Lecture 8: Secondary growth; TIMBER! Flashcards
What does anticlinal division promote?
breadth; perpendicular to the meristem
What does periclinal division promote?
depth; new cell wall parallel to the outside
true or false; secondary growth is rare for monocots
true
What is the purpose of the vascular cambium?
- adds secondary xylem (wood) and secondary phloem, increasing vascular flow and support for the shoot system
What does vascular cambium develop into
wood
What does cork cambium develop into
bark
what are the two lateral meristems of secondary growth?
cork cambium
vascular cambium
- overall increases the girth of the stem
What is the purpose of the cork cambium
produces tough, thick covering
- consisting mainly of wax impregnated cells that protect the stem from water loss and from invasion by insects, bacteria, fungi
true or false; secondary growth occurs simultaneously with primary growth
true
true or false; secondary growth occurs both inwards and outwards
true
What is bark made of?
all the tissues outside the vascular cambium
What does the bark consist of in trunks?
bark = phloem+ cortex+ periderm
What does the bark around roots consist of?
bark = phloem + periderm
true or false; in woody roots, cortex dies and is sloughed off
true
What is the Cork Cambium
- 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
Where does the cork cambium originate in stems?
-originates from layer immediately beneath epidermis
Where does the cork cambium for roots originate?
pericycle
Where is the cork located? And what is its’ function?
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
what is the phelloderm?
- thin layer of parenchyma cells that forms the interior of the cork cambium
- living parenchyma
true or false; cork cells are dead at maturity
true
Why are cork cells impermeable to water and gases
they are lined with suberin and waxes
What is the consequence of the stem/root splitting as it gets older?
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
the formation of bark depends on?
the phelloderm, cork cambium and cork
What are lenticels
these are ‘dots on the periderm’
- the inter cellular spaces allow gas exchange between the cells and the atmosphere
- raised circular or oval areas
What are the downfalls of periderms?
pathogens can enter through them
Why is respiration via the periderm necessary?
allows the release of stored energy
Describe the vascular cambium
- one cell thick (in atypical woody stem; the VC consists of a continuous cylinder of undifferentiated parenchyma cells)
- highly vacuolated
- dense initials
What is residual procambium?
fascicular cambium
What do you call parenchyma between vascular bundles
interfascicular cambium
How does the VC divide?
Periclinaly
What are the two types of meristematic cells that the VC consists of?
fusiform initials
ray initials
What is the orientation of fusiform initials?
vertical
Where is the secondary phloem
outside
Where is the secondary xylem
inside
What is the orientation of ray initials?
horizontal
What are ray cells made of
parenchyma
What are the shape of fusiform cells
longer/ wide
ray intials
square/ elongated
what is the purpose of ray initials
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
Describe secondary xylem and phloem
elongate longitudinally (vertical) - conduct water and food
What are rays for?
elongate radially (horizontal) - for food storage, ad transport across wood
true or false; wood is mostly secondary xylem and fibres
true
true or false; secondary phloem is crushed during growth
true
What are the three different planes you can cut wood
transverse
radial
tangential
What does transverse cut mean
slice across trunk
What does radial slice mean
slice cut parallel with radius
what does tangential cut mean
longitudinal slice, not parallel with radius
When are growth rings produced?
annually
What causes false rings
climate change
When is early wood formed?
early spring; in temperate regions
When is late wood formed
late summer
What is the appearance of early wood
large xylem cells
thin cell walls
What is the appearance of late wood
narrow cells; thick & dense cell walls
What happens when there is slow growth
results in less early wood and therefore harder wood
What is the purpose of early wood
maximizes the delivery of water to newly growing leaves
What is the purpose of late wood
support
- don’t transport as much water but contributes more to stem or root support
Why does the heartwood become non functional as the tree trunk matures?
- blockages appear in the xylem (tyloses)
- fill with resins, gums, tannins, or other dark pigmented materials
- heartwood (dark)
- can also be due to infection
true or false; only thick walled phloem fibres remain
- as primary phloem is crushed and pushed outward
true
What is heartwood
older layers of secondary xylem no longer transporting water and minerals (xylem sap)
- close to centre of the stem/ root
Why is heartwood dark
due to resins, tannins, pigments, etc…
What is sapwood
the newest layers of secondary xylem still transport xylem sap (usually has large circumference)
Why does the sapwood and secondary phloem increase in circumference?
to supply the increasing number of each years’ leaves
what does the periderm consist of?
cork cambium, phelloderm, cork
What is timber like for angiosperm trees?
known as hardwood
- high lignin content
- vessels + tracheids
What is is timber like for gymnosperms?
softwood
- low lignin
- tracheids only
What are the 4 characteristics of wood
grain
color
density
knots
What causes grain?
alignment of xylem cells
- can be parallel to the trunk or slanted or spiral
-
What is the density of balsa
0.13 g/cm^3
what is the density of pine
0.4 (for construction)
What is the density of oak
0.6 (for furniture
What does knots mean
bases of branches which have been covered by subsequent secondary growth
How does the color of timber come about
impregnation of xylem by colored compounds eg. tannins, resins
What are the properties of the Teak wood
- naturally resistant to insects, warping, splintering and the elements
- ideal wood for creating furniture
Where is Teak planted?
Indonesia (bu the Dutch in 1800)
How long does Teak reach maturity?
50 -60 years
How much of the Papuan Kwila is logged illegally?
70 - 80 %
What do virgin forests influence?
climate patterns; rain
