The term trichome includes all unicellular and multicellular appendgaes of the epidermis. Most trichomes are simply epidermal cells that have a drawn out cuticle. The majority of these form hair-like structures and are thus often referred to as "hairs". The most common trichome is the unicellular hair but there many other types as well.
Multicellular trichomes come in many disparate varieties. These include the multicellular hair, branched trichomes, and secretory trichomes. As their name suggests, secretory trichomes secrete various substances such as: sugar solutions (nectar), digestive enzymes which dissolve trapped insects and animals, and excess salt solution. Often times, these trichomes fill defensive roles and secrete anti-herbivory substances (irritants) which deter predation. A familiar example would be the poisonous irritating compounds found in the stinging nettle.
Not surprisingly, when you look close enough, you will find trichomes covering most surfaces of cotton plants. They are a multicellular type known as stellate and can be seen in the photographs to the left. They posess a single cell as the base and have four hair like extensions which project from this base, making a five cell complex. Almost every trichome on the cotton plant is of this type.
