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Chapter 8: Structure of Woody Plants (Secondary Xylem (Growth Rings…
Chapter 8: Structure of Woody Plants
Initiation
Provascular Tissue
Fascicular
Vascular Cambium
produces secondary plant body
Cells
Arrangement of Cambial Cells
fusiform
regular horizontal rows
storied
irregular no pattern
nonstoried
ray
short vertical rows
Ray initials
Phloem Rays
Xylem Rays
short and cuboidal
Fusiform Initials
axial xylem
axial phloem
long, tapered cells
periclinal wall
parallel
anticlinal wall
perpendicular
Pith
Interfascicular
Secondary Xylem
Types of Wood Cells
axial system
fusiform
tracheary elements
longitudinal conduction
hardwoods
fibers-stronger
softwoods
less fibers-softer
radial system
ray
parenchyma
ray cells
upright
procumbent
ray tracheids
horizontal rectangular cells
secondary walls
circular bordered pits
Growth Rings
quiescence
stress, winter, drought
no cell division
annual ring-1 year growth
early wood
spring wood
high vessel count
first wood
late wood
summer wood
less vessels
diffuse porous
vessels form constantly
ring porous
vessels restricted to early wood
indistinct
Heartwood & Sapwood
Heartwood
center
dark, dry
one annual ring converted to heartwood each year
Sapwood
outer
lighter, moister
new layer formed by vascular cambium every year
Reaction Wood
tension wood
angiosperms
upper side of branch=wider
rich in cellulose
little lignin
gravity
eccentric
compression wood
conifers
underside =wider
less cellulose
more lignin
wood
Outer Bark
Cork and the Cork Cambium
Initiation
phellogen
cells =cuboidal
cell division
inner cell =remains cork cambium
outer cell =cork cell
periderm
maturation
protection
short lived
new cork
keeps out pathogens
maintain water
Lenticels and Oxygen Diffusion
Blocks absorption of oxygen
tissues outside inner cork cambium
inner bark
all secondary phloem between vascular cambium and innermost cork cambium
Secondary Phloem
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formed from vascular cambium
no arrangement
only innermost layer of phloem capable of conduction
Secondary Growth in Roots
Anomalous Forms of Growth
Anomalous Secondary
Roots of Sweet Potatoes
Included Phloem
Unequal Activity of the Vascular Cambium
Secondary growth in Monocots
Unusual Primary Growth
make cork cambium
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made from fusiform and ray
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become indistinguishable and join together to make vascular cambium
axial and radial system
