258 KRAEMER — NATURE OF COLOR IN PLANTS. [Aprils, 



While Pringsheim believed that there were two modifications of 

 chlorophyl, one yellow and the other green, the former predom- 

 inating in germinating plants grown in the dark, and the latter or 

 green substance in leaves exposed to the light, still he did not 

 believe that they could be separated from each other by the method 

 proposed by Kraus. 



Yet notwithstanding Pringsheim's well-founded criticisms of the 

 method employed by Kraus, and taking for granted that there were 

 two principles composing chlorophyl, nearly all investigators since 

 Kraus's work was published have practically employed his method 

 as modified by Hansen^ for the separation of the so-called yellow 

 and green chlorophyl. According to this method of Hansen, 

 fresh material is extracted with 95 per cent, alcohol, the liquid 

 filtered, and to the filtrate 30 to 50 per cent, of water is added ; 

 the solution is shaken with petroleum ether and the liquids sepa- 

 rated, the ether taking up the green substance, or chlorophyl 

 proper, and the hydro-alcoholic solution holding the yellow prin- 

 ciple. 



If autumn leaves are treated in the same way, the ether solution 

 will contain very little chlorophyl, while the hydro-alcoholic solu- 

 tion will contain a yellowish or reddish substance, depending 

 upon the kind of material examined. It has usually been con- 

 sidered that this yellow substance in autumn leaves is associated in 

 summer with the active plastids, and on account of its having little 

 food value remains behind. It has furthermore been considered 

 by many that the yellow principle in young leaves is identical with 

 that in autumn leaves and the yellow substance found in yellow 

 flowers, fruits and roots. 



Kinds of Colors in Plants. 



Colors in plants may be considered to be due to definite con- 

 stituents which either themselves are colored or produce colors 

 when acted upon by other substances. These substances are found 

 in all parts of the plant, and apparently in all of the cells excepting 

 certain meristematic or dividing cells. They may be divided into 

 two well-differentiated classes, namely, (1) those which are associ- 

 ated with the plastids, or organized bodies in the cell, and (2) 

 those which occur in the cell-sap, or liquid of the cell. 



