ness and brilliancy of the reds, are, in fact, closely correlated 
with the sudden ending of our northern summers and the quick 
coming of our bright autumn skies. 
It is obvious that frost may help somewhat in fall coloring by 
abruptly checking the vitality of the leaves and thus hastening 
the disappearance of the green, but they do not, as is sometimes 
popularly believed, really cause fall colors. For these colors, as 
we well know, generally appear long before frosts. Further, the 
chlorophyll itself does not, as was once thought, break up into 
various colors, but instead fades away entirely as the leaf dies, 
precisely as it would in an alcoholic solution of the green, when 
exposed to a strong light. 
2. Yellow. Mixed with the chlorophyll in healthy leaves 
occur constantly two or perhaps more yellow pigments, collect- 
ively called xanthophyll (meaning “leaf yellow”). These serve 
an unknown function, but their constancy indicates that they 
play an important part in the vital activities of the leaf. The 
normal green color of leaves is in fact never a perfectly pure 
green, but it always tends more or less toward yellow, especially 
in unhealthy leaves, or in those of waning vitality. Strong light 
does not effect these yellow pigments as readily as it does the 
chlorophyll; so that after the fading of the green color, the more 
stable yellows often persist for along time in full intensity. This 
greater stability is strikingly shown by placing a fresh solution 
of leaf pigments, made by soaking green leaves in alcohol, in 
strong sunlight. Even in an hour or so the strong light causes 
the green color to fade, leaving the solution yellow. This experi- 
ment shows clearly just why leaves turn yellow in autumn; for the 
fading of the chlorophyll in bright light from dying leaves results 
in the exposure of the yellow always present. Yellow is therefore 
the most common of the autumn colors. 
3. Red. Less abundant than yellow as an autumn color but 
more conspicuous is red, due to the presence of pigments termed 
collectively erythrophyll (“leaf red”). Being soluble in the watery 
cell sap, the color is readily dissolved out by heating red autumn 
leaves in water. Erythrophyll is not ordinarily previously’ present 
in autumn leaves as was xanthophyll but it is made from various 
substances in solution during the fading of the chlorophyll. So far 
as we know, this red coloring matter is of no particular use in the 
leaf, but it arises incidentally, apparently as a chemical accident. 
This autumn red, so far as we know, is exactly similar to the red 
color in Japanese Maple, Copper Beeches, Coleus, Beets and Red 
Cabbages. In some of these cases, it is so abundantly dissolved 
in the cell sap as to cover up entirely the green. In the case of 
autumn leaves, it seems to be necessary that sugar be present in 
leaves, and probably tannin, in order to result in an abundance 
