Question

what is transpirational stream?

Answer 1

Transpiration is the loss of water from a plant by evaporation.In this process water is taken up by the roots to  leaves of a plant and lost into the air.Transpiration stream is passage of water from the soil to the air in plants.

Answer 2

In plants, the transpiration stream is the uninterrupted stream of water and solutes which is taken up by the roots and transported via the xylemvessels to the leaves where it evaporates into the air of the substomatal cavity.