Deprived of water, they soon wilt. Nearly all plants are at least two-thirds water, and some algae are 98 per cent water. Water fills up the tiny cells that make up each plant and keeps them rigid, like air in a balloon. For a plant, water is also like the blood in your body, carrying dissolved gases, minerals and nutrients where needed. The fine branching veins you can often see on leaves are xylem.
Plants lose water continually by transpiration.
This is the evaporation of water through the stomata. As water is lost through the stomata, more water is sucked up through the xylem to replace it, like drink through a straw. In every plant, water is drawn in continually through the roots, up through the xylem and into the leaves. The oldest plant in the world is a hawthorn bush in New England that is at least 10,000 years old. The longest plant in the world is the rattan vine, which can snake through tree tops for over 150m.