Colored Carnations 

What you need:

bullet 24 hours 
bullet white carnations (1 would be enough, but you can get a few and do different colors)
bullet flower vase(s)
bullet food coloring
bullet water

Directions:

bullet Fill vase 1/4 full of water.
  
bullet Add a fair amount of food coloring (10 to 20 drops) or more if your vases are large.
  
bullet Put a flower in each vase and let it sit for a day.   Just like you would for any cut flower, have an adult trim the stem at an angle before placing it in the vase.
  
bullet Check back every few hours to see how it's working.
  
bullet At the end of your experiment, examine the whole plant carefully (stem, leaves, buds, petals, etc) and discuss your observations with family and friends.
    

What Happened:

Most plants "drink" water from the ground through their roots.  The water travels up the stem of the plant into the leaves and flowers.  The plant uses the water to make food.

When a flower is cut, it no longer has roots.  But the stem of the flower still "drinks" up the water and provides it to the leaves and flowers.

Note:  Red and blue food coloring work the fastest.