88 A TEXTBOOK OF BOTANY [Ch. Ill, 11 



phyll was developed. The existing chemosynthetic Bac- 

 teria, indeed, may represent a survival from tnat ancient 

 epoch, in which case they are doubtless the most ancient type 

 of organisms now inhabiting the earth. 



11. The Autumnal and Other Coloration of Leaves 



The distinctive color of leaves is the chlorophyll green, 

 which most of them exhibit. Other colors, however, occur, 

 especially in " foliage" and " variegated" plants, and in the 

 autumnal foliage. 



The most prominent of the non-green colors of living leaves 

 is red. It is most intense in cultivated plants, such as Japanese 

 Maples, Copper Beeches, Coleus, Beets, and Red Cabbages. 

 In all cases, however, the color has been greatly intensified 

 under cultivation, from a very moderate quantity in the 

 ancestors of these plants. Little blotches or streaks of 

 red color are indeed very common in wild plants, as in- 

 tensive observation, centered on this point, soon reveals. 

 The color is due to the presence of a red substance, called 

 descriptively erythrophyll but chemically anthocyan or 

 anthocyanin, which is dissolved in the sap of the cells. 

 Being thus soluble in water, it is easily removed by hot 

 water from red leaves, which thereby are left green, showing 

 that chlorophyll is present in foliage plants, though masked 

 by the more brilliant and abundant erythrophyll. As to 

 the reason for its presence, that is greatly in doubt. Prob- 

 ably it has no functional utility in itself, but represents simply 

 an incidental product of the complicated metabolism of the 

 plant. 



In some cases, however, a functional utility has been 

 claimed for erythrophyll. Thus, a great many plants in our 

 own flora show in the leaves in early spring a blush of red 

 which later disappears. The claim has been made that here 

 the red forms a protective screen to the young developing 

 parts, by absorbing the blue and ultraviolet rays of the 

 sunlight believed to injure unscreened living protoplasm, 



