Figure 4. Typical images of transpiring P. trichocarpa leaves that were allowed to take up safranin solution.

(A) A control leaf was excised from a well-watered plant, and the petiole was immersed for 2 h in safranin solution. Transpiration during dye uptake was promoted by placing the leaf near a fan at ∼1,000 µmol m⁻² s⁻¹ photosynthetic active radiation. Most leaf veins were stained indicating minimal xylem embolism. (B) Dye uptake in a bench-dried leaf that was subsequently perfused with safranin solution for 2 h. Minor veins exhibited incomplete staining indicating the presence of embolized xylem conduits in minor veins. (C) Dye uptake of a bench-dried leaf subsequently perfused with safranin + HgCl₂ solution for 2 h. Mercury is an aquaporin inhibitor. Staining remained even more incomplete than in (B).