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"If
you live in the northeastern part of the continent, fall ushers
in a period of spectacular colour in the hardwood forests. Deciduous
leaves change colour before they drop from the tree because of
chemical changes taking place at this time of year. When the
hours of daylight reach a certain shortness, the tree begins
to conserve its resources by cutting off nutrition to the leaves.
Photosythesis ceases and the green chlorophyll fades away, allowing
the other pigments to dominate—yellow, orange and red. But
the unique vividness of North America’s colours are mainly
due to our sunnier fall climate. The brightness of a second set
of pigments—scarlet, purple and blue—depends on the
amount of sunlight falling on the leaf. These mix with the yellow,
orange and red to give us the familiar range of hues.” |
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