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Structure of Woody Plants (Vascular Cambian (Fusiform Initials (Typical…
Structure of Woody Plants
Vascular Cambian
Ray Initials
Similar to fusiform initials, EXCEPT;
They are short and more or less cuboidal
Undergo periclinal cell divisions
Most significant differences between fusiform & ray initials;
Fusiform initials
Elongate fusiform initials produce the longate cells of wood
Ray intials
Produce short cells
Mostly just storage parenchyma
In gymnosperms,
Almbuminous cells
Arrangement of Cambial Cells
Organized in specific patterns
Ray initials
Grouped together in short vertical rows
Only one cells wide,
Two cells wide, or
Many cells wide
Fusiform initials
Occur in regular horizontal rows, or
Irregularly w/out
Any horizontal pattern
Fusiform Initials
Long, tapered cells
Typical lengths:
140-462 um in dicots
700-8700 um in conifers
Periclinal wall
Wall parallel to the circumference of the cambium
Longitudinal cell division
Anticlinal walls
Perpendicular to the cambium's surface
Vascular cambium cells must occasionally divide here
Initiation of the Vascular Cambium
Vascular Cambian
One of the meristems that produce the secondary plant body
In woody species;
Cells located in this position
NEVER undergo cell cycle arrest
Continue to divide instead of maturing
Constitute the fascicular cambium
Bundle
Interfascicular cambium
Connects on each side with the fascicular cambia
Secondary Phloem
Formed from the vascular cambium just as secondary xylem
Has an axial & a radial system
Axial system
Conduction up & down the stem or root
Contains sieve tube members & companion cells
In angiosperms
Sieve cells
In conifers
Outer Bark
Lenticels and Oxygen Diffusion
Impermeability of cork has negative as well as adavantageous
Positive
Keeps out pathogens & retains water
Negative
Blocks absorption of oxygen
Interfering with the respiration of the:
Sapwood
Vascular cambium
Inner bark
Initiation of Cork Cambia
Delayed formation of bark is common is plants that depend on,
cortex chlorenchyma for much of their photosynthesis
The first cork cambium may arise in a number of tissues
Primary phloem
Secondary phloem
Cortex
Epidermis
Cork and the Cork Cambium
Production of differentiation of secondary xylem cells
Vascular cambium & secondary phloem to be pushed outward
Secondary Growth in Roots
Roots of conifers & woody angiosperms undergo,
secondary growth
Root vascular cambium contains both
Ray & fusiform initials
Anomalous Forms of Growth
Anomalous Secondary Growth
Development, cellular arrangement, & activity of
Vascular cambia in conifers & most woody angiosperms are similar
Alternative cambia produce secondary bodies that differ from
the common type
Unusual Primary Growth
Trunk is all primary tissue consisting of vascular bundles
distributed throughout ground tissue
Secondary Xylem
Types of Wood Cells
Secondary Xylem
Contains all of the types of cells that,
Occur in primary xylem but no new ones
Cells formed to the interior of the vascular cambium develop into;
Secondary xylem
Arrangement of secondary xylem reflect
Fusiform & ray initials
Growth Rings
Early wood
High proportion of wide vessles
Or conifers,
Wide tracheids
Late wood
Cuticle has thickened
Transpiration is less
& large numbers of newly formed vessels are conducting rapidly
Reaction Wood
Branches or trunks that are not vertical
Gravity causes a lateral stress
The branch would droop & become pendant
In response to the stress
reaction wood is created
Heartwood and Sapwood
Heartwood
Dark wood
Sapwood
Lighter, moister
They exist because;
Vessels & tracheids do not function forever in water conduction
Water columns breaks because:
Wind vibration
Tension
Freezing
Wood-boring
Insects
& other factors
After the water column breaks
There is no means of pulling water upward
Vessels & tracheids in which this occurred usually never conduct water again
Tylosis
Wood parenchyma cells adjacent to vessels,
push bubbles of protoplasm through the pits into the vessel,
forming a plug
