tissue introduction meristematic tissue ground tissue dermal tissue vascular tissue

Epidermal tissue is a single layer of cells, (except in velamen,pepperomia and rubber plants) that covers the plant body

Functions:

Specialized cells:

Root hairs- absorb water and the material it carries ( minerals).;they increase absorptive surface area of roots

Although single celled, they can be viewed by the eye on rapidly growing radishes

Leaf hairs (trichomes)- 1-2 cells; important in boundary layer and in defense;
* they reflect light to protect against overheating and excessive water loss. This is an incredibly important function for plants in dry regions where excess light may lead to photobleaching of pigments and excess absorption of light would overheat the tissue.

*the layer acts to hold in a layer of humidity 'trapped' between the epidermis and the tips of the trichomes. As water diffuses from a region of high to low density, less water will escape from the stomata to the outside air since the air layer outside the stomata is 'moist' due to its entrapment by the trichomes.
This layer also prevent air moving directly against the stomata which would encourage water loss. Its' rough surface breaks up wind currents.

*When in high density they act to deter herbivory by small animals ( image being an insect walking through a forest of these spiky trichomes). Dependent on species they may have barbs or tips that give off nasty compounds when hit. Some have rigid barbs that impale insects dropping onto them, as with flying insects)

Stomata-

created by guard cells; most abundant on underside of leaves;

regulate diffusion of CO2 into the leaf for photosynthesis as well as regulate loss of water from the leaf;

Stomata respond to turgor pressure

*stomata open when K+ and water enter, thereby increasing turgor pressure in guard cells, thus pushing them apart
*stomata close when K+ and water leave the guard cells, thus leaving them flaccid and closing upon each other.

Salt glands- dump sites for the excess salt absorbed in water from the soil; help plants adapt to life in saline environments;
a crust of salt forms on leaves which tastes bad and the white surfaces act to reflect light

The white mangrove pictured to the right has 2 salt glands on each leaf which exude salts taken up with water.