THE FLOWER AND THE BEE 



to a mixture of yellow plastids and red cell-sap. On the other 

 hand, dingy or dull colors result from a combination of violet 

 sap with yellow granules. Carrotin is much less sensitive to the 

 effects of light than chlorophyll, as may be readily shown by 

 the following experiment: If the carrotin contained in a few 

 slices of carrot-root be dissolved out in ether, the yellow solu- 

 tion will not lose its color under ten days, while the green 

 hue of a solution of chlorophyll will disappear in twenty-four 

 hours. 



Yellow was doubtless one of the first colors displayed by the 

 flowers of the primitive flora; and, in view of the wide distribu- 

 tion of yellow pigments in leaves, the development of yellow 

 petals offers little difficulty, and many leaves, fruits, and 

 flowers afford suggestions as to the way in which this change 

 might take place. The quantity of yellow pigment in the 

 foliage of different plants varies greatly; while in some species 

 it is scarcely perceptible, in others it is so abundant as to tinge 

 the whole plant yellow, and in a few golden-yellow species the 

 chlorophyll appears to be nearly or wholly excluded. Many 

 fruits change from green to yellow in ripening, and yellow color- 

 ing is especially prominent in foliage both in spring and autumn. 

 Not infrequently the change from green to yellow occurs in 

 flowers after they have opened, as in penny -cress (Thlaspi) 

 and bitter cress (Cardamine) ; in the yellow water-lily {Nymphcea 

 advena) the outer sepals are half green and half yellow; while 

 yellow tulips in expanding display every shade from dark green 

 to bright yellow. In double English buttercups in the bud the 

 petals are wholly green, becoming later golden yellow. Every 

 stage of the transition from green to yellow is constantly illus- 

 trated by fruits and flowers. 



According to Stahl it is more costly and difficult to produce 

 chlorophyll, which requires for its formation the presence of 



230 



