The experiment shows a plant in which the outer part of the stem containing phloem was removed while the xylem was kept intact. the setup was kept in the sun for a week and watered regularly. on the eighth day, the leaves appeared turgid and the upper part of the stem above the cut in the phloem appeared swollen. what could be the reason for this?

Vascular tissue of plants which consists of xylem and phloem. Xylem transport water and minerals from the root to the upper parts of the plant. Phloem transports food and nutrients from the leaves to the lower parts of the plants. 

In the experiment, since the xylem was kept intact, the transport of the water from the root to the upper parts of the plant was also intact. However, since it was in the sun, the plant was able to perform photosynthesis. Photosynthesis is a process during which plants produce food (carbohydrates) in the green leaves. That food should be transported through the phloem to the lower parts of the plant. But, the phloem was removed, so the food remained and accumulated in the upper parts of the plant. All of these is the reason why the leaves appeared turgid and the upper part of the stem above the cut in the phloem appeared swollen.