42 The Living Plant 



ordinarily completely masked by the far greater brightness of the 

 chlorophyll, though it has influence enough to give the living 

 leaf its yellow-green rather than a pure-green color. But xan- 

 thophyll is vastly more resistent to the action of light than is 

 chlorophyll, which explains its persistence in both leaves and 

 solutions. The precise function of the xanthophyll, by the way, 

 is not known, although it seems probable that this is to be found 

 in some incidental chemical connection with the chlorophyll, in 

 which case its persistence in autumn leaves is purely incidental 

 and of no service to them. 



Second in abundance, though first in brilliance, among autumn 

 colors is red, which has a very different origin. It is due to the 

 presence of that same erythrophyll which we have already con- 

 sidered in connection with foliage plants and the spring coloration. 

 This erythrophyll, also, the reader can extract for study in a beau- 

 tiful clear rose-red solution by aid of the method he used for the 

 chlorophyll, excepting that water must be used instead of alcohol, 

 and the material should be abundant and consist of the very 

 brightest red leaves he can find. Unlike the xanthophyll the 

 erythrophyll is not present in the leaves before the chlorophyll 

 fades away, at least not in appreciable amount; but it forms as 

 the disappearance of the chlorophyll admits the light to the in- 

 terior of the leaf cells. That the presence of bright light is es- 

 sential to its formation is easily proven by experiment, and by 

 the readily observable fact that in cases where one red autumn 

 leaf overlaps another closely enough to shield it largely from light, 

 the darkened portion is yellow not red; and this same fact further 

 proves that red autumn leaves are actually yellow underneath the 

 red. The brilliancy of the red, indeed, is proportional in general 

 to the brightness of the light. But light alone is not sufficient 

 to produce a formation of erythrophyll without the presence of 

 the chemical substances requisite to its formation, which include 

 certainly sugar and probably tannin; and it is only those leaves 

 which happen to contain a sufficiency of these materials that can 



