312 PIGMENTS 



With regard to the conditions necessary for the formation 

 of chlorophyll, light is the most important, but in addition a 

 certain degree of temperature, as well as the presence of certain 

 substances, such as iron and magnesium, are essential. There 

 is, however, some dispute regarding other factors. Palladin * 

 states that chlorophyll formation, is an oxidative process, and, 

 as a result of his experiments, finds that etiolated leaves on 

 exposure to daylight will not form chlorophyll unless a supply 

 of carbohydrate is available. If an etiolated leaf does not con- 

 tain carbohydrate, then greening will take place if the cut leaf 

 be placed in a solution of sugar. Almost any sugar will do, 

 e.g. sucrose, maltose, glucose, fructose, or rafhnose; success was 

 also obtained by the use of glycerol. The solution used must 

 be neither too weak nor too strong ; a strong solution of suc- 

 rose, for instance, will retard the chlorophyll formation because 

 it will depress oxidative processes. On the other hand, Issat- 

 chenko "f finds that etiolated leaves of certain plants, e.g. those 

 of Vicia Faba, when detached from the plant and placed in 

 strong sugar solution, even 50 per cent, will form chlorophyll. 

 He considers that light is the all-important factor. 



With regard to the substances which immediately precede 

 chlorophyll, and from which chlorophyll is formed, nothing 

 definite is known. 



The chemical study of chlorophyll dates from the year 

 1 8 19, when Pelletier and Caventou % first applied this name 

 to the green leaf pigment without, however, isolating the 

 substance. Since then, numerous workers have attempted 

 to prepare chlorophyll in a pure condition, but the methods 

 employed in most cases were of too drastic a nature for the 

 substance to escape destruction. Previous to 191 1, there was 

 no chemical evidence to show that chlorophyll was not a 

 single chemical individual, although Stokes, § Sorby,|| and 

 others had obtained spectroscopic evidence pointing to the 



* Palladin : " Ber. deut. bot. Gesells.," 1891, 9, 194, 229 ; 1902, 20, 

 224 ; " Rev. Gen. Bot.," 1897, 9, 385. 



f Lssatchenko : " Bull. Jard. Imp. Bot. St. Petersbourg," 1906, 6, 20. 

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

 § Stokes : " Proc. Roy. Soc," 1864, 13, 144. 

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



