This portion is a rectangle bounded roughly by a line drawn from southeastern Missouri to northeastern Georgia, and by another line from southern Minnesota through Quebec, east of the Great Plains. Even here in the Chicago area we have none of the spectacular splotches of color contributed by the black gum and the flowering dogwood. In the Dunes of Indiana we find the more modest corolla I of the tulip tree and beech, but not here. The elfin Jack Frost of poetry and fancy is traditionally the artist to whom credit is given. Given a mild Indian summer with lots of brilliant sunshine, certain chemicals, previously held inactive by the dominate chlorophyll, develop strongly and produce brilliant leaf color.
Xanthophyll produces the yellows, erithrosin and carotene the reds, and anthocyanin the blues.
Combinations of these produce such colors as orange, magenta and purple. The browns are colors of dead vegetable tissue. Too many and too heavy frosts deaden the fall colors, causing the leaves to turn brown and drop off early. And the less moisture, after the first light frost, the better. Only certain deciduous trees under certain conditions, such as we have in this rectangle of North America, produce the brilliant fall spectacle we love.