35 



example, whether growing in a greenhouse at Chicago or outdoors else- 

 where, yielded traces of taraxanthin. This xanthophyll formed a yel- 

 low zone just below and contiguous with the chlorophyll b^ zoneo It 

 was identified by absorption spectra and color reactions and by mixed 

 adsorption with taraxanthin from dandelion flowers as has been des- 

 cribed before^* ^°o For these chromatographic comparisons columns both 

 of sugar and of magnesia were employed » 



In some of the earlier experiments in which leaf xanthophylls 

 were isolated on a relatively large scale, traces of two xanthophylls 

 that resembled the flavoxanthin of buttercups were frequently ob- 

 served'^s^'^o It is not certain whether these small quantities of pig- 

 ments occur naturally or whether they arise from violaxanthin, which 

 is known to yield two flavoxanthin- like pigments when exposed to var- 

 ious mild conditions such as the action of weak organic acidSo These 

 pigments were rarely observed in the sugar columns^o 



Leaves of various species of flowering plants usually yielded the 

 same principal pigments even when the plants were growing \mder vastly 

 different conditions » Marine plants j as Phyllospadix (Najadaceae) and 

 Halophila (Hydrocharitaceae) , salt-marsh plants, as mangrove (Rhizophor- 

 aceae), Cotula coronopifolia (Compositae) and Salicornia ambigua 

 (Chenopodiaceae) , and various plants growing on the land at sea level 

 or near timber line, in fertile meadows or in barren desserts always 

 yielded these same green and yellow substances. Seed plants growing 

 in the tropics, in the temperate zone, or in the glacial zone of the 

 high Sierra Nevada Mountains also yielded these pigments,, Plants 

 native to Europe, Asia, Africa and South America produced the same 

 pigments when growing in Hawaii or in Califomiao 



