Xylem vessels, light micrograph. These are from the wood of a coast redwood tree (Sequoia sempervirens), the tallest tree in the world. The xylem vessels run horizontally here. Xylem is a vascular tissue in plants, whose main role is to carry water from the roots to other parts of the plant. Xylem cells (tracheids) are composed of dead tissue that provides the main support for the plant. In conifers such as the coast redwood, which is a softwood, tracheids are the only cell type for transporting water. In hardwood plants, which are typically flowering plants rather than cone-bearing ones, cells called vessel elements aid water transport.