What is "sessility"

Sessility may refer to:

• Sessility (motility), organisms which are not able to move about
• Sessility (botany), flowers or leaves that grow directly from the stem or peduncle of a plant
• Sessility (medicine), tumors and polyps that lack a stalk
• In crystallography, a type of dislocation that is not able to move in the slip plane (as opposed to glissile dislocations).

In botany, sessility (meaning "sitting", used in the sense of "resting on the surface") is a characteristic of plant parts which have no stalk. Flowers or leaves are borne directly from the stem or peduncle, and thus lack a petiole or pedicel. The leaves of the vast majority of monocotyledons lack petioles.

In addition to these plants, many insects practise sessile nesting practices. For example, Brachygastra scutellaris will build its nest starting with a sessile initiation onto a tree upon which the primary comb is built. Secondary combs are built randomly on this primary comb.

In biology, sessility (in the sense of positional movement or motility) refers to organisms that do not possess a means of self-locomotion and are normally immobile. This is distinct from the second meaning of sessility which refers to an organism or biological structure attached directly by its base without a stalk.

Sessile organisms can move through outside sources (such as water currents) but are usually permanently attached to something. Organisms such as corals lay down their own substrate from which they grow. Other organisms grow from a solid such as a rock, dead tree trunk, or a manmade object such as a buoy or ship's hull.