Transpiration:

Transpiration is the loss of water from the plant surface through evaporation.

Functions of cuticle and lenticels:

This loss may occur through stomata in leaves, through the cuticle present on leaf epidermis, or through special openings called lenticels present in the stems of some plants.

Stomatal Transpiration:

Most of the transpiration occurs through stomata and is called stomatal transpiration.

The function of Mesophyll Cell in Transpiration:

The mesophyll cells of the leaf provide enormous surface area for the evaporation of water. Water is drawn from the xylem into mesophyll cells, from where it comes out and makes a water film on the cell walls of the mesophyll. From here water evaporates into the air spaces of the leaf. By diffusion, water vapors then move from the air spaces towards the stomata and then pass to the outside air.

Note:

Roughly 90% of the water that enters a plant is lost via transpiration.