"Girdling Experiment" was performed by Plant Physiologists to identify the plant tissue through which:

"Girdling Experiment" was performed by Plant Physiologists to identify the plant tissue through which food is transported. On the trunk of a tree a ring of bark up to a depth of the phloem layer, can be carefully removed. In the absence of downward movement of food the portion of the bark above the ring on the stem becomes swollen after a few weeks. This simple experiment shows that phloem is the tissue responsible for translocation of food and that transport takes place in one direction, i.e., towards the roots.