The tendency of a sessile organism (a leaf or flower, that has no stalk but is attached directly to the stem) or structure to grow horizontally to the ground or perpendicularly to the line of gravity: The condition of diageotropism can be seen in tree branches or roots.

Diageotropism can be described as a response of a plant to gravity in which a part of the plant adopts a horizontal position.

Diageotropism can also characterize the tendency of growing parts, such as roots, to become oriented at right angles to the direction of any gravitational force.