PLANT STRUCTURE AND COMPOSITION 



197 



imported from Central Europe. Like nicotine, atropine is also syn- 

 thesized in the roots and later moved into the stems, leaves, and seeds. 



Space will not permit listing all the alkaloids of medical value. 

 Many of the structures are extremely complex and therefore difficult to 

 establish with certainty. The common medical compounds cocaine, 

 codeine, quinine, strychnine, and morphine are alkaloids. 



Alkaloids have no known function in plants. The suggestion has 

 been made that they represent nitrogen excretory products, or that 

 they are by-products of nitrogen metabolism. Why these by-products 

 should be formed in such quantities in the root and transported to 

 the leaves for storage remains to be explained. 



Flower Pigments 



The numerous blue, purple, magenta, and nearly all the red flower, 

 stem, fruit, and leaf pigments belong to a group of glycosides (page 

 72) designated as anthocyanins. The water-soluble yellow pigments 

 in flowers, stems, and roots are generally flavones (anthoxanthins) and 

 may occur as glycosides or uncombined as the free pigment. These 

 pigments are usually freely soluble in the cell sap, although some occur 

 in an amorphous or crystalline state, as in species of Delphinin. The 

 chemistry of these compounds has been studied in considerable detail. 

 Anthocyanins are all derivatives of 2-phenylbenzopyrylium salt. The 



2-phenylbenzopyrylium chloride 



principal difference between various members is the degree of hydroxyl- 

 ation of the phenyl ring and the presence or absence of methyl esters. 

 Pelargonidin, the pigment of scarlet pelargonium, orange-red dahlia, 

 and red cornflower, contains a p-hydroxy group on the phenyl ring. 

 Cyanidin pigments of the red rose, blue cornflower, and deep red 

 dahlia contain two phenolic hydroxy groups, and delphinidin (blue 

 delphinium) has three hydroxy groups. Both mono- and diglycosides. 



HO- 



-OH 



pelargonidin 



