September 2, 2011
I have a home in the upper Hudson Valley near the New York State-Massachusetts border. The Northeast and Mid-Atlantic States were just hit by the enormous rains and flooding caused by Hurricane Irene last weekend. Driving around looking at the swollen rivers and streams and the downed trees in some areas I realized that there was another, more seasonal, change in some of the trees. They were beginning to turn red, the way they do every autumn.
Autumn is one of my favorite times of year in the Northeast. Ideal autumn weather is bright, warm days and cool, crisp nights. The days grow shorter, the nights longer, pumpkins and tomatoes are ready to harvest, and yes, school is starting up again.
I wrote a series of books about the Seasons Across America. The photograph above is one that I took of autumn leaves for my book AUTUMN ACROSS AMERICA. Here is the explanation I wrote in that book about the change of color:
Yellows, oranges and golds are produced in leaves by pigments (coloring materials) called carotenes, reds by pigments called anthocyanins. You can’t see these colors during the growing season because they are hidden by the bright green of chlorophyll. Chlorophyll is the green pigment that helps plant cells use sunlight to make food, a process called photosynthesis. In autumn, as days grow shorter, chlorophyll production slows down and the green fades, revealing the yellows of the carotenes.
When chlorophyll production stops, a layer of woody cells develops and begins to seal off the leaf from the twig. Water can no longer reach the leaf. As the trapped sugar breaks down, red anthocyanin colors are produced by exposure to sunlight. Cloudy, rainy autumn weather prevents the red colors from forming. Ideal red colors come when autumn has bright sunny days followed by cool nights.
Posted by: Seymour Simon
