Vascular tissue is a complex conducting
tissue, formed of more than one cell type.
Found in vascular plants.
The primary components of vascular tissue
are the xylem and phloem.
These two tissues transport fluid and
There are also two meristems associated with
vascular tissue: the vascular cambium and the
All the vascular tissues within a particular
plant together constitute the vascular tissue
system of that plant.
Xylem cells are elongated cells.
Has lignified secondary thickening of the cell walls.
Xylem cells are specialized for conduction of water.
The possession of xylem defines the vascular plants or
Xylem tracheids are pointed, elongated xylem cells, the
simplest of which have continuous primary cell walls and
lignified secondary wall thickenings in the form of rings,
hoops or reticulate networks.
More complex tracheids with valve-like
perforations called bordered pits characterise
The ferns and other pteridophytes and the
gymnosperms only have xylem tracheids.
The angiosperms also have xylem vessels.
Vessel members are hollow xylem cells
Without end walls that are assembled into
long continuous tubes.
The bryophytes lack true xylem cells, but
their sporophytes have a water conducting
tissue known as the hydrome that is
composed of elongated cells of simpler
The bryophytes lack true xylem cells.
However, their sporophytes have a water
conducting tissue known as the hydrome that
is composed of elongated cells of simpler
It is a complex permanent tissue, which is
specialized for the conduction of water and
mineral substances in the plant body.
Xylem is a heterogenous tissue made up of
four different types of cellular elements.
Xylem tracheids (1)
Xylem tracheids (2)
Picture of tracheids(1), (2)
Xylem tracheae (1), (2), (3 ), (4)
Xylem vessel (1), (2)
Xylem fibers and
Of these, the tracheids and the tracheae are
described as essential elements since they are
directly involved in the translocation of water and
Xylem fibers and xylem parenchyma are
described as associated elements, since they are
only supporting structures.
The tracheids, the trachea and the xylem fibers
are non-living components, while xylem
parenchyma represents the only living
component of the tissue.
Xylem is commonly described as a dead, complex
They are found abundantly in pteridophytes,
gymnosperms and primitive angiosperms.
In these groups of plants, the tracheids represent
the most active water conducting elements.
In advanced angiosperms, the tracheids are found
restricted to leaf margin and leaf tip.
The tracheids are elongated, dead cells, with tapering
They are characterised by the presence of a thick cell
wall consisting of primary wall and a secondary wall.
The primary wall is composed of cellulose where as
the secondary wall is made up of lignin.
There is a spacious lumen that extends throughout
the length of the tracheid.
In some cases, due to the deposition of lignin, the
primary wall develops numerous concave depressions
When pits are present, the tracheid is described as
pitted and when pits are absent, it is described as
They are commonly known as xylem vessels.
They are the most active water conducting
elements in all higher angiosperms.
The tracheae are found arranged parallel to each
other, extending from one end of the plant body to
They are commonly known as xylem
They are the most active water
conducting elements in all higher
The tracheae are found arranged parallel
to each other, extending from one end of
the plant body to another.
The tracheae are long cylindrical dead cells. They
are characterised by a thick cell wall consisting of
a primary wall and a secondary wall.
The primary wall is made up of cellulose where
as the secondary wall is made up of lignin.
There is a spacious lumen that extends
throughout the length of the trachea.
The deposition of lignin in the secondary wall is
not always uniform.
As a result, the xylem vessels exhibit different
types of secondary thickenings.
On this basis, xylem vessels can be
distinguished into five types.
Annular vessels in which the secondary
thickening is in the form of rings placed more
or less at equal distance from each other.
Spiral vessels in which the secondary
thickenings are present in the form of a helix
Scalariform vessels in which the secondary
thickenings appear in the form of cross bands
resembling the steps of a ladder.
Reticulate vessels in which the secondary
thickenings are irregular and appear in the
form of a network.
Pitted vessels in which the secondary
thickenings result in the formation of
depressions on the primary wall called pits.
They are represented by the dead sclerenchyma fibers
that are found in between the vessels and the tracheids.
They are meant for providing mechanical support to the
This is the only living component in the xylem tissue.
It is represented by groups of parenchyma cells that are
found in between the vessels and the fibers.
They are meant for storage of reserve food.
Types of Xylem
Xylem can be distinguished into two types namely
Primary xylem and
Primary xylem is the xylem that is formed during
normal growth. It is a derivative of primary
It occurs in both monocots and dicots.
In the primary xylem, two types of xylem vessels
can be distinguished, namely protoxylem and
Secondary xylem is the xylem that is formed during
It is derivative of secondary meristem.
It is a characteristic feature of only dicots.
Secondary xylem is commonly known as wood.
It is of commercial importance since it is
extensively used in the manufacturing of doors,
windows and furniture
Phloem is a specialised tissue for food
conduction in higher plants.
Phloem consists of two cell types, the sieve
tubes and the intimately-associated
The sieve tube elements lack nuclei and
ribosomes, and their metabolism and
functions are regulated by the adjacent
nucleate companion cells.
Sieve tubes are joined end to end with
perforate end-plates between known as sieve
plates, which allow transport of
photosynthetic between the sieve elements.
The companion cells, connected to the sieve
tubes via plasmodesmata, are responsible for
loading the phloem with sugars.
The bryophytes lack phloem, but moss
sporophytes have a simpler tissue with
analogous function known as the leptome.
Phloem is a complex permanent tissue, which
is specialized for the conduction of food and
other organic substances.
Phloem is also a heterogenous tissue, made
up of four different types of cellular
Phloem parenchyma and
Of these, the sieve tubes and the companion
cells are directly involved in the translocation
of the organic substances.
Hence, they are commonly described as
Phloem parenchyma and phloem fibres are
described as associated elements since they
play only a supporting role in the process.
The sieve tubes, the companion cells and the
phloem parenchyma represent the living
components of the tissue while phloem fibres
represent the only nonliving component of
Phloem is commonly described as a living,
complex permanent tissue.
They represent the most active food conducting
elements in the phloem tissue.
The sieve tubes are found arranged parallel to one
another from one end of the plant body to another.
Each sieve tube is formed by a series of hollow,
cylindrical cells called sieve tube cells arranged one
above the other.
The sieve cells are separated from each other by
horizontal perforated plates called sieve plates.
The sieve cells communicate with each other
through the sieve plates.
Each sieve cell has a thin cell wall, which is
composed of only cellulose. The cell has a central
mass of dense cytoplasm.
The granular cytoplasm forms a number of
projections called cytoplasmic strands extending
towards the sieve plate.
The nucleus is absent.
They are more or less spindle shaped cells
associated with the sieve tube cells.
Each companion cell is found attached to any one
lateral surface of a sieve cell.
The companion cell and the neighbouring sieve cell
together represent a pair of sister cells.
The companion cell has a granular cytoplasm,
prominent nucleus and one or two small vacuoles.
The nucleus of the companion cell is said to be
capable of exerting its influence on the adjacent
Phloem parenchyma is represented by a group of
living parenchyma cells that are found in-between
the sieve tubes.
They are meant only for storage of organic food.
Phloem fibres are represented by the dead
sclerenchyma fibres that are found in between the
They are meant only for providing mechanical
Types of Phloem
Phloem can be distinguished into two
Primary phloem is the phloem that is formed during normal
growth in the plant body.
It is a derivative of primary meristem.
It is found in both monocots and dicots.
The primary phloem is further composed of protophloem and
The sieve tubes and the companion cells, which appear earlier
during normal growth, represent protophloem, while
metaphloem is represented by the sieve tubes and companion
cells that appear later.
However, there is no significant morphological difference
between protophloem and metaphloem.
Secondary phloem is the phloem that is formed
during secondary growth.
It is a derivative of secondary meristem.
Secondary phloem is characteristic feature of only
It is also known as bast.
It is also of commercial importance since it yields
The following table summarise the characteristics
of and difference between xylem and phloem
a) xylem cuticle
c) guard cells
d) palisade parenchyma
d) stems and leaves
e) roots and leaves
a) center ... Center
b) surface ... Surface
c) surface ... Center
d) center ... surface
e) top ... bottom
a) providing a site for photosynthesis
b) providing cells for secondary growth
insulation and waterproofing
c) providing cells for primary growth
d) regulating the opening and closing of
a) by the differentiation of secondary xylem
b) by the differentiation of secondary phloem
c) by the differentiation of cork by the division
of its cells
d) by the differentiation of apical meristem