The Formation of the Anthocyan Pigments of Plants. 125 



diphenyl NH 2 .C 6 H 4 .C 6 H4.N:KC 6 H4.C 6 H 4 .NH 2 . The blue- and violet-browns, 

 so characteristic of the action of oxydases on benzidine, are due to complex, 

 partially or meW-quinonoid salts of diphenoquinone di-imine with benzidine 

 itself : — 



NH:C 6 H 4 :C 6 H 4 :NH = Quinone diimine. 



NH a .C 6 H4.C 6 H4.NH 8 = Benzidine. 



The molecules are united through the partial valencies of the nitrogen 

 atom. These compounds are meri-quinonoid, in that the quinone di-imine 

 may be combined with several molecules of benzidine. For example, 

 Willstatter and Piccard* describe a blue compound of the di-imine with 

 four molecules of benzidine, and a brownish-violet compound with three 

 molecules of the amine. Upon reduction, such men-quinonoid compounds 

 are converted into benzidine, whilst oxidation transforms them gradually 

 into the quinone di-imine, as more and more of the benzidine is oxidised. 



For the investigation of plant oxydase, and of inhibitors of oxydase, we 

 find that it is convenient to use benzidine in two forms, viz., a -|-per-cent. 

 solution in 50-per-cent. alcohol, and a saturated solution in 1-2 per cent, 

 of sodium chloride, f When rapidity of action is required, the latter solution 

 is employed, but, when inhibition is under investigation, the alcoholic 

 solution should be used side by side with the sodium chloride solution. In 

 illustration of the rapidity of action of the sodium chloride benzidine 

 solution, it may be mentioned that, if young seedlings of maize, etc., or 

 mature roots of water plants such as Hydrocharis morsus-rance (frog bit) be 

 immersed for a few minutes in this solution, the subsequent addition of a 

 few drops of hydrogen peroxide causes almost instantaneously a bright blue 

 coloration of their root-hair regions. 



Again, if flowers known to contain an inhibitor of oxydase be treated with 

 some agent, for example, absolute alcohol, which is known to remove the 

 inhibitor (see Part IV), they fail to react with the alcoholic benzidine 

 solution until the whole or greater part of the inhibitor has been removed, 

 whereas such flower sgive a definite reaction with sodium chloride benzidine, 

 even though the inhibitor has been only in part removed. 



The subject with which we deal in this section is that of the cause of the 

 range of flower-colour which occurs within a species. In illustration of 

 the nature of this problem we may mention the facts known in the case of 

 the flowers of the Chinese primrose {Primula sinensis). In addition to white- 

 * ' Ber.,' 1908, vol. 41, pp. 1458, 3245. 



t Cf. Madelung, ' Zeitsch. physiol. Cheiu.,' 1911, vol. 71, p. 204. 



