80 Kraemer : Color in plants 



Cell-sap colors 



All the other color-substances found in plants besides the 

 green and yellow principles just mentioned occur in the cell-sap, 

 and may be in the nature of secondary substances derived from 

 the plastid pigments, or they may be produced directly by the 

 activities of the protoplasm. During the course of my work I 

 have been much impressed by the fact that in tissues containing 

 cell-sap color-substances, or as they might be termed unorganized 

 color-substances y not infrequently strikingly contrasting colors are 

 observed in contiguous cells; as in the petals of the poppy and 

 petals of certain lilies, where we find some cells of a deep-purple, 

 others of a deep-red and still others of intermediate shades. The 

 same may be said of the germinating kernels of black Mexican 

 corn. This observation has led me to believe that the shades of 

 color in the pigmented cells are largely dependent upon the nature 

 of the substances associated with the fundamental color-substance. 

 The unorganized color-principles are easily extracted with water 

 or dilute alcohol. I have examined the principles from several 

 hundred plants, and find that they are all more or less affected by 

 certain chemicals (many of which occur naturally in the plant), such 

 as citric acid, oxalic acid, salts of calcium, iron, aluminum, etc. 



A solution of the mallow flowers of the garden is of a purplish- 

 red color and becomes green with lime water ; deep-red with oxalic 

 acid ; purplish-red with alum ; and deep brownish-red with ferric 

 chloride. 



A solution of rose petals (J 



becomes 



lime water ; deep yellowish-red with oxalic acid or citric acid ; 

 purple with alum ; and deep-blue with ferrous sulphate. 



These reactions show that these color-substances are quite 

 sensitive to the influence of chemicals, and many of them corre- 

 spond to the class of substances known as indicators ; in fact a 

 number of plant pigments are used as indicators in volumetric 

 chemical analysis, their use in this connection being dependent 

 upon their sensitiveness to acids and alkalies. The fact that they 

 respond to iron salts, that is, give a blue or green reaction with 

 these salts, would indicate that they are associated with tannin or 

 that they are tannin-like compounds, as has been supposed by 



