Plant Org anization:
Tissue system s
Apical organization
Organization in plants is dependent
upon programmed, controlled cell
division, followed by growth, further
cell division and ultimately,
differentiation.
Programmed and controlled cell
division occurs within the domain of
the vegetative apex.
the apex
All the tissues w ithin the ap ex
d ifferentiate rap id ly. By ab out 1 5 0
µm, cells within the apical region are
starting to differentiate. In the pine apex
(above), you can see developing leaflets.
The Coleus ap ex to the rig ht,
show s rap id ly d evelop ing leaf le ts
b eneath the ap ical d om e.
Cell division
Cell division is
responsible for the
formation of all cells
and tissues in the
primary plant body as
well as in the
secondary plant body.
Cell source
apical and sub apical primary division
undifferentiated
generative
source
protoderm
primary
lineage
epidermis
Secondary cell
lineage
apical meristem
provascular
tissue
primary
xylem
primary
phloem
fascicular
cambium
ground
meristem
pith
cortex
the secondary lineage
COMPLETE RING OF CAMBIUM
fascicular
cambium
ASSOCIATED W ITH THE
VASCULAR BUNDLE
ONLY
vascular
cambium
secondary
xylem
secondary
phloem
cork
cambium
the secondary protective lineage
subepidermal
layers
the
cork cambium
(bark layer)
phellogen
phellem
click t he p erid erm a p ro tective b arrier
phelloderm
Development of the periderm
subepidermal
layers
The f ir st p erid erm
is fo rm ed just
b eneath the
ep id erm is
phellogen
phellem
a w aterp roof,
f ir ep roof
insulator
phelloderm
p hellem
p hello g en
p hello d erm
primary organization
ground
meristem
PITH
CORTEX
fascicular
cambium
interfascicular
cambium
vascular
cambium
secondary
xylem
secondary
phloem
cork
cambium
Click for Filling spaces notes
phellem/cork
cambium
primary mechanical tissues
ground
meristem
ground
meristem
PITH
CORTEX
CORTEX
collenchyma
interfascicular
cambium
PITH
phellem/cor
k cambium
sclerenchyma
collenchyma
(rare)
sclerenchyma
development of the vascular cambium
fascicular
cambium
fascicular
cambium
fusiform
initials
vascular
cambium
secondary
xylem
secondary
phloem
axial
xylem
ray
initials
axial
phloem
cork
cambium
xylem
rays
to cambial derivatives notes pages
phloem
rays
cambial division
d
ra
le
xy
ia l
axial
initial
lo
ph
em
m
Cell division within the
ray and fusiform
initials results in the
formation of derivative
cells that are placed
either on the outside
of the mother cell, in
which case they add
to the secondary
phloem (green cells),
or on the inside
endarch to) the mother
cell, thus adding to the
secondary xylem
(blue cells).
Cell source

The apical meristem is the principle source of new cells
in the primary as well as within the secondary plant
body. All cell division linked to vegetative growth,
involves mitosis, and, as a result, the cells that are
produced are exact copies of each other. Lineage
depends on the position of the initial within the
meristem.
the periderm a protective barrier




During secondary growth, the diameter of
stems and roots increases rapidly, which results
in tension and splitting of the existing dermal
tissues, which subsequently, will stretch and
become disrupted.
The generative layer of the first periderm
(phellogen) is initiated within parenchymatous
elements in the outer cortex of stems and
roots. It offers protection from invasion by
insects, pathogens and fungi.
As the stem or root continues to increase in
diameter, so successive peridems are
formed. These are formed within the secondary
phloem.
The periderm is a natural waterproof, fireproof
insulator.
Filling spaces

Within all plants the primary packaging tissues are
composed of cells that either fill in spaces, or
support other areas of the stem, root or leaf. Thus,
the parenchymatic elements that are produced (and
have lineage back to the apical meristems) are
produced from what is termed the ground
meristem. In simple terms, the ground meristem is
that region of a shoot or root apical meristem that is
NOT involved in the production of vascular tissue.
cambial derivatives


The vascular cambium is the source of all need
(secondary) differentiation in plants. It contains two
systems, the secondary xylem, and the secondary phloem
tissue. Each of these tissues is complex, and is developed
and has evolved for specific functions – the xylem for th
transport of water and water-soluble molecules, and the
phloem for the transport of assimilated materials, which
consist of sugars and related carbohydrates translocated in
water.
Physiologically, the transport xylem is dead at maturity,
has secondarily-lignified cell walls, and functions under
extreme negative pressure potentials. Transport phloem
on the other hand, contains a majority of living cells, with
specialized sieve elements, which are geared for rapid,
long-distance translocation of the assimilated carbohydrate
pool. There transport elements, have thickened walls, are
living at maturity and function under a high positive
pressure potential.
click here for the next page
transport functionality

The xylem and phloem conduits form axial tubes. These
tubes facilitate rapid, long-distance movement of water
and dissolved materials. It follows therefore that the
fascicular cambial derivatives that form these transport
cells are longer than they are wide, and that the cells will,
depending on position form either xylem or phloem.
click here for cambial derivatives
click the need for lateral communication
b ack
the need for lateral communication


As the secondary plant body enlarges, so the
carbohydrate conducting, and water transporting
systems become laterally spatially and physiologically
further removed from each other. The core of a stem
or root, for example, may well contain a number of
living cells, that not only require water, but a supply
of assimilate and other carbohydrates, in order to
maintain their functional state. If this does not happen
or if the supply is cut off for some reason, then the
core will die.
Lateral communication, and the production of these
cells, is due o the activity of specialised cambial cells,
called the ray cells. These cells are sort, often cubic in
shape and the produce rows (files) of parenchymatous
living cells, that interconnect the phloem with the
inner xylem core, thereby facilitating exchange of
carbohydrate inwards, and water outwards in the
living plant.
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to the presentation
leaf development
tw o typ es o f initials
these fo rm the
ep id erm is and
asso ciated t ructures
m arg inal
sub m arg inal
these fo rm m eso p hyll
as w ell as the
p rocam b ial and
cam b ial tissue