The plant tissue in which the process of growth has stopped are called the permanent tissue and it originates from both primary and secondary meristematic tissue. These cells have a definite shape and configuration but they do not have the power of division. The permanent tissues can be classified into three major types on the basis of its constituent cells. Those are :
(a) Simple tissue including parenchyma, collenchyma and sclerenchyma.
(b)Complex tissue including the xylem and phloem.
(c) Special tissue including the external and internal secretory tissue.
Here we shall discuss about the simple tissue of plants.
What is simple tissue?
The homogeneous group of non-meristematic or permanent cells having similar structure, function and origin is collectively known as simple tissue.
Classification of simple tissue:
There are three major types of simple tissues viz., parenchyma, collenchyma and sclerenchyma.
The Parenchyma is walled living cells. It is very soft in nature because of the presence of thin walled cells.
Origin : It usually develops from ground meristems. The parenchyma of vascular bundle develops from procambium ; but that of secondary vascular tissues develop from inter-fascicular cambium. The parenchyma of secondary epidermis is formed from phellogen or cork cambium.
Structures of Parenchyma :
The simple tissue, parenchyma shows the following characteristics: -
(1) They are living cells with thin cellulose wall, though secondary xylem. Parenchyma tissue are lignified as observed in the endosperm of date-palm.
(2) They are with equal diameter, more or less spherical or star shaped in Scirpus, and usually with intercellular spaces.
(3) The cells contain large nucleus and large vacuoles.
(4) They are either photosynthetic or non-photosynthetic, containing leucoplasts.
Occurrence of Parenchyma:
Functions of parenchyma :
(1) The parenchyma of the epidermis protects the plant organs.
(2) It carries out functions like regeneration, repairing of tissues and reproduc
(3) It is the major organ taking part in diffusion and osmosis.
(4) It is the storage tissue for food and water.
(5) It helps in the transport of food matter.
(6) Photosynthesis occurs in chlorophyllous parenchyma.
There are mainly three types of parenchyma found in plant tissue. Those are : -
(1) Chlorenchyma:The chlorophyllous parenchyma is called chlorenchyma
(2) Aerenchymaparenchyma contai air cavities. e.g. chyma of the leaf and of plants giving buoy
*(3) Idioblast: specialized parenchyma with variable size storing oils, tannins and mineral crystals e.g. leaf of banyan.
The permanent simple tissue consisting of unevenly thick walled living cells are called collenchymas. The uneven thickening of these cell walls makes it partially hard giving mechanical support. It is derived mostly from the elongated cells of the ground meristem and sometimes from the procambium.
Structure of collenchyma:
This type of simple tissue shows the following characteristics:
(1) The living cells with unevenly thickened walls composed of hemicellulose and pectin.
(2) The cells are elongated containing scanty vacuolated rotoplasm, appear polygonal in cross section.
(3) They are constituted by short and long fibre like cells, the short cells remain ong the long axis but the long cells are interlocked with overlapping tapering end.
(4) The primary pit fields are present.
(5) The intercellular spaces may or may not be present.
(6) They may contain chloroplast, helping in photosynthesis.
Occurrence and function of collenchymas :
The collenchymas usually remain in the hypodermis of stem and also in the base petiole and pedicel. The functions are as follows:
(1) It gives rigidity to plant body.
(2) It has extensible and plastic cell walls, which gives effective mechanical strength.
(3) They may contain chlorophyll and help in photosynthesis.
Types of collenchymas
The simple tissue Collenchymas can be classified into three major types on the basis of the ***thickening. Those are :
(1) Angular : The thickening is localised to the corners of the cell making the cells
pact without intercellular spaces e.g. Stems of Cucurbita, Beta and Datura.
(2) Lacunate: The cells contain intercellular space and the thickening is restri( to the wall in the intercellular spaces, e.g. Roots of Monostera; stems of Ma Salvia, Calotropis.
(3) Lamellate : The radical walls are thin and elongated band li thickening restricted to the tangential wall. e.g. Stems of Clerodendron, Rhamnus.
(v) The walls contain simple pits.
They occur singly or in groups in the soft tissues like pith, phloem flesh of fruit and also in seed coat and fruit walls.They provide mechanical support to the plant body.