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Structure of Woody Plants (Secondary Xylem (Growth Rings (after wood…
Structure of Woody Plants
Secondary Xylem
Heartwood
the dark wood is the heartwood
the center of the log is always darker in color
center is usually more dry and fragrant
Growth Rings
after wood produced is called the late wood
in strongly seasonal climates
can see annual ring after one year
cambium is quiscent during the time of the stress
cuticle is neither thick nor polymerized
Reaction wood
gravity causes lateral stress
most of the plants produce lateral roots
found in branches or trunks that are not vertical
Types of Wood Cells
Secondary Xylem known as wood
Secondary xylem contains all kinds of Cells
Hardwood
useful for construction
it contains large amounts of fibers
radial system develops from ray initials
Soft Wood
has few or no fibers
redwood, pines, etc.
Sapwood
the lighter outer region is the sapwood
it is more moist and always light in color
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Secondary Phloem
contains sieve tube members
companion cells in angiosperms or sieve cells in conifers
the innermost layer of phloem is capable of conduction
it is former from the vascular cambium
it has radial or an axial system
Secondary growth in roots
woody angiosperm undergo secondary growth
vascular cambium has the same shape as xylem
vascular cambium arises just as the interfascicular cambium
outer bark
initiation of cork cambia
arises before twig or root is even one year
epidermis and cortex are retained
it may arise in number of tissues
timing of the initiation of the first cork cambium is variable
lenticels and oxygen diffusion
it keeps pathogens away and retains water
the bark becomes permeable to oxygen
it blocks the absorption of the oxygen
interfering with respiration of the sapwood, vascular cambium
Cork and the Cork Cambium
secondary phloem to be pushed outward
differentiation of secondary xylem causes the vascular cambium
innermost phloem cells form and mature
it contributes to the larger amount of stem or root
Cork cell
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they are the mature layers called phelloderm
they are also called phellem cells
anomalous form of growth
Usual primary growth
they are distributed throughout the ground tissues
they donot branch
anomalous secondary growth
roots of sweet potatoes
most of the woody angiosperm are similar
activity of vascular cambia in conifers
alternative cambia produce secondary bodies
Vascular Cambium
Fascicular cambium
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it is an old type of bundle which divides plant cells
Ray initials
the store parenchyma cells
they are short
they undergo periclinal cell divisions
they are more or less cuboidal
Interfascicular cambium
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connects each side with fascicular cambia
Arrangement of cambium cells
may occur in a horizontal row
non stored cambium
they are organized in a specific patterns
initials are grouped together in short vertical rows
initiation of vascular cambium
produce secondary plant body
one of the meristem
located between meta xylem and phloem
Functional Connection
Types connection