Old meristematic cells lose the capacity to divide and transform into permanent tissues. This process of taking up a permanent shape, size, and function is called differentiation.

These are cells which have lost their capacity to divide but are specified to provide strength, flexibility and elasticity to the plant. These tissues can be further classified into simple permanent, complex permanent and special tissues.

Simple permanent can be categorized into parenchyma, collenchyma and sclerenchyma based on their function.

Parenchyma- they are live cells. They are usually loosely packed. This tissue provides support to plants and also stores food. In some situations it contains chlorophyll and performs photosynthesis and then it is called chlorenchyma. Parenchyma which contains large air cavities in aquatic plants is called aerenchyma. The aerenchyma helps in buoyancy.

Collenchyma – These are elongated living cells with small intercellular spaces. Their cell walls are made up of cellulose and pectin. Collenchyma occurs in the peripheral regions of stems and leaves to provide mechanical support and flexibility in plants.

Sclerenchyma – These are long, dead cells with a deposit of lignin in their cell wall. They have no intercellular spaces. Sclerenchyma occurs around the vascular tissues in stems, in the veins of leaves, and in the hard covering of seeds and nuts. They provide strength to the plant.

Epidermis aids in protection against loss of water, mechanical injury and invasion by parasitic fungi. Since it has a protective role to play, cells of epidermal tissue form a continuous layer without intercellular spaces. Epidermis of the leaf contains small pores called stomata. These are necessary for gases exchange and transpiration.

Cork – This is the outer protective tissue which replaces the epidermal cells in older roots and stems. Cork cells are dead and lack intercellular spaces. Their cell walls are thickened by suberin which makes them impermeable to water and gas molecules.