DR. EDWARD SCHUNCK ON INDIGO-BLUE. 329 



coloration was followed by a dark blue one^ commencing at 

 the base of eacli leaf and extending towards the apex, but 

 never quite reaching the latter except in the lower leaves. 

 When the change in colour had begun to show itself in the 

 uppertenderer leaves, the whole showed symptoms of fading, 

 all further power of absorbing the acid liquid seemed to be 

 lost, and the sprigs were then at once immersed in hot 

 spirit of wine. After remaining in the spirit until the 

 chlorophyll was removed, the part of each leaf which had 

 undergone a change appeared blue, whilst the part into 

 which the acid had not penetrated appeared almost colour- 

 less. In this case it is probable that the indican was de- 

 composed not so much in consequence of the loss of 

 vitality in the cells, as by the direct action of the acid. 

 In some of the leaves there was another .distinct blue co- 

 loration towards the apex, in the part to which the acid had 

 not penetrated, separated from the blue part at the base 

 by a white zone. This second coloration may be attributed 

 to the loss of vitality in that part of the leaf. 



All these experiments must be made with plants whilst 

 in a state of vigorous growth. If made when the season is 

 advanced (that is, after the flowers have begun to appear), 

 the leaves, though apparently unchanged, show only traces 

 of blue colour after treatment and subsequent immersion 

 in hot alcohol. This shows either that the indican has 

 disappeared, being applied to other purposes in the economy 

 of the plant, or that it has undergone the peculiar molecular 

 change before referred to, into a substance which no longer 

 yields indigo-blue by decomposition, but indirubine and 

 other products. The latter is the more probable way of 

 accounting for the diff'erence ; for the parts of the leaf 

 which have been accidentally injured by the bites of insects 

 or from other causes at the later stage of the plant^s deve- 

 lopment become red, not blue, as at the earlier stages. 



