PERMANENT TISSUES

Permanent tissues are composed of cells which have lost the power of division temporarily or permanently. They are formed by division and differentiation of meristematic tissues. The cells of permanent tissues do not generally divide further.

Their cells may be living or dead. Permanent tissues are of three types :

A. Simple tissue (Homogenous tissue)

B. Complex tissues (Heterogenous tissue)

C. Special tissue (Secretory tissue)

Mainly of 2 types i.e. simple and complex tissues :

(A) SIMPLE PERMANENT TISSUE

This tissues is made up of structurally similar type of cells or only one type of cells that perform a common function .Simple Tissues are of three types - L IL. 

1. Parenchyma

2. Collenchyma

3. Sclerenchyma

PARENCHYMA: It is very primitive type of tissue. It is first evolved tissue. Remaining different types of tissues are derived from this tissue, so it is also called fundamental tissue or precursor of other tissues Parenchyma forms the major component within organs.

Parenchyma term was coined by Grew

CHARACTERISTIC FEATURES:

• It is a living tissue
• It is first differentiated tissue.
• It is a universal tissue.
• Pulp of a fruit is mainly composed of parenchyma.
• Body of bryophytes is mainly composed of parenchyma.
• The cells of parenchyma are thin walled. Cell wall is made up of pectocellulose means pectin + cellulose.(mainly cellulose),So parenchyma is a soft tissue.
• Each cell contains large central vacuole. So the main function of a parenchyma cell is storage of food.
• Parenchymatous cells may either be closely packed or have small intercellular spaces
• It is found in cortex. pericycle, medullary raa. pith leaf mESophyll etc It forms major component within organs.

SHAPE:

The cells of parenchyma are generally isodiametric. They may be spherical (rounded), oval elongated or polygonal in shape.

MODIFICATIONS OF PARENCHYMA:

Prosenchyma - The cells of this parenchyma are thick walled, long with pointed ends. This parenchyma forms the pericycle of roots. Function: To provide strength.

Aerenchyma :- This parenchyma is made up of rounded cells. These cells surround the large air chambers.Aerenchyma is usually found in cortex region. It provides buoyancy to hydrophytes (aquatic plants)

Stellate parenchyma : Found in leaf bases of banana.

The cells of this tissue are stellate (star shaped). Main function of this parenchyma is to provide mechanical support/mechanical strength to leaf bases (pseudo stem) of banana.

Chlorenchyma: Such type of parenchyma contains abundant quantity of chloroplasts. It is found in the mesophyll of leaves. Its function is to perform photosynthesis

Mucilage Parenchyma : In the mucilage parenchyma large vacuoles and mucilage are present. eg. Succulent (fleshy) xerophytic plants.eg. Aloe. Opuntia Cactus, Euphorbia. Function - storage of water.

Functions of parenchyma

• The parenchyma performs various functions like storage, photosynthesis. secretion etc.
• The main function of this tissue is storage of food.
• Some cells of parenchyma store waste materials. They are called "idioblast cells". Idioblast cells store oils, tannin and crystals.
• Photosynthesis (by chlorenchyma).

COLLENCHYMA: Term was coined by Schleiden.

Main characteristics :

• Collenchyma is a living mechanical tissue.
• It is made up of more or less elongated cells (In transverse section cells.appear oval, spherical/round or polygonal in shape).
• Localized deposition of pectin (mainly). cellulose & hemicellulose occurs mainly at corners.
• Usually intercellular spaces are absent.
• Generally chloroplasts are found in the cells of collenchyma or cells often contain chloroplasts.
• These cells assimilate food when they contain chloroplasts.

Occurrance :

• Collenchyma is not a universal tissue. It is found in the stems of herbaceous dicotyledons (young dicot stem) below the epidermis either as a homogenous layer (in sunflower stem) or in patches (in cucurbita steam).
•  Collenchyma forms the hypodermis of dicotyledon stems Cells of collenchyma are flexible de to hydrophilic nature of pecto cellulose, so flexibility occurs in dicotyledonous/dicot stems.
• Margins of leaf lamina and petiole of leaves also bear collenchyma, It protects the lamina margins from cracking by the action of wind.
• Collenchyma is absent in mature/woody plant parts (After secondary growth in dicot stem), roots and monocotyledons.

FUNCTIONS :

• Collenchyma performs both functions mechanical as well as biological/vital functions Provides tensile strength against bending & swaying (mechanical function)
• They provide mechanical support to the growing parts of the plant such as young stem and petiole of a leaf.
• Due to the presence of chloroplast, photosynthesis process (assimilation of food) takes place in collenchyma (vital function).

SCLERENCHYMA:

Term was coined by Mettenius

Main features : 

• Sclerenchyma is the main mechanical tissue. It is dead mechanical tissue.
• Cells of sclerenchyma are generally long, narrow, thick walled, lignified without protoplasts and dead (Cells become dead at maturity).
• Sclerenchyma is found in the hypodermis of monocot stem .Function: It provides mechanical support/mechanical strength to plant organs.

• Various types of pits are formed due to the deposition of lignin on the walls.

Types of sclerenchyma :

On the basis of variation in form, structure, origin & development sclerenchyma cells are of two types.

(i) Sclereids

(ii) Sclerenchymatous fibres

SCLEREIDS: These cells are small dead extremely thick walled (highly thickened) and generally their ends are not pointed. Sclereids are of various shaped.(Spherical.oval or cylindrical) Sclereids cells have pits and lumen (cavity) is almost very small/very narrow. Sclereids are commonly found in fruit walls of nuts, pulp of guava, pear & sapota (Stone cells); seed coats of legumes and leaves of tea etc.

SCLERENCHYMATOUS FIBRES :

The fibres are thick walled. elongated and pointed cells.

Fibres are longest cells in plant body. Their both ends are pointed (tapering). Due to thick cell wall, lumen is reduced and generally occurring in groups in various parts of the plant. Their cell wall contains pits.

On the basis of position, fibres are divided into three types

A.Surface fibres :- They are present on the surface of seeds, fruits etc. These fibres are also called filling fibres.

(i) Seed surface fibres -

Example 1: Cotton fibres (Gossypium fibres) - Cotton fibres are out growth of seed coat Testa.

Cotton fibres are composed of cellulose. They are non-lignified. So cotton fibres are not true fibres. Two types of fibres are found in cotton. Long fibres are called 'lint' and small fibres are known as 'fuzz'. Lint fibres are used in cloth industry. Fuzz are filling fibres

(ii) Coir of coconut is also a type of surface fibres. They are derived/obtained from the fibrous mesocarp of coconut (Cocos nucifera). These are true fibres, because they are lignified

B. Xylary fibres/Intraxylary fibres/Wood fibres: These are hard fibres. These fibres are not flexible. These fibres are obtained from xylem (mainly from secondary xylem or wood).Eg.. Munj fibre (Saccharum munja)

C. Phloem fibres/Extra xylary fibres / Bast fibres These are commercial fibres These fibres are flexible and can be Knitted (weave easily. They have great economic value.

• These fibres are obtained from the phloem and pericycle of plants.

• The bast fibres of Corchorus capsularis (Jute),Crotalaria juncea (Sunn hemp) and Hibiscus sabdariffa (patua) are obtained from the phloem (secondary phloem) of stem.
• The bast fibres of Hemp (Cannabis sativa) and Flax (Linum usitatissimum) are obtained from the pericycle.

• Phloem fibres of jute, flax and hemp are used commercially.
• Fibres are longest plant cells. Longest fibres occur in phloem of Boehmeria nivea (Ramie plant) length-55 cm.
• In plant kingdom hardest, thickest and Largest leaves are found in Victoria regia.

• Longest commercial timbres -Jute fibres

[B] COMPLEX PERMANENT TISSUE

• The complex tissues are made of more than one type of cells or different types of cells and these work together as a unit. Complex tissues are heterogenous.
• Complex tissues are absent in gametophytes.

• During vascularisation in plants differentiation of procambium is followed by the formation of primary phloem and primary xylem simultaneously.
• Complex tissues are also known as vascular tissues or conducting tissues.
• Complex tissues are of two types - 1. Xylem 2. Phloem

(a) XYLEM

• The term Xylem was coined by Nageli.
• The function of xylem is to conduct water & mineral salts upwards from the roots to stem & leaves and to give mechanical strength to the plant parts.
• For efficient conduction of water death of protoplasm is must. Dead tissues are more developed in water scarce conditions.
• In hydrophytes xylem is poorly developed, while in xerophytes xylem is well developed. 
• On the basis of origin, xylem is divided into primary xylem and secondary xylem.
• Primary xylem originates from procambium during vascularisation. Xylem which is formed early in the life of a plant is known as primary xylem. On the basis of primary xylem is divided into two parts. 

        1. protoxylem               2. Metaxylem

• Cells of protoxylem are small as compared to metaxylem. The first formed primary xylem elements are called protoxylem and the later formed primary xylem is called metaxylem.
• Secondary xylem originates from vascular cambium during secondary growth. Xylem which is formed during secondary growth is known as secondary xylem. Secondary xylem is not differentiated into protoxylem and metaxylem.

Xylem is composed of four different kinds of elements. The elements of xylem are

(1) Tracheids, - dead element

(2) Vessels or tracheae, - dead element

(3) Xylem fibres. - dead element

(4) Xylem parenchyma - living element

1. TRACHEIDS :

• Tracheids are primitive conducting elements of xylem.
• Single tracheid is elongated or tube like cell with thick and lignified walls and possess a narrow lumen. The ends of tracheids are tapering or chisel like.
• The tracheids found one above the other and are separated by cross wall / end wall which bears bordered pits.
• Usually bordered pits are present at the end walls of tracheids. The maximum bordered pits are found in the tracheids of Gymnosperm plants.
• Tracheids are dead (without protoplasm) and lignified cells.
• Tracheids are found in pteridophytes, gymnosperms and angiosperms.
• End walls of tracheids are imperforate (not porous) but pitted (Pits are present)
• Tracheids are unicellular.
• The inner layers of cell walls have thickenings which vary in form.
• Types of thickening in tracheids and vessels are annular, spiral, reticulate, pitted and scalariform.
• The deposition of lignin on cell wall is responsible for the formation of different types of thickenis annular (primitive type), spiral, scalariform, reticulate and pitted.
• Annular and spiral type of thickening of lignin is found in protoxylem.
• Reticulate and pitted (mainly) type of thickening of lignin is found in metaxylem.
• Scalariform (ladder like) type of thickening is found in metaxylem tracheids of pteridophytes mata xylem tracheids of Cycas (gymnosperm).
• Maximum deposition of lignin is found in pitted type of thickening and pits are formed in this type of th
• Pits are unlignified areas on lignified walls.

2) VESSELS - TRACHEAE

• Vessel is an advanced conducting element of xylem.

• Vessel is a long cylindrical tube like structure with lignified walls and a wide (large) central lumen cavity.

• Vessel is multicellular, it is made up of many.cells called vessel members or vessel elements.

• Vessel is an example of dead syncyte. Vessel cells are also devoid of protoplasm.

• The end wall is perforated. Thus vessels are more capable for conduction of water than tracheids. Due to presence of perforated end walls, vessels work as a pipe line during conduction of water.

• Vessel members ao interconnected through perforations in their common walls. The perforation may be simple (only one porel) or multiple (several pores). Vessels contain usually simple pits on their lateral walls.

1. Presence of vessels is a characteristic feature of angiosperms Vessels are usually absent in gymnosperms but exceptionally vessels are present in some gymnosperms like Ephedra, Gnetum and Welwitschia (Order Gnetales).

2. Vessels are absent in some angiosperm plants such as Dracaena, Yucca, Dagenaria, Drimys. There are some angiosperm families in which vessel less angiosperms are included e.g. Winteraceae Tetracentraceae and Trochodendraceae.

3. Tracheids and vessels are called tracheary elements of xylem

4. In flowering plants. tracheids and vesselsace.be main water transporting elements.

Syncyte: Structure which is formed by fusion of cells is called syncyte

3. XYLEM FIBRES - WOOD FIBRES :

• They may either be septate or aseptate.

• Xylem fibres provide strength to the tracheids and vessels They have highly thickened wall and obliterated.central lumen.

• That are abundantly found in secondary xylem (wood)

• They are generally not found in gymnosperm wood to gymnosperms are also called soft wood spermatophytes)

4. XYLEM PARENCHYMA

Cell living and thin walled and their cells are madesinof.celulose.

Function: Storage of food material in the form.of starch.or.fat and storage of other substance, like tannins.

Hadrome - Conducting part of xylem is known as hadrome.

Tracheid And vessels are collections own water conducting element or Hadrome', term was proposed by Haberlandt.

PHLOEM 

• The term Phloem was coined by Nagell.
• The main function of the phloem is to conduct/transport food materials usually from the leaves to other parts of the plants.
• On the base of origin, phloum is dassified into two categories primary and secondary phloem.
• Primary phloem originates from procambium during vascularisation and secondary phloem originates from vascular cambium during secondary growth.
• On the basis of development primary phloem is categorised into protophloem and metaphloem.
• The protophloem (first formed primary phloem) has narrow sieve tubes whereas metaphloem (later formed primary phloem) has bigger sieve tubes.
• Phloem remain active for less duration as compared to xylem.
• Phloem consist 4 types of cells / elements.
• Sieve tube elements, companion cells, phloem parenchyma & phloem fibres (In angiosperms).
• Sieve cells albuminous cells, phloem parenchyma and phloem fibres (In Gymnosperms). 

• sieve cell element - In Gymnosperms and pteridophytes 
• sieve tube element In Angiosperms

• Sieve element was discovered by Hartig.
• In Angiosperm plants, sieve tube elements are joined from their ends to form sieve tube. Their end walls are perforated means having sieve pores in a sieve plates   (oblique perforated septal. Translocation of food material takes place through these pores.
• Sieve tube is an example at living syncyte.
• Sieve tube elements are long, tube like structures arranged longitudinally and associated with companion cells.
• Sieve cells and sieve tube elements are living and thin walled.
• A mature sieve tube element possess, a peripheral cytoplasm & a large vacuole but lacks a nucleus.
• Mature sieve tube elements are enucleated living cells (enucleated means without nucleus).
• The function of sieve tubes are controlled by the nucleus companion cells.
• A central large vacuole is present in each sieve cell and sieve tube element and around the central vacuole thin layer of cytoplasm is present.

Notes : 

• Callose deposition takes place on the radius of sieve pores during dropping season/falling season of leaves (autumn), to form a thick layer. This called calls pad /callose pad. It is formed mainly in deciduous plants

• Sieve plate is protected by callose pad, it is protects sieve plate from bacterial infection and drought dryness.
• Callose dissolves during spring season. Callose is a polymer of beta-1, 3-glucan.
• Siee elements contain special type cof Protein P-protein (P=phloem). Most likely function of p-protein is sealing mechanism on wounding along with callose and it is also  related with conduction of food.
•  In Pteridophyte and gymnosperm, sieve cells arranged in zigzag manner. In sieve cells, seve areas are located laterally. Sieve cells are narrow elongated cells.

COMPANION CELLS

• These are thin walled and specialised parenchymatous cells, which are closely associated with sieve tube elements.
• The sieve tube elements and companion cell are connected by pit fields presents in their common longitudinal walls.
• Companion cells laterally associated with each sieve tube element in angiospermic plants.
• Sieve tube element and companion cell originate together. Both of the originate from a single mother cell. So they are called sister cells.
•  Comparison cell a living cell with large elongated nucleus. This nucleus also controls the activity/function  of sieve tube element.
• Companion cells are found only angiosperms.
• The companion cells help in maintaining the pressure gradient in the sieve tubes.

Note: Special type of cells are attached with the sieve cells in gymnosperm and in pteridophytes in place of companion cells. These cells are called albuminous cells/Strasburger cells.

PHLOEM FIBRES/BAST FIBRES

• These are Made up of sclerenchymatous cells.
• These are much elongated, unbranched and have pointed needle like apices. The cell wall of phloem fibres in quite thick.
• These fibres are generally not found in primary phloem but  are found in the secondary phloem.
• At maturity fibres lose their protoplasm and become dead.

PHLOEM PARENCHYMA

• It's cells are living, elongated, tapering, cylindrical which have dense cytoplasm and nucleus.
• The wall is composed of cellulose and has pit fields through which plamodesmatal connection exist between the cells.
• It stores food material and other substances like resins, latex, mucilage etc.
• The main function of phloem parenchyma storage of food material and function of phloem is ray(ray parenchyma) is conduction of food in radial direction.
• Phloem parenchyma absent in most of the monocotyledons.
• The conducting ring of phloem in called Leptome.
• Leptome term was  given by Haberlandt.

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