CAROTINOIDS IN THE PHANEROGAM* 67 



JLSOj, so that observations regarding flower caret ino'n Is may right - 

 fully 1)0 said to have begun with this investigator. 



Beginning with Fremy and Cloez (1854), however, it has been rec- 

 ognized that yellow flower colors may be divided, at least roughly, into 

 two groups, one insoluble in water and the other soluble in water. 

 Fremy and Cloez called the former xanthin, and regarded the pigment 

 of the sunflower (Helianthus annus) as the type. The pigments of 

 the water-soluble group were called xanthe'in, and the yellow pigment 

 which may be obtained from certain dahlias was regarded as the type. 

 Frciny and Cloez's xanthin was, of course, a mixture of carotinoids, 

 and their xantheins are recognized today as anthocyanins and flavones, 

 only a few of which, however, have been isolated and closely studied. 

 We are concerned in this monograph only with the carotinoids, but 

 the subject of yellow flower pigments is somewhat complicated because 

 of the fact that yellow, orange and orange-red pigments of a consti- 

 tution entirely foreign to that of the carotinoids are frequently the 

 cause of the color of flowers and sometimes associated with the caro- 

 tinoids in causing the coloration. 



It does not appear to be possible to determine with certainty by 

 mere inspection whether a yellow colored flower owes its color to 

 carotinoids or to pigments of the water-soluble group, although Bid- 

 good (1905) states that in general all floral colors of a primrose or 

 sulfur-yellow color are produced by the latter pigments, and that such 

 flowers have a more delicate, transparent appearance. Microscopic 

 observation, however, readily reveals the character of the pigment 

 present, for the carotinoids appear to be always present in flowers in 

 the form of chromoplastids, while the anthocyanins and flavones are 

 always present in solution in the cell sap. There may be some excep- 

 tions to both statements but the differentiation is sufficiently general 

 to serve as the basis for determining the character of the flower color- 

 ation. Confirmatory tests for carotinoids can, of course, always be 

 carried out. Yellow and orange colored anthocyanins, giving a red 

 color with sulphuric acid, are more common in flowers than are flav- 

 ones, according to Bidgood, who lists a number of flowers whose color 

 is due to the former, but very few that owe their tints to the latter. 



The vast majority of yellow to orange-red colored flowers, however, 

 owe their color to carotinoid containing chromoplastids. Thudichum 

 (1869) gave a list of 32 flowers whose yellow pigment he regarded as 

 due to lutein. Carotinoids have since been demonstrated in practi- 

 cally all these cases. Gregor Kraus (1872) first noticed the spectro- 



