For this activity you need some cress seeds, two lightproof tins and some damp kitchen towel.

Put a piece of damp towel in the bottom of each tin and sprinkle a few seeds on it.

Put the lid on one tin and leave the other lid off. Put both tins on a sunny windowsill.

Leave the tins and check them each day. If the towel in the open tin dries out, water it.

When the seeds in the tin without the lid reach the top of the tin, take the other lid off and look at the seeds inside.

What do you notice?

What happens if you now leave the lid off? It may take a day or two to happen.