COLOR. 131 



These constitute what is called the yellow, xanthic, or oxydized 

 series. 



This theory has been attacked by the most able physiolo- 

 gists, and they have considered themselves successful in point- 

 ing out errors in experiments and observations which are suffi- 

 cient to invalidate this extensively received theory. Mohl, in 

 a memoir in the Annales des Sciences JSFaturelles, vol. ix., p. 

 212, examines various theories on this subject with apparent 

 impartiality, and gives his decided preference to the following 

 theory of Macquart, although it does not receive his unqualified 

 approbation. 



245. Macquart admits that the various colors are owing to 

 the various modifications of Chlorophyll, but denies that it is 

 owing to its being oxydized by acids, or deoxydized by alkalies, 

 but that it is converted into two distinct substances by the ad- 

 dition and abstraction of water. By the loss of water it is con- 

 verted into a blue substance, called anthocyane, which is soluble 

 in water, but not in alcohol. By the addition of water, the 

 chlorophyll is converted into a yellow substance, called antho- 

 xanthine, which is partly soluble in alcohol, and partly in water. 

 These two substances form the basis of the two series of colors 

 above given. They both sometimes exist in the same flower, 

 but occupy different cells ; the anthoxanthine being situated in 

 the inferior cells, while the anthocyane occupies the superficial 

 ones. This gives a great variety of tints, according as the colors 

 of the inferior cells are more or less distinctly exhibited through 

 the superior layers. By the action of acid and alkaline secre- 

 tions, these substances assume every variety of hue ascribed to 

 the action of the same agents on chromule. 



246. The outward circumstances which tend to change the 

 color of vegetable organs are various. The action of light is 

 one of the most efficient agents in the production and change 

 of colors, and it is not a little singular that the power which is 

 absolutely necessary to the production of color, in the great 

 majority of cases, should be the most powerful agent in de- 

 stroying it. We are all acquainted with the influence of light 

 in blanching vegetable substances when dead. 



247. The change of the color of leaves in autumn, of fruit 

 when ripening, of some evergreen leaves during the winter, are 

 phenomena whose explanation has as yet baffled the most acute 

 observers. The memoir of Mohl, above quoted, leads us ono 



245. What is MacquartV theory? How converted into anthocyane? 

 How into anthoxanthine ? How are these arranged ?— 246. The most effi- 

 cient agent in changing colors ? What singular about it ? 



