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Ch. HI, 11] COLORATION OF LEAVES 91 



on by old age or the coming of autumn, a leaf makes no more 

 chlorophyll, while that already present fades rapidly away, 

 permitting other colors which are present to show, and 

 likewise some new ones to form under the altered conditions. 

 The rapidity with which chlorophyll can fade in the light is 

 strikingly shown by the simple experiment of exposing a 

 fresh alcoholic solution to strong light in contrast with a 

 control kept in the dark (page 17). In an hour or two the 

 green color is gone, leaving the solution colored yellow by 

 the xanthophyll. This experiment shows why leaves turn 

 yellow in autumn, for the fading of the chlorophyll exposes 

 the xanthophyll, always present with chlorophyll but far 

 more resistant to destruction by light. Thus all autumn 

 leaves are yellow, though some acquire additional colors. 

 The xanthophyll is easily extracted in a clear solution by 

 simply warming yellow leaves in alcohol ; and it is also ob- 

 tainable by blanching an alcoholic extract from green leaves, 

 as just mentioned. As to the function of this widely present 

 xanthophyll (a mixture of carotin and xanthophyll proper), 

 that is still unknown, though the constancy of the substances 

 indicates some important functional utility. Herein lies 

 another of the problems inviting the future investigator. 



Less abundant but more conspicuous than yellow, as an 

 autumn color, is red, which is due to the erythrophyll (an- 

 thocyanin) already described. Being soluble in the cell 

 sap, it is easily removed, in a clear solution, by heating 

 the red autumn leaves in water. It is indeed worth one's 

 while, for aesthetic as well as educational reasons, to extract 

 the green, yellow, and red pigments in their beautiful clear 

 solutions, and view them side by side in glass cylinders 

 •gainst the light; for these are the three which give almost 

 the entire coloration to all foliage. The erythrophyll origi- 

 nates in autumn leaves very differently from xanthophyll, 

 for it is not previously present, but is made during the fading 

 of the chlorophyll. There is much uncertainty about the 

 details, but it seems reasonably certain that it results in- 



