226 PIGMENTS 



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

 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 raffinose ; success was 

 also obtained by the use of glycerine. 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- 

 chenkof finds that etiolated leaves of certain plants, e.g. those 

 of Vicia Faba y 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, arid from which chlorophyll is formed, nothing 

 definite is known. 



The chemical study of chlorophyll dates from the year 

 1819, 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 1911, 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 

 existence of more than one substance ; confirmatory evidence 

 was subsequently obtained by TswettlT In 1912, however, 

 Willstatter and Isler** definitely showed that chlorophyll as 



* Palladin : " Ber. deut hot. Gesells.," 1891, 9, 194, 229; 1902, 20, 224; 

 ! Rev. Gdn. Bot.," 1897, 9, 385. 



t Issatchenko : "Bull. Jard. Imp. Bot., St. Petersbourg," 1906, 6, 20. 



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



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



HSorby : id., 1872, 21, 442. 



HTswett: "Ber. deut. hot. Gesells.," 1906, 24,326; 1907, 25, 137; "Ber. 

 deut. chem. Gesells.," 1908, 41, 1352 



** Willstatter and Isler: " Annalen," 1912, 390, 269. 



