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Structure of Woody Plants
Structure of Woody Plants
Secondary xylem
Types of wood cells
All same cell types as primary xylem but no new ones
Axial system
Derived from fusiform initials
Radial system
Develops from ray initials
Hardwoods
Wood of all basal angiosperms and eudicots
Softwoods
Woods from conifers
Ray parenchyma cells
Upright cells
Procumbent cells
Sometimes ray tracheids
Growth rings
Early wood
First wood formed
Late wood
Has a lower proportion of vessels
Annual ring
Formed from early wood and late wood
If summer is cold, may not grow and form rings
Diffuse porous
Vessels throughout growth ring
Ring porous
Vessels restricted to early wood
Heartwood and sapwood
Heartwood
Dark wood
Sapwood
Lighter, moister outer region
Tylosis
Mechanism that plugs water vessels
Prevents fungus from entering it
Reaction wood
Helps lateral stems and branches stay in position
Has special gelatinous fibers
Walls are rich in cellulose
Have little lignin
Also know as wood
Vascular cambium
Initiation of the vascular cambium
Meristem that produces secondary plant body
Fasicular cambium
Cells that divide instead of maturing
Interfasicular cambium
Mature parenchyma that resume mitosis
Fusiform initials and ray initials
Fusiform initials
Periclinal wall
Parallel to the circumference of the cambium
Anticlinal wall
Perpendicular to the cambium's surface
Long, tapered cells
Produce elongate cells of wood and phloem
Ray initials
Short, cuboidal cells
Produce storage parenchyma, albuminous cells
Arrangement of cambial cells
Storied cambium
Fusiform initials in horizontal rows
Nonstoried cambium
Irregular fusiform initials
Concepts
Primary tissues
Epidermis
Cortex
Vascular bundles
Pith
Leaves
Secondary tissues
Vascular cambium
Cork cambium
Bark
Contains conducting tissues
Secondary phloem
Axial system
Responsible for up and down conduction
Radial system
Consists of parenchyma cells for storage
Formed from vascular cambium
Outer bark
Cork and the cork cambium
Results from division of storage parenchyma cells
Also: phellogen
All cells are cuboidal
Inner cells remain cork cambium
Outer cells become cork cells
Periderm
Cork cambium + cork cells + phelloderm
Outer bark
All tissues outside the innermost cork cambium
Inner bark
All secondary phloem between vascular cambium and cork cambium
Initiation of cork cambia
Varies from tree to tree
Can arise before twig or root is one year old
Can arise after a few years
Lenticels and oxygen diffusion
Cork is impermeable
Prevents oxygen absorption
Lenticels
Regions of aerenchymatous cork
Permit oxygen diffusion
Anomalous forms of growth
Anomalous secondary growth
Alternative cambia produce secondary bodies
Different from common type
Amount of storage parenchyma is increased in potatoes
Included phloem
Phloem between two layers of xylem
Monocots
Secondary vascular bundles
Cambium produces only parenchyma
Parenchyma cells divide rapidly
Produce cells that differentiate into xylem and phloem
Unusual primary growth
Palm trees
Trunks do not taper at tips
Trunk is all primary tissues
Vascular cambium never develops
True wood and secondary phloem never occur
Trunk's stability is from heavy fibers surrounding vascular bundles
Secondary growth in roots
Vascular cambium arises
Parenchyma cells become active mitotically
