Transport of rubidium absorbed by the apex of the bean root.

Rubidium-86 was applied to the terminal 5.0 mm region of intact roots for a 6 hour period. The plants were then harvested after 0, 18, 24, 48, 72, or 96 hours additional growth in a rubidium-free continuously renewed nutrient solution. A substantial portion of the rubidium absorbed in a region of the root devoid of functional xylem tissue was ultimately transported to more basipetal regions.