pulvinus

1. A prominent swelling at the base of a petiole or pinna. It consists of cells (motor cells) that can rapidly move water into or out of their vacuoles. Such changes in turgor alter the position of the leaf or leaflet and are responsible for certain sleep movements and haptotropic movements. Pulvini are found in many members of the Leguminosae.

2. A thickened region in the stem or leaf sheath of grasses, often containing an *intercalary meristem.