Transverse view of pine cambium & derivatives

A cross (transverse) section of eastern white pine (Pinus strobus) stem showing vascular cambium. The blue-stained cells at the bottom represent secondary xylem and, as is typical of gymnosperms, are primarily composed of tracheids (note the bordered pit pairs in their radial walls).

The vascular cambium is the second or third layer of cells outside of the secondary xylem, and adjacent to the xylem are xylem derivatives. Note how thin are the tangential walls of the cambial cells. Mature secondary phloem cells can be seen to the top and are recognized by blue colored (due to the aniline blue staining) deposits representing callose.