Laura Burgess, aged 10, of Williamsport, PA.for her question:

Does the frost make the leaves change color?

Flowers, fruit and leaves get their colors from special plant substances. These substances have names as beautiful as the colors they paint. There are three main color substances. Each is a different chemical. Each eon vary its tones to make many shades of color. The one we know beat is the chlorophyll which paints the leaves green. It varies from the pale green of a near birch leaf to the deep, tropical green of a fog leaf.

Next in popularity comes carotinoid. This gives the color to the carrot, the pale yellow to the lemons, the gold to the corn. It ranges from pale yellow to vivid orange‑red. Strange to say, carotinoid is present in most green leaves all summer long. The strong green chlorophyll just paints over it and hides it from us.

The bright reds, blues and purples are painted by stuff called anthocyanin. In some plants, it, too, is there all the time, hidden by the green chlorophyll. In other plants it is made only when the delicate chlorophylls and carotinoids break down. These three plant paints give us most of the beautiful colors of the gardens, fields, forests and orchards.

Chlorophyll is made from sunshine, moisture and plant sugar. It is strong enough to mask and hide the other plant paints during the summer. Pines and evergreens can keep it bright all winter. This is because they protect their leaves from frost and dry weather with heavy coats of wax.

The thin delicate leaves of the birch, oak and elm have no such protection. The weather must be gust right or their chlorophyll breaks down. These trees lose their green color even during a long warm summer drought, A green deaf will fade also when it is injured, because the broken veins shut off the supply of moist sap. Chlorophyll, then, dust have sunshine and moisture to stay green.

So naturally the delicate thin leaves cannot stay green after the frost. For this freezes the needed moisture in the veins solid.  It also tends to dry the air around the tree. However, most trees do not wait for the frost to put on their fall colors. The chlorophyll begins to break down as the autumn days grow shorter. For then the necessary hours of sunshine are cut down.

The trees begin by shutting off the supply of sap to the leaves. The greens fade for want of moisture and long hours of sunlight. Then we see the taffy colors of the carotinoids that were hidden all summer. Here and there the anthocyanins add reds, blues and violet tints to the candy colors of fall.

The trees put on their gayest colors when fall weather is cold and moist. Even the reds and yellows are dull when fall weather is dry and warm. So, Jack Frost may help to brighten the colors of fall. But the trees try to be all decked out in their best before he arrives.