What are cell kind that form the xylem? What are the major features of those cells?

The major cells of the xylem are the tracheids and the vessel elements (these only in angiosperms). The tracheids and the vessel elements are dead cells that have lost their cytoplasm and only their cell wall impregnated with lignin (an impermeable biopolymer) remained. Tracheids form tubes that communicate with neighboring tubes through pores; the vessel elements do not present pores but instead they communicate with the successive vessel element through perforations in their extremities.