SECTION VI. 



PIGMENTS. 



CHLOROPHYLL. 



As is well known, chlorophyll is contained in the chloro- 

 plasts which are universally present in green plants and vary 

 considerably in their size, shape, and number within the cell. 

 With regard to their structure there has been much dispute. 

 It is, however, generally agreed that the structure of the 

 plastids is either reticulate or vacuolate. 



The pigment itself is variously stated to be dissolved in 

 some oily substance which is held in the channels and meshes 

 of the plastids, or to exist in the form of a precipitate. Recent 

 evidence based on the spectrum and the solubilities of chloro- 

 phyll leads to contradictory conclusions. Iwanowski * found 

 that the absorption spectrum of leaves and of colloidal solu- 

 tions of chlorophyll, although similar, are not identical in that 

 the spectrum of the colloidal solution lies between that of the 

 leaf and a true solution of chlorophyll ; identity was obtained 

 by the addition of an electrolyte to the colloidal solution. He 

 concludes that spectrum analysis cannot solve the problem. 

 Willstatter and StoUf found the absorption bands of the 

 green leaf and of a colloidal solution of chlorophyll to be iden- 

 tical. As will be seen later on, dry solvents will not extract 

 chlorophyll from dry leaves, but immediately a little water is 

 added, solution is effected ; further, chlorophyll in a colloidal . 

 solution cannot be extracted with ether unless there is present 

 an electrolyte such as magnesium sulphate or calcium chloride. 

 Willstatter and Stoll for these reasons assume that the addition 



* Iwanowski : " Ber. deut. bot. Gesells.," 1907, 25, 416 ; " Biochem. 

 Zeit.," 1913, 48, 328. 



t Willstatter and Stoll : " Untersuchungen iiber Chlorophyll," Berlin, 



1913- 



307 20 • 



