Nature Bulletin No. 38   October 27, 1945
Forest Preserve District of Cook County
Clayton F. Smith, President
Roberts Mann, Supt. of Conservation

****:AUTUMN COLOR

This is a colorful fall; one oil the best in recent years. Folks who get a 
thrill out of masses of color have been reveling in the rich pageantry of 
the woodlands. It started about six weeks ago when the sumacs turned 
magenta and crimson. Gradually the Smaller species of trees and then 
the larger ones began to "turn". The leaves of the hard maple became a 
brilliant orange-yellow, the red maples scarlet, the hickory and the ash a 
rich yellow, the oaks mingled red-and-green, deep red, or even purple. 
Only such trees as the elms and sycamores turned a nondescript brown.

In the southeastern portion Or Cook County the yellow of a few 
sassafras and the peculiar scarlet of a few sour gum trees punctuate the 
landscape. Along the banks oi the upper Des Plaines River the hard 
maples created a fairyland of beauty.

In all the world, only in North America -- and in one portion of North 
America -- does this colorful phenomena occur. 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.

Why? The elfin Jack Frost of poetry and fancy is traditionally the artist 
to whom credit is given. As a matter of fact, the principal function of 
frost is to hasten the death of the chlorophyll--the substance that 
produces the green color in leaves. 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.

But until your children are nearly grown and can glibly spell 
"xanthophyll" and "erithrosin" and "anthocyanin", give Jack Frost the 
credit.