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Structure of Woody Plants (Anomalous Forms of Growth (Unequal Activity of…
Structure of Woody Plants
Vascular Cambium
meristem that produce secondary plant body
continue to divide instead of maturing
fascicular cambium
interfascicular cambium
only two types of cells
Fusiform Initials
long tapered cells
periclinal wall
anticlinal wall
produce elongated cells of wood
xylem
tracheids
vessel elements
fibers
phloem
sieve cells
sieve tube members
companion cells
fibers
Ray Initials
short & cuboidal
produce short cells
storage parenchyma
albuminous cells
Arrangement of Cambial Cells
storied cambium
regular horizontal rows
nonstoried cambium
without horizontal pattern
Secondary Xylem
Types of Wood Cells
all cells interior of vascular cambium=wood
all cell types of primary xylem
no new ones
axial system
derived from fusiform initials
always contains tracheary elements
longitudinal conduction of water
fibers
hardwoods
large amount of fibers
softwoods
few or no fibers
radial system
develops from ray initials
usually simple
containing only parenchyma
rays
uniseriate
biseriate
multiseriate
upright cells
procumbent cells
store carbohydrates
store nutrients
Growth Rings
vascular cambium quiescent during times of stress
early wood/ spring wood
first wood formed
wide vessels/wide tracheids
late wood/summer wood
lower proportion of vessels
numerous fibers/ thick-walled tracheids
annual ring/ growth ring
spring & summer wood combined
diffuse porous
vessels form throughout growing season
ring porous
vessels restricted mainly to early wood
Heartwood and Sapwood
heartwood
center of log
dryer and more fragrant
almost always darker in color
one annual ring converted to heartwood each year
sapwood
outer region
lighter in color
moister
new layer formed each year
different regions because water columns break
freezing
wind
tension
wood-boring insects
tylosis
bubbles of protoplasm
forms plug in vessels
Reaction Wood
response to stress
tension wood
eccentric
wider on top of the branch
prevent drooping
Outer Bark
Cork and the Cork cambium
secondary phloem
cork cambium/phellogen
cells are cuboidal
after division inner cell remains cork cambium
outer cell differentiates into cork cell/phellem cell
phelloderm
layer of parenchyma
periderm
cork cambium, cork cells, & phelloderm
outer bark
inner bark
Lenticels and Oxygen Diffusion
lenticels
permits oxygen to penetrate bark
Iniitiation of Cork Cambia
variable
first cork cambium
depending on species can arise
before twig or root is even 1 year old
region is several years old
epidermises more than 40 years old reported
Secondary Growth in Roots
roots of conifers
woody angiosperms
vascular cambium arises
ray initials
fusiform initials
wood produced in root
not identical to that of stems
Secondary Phloem
formed from vascular cambium
axial system
conduction up/down stem/root
sieve tube members
conduct for less than 1 year
companion cells
fibers
nonconducting parenchyma
radial system
ray initials
phloem rays
only parenchyma cells
storage
Anomalous Forms of Growth
Anomalous Secondary Growth
roots of sweet potoatoes
storage parenchyma increased
numerous vascular cambia arise
around individual vessels
large
hundreds of cambia at various ages
irregular matrix of parenchyma
few sieve tubes
some vessels
Included Phloem
new vascular cambium arises
located between two bands of xylem
protection from insects
Unequal Activity of the Vascular Cambium
2 sectors of cambium very active
2 sectors almost completely inactive
stem grows outward in two directions
remains thin in the other two
thin flat woody ribbon
flexibility
Secondary Growth in Monocots
some become tree-like and "woody"
Joshua trees
dragon trees
palms
secondary vascular bundles
develop into fibers
thick secondary walls
Unusual Primary Growth
palm trees
trunks do not taper at tips
do not branch
all primary tissue
vascular bundles
primary xylem
primary phloem
derived from shoot apical meristem
vascular cambium never develops
true wood does not occur
secondary phloem does not occur
trunk does not grow radially
hard and "woody"
vascular bundle enclosed in strong fibers
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ground tissue
