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Structure of Woody Plants (Vascular Cambium (Fusiform Initials (periclinal…
Structure of Woody Plants
Vascular Cambium
Fusiform Initials
long, tapered cells
periclinal wall
fusiform initial undergoes longitudinal cell division w/ a parallel wall
produces 2 elongate cells
one cell continues to be a fusiform cell
the other differentiates into a cell of secondary xylem or secondary phloem
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wood never forms to the exterior of the vascular cambium
bark never forms on the interior side
Ray Initials
similar to fusiform initials
short and more or less cuboidal
produce mostly just storage parenchyma
in gymnosperms, they are albuminous cells
Initiation of the Vascular Cambium
vascular cambuim
one of the meristems that produce the secondary plant body
never occurs in flowers, fruits, or seeds
fascicular cambium
cells that continue to divide instead of maturing
interfascicular cambium
mature parenchyma cells between vascular bundles that come out of cell cycle arrest and resume mitosis
connects on each side with the fascicular cambia
only 2 types of cells
fusiform initials
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ray initials
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Arrangement of Cambial Cells
specific patterns
ray initials
short vertical rows, 1 cell wide, 2 cells wide, or many cells wide
fusiform initials
regular horizontal rows (storied cambium)
irregularly, w/out any horizontal patterns (nonstoried cambium)
Secondary Xylem
Growth Rings
early wood
aka spring wood
high proportion of wide vessels
late wood
aka summer wood
large number of newly formed vessels are conducting rapidly
annual ring
early wood and late wood, the 2 making up 1 year
also can be called growth ring
Heartwood and Sapwood
dark wood = heartwood
lighter, moister outer region= sapwood
tylosis
bubbles of protoplasm through the pits into the vessels, forming plug
Types of Wood Cells
axial system
derived from the fusiform initials
contains tracheary elements
carry out longitudinal conduction of water through the wood
radial system
develops from the ray initials
rays
xylem
contains parenchyma, arranged as uniseriate, biseriate, or multiseriate masses
hardwoods
wood of all basal angiosperms and eudicots
contain fibers making them strong
softwoods
woods from conifers
few or no fibers
softer consistency
Reaction Wood
branches that are stresses and droop and become pendant
aka tension wood
Secondary Phloem
formed from vascular cambium
axial system
conduction up and down the stem or root
contains sieve tube members and companion cells in angiosperms
conduct for usually less than 1 year
fibers and nonconducting parenchyma are present
only innermost layer of phloem is capable of conduction
Outerbark
Lenticels and Oxygen Diffusion
lenticles
intercellular spaces penetrate the cork layer, creating a diffusion pathway for oxygen
contain more layers of cells and protrude outward
more active than adjacent regions that produce only ordinary impermeable cork
can be impossible to see in plants with thick rough bark
can be easy to see in species with smooth bark
Initiation of Cork Cambia
initiation of the first cork cambium is variable
some species it comes before a twig or root is even 1 year old
first bark on young stems usually differs from older bark
Cork and the Cork Cambium
new camium
aka phellogen
cuboidal cells
inner cell remains cork cambium and outer cell differentiates into a cork cell
cork cell also called phellem cell
layer of matured cells = phelloderm
periderm
layers of cork cells and the phelloderm
outer bark
all tissues outside the innermost cork cambium
inner bark
all secondary phloem between the vascular cambium and the innermost cork cambium
Secondary Growth of Roots
root vascular cambium contains both ray and fusiform initials
wood produced is similar to the shoot
has sapwood and heartwood
Anomalous Forms of Growth
Anomalous Secondary Growth
growth when alterative cambia produce secondary bodes that differ from the common type
Unusual Primary Growth
form of primary growth
this process ceases at some point
Basic Concepts
Primary tissues derived from the meristem:
vascular bundles
pith
cortex
leaves
epidermis
these make up the primary plant body
secondary tissues/secondary plant body
wood (secondary xylem)
bark (secondary phloem and cork)
woody plant examples:
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trees:
chestnuts
pines
sycamores
firs
shrubs:
roses
oleanders
azaleas
woody plants
grow taller from apical meristem
become wider through accumulation of wood and bark
