Simple Permanent Tissue
Simple Permanent Tissue
Permanent tissue that are composed of only one type/kind of cell thus forming a homogenous mass is called Simple Permanent Tissue. On the basis of functional and structural variation, they are of three types:-
It is composed of only living cells. Cells are arranged loosely with intercellular spaces. Cells are isodiametric in shape with oval , spherical or polygonal in outline. Cell wall is very thin composed of cellulose. They are considered as “Universal Tissue” as it is found in almost all plant and each part of the plants.
Modified parenchyma– Sometimes parenchyma tissue may be modified to form special function other than storage of food called modified parenchyma. They are:-
Like parenchyma, collenchyma is a type of simple permanent tissue composed of little elongated living cells. Peculiar feature of collenchyma is presence of unevenly thicken cell wall due to deposition of cellulose and pectin against the intercellular spaces. Due to this thickening, it is elastic in nature hence function to give tensile strength. It is thus called living mechanical tissue which can support plant in stretching without damaging them. It is totally absent in roots and monocots.
On the basic of arrangement and thickening laid down they are of three types:-
- Lamellar- Cells are arranged in tangential row and thickening develop at tangential wall. Eg. Sunflower
- Angular- Cells are angular or polygonal and thickening develops at the angles only. Eg. Cannabis, Datura
- Lacunate- Cells are with inter cellular spaces as thickening deposits only bodering the intercellular spaces.
Unlike parenchyma and collenchyma ,sclerenchyma is totally a different type of simple permanent tissue. It is composed of dead cells which are thick walled and lignified with the cell cavity(lumen) highly reduced with here and their pits(unthicken area) as well. It is the chief mechanical tissue which can withstand various types of force such as bending ,twisting etc. without damaging the plant organs. Sclerenchyma tissues are of various shaped and sized ,thus are classified into two types:-
- Sclerenchyma fibre-They are elongated, compactly arranged without intercellular spaces , spindle shaped having both end tapered. They are however polygonal in transverse section. They always develop in group along the longer axis of plant. Fibre is a chief mechanical tissue which can bear various type of forces like bending, twisting etc. as pointed end of one sclerenchyma fibre get interlocked with the neighbouring fibre ,thus making it the strongest tissue among the plants.They are commercially utilized in mat , cordage etc.
- Sclereids or stone cell- They are short,broad dead and highly thick walled lignified as fibre. But unlike fibre,sclereids may develop singly or in group. Grittyness of flesh of pear and apples , hardness of sead coat is due to sclereids. Sclereids are of various shapes , accordingly they are named variously as follows:-
Brachysclereids– Iso diametric in shape. Eg. Pith , cortex
Astrosclereids– Star shaped . Eg. Legume seed
Macrosclereids– Elongated , columnar . Eg. Legume seed
Osteosclereids– Elongated with the end dilated hence look like bone.
Filiform– Elongated and sparingly branched . Eg. Olea