Watch and in time the food colouring will be sucked
up the stem along tiny tubes (called vessels) and the petals of the
flower will start to change in colour.
Another way to try this experiment is to get a flower
with a long, thick stem (or a celery stalk with leaves) and slit it
carefully from the bottom and put one end in separate test tubes (with
different food colourings). Your flower (or celery) should have
petals (or leaves) in two different colours.
Did you know that plants need water to live? As
well as absorbing water from the atmosphere (air) through their leaves,
they suck water up through their stems. If you used the celery
stalk for the above experiment you could cut the stalk and see that
the little holes inside are coloured.