Epidermal Tissue System: A group of tissues performing a common function irrespective/ regardless (different) of their position and origin is called as epidermal tissue system. Epidermal tissue system is also known as, ‘dermal tissue system’.

• It forms the outermost protective covering of various plant organs which remains in direct contact with the environment.
• It originates from the outermost layer of the apical meristem.
• It performs various functions including protection, absorption, excretion, gaseous exchange, restriction of transpiration, secretion etc.

Epidermal Tissue System Components

1. Epidermis
2. Cuticle
3. Stomata
4. Trichomes

1) Epidermis-

• It is uniseriate in most of the plant organs but in some plants it may be multilayered. e.g. Ficus, Nerium.
• Its cells are parenchymatous and compactly arranged. The outer tangential walls are usually thicker as compared to inner walls.
• Each cell has a large central vacuole & a peripheral thin cytoplasm. They may contain chloroplasts, anthocyanin pigments, tannins, oils and crystals etc.
• Some upper epidermal cells in some monocot leaf become larger, thin-walled, have vacuoles & are called bulliform cells. They play an important role in the folding of leaves during deficiency of water e.g. Grasses.
• In aerial roots of epiphytes, the multiple epidermal cells are modified to velamen which absorbs moisture from the atmosphere.

2) Stomata-

• Stomata are minute pores in the epidermis. Each pore is surrounded by two kidney-shaped cells, called guard cells.
• Guard cells are dumb-bell shaped in the members of the Gramineae family (Monocots).
• Guard cells contain chloroplasts. The inner wall of the guard cell is thickened.
• Guard cells in some cases are surrounded by another group of less modified epidermal cells called subsidiary cells.
• All these components together are termed as stomatal apparatus.
• Usually, there is a large air cavity below each stomata. It is called a substomatal cavity.
• Stomata are absent in roots, underground parts and submerged hydrophytes.
• In xerophytes stomata are sunken in grooves due to which transpiration is greatly reduced, stomata are embedded in Pinus.
• The function of stomata is the exchange of gases and control of transpiration.

3) Cuticle and Wax-

• Cutin is a fatty substance deposited over the outer surface of epidermal cells in the form of a separate layer which is called the cuticle.
• The cutinised walls are less permeable to water. The impermeability depends upon the thickness of the cutin.
• Cuticle is-
  – thick in xerophytes,
  – thin in mesophytes and
  – absent in submerged parts of hydrophytes.
  – It is also absent in underground parts.

4) Trichomes:

• They are found on the stems of plants.
• They are multicellular structures, unlike root hairs.
• They are found in two different types, i.e. scales and hairs.
• These could be branched (scales) or unbranched (hairs).
• These might be stiff or soft in nature.
• These can also act as secretory cells.
• They help in preventing water loss due to transpiration.

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By Team Learning Mantras