The Prevalence of Green Color in Plants 41 



phyll left in the leaf when the new supply ceases to form, breaks 

 down in the light to other substances, which either themselves 

 are highly colored, especially red, or else unite chemically with 

 other materials in the cells to form colored compounds, the autumn 

 colors being supposed, on this view, to be simply an incidental 

 product of chlorophjdl decay. But later research has shown this 

 supposition to be wrong, for chlorophyll, in breaking down, does 

 not form colors, but fades away to transparency in the leaf pre- 

 cisely as it does in the alcoholic solution which the reader has 

 placed in the sun. Now, sooner or later in the autumn the waning 

 activity of the leaf reaches a point where no more chlorophyll 

 is made, after which all of that substance already present fades 

 away, with this notable result, — that its disappearance renders 

 visible any other colors which may have been present in the 

 leaf, but masked by the greater brilliance of the green; and this 

 fact constitutes the basal step in the explanation of autumn color- 

 ation. As a matter of fact leaves do contain other coloring mat- 

 ters, especially a bright yellow material, called xanthophyll, 

 occurring in tiny grains associated with the chlorophyll. It is 

 the exposure of this xanthophyll by the fading away of the chloro- 

 phyll w^hich gives the yellow, most conmion of the autumn colors, 

 to autmiin leaves. If the reader desires, he can himself extract 

 this xanthophyll, and very easily, in a beautiful clear yellow solu- 

 tion, by treating yellow autumn leaves precisely as he did the 

 green leaves for extraction of chlorophyll, but using much leaf 

 in proportion to the quantity of alcohol. Indeed the reader has 

 seen the xanthophyll already, for, as he will recall, w^hen he placed 

 his solution of chlorophyll in the sun it faded away not to a trans- 

 parent whiteness but to a clear yellow; this was xanthophyll, 

 which itself fades away extremely slowly to whiteness. The 

 whole situation must now be quite clear. Chlorophyll and xan- 

 thophyll exist together in leaves, from which indeed they can be 

 extracted and separated in beautiful solutions well known to 

 all students in physiological laboratories; but xanthophyll is 



