Permanent Tissues

 The permanent tissues are those in which growth has stopped either completely or for the time being. Sometimes, they again become meristematic partially or wholly.

The cells of these tissues maybe living or dead and thin-walled or thick-walled. The thin walled permanent tissues are generally living whereas the thick-walled tissues maybe living or dead. The permanent tissues may be simple or complex.
A simple tissue is made up of one type of cells forming a uniform of homogeneous system of cells. The common simple tissues are parenchyma, collenchyma and sclerenchyma. A complex tissue is made up of more than one type of cells working together as a unit. The complex tissues consist of parenchymatous and sclerenchymatous cells; collenchymatous cells are not present in such tissues. The common examples are the xylem and the phloem.
Simple Tissues:-
 Parenchyma:
The Parenchyma tissue is composed of living cells which are variable in their morphology and physiology, but generally having thin walls and a polyhedral shape, and concerned with vegetative activities of the plants.
The individual cells are known as Parenchyma cells. The word Parenchyma is derived from the greek – para- beside and enchain-to pour. This combination of words expresses the ancient concept of Parenchyma as a semi-liquid substance poured beside other tissues which are formed earlier and are more solid. Phylogenetically the parenchyma is a primitive tissue since the lower plants have given rise to the higher plants through specialization and since the single type or the few types of cells found in the lower plants have become by specialization the many and elaborate types of the higher plants.
The Parenchyma consists of isodiametric, thin-walled and equally expanded cells.
The Parenchyma cells are oval, rounded or polygonal in shape having well developed spaces among them
  The cells of this tissue are living and contain sufficient amount of cytoplasm in them.
Usually each cell possesses one or more nuclei.
The cell wall is made up of cellulose, hemi-cellulose and pectin.
Parenchyma makes up large parts of various organs in many plants. Pith, mesophyll of leaves, the pulp of fruits, endosperm of seeds, cortex of stems and roots, and other organs of plants consist mainly of parenchyma. The Parenchyma cells also occur in xylem and phloem
In the aquatic plants, the parenchyma cells in the cortex possess well developed air spaces (intercellular spaces) and such tissue is known as aerenchyma. It helps in the buoyancy of the plants.
Parenchyma maybe specialized as water storage tissue in many succulent and xerophytic plants. In Aloe, Agave, Hakea and many other plants chlorophyll-free, thin-walled and water-turgid cells are found which represent water storage tissues this called as storage parenchyma
When the Parenchyma cells are exposed to light they develop chloroplasts in them, and such tissue is known as chlorenchyma. The chlorenchyma possesses well developed aerating system. Intercellular spaces are abundant in the photosynthetic parenchyma of stems too. Chlorenchyma is most commonly found in mesophyll of leaves and outer cortex of young stems.                                                                                                                                                              Commonly the Parenchyma cells have thin primary walls. Some such cells may have also thick primary walls. Some storage parenchyma develop remarkably thick walls and the carbohydrates deposited in these walls, the hemicellulose, are regarded by some workers as reserve materials. Thick walls occur in the endosperm of Phoenix dactylifera, Diospyros, Asparagus and Coffee arabica. The walls of such endosperm become thinner during germination.
Functions:
The turgid Parenchyma Cells help in giving rigidity to the plant body.
 Partial conduction of water is also maintained through parenchymatous cells.
 The Parenchyma acts as special storage tissue to store food material in the form of starch grains, proteins, fats and oils.
The Parenchyma cells that contain chloroplasts in them make chlorenchyma which are responsible for photosynthesis in Green plants.
In water plants the aerenchyma keep up the buoyancy of the plants. Such air spaces also facilitate exchange of gases. In many succulent and xerophytic plants such tissues store water and known as water storage tissue.
Vegetative propagation by cuttings takes place because of meristematic potentialities of the Parenchyma cells which divide and develop into buds and adventitious roots.
 Origin :- As regards their origin, the Parenchyma tissue of the primary op plant body, that is, the Parenchyma of the cortex and the pith, of the mesophyll of leaves, and of the flower parts, differentiates from the ground meristem.
The Parenchyma associated with the primary and secondary vascular tissues is formed by the procambium and the vascular cambium respectively. Procambium - Parenchyma associated with the primary vascular tissues. Vascular cambium - parenchyma associated with the secondary vascular tissues.  Parenchyma may also develop from the phellogen in the form of phelloderm, and it may be increased in amount by diffuse secondary growth.

Collenchyma:
 Collenchyma is a living tissue composed of somewhat elongated cells with thick primary non-lignified walls. Important characteristics of this tissue are it's early development and it's adaptability to changes in the rapidly growing organ, especially those of increase in length.
It gives support to the growing organs which do not develop much woody tissue. Morphologically, collenchyma is a simple tissue, for it consists of one type of cells.
 Collenchyma is a typical supporting tissue of growing organs and of those mature herbaceous organs which are only slightly modified by secondary growth or lack such growth completely. It is the first supporting tissue in stems, leaves and floral parts. It is the main supporting tissue in many dicotyledonous leaves and some green stems. Collenchyma may occur in the root cortex, particularly, if the root is exposed to light. It is not found in the leaves and stems of monocotyledonous.
Collenchyma chiefly occurs in the peripheral regions of stems and leaves. It is commonly found just beneath the epidermis. In stems and petioles with ridges, collenchyma is particularly well developed in the ridges. In leaves it may be differentiated on one or both sides of the veins and along the margins of the leaf blade.
The collenchyma consists of elongated cells, various in shape, with unevenly thickened walls, rectangular, oblique or tapering ends, and persistent protoplasts.
The cells overlap and interlock, forming fibre - like strands.
The cell wall consists of cellulose and pectin and have a high water content(60%).
They are extensible, plastic and adapted to rapid growth. In the beginning the strands are of small diameter but they are added to, as growth continues, from surrounding meristematic tissue.  The border cells of the strands may be transitional in structure, passing into the parenchyma type.
Three types of collenchyma are recognised on the basis of cell wall thickening  - angular, lamellar and tubular.
 In Angular collenchyma the cells are irregularly arranged  and wall material is deposited at the corners or angles of the cells. eg:- Ficus, Vitis, Polygonum, Beta, Rumex, Boehmeria , Morus, Cannabis, Begonia;.
In Lamellar collenchyma the thickening is restricted to the tangential walls of the cells. As a result, the tissue appears like a plate or a band (lamellum – plate). ( eg:- Sambucus, Rheum, Eupatorium) 
In Lacunar collenchyma the intercellular spaces are present and the thickening takes place on the walls around the intercellular spaces (Lacuna – intercellular space). (eg:- Compositae , Salvia, Malva, Althaea).
The chief function of the tissue is to give support to the plant body. Its supporting value is increased by its peripheral position in the parts of the stems, petioles and leaf mid-ribs.
Young stems resist bending and pulling action of wind due to collenchyma.
It gives flexibility and elasticity.
When chloroplasts are present, the cells carry out photosynthesis

Sclerenchyma:
The sclerenchyma ( Greek. Sclerous – hard, enchyma – an infusion) is a simple permanent tissue, made up of thick walled, lignified cells. The main function of sclerenchyma is to provide mechanical support to the plant body. This is a supporting tissue that withstands various strains which result from the stretching and bending of plant organs without any damage to the thin-walled softer cells.
Sclerenchyma cells do not possess living protoplasts at maturity. The wall of these cells are uniformly and strongly thickened.
Sclerenchyma cells are grouped into fibres and sclereids.
Fibres :
Long, elongated, narrow sclerenchyma cells, usually with pointed or tapering ends. The walls of fibres are lignified. The walls are so much thickened that the lumen or cell cavity is very much reduced. The pits on the walls are usually simple and appear slit – like. The middle lamellae is conspicuous in the fibres. The walls are made up of cellulose in Linum, Cannabis.
Fibres are usually defined as dead cells with no protoplast. Very rarely the fibres retain protoplasts in them, eg., Coleus.
The average length of fibres is 1 to 3 mm, but in Linum usitattissimum (flax), Cannabis sativa (hemp), Corchorus capsularis (jute), Boehmeria nivea (ramie), the fibres are of length ranging from 20 to 550 mm. Such long, thick-walled and rigid cells constitute exceptionally good fibres of commercial importance.
On the basis of their position in the plant body, the fibres are classified into Xylary fibres and Extra Xylary fibres.
Xylary Fibres :
Also known as wood fibres. They are an integral part of xylem. They develop from the same meristematic tissues as the other xylem cells. They help in conduction as well as support.
Extra Xylary Fibres:
These fibres occur in various tissues outside Xylem such as cortex, pericycle or phloem. They are also known as bast fibres.
The fibres that form continuous cylinders in monocot stems arise in the ground tissue under the epidermis. They are known as cortical fibres. Eg- Grasses, Palms, Casuarina
The fibres present in the peripheral region of the vascular cylinder are known as pericyclic fibres or peri-vascular fibres. Eg- Aristolochia, Helianthus, Cucurbita.
The fibres originating in primary and secondary phloem are known as phloem fibres or bast fibres. Eg., Linum, Corchorus, Tilia, Nicotiana.
Functions:
Fibres provide mechanical strength to the plant parts
They protect the plant parts from stretching, bending, weight andpressures
They are commercially useful in textile and jute industries in the manufacture of cloth, threads, ropes and other coir products like mats, carpets, etc.
Eg –  Hemp – Cannabis sativa
Jute – Corchorus capsularis
Flax – Linum utitatissimum
Manila hemp – Musa textilis
Bow-string hemp – Sansivieria
Sisal – Agave sisalina
Ramie – Boehmeria nivea

Sclereids:
Also known as stone cells because of their thick and hard cell walls. They vary widely in shape, size and are usually not much longer than broad. They occur singly or in groups.
The cells are isodiametric with excessively thickened walls due to the deposition of lignin, narrow lumen and with simple or rarely with bordered pits.
They are commonly found found in the cortex and pith of gymnosperms and dicotyledons. They are common in fruits and seeds. The hardness and strength of the seed coats is due to the presence of abundant sclereids.
Based on their shape and thickening of walls, sclereids are classified into five types:
Brachysclereids: They are short, isodiametric. Commonly found in cortex, phloem (e.g., Cinnamomum) and pith of stems and pericarp of fruits (e.g, Pyrus, Cocos).
Macrosclereids: They are elongated rod like or columnar and appear as palisade layer beneath the epidermis of legume seeds. They are also known as malphighian cells. Eg., Bean seeds (Dolichos lab lab), Pea seeds (Pisum sativum)
Osteosclereids: They are long and columnar with enlarged ends and are bone shaped. They occur in hypodermal layers of many seeds and fruits. Eg., Hakea(leaves), Mouriria (cotyledons).
Astrosclereids: They are star shaped sclerieds with lobes projecting. Commonly found in the intercellular spaces of the leaves and stems of hydrophytes. Eg., Nymphaea ( petioles and leaf blades), Thea, Trochodendron (leaves)
Trichosclereids: They are elongated, branched, thin walled cells resembling hairs with the branches extending into the intercellular spaces. Eg., Leaves of Olea and aerial roots of Monstera