68 THE NATURE AND WORK OF PLANTS 



the oaks vary through yellow orange to reddish 

 brown, the red maple is generally a scarlet varying 

 to a dark red, the tulip tree a light yellow, and 

 sumachs become a flaming scarlet. These colors 

 show some variation with the amount of moisture 

 and character of the soil. 



79. Uses of autumnal colors. — The actual pur- 

 pose of the autumnal colors cannot be determined. 

 There is no doubt, however, that their presence pre- 

 vents damage by sunlight to delicate substances 

 which are withdrawn from the leaf to the stem 

 before they are cast off. 



80. Uses of red and other colors in flowers and 

 fruits. — The purpose of the brilliant colors of 

 flowers, fruits, and leaves is not clearly made out. 

 The colors of flowers may serve to attract insects, 

 but this is the case in only a few instances An 

 insect is attracted to a flower generally by the scent 

 of nectar or honey, and it recognizes the flower by 

 its size and form rather than by the color. The 

 same is true of fruits which need the aid of insects 

 for their dissemination. It is to be noted that very 

 vivid colors are often found in the centre of large 



