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Chapter 8: Structure of woody plants, Radial systems develop from ray…
Chapter 8:
Structure of woody plants
Vascular Cambium
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Initiation of vascular cambium
produces secondary plant body
vascular bundle
cells between
metaxylem
metaphloem
herbaceous species
stop dividing
differentiate into
conducting tissues
woddy species
cells
never stop dividing
no cell arrest
constitute fascicular cambium
old term for bundle
interfascicular cambium
mature parenchyma
out of cell arrest
resume mitosis
form with fascicular cambium
complete cylinder
extended each year
root and stems
initially only primary tissue
vscular cambium arises
primary tissues
secondary tissue
next growth season
apical meristem extends
beyond axis
new segment forms
new ground
oldest
close to tip
younger
two cell types:
fusiform initials
long tapered cells
140-462um in dicots
700-8700um in conifers
longitudinal cell division
wall parallel
periclinal wall
produces two elongated cells
one stays fusiform
one turns into:
secondary phloem
secondary xylema
grouped
regular horizontal rows(storied cambium)
nonstoried cambium
irregular
no horizontal pattern
ray initials
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short
cuboidal
periclinal cell division
xylem parenchyma
inner cell
phloam parenchyma
outer cell
produce shot cells
mostly storage parenchyma
grouped
short vertical rows
one cell wide(uniseriate)
two cells wide(biseriate)
many cells wide(multiseriate)
narrow cylinder
pushed outward
production of wood cells
inner surface
Secondary Xylem
types of wood cells
interior cells
vascular cambium
secondary xylem
all types of cells
primary xylem
no new cells
arrangement reflects
ray intitials
radial system
simple
woody angiosperms
only parenchyma
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ray parenchyma cells
store carbohydrates
conduct material
radial movement through wood
fusiform initials
axial system
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tracheary elements
carryout longitudinal conduction
water through wood
angiosperms
contains fibers
give strength
flexibility
wood
trachieds
vessel elemnats
fibers
sclereids
parenchyma
hardwood
large amounts of fiber
strong
tough
useful in construction
angiosperm wood
all basal angiosperm and eudicots
softwood
soft
few-to fibers
conifers
little to no axial parenchyma
little water reserve
some harder than hardwood
axial xylem parenchyma
transverse division
differentiate
columns of xylem parenchyma
temporary reservoir of water
growth rings
early wood(spring wood)
high proportion wide vessels
late wood(summer wood)
low proportion wide vessels
stronger
numerous fibers
diffuse porous
vessels throughout
yellow birch, aspen, sugar maple, American holly
ring porous
vessels restricted to
early wood
redoak, sassafras, honey locust
heartwood and sapwood
heartwood
darker
drier more fragrant
center region
phenolic compounds
lignin
aromatic substances
prevents bacteria
prevent fungi
wider with age
sapwood
lighter
moister
outer rigion
new layer each year
constant thickness
tylosis
plug
adjacent cells from vessels
bubbles through pits into vessels
Reaction Wood
not vertical
causes lateral stress
response to stress
agiosperms
mostly upper side of branch
tension wood
growth wings wider on top
conifers
reaction wood on lower side branch
compression branch
Secondary Phloem
formed from vascular cambium
axial system
conduction up and down stem
sieve tube members
companion cells
angiosperms
conifers
sieve cells
radial system
fibers
nonconducting parenchyma cells
inner most layer conducts
Outer Bark*
cork cambium
also called phellogen
bark
outer
inner
cuboidal cells
cells differentiate into cork cells
phellem cells
differs greatly from vascular cambium
phelloderm
one-two cells
layer of parenchyma
increase in volume
thin walls encrusted with suberin
waterproof
chemically inert
they die
short lived
lenticels and oxygen diffusion
lenticels
regions of aerenchymatous cork
contain more layers of cells
protrude outward
outer and inner aligned
permit oxygen to penetrate
more active
located at base of cracks
initiation of cork cambium
timing is variable
barks of different ages are dramatically different
first cork cambium
arise in number of tissue
epidermis
cortex
primary phloem
secondary phloem
reactivation of epidermal cells
subsequent cork cambium
shortly after first
sometimes in same season
1-2 years later
secondary xylem cells
secondary phloem
vascular cambium
pushed outward
periderm
cork cambium
cork cells
impervious
tough
impermeable barrier
temporary protection
all tissue outside innermost cork
all phloem tissue between vascular cambium
and inner most cork is inner bark
Anomalous Forms of Growth
Anomalous secondary growth
alternative cambium structures
secondary bodies
differ from common type of growth
Sweet potato root
large amounts of storage parenchyma
numerous vascular cambium
around individual vessels or groups of vessels
purely parenchyma
xylem
phloem
Included phloem
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protects phloem from insects
located between two bands of xylem
secondary phloem
Unequal activity of the vascular cambium
advantage: flexibility
two sectors are active
two sectors are inactive
stem grows out in two directions
remains thin in other section
Secondary growth in monocots
secondary vascular bundle
parenchyma cells
rapid division
produce narrow cells
contains phloem and xylem
woody
fibers
more conducting capabilities
Joshua tree
produces only parenchyma
cambium
becomes "woody"
Unusual primary growth
palms
trunk doesnt taper at tip
do not branch
numerous adventitious roots
base of short stem
adds extra vascular bundles
establishment growth
increase in width
increase in adventitious roots
palm trunk
all primary tissue
vascular bundles throughout ground tissue
primary phloem
primary xylem
derived from shoot apical meristem
enclosed in strong heavy fibers
hard
woody
Comparison of Palm(A) and Oak(B)
Radial systems develop
from ray initials
Included phloem is between two bands of xylem
Axial systems develop from fusiform initials
Secondary phloem is formed from vascular cambium
