pulvinus(redirected from pulvini)
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pulvinusa mass of thin-walled cells at the base of the leaf petiole in certain plants, forming a swollen area surrounding the vascular tissue. The pulvinus is subject to large changes in TURGOR. For example, in the runner bean the pulvinus is turgid during the day and supports the petiole, so that the leaf is held outwards. At night the pulvinal cells loose turgidity and the leaf droops. These diurnal leaf positions are sometimes called sleep movements. The sudden change in leaf posture observed in Mimosa sensitiva when touched is also controlled by pulvinal cells.
Collins Dictionary of Biology, 3rd ed. © W. G. Hale, V. A. Saunders, J. P. Margham 2005