green plants use the energy in sunlight to convert carbon dioxide and water into food for the plant and oxygen. (Remember?) Thus as the plant grows, it supplies the atmosphere with oxygen.

     The release of oxygen by this process is easily shown by the following experiment: Fill the large jar with water to within a couple inches of the top. Add the Elodea, and cover it with the funnel.

    The next part is a little tricky. We want to end up with the slender jar filled with water and inverted over the funnel. But first, make the coat-hanger clamp, as shown, and keep it handy. Now fill the small jar to the brim with water. Cover it with your fingers as you plunge it into the larger jar, over the funnel. Attach the clamp. To get any trapped air out of the small jar, suck it out through a piece of tubing or a gradually bent straw.

     Set the entire assembly out in strong sunlight. After a while, tiny bubbles will appear on the leaves and eventually rise in the small jar. These bubbles will slowly force water out of the jar. They are pure oxygen.

    To prove it, when a fair amount of gas has entered the jar (which may take a whole day or more), ignite the wood strip and blow out the flame. Remove the jar from the assembly, and insert the glowing strip. If you’ve collected enough oxygen, the strip will glow brighter. It may even relight.

     You can also do this experiment another way, except you won’t be able to test for oxygen. Simply put the Elodea in a clear drinking glass. Fill the glass with water, and invert it into the jar of water.

     You’ll still be able to see the oxygen forming on the leaves and collecting at the top of of the glass. But the oxygen willbe spread out too much to be able to do anything to the glowingwood strip.