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Structure of woody plants (8) (Vascular Cambium (Fusiform Initials (Long,…
Structure of woody plants (8)
Vascular Cambium
Initiation
continues to divide
Constitutes fascicular cambium
Fusiform Initials
Long, tapered cells
140 to 462 micrometers in dicots
700 to 8,700 micrometers in conifers
Undergo periclinal division
produces 2 elongate cells
1 becomes cell of secondary xylem or phloem
Ray Initials
Short and cuboidal
Periclinal division
1 becomes xylem or parenchyma if inner cell
or becomes phloem parenchyma if outer cell
Arrangement of Cambial Cells
Ray: grouped together in short vertical rows
1 cell wide
2 cell wide
many cells wide
Fusiform
Regular, horizontal rows
Irregular, no horizontal pattern
Produces secondary
plant body
Outer Bark
Cork Cambium
Phellogen
Cuboidal Cells
Inner cell remains cork cambium
outer cell differentiates
Cork cell (phellem)
Phelloderm
layer of parenchyma
Periderm
Cork Cells
Cork Cambium
Phelloderm
Lenticels & Oxygen Diffusion
Initiation of Cork Cambia
All tissues outside the innermost cork cambium
Anomalous Forms of Growth
Secondary Growth
Secondary bodies
produced by alternative cambia
Differ from common type
Unsual Primary Growth
Example:
Palm tree
trunks don't taper at tips
Types of Wood Cells
Secondary Xylem
Wood
Developed from cells formed interior to vascular cambium
Contains all types of cells of primary xylem
No new cells
May contain
Tracheids
vessel elements
fibers
sclereids
parenchyma
Secondary Phloem
Formed from vascular cambium also
Contains
Sieve tube members
Companion Cells
In angiosperms
Sieve cells
In conifers
Difference bt Primary & secondary xylem
origin of cells
arrangement of cells
Hardwood
Most commercially important angiosperm wood
Contains fibers making them
strong
tough
useful for construction
Term used for woods of
All angiosperms
All eudicots
Even balsa
Lack fibers
Very soft
Softwood
Have few/no fibers
Softer consistency
Some instances are harder than hardwood
Growth Rings
Early Wood
Spring wood
First wood formed
Must have high proportion of wide vessels
Wide tracheids in conifers
Late Wood
Summer wood
Thickened Cuticle
Less transpiration
Large #'s of newly formed vessels
Lower proportion of vessels
Needs more mechanical strength
Annual Ring
Early wood
Late wood
One year's growth containing
Heartwood
Dark wood
Dry
Inner portion (center)
More fragrant
Sapwood
Lighter
Moister
Outer region
Reaction Wood
Forms in place of normal wood
Forms in response to stress
In angiosperms
Upper side of branch
tension wood
Inner Bark
All secondary phloem between
vascular cambium
innermost cork cambium
