Figure 5.

Profiles of surface pH along the apical 12 mm of one growing root (position 0 refers to the tip of the root cap) measured consecutively in stagnant media at pH 7.8, 6.5, and 4.2, as indicated. A distal acidic region around the meristematic zone (between about position 0–1.5 mm) can be distinguished from a proximal acidic zone along the elongation zone proper (about 2.5–8 mm). The pattern as such is independent of bulk pH, although the pH range covered by one profile tends to decrease with decreasing bulk pH. Note that the complete profile of surface pH is more alkaline than the bulk at medium pH 4.2. Similar results were obtained from four repetitions with different plants.