160 On the Formation of Anthocyanin 



This retardation is doubtless due to the fact that the water extract 

 contains, in addition to the enzyme, the glucosides and sugars present 

 in the plant. Thus the products of hydrolysis of the glucosides derived 

 from the plant would retard or entirely prevent hydrolysis of the salicin 

 added. By treatment with alcohol, all glucosides and some part of the 

 sugars are removed previous to extraction with water. 



Oxidases. It has been previously mentioned that Palladin(14) 

 considers anthocyanin to be a respiration pigment. That oxygen is 

 necessary for its production has been shown experimentally both by 

 Molliard(ll) and Katic(5). 



The dependence of pigment formation on the presence of oxygen 

 can be readily demonstrated in a very simple way. If cut leaves of 

 Taraxacum officinale are placed in sugar solution so that the lamina is 

 partially immersed, reddening only takes place in the portion exposed 

 to air and not in the submerged part. The oxygen may also be 

 excluded by greasing part of the leaf with vaseline. The greased 

 portion remains green while the ungreased portion develops a con- 

 siderable quantity of pigment. Similar results have been obtained 

 with leaves of Heracleum sphondylium, Sambucus nigra and Hiera- 

 cium sp. 



Apparently no reverse process of deoxidation takes place when a 

 coloured leaf is greased so as to prevent all gaseous exchange. If 

 anthocyanin constitutes a medium for the transference of oxygen, we 

 should expect the colour to disappear as a result of reduction when 

 coloured leaves are deprived of oxygen, especially since respiration is 

 one of the last " vital processes " to disappear. The strongest argument 

 against Palladin's hypothesis is the existence of well-developed albino 

 varieties of an almost innumerable number of species. 



The question of the oxidising enzyme presents some difficulty. In 

 all plants forming post-mortem pigments, oxidases can be detected by 

 means of guaiacum tincture, with which the extracts give a strong and 

 rapid direct action. Yet blueing of guaiacum is not limited to these 

 cases, for a less rapid direct action is also given by other plants 

 (Lathyrus, Matthiola), which do not form pigments on autolysis. All 

 the guaiacum-blueing species I have examined have been anthocyanic, 

 and the possibility suggests itself that the oxidases may form antho- 

 cyanin in the living plant but a post-mortem pigment after death. 

 There is some evidence in favour of this supposition : first, when a 

 plant forms anthocyanin and also a post-mortem pigment, the former is 

 converted into the latter on autolysis and the organs which contain 



