Transpiration is the water loss from the plant via evaporation. The transpiration stream is the flow of water through the plant xylem from the roots to the leaves of the plant. Xylem are thin tubes where there is adhesion with water due to the polarity of water molecules. The water molecules also stick to each other in a process called cohesion due to polarity caused by hydrogen bonds. The water evaporates out from the spongy mesophyll cells and through the stomata. This water is replaced by water from the xylem via osmosis. This creates suction to pull through more water through the xylem resulting in the transpiration pull, due to the adhesion of water there is a constant transpiration stream.