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Tissue System in Plants

A group of tissues carrying out a common function irrespective of their position is called a tissue system. There are 3 types of tissue systems in plants.

  1. Dermal /Epidermal tissue: They are protective tissues.
  2. Vascular tissue: Conduction of water, minerals and organic food materials.
  3. Ground tissue: All tissue except dermal and vascular tissues.

Dermal Tissue

  • Dermal tissue (or epidermal tissue) forms the outermost protective covering of a plant body.
  • It is derived from specialized cells called dermatogens.
  • It is composed of epidermal cells, stomata and different epidermal outgrowths such as trichomes and hairs.

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  1. Epidermis:
  • The epidermis is usually uniserate (single layered).
  • It is the outermost covering of a plant body.
  • The cells are parenchymatous with small amount of cytoplasm and a large nucleus.
  • The epidermis is covered on the outer surface by a thick waxy coating called cuticle. It protects the plant from water loss, mechanical injury and pathogen attack.
  • Cuticle is absent in the roots.
  1. Stomata
  • Stomata are special structures found on the epidermis of leaves.
  • Gaseous exchange and transpiration takes place through the stomata.
  • Each stoma is composed of two bean shaped cells called guard cells which enclose a stomatal pore.
  • Certain epidermal cells around the guard cells modify their shape according to the guard cells and are called subsidiary cells.

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  • In grasses, the guard cells are dumbbell shaped.
  • The outer walls of guard cells are thin while the inner walls are highly thickened. The guard cells contain chloroplasts.
  • The opening and closing of stomatal pore is regulated by the guard cells.
  • The stomatal pore, guard cells and the surrounding subsidiary cells are together known as the stomatal apparatus.
  1. Epidermal outgrowths
  • In some plants, unicellular or multicellular hairs are found on the epidermis.
  • Some hairs are secretory in function (e.g. Nepenthes).
  • Trichomes: Epidermal stem hairs are called trichomes. They are usually multicellular and prevent water loss by transpiration.
  • Epidermis of root is called piliferous layer or epiblema. Unicellular outgrowths from this piliform layer are called root hairs. They help in absorbing water from soil.

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