How do plants drink water?

The longer answer

Water likes to stick to things. In a wide glass you hardly notice, but in a very thin tube, the water clinging to the sides drags the rest of the water up with it. Scientists call this capillary action.

A plant's stem is packed with these thin tubes. Leaves have tiny holes that let water escape into the air, and as it leaves, it tugs on the water behind it, pulling more up the stem like someone sipping through a straw.

You can see it happen. Stand a white flower in water with food coloring in it, and the colored water climbs up the stem and tints the petals.

Three things to know

• Trees pull water higher than a ten-story building. The tallest trees pull water from their roots to their top leaves with the same straw trick, without any pump at all.
• Celery stalks have straws too. Stand a stalk in colored water overnight and the color creeps up into the leafy top.
• A paper towel drinks the same way a flower does. Dip a corner in water and the wet line creeps upward through thousands of tiny gaps in the paper.

Try it at home: a color-changing flower

1. Put a little water in two glasses, and stir plenty of blue or red food coloring into one.
2. Ask a grown-up to trim the stems of two white flowers, like daisies or carnations.
3. Stand one flower in each glass and leave them overnight.
4. In the morning, compare the petals. Which flower changed color, and how did the color get there?

A celery stalk with its leaves on works too. Cut across the stalk afterward to see the colored dots where the tiny tubes are.