The Autumn Foliage 
THE prevailing color of the summer vegetation is 
green, and so closely do we associate this color 
with the foliage of vegetation as a whole, that we 
scarcely think of it as a color, but rather as the normal ef- 
fect. Throughout most temperate regions of the earth, 
and particularly in North America and Europe, the onset 
of the autumn season initiates a riot of color in foliage 
with which, in favorable sections, -there is nothing in 
nature to compare. Regarding these eiTects in central 
Europe it has been written : "What abundance of color 
is then unfolded ! The crowns of the pines bluish-green, 
the slender summits of the firs dark green, the foliage of 
hornbeams, maples, and white-stemmed birches pale 
yellow, the oaks brownish-yellow, the broad tracts of 
forests stocked with beeches in all gradations from yel- 
lowish to brownish-red, the mountain ashes, cherries and 
barberry bushes scarlet, the bird cherry and wild service 
trees purple, the cornel and spindle-tree violet, aspens 
orange, abeles and silver willows white and gray, and 
alders a dull brownish-green. And all these colors are 
distributed in a most varied and charming manner * * *." 
While the autumn coloring of trees and shrubs in the 
Mississippi Valley region is scarcely equal to that of New 
England and the Appalachians, except during the most 
favorable seasons, it is always attractive and worthy of 
an analysis which may serve to relate effect and cause. 
Contrary to the popular belief, the change of color in 
the autumn season is not an index of death, but rather an 
indication of gradual maturity which may lead toward 
death. In general, the autumn colors may be classed as 
yellows and reds, although orange, brown, bronze, and 
purple may be found in the varied effects. The yellow 
and orange tints are due primarily to a group of pig- 
ments called xanthophyll, in reality, xanthophylls and 
carotins, while the reds are almost invariably anthocyanin. 
These names mean little more than the colors themselves 
until one discovers that there are extensive groups of 
plant pigments which have merited careful chemical and 
physiological study and classification. 
Even the green leaves of the summer season exhibit 
sometimes a shade of yellow, and with a host of plants 
yellowing is associated with waning vigor and health. 
As a matter of fact, yellows are always present in the 
leaves, associated with the chlorophyll, or leaf green, so 
that when the conditions become unfavorable for the 
maintenance of health, the chlorophyll is broken down 
and the yellow pigments (in those plants which do not 
produce reds) become more conspicuous. These yellow 
pigments, like the chlorophyll, are not sap colors ; more- 
over, they are more stable than the green, and may 
persist until the living cells are killed by cold. One of 
these yellow pigments, carotin, is also characteristic of 
many fruits, of certain mushrooms, and it is even found 
in various animal tissues. 
In the vicinity of St. Louis yellow is the autumn color 
of the ginkgo among conifers, likewise of many species 
of willow, poplar, birch, and certain maples, also of box 
elder, mulberry, elm, hornbeam, chestnut, tupelo, and 
sycamore. It appears as an undertone where browns 
and reds are more prominent, as in the sassafras and 
horse-chestnut. The yellow in some foliage plants con- 
spicuous in the summer season, as in certain varieties of 
coleus, are simply indicative of a preponderance of yel- 
low pigment, veiling the leaf green but not excluding it. 
The red pigments of autumn leaves are cell-sap colors, 
and nearly all such anthocyanins are soluble in the 
aqueous solution constituting the plant juices. It is 
significant that those plants exhibiting conspicuous red 
coloration in the autumn are often those which give in- 
dication of reddening with the first shoots of the spring 
growth. In this region there is no plant more loyal to 
autumn scarlet than the sumac, and in the spring the 
young shoots are reddened until the vigorous growth 
of warmer weather disperses the tint. Instances of this 
sort might be multiplied many fold. 
In our own flora some species exhibiting pronounced 
reds are hard maple, sassafras, thorn-apples, sumac, dog- 
wood, poison oak, Virginia creeper, and many others. 
Brown and purplish tones are often exhibited by hickory, 
persimmon, and ash. The vegetation that is suddenly 
cut off by severe frost seldom exhibits the best reds. 
Climatic influences are important, and it is clear that 
regions with a fairly high humidity and cool night, as 
the autumn approaches, are those in which the highest 
coloration is attained. Nevertheless, similar pigmenta- 
tion may be developed (in those plants capable of it) 
almost any season. In the middle of the summer a 
branch of hard maple or an isolated shoot of sumac may 
show high coloration. The heightened color is usually 
to be associated with some injury whereby the food ma- 
terials manufactured in the leaves are not conducted 
away from the shoot or branch. 
The production of anthocyanin in plants has been made 
the subject of much experimental study and careful an- 
alysis. It appears that the abundance of color in plants 
capable of producing it at all is related to the sugar 
content, and it also appears to be dependent upon oxida- 
tion phenomena. During the growing season the sugar 
produced in the leaves is rapidly utilized, but in the fall 
it is not required to such an extent in respiration, nor is 
it conducted away so freely. At the same time, the con- 
ditions are most satisfactory for the oxidation of the 
mother substance, or chromogen. The pigment belongs 
to the group of substances chemically known as gluco- 
sides, containing glucose or fruit sugar as one constituent. 
It is interesting to note that twigs placed in a sugar solu- 
tion, and under conditions otherwise favorable, have been 
found to redden conspicuously. 
The red pigments of autumn coloring belong to the 
same group of substances as the pigments of red beets 
and purple grapes, of most red, purple and blue flowers, 
and the red colors of such summer foliage plants as many 
varieties of coleus, begonia, croton and the purple 
beeches and maples. In these last-mentioned foliage 
plants, however, the red color is distinctive of the variety 
or species practically throughout its period of growth, 
and it is developed so abundantly in the cell sap as to com- 
pletely veil the chlorophyll. The simple experiment of 
plunging a red coleus leaf into boiling water for a few 
minutes is sufficient to demonstrate that the soluble red 
pigment is removable, and this removal makes visible in 
striking manner the green chlorophyll which is insoluble 
in water. 
The landscape architect uses to advange shrubs and 
other perennials which offer the possibility of autumn fol- 
iage colors, and likewise those — like the osier dogwood — 
whose twigs are reddened in the fall and remain brilliant 
for a considerable part of the winter. In the vicinity of 
St. Louis, where fall and spring efl^ects are often those 
chiefly sought in the garden, the autumn coloration of 
leaves, fruits and stems is a matter of special interest in 
the planning of the home ground. — From Missouri Bo- 
tanical Garden Bulletin. 
365 
