The contrasting temperature between night and day speeds up the loss of chlorophyll from leaves, leaving behind the secondary photosynthetic pigments( carotenoids) that give us the yellow and orange colors.

William Keeton

William Tinsley Keeton (February 3, 1933 – August 17, 1980) was an American zoologist known internationally for his work on animal behavior, especially bird migration, and for his work on millipede taxonomy. He was a well-liked professor of biology at Cornell University in Ithaca, New York and author of a widely used introductory textbook, Biological Science.

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