Structure of Woody Plants
Vascular Cambium
Initiation of the Vascular cambium
Fusiform initials
Ray initials
Arrangement of Cambial cells
Secondary Xylem
Heartwood and Sap wood
Reaction wood
Growth rings #
Secondary Phloem
Outer Bark
Initiation of the cork cambium
Lenticels and oxygen Diffusion
Secondary Growth in Roots
Anomalous Forms of Growth
Anomalous Secondary Growth
Unusual Primary Growth
Concepts
Primary Tissue
Secondary Tissues
Epidermis
Cortex
Vascular Bundles
Pith
leaves
Vascular cambium
cork cambium
secondary xylem
wood
bark
Secondary Phloem
cork
not found in herbs
Vascular cambium
meristem
makes secondary plant body
Fascicular cambium
Interfascicular cambium #
Resume mitosis
Never undergo cell cycle arrest
term only used for young plants
term only used for young plants
only two types of cells
Fusiform initials
ray initials
Typical length
140-462 UM in dicots
700-8700 UM in conifers
divide longitudinally
anticlinal walls
division parallel to cambium
periclinal wall
two elongate cells
Short and cuboidal
undergo periclinal division
produce short cells
elongate cells
tracheids
vessel elements
fiber
Sieve tube members
companion cells
store parenchyma
aluminous cells
ray initials grouped
uniserite
one cell wide
biseriate
two cells wide
multiseriate
many cells wide
fusiform initials grouped
storied cambium
regular horizontal rows
nonstoried cambium
irregular, no horizontal patterns
evolved after nonstoried cambium
only occur in
few advanced eudicots species
AKA wood
difference between secondary and primary xylem
Origin
arrangement
Arrangement
axial system
derived from fusiform initials
radial system
derived from ray initials
always contains tracheary elements
contain fibers
has ray parenchyma cells
store nutrition
upright cells
procumbent cells
can contain ray tracheids
early wood
first wood formed
late wood
many wide vessels
wide tracheids
less vessels
more strength
annual ring =
early + late wood
one year of growth
diffuse porous
vessels throughout
ring porous
vessels restricted to early wood
Heartwood
Sap wood
darker
drier
lighter
moister
tylosis
protoplasm plug
prevents fungal and bacterial growth
darkenss wood
thicker with age
mostly consistent thickness
develops on upperside of branch
prevents branches from drooping
= tension wood
have little to no lignin
rich in cellulose
formed from vascular cambium
radial system
axial system
conducts up and down stem or root
angiosperms
sieve tube members
companion cells
conifers
sieve cells
phloem rays more importaint
than xylem rays
Cork and the Cork Cambium
phellogen
different from vascular cambium
in structure
in morphogenic activity
all cells cuboidal
after division
inner cells stay phellogen
outer cells turn into phellem
some produce phelloderm
periderm
phellem
phellogen
phelloderm
mature cells die
outer bark
all cells outside innermost cork cambium
all secondary phloem between
vascular cambium and innermost cambium
is inner bark
lenticels
provide oxygen pathways
look like cracks in bark
more variable than vascular cambium
first cork cambium by reactivation epidermis
outer bark contains cuticle
outer bark contains periderm
is smooth
first cork cambium arises by cortex
outer bark contains periderm
outer bark contains cortex
outer bark contains epidermis
root vascular cambium
contains ray initials
contains fusiform initials
perennial roots form bark
first cork cambium arises in
pericycle
wood of roots
not identical to wood of stem
secondary bodies different from common type
roots of sweet potatoes
storage parenchyma increased by
anomalous secondary growth
vascular cambium arise
around individual vessels
xylem and phloem produced
almost entirely made of parenchyma
multiple vascular cambia provide
increased storage capacity
included phloem
provides protection to normal phloem
unequal activity of the vascular cambium
some species of wood
two very active cambium
two almost inactive cambium
stem grows outward in two directions
stays thin in the other two
secondary growth in monocots
no monocots have secondary growth
some do become tree like
joshua trees
vascular cambium originates from cortex
cambium produces only parenchyma
non conducting
secondary vascular bundles
palm trees #
palm trunk made of primary tissue
vascular cambium never develops
true wood does not occur
secondary phloem does not occur
establishment growth
increase in advenitious roots
increase in width
the vascular cambium originates from the cortex cells in the same way interfascicular vascular cambium arises in eudicots
Although trees are associated with secondary tissue, palm trees never develop vascular cambium. Thus, they never have true secondary growth.
Because palm trees are monocots, they have many vascular bundles instead of wood. They do not exhibit true secondary growth and do not have growth rings.