Trees, trees, trees are nearly everywhere and come fall, many of them burst into color. Dogwood, sourwood and blackgum turn deep red in late September. Tulip-trees and hickories turn bright yellow, sassafras a vivid orange and red maples add their multi-colored brilliance. Finally, various oaks put on a dash of russet and maroon. Evergreen trees include Virginia pine, white pine, hemlock, spruce and fir.
Trees enrich our lives throughout the year. They reassure us with the rustle of their leaves, give us shade to soothe our overheated bodies and they bring delight to us when we watch birds nest in their boughs.
However, it is only during the fall that they wave flamboyant foliage that seems to demand our attention.
Autumn leaves seem to scream to us some years while other years they simply speak to us. The intensity of their announcements depends upon weather conditions.
Bright sunny days and cool, but not freezing, nighttime temperatures are requirements for a vivid autumn show. If there is an early frost, the leaves are likely to become brown and drop.
In autumn, chlorophyll, the green coloring agent in leaves that makes photosynthesis possible, begins to decrease. As chlorophyll fades, other colors such as red, orange and yellow appear.
Carotenes and xanthophylls are pigments that produce the lively yellows, golds and oranges of autumn leaves. These pigments are present in summer but they are hidden by the green of chlorophyll. Only when chlorophyll production stops, do they show their presence.
The scarlet, rust and purple leaves are caused by anthocyanin pigments. Unlike the carotenes and xanthophylls, these pigments are not already present in the leaves but are synthesized in the leaf after chlorophyll production stops. When chlorophyll production stops, so does the flow of water and glucose between the leaves and the tree. A layer of cells called the abscission layer, develops to block the flow. Some glucose will be trapped inside the leaf and it will change to anthocyanin pigments with the help of certain weather conditions.
Whatever the weather and however loud its statement, the foliage flashes a "goodbye" to another summer.
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