Ch.8 Roots
Concepts
External Structure of Roots
organization of root systems
structure of individual roots
Internal Structure of Roots
root cap
zone of elongation
root apical meristem
zone of maturation/root hair zone
mature portions of the root
Origin and Development of Lateral Roots
Other Types of Roots and Root Modifications
storage roots
prop roots
aerial roots of orchids
contractile roots
mycorrhizae
root nodules and nitrogen fixation
haustorial roots of parasitic flowering plants
roots of strangler figs
roots
three
functions
1
anchoring
2
plant
firmly
to
substrate
3
absorbing
water
and
minerals
producing
hormones
provides
stability
sunlight
comes
from
sky
distributed
on
all
sides
cylindrically
shaped
higher
surface
to
volume
ratio
cytokinin
gibberellin
taproots #
fleshy
beet
carrot
radish
main
site
carb
storage
during
winter
highly
branched
seed plants
have
single
prominent
large
taproot
numerous
lateral roots
small
branch #
develops
from
embryonic
root
radicle
grows
extensively
becomes
largest
root
fibrous root system
many
similarly
sized
roots
most
monocots
some
eudicots
arises
radicle
dies
during
after
germination
adventitious roots
not radicles
don't
arise
on
prexisiting
roots
increase
absorptive
and
transport
capacities
of
root system
perinneal
undergo
secondary growth
results
in
increased
quantity
healthy
functional
wood (xylem)
trunks
roots
after
stem
formed
number
is
set
vascular bundles
tracheary elements
sieve tubes
can
increase
size
by
stolons
rhizomes
simple
no
leaves
leaf scars
leaf axils
axillary buds
root tip
region
where
growth
in length
occurs
root cap
protects
root
apical meristem
thick
layer
of
cells
constantly
worn
away
renewed
by
cell
multiplication
dictyosomes
secrete
mucigel
complex
polysaccharides
lubricates
passage
of
root
through
soil
causes
soil
to
release
nutrient
ions
permits
them
from
diffusing
rapidly
towards
root
rich
in
carbohydrates
amino acids
zone of elongation
just
behind
root cap
root
apical meristem
few
mm
long
within
cells
undergo
division
expansion
root hair zone
behind
zone of elongation
many
epidermal cells
extend
out as
narrow
trichomes
root hair
formed
only
in
part
of
root
not
elongating
increase
surface
area
can
enter
any
crevice
extract
water
minerals
specific
structure
provide
effective
protection
remain
in
place
cells
small
pushed
forward
develop
dense
when
first
formed
at
base
of
root cap
closest
to
root meristem
meristematic
originate
merisem
extend
into
regions
of
mture
root
tissues
quiescent center
mitotically
inacitve
central region
cells
more
resistant
to
harmful
agents
radiation
toxic chemicals
behind
root apical meristem
region
where
cells
expand
greatly
begin
to
differentiate
into
visible
pattern
outermost
protoderm
differentiate
into
epidermis
center
provascular tissue
develop
into
primary xylem
primary phloem
tissues
permeable
little
absorption
several
important
proccesses
occur
root hairs
grow
outward
greatly
increasing
absorption
water
minerals
merges
gradually
with
zone of maturation
no distinct
boundary
exists
don't
have
access
to
innermost
layer
differentiates
into
cylinder
endodermis
cells
have
tangential
walls
thin
radicle
walls
lignin
suberin
vascular tissues
altered walls
casparian strips
control
minerals
that
enter
xylem
water
stream
undergo
secondary growth
become
woody
extremely
strong
support #
monocot stem
becomes
wider
with
more
vascular bundles
make
contact
with
soil
contract
place
tension
on
stem
stabilizing
transport
additional
water
nutrients
to stem
symbiotic relationship
with
fungi
two types
endomycorrhizal relationship
woody
forest
plants
fungal hyphae
penetrate
outermost
root cortex
endomycorrhizal assosiation
herbaceous
plants
hyphae
cannot
pass
casparian strip
penetrate
root cotex
far as
endodermis
between
vascular tissue
endodermis
are
parenchyma cells
form
irregular
region
called
pericycle
passage cells
only
have
casparian strips
thought
to
represent
passageways
for
absorption
of
minerals
actually
slow
to
develop
root pressure
powerful
absorption
of
water
and
water
pressure
cause
it
to
build up
lateral roots
initiated
by
cell
divisions
in
pericycle
once
emerged
formed
root cap
first protoxylem
protophloem elements
begin
differentiation
deep
within
the
root
mature regions
never
develop
into
flowers
provide
long-term
storage
for
carbs
subterranean
roots
less
available
as
food
stems
swollen
highly nutritious
easily visible
stable
environment
survival
storage
parenchyma cells
buttress roots
tall
plate-like
upper
side
grows
more1
rapidly
than
other
parts
brace
trunk
from
being
blown
over
by
wind
epiphytic
living
attached
to the
branches
of
trees
spread
along
surface
of
bark
dangle
freely
epidermis
velamen
composed
several
layers
large
dead
cells
white
waterproof barrier
after
extending
through
soil
becomings
anchored
uppermost
portions
contract
slowly
stem
pulled
downwards
base
soil
level
keep
at
proper
depth
plants
have
no
enzyme
systems
that
can
use
nitrogen
some
prokaryotes
can use
N2
by
incorporation
into
amino acids
nucleotides
nitrogen fixation
chemical
conversion
of
atmospheric
nitrogen
into
usable
compounds
infection thread
tube
bacterium
sits
in
extends
into
roots
inner
cortex
root nodule
roots
swollen
occupied
by
nitrogen-fixing
bacteria
roots
of
parasitic
plants
highly
modified
known
as
haustoria
adheres
to host
by
secreting
adhesive
growing
around
branch
root
when
germinating
roots
cling
bark
of
host
tree branch
grow
rapidly
downward
hugging
trunk
absorb
nutrients
from
rainwater
pentrate
soil
rapidly
and
branch
profusely
roots
Cross Connection: A tree in the Everglades National Park is encased in the roots of a strangler fig. The large "branch" of the fig is actually the trunk of the fig, which is where the seed is germinated. All below it are the roots. It is easy to mistakenly assume the fig is a vine and the parts encasing the host tree are steam of the fig, but a close examination shows they are roots not branches.
Cross Connection: Banyan trees (eudicots) produce adventitious roots, which, as in monocots, provide increased support and absorptive capacity. Because the giant branches are supported along their entire length they can become much larger and more extensive than branches that are supported only at the point of attachment to the trunk.
Cross Connection: Some taproots such as a carrot become extremely swollen and are much larger than the numerous lateral roots, whereas the sunflower species the taproot is about the same size as the lateral roots