Fall Colors

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According to the USDA "three factors influence autumn leaf color; leaf pigments, length of night, and weather... The timing of color change and leaf fall are primarily regulated by the calendar, that is, the increasing length of night. None of the other environmental influences -temperature, rainfall, food supply, and so on- are as unvarying as the steadily increasing length of night during autumn. As days grow shorter, and nights grow longer and cooler, biochemical processes in the leaf begin to paint the landscape with Nature's autumn palette..."