Permanent Tissue: Permanent tissues are those tissue which have lost the power of cell division. Cells of permanent tissues are matured, assume a definite shape, size and function. On the basis of constituents cell permanent tissues are classified into three types: simple, complex and secretory or special tissues.
Different Kinds of Permanent Tissue
1. Simple Permanent Tissue : It consists of similar cells performing the same function or similar set of functions.
- It is the fundamental tissue which occurs in almost all parts of the body.
- Parenchyma cells show various shapes according to their function e.g., oval (ground parenchyma), cylindrical (palisade parenchyma), irregular (spongy parenchyma) etc.
- Cells are thin walled (primary wall only except wood parenchyma), with large vacuole and wide intercellular spaces.
Functions: It may perform photosynthesis (chlorenchyma), secretion and storage (e.g., idioblasts); provides protection (in epidermis), Mechanical support (by turgidity) and buoyancy (aerenchyma); give rise to secondary meristem for wound healing, regeneration.
b) Collenchyma: Collenchyma (Schleiden, 1839) cells are refractile, non lignified, living cells with pectocellulose thickening in specific areas of walls and without intercellular spaces.
Functions: It provides mechanical strength with flexibility thus allows bending. Besides, it shows growth and elongation of organs, photosynthesize and stores food and prevents tearing of leaves. (Refer: Parenchyma vs Collenchyma)
c) Sclerenchyma: It consists of cells which are dead at maturity. Cells have thickened, lignified walls and highly reduced or sometimes almost closed cell cavity. The cells of sclerenchyma vary in size and shape. They are placed in two groups: the fibres and sclereids.
- It is mechanical tissue which provides rigidity with harness.
2. Complex Permanent Tissue: Permanent tissue with more than one kind of cells that act as a functional unit and carry on a common function.
- Xylem: It is the main water conducting tissue of vascular plants. It is dead tissue except its parenchyma. It also consists of four types: Tracheids, Vessels, Xylem fibres and Xylem parenchyma
- Phloem: It is the food conducting tissue of vascular plants.
(Refer: Xylem vs Phloem)
3. Secretory tissues or Special Tissues: It consists of cells concerned with secretion or excretion of materials.
- Glandular tissue: Cells contain dense cytoplasm an prominent nucleus which secrete substances like enzymes etc.
- Laticiferous tissue (Laticifers): It consists of cells that produce white or yellow alkaloid called latex.