Water travels through long, thin tubes running up from the roots through the stems and leaves called xylem.Water moves up the xylem through a process called capillary action.
Capillary action allows water to be pulled through the thin tubes because the molecules of the water are attracted to the molecules that make up the tube. The water molecules at the top are pulled up the tube and the water molecules below them are pulled along because of their attraction to the water molecules above them.