Answer 38

square/ elongated

Question 39

what is the purpose of ray initials

Answer 39

radial files that connect the secondary xylem with the secondary phloem; the cells of vascular ray move water and nutrients between the secondary xylem and phloem store carbohydrates

Question 40

Describe secondary xylem and phloem

Answer 40

``` elongate longitudinally (vertical) - conduct water and food ```

Question 41

What are rays for?

Answer 41

``` elongate radially (horizontal) - for food storage, ad transport across wood ```

Question 42

true or false; wood is mostly secondary xylem and fibres

Answer 42

true

Question 43

true or false; secondary phloem is crushed during growth

Answer 43

true

Question 44

What are the three different planes you can cut wood

Answer 44

transverse radial tangential

Question 45

What does transverse cut mean

Answer 45

slice across trunk

Question 46

What does radial slice mean

Answer 46

slice cut parallel with radius

Question 47

what does tangential cut mean

Answer 47

longitudinal slice, not parallel with radius

Question 48

When are growth rings produced?

Answer 48

annually

Question 49

What causes false rings

Answer 49

climate change

Question 50

When is early wood formed?

Answer 50

early spring; in temperate regions

Question 51

When is late wood formed

Answer 51

late summer

Question 52

What is the appearance of early wood

Answer 52

large xylem cells | thin cell walls

Question 53

What is the appearance of late wood

Answer 53

narrow cells; thick & dense cell walls

Question 54

What happens when there is slow growth

Answer 54

results in less early wood and therefore harder wood

Question 55

What is the purpose of early wood

Answer 55

maximizes the delivery of water to newly growing leaves

Question 56

What is the purpose of late wood

Answer 56

support | - don't transport as much water but contributes more to stem or root support

Question 57

Why does the heartwood become non functional as the tree trunk matures?

Answer 57

- blockages appear in the xylem (tyloses) - fill with resins, gums, tannins, or other dark pigmented materials - heartwood (dark) - can also be due to infection

Question 58

true or false; only thick walled phloem fibres remain | - as primary phloem is crushed and pushed outward

Answer 58

true

Question 59

What is heartwood

Answer 59

older layers of secondary xylem no longer transporting water and minerals (xylem sap) - close to centre of the stem/ root

Question 60

Why is heartwood dark

Answer 60

due to resins, tannins, pigments, etc...

Question 61

What is sapwood

Answer 61

the newest layers of secondary xylem still transport xylem sap (usually has large circumference)

Question 62

Why does the sapwood and secondary phloem increase in circumference?

Answer 62

to supply the increasing number of each years' leaves

Question 63

what does the periderm consist of?

Answer 63

cork cambium, phelloderm, cork

Question 64

What is timber like for angiosperm trees?

Answer 64

known as hardwood - high lignin content - vessels + tracheids

Question 65

What is is timber like for gymnosperms?

Answer 65

softwood - low lignin - tracheids only

Question 66

What are the 4 characteristics of wood

Answer 66

grain color density knots

Question 67

What causes grain?

Answer 67

alignment of xylem cells - can be parallel to the trunk or slanted or spiral -

Question 68

What is the density of balsa

Answer 68

0.13 g/cm^3

Question 69

what is the density of pine

Answer 69

0.4 (for construction)

Question 70

What is the density of oak

Answer 70

0.6 (for furniture

Question 71

What does knots mean

Answer 71

bases of branches which have been covered by subsequent secondary growth

Question 72

How does the color of timber come about

Answer 72

impregnation of xylem by colored compounds eg. tannins, resins

Question 73

What are the properties of the Teak wood

Answer 73

- naturally resistant to insects, warping, splintering and the elements - ideal wood for creating furniture

Question 74

Where is Teak planted?

Answer 74

Indonesia (bu the Dutch in 1800)

Question 75

How long does Teak reach maturity?

Answer 75

50 -60 years

Question 76

How much of the Papuan Kwila is logged illegally?

Answer 76

70 - 80 %

Question 77

What do virgin forests influence?

Answer 77

climate patterns; rain