The "Girdling Experiment" was performed by plant physiologists to identify the plant tissue through which:

In the girdling experiment, a ring of bark (which includes the phloem) up to a depth of the phloem layer is carefully removed from the trunk of a tree. It is observed that after some time, the portion of the bark above the ring swells due to the accumulation of food, while the tissue below the ring dies first due to lack of nourishment. This demonstrates that phloem is the tissue responsible for the translocation of food (organic nutrients) from leaves to other parts of the plant.