Please enable JavaScript.
Coggle requires JavaScript to display documents.
Structure of Woody plants (Secondary Growth in Roots (root VB contains ray…
Structure of Woody plants
Vascular Cambium
Initiation
Produce secondary plant body
cells don't undergo cell cycle arrest
continue dividing
make the fascicular cambium
interfascicular cambium
must be extended each year
rarely forms in leaves
Two types of cells
Fusiform Initials
140-462 micrometers
longitudinal cell division
two elongate cells
1 fusiform initial
1 secondary cell
anticlinal walls
longitudinal division
increases cambium cells
Thin primary walls
periclinal wall
division with a wall parallel
Ray Initials
short and cubidial
periclinal cell division
#
produce short cells
storage parenchyma
albuminous cells
Arrangement of Cambial Cells
ray initials
short vertical rows
1,2, or more cells wide
Fusiform initials
regular horizontal rows
irregular patterns
Never mostly one type of cell
ratio quite constant
Secondary Xylem
Types of wood cells
secondary xylem
"wood"
contains all cells in primary xylem
no new cells
axial system
from fusiform initials
contains tracheary elements
conifers
only axial wood
radial system
from ray initials
simple
contains only parenchyma
ray parenchyma
stores sugars
Growth rings
early wood, "spring"
high proportion of wide vessels
cuticle has thickened
transperation is less
late wood, "summer"
low proportion of vessels
stronger
contains more fibers
form 1 year ring, growth ring
diffuse porous
growth ring with vessels
ring porous
vessels restricted to early wood
Heartwood and sapwood
heartwood
center of log, darker
more fragrant
water column breaks
no way to pull water
10 years to become hard wood
sapwood
lighter
moister
outer region
tylosis
plug of protoplasm bubbles
Reaction wood
Response to stress
stress is caused by gravity
growth rings wider on low side of limb
angiosperms
mainly upper side of branch
tension wood
prevents drooping
confifers
underside of branch
compression wood
rich in lignin and less cellulose
growth rings wide on underside of branch
Outer Bark
Cork and the Cork Cambium
cork cambium (phellogen)
results from secondary phloem
#
cells cubidial
inner cells remains cork cambium
outer cell becomes a cork cell
periderm
cork cambium, cork cells, and phelloderm
temporary protection
cork cambium short lived
Initiation of Cork Cambia
some arise before 1 year
stem changes from green to tan
some several years old
young stems
first bark differs from old stems
young tree bark different from older trees
new cambia could arise every ten years
Lenticels and O diffusion
lenticels
region of aerenchymatous cork
permit oxygen to enter though the cork
contain more layers of cells
located at bases of cracks in bark
Secondary Phloem
formed from vascular cambium
#
axial and radial system
#
axial system
conduction up and down stem/root
sieve tube members
conduct -1 year
companion cells
Radial system
Secondary Growth in Roots
vascular cambium arises
root VB contains ray and fusiform initials
wood in root similiar to shoot
ring/porous as stem
conduction by diffusion
xylem and phloem rays gigantic
large region of water storage
perennial roots form bark
Anomalous Forms of Growth
Anomalous Secondary Growth
cambia produce secondary bodies
roots of sweet potatoes
storage parenchyma increased
xylem and phloem are parenchyma
new vessels surrounded by new cambium
large sweet potaot
may contain 100s of ages of cambia
included phloem
secondary phloem between xylem
protection from pests
one to several layers of wood
Unequal activity of vascular cambium
advantage may be flexibility
stem grows outward in two directions
remains thin in other two
Unusual Primary growth
palm trees
trunk doesnt taper at tip
no branches
trunk hard because VB enclosed in fiber
established growth
form of primary growth
increase in width and addition
shoots and roots
become longer
new cells are added
become wider
VB attaches itself to preexisting cambium