Figure 7.26 Diagram of the steady growth of a plant organ. Water uptake for growth ($dV/dt$) is a simple linear function of the conductance ($L$) between the water supply ($\Psi_o$, usually the vascular system) and the average water potential ($\Psi_{growth-induced}$) of all the expanding cells in the organ (top of diagram, Eq. 7). In the same organ, the cells have walls that can slip a little ($m$) when turgor ($P$) is above a threshold ($P_th$) (middle, Eq. 8). Combining the two relations defines the $\Psi_{growth-induced}$ and $P$ for the organ (Eq. 10, bottom). Notice that the $\Psi_{growth-induced}$ is always lower than the ($\Psi_o$. Furthermore, the position of $\Psi_{growth-induced}$ is determined by $L$ and $m$. (Diagram courtesy JS Boyer)