Chapter 8: Structure of Woody Plants
Vascular Cambium
Secondary Xylem
Secondary Phloem
Outer Bark
Fusiform Initials
Ray Initials #
Initiation of the Vascular Cambium
Arrangement of Cambial Cells
Fascilar Cambium
Interfascicular Cambium
Vascular Cambium
Periclinal walls - produces 2 elongate cells
Anticlinal walls - Perpendicular to the cambium's surface
Fusiform initials are long, tapered cells
Conifers - 700 to 8,700 um
Dicots - 140 to 462 um
The other differentiates into a cell of secondary xylem or secondary phloem
Cambial cells produce narrow daughter cells, all of which enlarge during differentiation
One continues to be a fusiform initial
Plastids are present as proplastids
Phragmoplast grows about 50 to 100 um per hour
Fusiform initials have thin primary walls
Cell division may take as long as 10 days in species with long fusiform initials
They are short and more or less cuboidal
They undergo periclinal cell divisions
Ray initials are similar to fusiform initials
Produces short cells, mostly just storage parenchyma and, in gymnosperms, albuminous cells
Gymnosperms
Albuminous Cells
Ray initials
Ray and fusiform Initials are organized in specific patterns
Two cells wide (biseriate),
or many cells wide (multiseriate).
Either grouped together in short vertical rows only one cell wide (uniseriate),
Fusiform initials
Or irregularly, without any horizontal pattern (a nonstoried cambium)
May occur in horizontal rows (storied cambium)
Secondary xylem contains all of the types of cells that occur in primary xylem but no new ones
Wood may contain
All cells formed to the interior of the vascular cambium develop into secondary xylem, known as wood
Fibers
Sclereids
Vessel Elements
Parenchyma
Tracheids
The only real difference between primary and secondary xylem are the origin and arrangement of cells
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The arrangement of secondary xylem cells reflect that of the fusiform and ray initials
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Fusiform Initial
Ray Initial
Axial System
Radial System
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Softwood
Hardwood
A term used for wood if all basal angiosperms and eudicots
Woods from conifers such as pines and redwoods
Growth Rings
Heartwood and Sapwood
Reaction Wood
Annual Ring
Growth Ring
Late Wood
Ring Porous
Diffuse Porous
Because the wood of a growth ring has vessels located throughout it
Whereas species with species with vessels restricted mainly to early wood
Ex) Yellow birch, aspen, sugar maple, and American holly
Ex) Red oak, sassafras, and honey locust
Also called summer wood
Plant is a year older
Needs more mechanical strength to hold up the increased number of leaves and larger branches
Larger and heavier
Early Wood
Also called spring wood
The first wood formed
Early Wood
Late Wood
Both - The 2 together making up 1 year's growth
In response to this stress. most plants produce reaction wood
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In branches or trunks that are not vertical, gravity causes a lateral stress
Reaction wood is a type of wood developed during a gravity reaction of trees and shrub.
Heartwood
Sapwood
The dark wood
The lighter moisture region
The different 2 regions exist because vessels and tracheids do not function forever in water conduction
And a radial system
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Has both an axial system
Contains sieve tube members and companion cells in angiosperms
Contains sieve cells in conifers
Responsible for conduction up and down the stem or root
In some species, there may be bands of fibers alternating with sieve tube members
The size, shape, and number of phloem rays match those of xylem rays because both are produced by the same ray initials
In both group of plants, fibers and nonconducting parenchyma are also typically present in axial secondary phloem
Phloem rays consist only of parenchyma cells that are used for storage
Lenticels and Oxygen Diffision
Initiation of Cork Cambia
Cork and the Cork Cambium
Cork Cell (Phellem Cell)
Phelloderm
Cork Cambium (Phellogen)
Periderm
The production and differentiation of secondary xylem cells cause the vascular cambium and secondary phloem to be pushed outward
Outer Bark
Inner Bark
All tissues outside the innermost cork cambium
All secondary phloem between the vascular cambium and the innermost cork cambium
The cork cambium
And the phelloderm
The layers of cork cells
The cork cambium can produce a cell or 2 to the inside that mature into a layer of parenchyma
Intercellular spaces penetrate the cork layer
Diffusion pathway for oxygen is made - these regions of aerenchymatous cork are lenticels
Bark becomes permeable to oxygen
Lenticel-producing regions of cork cambia are more active than adjacent regions
Lenticels contain more layers of cells and protrude outward
As the first bark is shed and later cork cambia arise in the secondary, they produce an outer bark that contains only cork and phloem
Fiber cells produce fibrous, stringy bark
The first bark on young stems usually differs from bark formed when the stem gets older
The timing of initiation of the first cork cambium is far more variable than that of the vascular cambium
