Turgor Pressures in Phloem: Measurements on Hevea Latex.

Hydrostatic pressures in laticiferous phloem tissues of Hevea brasiliensis trees exhibit a diurnal fluctuation, with minimum values occurring during the day. Pressure decreases with increasing height up the trunk, the gradient becoming greater under conditions of rapid transpiration. Sieve-tube turgor must be controlled independently if pressure-flow is to occur in the expected direction.