Leaves: Seeing Green
 

	Fun Experiment to Try at Home!
		Purpose To see the pigment chlorophyll, the source of green in leaves and grass.   Materials - blades of grass - paper plate - sheet of white paper   Procedure 1.  Break off blades of grass, and use them to cover the bottom of the paper plate. 2. Set the plate of grass on the ground, and place the sheet of white paper on top of it. 3. Step on the paper, and twist the ball of your foot to crush the grass without tearing the paper. 4. Now lift the paper and look at it — the green stain on the paper is chlorophyll from the grass.   Sum It Up! Why do these dead leaves stay on the stem when the leaves outside are falling? Because they died before the abscission layer dissolved. Remember: It's the chemical produced by the decrease in daylight that causes leaves to fall, not the death of the leaves themselves.

A period of bright autumn days and cool nights produces the most vivid colors in leaves.
 
The leaves of evergreen trees stay green and remain on trees all year long. The leaves of deciduous trees, however, are green in the spring and summer only; then they change colors and fall off during autumn.

Where does the green come from, and where does it go in the fall? The pigment chlorophyll produces a leaf's green color. Like all pigments, it absorbs, reflects, and transmits visible light. As a deciduous tree prepares for winter, many of the molecules in its leaves, including chlorophyll, break down and are recycled. This means the atoms in the chlorophyll molecule of a deciduous leaf are used to make other kinds of molecules, which are then stored in different parts of the tree.

With the green chlorophyll gone, the yellow and orange carotene pigments in the leaves can be seen. Because carotene molecules are more stable (don't break down as easily), they remain after the chlorophyll is gone.

Autumn's weather also helps create the glorious red and purple colors we see in fall leaves. These colors are from anthocyanin pigments, which need both high light intensity and high sugar content to be produced. The high light intensity from bright fall days helps create a high sugar content, and autumn's cool nights prevent the sugar from leaving the leaves.

For more information on leaves, seeJanice VanCleave's Plants(New York: Wiley, 1996)