Parenchyma : It is the fundamental tissue.
• Tissue first time evolved in bryophyte.
• Thin walled cells, oval or spherical in structure.
• Cell wall mainly composed of cellulose & pectin.
• Large central vacuole for food & water storage.
• Primary function is food storage.
• Some parenchyma involved in excretory substance storage are so called as idioblast, storing such as resin, tannin, gums & oils.
• In typical parenchyma chlorophyll is absent.
• Chloroplast containing parenchyma tissue are chlorenchyma which perform photosynthesis e.g., mesophyll of leaves.
• In hydrophytic plants aerenchyma (a type of parenchyma containing air spaces) provides buoyancy.
• Parenchyma provides turgidity to cells.
Collenchyma : It is the living mechanical tissue.
• Elongated cells with thick corners.
• Localized cellulose & pectin thickening.
• Provides flexibility to plant parts & easy bending of various parts of plant.
• Present only in herbaceous dicot stem.
• Present at thin margin of leaves.
• Few chloroplasts may be present.
• Gives mechanical strength & elasticity to the growing stems.
Sclerenchyma : (Scleras – hard) Strengthening tissue.
• Composed of extremely thick walled cells with little or no protoplasm.
• Cells are dead & possess very thick lignified walls.
• Lignin is water-proof material.
• Intercellular spaces are absent.