PRODUCTION OF OXYGEN 155 



Polacci * as a result of his observations came to the con- 

 clusion that formaldehyde is of constant occurrence in green 

 leaves ; also that the carbonic acid is reduced by hydrogen, 

 which is given off by the plant, to formaldehyde, water and 

 oxygen. 



According to Friedel, the presence of living organisms is 

 not essential in this synthetic process, as indicated by the 

 evolution of oxygen and absorption of carbon dioxide. The 

 process takes place by means of an enzyme which he obtained 

 from the leaves of the spinach by extraction with glycerine. 

 This extract is mixed with alcohol sufficient in amount to 

 precipitate the enzyme, which is then filtered off and dissolved 

 in water. Leaves of the same plant are dried at 100° C, and 

 powdered up. If a mixture of the powder and the extract be 

 exposed to light, carbon dioxide will be absorbed and oxygen 

 evolved. 



Macchiati f obtained similar results, and further found that 

 the leaf powder alone would give off oxygen when suspended 

 in water and exposed to sunlight. 



On the other hand Bernard + and others from similar ex- 

 periments obtained no positive results. 



Beyerinck, by using different methods, also found that 

 leaf powder would give off oxygen in the presence of light. 



In this particular connexion, the work of Molisch § is of 

 much importance. He found that the extracted sap from 

 fresh leaves can give off oxygen in the presence of sunlight, 

 and the same result is obtained by using the leaves of Lamium 

 album dried at 35° C. and exhibiting no .signs of life. If, how- 

 ever, these extracts be filtered through a fine porcelain candle, 

 no such positive results are obtained, and further, the unfiltered 

 extracts lose their power after boiling. 



In considering these results Blackman || points out that in 

 all experiments designed to show extra-cellular photosynthetic 

 processes, in which powdered leaves or leaf extracts are used, 

 it must be borne in mind that the results may be due to the 



* Polacci : " Atti. Inst. Bot. Pavia," igoo, 6 ; 1902, 8 ; 1904, 10. 



f Macchiati: " Rev. Gen. Bot.," 1903, 15, 20. 



X Bernard: " Beih. bot. Centrbl.," 1904, 16, 36. 



§ Molisch : " Bot. Zeit.," 1904, 62, i. 



II Blackman ; "New Phytol.," 1904, 3, 33. 



