Pith, or medulla, is a tissue in the stems of vascular plants. Pith is composed of soft, spongy parenchyma cells, which store and transport nutrients throughout the plant. In eudicots, pith is located in the center of the stem. In monocots, it extends also into flowering stems and roots.
Pith, or medullary, rays function to transport sap through wood. They are a key component to tylosis, a psysiological process by which wooded plants heal injury