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Structure of Woody Plants (secondary xylem (arrangement: (radial system…
Structure of Woody Plants
secondary xylem
all cells formed to interior of vascular cambium
AKA wood
contain same cell types as 1* xylem
may contain tracheids, vessel elements, fibers, sclereids & parenchyma
differ from 1* xylem in origin and arrangement
arrangement:
radial system
develops from ray intials
xylem is simple; arranged in rays
ray parenchyma cells
conduct materials radially over short distances within wood
store carbs/nutrients in dormant periods
two types
upright cells
precumbent
ray tracheids
horizontal, rectangular
axial system
develops from fusiform initials
always contains tracheids and/or vessel elements
carry out longitudinal conduction of H2O thru wood
contains fibers
give wood strength and flexibility
few or no fibers = softwoods
large amounts of fibers = hardwoods
growth rings
formed by early and late wood
ring porous vs fuse porous
reaction wood = tension wood
outer bark
cork & cork cambium
differs from vascular cambium in structure and morphogenic activity
phelloderm = inner layer of parenchyma
all cells are cuboidal
periderm = cork cambium + cork cells + phelloderm
outer bark = tissues outside innermost cork cambium
inner bark = 2* phloem between vascular cambium and innermost cork cambium
lenticels and O2 diffusion
O2 able to diffuse thru cork when cells become round
lenticels = regions of aerenchymatous cork
initiation of cork cambia
initiation of cork cambia = variable
anomalous forms of growth
anomalous 2* growth
alternative cambia
examples
unequal activity of vascular cambium
roots of sweet potatoes
amount of storage parenchyma increased dramatically
included phloem between two hands of xylem
secondary growth in monocots
secondary vascular bundles
unusual 1* growth
establishment growth
increase in width & addition of adventitious roots
meristems that produce 2*
vascular cambium
only has two types of cells
ray initials
short, cuboidal
division- one daughter remains cambium and other becomes either xylem or phloem parenchyma
produce short cells
storage parenchyma
arrangement:
grouped together in short vertical rows that are either:
uniseriate (one cell wide)
biseriate (two cells wide)
multiseriate (many cells wide)
fusiform initials
long, tapered
division along periclinal or anticlinal walls
produce elongate cells of wood
tracheids, vessel elements and & fibers
produce elongate cells of phloem
sieve cells, sieve tube members, companion cell, & fibers
arrangement in:
nonstoried cambium (irregular, no horizontal pattern)
storied cambium (regular horizontal rows)
fascicular cambium
each side connected by interfascicular cambium
term used only when cambium is young
when regions become indistinguishable->"vascular cambium"
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secondary phloem
also has axial and radial system
axial does conduction up and down stem/root
axial has sieve tube members and companion cells
not arranged in early/late wood
