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Structure of Woody Plants (Secondary Growth in Roots (Roots (Do not store…
Structure of Woody Plants
Vascular Cambium
Initiation of the vascular Cambium
Vascular Cambium
Produce secondary plant body
Two cells:
Fusiform initials
Ray intials
Fascicular Cambium
Bundle of cells
Young cells
Interfascicular Cambium
Young Cells
Connects to fascicular cambia
Fusiform Initials
Long + tapered cells
Periclinal Wall
Two elongated cells
Longitudinal cell division
Anticlinal Wall
Perpendicular to cambiums surface
Increases numbers of cambial cells
Axial Xylem
Axial Phloem
Thin primary walls
Plastids are proplastids
Ray Initials
Short
Less cuboidal
Undergo periclinal cell division
Xylem parenchyma
Inner cell
Phloem parenchyma
Outer cell
Storage parenchyma
Arrangement of Cambial Cells
Storied cambium
Nonstoried cambium
Secondary Phloem
Vascular cambium
Axial system
Conduction of up and down stem
Sieve tubes and companion cells
Nonconducting Parenchyma and fibers preset
Radial system
Only parenchyma cells
Outer Bark
Cork and Cork Cambium
Vascular cambium and secondary phloem pushed outward
Cork Cambium "Phellogen"
Cuboidal cells
Inner cell remains cork cambium after division
Outer cell differentiates into cork cell "Phellem cell"
Phelloderm
Mature layer of parenchyma
Periderm
Waterproof
Lenticels and Oxygen Diffusion
Keeps out pathogens
Retains water
Block of absorption of water
Initiation of Cork Cambia
Arises before 1 year
Delayed formation of bark
Secondary Xylem "Wood"
Types of Wood Cells
Wood may contain:
Tracheids
Vessel Elemnts
Sclereids
Fibers
Parenchyma
Axial System
Developed from fusiform initials
Contains tracheary elemnts
Carry out longitudinal conduction of water
Radial System
Developed from ray initials
Hardwood
Large amounts of fibers
Strength
Durability
Useful for construction
Angiosperm and Eudicot
Softwood
Few or no fibers
Soft consistency
Growth Rings
Annual Ring
Early Wood
Spring wood
Porous ring
High proportion of wide vessels
Late Wood
Summer wood
Lower proportion of vessels
Heartwood and Sapwood
Heartwood
Dark wood
Center of a log
Drier
More fragrant
One annual ring is converted into heartwood
Widens with age
Sapwood
Lighter
More moist
New layers formed yearly by vascular cambium
Constant thickness
Reaction Wood
Lateral stress
Growth rings wider at top of branch
Walls rich in cellulose
Little or no lignin
Anomalous Forms of Growth
Annomalous Secondary Growth
Roots of Sweet Potatoes
Increased amount of storage
Secondary tissues=irregular matrix of parenchyma
Included Phloem
Protection from insects and pests
Unequal Activity of the Vascular Cambium
Secondary Growth in Monocots
Unusual Primary Growth
Palm trees
Do not taper at tips
Do not branch
Palm Trunk
Primary xylem and Primary Phloem only
Does not grow radially
Vascular cambium never develops
True wood does not occur
Secondary Growth in Roots
Vascular cambium and primary xylem =star shape
Sapwood
Heartwood
Ring porous
Diffuse porous
Roots
Do not store water
Rays are small and narrow
Consist of sclerenchyma
