of red. Bright light is also essential to the process, as is proved 
by the fact that any leaf which ordinarily turns red does not do 
so if closely covered by another. Apparently the fading away of 
the chlorophyll admits a sufficient intensity of light to produce in 
the sugary sap the proper chemical reaction. The reason why 
some leaves turn red and others only yellow appears tobe simply 
because some kinds contain sugar at the time the chlorophyll 
fades and other kinds do not. If sugar is plentifully present, and 
if favorable light strikes the leaf, red will result in such abundance 
as to obscure the yellow; but if little or no sugar be present, 
yellow only results. It therefore seems clear that the appearance 
of the red in autumn foliage is a chemical incident, dependent 
upon the presence of sugar. The Maples, Oaks, Sumacs and 
Dogwoods are noted either for their abundance of sugar, or of 
tannin, or of both; they have therefore the reddest of autumn 
foliage. 
4. Brown. This color also has no functional use, so far as we 
know, but simply results from certain chemical or physical con- 
ditions which prevail in the dying or dead leaves. In some dying- 
leaves it is apparently a product resulting from the oxidation of 
yellow substances in the cell sap; in others, it results from oxida- 
tion of tannins present in cell walls. Similarly, wood and bark turn 
brown in time due to the effect of light and air on the tannin they 
contain. When the browning takes place not too rapidly, it some- 
times combines with the yellow of xanthophyll into a beautiful 
golden bronze, as in some Oaks. With the brown, as with other 
colors, the exact shade is often determined by the degree of 
mixture with other substances, such as resins, or with reds or 
remnants of unfaded chlorophyll. 
5. White, the rarest of all in autumn coloration, is the natural 
color of the bleached-out leaf structure, much as cotton is white. 
In our Birches, for instance, the fading first of the green, then of 
the yellow, leaves the tissues finally nearly white. 
It is thus seen that not one of the so-called autumn colors 
really serves any useful function, for they all result from the 
various chemical and physical changes that go on during the slow 
dying and fall of the leaves. Though but incidental, they are 
nevertheless happy incidents for mankind, contributing greatly 
to human enjoyment. 
E. W. O. 
