If a potted plant is covered with a glass jar, water vapours appear on the wall of glass jar. Explain why?

Explanation

Epidermis of a leaf is not continuous at all the places due to the presence of small pores called stomata. Each stoma is bounded by a pair of specialised epidermal cells or two kidney-shaped cells called guard cells. The concave sides of these guard cells face each other and have a space forming the stomatal opening.
The stoma allows gaseous exchange to occur during photosynthesis and respiration. During transpiration water vapour escapes through stomatal opening, this results in appearance of water vapour on the wall of glass jar, if a potted plant is covered with it.