SECTION V. 

 PIGMENTS. 



CHLOROPHYLL. 



The term Chlorophyll was first applied by Pelletier and 

 Caventou * to the green colouring matter of plants ; these 

 authors, however, did not actually isolate the substances. 



Later it was observed by Stokes, f Sorby + and others that 

 an alcoholic extract of green leaves contained not only green 

 but also blue and yellow pigments ; further, Sorby pointed out 

 that there were two distinct green compounds, one of which 

 was contained in the higher plants only. 



More recently Tswett, § by his new method of absorption 

 spectrum analysis (see below), has obtained evidence of at 

 least seven different colouring matters in leaf-pigment. 



At the present time the term chlorophyll is applied only 

 to the green constituents of this mixture, and according to 

 Marchlewski II it may be defined as the green colouring matter 

 occurring in all extracts of green plants which shows three 

 absorption bands in the less refrangible region of the spectrum 

 and three more behind the F line. The term allochlorophyll is 

 applied by the same author to Sorby' s second green compound 

 which occurs only in the higher plants. 



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. 



* Pelletier and Caventou: " Ann. Chim. Phys.," 1819, 9, 194. 

 t Stokes: " Proc. Roy. See," 1864, 13, 144. 

 X Sorby : id., 1872, 21, 442. 



§ Tswett: " Ber. deut. bot. Gesells.," 1906, 24, 326 ; 1907, 25, 137. 

 II Marchlewski: *' Die Chemie d. Chlorophylls," Braunschweig, iQog. 

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