276 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



Similar coloured compounds have also been obtained 

 in this manner by Laborde (1908), by Dezani (1910), and 

 by Keegan (1913). In the course of a chemical investiga- 

 tion upon the red-coloured substances obtained by warming 

 tannins with dilute sulphuric acid, Kunz-Krause (1898, 

 1899) came to the conclusion that they were dehydration 

 products of aromatic hydroxy-acids. Very probably 

 the derivatives described by the later workers are of a 

 like nature, and have no relationship to anthocyanin. 



Merenstein and Wheldale (1911, 1912) also obtained 

 substances bearing a resemblance to anthocyanin as far 

 as colour is concerned, by means of oxidizing quercetin 

 and chrysin. These again, as the authors point out, are 

 far simpler in constitution than are the naturally occurring . 

 anthocyanins. 



A reaction somewhat similar to that described by Mal- 

 vezin has been investigated by Peche (1913) as a micro- 

 chemical test for tannin. Sections of leaves or stems 

 which contain iron-greening tannins are placed in 20 per 

 cent, caustic potash, mixed with about an equal volume 

 of formalin, and heated quickly over a strong flame till 

 the cells in which tannin is located become blue-green. 

 When acid is added the colour changes to a cinnabar-red; 

 this pigment in its solubilities and colour somewhat 

 resembles anthocyanin. 



Peche suggests that the function of the formaldehyde is 

 to prevent the unlimited oxidation of the phenolic hydroxyl 

 groups. He also gives a figure illustrating the similarity 

 in the distribution of tannin cells and of those containing 

 natural anthocyanin as shown in cross-sections of the 

 leaf of Prunus padus. This he believes to be evidence of 

 the origin of anthocyanin from tannin. 



It was furthermore found by Peche that an alteration in 

 colour took place in his artificial anthocyanin upon the 



