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Structure of Woody Plants (Anomalous Forms of Growth (Roots of Sweet…
Structure of Woody Plants
Vascular Cambium
Initiation of Vascular Cambium
produces the secondary plant body
fascicular cambium- cells between metaxylem and metaphloam reproduce
terms used when when cambium is young (crosslink)
interfascicular cambium-parenchyma cells connect with the fascicular cambium
fusiform initials
ray initials
Fusiform Initials
long tapered cells
longitudinal cell division- periclinal wall
fusiform initial
secondary phloem or xylem
wood never forms externally
bark never forms internally
always much more xylem produced than phloem
anticlinal walls-cells divide longitudinally
Ray Initials
short and more cuboidal
periclinal cell division
cambial ray initial
xylem and phloem parenchyma
produce short cells for storage parenchyma
albuminous cells store gymnosperms
Arrangement of Cambial Cells
ray initials are in short vertical rows
ray initials are uniseriate, biseriate or multiseriate
Crosslink
fusiform are in horizontal rows
storied cambium
or fusiform are irregular, no horizontal pattern
nonstoried cambium
storied cambia evolved more than unstoried cambia
large region of fusiform, the central one will become ray initial
large region of ray initials, central will become fusiform initial
Secondary Growth in roots
becomes round when more secondary xylem produced
root vascular cambium has both ray and fusiform initials
new cambium same star shape
parenchyma cells located between primary xylem and phloem
Secondary Xylem
Types of Wood Cells
secondary xylem-wood
axial system-fusiform
radial system- ray initials
axial system-conduction of water
axial system fibers make them strong and tough
hardwood-fibers
softwoods- no fibers
wood holds water
radial system of xylem- rays
upright cells
procumbent cells
ray tracheids
Growth Rings
early wood-high proportion of wide vessels
late woods-lower proportions of vessels
annual ring- early and late wood
growth ring-no growth
diffuse porous
ring porous
Heartwood and Sapwood
heartwood-dark center wood
sapwood- moister outer region
tylosis-protoplasm through pits
chemicals are aromatic and darker
conversion from sapwood to heartwood
new layer of sapwood each year
Reaction
so the branch will not droop
growth rings wider at top of branch
rich in cellulose but no lignin
tension wood contact-lifting branch
reaction wood underside-compression wood
rich in lignin and has less cellulose
Outer Bark
Cork and the Cork Cambium
some species produce phelloderm
cork cambium and cork cells- periderm
outermost cells become cork cells
primary wall encrusted with suberin
new cambium- cork cambium
making them waterproof, then the cell dies
secondary phloem- inner bark
innermost cork cambium comprise outer bark
Lenticels and Oxygen Diffusion
new cork cambium and outer and inner lenticels align
lenticel-producing regions more active
arenchymatous cork- lenticels
lenticels contain more layers of cells
rounded cork cell make bark permeable
generally located at the base of tree
impermeable cork blocks absorption of oxygen
Initiation of Cork Cambia
not unusual for bark to look different when tree is older
cork cambium arises from reactivation of epidermal cells
surface changes from green to tan
first cork cambium is variable
Anomalous Forms of Growth
Roots of Sweet Potatoes
xylem adn phloem are purely parenchyma
contains hundreds of cambia
vascular cambia arise individual vessls
cell production is important
increased parenchyma storage
Included Phloem
new vascular cambium
produce ordinary xylem and phloem
cells outermost become reactivated
protection from insects
secondary phloem located between two xylem- included phloem
Anomalous Secondary Growth
secondary bodies that differ
Unequal Activity of Vascular Cambium
two sectors are completely inactive
stem grows outward in two directions
two sectors are very active
stem is thin in the other directions
advantage is the flexiblity
Secondary Growth in Monocots
originates from cortex cells
produces only parenchyma
vascular cambium arise from vascular bundles
secondary vascular bundles
some monocots become tree-like
Unusual Primary Growth
palm trees
does not have leave
produce numerous roots
do not branch
establishment growth
crosslink
