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Definition of Plant Tissue
A plant tissue can be defined as a cell or a group of cells dividing, to give rise to large number of cell,
which is collectively referred as tissues. They are structurally and functionally similar to these cells.
Types of Plant Tissue
There are two types of tissue systems.
1. Meristematic Tissues
(Meristos – divisible)
Initially all embryonic cells of an embryo have the capacity to divide and multiply but as the embryo
develops into a plant body, this capacity for division is restricted to certain parts of the plant body called
meristems which are active throughout the life of the plant body (unlike that of an animal body). When
meristematic cells divide, a group of the daughter cells remain meristematic; the other daughter cells
called derivatives differentiate into various tissue elements.
Meristematic tissues are group of cells, which have the ability to divide. This tissue consists of small,
cubodial densely packed cells, which keeps on dividing to form new cells. These tissues are capable of
stretching, enlarging and differentiate into other types of tissues as they mature. Meristematic tissues
give rise to permanent tissues.
Meristematic cells are isodiametric, compactly arranged with dense cytoplasm, large nucleus, and small
vacuoles or without vacuoles. Cell walls are thin.
General characteristics of Meristematic tissues
They have very small cells with thin cell walls.
Their cells have large nuclei.
Their cells have very small vacuoles and they lack intercellular spaces.
They remain young forever and divide actively throughout the life of the plant.
In plants, these tissues are found in the -Tips of roots, stems, nodes of stems, buds, in between the
xylem and phloem, under the epidermis of dicotyledonous plants and also producing branch roots.
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Kinds of Meristematic tissues
 Apical meristems : They are found at the tip of stems and roots. During the cell division, this
meristem helps in cellular enlargement and also it influence the shapes of the mature plants.
 Lateral meristems : They are found along the sides of roots and stems .They play a vital role in
increasing the width or diameter of stems and roots.
 Intercallary meristems : They are found at the bases of young leaves and internodes. They are
mainly responsible for further lengthening of stems and leaves.
Permanent Tissues or Mature Tissues
The tissues, which are derived from the Meristematic tissues, are called as permanent tissues. They are
the tissues, which have lost their ability to divide as they have attained their mature form.
Cells derived from meristems gradually change in their structure, metabolism and chemistry and acquire
specialized characters by their various modes of differentiation. Not all the cells totally differ from the
meristems. Some cells retain the power of division and others cannot divide. In a strict sense only cells
which have lost the power for division must be regarded as permanent tissues, but in a broad sense,
cells derived from meristem that have acquired a special function like photosynthesis, secretion, storage
are treated as part of matured tissue. There are different types of mature tissues. Example:
Parenchyma, Collenchyma, Sclerenchyma, Xylem and Phloem.
Types of Permanent or Mature Tissue
Simple permanent tissue and Complex permanent tissue.
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Simple permanent tissue: They are the tissues, which are similar in function and are called as
simple because they are composed of similar types of cells, which have common origin and
function.
1. Parenchyma (Para-beside, enchyma-In poured)
Parenchyma is the fundamental tissue of the plant body. It is found in every part of the plant body like
pith and cortex of stem and root, mesophyll of leaves, flesh of fruits, floral parts and even in xylem and
Phloem. It is the least specialised among the permanent tissues Cells have thin primary walls and
polyhedral shapes.Least specialized plant cells
Thin and somewhat flexible cell walls
Living at maturity
Carry on most of the plant's metabolic functions
Generally have a large central vacuole
Most parenchyma cells have the ability to differentiate into other cell types under special conditions
During repair and replacement of organs after injury. Cells are compactly arranged or more commonly
spaciously arranged with intercellular spaces as in cortex and pith. Cells possess dense cytoplasm and
are active metabolites.
Generally cells of parenchyma are involved in storage of starch, sucrose, protein, water, phenol
derivatives, many mineral substances, etc. Other metabolisms like respiration, protein synthesis etc.,
are active. Parenchymatous cells may also perform specialized functions and are structurally modified.
The following are the different types of parenchyma.
 Aerenchyma: Intercellular spaces filled with air, are large in size and many in number. Cells
occupy a smaller area. Though the cells are smaller, they provide the required strength to the
aquatic plants. In these plants air spaces are common, helping in aeration and buoyancy. Air
spaces are also seen in roots of grasses, petioles of canna ( like the plant in front of 3F1), aroids
(also called arum..belongs to the Aracea family).etc.
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 Chlorenchyma: Cells of photosynthetic parenchyma contain numerous chloroplasts. These cells
are commonly seen in leaves, some times in young shoots. Cells of Chlorenchyma are of two
types –
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 1) Palisade cells that is elongated and compactly arranged.
 2) Spongy cells that are spaciously arranged and irregularly shaped.
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 Prosenchyma (Pros-to): Cells are elongated, have thick walls and serve as a supporting tissue.
Example: Endosperm cells of seeds.
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 Armed Parenchyma: Cells are stellate in shape with inward projections of cell wall as arms. The
cells have many spiny projections. It is defensive in function. Example: Pinus leaf Mesophyll.
Collenchyma (Kolla – Glue) (Plastics) (Pectin)
Thicker primary cells walls (usually with uneven thickness)
Living at maturity
Role in support of herbaceous plants
Example - the "strings" of celery
Collenchyma is a simple, living tissue. Cell walls are thickened due to deposition of pectin.
Collenchyma is the primary supporting tissue in stems, leaves and floral parts of dicots, where as in
stems and leaves of monocots collenchyma is usually absent, (instead, sclerenchyma is present in
monocots).
Collenchyma is usually hypodermal in position. Cells are more elongated and narrower than parenchyma. Like Parenchyma,
collenchyma may also contain chloroplasts or may regain the thickening. Intercellular spaces may or may not be present. Three
forms of collecnchyma are recognized based on the types of thickenings –
1. Thickening is on the tangential (a straight line or plane that touches a curve or curved surface at a
point) wall – lamellar collenchyma.
2. Deposition of pectin is in the corners where several cells meet-angular collenchyma.
3. Thickenings are around the intercellular spaces – lacunar collenchyma.
Being plastic, collenchyma differs from elastic fibers of sclerenchyma.
Sclerenchyma (Scleros-hard)
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Cells of sclerenchyma are thick walled and are usually lignified. The thickness is due to
formation of secondary wall. Thick secondary cell walls
Dead at functional maturity
Cannot increase in length - occur in parts of the plant which have quit growing in
length At least initial the secondary wall is free from primary wall. At maturity,
usually the cells are devoid of protoplast. The cell wall encloses a cavity lumen. On
the cell wall, pits are usually present (simple type). Commonly sclerenchyma cells are
classified into fibers and sclereids. The primary function is mechanical. (Pits-thin
areas without secondary wall material deposition).
Fibers: These are usually long, spindle shaped structures, with tapering or blunt ends. Longest fiber is
seen in Boehmeria nivea (55 cms), cotton, jute, kenaf, hemp, ramie and sisal.
Fibers are grouped into xylary fibers and extraxylary fibers. Xylary fibers, also called wood fibers are parts of
xylem and are longest among xylem elements. Extraxylary fibers are classified as – Bast or phloem fibers,
cortical fibers and perivascular fibers (peripheral to the vascular bundles). These are lignified or non lignified
 Bast fibers (Stem-skin fibers) (Jute, widely used, it is the cheapest fiber after cotton, Flax,
produces linen, Indian hemp, the Dogbane used by native Americans, Hemp, a soft, strong fiber,
edible seeds, Hoopvine, also used for barrel hoops and baskets, edible leaves, medicine, Kenaf).
 Leaf fibers (banana leaves)
 Seed fibers and fruit fibers (Coirfiber from the coconut husk, Cotton, Luffa, a gourd which
when mature produces a sponge-like mass of xylem, used to make loofa sponge)
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is the species usually cultivated for fibre, called China grass. industrial sewing thread,
packing materials, fishing nets, and filter cloths. It is also made into fabrics for
household furnishings (upholstery, canvas) and clothing, frequently in blends with
other textile fibers. (for instance when used in admixture with wool, shrinkage is
reported to be greatly reduced when compared with pure wool.) Shorter fibers and
waste are used in paper manufacture. Ramie ribbon is used in fine bookbinding as a
substitute for traditional linen tape.
r They are arranged in groups. Secondary thickening may account for 90% of the area of the cell; the
lumen is narrow. .
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On account of their elasticity, fibers enable the plant body to withstand various strains.
Commercial fibers like jute, flax, ramie are extraxylary fibers.
Sclereids: These are shorter than fibers. Sclereids occur singly or in groups. Sclereids
are commonly found in fruit wall, seed coat (Mango), epidermal scales, and
occasionally found in cortex, pith, mesophyll and petiole of submerged aquatics.
The shell of many seeds like those of nuts as well as the stones of drupes like cherries or
plums are made up from sclereids. These structures are used to protect other cells.
There are many types of sclereids –
1. Asterosclereids are star shaped E.g. Water Lilliy
2. Macrosclereids (Columnar) are similar to palisade cells E.g. Bean seed
3. Osteosclereids are bone like that are enlarged at their ends
4. Brachysclereids (round/ stone cells)are isodiametric like parenchyma E.g. in Pears
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Complex permanent tissue: They are the tissues, which are composed of two or more types
of cells but contribute to a common function are called complex tissues.
Kinds of Permanent Tissues
Permanent tissues may be classified into three main groups:
1. Simple
2. Complex
3. Special tissues
I. Simple Tissues:
Simple tissues are homogenous and composed of structurally and functionally similar cells.
These are of three types: Parenchyma, collenchyma and sclerenchyma.
(i)
Parenchyma: Parenchyma is the most common tissue which is morphologically and
physiologically simple and unspecialized. These cells are found in epidermis, cortex,
pericycle, pith etc. They are responsible for photosynthesis, storage of food, secretion etc.
(ii) Collenchyma:
Collenchyma are living tissues composed of more or less elongated cells and often have
some chloroplast to carry on photosynthesis. It is generally situated below the epidermis.
(iii) Sclerenchyma:
Cells are long, thick-walled and lignified with tapering ends. These are fibre like in
appearance and also known as sclerenchymatous fibre. These are dead cells and
perform mechanical function.
II. Complex Tissues:
The complex tissues are composed of different types of cells performing diverse functions. These
are of two types xylem and phloem.
(i) Xylem:
Structurally, xylem consists of both living and nonliving cells. Xylem consist of four elements:
tracheids, vessels, xylem fibers and xylem parenchyma (Fig. 3.3).
Tracheids:
Tracheids are elongated or tube-like dead cell with hard, thick and lignified walls. Their ends are
tapering, blunt or chisel-like. Their function is conduction of water and providing mechanical
support to the plant.
Vessels:
Vessel is long cylindrical, tube like structure with lignified walls and a wide central lumen. The
cells are dead as these do not have protoplast. The cells are arranged in longitudinal series in
which the partitioned walls (transverse walls) are perforated, so the entire structure looks-like a
water pipe. Their main function is transport of water and minerals. It also provides mechanical
strength.
Xylem fibers:
These cells are elongated, lignified and pointed at both the ends. A xylem fiber helps in
conduction of water and nutrients from root to the leaf and provides mechanical support to the
plant.
Xylem Parenchyma:
The cells are living and thin walled. The main function of xylem parenchyma is to store starch
and fatty substances.
(ii) Phloem:
Phloem consists of four types of elements – sieve tubes, companion cells, and phloem
parenchyma and phloem fibers (Fig. 3.3 (ii).
Sieve tube:
These are elongated, tube-like slender cells placed end to end. The transverse walls at the ends
are perforated and are known as sieve plates. The main function of sieve tubes is translocation of
food, from leaves to the storage organs of the plants.
Companion Cells:
These are elongated cells attached to the lateral wall of the sieve tubes. These are mostly found
in angiosperms.
Phloem Parenchyma:
The phloem parenchymas are living cells which have cytoplasm and nucleus. Their function is to
store food materials.
Phloem fibers or bast fibers:
Sclerenchymatous cells associated with primary and secondary phloem are commonly called
phloem fibers. These cells are elongated, lignified and provide mechanical strength to the plant
body.
III. Special tissues ):
Special tissues are structurally modified and specially organized for secretary function.
These are of two types:
Laticiferous tissues:
These are specialized tube like structures known as laticiferous ducts found in many
angiosperms. These ducts are filled with white or yellow latex. Laticiferous ducts are of two
types: Latex cells as found in madar and Latex vessels as found in rubber, papaya etc.
Glandular tissue:
It consists of different types of glands which are formed by single cell or group of cells. These
secrete resin, oil, mucilage, tannin, gums
etc.
Theodor Hartig: successively lecturer and professor of forestry at the University of Berlin (1831–1838)
and at the Carolinum, Braunschweig
Carl Wilhelm von Nägeli was a Swiss botanist,
PLANT TISSUE SYSTEM
The tissues of a plant are organized into three tissue systems: the dermal tissue system, the
ground tissue system, and the vascular tissue system.
Tissue System
and Its Functions
Dermal/epidermal Tissue System
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protection
prevention of water loss
Component Tissues
Location of Tissue Systems
Epidermis
Periderm (in older stems
and roots)
Ground/Fundamental Tissue
System
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photosynthesis
food storage
regeneration
support
protection
Parenchyma tissue
Collenchyma tissue
Sclerenchyma tissue
Vascular/Conducting Tissue
System
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transport of water and
minerals
transport of food
Xylem tissue
Phloem tissue
Plant Tissue Systems
Like other organisms, plant cells are grouped together into various tissues. These tissues can be
simple, consisting of a single cell type, or complex, consisting of more than one cell type. Above
and beyond tissues, plants also have a higher level of structure called plant tissue systems. There
are three types of tissue systems: dermal tissue, vascular tissue, and ground tissue systems.
Plant Tissue Systems: Dermal Tissue
The dermal tissue system consists of the epidermis and the periderm. The epidermis is generally
a single layer of closely packed cells. It both covers and protects the plant. It can be thought of as
the plant's "skin." Depending on the part of the plant that it covers, the dermal tissue system can
be specialized to a certain extent. For instance, the epidermis of a plant's leaves secretes a coating
called the cuticle that helps the plant retain water. The epidermis in plant leaves and stems also
contain pores called stomata. Guard cells in the epidermis regulate gas exchange between the
plant and the environment by controlling the size of the stomata openings.
The periderm, also called bark, replaces the epidermis in plants that undergo secondary growth.
The periderm is multilayered as opposed to the single layered epidermis. It consists of cork cells
(phellem), phelloderm, and phellogen (cork cambium). Cork cells are nonliving cells that cover
the outside of stems and roots to protect and provide insulation for the plant.
The periderm protects the plant from pathogens, injury, prevents excessive water loss, and
insulates the plant.
Plant Tissue Systems: Ground Tissue
The ground tissue system synthesizes organic compounds, supports the plant and provides
storage for the plant. It is mostly made up of plant cells called parenchyma cells but can also
include some collenchyma and sclerenchyma cells as well. Parenchyma cells synthesize and
store organic products in a plant. Most of the plant's metabolism takes place in these cells.
Parenchyma cells in leaves control photosynthesis. Collenchyma cells have a support function in
plants, particularly in young plants. These cells help to support plants while not restraining
growth due to their lack of secondary cell walls and the absence of a hardening agent in their
primary cell walls. Sclerenchyma cells also have a support function in plants, but unlike
collenchyma cells, they have a hardening agent and are much more rigid.
Plant Tissue Systems: Vascular Tissue
Xylem and phloem throughout the plant make up the vascular tissue system. They allow water
and other nutrients to be transported throughout the plant. Xylem is consists of two types of cells
known as tracheids and vessel elements. Tracheids and vessel elements form tube-shaped
structures that provide pathways for water and minerals to travel from the roots to the leaves.
While tracheids are found in all vascular plants, vessels are found only in angiosperms.
Phloem is composed mostly of cells called sieve-tube cells and companion cells. These cells
assist in the transport of sugar and nutrients produced during photosynthesis from the leaves to
other parts of the plant. While tracheid cells are nonliving, sieve-tube and companion cells of the
phloem are living. Companion cells possess a nucleus and actively transport sugar into and out of
sieve-tubes.