Talk about the secondary walls of tracheid.

In primary xylem, their secondary walls are usually in the form of rings (annular tracheid) or spiral (spiral tracheid) it will be replaced by a secondary tracheid. Secondary xylem tracheid arise after all lengthwise growth has ceased, they are not stretched, they are thicker and more continuous, being interrupted by only a numerous pits (pitted tracheid) in Gymnosperms, In pteridophytes they are ladder like (Scalariform)