(order-4)remaining part of complex tissue and secretory tissue

b. Phloem Tissue

Phloem is a complex permanent tissue which transports food in plant. It consists of
four types of cells: sieve elements, companion cells (absent in pteridophytes and
gymnosperms), phloem parenchyma and phloem fibres or bast fibres.

T. S. of phloem

i. Sieve elements:

 They are of two types i. e. sieve tubes and sieve cells.
Sieve tubes are elongated tubular conducting structure present in angiosperms.
They are joined in end to end manner .
They have transverse or oblique end wall.
They have sieve pores which are lined by callose.
 Due to presence of pores, end wall are called sieve plates.
Sieve cells are narrower and elongated as compared to individual sieve tube.
 The end wall are pointed.
Sieves cells are present in pteridophytes and gymnosperms only.
Both sieve tube and sieve cells have peripheral layer of cytoplasm without nucleus.
The central part of sieve tube is occupied by network of channel containing fibrils of
p- protein.
[Note: P-protein and callose protein act as damage control team. P-protein is also called

as phloem protein. If there is disruption of sieve element, P-protein aggregates at the sieve plate
and prevents the leakage of phloem exudates].

Difference between sieve tube and sieve cells

Sieve tube Sieve cell

 Sieve tube is comparatively shorter and  Sieve cell is comparatively longer and

broader as compared to sieve cell. narrower as compared to sieve tube.

 The end wall is broad and blunt.  The end wall is pointed.

 Sieve tubes are placed in end to end  Sieve cell is independently functioning
manner. unit.

 Sieve tubes are usually associated with  Sieve cells are associated with
companion cells. albuminous cells.

 Sieve pores comparatively larger and  Sieve pores are smaller and more
fewer. numerous.

 Sieve pores are restricted to transverse  Sieve pores are found on both end walls
end walls. as well as lateral walls.

 They are found in phloem of  They are found in phloem of
angiosperms. gymnosperms and pteridophytes.

 P-protein(Phloem protein) is mostly  P-protein is absent.
present and is acts as damage controller.

ii. Companion cells or albuminous cells:
Companion cells are narrow, elongated and thin walled living cells

associated with sieves.

They are present in phloem of angiosperms.

Each cell has dense cytoplasm and nucleus. In pteridophytes and

gymnosperms albuminous cells are present instead of companion cells. [

[Note: sieve tubes and companion cells are sister cells while the sieve

cells and albuminous cells are non sister cells . Albuminous cells are also

called Strasburger’s cells.]
iii. Phloem or bast parenchyma:
They are thin walled living parenchyma without intercellular space which are
associated with phloem. They help in storage and slow lateral conduction of
food.

iv. Phloem fibres( bast fibres):
They are thick walled dead fibrous sclerenchyma. They help in mechanical
support.

Vascular bundles and its types

Strands of conducting tissues consisting of xylem, phloem and sometimes
with cambium are called vascular bundles. Those plants with vascular
tissue are called vascular plants or tracheophytes. E.g. Pteridophytes,
gymnosperms and angiosperms.

Vascular Bundle and Types:

Vascular bundle consists xylem and phloem with or without cambium. On
the basis of arrangement of xylem and phloem, vascular bundles are
classified into following types:

Vascular bundles

Radial vascular Conjoint vascular
bundles bundles

Collateral vascuar Bicollateral Concentric
bundles vascular bundles vascular bundle

Open type Closed type Amphicribal (Amphivasal
( hardocentric) (leptocentric)

1. Radial vascular bundle:
In radial type of vascular bundle xylem and phloem tissues lie in
separate bundles or in different radii i.e. xylem alternate with
phloem and vice versa. These type of vascular bundles are found in
roots.

2. Conjoint vascular bundles
In this type of vascular bundle, both xylem and Phloem are Present in the
same radius. Conjoint vascular bundles are of following types:

A. Collateral vascular bundles
In this type phloem lies toward periphery and xylem lies toward centre.
On the basis of cambium , conjoint vascular bundle is of following three
types:

i. Open type:
In this type of vascular bundle cambium is present in between
xylem and phloem. Open type of vascular bundle is found in
stem of dicot plant and gymnosperms.

ii. Closed type:
In this type of vascular bundle, cambium is absent . E.g. leaves and
monocot stem.

B. Bicollateral vascular bundle:
In this type of conjoint vascular bundle , xylem lies at the middle position and
phloem lies on either side of it i.e. Xylem act as sandwiches between the
phloems. It is also open type and found in the stem of family Cucurbitaceae,
Convolvulaceae and Solanaceae.

C. Concentric vascular bundle:
In this type xylem and phloem lie in two concentric rings that is xylem is
surrounded by phloem and vice versa. It is of two types:

i. Amphicribal ( hardocentric) vascular bundle:

Xylem forms a central core while phloem surrounds it in all sides. It is also
called xylocentric vascular bundle. It is found in some aquatic angiosperm ,
rhizome of ferns and the staminal bundles od many dicot plants.

ii. Amphivasal (leptocentric) vascular bundle:
Phloem lies in the central region and it is surrounded by xylem. It is found in
the stem of Dracaena, Yucca, Aloes, etc,.

C. Secretory or excretory tissues

A group of permanent cells which secretes certain chemical such as resin,
latex , gum, mucilage etc, is called secretory tissue. It is of two types:
a. Laticifers or laticiferous tissues:
It is thin walled multinucleated highly branched tubes or ducts which
secrete milky juice. It is distributed in parenchyma tissue. Laticifers
consists of two types of cells i. e. latex cells and latex vessels.

a. Latex cells :
They are branched , long individual cells which do not fuse and networks
are not formed. e. g. Calotropis, Vinca, Nerium, Euphorbia, Cannabis,
Urtica, Ficus, and Mulberry.

b. Latex vessels:
They are long branched ducts which are fused to each other and form

a network e.g. Papaver, Argemone, banana, sunflower, Papaya, cactus,
rubber(Hevea) plant etc.

Important of latex producing plants
Latex may be watery in banana, milky in Euphorbia, papaya, banyan, colored in
Opium(poppy).
Latex of banana consists of tanin which may have antioxidant property.
Latex from stem of Hevea brasiliensis is the source of rubber.
Latex of Achras sapota is source of chewing gum.
Larex of papaya (Carica papaya) is the source of enzyme papain that helps in
digestion of proteins.
Laex of poppy (Papaver somniferum ) is the source of opium.

Note : Types of rubber source

Para rubber Hevea brasiliensis

Indian rubber Ficus elastica

Panama rubber Castilla elastica

Cera rubber Manihot glaziovi

Glandular tissues or glands:
Glands secrete oils, gums, mucilage, tannins, water drops, essential oils etc.
These tissues are mainly categorized into two types:
 External glandular tissues
 Internal glandular tissues
External glandular tissues include hydathodes, nector glands, glandular hairs,
stinging hairs, digestive glands etc,.
Internal glandular tissues includes oil glands, mucilage glands, resin ducts,
etc.[Note: stinging hairs are found in Urtica , digestive glands are found in
Drosera, Nepenthes, resin canal is found in Pinus. Mucilage secreting glands are
found in betel leaf. Hydathodes are found in Colocassia, Tomatoes, Cucurbits,
and in many grasses ].

Difference between meristematic tissues and permanent tissues

Dfinition
Cell differentiation
Cell division
Complexity
Living/ non living
Nucleus and cytoplasm
Intercellular space
Vacuoles
Metabolism of cells
Cell wall composition
Secondary wall thickening
 cell inclusions
Reserved food,
 function,
 types

some NEB questions
Very short question
 Name two elements of phloem.
short questions
Explain the type of meristems on the basis of position.
What are the roles of meristems? Explain.
Give difference between meristematic tissue and permanent tissue.
Describe the structure and function of different types of parenchyma.
Describe different types of vascular bundles present in plants.
 Describe the structure and function of aerenchyma.
Describe the structure and function of xylem tissue.
Differentiate between spongy and pallisade parenchyma.
Differentiate between parenchyma and sclerenchyma.
Long questions
What is permanent tissue in plants? Describe different types of simple permanent tissues
with well labelled diagrams.