Figure 5

Anatomical planes in BSPO. A) The three anatomical planes used to describe bilaterally symmetrical organisms are ‘midsagittal plane’ (blue), ‘horizontal plane’ (red), and ‘transverse plane’ (purple). B) Anatomical planes used to describe wood (secondary xylem) anatomy. A ‘transverse plane’ (purple), or cross-section, is perpendicular to the ‘apical-basal axis relative to direction of growth’ in an axial organ or to a ‘proximal-distal axis’ in a lateral organ. A ‘radial plane’ (green) follows the two dimensions specified by an ‘apical-basal axis relative to direction of growth’ and a ‘medial-lateral axis’. A ‘tangential plane’ (orange) is perpendicular to a radial plane.