transverse or cross section: Pinus stem magnification: 100x iron-alum hematoxylin and safranin stain

Well defined annual rings of large diameter spring wood and smaller diameter autumn wood are composed entirely of narrow, relatively thin walled tracheids. The lumen of many tracheids is crossed by branched trabeculae. Tracheid side walls contain large circular bordered pits that function to move water from tracheid to tracheid while preventing air flow from embolized tracheids.

Gymnosperms like Pinus rely entirely on tracheids for water flow and mechanical support. True xylem vessels and wood parenchyma are lacking. While fibers are generally absent older stems may contain some fiber tracheids.

Xylem rays are uniseriate and composed of clear, thin walled parenchyma cells.