M. Wheldalb 



111 



The Yelloiu Pigments of Antirrhinum. 



Examination was first made of the yellow pigments of Antirrhinum 

 and they were found to be members of a group of natural yellow 

 colouring matters known as flavones. These substances are derivatives 

 of /S-phenylbenzo-7-pyrone : 



and they differ from each other, as regards constitution, in the number 

 and position of their hydroxyl gi'oups. The accompanying table (on 

 page 112) sets forth the reactions and distribution of the more common 

 flavones. The actual extent of their distribution, however, is by no 

 means represented by the genera mentioned, for our knowledge of the 

 occurrence of the flavones in plants is practically limited to the researches 

 of Perkin (21), and a few other workers who have investigated these 

 particular species solely from the point of view of the dyeing properties 

 of the plant extracts. The results of these investigations have shown 

 that the capacity for dyeing in the above cases is due to the presence 

 of particular flavones. 



There is little doubt that the flavones are universally distributed 

 among plants and form a class comparable to sugars, proteins, tannins, 

 etc., but no work has yet been done with a view to ascertaining the 

 distribution of the various members of the class. 



The flavones occur as a rule in the plant in the form of glucosides, 

 one or more of the hydroxyl groups being replaced by sugar, as for 

 instance : 



HO 



OC,H„0, 



HO CO 



In this condition the flavones are very little coloured (see below) 

 and readily soluble and as such they occur in the cell-sap throughout 

 the plant. A characteristic reaction of the flavones is to give an 



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