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Structure of Woody Plants (Vascular Cambium (Fusiform initials (Periclinal…
Structure of Woody Plants
Secondary Phloem
Formed from vascular cambium
Has both axial & radial system
Axial
Responsible for conduction
Phloem rays
#
Produced by same ray initials as xylem rays
Secondary Xylem
Growth rings
Early wood
AKA spring wood
Ring porous
First wood formed
High proportion of wide vessels
Late wood
AKA summer wood
Lower proportion of vessels
Annual rings
1 year of growth
AKA growth rings
Vessels throughout=diffuse porous
Vessels restricted=ring porous
Heartwood and Sapwood
Heartwood
Dark wood
Tree's waste
Sapwood
Lighter, more moist
Formed each year
By vascular cambium
Types of wood cells
Cells on the interior of the vascular cambium
Develop into secondary xylem
Known as wood
May contain
Trachieds
Vessel elements
Fibers
Sclereids
Parenchyma
Axial system
Derived from fusiform initials
Contains tracheary elements
Radial System
Derived from ray initials
Contains ray parenchyma
Hardwoods
Strong & tough, used for construction
Terms used for basal angiosperms & eudicots
Softwoods
Softer consistency
Have few to no fibers
Some can be harder than hardwoods
Example: Bald-cypress,
Taxodium
Reaction wood
Plants response to stress
In angiosperms
Tension wood
In conifers
Compression wood
Vascular Cambium
Initiation of the vascular cambium
Vascular cambium
Produce secondary plant body
Fascicular cambium
Continue to divide, never maturing
Interfascicular cambium
Resume mitosis, connects fascicular cambia
Two types of cells
Ray initials
Fusiform initials
Fusiform initials
Long, tapered cells
Periclinal wall
One continues to be fusiform initial
One becomes secondary xylem or phloem
Anticlinal wall
Perpendicular to cambiums surface
Ray initials
Produce short cells
Shorter than fusiform
More or less cuboidal
Store parenchyma
Arrangement of cambial cells
Fusiform initials
Regular horizontal rows
Storied cambium
Irregular, no horizontal pattern
Nonstoried cambium
Ray initials
Typically grouped together
One cell wide
Uniseriate
Two cells wide
Biseriate
Many cells wide
Multiseriate
Outer Bark
Lenticels & oxygen diffusion
Lenticels
Regions of aerenchymatous cork
Bark becomes permeable to O2
When cork cambium produces cork cells
Become rounded when maturing
Initiation of cork cambia
Arise in a number of tissues
Epidermis
Cortex
Primary phloem
Secondary phloem
Timing can be variable
When it can arise
1 year old
Several years old
Cork & the cork cambium
Cork cambium
Produced cells turn into phelloderm
AKA phellogen
Cuboidal cells
Cork cell
AKA phellem cell
Periderm
Layers of cork cells
Temporary protection
Layers of phelloderm (if any)
Outer bark
Tissues outside cork cambium
Inner bark
Between vascular cambium & cork cambium
Secondary Growth in Roots
Vascular cambium arises
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Arises just like interfascicular cambium
New cambium
Same star shape as primary xylem
Becomes round
When circular cambium is achieved
Unequal growth stops
Equal growth rates begin
Some are pushed outward
Some more rapid than other
Perennial roots
Form bark
First cork cambium arises in pericycle
Causes shedding of
Cortex
Epidermis
Endodermis
Lenticels occur near lateral roots
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Anomalous Forms of Growth
Anomalous secondary growth
Alternative cambia produce secondary bodies
Which differ from the common type
Roots of sweet potatoes
Amount of storage parenchyma increases
By anomalous secondary growth
Numerous vascular cambia arise
Around individual vessels
Or around groups of vessels
Included phloem
Type of secondary phloem
Located between two bands of xylem
Unequal activity of the vascular cambium
Stems grow outward in two directions
Remains thin in the other two
Becomes thin, flat, woody ribbon
As
Bauhinia
become wider
Conducting capacity increases
Flexibility remains the same
Secondary growth in monocots
Joshua tree (genus
Yucca
)
Becomes "tree-like" & woody
Vascular cambium arises outside
The outermost vascular bundles
Secondary vascular bundles
Contains xylem and phloem
Parenchyma cells undergo rapid division
Produce narrow cells that differentiate
Unusual primary growth
Palm trees
Do not branch
Trunks do not taper at the tips
Primary tissue=vascular bundles
Distributed throughout ground tissue
Establishment growth
Form of primary growth
Increase in width & addition of adventitious roots
Produced by these
Considered secondary growth
Occur in secondary growth
