Autumn is a colorful time in Northwest Illinois. The leaves slowly
change color, green giving way to yellow, orange, scarlet, deep red,
and shades of brown and tan. More than any other feature, we recognize
the change of the seasons by the changes in color.
The length of day and temperature are the chief factors that influence
when leaves start to change. The combination of shortening days and
cooler nights triggers changes in the cells between the leaf and stem,
eventually depriving the leaf of water and nutrients.
Leaves get their green color from chlorophyll, the predominate pigment
in the leaf. When the chlorophyll dies due to the lack of water and
nutrients, other pigments, previously masked by the chlorophyll, become
Pigments called carotenoids and xanthophylls give leaves yellowish
and brownish colors. The reds in sumacs and maples are caused by anthocycyanin,
a pigment produced by leaves with a high sugar content.
Abnormally dry weather will reduce the color intensity of these
leaves because the parched leaves do not produce enough sugar.
Thus, a number of natural processes produce the colorful displays
throughout the countryside. In too short time, however, the leaves
will begin to fall, signaling the approach of winter.