CHAP, ii Photosynthesis 293 



out difficulty. The process of disintegration which sets 

 in as the sugar solution becomes dilute must be arrested 

 at the first sign of bursting, which can be done by adding 

 some sulphate of copper. The preparation, if stained then 

 with eosin, shows the pink plastid protruding slightly 

 between the gaping lips of the green outer layer. Timiria- 

 zeff said that Naegeli made a similar observation much 

 earlier. 



From the thickness of the layer Timiriazeff computed 

 the concentration of the pigment, which he held to be 

 about four thousand times as great as that of a solution 

 of an emerald green colour, such as presents the charac- 

 teristic spectrum. He said the pigment is nearly solid, 

 and its superficial colour almost black. This very great 

 concentration may explain the absence of fluorescence 

 noticed by Reinke, as fluorescence is only exhibited by 

 solutions of moderate strength. 



The nature and relations of the colouring matter 

 attracted considerable attention on the part of chemists 

 as well as botanists ; but it cannot be said that the results 

 of their investigations were satisfactory. 



In 1860 Fremy showed that an alcoholic extract of 

 leaves, if shaken with a mixture of ether and hydro- 

 chloric acid, deposits two pigments, one greenish-blue and 

 the other yellow. He was uncertain whether these pre- 

 exist separately in the chlorophyll, or whether they are 

 formed from a single antecedent by the action of the acid. 

 Fremy called them phyllocyanin and phylloxanthin respec- 

 tively. 



Timiriazeff argued in 1869 that they arise from a splitting 

 of the pigment of the leaf. 



In 1872 Kraus determined the existence of two colouring 

 matters in the plastids ; a green one, which he considered 

 the proper chlorophyll, and a yellow one, to which he gave 

 the name xanthophyll. He traced no relation between 



