CHAPTER SIX 



LEAF COLORATION AND THE FALL OF LEAVES 



In spring and summer the most prominent feature of the 

 landscape is the green color of the vegetation. The most 

 striking feature in autumn is the varied colors of the foliage 

 on the trees and shrubs. In the northern provinces of Canada 

 most of the trees are evergreen, and the most abun- 

 dant deciduous trees, like the aspen, birch, and tamarack, 

 merely turn yellow. But in our Northern states the vivid 

 greens of the sugar maple, white oak, gum, and sumac dis- 

 appear in a blaze of red that contrasts strongly with the 

 yellows of the hickory, linden, and poplar and with the dark 

 greens of the hemlock, spruce, and pine. Every one who has 

 seen the colors of autumn woods and the aimual falling of the 

 leaves must have wondered what processes go on within the 

 leaves to bring about these changes. 



The pigments in green leaves. We can best approach the 

 matter of autumn colors by inquiring into the composition of 

 the pigments that give the color to the leaves of deciduous 

 trees in summer and to the leaves of evergreen trees through- 

 out the year. The most abundant of these pigments is chlo- 

 rophyll (Greek : chloros, green, and phyll, leaf), which is bright 

 green in color. In addition to chlorophyll, two other pigments, 

 one yellow and one orange, are found in a green leaf. These 

 three pigments may exist quite independently of one another.^ 



^ The coloring matter in a green leaf is composed of about 66 per cent green 

 pigment (chlorophyll) ; 23 per cent yellow pigment (xanthophyll) ; and 10 per 

 cent orange pigment (carotin, so named because of its abundance in the carrot). 

 The green pigment is not a simple substance, however, but a mixture of two 

 kinds of cUorophyll, one of which is blue-green and the other yellow-green. 

 The depth of the green color in a leaf depends in part on the proportions in 

 which these various pigments are combined. 



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