CELL-CONTEXTS AND FORMS OF CELLS. 181 



istic of the normal plant, is due to local variation in concentration 

 of either the free sugars or the glucosides in the tissues in which 

 the pigment appears. The abnormal formation of pigment under 

 altered conditions is due to differences in the concentration of 

 these same substances due to changes in metabolism brought about 

 by these conditions. 



(6) On the above hypothesis the formation of anthocyanin is 

 brought into line with that of other pigments produced after the 

 death of the plant, as, for example, indigo and the post-mortem or 

 respiration pigments, so termed by Palladin. 



FUNCTION OF PLANT COLORS. A great many theories have 

 been advanced as to the nature and uses of color-substances by 

 the plant. With the exception of chlorophyll present in the chloro- 

 plastid and its relation to photosynthetic processes little is known 

 concerning the other pigments. Without attempting to discuss the 

 various theories which have been proposed concerning their uses, 

 the following facts should be borne in mind : 



1. The occurrence of chromoplastids in a reserve organ, as in 

 the tuberous root of carrot, and the similar occurrence of chromo- 

 plastids and of reserve starch in the petals of the buttercup, lead 

 to the inference that the petal of the buttercup, like the root of the 

 carrot, has the function of storing nutrient material. In each case 

 cells containing chromoplastids rich in nitrogenous substances are 

 associated with cells containing reserve materials. 



2. The distribution of the so-called flower color-substances in 

 other parts of the plant than the flower shows them to be in the 

 nature of metabolic substances, and that the part \vhich they play 

 in attracting insects to flowers is incidental rather than funda- 

 mental. (The fact that certain colored flowers as in spruce are 

 pollinated by the wind would tend to confirm this view.) 



3. Unorganized or cell-sap color-substances are distributed 

 usually in largest amount at the termini of the branches, as in 

 flowers and terminal leaves, or in roots, or in both tops and roots. 

 Their occurrence in those portions of the plant which are young 

 and growing points to the conclusion that they are not to be disre- 

 garded in the study of metabolic processes. Goebel likewise 

 holds to this view. He says that it is " very probable that the 



