Leaves have a color for every season of the year. With the coming of killing frost the leaves change into fall colors.
Spring brings a delicate light green. The green darkens over the summer. About mid August yellow creeps into the green.
Over the week after killing frost, especially if there is another one or two frosts, that yellow spreads. Reds begin to appear. Length of day may trigger the changes, but frost makes the leaves change into fall colors.
One interesting experiment in my science classes was the chromatography of leaf pigments. It isn’t hard to do.
Take an eight inch or more long strip about 1 1/2 to 2 inches wide from a filter. A finer grained one is best and some coffee filters are like that.
Have a tall jar so the strip barely touches the bottom and folds a little over the top. Tape the fold onto a pencil so the strip will dangle down from the pencil into the jar.
Draw a line in pencil (it must be pencil) across the strip 1 1/2 inches above the end.
Gather a couple of leaves. These can’t be dried out These can be spring, summer or fall leaves.
Place the leaf over the line and rub it with the side of a penny. You may have to move the leaf and repeat the rubbing to get a dark spot on or barely over the line.
Pour isopropyl or rubbing alcohol in the jar an inch deep. Hang the strip into the jar and wait. You will see the alcohol move up the strip. When the alcohol reaches the top of the strip, take it out and look what happened to the leaf spot.
The alcohol pulls the spot up the strip with it. But not all of the spot moves the same. There should be darker spots of slightly to very different colors in a line over the spot. These spots will fade as the strip dries so look quickly.
Using acetone or ethanol works too and can give slightly different spot arrangements. Each likes different parts of the leaf pigments better than others and carries them farther.
The striking thing for many students was that green leaves could have more than one green and colors other than green in them. The colors weren’t always the colors they saw. In class we discussed what the different chlorophylls and anthocyanins were and did.
Now I stand and watch as the leaves change into fall colors.