Talk about the vessels of xylem.

Highly specialized conducting element of the most evolved vascular plants (angiosperm) made up of dead cells called vessel elements or vessel cells. These dead cells form a large diameter cavities bounded by a lignified cell wall. During the differentiation process vessels are formed by the breaking down of the transverse wall forming the perforation plate. If the transverse walls are extensively perforated they form compound perforation plates, whereas if they are completely dissolved they form a simple perforation plate. As in tracheid vessels may be annular , spiral, reticulate or pitted.