Permanent Tissues and It’s Types

Some of the most important types of permanent tissues are as follows:

The tissues that have lost the capacity of growth and division temporarily or permanently are known as permanent tissue. It is formed as a result of division and differentiation of meristematic tissue.

This tissue maybe living or dead thin (living tissue) or thick walled (dead tissue).

Types of Permanent Tissue:

Permanent tissues are of three types:

1. Simple tissue

2. Complex tissue

3. Special tissue or Secretory tissue

1. Simple Tissue:

Simple tissues called homogenous tissues. A simple tissue may be defined as a group of similar cells that perform a common function.

These are classified into three groups:

(a) Parenchyma

(b) Collenchyma

(c) Sclerenchyma.

(a) Parenchyma: (Para= Soft, Enchyma = Tissue)

i. These are composed of isodiametric living cells which may be oval or rounded.

ii. Cells have intercellular spaces.

iii. Cell wall is thin and made up of hemicellulose and cellulose.

iv. Vacuole is present and nucleus size is small.

v. Cells have dense and living protoplasm.

vi. Cells may show meristematic activity. So these are also called as potential meristematic tissue.

vii. It is found in cortex, pith, mesophyll tissue, and endosperm and also associated with xylem and phloem.

According to specific function, parenchyma is classified into four groups:

1. Aerenchyma:

Parenchyma having large air spaces is known as aerenchyma. It is found in hydro­phytes and it gives buoyancy to plant.

2. Chlorenchyma:

Parenchyma with large amount of chloroplast is known as chlorenchyma. It is found in mesophyll of leaf and helps in photosynthesis.

3. Prosenchyma:

Parenchymatous cell becoming long and tapper at both ends, without intercellular space is known as prosenchyma. It helps in mechanical support.

4. Idioblast:

Parenchyma that stores unwanted or ergastic substances is known as Idioblast.

Functions of Parenchyma:

1. Parenchyma mainly serves as storage tissue.

2. Being meristematic in nature, parenchyma is associated with regeneration, formation of adventitious root, graft union, wound healing.

3. Aerenchyma renders buoyancy, prosenchyma gives mechanical support, chlorenchyma helps in photosynthesis and idioblast stores ergastic substances.

(b) Collenchyma: (Colla = Give, Enchyma = Tissue):

i. Collenchyma term was coined by Schlieden.

ii. It is living mechanical dicot tissue.

iii. Cells are longer than parenchyma cells.

iv. Cell wall is thick and made up of cellulose and pectin.

v. Cell carries less amount of chloroplast.

vi. Due to presence of pectin it is the tissue with highest refractive index.

vii. Intercellular spaces are absent, because at the corner of the cells, secondary cell wall substance develops due to which the cell wall become rigid and thick at corners.

viii. It is found in hypodermis of dicot stem and upper and lower portion of vascular bundle of dicot leaf.

ix. On the basis of distribution of wall thickening chloenchyma can be classified into

1. Angular collenchymas:

It is most common type of collenchyma, where thickening occurs only at corners of the cells and side walls remain thin, e.g., – Vitis. Ficus.

2. Lamellar/Plate collenchyma:

Thickenings are plate like and occur only in tangential wall, e.g., – Rheum.

3. Tubular/Lacunar collenchyma:

Thickenings are distributed all around the intercellular spaces, e.g., – Malva, Salvia.

Functions:

1. It provides mechanical support to the young and growing organs of the plant in the form of elasticity.

2. It helps in photosynthesis.

(c) Sclerenchyma (Secros = hard, Enchyma = Tissue):

i. Sclerenchyma term was coined by Mettenius.

ii. These are hard, rigid and dead tissues.

iii. Cell wall is very thick due to deposition of lignin.

iv. These are of various shapes and size.

v. It provides mechanical support as well as rigidity to plant body.

Classification of Sclerenchyma:

It is of two types:

(1) Fibre;

(2) Sclereids

1. Fibre:

i. These are very much elongated cells with tapering or pointed ends.

ii. At maturity it losses it protoplasm and becomes dead.

iii. Presence of wider lumen at middle.

iv. Wall is made up with lignin.

v. Fibres are present in pericycle of many dicots and secondary xylem and phloem tissue.

vi. Fibre is the longest cell (Boehmeria fibre, length is upto 55 cm) in plant.

vii. According to position, fibres are of two types:

1. Xylary fibres – Fibres associated with xylem is known as Xylary fibres.

2. Extra Xyfary fibres – Fibre present in any other part of the plant except xylem. e.g., Phloem fibres, cortical fibres, Perivascular fibres, etc.

Functions:

1. It mainly helps in mechanical support to plant body in the form of plasticity.

2. Commercially important fibres are Hemp (Cannabis sativa), Jute (Corchorus capsularis), Flex (Linuin usitatissimum), and Ramie (Boehmeria nivea).

2. Sclereids:

i. Sclereid term was coined by Tschierch.

ii. They have extremely thick wall of lignin with narrow leumen.

iii. These are generally found in hard part of the plant and gives rigidity.

iv. According to different shapes and size it is classified into five groups:

1. Macrosclereid (rod cell):

It is large and rod shape. It is found in hard seat coat of family – Fabaceae.

2. Brachysclereid (stone cell):

It is small, oval or rounded. It is found in cortex, pith and phloem.

3. Trichosclereid (Trichoblast):

It is hair like and found in epidermis.

4. Astrosclereid (stellate):

It is star shape. It is found in intercellular spaces of leaf and stems of hydrophytes.

5. Osterosclereid (propcell):

It is bone shape and found in hypodermal layer of many seeds and fruits.

2. Complex Tissue:

i. A group of different types of cells performing same function is known as complex tissue.

ii. It is also known as vascular tissue.

iii. It is classified into two groups:

1. Xylem

2. Phloem

1. Xylem:

The term xylem was introduced by Nageli. It is the main sap (water and minerals) conduction complex tissue of the plant. It is associated with phloem and form the vascular bundles. It consists of both parenchymatous as well as sclerenchymatous cells. On the basis of components xylem can be classified into primary xylem and secondary xylem. Primaryxylem is present in primary growth of the plant body and derived from procambial cells. It is differentiated into protoxylem and metaxylem. Secondary xylem is present in secondary plant body. It is made up with four components.

(a) Tracheids

(b) Vessels

(c) Xylem fibre

(d) Xylem parenchyma

Out of four components only xylem parenchyma is living and rest of the components are dead.

(a) Tracheids:

1. These are elongated, narrow lumen cells with tapering ends.

2. Cell wall is made up of lignin and thickening may be scalariform, annular, and reticulate or pitted (generally bordered pit).

3. Tracheids are found in Pteridophytes, Gymnosperms and Angiosperms.

4. It develops softwood (Nonporous wood).

5. Tracheids form a long row placed one above the other.

6. It helps in conduction of water, mechanical support and formation of wood.

(b) Vessels:

1. These are elongated, broad ended, cylindrical elements with wider lumen.

2. These are commonly found in angiosperm (except family – winter- aceae, Tetracentraceae, Trochodendraceae) and also in advanced Gymnosperm i.e., Order-Gnetales (Gnetum, Welwitschia and Ephe­dra). Vessels are absent in stem and leafs of Yucca and Dracaena.

3. Walls of vessels are lignified and thickening may be annular, spiral, scalariform or reticulate.

4. Cell wall possesses many bordered pits but the pits are smaller than those found in tracheids.

5. The end wall of vessels is perforated known as perforated plates. It may be simple (with single opening) or multiple (with two or more openings).

6. Vessels develop hard wood or porous wood. Vessels with narrow lumen are protoxylem and wider lumen is known as metaxylem.

7. It also helps in conduction of water, mechanical support and formation of wood.

(c) Xylem fibre:

1. It is dead sclerenchymatous cell found in xylem.

2. These are long, narrow with thick lignified wall and tappering ends.

3. It is of two types (i) Fibre tracheids (it is similar to tracheids with bordered pit); (ii) Libriform fibre (with simple pit).

4. It helps in mechanical support.

(d) Xylem parenchyma:

1. Xylem or wood parenchyma is only living component of xylem.

2. These are parenchymatous, thin walled, oval or elongated and present in both primary and secondary xylem.

3. It mainly helps to stores starch and fats.

4. It is responsible for the formation of medullary rays.

Functions of Xylem:

1. Tracheids and vessels help in conduction of water and minerals from base to top of the plants. They also help in formation of soft and hard wood, respectively.

2. Xylem parenchyma stores food.

3. Xylem fibre helps in mechanical support.

2. Phloem:

The term phloem was coined by Nageli (1858). It is a permanent living complex tissue.lt helps in translocation of organic food (in the form of sucrose) from leaves to various parts of the plant. It is also called bast or leptome. On the basis of origin phloem is classified as primary phloem (in primary growth) and secondary phloem (in secondary plant body).

On the basis of position it is distinguished into:

(1) External phloem. Present outside the xylem in vascular bundle.

(2) Internal phloem. Present inner to the xylem along with outer phloem – e.g., Cucurbita and

(3) Included phloem, embedded in the secondary xylem e.g., Salvadora. Phloem is made up of four components.

(a) Sieve tubes

(b) Companion cells

(c) Phloem parenchyma

(d) Phloem fibres

Out of four components only phloem fibre is dead and rests are living.

(a) Sieve tubes:

1. These are elongated cylindrical, tube like living cells.

2. Presence of thin cellulosic wall and are placed end to end.

3. They are non-nucleated at maturity but protoplasm possesses large vacuole.

4. In Gymnosperm, sieve cells are present in place of sieve tubes.

5. Between two sieve tubes there are present perforated sieve plates with many sieve pores.

6. During winter season, polysaccharide substances, callose, get deposited on sieve plates. These calluse pads inhibit conduction of food. On return of spring, callose pads get dissolved with the help of enzyme callose and conduction of food restarts and growth of plant starts.

(b) Companion cells:

1. These are elongated, narrow, thin walled living cells associated with seive tubes and are placed side by side with them.

2. The sieve tubes and companion cells are connected through pits.

3. In Gymnosperm, albuminous cells are present in place of companion cells.

4. Companion cells help in transport of food along with sieve tubes.

(c) Phloem parenchyma:

1. It is elongated, pointed, living, thin-walled parenchymatous cell inter mixed with sieve tube elements.

2. It is absent in monocot plants (also in dicot Ranunculus)

3. It helps in conduction and stores food. It also contains oil, starch, mucilage and latex.

(d) Phloem fibre:

1. These are dead elongated sclerenchymatous cells having lignified walls with pits.

2. These are found both in primary and secondary phloem.

3. It serves to provide mechanical support.

Functions of Phloem:

1. It helps in translocation of solute from apex to base of the plants.

2. Secondary bast fibres (jute fibre) are of economic value.

3. Specialized tissues (secretory tissues):

Unlike animals, in plants, excretory system is not found. The cell protoplasm secretes certain— products. They may be utilised in future cell metabolism, e.g. enzymes and hormones are stored as waste excretory products which have great economic value to man (e.g.-resins, gums, rubber, oils and volatile oils etc.) or move outside the tissue for the benefit of the plant which is called excretion (e.g.- nectar, digestive enzymes and poisonous substance etc.).

Both secretion and excretion are performed by special type of tissues called special tissues OR secretory tissues. The secretory cells or tissues either may occurs at certain localized areas or may be distributed through the plant body. The cells have denser granular cytoplasm and nucleus.

On the basis of morphological and physiological characters, the Secretory tissues are classified as:

I. Laticiferous Tissue

II. Glandular Tissue

(I) Laticiferous Tissue:

a. The tissue which contains latex is known as laticiferous tissue.

b. The laticiferous tissue originates from meristematic tissue and matures along with other tissues.

c. The tissue is composed of elongated, thin walled, branched or unbranched multinucleated living cells.

d. They are scattered in ground tissue of all organs of the plant body.

e. The latexis generally milky whitish (Calotropis) in colour. Sometimes it may be watery (Musa) yellowish (Argertione) or orange (Papaver) in colour.

f. The latex is a emulsified substance that contains different organic materials such as sugar, proteins, enzymes, starch, alkaloids, resins, tannis, mucilages, rubber etc.

The laticiferous tissue is found in large number of families such as Apocynaceae; Asclepiadaceae; Euphorbiaceae. Compositate (Asteraceae), Papaveraceae, Moraceae, Urticaceae, Musaceae etc.

On the basis of structural variations the tissue is divided into two types:

1. Latexcell and

2. Latex vessels

1. Latex Cells:

a. These are long tubular branched or unbranched living cells.

b. The young latex cells are very small and uninucleated.

c The cell walls are very thin and made up of cellulose.

d. Big central vacuole is surrounded by thin film of cytoplasm.

e. As the plant grows, these cells also elongate and nucleus undergoes several free nuclear divisions without cytokinesis. Hence the cells become coenocytic structures.

f. The cells do not anastomose (fuse) with each other as in latexvessels, hence the latexcells are called simple laticiferous or non-arliculated laticifers.

Example:

The latex cells are found in Apocynaceae, Asclepidiaceae, Euphorbiaceae and Urticaceae.

2. Latex Vessels:

a. The latex vessels are formed by the disintegration of cross walls of latex cells placed end Lo end.

b. The cells are living and contain multinucleated protoplasm.

c. The vessels are unbranched in the beginning, but during maturation they branch several times.

d. Two or more vessels which are present side by side in the ground tissue anastomose with each other to form a coenocytic network. Hence, the latex vessels are called as articulated laticifers, or compound laticifers.

Example:

Latex Vessels are found in Compositae (Sonchus) Papaveraceae (Argemone) and Euphorbiaceae (Hevea) families.

Functions:

1. Laticiferous tissue stores the food material in the form of starch (e.g., Euphorbia sps)

2. It absorbs and stores the water in xerophytes (Calotropis, Nerium).

3. It protects the plants from grazing animals by containing poisonous substances.

4. Opium is prepared from the latex of Papaversomniferum.

5. Rubber is prepared from Heuea brassiliemis and Ficus elastica latex.

6. Papain protein is prepared from the latex of Carica papaya.

7. Chewing gum is prepared from the latex of Sapota fruits.

8. Asafoetida is prepared from the latex of Ferula asafoetida root stocks.