12 Carbon Asshnilation. 



Now, owing to Willstatter's work, which is undoubtedly one of 

 the most brilliant achievements of organic chemistry, our knowledge 

 of the chemistry of chlorophyll is as complete as, or more complete 

 than, that of any other plant substance. His researches have 

 therefore cleared the way for a vast amount of plant physiological 

 work of the greatest importance. It seems impossible that this 

 unique work of WiUstatter and his co-workers should not influence 

 and stimulate work in plant physiology, and it is surprising how 

 little this work has influenced plant physiological research so far. 

 Thus, in some recent work (Ewart, 1915) where it is contended 

 that Willstatter's methods of extraction have been followed, it 

 would have been more convincing if the author of the paper had 

 stated what chemical tests he applied to test the purity of his 

 extracted pigment. 



B. The Chemistry of Chlorophyll. 



Chlorophyll is a neutral substance which on treatment with 

 alkalis yields salts of acids which are known as chlorophyllins. 

 These salts of the chlorophyllins are soluble in water and are also 

 green in colour like chlorophyll. In the production of chlorophyllins, 

 a group which was bound to an acid radicle, has been split off from 

 the chlorophyll molecule, that is, the chlorophyll has undergone 

 saponiflcation like an ester. 



The chlorophyllins which are formed by alkaline hydrolysis 

 from alcoholic extracts of leaves are easily decomposed. They 

 were, however, isolated by WiUstatter, and were found on analysis 

 to contain magnesium, which was bound to the nitrogen in a 

 complex way. The magnesium cannot be electrolytically disso- 

 ciated as in a magnesium salt. The magnesium containing group 

 is very easily affected by acids, but is stable in presence of alkalis. 



On heating chlorophyllins with concentrated alcoholic alkalis, 

 a series of decomposition products, phyllins, are obtained by 

 removal of carboxyl groups, until in the final phyllin only one 

 remains. The phyllins are also acids containing magnesium. On 

 removal of the last carboxyl group a substance devoid of oxygen, 

 astiophyllin, is produced, having the composition CgiHg^N^Mg, in 

 which also the magnesium is bound to the nitrogen. 



If mineral acids and acetic acid are allowed to act on the 

 phyllins, these lose their magnesium. The series thus obtained 



