Answer
TRANSPIRATION is the loss of water in the form of WATER VAPOUR from the aerial parts of a plant — mainly through the STOMATA of the leaves, and to a smaller extent through the cuticle and the lenticels of the stem.
Two elements must appear: the water is lost as VAPOUR, and it is lost from the AERIAL parts.
THE WORD VAPOUR distinguishes transpiration from GUTTATION, in which water is lost as visible LIQUID DROPS through hydathodes at the leaf margins.
The three kinds, by how much each contributes: STOMATAL — through the stomata; about 90% of the total CUTICULAR — through the waxy cuticle; small LENTICULAR — through the lenticels of woody stems; least
Transpiration is sometimes called a NECESSARY EVIL: the plant loses enormous quantities of water, but the loss is unavoidable, because the stomata must open to admit carbon dioxide for photosynthesis and water escapes through the same pores.