radial section: Pinus stem magnification: 400x iron-alum hematoxylin and safranin stain

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. The uniform wood of Gymnosperms like Pinus consists almost entirely of longitudinally oriented bands of narrow, pale staining tracheids. Emerging at right angles are narrow xylem rays, one cell thick and a few cells high, and composed of clear, thin walled parenchyma cells. 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. The membrane of each bordered pit is marked by a pale, thin, porous outer margo and thicker, darker, inner torus.