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