I70 BOTANY AND PHARMACOGNOSY. 



These substances are easily extracted with water or dilute 

 alcohol and 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 number of plant pigments of this class are used as indi- 

 cators 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 ur 

 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 some writers, but they behave very differ- 

 ently from tannin toward other reagents, such as organic acids, 

 alkalies, lime water and solution of alum. 



An examination of the color-substances of a large number of 

 plants shows that the flower color-substances are distributed in 

 all parts of the plant. For example, the flower color-substance of 

 the rose occurs in the leaves and prickles as well as in the petals. 



The color-substance in the root of the radish closely corre- 

 sponds to that in the flowers, while the one in the grains of black 

 Mexican corn corresponds to that in corn- silk. 



The cell-sap color-substances are usually found in greatest 

 amount at the tips of the branches, this being well marked in the 

 foliage of the rose, and may be said to be rather characteristic 

 of spring foliage. Not infrequently in the purple beech the young 

 leaves will be of a distinct purplish-red color and almost entirely 

 free from chlorophyll, suggesting a correspondence in position 

 and color to a flower. 



Color in Autumn Leaves. — The coloring matters in both 

 spring and autumn leaves closely resemble the cell-sap color- 

 substances of flowers, although it is the spring leaves which give 

 the most satisfactory results when examined. The fact that in 

 the autumn leaves there is little or none of the plastid pigment 

 present would point to the conclusion that the color-substances 

 occurring in these leaves are in the nature of by-products and of 

 no further use to the plant. Of course in the case of autumn 

 leaves we know that these products cannot be further utilized 

 by the plant, and for this reason we are justified in regarding 

 them as waste products. 



