Structure of Woody Plants
secondary xylem
outer bark
anomalous forms of growth
meristems that produce 2*
secondary phloem
vascular cambium
fascicular cambium
each side connected by interfascicular cambium
term used only when cambium is young
when regions become indistinguishable->"vascular cambium" #
only has two types of cells
ray initials
fusiform initials
long, tapered
division along periclinal or anticlinal walls
produce elongate cells of wood
short, cuboidal
division- one daughter remains cambium and other becomes either xylem or phloem parenchyma
tracheids, vessel elements and & fibers
produce elongate cells of phloem
sieve cells, sieve tube members, companion cell, & fibers
produce short cells
storage parenchyma
arrangement in:
nonstoried cambium (irregular, no horizontal pattern)
storied cambium (regular horizontal rows)
arrangement:
grouped together in short vertical rows that are either:
uniseriate (one cell wide)
biseriate (two cells wide)
multiseriate (many cells wide)
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
axial system
develops from ray intials
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
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
growth rings
formed by early and late wood
ring porous vs fuse porous
reaction wood = tension wood
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
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 2* growth
alternative cambia
unusual 1* growth
examples
unequal activity of vascular cambium
roots of sweet potatoes
secondary growth in monocots
establishment growth
increase in width & addition of adventitious roots
secondary vascular bundles
amount of storage parenchyma increased dramatically
included phloem between two hands of xylem
