308 PHOTOSYNTHESIS 



ficial prei>arations of chlorophyll no conclusions can be drawn regard- 

 ing the photosynthetic process. 



Willstatter and StoU ^^^ have given this problem critical examination 

 and find that it is not the chlorophyll from which the aldehyde is formed, 

 l)ut from some substance which accompanies the leaf pigment. The at- 

 tempts of these investigators to obtain evidence of an extracellular photo- 

 synthesis with preparations of chlorophyll containing catalase or per- 

 oxidase were entirely negative or gave such slight tests for formaldehyde 

 that they did not consider them sufficiently decisive. Regarding the 

 formation of formaldehyde from chlorophyll Willstatter and StoU point 

 out that a chlorophyll preparation for investigations of this nature may 

 possess two sources of error : it may be contaminated with some for- 

 eign substance or it may have undergone decomposition during prepara- 

 tion. Although the physiological experimentation in the work of Usher 

 and Priestley and of Chodat and Schweizer were carried out with great 

 care, these workers were, according to Willstatter and StoU, quite dis- 

 regardful of the principles of making chlorophyll preparations and of 

 chemical technique. The latter find that chlorophyll which is illuminated 

 in an atmosphere of oxygen is quite stable, and that in the first stages of 

 the oxidation of chlorophyll in light no formaldehyde or any other alde- 

 hyde is formed. Nor are there any lower peroxides formed in this 

 process. They conclude that in those cases in which formaldehyde was 

 found as a product of photo-oxidation of chlorophyll, the substances which 

 contaminated the chlorophyll probably were subjected to photo-oxidation 

 and that this resulted in the formation of formaldehyde directly, or in- 

 directly by the action of these oxidation products (peroxides) on the 

 chlorophyll. Pure chlorophyll is apparently quite resistant to oxidation ; 

 even after illumination of 4 to 8 hours in the presence of oxygen it is 

 not bleached. Jorgensen and Kidd ^^^ have also shown that formalde- 

 hyde is not formed from carbon dioxide when chlorophyll preparations 

 are illuminated. 



Recently Eisler and Portheim ^^^ have described experiments in which 

 oxygen was Uberated from illuminated chlorophyll preparations. The 

 latter were prepared by extracting leaves with 95 per cent alcohol and 

 adding diluted horse serum to the alcoholic chlorophyll solution. A 

 flocculent precipitate is formed, from which the alcohol is removed, and 

 the precipitate is dissolved in 0.85 per cent sodium chloride solution 

 or in M. .01 sodium carbonate-sodium bicarbonate mixture. Similar 

 chlorophyll-albumin preparations have been prepared from a number of 

 plants ; they possess the color, spectrum and fluorescence of a living leaf 

 and the chlorophyll can again be extracted from them with alcohol. 



When solutions of such chlorophyll preparation (from grass) are 



'" Willstatter and StoU, "Untersuchungen ii. die Assimilation der Kohlensaure," 



p. 395. 



"Morgensen and Kidd, Proc. Roy. Soc, 89 B, 342 (1916). 



^"Eisler and Portheim, Biochem. Zeit.. 135, 293 (1923); 130, 497 (1922). 



