Protective permanent tissues form the outermost layers of plants, shielding them from the environment and various stresses.
These tissues primarily function to protect the plant body from:
- Desiccation: Preventing water loss.
- Mechanical Injury: Providing a physical barrier against damage.
- Infection: Blocking the entry of pathogens.
Protective tissues are typically found in the epidermis and cork.
Epidermis
- The epidermis is the outermost layer of cells covering leaves, stems, and roots.
- Epidermal cells are generally flattened and closely packed, often covered with a waxy cuticle (cutin layer) to reduce water loss.
- In some plants, the epidermis may bear hairs (trichomes) or other specialized structures for protection.
Cork
- As plants age, the outer protective tissue, the epidermis, is replaced by cork (or phellem).
- Cork cells are dead at maturity and contain suberin, a waxy substance that makes them impermeable to water and gases.
- Cork provides insulation and protection against mechanical injury and infection.
- Cork is derived from a secondary meristem called the cork cambium (or phellogen).
In summary, protective permanent tissues are vital for plant survival, providing a barrier against environmental stresses and maintaining the plant's integrity.
