CONSTITUTION OF CHLOROPHYLL 229 



activity. Attempts to bring about assimilation with chloro- 

 phyll outside the leaf failed, presumably owing to the absence 

 of this enzyme. The removal of epidermis from the under 

 surface of leaves had no deterrent effect on assimilation, but a 

 slight pressure applied to the leaves brought assimilation to a 

 complete standstill. 



THE CONSTITUTION OF CHLOROPHYLL. 



As already stated, chlorophyll was first isolated from its 

 accompanying yellow pigments, the carotinoids, by Willstatter 

 and Hug in 1911, and in the following year it was shown by 

 Willstatter and Isler that the chlorophyll so obtained was not 

 a single substance, but a mixture of two distinct substances, 

 chlorophyll a and chlorophyll b, in the proportion roughly of 

 three molecules of the former to one of the latter. The con- 

 stitutions provisionally assigned to these two substances are 

 given by the following formulae : 



/COOCH /COOCH 



C 3l H M N 3 Mg 



NH 

 Chlorophyll a Chlorophyll b 



from which it may be seen that they are both esters of methyl 

 and phytyl alcohol (C 20 H 39 OH), and that the former contains 

 what is known as a lactam grouping. 



The recognition of magnesium as an essential constituent 

 of chlorophyll, which is due to Willstatter,* has proved of 

 immense value in the study of the degradation products of 

 chlorophyll. 



By the action of alkalies and acids respectively upon the two 

 chlorophylls, it has been found possible to divide the degrada- 

 tion products of chlorophyll into two groups : 



1. Those that retain magnesium, known as Phyllins. 



2. Those that are free from magnesium, known as Por- 

 phyrins. 



* Willstatter : " Annalen," 1906, 350, 48. 



