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Structure of Woody Plants (Vascular Cambium (Arrangement of Cambial Cells…
Structure of Woody Plants
Vascular Cambium
Initiation of the Vascular Cambium
Keep dividing; fasciular cambium
maturing ones= Interfascicular cambium
made of Fusiform and ray initials
Ray Initials
short, less cuboidal
xylem parenchyma= inner cell
phloem parnchyma=outer cell
produce short cells for storage
Fusiform Initials
long cells
secondary xylem=cambium outside. more common
secondary phloem=inner cambium
produce elongate cells of wood
Arrangement of Cambial Cells
ray initials
usually short vertical rows
fusiform initials
reg. horizontal rows=storied; irregular=nonstoried
ray inirials vs fusiform initials ratio is broad
each tree=one vascular cambium
Secondary Xylem
Types of Wood Cells
interior formed cells=secondary xylem(wood)
axial system=fusiform initials
radial system=ray initals
hardwoods=all basal anfiosperms and eudicots; a lot of fibers
softwoods=from conifers few or no fibers
Growth Rings
first wood=early wood/spring wood wide vessels
cuticle thickens less transpiration, vessels conducting rapidly=late wood/summer woodtext
annual ring/growth ring= early wood and late wood
vessels located throughout growth ring=diffuse porous
vessels strictly mainly in early wood=ring porous
Heartwood and Sapwood
dark wood=heartwood
becomes wider with age
lighter moister region=sapwood
new layer each year by vascular cambium; one annual ring each year
tylosis= plug that forms when vessels push bubbles through pits into vessel
inhibit growth of bacteria and fungi
after all parenchyma cells die sapwood turns into hearwood
Reaction Wood
help branches/trunks stay up when not vertical
known as tension wood in angiosperms; develops on upper side
compression wood in conifers on underside of branch
Secondary Phloem
axial root contain sieve tube members and companion cells; conducts up and down movement
fibers and nonconducting parenchyma present
size and shape of phloem rays=xylem rays
Outer Bark(all tissues outside cork cambium)
Cork(phellogen)/Cork Cambium
different structure and activity than vascular cambium
outer cell=cork cell(phellem cell)
phelloderm=cell inside that mature into layer of parenchyma
periderm=cork cambium, layers of cork, phelloderm
short lived. cork cells also help block..so they tend to accumulate
Lenticels and Oxygen Diffusion
rounded cork cells=cant fit tightly so spaces penetrate cork layer=diffusion pathway for oxygen
regions that allow this are lenticles
easy to see with smooth bark trees
Initiation of Cork Cambia
timing can be before 1 year old..or when region is several years old
fist cork cambium arises by reactivation of epidermal cells
Inner bark= all secondary phloem b/w vascular cambium and cork cambium
Anomalous Forms of Growth
Anomalous Secondary Growth
alternative cambia produce secondary bodies that differ from common type
Unusual Primary Growth
ex. are palms..have numerous vascular bundles containing many fibers
secondary growth in roots
vascular cambium arises..soon becomes round, pushed outward more when circular cambium is made the unequal growth stops and all parts grow together
