66 Science of Plant Life 



likewise are due to anthocyan. Here again we may see the 

 effects of sunlight on the intensity of color by comparing fruits 

 from the brightly illuminated top of the tree with others from 

 the shaded under parts. The apples grown in the Northwest- 

 ern states are more brilliant in color than the same varieties 

 grown in the Eastern states, and this higher coloration is 

 probably due to exposure to more intense light. 



Among different plants there is much variation in the 

 amount of light that is required for the development of an- 

 thocyan colors. This accounts for the great variation in the 

 brilliancy of autumn coloration in different years. One 

 autumn affords light conditions which promote the forma- 

 tion of anthocyan in only a few trees and shrubs ; another 

 autumn furnishes conditions so favorable that many plants 

 become brilliant. 



The brown colors. In some trees the leaves turn brown 

 immediately after the loss of their chlorophyll. In other 

 trees the leaves may first turn yellow or red, and then grad- 

 ually assume the shades of brown. These brown colors re- 

 sult from chemical and physical changes in the substances 

 within the leaf. Just what the processes are is not fully 

 understood, but it is reasonably certain that tannins and 

 tannic acid are connected with the making of the brown pig- 

 ments. The dead bark of trees also turns brown, probably 

 because of chemical processes within it similar to those which 

 take place in the leaves. 



White leaves. One occasionally finds on plants leaves 

 that are wholly or partly white. This is simply the natural 

 color of living plant tissues that lack chlorophyll or other 

 pigments. The protoplasm, cell sap, and cell walls are 

 transparent and colorless. The presence of air spaces among 



