the ground meristem produces parenchyma cells of the
DESCRIPTION
ANATOMY OF STEM. Three primary meristems namely, protoderm, procambium and ground meristem originate from the apical meristem found at the tip of stems. The ground meristem produces parenchyma cells of the cortex and pith region. These parenchyma cells store food, - PowerPoint PPT PresentationTRANSCRIPT
The ground meristem produces parenchyma cells of the cortex and pith region. These parenchyma cells store food, and also manufacture food in the presence of chloroplasts.
Three primary meristems namely, protoderm, procambium and ground meristem originate from the apical meristem found at the tip of stems.
The procambium produces the vascular bundles, while the protoderm forms the epidermis
ANATOMY OF STEM
During the formation of primary tissues, the leaf primordia produce mature leaves and the bud primordia produce buds.
A layer of meristematic cells found between the primary xylem and primary phloem forms the vascular cambium.
Branches of the stem xylem and phloem tissue enter the leaves and buds forming leaf traces, while the leaf gaps are filled with parenchyma cells.
Bud gap
Bud
Leaf gap
Leaf scar
Leaf gap
Leaf
Vascular
A portion of a young stem showing leaf gaps and bud gaps in the cylinder of vascular tissue
The vascular cambium produces tracheid, vessel elements, and parenchyma cells (secondary xylem) internally, and sieve elements, companion cells, fibre and parenchyma (secondary phloem) externally.
In woody species, a second cambium (cork cambium or phellogen) is formed either from the cortex, epidermis or phloem tissue.
The cork cambium produces cork cells or phellem externally and parenchyma cells (phelloderm) internally.
The cork cells have suberin deposition on their cell wall making the cells water proof.
The cork tissue reduces water loss from the stem and protects the stem from mechanical damage.
During the formation of cork tissue, parenchyma cells that are below the stomata form the lenticels (for gaseous exchange)
Lentisel
Herbaceous Dicot Stem
Most herbaceous dicot stems contain primary tissues,
even though the cambium may produce some secondary
tissues
Possess individual vascular bundles, arranged in a
cylinder, that separates the cortex from the pith.
In some species, the xylem and phloem tissues form a
continuous cylinder, and a vascular cambium forms later
in between the two primary tissues. The vascular
cambium produces secondary xylem and phloem.
A cross section of a typical herbaceous dicot stem
Helianthus stem cross section
Woody Dicot Stem
The formation of primary tissues in both herbaceous and
woody stems are similar.
During secondary growth, the parenchyma cells form
the xylem rays and phloem rays.
.
However, the difference occurred when secondary xylem
or wood is formed in woody species, and a greater
portion of the stem consists of wood.
Secondary phloem
Primary phloem
Secondary xylem
Pith
Primary xylem
Narrow xylem rays
Broad xylem ray
Annual ring of xylem
Vascular cambium
Narrow phloem ray
Broad phloem ray
Primary phloemCortex
Phelloderm
CorkCork cambium
A cross section of a woody Tilia stem
Transverse surface
Bark
Vessel
Ray
Tracheid
Vessel
Ray
Fiber
Sieve tube memberCambium
Xylem
Phloem
Radial surface
A three-dimensional, magnified view of a block of a woody dicot
A cross section of a woody dicot stem
In older trees, a large portion of the protoplast of
parenchyma cells that surround vessels and tracheids
grows through the pits of the conductive cells enlarging
into a balloon that almost fills the tracheary elements.
Such outgrowth is termed tylose. It restricts the flow of
water and nutrients through the tracheary elements. As a
result, gums, tannins and stains begin to accumulate and
darkens the wood tissue.
Small resin canals in Yellow PineLarge resin canals in Sugar Pine
Resin canals in a portion of a pine (Pinus)
Tylose-forminglayer
Tylose
Xylem: Variations in Wood Structure
Primary wall
Secondary wall
Pit withplasmodesmata
VesselRay cell
Pine trees have xylem tissue consisting of only tracheids,
without fibre or vessel elements, termed softwood.
The xylem tissue which is close to the cambium, lighter in
colour, and still functional as a conductive tissue is termed
sapwood.
The old, dark coloured wood found in the centre of a
woody dicot stem is termed heartwood. Heartwood does
not function anymore as a conductive tissue, instead it
provides strength and support to the tree.
The bark refers to all tissues outside the cambium, and
including the phloem.
The wood of a dicot tree is termed hardwood.
The inner bark consists of the primary and secondary
phloem. The outer bark is the periderm.
Hardwood (18X)
Softwood (18X)
Hardwood (18X)
Bark (Kulit kayu )
Monocot Stem
Most monocot species are herbaceous, their stems
are without a vascular cambium or a cork cambium.
Xylem and phloem tissues are found inside the
vascular bundles that are scattered inside the stem.
In most grass species, intercalary meristems are
present for stem elongation.
A typical monocot stem with scattered vascular bundles
Bundle sheath cell
Sieve tube member
Companion cell
Vessel element
Air space
Ground tissue(parenchyma)
Phloem
Xylem
A portion of a cross section of a Monocot (corn-Zea mays) stem.
A single vascular bundle of corn (Zea mays)
The stem of Dracaena and Sansevieria possess
secondary meristems that are different from the vascular
cambium found in dicot plants and conifers. Their
secondary meristems produce only parenchyma cells on
the outside and secondary vascular bundles internally.
Palm trees differ from other monocots due to their large
size. Even though without a cambium, their parenchyma
cells continue to divide and enlarge to increase the tree
size.
Bicollateral vascular bundle
Vascular bundles
Concentric - amphicribral Concentric - amphivasal