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Structure of Woody Plants (Secondary Xylem (Woods) (Heartwood and Sapwood …
Structure of Woody Plants
Concepts
derived from the meristem :red_flag:
primary tissues
primary plant body
in woody plants
additional tissues produced in stems/roots
new tissues
wood and bark
secondary xylem
secondary phloem and cork
herbs
only body that develops
secondary tissues
secondary plant body
sycamores, chestnuts, pines, firs
woody plants
roses, oleanders, and azaleas
important consequences :red_flag:
conducting capacity
needs of leaves and roots
helps with overproduction and water loss
rhizomatous
irises, bamboo, ferns
adventitious roots
produced to get sugar/water to new stems
taller and wider :red_flag:
conducting tissues'
minerals/ water, upward; carbs, downward
support increases
photosynthetic capacity increase
seeds production/ defensive chemicals increase
grow into adults and reproduce
must be in good, suitable sites
DIsadvantages :red_flag:
low germination time
fight insects, fungi, harsh environment
perennials
need greater defense
adapt to temperate climate
expensive
energy rich
wood burn readily
most don't reproduce for years
if killed b4 reproduction
waste of resources
Secondary Xylem (Woods)
Types of Wood Cells :red_flag:
all cells that occur in primary xylem
may contain tracheids. vessel elements, fibers, schlereids, parenchyma
different from primary xylem? :red_flag:
origin and arrangement
reflects that of fusiform and ray
axial system - from fusiform
radial system - ray initials
axial system
contains tracheary elements
longitudinal conduction of water
xylem parenchyma
woody angiosperms
fibers ~ give strength + flexibility
hardwoords
basal angiosperms + eudicots
Softwoods
few/no fibers, soft consistency
Radial system
woody angiosperms
only parenchyma
uniseriate, biseriate, multiseriate
called rays cells
2 basic types
upright cells
1 more item...
procumbent cells
store carbs +nutrients during dormant
Growth Rings :red_flag:
quiescent during stress
later unstresses
new leaves are thin/delicate
lose water quickly
need high conducting capacity
first wood formed :warning: EARLY WOOD
high proportion of wide vessels
later cuticle thickens, transpires less, conducts fast
after early wood: LATE WOOD
lower proportion of vessels
older, larger, needs more strength
ANNUAL RING
early wood + late wood 1 year's growth
Heartwood and Sapwood :red_flag:
dark wood: heartwood
lighter wood: sapwood
vessels/tracheids don't function forever in conduction
water columns breaks
new water filled tracheary
tylosis
plug
Reaction Wood :red_flag:
produced in response to stress
in angiosperms
upper side of the branch
tension wood
special gelatinous fibers
prevents branches from drooping
conifers
underside of the branch
compression wood
lignin and less cellulose
wide growth rings
Vascular Cambium
Initiation of the Vascular Cambium :red_flag:
in herbaceous species
located b/w metaxylem and metaphloem
become conducting tissues
in woody
continue to divide
become fascicular cambium
never undergo cell cycle arrest
mature parenchyma cells resume mitosis
interfacicular cambium produced
connects to fascicular cambia
complete cyinder
Near ground
older
closest to the tips
younger
contains both primary and secondary tissues
Fusiform initials and ray initials
Fusiform initials :red_flag:
long, tapered cells
140 - 462 um on dicots
700 - 8,700 in conifers
longitudinal cell division
wall parallel
to periclinal wall
makes 2 elongate cells
1: continues to fusiform initials
2: secondary xylem and secondary phloem
outer daughter cell in cambium, inner is xylem
inner daughter cell in cambium, outer cell, phlem
anticlinal walls
perpendicular to cambium's surface
increase # of cambial cells
thin primary walls
plastids present as proplastids
Ray initials :red_flag:
short, more or less cuboidal
undergo cell division
1 in cambium & other in xylem or phloem
different from fusiform
produces short cells
storage parenchyma
in gymnosperms, albuminous cells
Arrangement of Cambial Cells :red_flag:
ray initials
short, vertical rows
one, two,or many cell wide
Fusifrom initials
regular horizontal rows
storied cambium
redbud and persimmon
or irregularly, w/o horizontal rows
nonstoried cambium
Secondary Phloem
Axial and radial system
#
:red_flag:
no similar arrangement
axial system
conduction up and down the stem/root
sieve tube members/companion cells
angiosperms
sieve cells
conifers
fibers and nonconducting parenchyma
sieve tube/sieve cells conduct for less than 1 year
innermost layer ~ capable of conductio
shape, size, number match with xylem ray
made by same ray initials
Outer Bark
Cork and the Cork Cambium :red_flag:
vascular cambium and secondary phloem gets pushed back
new cambium
cork cambium (phellogen)
different from vascular cambium
structure and morphogenic activity
cuboidal cells
inner cells in cambium
outside comprise the outer bark
outer cells into cork cells
phelloderm
periderm
cork cambium
short lived
layers of cork cells
cell death critical
maturing increase in volume
phelloderm (if any)
impermeable barrier
temporary protection
growing inside of it
secondary phloem
inner bark
Lenticels and Oxygen :red_flag:
impermeability
advantage and disadvantge
disadvantages
blocks oxygen
interferes with respiration
sapwood, vascular cambium, and inner bark
advantages
keeps pathogens out
retains water
permeable when cork cells are produced
become rounded as they mature
intercellular spaces
diffusion pathway for oxygen
erenchymatous cork
Initiation of Cork Cambia :red_flag:
very variable
some appear before twig or root is 1 year old
detectable in stems
color change from green to tan
in some, takes several years
delayed formation is common
first may arise in number of tissues
epidermis, cortex, primary phloem, or secondary phloem
Secondary Growth in Roots
vascular cambium arises :red_flag:
pericycle cells become active+mitosis
first star shaped than rounded
bc of more production of secondary xylem
ray and fusiform initials
#
sapwood, heartwood, ring porous or diffuse porous
different in conductivity matters from the stem
nonsucculent must become succulent
take in+store water rapidly
perennial roots form bark :red_flag:
first cork cambium - pericycle
endodermis, cortex, epidermis shed
cork cells outside - protection
storage capacity increase
ray parenchyma - big volume
ray parenchyma becomes larger, capacity increases
Anomalous Forms of Growth
Anomalous Secondary Growth :red_flag:
alternative cambia produce secondary bodies
different from common type
Roots of Sweet Potatoes
storage parenchyma ~ increased by a lot
numerous vascular cambia arises
cell production rate is important
speed storage capacity
new vessels ~ surrounded by another new cambium
Included Phloem :red_flag:
located b/w 2 xylem bands
keep differentiating
secondary and new phloem
advantage
protection :star:
insects/pests
:
Secondary Growth in Monocots :red_flag:
none has secondary growth
some become tree like and woody
Joshua tree
type of V.C arises outside outermost vascular bundle
cortex cells
parenchyma cells ~ rapid division
dragon tree
palms
Unequal Activity of the Vascular Cambium
Bauhinia and certain other woody vines
2 sectors active, other inctive
stem grow outward in 2 directions
thin in other 2
advantage?
flexibility
adaptive
Unusual Primary Growth :red_flag:
Palm trees
trunks don't taper at tips
all primary tissues
#
vascular bundle in ground tissue
FIBERS
makes it hard and "woody"
Establishment growth
form of primary growth
