A CAROTENOIDS IN PLANTS 69 



and Brockmann^", who confirmed the disappearance of carotene in the course 

 of necrobiosis, these autumn xanthophylls are phytoxanthin esters, which are 

 formed only in the autumn by the esterification of free phytoxanthins. The 

 matter has not been completely elucidated, however, as with one exception 

 no crystalline pigments could be obtained^^. 



Karrer and Walker isolated the carotenoids by precipitation in the form 

 of sparingly soluble iodides and regeneration with sodium thiosulphate^*. The 

 main results of their investigations are as follows: as the leaves decay, the 

 content of carotene and xanthophyll decreases, but the former decreases more 

 rapidly. Xanthophyll can still be isolated in the crystalline state long after no 

 carotene can be detected. Eventually the xanthophyll also disappears com- 

 pletely. The autumn xanthophylls observed by Tswett were also found. 

 These compounds first appear at the beginning of necrobiosis and their con- 

 centration steadily increases at the expense of the carotenoids, so that they 

 become mainly responsible for the colouration of the leaves shortly before the 

 postmortal phase. Nothing definite is yet known regarding the nature 'of these 

 pigments, but they appear to consist of oxidation and degradation products of 

 xanthophyll. Other pigments which absorb more strongly in the ultraviolet 

 are also observed. Further investigations of these autumn xanthophylls would 

 be of interest. 



The pigments of red winter leaves have also been much studied. It has been 

 found that some leaves owe their red colouration to anthocyanins, while others 

 contain rhodoxanthin. 



c) Carotenoids in Blossoms 



Nature has been lavish in the distribution of carotenoids in blossoms. 

 About 35 different carotenoids, i.e. about half of all the known polyene pigments, 

 have been isolated from blossoms up to the present time. This variety is 

 the more remarkable since nothing is at present known regarding the function 

 of carotenoids in blossoms. 



The following is a summary of the blossoms examined in this respect up 

 to the end of 1948. Many of the older investigations, e.g. those of Courchet, 

 Tammes and Van Wisselingh were carried out using inadequate techniques 

 and only limited significance can be attached to them. 



References p. 108. 



