Figure 6. A cross section of the stem of a Wisteria sinensis (Leguminosae) stem.  Note that the xylem vessels were initially small in diameter (i.e., near the central pith), while this seedling was self-supporting, but those produced later (i.e., nearer to the vascular cambium and bark), while it was climbing, were much larger.  Photograph by Francis E. Putz.