Figure 33.8 Vascular Tissue Cell Types (A, B) Tracheary elements: (A) Tracheids in pinewood. The thick secondary walls are stained dark red. (B) Vessel elements in the stem of a squash. The secondary walls are stained red; note the different patterns of thickening, including rings and spirals. (C) Sieve tube elements and companion cells in the stem of a cucumber.