CHLOROPHYLL AXD THE CHLOROPLASTS 371 



the red phosphorescent rays are used in photosynthesis, the intensity of 

 these ought to increase when photosyntliesis is artificially inhibited. The 

 results of investigations of this point are still incomplete. 



Dixon and Poole -'^ endeavored to determine whether a photo-electric 

 effect was produced on illuminating various chlorophyll preparations. 

 They found that the wave lengths of light which are effective in photo- 

 synthesis do not expel electrons from chlorophyll in sufficient quantity 

 to account for the formation of carbohydrates external to the chlorophyll. 

 It is possible that the electrons are not ejected, but are merely displaced 

 within the molecule. This displacement may possibly cause a rearrange- 

 ment within the chlorophyll molecule or within a chlorophyll-carbonic acid 

 complex. Dixon and Ball ''° showed that the sensitization of photographic 

 films with chlorophyll is effective at the temperature of liquid air. They 

 are of the opinion that the absorbed visible light causes a displacement 

 of electrons within the chlorophyll molecule and suggest the following 

 scheme : 



C5.,H,205N4Mg + CO2 > C5.,H,oOeN4Mg + CH^O 



chlorophyll a chlorophyll h 



C55Hro06N4Mg -f H2O ^ C5gH7205N4Mg + O2 



chlorophyll h chlorophyll a 



A cycle of reactions of this nature would account for the constant pro- 

 portions of the two chlorophyll components which have been found to 

 exist in most leaves before and after a period of active photosynthesis. 



Czapek ''1 pointed out that if chlorophyll acted as a sensitizer it would 

 probably be decomposed by the light as fiuorescent dyes are which act as 

 optical sensitizers. This led to the conclusion that the well-known decom- 

 position of chlorophyll in the light, which takes place quite rapidly in 

 solutions /■;/ vitro, may play a role in the normal photosynthetic process. 

 Similar expressions were made by other investigators."- Thus, basing his 

 opinions upon experiments on the action of light on chlorophyll prepara- 

 tions and upon published reports of the decomposition of chlorophyll 

 in illuminated plants by Ewart and Lubimenko, Wager concluded that 

 "the carbon dioxide before it can be used is built up independently into 

 the chlorophyll molecule, and it is possible that the production of sugars 

 and starch may be initiated by photo-oxidation of the chlorophyll rather 

 than by direct photosynthesis of carbon dioxide and water." 



However, the theory that in the photosynthetic process chlorophyll is 

 constantly being decomposed and reformed is now untenable.**^ Much 



^ Dixon and Poole, Notes from Bot. School, Trinity College, Dublin, 3, 90 



(1920). 



•» Dixon and Ball, ibid., 3, 199 (1922). 



"Czapek, Bcr. bot. Gcs., 20, 52 (1902). 



"^ Wager, Proc. Roy. Soc. 87 B, 405 (1914). Ewart, Jotini. Linncan Soc. 31, 

 554 (1897).' Askenasy, Bot. Zeitcj., 33, 498 (1875). 



"'Jorgensen and Kidd, Proc. Roy. Soc, 89 B, 342 (1916). Ewart, ibid., 89 B, 

 1 (1915). 



V 



