You know that plants need water to grow, make seeds, and stay healthy.
Fill a plastic container with water and add a few drops of food coloring.
Cut a small piece of the stem off of the flower.
Put the flower in the container of food coloring and water.
Check every few hours to see how the petals are changing color. The only way the petals can change color is if the food coloring travels up the stem and goes to the petals.
After about one day, the petals of the flower will turn from white to the color of the food coloring.
Here's how this works. The leaves and petals of plants have lots of small holes called stomates. They're too small to see. Water evaporates through these holes. This is called transpiration. After the water evaporates, the plant needs more water to grow.
If the flower is planted in soil, the roots of the plant get the water from the soil and then the water travels up through its stem.
But, if the flower is in a container of water, it doesn't have any roots so it just sucks up the water through its stem.
So, now when you see a flower that's an unnatural color, like a bright green carnation on St. Patrick's Day, you'll know how it was made. You can also dye a flower two different colors by splitting the stem in half and putting it in two different containers of colored water.