CHLOROPHYLL FORMATION 397 



he supposed was a colorless chromogen which is distributed in the proto- 

 plasm of leaves and which is transformed to chlorophyll by an oxidation 

 analogous to the oxidation of indigo white to indigo. 



2. Chlorophor. Chlorophor is the name given to the outer layer of 

 chloroplasts by Boehm (1856, 1859) from which chlorophyll is formed 

 and to which it is attached. 



3. Carotenoid pigments. Kraus (1872) assumed that chlorophyll was 

 formed at the expense of the yellow pigments present in etiolated leaves. 



4. Etiolin. A pigment mixture extracted from supposedly etiolated 

 leaves was called "etioUn" by Pringsheim (1874). Its function as a 

 chlorophyll precursor was enunciated by Wiesner (1877). Concepts con- 

 cerning its properties underwent continual change in order to keep pace 

 with the advance in knowledge of the chlorophyll-forming process 

 (Mikosch and Stohr, 1880; Reinke, 1893; Greilach, 1904). Monteverde 

 (1893-1894) and Timiriazeff (1903) clearly recognized it as a mixture of 

 chlorophyll, protochlorophyll, carotene, and xanthophyll. 



5. Protophyllin. Protophylhn was obtained artificially by Timiriazeff 

 (1885, 1886a,b, 1903) as a nearly colorless reduction product of chloro- 

 phyll. It was readily oxidized by air to give a green color. Because the 

 color change produced by its oxidation was similar to the color change 

 observed in the greening of etiolated leaves, protophyllin was assigned 

 the role of chlorophyll precursor in leaves. 



6. Protochlorophyll. From his experiments on etiolated leaves, Mon- 

 teverde (1893-1894) came to the conclusion that such leaves contained a 

 pigment that was transformed to chlorophyll by the action of light. This 

 substance he extracted from etiolated leaves with alcohol and called 

 ' ' protochlorophyll. ' ' 



7. Chlorophyllogen. Because the positions of the spectral absorption 

 bands of protochlorophyll extracted from pumpkin inner seed coats did 

 not agree with those of the pigment in the plant tissue, Monteverde and 

 Lubimenko (1909, 1911) thought that the pigments were different and 

 proposed the name "chlorophyllogen" for the pigment in the living tissue. 

 In a later publication, Lubimenko (1927, p. 181) stated that the two terms 

 "protochlorophyll" and "chlorophyllogen" were synonymous. 



8. Chlorophyllin 8. The term "chlorophyllin 8" was used by Tswett 

 (1907) to bring the chlorophyll-like pigment of etiolated leaves into his 

 system of nomenclature for the chlorophylls. 



9. Protochlorophylls a and b. Seybold and Egle (1939) and Seybold 

 (1948-1949) have obtained evidence from the examination of pumpkin 

 seed coats for the existence of immediate precursors of both chlorophylls 

 a and b. They have called these precursors "protochlorophylls a and b." 



Comparison of the actual and assigned properties of the precursor 

 leaves no doubt but that the name best suited to designate the immedi- 

 ate precursor of chlorophyll is "protochlorophyll." There are objections 



