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Structure of Woody Plants (Vascular Cambian (Initiation of the Vascular…
Structure of Woody Plants
Vascular Cambian
Ray Initials
Short and more or less cuboidal
Produce storage parenchyma and albuminous cells
Arrangement of Cambial Cells
A single tree or shrub has a single vascular cambium
The cells in between the xylem and phloem keep dividing which pushes out the trunk and the branches
Fusiform Initials
long tapered cells
Anticlinical walls allow the vascular cambium cells to divide longitudinal
Initiation of the Vascular Cambium
Cells in between the metaxylem and the metaphlloem keep dividing
Metaxylem and metaphloem mature, vascular cambia rises
Produce Secondary Plant body
Anomalous Forms of Growth
Anomalous Secondary Growth
Secondary vascular bundles
Outermost, oldest secondary phloem are reactivated
Unusual Primary Growth
Vascular bundle is enclosed- the trunk is hard and woody
Establishment growth
Secondary Xylem
Growth Rings
Early wood- spring wood, late wood- summer wood
Annual ring v. growth ring
Heartwood and Sapwood
Heartwood- dark, sapwood- light
Sapwood is converted to heartwood
Types of Wood Cells
Secondary xylem is wood
Softwood and Hardwood
Axial system- fusiform initials, radial system- ray initials
Reaction Wood
Tension wood on the upper side
On the underside reaction wood is compression wood
Secondary Phloem
Only innermost layer of the phloem is capable of conduction
In conifers albuminous cells are ray cells
Phloen rays only consist or parenchyma
Outer Bark
Lenticels and Oxygen Diffusion
Cork keeps out pathogens and retains water but it also blocks out oxygen
Aerenchymatous cork- Lenticels
Initiation of Cork Cambia
Arise before root or twig is one year old
First outer bark contains only periderm and cuticle
Cork and the Cork Cambium
All tissues outside the innermost cork cambium are the outer bark
Phelloderm and periderm
Secondary Growth in Roots
Circular cambium causes all parts to grow at the same rate
The wood of roots is different then the wood of the stem
Wood is almost pure parenchyma
