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Structure of Woody Plants (Vascular Cambium (Fusiform Initials (Long,…
Structure of Woody Plants
Vascular Cambium
Initiation of the Vascular Cambium
Fascicular cambium
Interfascicular cambium
After 2-3 years the fascicular and interfascicular cambium are indistinguishable and are referred to jointly as "Vascular cambium"
One of the meristems that produce the secondary plant body
Shares many similarities with apical meristem
Fusiform Initials
Long, tapered cells
140-462 um (dicots)
700-8,700 um (conifers
Undergoes logitudinal division
Periclinal wall
2 elongate cell
One contiues to be a fusiform initial
One differentiates into secondary vascular tissue
Cambial cells occasionally undergo anticlinal division to maintain functioning and prevent LOF via circumferential spreading
Thin primary walls
Ray Initials
Similar to Fusiform initials, but shorter and more cuboidal
Undergo similar periclinal division
Outer ---> Xylem parenchyma
Inner ----> Phloem Parenchyma
Production of short cells; storage parenchyma, albuminous cells in gymnosperms
Arrangement of Cambial Cells
Ray initials grouped together in short vertical rows
One cell wide (uniseriate)
Two cells wide (Biseriate)
Many cells wide (multiseriate)
Fusiform initials may occur in
Regular, horizontal rows (stored cambium); only evolved recently, very rare
irregularly, w/out any horizontal pattern (nonstored cambium)
Vascular cambium rarely has large regions of just ray or fusiform initials
Central fusiform initials may elongate to differentiate into a ray initial, and vice versa, to restore the ray:fusiform ratio
Secondary Xylem
Types of Wood Cells
Secondary Xylem
All cells formed to the interior of the vascular cambium
Referred to as Wood
Contents
All of the types of cells that occur in primary xylem, but no new ones
Tracheid, vessel elements, fibers, sclereids, and parenchyma
Difference between primary and secondary xylem is in the origin and arrangement of cells
Arrangement of 2nd xylem reflects that of fusiform and ray initials
Axial system is derived from Fusiform initials
Contains tracheary elements --->Longitudinal conduction of water through the wood
In many species of woody angiosperms, fibers give strength and flexibility to the wood
Hardwoods
Useful in construction industry
Conifers and such that do not have these fibers, referred to as Softwoods
Axial xylem parenchyma
Important as temporary reservoir of water
Many desert plants have an abundance of axial xylem parenchyma
Radial system develops from Ray initials
Simple
2 cell types
2 more items...
In woody angiosperms, contains only parenchyma, which form rays
Storage of carbs and other nutrients in dormancy
Conduction of material over short distances radially within wood
Ray tracheids
Page 196 in textbook has great Pics of Wood in 3D
Growth Rings
Early wood
High proportion of wide vessels
Late wood
Thickened cuticle
Less transpiration
Annual ring
Example
Heartwood and Sapwood
Heartwood= Dark wood
Sapwood=Lighter, outer region
Reaction wood
Formed in response to gravity, cellulose-rich fibers exert tension on the branch and cause it to be lifted; thereby negating the effect of gravity.
Secondary Phloem
Axial system
Conduction up and down the stem/root
Sieve tube members and companion cells
Radial system
Same size, shape, and number of xylem rays
Outer Bark
Cork and the Cork Cambium
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Cork Cambium
Phellogen
After each division, the inner cell remains as cambium and the outer cell differentiates into Phellem
Periderm
Cork Cambium
Layers of Phellem
Phelloderm
Typically short-lived
Outer bark
All tissues outside the innermost cork cambium
Impermeable to water
Inner bark
All secondary phloem between the vascular cambium and the innermost cork cambium
Lenticels and Oxygen Diffusion
Regions of aerenchymatous cork are called...
Lenticels
Inner and outer lenticels are aligned
Permits diffusion of oxygen throughout the bark
Initiation of Cork Cambia
Far more variable than vascular cambium
The first cork cambium may arise in a variety of tissues
Epidermis
Cortex
Primary or Secondary Phloem
Anomalous Forms of Growth
Anomalous Secondary Growth
The growth of alternative secondary bodies produced by the cambia
Roots of Sweet Potatoes
Amount of storage parenchyma increased dramatically via anomalous secondary growth
Numerous vascular cambia arise around individual vessels/groups of vessels
Root must become very large in a short amount of time, just one cambium is too slow
Included Phloem
Cells in the outermost, oldest secondary xylem differentiate into a new vascular cambium
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Secondary phloem located between two bands of xylem is the included phloem
Unequal Activity of the Vascular Cambium
In ordinary growth, all areas of the vascular cambium have equal activity
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In some species of
Bauhinia
2 sectors of the cambium are very active
Results in a thin, flat, woody ribbon
Flexibility and conducting capacity increased
Secondary Growth in Monocots
Does not occur in the same manner as is evident in eudicots
Secondary vascular bundles are produced by vascular cambium, but only parechnyma cells
No conducting cells
Unusual Primary Growth
Palm tree
Palm trunk is all primary tissue consisting of vascular bundles distributed throughout ground tissue
The trunk is hard and "woody" bc each vascular bundle is enclosed in a sheath of strong, heavy fibers
Production of numerous adventitious roots early on plus widening of trunk
Establishment growth
