Permanent tissue is divided into three parts. Simple tissue, complex tissue and secretory tissue.
Simple tissue
A permanent tissue whose cells have the same size, shape and structure is called simple tissue. Simple tissue is divided into three parts. These are-
1. Parenchyma: The length, width and depth of the tissue cells are almost the same is called parenchyma. Cells are concentric and round, ovoid, multilobed or oblong. Intercellular spaces exist. Parenchyma tissue consists of stem and root skin, cortex, pith, medulla, pericycle, leaf mesophyll, fruit shell, seed and embryo.
Functions of parenchyma tissue
(i) Chlorophyll-containing parenchyma (chlorenchyma) produces food in the process of photosynthesis.
(ii) Parenchyma of aquatic plants holds air deposits (arenchyma) and helps the plant to float.
(iii) Lower stems, roots, fruits and seeds contain sugars, proteins and carbohydrates.
(iv) Helps in plant wound healing and regeneration.
(v) Provides strength to leaves and stems.
(vi) Stamens keep the plant upright by hydrostatic pressure.
(vii) Propagation by asexual roots and shoots.
(viii) Tissues containing xylem and phloem transport water and mineral salts.
2. Collenchyma: Collenchyma consists of living cells without lignin, having thick walls. Cells are multilobed or elongated. There are no intercellular spaces. Cells are proliferative.
Functions of collenchyma tissue
(i) Collenchyma containing chloroplasts (chlorenchyma) produces food.
(ii) Provides mechanical strength to growing and soft organs of plants.
(iii) Helps plants to bend due to elastic and extensible properties.
(iv) Plant organs do not break easily as they are elastic.
3. Sclerenchyma: Sclerenchyma consists of lignin-rich, thick-walled cells. The transformed cells are dead and do not contain protoplasm. There are no intercellular spaces. Cells are tough and elastic. Cells are longer than wide.
Functions of Sclerenchyma Tissue
(i) Provides mechanical advantage to plants.
(ii) Protects the plant from various environmental stresses and strains.
(iii) Contains waste material in the dead state.
(iv) Protects soft parts of fruits and seeds.
(v) Transports little water.