The correct option is D Vessels
Xylem is one of the two types of transport tissue in vascular plants, phloem being the other. The basic function of xylem is to transport water from roots to shoots and leaves. Xylem tissue consists of tracheids, vessels, xylem parenchyma and fibres. The xylem in gymnosperms consists of only tracheids and xylem parenchyma, vessels are absent (exception - Gnetales).