TJie Formation of the Anthocyan Pigments of Plants. 



123 



ment with the fact that the red colour is produced no matter what 

 amino-acid he used. A series of similar experiments was made differing 

 only in that different amino-acids in equivalent quantity were added in the 

 several cases. The colours produced were compared with one another by 

 means of the tintometer in order to obtain a rough indication of their 

 relations with one another. The same series was again examined a few days 

 later, when the solutions had become darker. 



Amino-compound used. Colour produced. 



Glycine value = 8 red + 13 yellow. 



Alanine „ =8 „ +11 „ 



Leucine „ = 7"5 „ +10 „ 



Phenylalanine „ = 5 „ + 6 „ 

 Tyrosine „ = 5 - 5 „ + 6 „ 



The three aliphatic acids give similar colours, the two aromatic acids 

 yield a somewhat different shade. Hence these pigments differ essentially 

 from those obtained by Chodat from ^-cresol, inasmuch as the colours of the 

 latter depend on the nature of the amino-acid. Whatever be the explanation, 

 the formation of pigment from arbutin and protein degradation-products is 

 one which may well be of natural occurrence. In passing, it may be observed 

 that qiiinone, like alloxan and triketohydrindene, may prove to be of use in 

 the diagnosis of amino-compounds. 



Substituted quinones such as 1 : 4-xyloquinone or 1 : 4-thymoquinone 

 resemble quinone in giving a colour reaction with glycine on warming in 

 aqueous- alcoholic solution ; but in the case of these substances the reaction 

 takes place much more slowly. Xyloquinone give rises to a claret red, 

 thymoquinone to a tawny or brown red. There is apparently a difficulty in 

 reducing the quinones, as neither of them gives a colour reaction with 

 formaldehyde and ammonia. 



We are investigating the behaviour of other glucosides and find that salicin, 

 the glucoside of the willow and many other plants, gives an orange, passing 

 to an orange-red, coloration when hydrolysed by emulsin and oxidised by 

 an oxydase in presence of an amino-acid. Similar colours are obtained 

 with glycine and with phenylalanine, the tintometer reading in a half-inch 

 cell being in each instance 4 - 5 red + 1*8 yellow. Salicin incubated with 

 ground sweet almond and a few drops of hydrogen peroxide gives a similar 

 colour reaction. 



Phloridzin, the glucoside present in the roots of many rosaceous trees, is 

 composed of glucose and phloretin, a condensation product of p-hydroxy- 

 hydratropic acid and phloroglucinol. When hydrolysed by emulsin in 



k 2 



