Evidence for the Downward Movement of Materials Injected into Trees

Movement of the xylem-mobile dyes (acid fuchsin, saffranin O, and gentian violet) after lower trunk or root flare injection was found to occur both upward into the xylem of stems, twigs, and leaves and downward into the xylem of woody roots, at most times of year when soil temperatures equaled or exceeded 5°C (40°F). Similar patterns of movement of xylem-mobile dyes were observed on the following species tested: American chestnut, black birch, eastern hemlock, eastern white pine, red maple, red oak, weeping willow, white ash, and white birch. Downward movement of dye into root systems involved all ages of xylem tissues present within a root, while upward movement was confined to the most recently formed xylem growth ring. Evidence is presented of initial downward dye movement followed by later upward movement within a 12-hour period. Our results suggest that xylem-mobile materials injected into trees may be distributed into stem, leaf and root tissues under most growing conditions.