DOES HYDROGEN PEROXIDE OCCUR IN PLANTS. 227 



uninjured, and the cuticula had prevented the entrance of 

 the acid solution into the cells. In order to see whether the 

 reaction obtained was, indeed, due to hydrogen peroxide, I 

 added 0.5 gr. of platinum black to 20 cc. of the diluted oxalic 

 acid solution that had been in contact with the leaves for twenty- 

 four hours, and let the mixture stand with occasional stirring in 

 a porcelain dish for one hour. A control experiment with a 

 0.1 % solution of hydrogen peroxide, having shown that by this 

 means hydrogen peroxide^ is so perfectly decomposed, that 

 Bach's reaction shows not a trace of it, it was remarkable to find 

 that in all the plants mentioned the reddish coloration was obtained, 

 and still of the same intensity as before treatment with platinum black. 

 The only conclusion to be drawn is that there was no hydrogen 

 peroxide ever present, and it seems to me that Bach was not 

 justified in declaring that it was so in any of the plants he ex- 

 amined, because he omitted to apply the platinum test to see 

 whether the faculty of giving this reaction would be destroyed 

 or not. 



The coloration mentioned can very probably be obtained 

 only in those cases where the leaves have been partially killed 

 by the oxalic acid solution, and thus certain easily oxidisable 

 organic matters made able to leave the cells by osmosis. These 

 might by oxidation in presence of the aniline oxalate yield 

 coloured products. 



I doubt whether Bach ever observed his reaction in leaves 

 that had remained alive in all parts. 



(1) The energetic decomposition of hydrogen peroxide by platinum black is an 

 old and well known fact. 



