The components of xylem with various patterns of secondary wall thickenings are seen inI. Tracheids    II. Vessels    III. Xylem parenchyma    IV. Xylem fibers

Only the main conducting elements of xylem such as tracheids and vessels have different types of secondary wall thickenings such as annular, spiral, scalariform, reticulate and pitted thickenings. Other components do not have such patterns of secondary wall thickenings.