Ringing or Girdling Experiment

The ringing (or girdling) experiment removes every tissue lying outside the vascular cambium of a woody stem - the bark, the cortex, and specifically the phloem - while deliberately leaving the xylem beneath completely untouched, so that the xylem remains the only tissue still physically connecting the upper and lower halves of the stem across the girdled gap; the whole setup is then placed in a beaker of water. After some time, a visible swelling develops just above the upper edge of the ring, caused by organic food material arriving from the leaves above but then being unable to cross the gap where the phloem has been removed, so it simply accumulates there instead. If the experiment is allowed to continue for several days, the roots die first - because with the phloem gone, no food can reach them from the leaves, and roots, lacking chlorophyll, cannot synthesise their own food. Once the roots have died, the upper part of the plant (the stem), which itself depends on the roots for its continued water supply via the ascent of sap, eventually dies …