Figure 7.25 Water potential fields (three dimensions) in two regions of soybean hypocotyls growing at about 1.5 mm h-1. Fields show highest water potential in the xylem and lowest in the pith and cortex. Steepest field was in the elongating tissues and is growth-induced because the yielding walls in the elongating cells prevented $P$ from become as high as in mature cells. The steeper field allows the growing region to extract water from the mature region when other water sources are not available. Fields were directly measured in the same intact plant while transpiration was prevented, using a microcapillary of a pressure probe. (Redrawn from H Nonami and JS Boyer, Plant Physiol 102: 13-19, 1993).