Morphologically, the DZ in the wild
type (WT) is marked by the appearance of epidermal root
hairs on the
external surface of outer cell files (trichoblast) and the existence of fully differentiated xylem for internal cell files (Dolan et al, 1993; Ishikawa & Evans, 1995; Beemster et al, 2003; Verbelen et al, 2006; Zhang et al, 2010; Mähönen et al, 2014).