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09/27/2013

Calling All Leaf Peepers: Check Out The Fall Foliage Forecast...

Notice how parts of the northeast have already reached their seasonal peak! There is quite the show going on in the mountainous terrain of Upstate New York, Vermont, New Hampshire, and northern Maine. Pretty soon we will see our own share of red, yellow, and orange foliage. Parts of Indiana will reach their peak in just a few short weeks as the middle of October rolls around. That line shifts further south through Kentucky by the end of the month...   

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A green leaf is green because of the presence of a pigment known as chlorophyll, which is inside an orangeelle called a chloroplast. When they are abundant in the leaf's cells, as they are during the growing season, the chlorophylls' green color dominates and masks out the colors of any other pigments that may be present in the leaf. Thus the leaves of summer are characteristically green. 

In late summer, as daylight hours shorten and temperatures cool, the veins that carry fluids into and out of the leaf are gradually closed off as a layer of special cork cells forms at the base of each leaf. As this cork layer develops, water and mineral intake into the leaf is reduced, slowly at first, and then more rapidly. It is during this time that the chlorophyll begins to decrease.

Often the veins will still be green after the tissues between them have almost completely changed color. Here is an example...

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Image Courtesy: Wiki

Pigments That Contribute To The Colors

Carotenoids are present in leaves the whole year round, but their orange-yellow colors are usually masked by green chlorophyll. As autumn approaches, certain influences both inside and outside the plant cause the chlorophylls to be replaced at a slower rate than they are being used up. During this period, with the total supply of chlorophylls gradually dwindling, the "masking" effect slowly fades away. Then other pigments that have been present (along with the chlorophylls) in the cells all during the leaf's life begin to show through. These are carotenoids and they provide colorations of yellow, brown, orange, and the many hues in between.

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The reds, the purples, and their blended combinations that decorate autumn foliage come from another group of pigments in the cells called anthocyanins. Unlike the carotenoids, these pigments are not present in the leaf throughout the growing season, but are actively produced towards the end of summer. They develop in late summer in the sap of the cells of the leaf, and this development is the result of complex interactions of many influences — both inside and outside the plant. Their formation depends on the breakdown of sugars in the presence of bright light as the level of phosphate in the leaf is reduced.

The brown color of leaves is not the result of a pigment, but rather cell walls, which may be evident when no coloring pigment is visible.

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-Rick DeLuca

 

Rick

https://www.facebook.com/RickDeLucaWeather

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