CAROTINOIDS IN THE PHANEROGAMS 55 



Tswett's (1908b) group of colorless chroniogcns, whose alkali com- 

 pounds arc characterized by a dark yellow or brown color. No xan- 

 thophyll pigment showing spec) roscopic absorption bands is present 

 in leaves having yellow plastids, according to Kohl. 



Van Wisselingh (1915) made some microscopic observations of the 

 crystals which he produced in the yellow spotted leaves of Croton 

 ovalfolius Vahl., Graptophyllum pictum Griff, (caricature plant), and 

 Siinthux niiira L. foliix var., using both the alkali method of Molisch 

 and the acid method of Frank. The crystals produced by the latter 

 method are described by van Wisselingh as brown crystal aggregates, 

 the yellow spots in the leaves of Sambm nigra showing reddish colored 

 crystals also, and the similar spots in the leaves of Graptophyllum pic- 

 tum showing orange-red platelets and small orange-yellow crystal 

 aggregates. 



Summarizing our knowledge of the pigments in naturally yellow 

 or yellow spotted leaves, it seems certain that carotinoids are con- 

 cerned in part in the pigmentation, but the information is lacking 

 regarding the types and distribution of the carotinoids between carotin 

 and xanthophylls. It also remains to be determined whether water- 

 soluble pigments of the type whose alkali salts are golden yellow in 

 color, which are probably related to flavones, are, as Kohl believed, 

 normally a part of the pigmentation. 



Carotinoids in Yellow Autumn Leaves 



The hidden beauties of the forest, revealed in the passing of the 

 chlorophyll of the leaves in the autumn, were among the earliest to 

 attract the attention of the plant chemists. The author has not had 

 an opportunity to determine how far back scientific observation on 

 the autumn leaf pigment can be traced. Guibourt, however, as early 

 as 1827, expressed the belief that the yellow and red pigments of 

 autumn, leaves were due to a coloring matter which persisted after 

 the green chromula of the leaves had disappeared. Guibourt observed 

 that those families whose flowers and fruits were characterized by 

 yellow pigments had yellow leaves in the autumn, while the families 

 with red co.lored llowers and fruits had red autumn leaves. 



Macaire-Prinsep (1828) apparently made the first chemical exami- 

 nation of the autumn pigments. He found that the yellow pigment of 

 the autumn leaves of the Lombardy poplar (Popuhiji jastigiata) could 

 be extracted with ether or hot alcohol; that the pigment thus extracted 



