The xylem cells that most of a wood is made up of are tracheids and vessel elements. Tracheids are elongated cells with thick, lignified cell walls and tapering ends. They are responsible for the transport of water and minerals from the roots to the leaves. Vessel elements are wider than tracheids and have thinner cell walls. They are also responsible for the transport of water and minerals, but they are more efficient in doing so than tracheids.