Epidermis

The epidermis is the outermost cellular layer which covers the whole plant structure, i.e. it covers roots, stem, leaves, flowers and fruit. It is composed of a single layer of living cells, although there are exceptions. Epidermis is usually closely packed, without intercellular spaces or chloroplasts. The outer walls, which are exposed to the atmosphere and usually thickened, and may be covered by a waxy, waterproof cuticle which are made up of cutin. Apart from the normal epidermal cells there are also stomata in the epidermis of leaves and stem. A stoma is an opening (pore) which is bounded by two beanshaped cells called guard cells . The guard cells differ from normal epidermal cells in that they have chloroplasts and the cell walls are thickening unevenly; the outer wall is thin and the inner wall (nearest the opening) is thick. The thin-walled epidermal cells of roots give rise to root hairs. Hair- like outgrowths may also be found in the epidermis of leaves and stems.

• the epidermal cells protect the underlying cells,
• the waxy cuticle prevents the loss of moisture from the leaves and stems,
• the transparent epidermal cells allow sunlight (for photosynthesis) to pass through to the chloroplasts in the mesophyll tissue,
• the stomata of leaves and stems allow gaseous exchange to take place which is necessary for photosynthesis and respiration,
• water vapour may be given off through the stomata during transpiration,
• the root-hairs absorb water and dissolved ions from the soil.