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Ch.8 Structure of Woody Plants, Ch.8 Structure of Woody Plants (Vascular…
Ch.8 Structure of Woody Plants
Ch.8 Structure of Woody Plants
Vascular Cambium
Initiation
vascular cambium
meristems that produce secondary plant body
must be extended each year
both primary & secondary tissues
apical meristem extends beyond this point
new vascular cambium forms
join with previous formed cambium
near ground oldest
closer to tips younger
never occurs in flowers, fruits, or seeds
only two cell types
fusiform initials
ray initials
metaxylem & metaphloem cells never undergo cell arrest
continue to divide
form fascicular cambium
aka bundle
parenchyma cells between bundle come out of arrest
resume mitosis
form interfascicular cambium
connects to fascicular cambia
now complete cylinder
young, 2-3 yrs
regions indistinguishable
Fusiform Initials
long tapered cells
140-462 micrometers dicots
700-8,700 conifers
longitudinal divison
two elongate cells
fusiform initial
thin primary walls
plastids present
proplastids
nuclear division
phragmoplast forms & elongates
grows up to 50-100 micrometers per hour
cell division as long as 10 days
secondary xylem or phloem
secondary xylem
daughter cell remain cambium cell
increase greatly in diameter
cambium cells pushed outward
results larger circumference
cells occasionally divide longitudinally
anticlinal walls
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secondary phloem
continues as cambium
outer cell differentiates & matures
Ray initials
short & more or less cuboidal
produce mostly storage parenchyma cells
albuminous cells
gymnosperms
periclinal cell divisions
one daughter remains a cambial ray initial
one daughter differentiates
xylem parenchyma
inner cell
phloem parenchyma
outer cells
elongate fusiform
elongate cells of wood
tracheids
vessel elements
fibers
elongate cells of phloem
sieve cells
sieve tube members
companion cells
fibers
Arrangement of Cambial Cells
specific patterns
ray initials
grouped together
short vertical rows
only one cell wide
uniseriate
two cell wide
biseriate
many cells wide
mutiseriate
fuisform initials
regular horizontal rows
storied cambium
occur in few eudicots
examples
redbud
persimmon
irregular rows
nostoried cambium
short
less than 200 micrometers
Secondary Xylem
Types of Wood Cells
cells formed to the interior of vascular cambium
secondary xylem
aka wood
tracheids
vessel elements
fibers
scelerids
parenchyma
angiosperm wood
hardwoods
conifer wood
softwoods
axial system
derived from fuisform initials
contains tracheary elements
carry out longitudinal conduction of water
gives strength & flexibility
water storing parenchyma may be immediately adjacent to vessels
radial system
usually simple
woody angiosperms
only parenchyma
arranged in rays
store carbs
store nutrients
conduct material short distances
ray parenchymas
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ray tracheids
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Growth Rings
regions w/strongly season climates
quiescent
stress
winter cold
summer drought
ceases
vascular cambium active
cell division begins
new expanding leaves thin/delicate
lose water @ rapid rate
tree has high capacity for conduction
cuticle not thick or polymerized
wood formed
early wood
spring wood
high proportion wide vessels
late wood
summer wood
lower proportion of vessels
plant older & heavier
make up annual ring
Heartwood and Sapwood
Heartwood
darker
drier
more fragrant
dark & aromatic chemicals
ex: cedar wood
Sapwood
lighter
moister
outer region
new layer each year
constant thickness
Diff regions form
vessels & tracheids don't function forever
water columns break
freezing
wind vibration
tension
wood-boring insects
after broken no means pull up water
tylosis
plug for vessels
cells undergo numerous metabolic changes
produce large quantities of phenolic compounds
ligin
dark colored aromatic substances
inhibit growth of bacteria
once dead convert to heartwood
Reaction Wood
branches & trunks not vertical
lateral stress
response to stress
conifers
reaction wood upper side
compression wood
enriched lignin
less cellulose
growth rings especially wide
angiosperms
develops mostly upper side of branch
tension wood gelatinous fibers
rich in cellulose
little/no lignin
exert tension on branch
prevents dropping
contract, slowly lifting branch
Secondary Phloem
formed in vascular cambium
axial system
conduction up & down stem or root
contains sieve tube members
companion cells in angiosperms
sieve cells in conifers
fibers & nonconducting parenchyma
sieve members conduct less than 1 yr
only innermost layer phloem capable
phloem rays match xylem rays
both produced by initial rays
Outer Bark
Cork and Cambium
production & differentiation of secondary xylem cells
push vascular cambium & secondary phloem outward
innermost phloem cells form & mature
contribute to larger diameter
increase pressure
some tissues grow in circumference
older sieve elements die
some storage parenchyma cells reactivate
undergo cell division
new cambium aka cork cambium
cells cuboidal
inner cell remains same
outer cells differentiate into cork cell
phelloderm
inside
mature into later parenchyma
periderm
layers of cork cells
phelloderm
cork cambium
increase slightly in volume
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short lived
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temporary protection
innermost cork cambium
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secondary phloem between vascular cambium & innermost cork cambium
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other tissues tear apart
Lenticels and Oxygen Diffusion
regions of arenchymatous cork
more active than adjacent regions
adjacent regions only produce ordinary impermeable cork
outer & inner lenticels aligned
permit oxygen to penetrate across layers
more layers cells
protrude outward
located @ base of cracks in bark
Initiation of Cork Cambium
timing more variable
first may arise in in number of tissues
epidermis
cortex
primary phloem
secondary phloem
cork cambium may form shortly afterwards
growth diameter slow, cork cambia arises in intervals
form deep in secondary phloem
first bark
differs from bark formed when older
arises by reactivation
first outer bark ha only periderm & cuticle
very smooth
arises in cortex
first outer bark contains periderm, cortex & epidermis
smooth
cortical secretory cells
outer bark
first bark shed
later cork cambia arise in secondary phloem
produce bark
fiber cells
fibrous stringy bark
sclereid-filled phloem
hard bark
only contains cork & phloem
Secondary Growth in Roots
vascular cambium arises
parenchyma cells between primary xylem & phloem become active mitotically
pericycle cells also active
becomes round
circular cambian
unequal growth stops
all parts grow @ similar rates
more secondary regions pushed out
root vascular cambian
contains ray and fusiform initials
wood produced similar to shoot
sapwood
heartwood
ring or diffuse porous
pure parenchyma
example: carrot peel
carrot wood
peel bark
perennial roots
cork cambium arises in pericycle
endodermis, cortex, exodermis shed
cork cambium produces cork cells to outside
protective layer
phelloderm
lenticels also occur
prominent near lateral roots
bark created
ray parenchyma of secondary xylem
volume
storage capacity
Anomalous Forms of Growth
Anomalous Secondary Growth
Roots of Sweet Potatoes
storage parenchyma increased dramatically
anomalous method of of secondary growth
numerous vascular cambia arise
around individual vessels/groups
xylem & phloem almost purely parenchyma
new vessels surrounded by new cambium
process repeated
hundreds all at various ages
secondary tissues irregular matrix of parenchyma
few sieve tubes
some vessels
vascular cambia
benefits
multiple cambia
high speed of production
Unequal Activity of the Vascular Cambium
all vascular cambium
root & stem round is c.s.
some species active
examples
Bauhinia
woody vines
two sectors almost completely inactive
two sectors completely active
stem grows outward two directions
thin flat woody ribbon
allows flexibility
Secondary Growth in Monocots
some tree-like & woody
anomalous growth
examples
dragon trees
Dracaena
Joshua trees
Yucca
vascular cambium arises outside outermost vascular bundles
cambium only produces parenchyma
conducting cells absent
some columns undergo rapid division
produce narrow cells
secondary vascular bundles
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primary growth
ex: palm trees
unusual
alternative cambia produce secondary bodies
differ from common type
Included Phloem
several eudicots
vascular cambium of common type arises
produces ordinary secondary xylem & phloem
cambium cells stop dividing & differentiate into xylem
no longer cambium
cells in outermost
reactivated
differentiate
create new vascular cambium
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from interior to exterior
first xylem
first phloem
second xylem
outermost
new vascular cambium arises
included phloem
located between two bands xylem
advantages
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second phloem
Unusual Primary Growth
occurs in palm trees
trunks do not taper @ tips
trunks do not branch
trunks primary tissue
vascular bundles distributed throughout ground tissue
bundle contains primary xylem & primary phloem
derived from shoot apical meristem
never develops true wood
secondary phloem does not occur
does not grow radically
woody & hard
bundles sheathed in heavy fibers
seedling
1st yrs becomes wider w/more leaves
no secondary growth
numerous adventitious roots
adds extra bundles each root
establishment growth
increase in width
increase in addtion of adventious roots
form primary growth
