400 THE PIGMENT SYSTEM CHAP. 15 



the more rapid and versatile of the two methods, was invented by 

 Tswett in 1906. Several monographs have been devoted to it (e. g. 

 Zechmeister and von Cholnoky 1937, and Strain 19420- Specific 

 applications of chromatography to plant pigments have been described 

 by Winterstein and Stein (1934), Strain (1938, 1942^), Seybold and Egle 

 (1938), Masood, Siddiqi, and Qureshi (1939), Zscheile and Comar (1941), 

 and Zscheile (1941). Meyer (1939) and Hanson (1939) found that an 

 " allomerization " of chlorophyll (c/. page 459) may occur during the 

 chromatographic procedure and therefore suggested that the Willstatter- 

 Stoll "all-liquid" method is preferable to the adsorption method. A 

 simple separation method which combines the use of immiscible solvents 

 with chromatography was described by Spohn (1935). 



As mentioned above, great care must be exercised in working with 

 plant pigments in order to avoid decomposition during the separation. 

 Low temperature, neutral adsorbers, rapid working, absence of oxygen 

 and light — all have been recommended by Hanson (1939), Zscheile 

 (1941), and other authors. According to Zscheile, drying is to be avoided 

 in the preparation of pure chlorophyll (c/. however, Vol. II, Chapter 21). 

 It is particularly dangerous to leave chlorophyll in contact with other 

 plant constituents after the leaves have been killed, since killing breaks 

 down permeability barriers, denatures the proteins, and deprives the 

 pigments of protection which they enjoy in the living cells. Strain and 

 Manning (1942) mention that, after fresh plant material has been left 

 standing in dilute alcohol for a single day, not less than 15 distinct green 

 bands could be observed in the "chromatogram," indicating the presence 

 of as many different transformation products of the two original green 

 pigments. 



Without a complete separation of the pigments, their presence and 

 often their relative and absolute concentrations can be determined by a 

 spectrophotometric analysis of the extracts (cf. Vol. II, Chapter 21). 



A fundamental result of the analytical study of the pigments of green 

 plants and colored algae is the proof of the invariable presence of at 

 least one green pigment. 



The importance of green color for the regeneration of foul air by 

 plants was recognized by Ingen-Housz, who, in 1776, wrote (cf. page 19) 

 that "this office is not performed by the whole plant, but only by the 

 leaves and the green stalks." (He considered the establishment of this 

 fact as one of his most important achievements.) With the recognition 

 of the role of photosynthesis in the nutrition of plants and animals, the 

 green pigment of leaves (to which the name of chlorophyll, from x^opos, 

 green, was given by Pelletier and Caventou in 1818) appeared as a true 

 "philosopher's stone" of organic synthesis, a veritable "elixir of life" 

 (Dutrochet 1837). 



